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https://oercommons.org/courseware/lesson/56366/overview
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Axial Skeleton
Introduction
Figure 7.1 Lateral View of the Human Skull
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Describe the functions of the skeletal system and define its two major subdivisions
- Identify the bones and bony structures of the skull, the cranial suture lines, the cranial fossae, and the openings in the skull
- Discuss the vertebral column and regional variations in its bony components and curvatures
- Describe the components of the thoracic cage
- Discuss the embryonic development of the axial skeleton
The skeletal system forms the rigid internal framework of the body. It consists of the bones, cartilages, and ligaments. Bones support the weight of the body, allow for body movements, and protect internal organs. Cartilage provides flexible strength and support for body structures such as the thoracic cage, the external ear, and the trachea and larynx. At joints of the body, cartilage can also unite adjacent bones or provide cushioning between them. Ligaments are the strong connective tissue bands that hold the bones at a moveable joint together and serve to prevent excessive movements of the joint that would result in injury. Providing movement of the skeleton are the muscles of the body, which are firmly attached to the skeleton via connective tissue structures called tendons. As muscles contract, they pull on the bones to produce movements of the body. Thus, without a skeleton, you would not be able to stand, run, or even feed yourself!
Each bone of the body serves a particular function, and therefore bones vary in size, shape, and strength based on these functions. For example, the bones of the lower back and lower limb are thick and strong to support your body weight. Similarly, the size of a bony landmark that serves as a muscle attachment site on an individual bone is related to the strength of this muscle. Muscles can apply very strong pulling forces to the bones of the skeleton. To resist these forces, bones have enlarged bony landmarks at sites where powerful muscles attach. This means that not only the size of a bone, but also its shape, is related to its function. For this reason, the identification of bony landmarks is important during your study of the skeletal system.
Bones are also dynamic organs that can modify their strength and thickness in response to changes in muscle strength or body weight. Thus, muscle attachment sites on bones will thicken if you begin a workout program that increases muscle strength. Similarly, the walls of weight-bearing bones will thicken if you gain body weight or begin pounding the pavement as part of a new running regimen. In contrast, a reduction in muscle strength or body weight will cause bones to become thinner. This may happen during a prolonged hospital stay, following limb immobilization in a cast, or going into the weightlessness of outer space. Even a change in diet, such as eating only soft food due to the loss of teeth, will result in a noticeable decrease in the size and thickness of the jaw bones.
Divisions of the Skeletal System
- Discuss the functions of the skeletal system
- Distinguish between the axial skeleton and appendicular skeleton
- Define the axial skeleton and its components
- Define the appendicular skeleton and its components
The skeletal system includes all of the bones, cartilages, and ligaments of the body that support and give shape to the body and body structures. The skeleton consists of the bones of the body. For adults, there are 206 bones in the skeleton. Younger individuals have higher numbers of bones because some bones fuse together during childhood and adolescence to form an adult bone. The primary functions of the skeleton are to provide a rigid, internal structure that can support the weight of the body against the force of gravity, and to provide a structure upon which muscles can act to produce movements of the body. The lower portion of the skeleton is specialized for stability during walking or running. In contrast, the upper skeleton has greater mobility and ranges of motion, features that allow you to lift and carry objects or turn your head and trunk.
In addition to providing for support and movements of the body, the skeleton has protective and storage functions. It protects the internal organs, including the brain, spinal cord, heart, lungs, and pelvic organs. The bones of the skeleton serve as the primary storage site for important minerals such as calcium and phosphate. The bone marrow found within bones stores fat and houses the blood-cell producing tissue of the body.
The skeleton is subdivided into two major divisions—the axial and appendicular.
The Axial Skeleton
The skeleton is subdivided into two major divisions—the axial and appendicular. The axial skeleton forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back (Figure 7.2). It serves to protect the brain, spinal cord, heart, and lungs. It also serves as the attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs.
The axial skeleton of the adult consists of 80 bones, including the skull, the vertebral column, and the thoracic cage. The skull is formed by 22 bones. Also associated with the head are an additional seven bones, including the hyoid bone and the ear ossicles (three small bones found in each middle ear). The vertebral column consists of 24 bones, each called a vertebra, plus the sacrum and coccyx. The thoracic cage includes the 12 pairs of ribs, and the sternum, the flattened bone of the anterior chest.
Figure 7.2 Axial and Appendicular Skeleton The axial skeleton supports the head, neck, back, and chest and thus forms the vertical axis of the body. It consists of the skull, vertebral column (including the sacrum and coccyx), and the thoracic cage, formed by the ribs and sternum. The appendicular skeleton is made up of all bones of the upper and lower limbs.
The Appendicular Skeleton
The appendicular skeleton includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton. There are 126 bones in the appendicular skeleton of an adult. The bones of the appendicular skeleton are covered in a separate chapter.
The Skull
- List and identify the bones of the brain case and face
- Locate the major suture lines of the skull and name the bones associated with each
- Locate and define the boundaries of the anterior, middle, and posterior cranial fossae, the temporal fossa, and infratemporal fossa
- Define the paranasal sinuses and identify the location of each
- Name the bones that make up the walls of the orbit and identify the openings associated with the orbit
- Identify the bones and structures that form the nasal septum and nasal conchae, and locate the hyoid bone
- Identify the bony openings of the skull
The cranium (skull) is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the facial bones and the brain case, or cranial vault (Figure 7.3). The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws. The rounded brain case surrounds and protects the brain and houses the middle and inner ear structures.
In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The 22nd bone is the mandible (lower jaw), which is the only moveable bone of the skull.
Figure 7.3 Parts of the Skull The skull consists of the rounded brain case that houses the brain and the facial bones that form the upper and lower jaws, nose, orbits, and other facial structures.
INTERACTIVE LINK
Watch this video to view a rotating and exploded skull, with color-coded bones. Which bone (yellow) is centrally located and joins with most of the other bones of the skull?
Anterior View of Skull
The anterior skull consists of the facial bones and provides the bony support for the eyes and structures of the face. This view of the skull is dominated by the openings of the orbits and the nasal cavity. Also seen are the upper and lower jaws, with their respective teeth (Figure 7.4).
The orbit is the bony socket that houses the eyeball and muscles that move the eyeball or open the upper eyelid. The upper margin of the anterior orbit is the supraorbital margin. Located near the midpoint of the supraorbital margin is a small opening called the supraorbital foramen. This provides for passage of a sensory nerve to the skin of the forehead. Below the orbit is the infraorbital foramen, which is the point of emergence for a sensory nerve that supplies the anterior face below the orbit.
Figure 7.4 Anterior View of Skull An anterior view of the skull shows the bones that form the forehead, orbits (eye sockets), nasal cavity, nasal septum, and upper and lower jaws.
Inside the nasal area of the skull, the nasal cavity is divided into halves by the nasal septum. The upper portion of the nasal septum is formed by the perpendicular plate of the ethmoid bone and the lower portion is the vomer bone. Each side of the nasal cavity is triangular in shape, with a broad inferior space that narrows superiorly. When looking into the nasal cavity from the front of the skull, two bony plates are seen projecting from each lateral wall. The larger of these is the inferior nasal concha, an independent bone of the skull. Located just above the inferior concha is the middle nasal concha, which is part of the ethmoid bone. A third bony plate, also part of the ethmoid bone, is the superior nasal concha. It is much smaller and out of sight, above the middle concha. The superior nasal concha is located just lateral to the perpendicular plate, in the upper nasal cavity.
Lateral View of Skull
A view of the lateral skull is dominated by the large, rounded brain case above and the upper and lower jaws with their teeth below (Figure 7.5). Separating these areas is the bridge of bone called the zygomatic arch. The zygomatic arch is the bony arch on the side of skull that spans from the area of the cheek to just above the ear canal. It is formed by the junction of two bony processes: a short anterior component, the temporal process of the zygomatic bone (the cheekbone) and a longer posterior portion, the zygomatic process of the temporal bone, extending forward from the temporal bone. Thus the temporal process (anteriorly) and the zygomatic process (posteriorly) join together, like the two ends of a drawbridge, to form the zygomatic arch. One of the major muscles that pulls the mandible upward during biting and chewing arises from the zygomatic arch.
On the lateral side of the brain case, above the level of the zygomatic arch, is a shallow space called the temporal fossa. Below the level of the zygomatic arch and deep to the vertical portion of the mandible is another space called the infratemporal fossa. Both the temporal fossa and infratemporal fossa contain muscles that act on the mandible during chewing.
Figure 7.5 Lateral View of Skull The lateral skull shows the large rounded brain case, zygomatic arch, and the upper and lower jaws. The zygomatic arch is formed jointly by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. The shallow space above the zygomatic arch is the temporal fossa. The space inferior to the zygomatic arch and deep to the posterior mandible is the infratemporal fossa.
Bones of the Brain Case
The brain case contains and protects the brain. The interior space that is almost completely occupied by the brain is called the cranial cavity. This cavity is bounded superiorly by the rounded top of the skull, which is called the calvaria (skullcap), and the lateral and posterior sides of the skull. The bones that form the top and sides of the brain case are usually referred to as the “flat” bones of the skull.
The floor of the brain case is referred to as the base of the skull. This is a complex area that varies in depth and has numerous openings for the passage of cranial nerves, blood vessels, and the spinal cord. Inside the skull, the base is subdivided into three large spaces, called the anterior cranial fossa, middle cranial fossa, and posterior cranial fossa (fossa = “trench or ditch”) (Figure 7.6). From anterior to posterior, the fossae increase in depth. The shape and depth of each fossa corresponds to the shape and size of the brain region that each houses. The boundaries and openings of the cranial fossae (singular = fossa) will be described in a later section.
Figure 7.6 Cranial Fossae The bones of the brain case surround and protect the brain, which occupies the cranial cavity. The base of the brain case, which forms the floor of cranial cavity, is subdivided into the shallow anterior cranial fossa, the middle cranial fossa, and the deep posterior cranial fossa.
The brain case consists of eight bones. These include the paired parietal and temporal bones, plus the unpaired frontal, occipital, sphenoid, and ethmoid bones.
Parietal Bone
The parietal bone forms most of the upper lateral side of the skull (see Figure 7.5). These are paired bones, with the right and left parietal bones joining together at the top of the skull. Each parietal bone is also bounded anteriorly by the frontal bone, inferiorly by the temporal bone, and posteriorly by the occipital bone.
Temporal Bone
The temporal bone forms the lower lateral side of the skull (see Figure 7.5). Common wisdom has it that the temporal bone (temporal = “time”) is so named because this area of the head (the temple) is where hair typically first turns gray, indicating the passage of time.
The temporal bone is subdivided into several regions (Figure 7.7). The flattened, upper portion is the squamous portion of the temporal bone. Below this area and projecting anteriorly is the zygomatic process of the temporal bone, which forms the posterior portion of the zygomatic arch. Posteriorly is the mastoid portion of the temporal bone. Projecting inferiorly from this region is a large prominence, the mastoid process, which serves as a muscle attachment site. The mastoid process can easily be felt on the side of the head just behind your earlobe. On the interior of the skull, the petrous portion of each temporal bone forms the prominent, diagonally oriented petrous ridge in the floor of the cranial cavity. Located inside each petrous ridge are small cavities that house the structures of the middle and inner ears.
Figure 7.7 Temporal Bone A lateral view of the isolated temporal bone shows the squamous, mastoid, and zygomatic portions of the temporal bone.
Important landmarks of the temporal bone, as shown in Figure 7.8, include the following:
- External acoustic meatus (ear canal)—This is the large opening on the lateral side of the skull that is associated with the ear.
- Internal acoustic meatus—This opening is located inside the cranial cavity, on the medial side of the petrous ridge. It connects to the middle and inner ear cavities of the temporal bone.
- Mandibular fossa—This is the deep, oval-shaped depression located on the external base of the skull, just in front of the external acoustic meatus. The mandible (lower jaw) joins with the skull at this site as part of the temporomandibular joint, which allows for movements of the mandible during opening and closing of the mouth.
- Articular tubercle—The smooth ridge located immediately anterior to the mandibular fossa. Both the articular tubercle and mandibular fossa contribute to the temporomandibular joint, the joint that provides for movements between the temporal bone of the skull and the mandible.
- Styloid process—Posterior to the mandibular fossa on the external base of the skull is an elongated, downward bony projection called the styloid process, so named because of its resemblance to a stylus (a pen or writing tool). This structure serves as an attachment site for several small muscles and for a ligament that supports the hyoid bone of the neck. (See also Figure 7.7.)
- Stylomastoid foramen—This small opening is located between the styloid process and mastoid process. This is the point of exit for the cranial nerve that supplies the facial muscles.
- Carotid canal—The carotid canal is a zig-zag shaped tunnel that provides passage through the base of the skull for one of the major arteries that supplies the brain. Its entrance is located on the outside base of the skull, anteromedial to the styloid process. The canal then runs anteromedially within the bony base of the skull, and then turns upward to its exit in the floor of the middle cranial cavity, above the foramen lacerum.
Figure 7.8 External and Internal Views of Base of Skull (a) The hard palate is formed anteriorly by the palatine processes of the maxilla bones and posteriorly by the horizontal plate of the palatine bones. (b) The complex floor of the cranial cavity is formed by the frontal, ethmoid, sphenoid, temporal, and occipital bones. The lesser wing of the sphenoid bone separates the anterior and middle cranial fossae. The petrous ridge (petrous portion of temporal bone) separates the middle and posterior cranial fossae.
Frontal Bone
The frontal bone is the single bone that forms the forehead. At its anterior midline, between the eyebrows, there is a slight depression called the glabella (see Figure 7.5). The frontal bone also forms the supraorbital margin of the orbit. Near the middle of this margin, is the supraorbital foramen, the opening that provides passage for a sensory nerve to the forehead. The frontal bone is thickened just above each supraorbital margin, forming rounded brow ridges. These are located just behind your eyebrows and vary in size among individuals, although they are generally larger in males. Inside the cranial cavity, the frontal bone extends posteriorly. This flattened region forms both the roof of the orbit below and the floor of the anterior cranial cavity above (see Figure 7.8b).
Occipital Bone
The occipital bone is the single bone that forms the posterior skull and posterior base of the cranial cavity (Figure 7.9; see also Figure 7.8). On its outside surface, at the posterior midline, is a small protrusion called the external occipital protuberance, which serves as an attachment site for a ligament of the posterior neck. Lateral to either side of this bump is a superior nuchal line (nuchal = “nape” or “posterior neck”). The nuchal lines represent the most superior point at which muscles of the neck attach to the skull, with only the scalp covering the skull above these lines. On the base of the skull, the occipital bone contains the large opening of the foramen magnum, which allows for passage of the spinal cord as it exits the skull. On either side of the foramen magnum is an oval-shaped occipital condyle. These condyles form joints with the first cervical vertebra and thus support the skull on top of the vertebral column.
Figure 7.9 Posterior View of Skull This view of the posterior skull shows attachment sites for muscles and joints that support the skull.
Sphenoid Bone
The sphenoid bone is a single, complex bone of the central skull (Figure 7.10). It serves as a “keystone” bone, because it joins with almost every other bone of the skull. The sphenoid forms much of the base of the central skull (see Figure 7.8) and also extends laterally to contribute to the sides of the skull (see Figure 7.5). Inside the cranial cavity, the right and left lesser wings of the sphenoid bone, which resemble the wings of a flying bird, form the lip of a prominent ridge that marks the boundary between the anterior and middle cranial fossae. The sella turcica (“Turkish saddle”) is located at the midline of the middle cranial fossa. This bony region of the sphenoid bone is named for its resemblance to the horse saddles used by the Ottoman Turks, with a high back and a tall front. The rounded depression in the floor of the sella turcica is the hypophyseal (pituitary) fossa, which houses the pea-sized pituitary (hypophyseal) gland. The greater wings of the sphenoid bone extend laterally to either side away from the sella turcica, where they form the anterior floor of the middle cranial fossa. The greater wing is best seen on the outside of the lateral skull, where it forms a rectangular area immediately anterior to the squamous portion of the temporal bone.
On the inferior aspect of the skull, each half of the sphenoid bone forms two thin, vertically oriented bony plates. These are the medial pterygoid plate and lateral pterygoid plate (pterygoid = “wing-shaped”). The right and left medial pterygoid plates form the posterior, lateral walls of the nasal cavity. The somewhat larger lateral pterygoid plates serve as attachment sites for chewing muscles that fill the infratemporal space and act on the mandible.
Figure 7.10 Sphenoid Bone Shown in isolation in (a) superior and (b) posterior views, the sphenoid bone is a single midline bone that forms the anterior walls and floor of the middle cranial fossa. It has a pair of lesser wings and a pair of greater wings. The sella turcica surrounds the hypophyseal fossa. Projecting downward are the medial and lateral pterygoid plates. The sphenoid has multiple openings for the passage of nerves and blood vessels, including the optic canal, superior orbital fissure, foramen rotundum, foramen ovale, and foramen spinosum.
Ethmoid Bone
The ethmoid bone is a single, midline bone that forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, and contributes to the medial wall of the orbit (Figure 7.11 and Figure 7.12). On the interior of the skull, the ethmoid also forms a portion of the floor of the anterior cranial cavity (see Figure 7.8b).
Within the nasal cavity, the perpendicular plate of the ethmoid bone forms the upper portion of the nasal septum. The ethmoid bone also forms the lateral walls of the upper nasal cavity. Extending from each lateral wall are the superior nasal concha and middle nasal concha, which are thin, curved projections that extend into the nasal cavity (Figure 7.13).
In the cranial cavity, the ethmoid bone forms a small area at the midline in the floor of the anterior cranial fossa. This region also forms the narrow roof of the underlying nasal cavity. This portion of the ethmoid bone consists of two parts, the crista galli and cribriform plates. The crista galli (“rooster’s comb or crest”) is a small upward bony projection located at the midline. It functions as an anterior attachment point for one of the covering layers of the brain. To either side of the crista galli is the cribriform plate (cribrum = “sieve”), a small, flattened area with numerous small openings termed olfactory foramina. Small nerve branches from the olfactory areas of the nasal cavity pass through these openings to enter the brain.
The lateral portions of the ethmoid bone are located between the orbit and upper nasal cavity, and thus form the lateral nasal cavity wall and a portion of the medial orbit wall. Located inside this portion of the ethmoid bone are several small, air-filled spaces that are part of the paranasal sinus system of the skull.
Figure 7.11 Sagittal Section of Skull This midline view of the sagittally sectioned skull shows the nasal septum.
Figure 7.12 Ethmoid Bone The unpaired ethmoid bone is located at the midline within the central skull. It has an upward projection, the crista galli, and a downward projection, the perpendicular plate, which forms the upper nasal septum. The cribriform plates form both the roof of the nasal cavity and a portion of the anterior cranial fossa floor. The lateral sides of the ethmoid bone form the lateral walls of the upper nasal cavity, part of the medial orbit wall, and give rise to the superior and middle nasal conchae. The ethmoid bone also contains the ethmoid air cells.
Figure 7.13 Lateral Wall of Nasal Cavity The three nasal conchae are curved bones that project from the lateral walls of the nasal cavity. The superior nasal concha and middle nasal concha are parts of the ethmoid bone. The inferior nasal concha is an independent bone of the skull.
Sutures of the Skull
A suture is an immobile joint between adjacent bones of the skull. The narrow gap between the bones is filled with dense, fibrous connective tissue that unites the bones. The long sutures located between the bones of the brain case are not straight, but instead follow irregular, tightly twisting paths. These twisting lines serve to tightly interlock the adjacent bones, thus adding strength to the skull for brain protection.
The two suture lines seen on the top of the skull are the coronal and sagittal sutures. The coronal suture runs from side to side across the skull, within the coronal plane of section (see Figure 7.5). It joins the frontal bone to the right and left parietal bones. The sagittal suture extends posteriorly from the coronal suture, running along the midline at the top of the skull in the sagittal plane of section (see Figure 7.9). It unites the right and left parietal bones. On the posterior skull, the sagittal suture terminates by joining the lambdoid suture. The lambdoid suture extends downward and laterally to either side away from its junction with the sagittal suture. The lambdoid suture joins the occipital bone to the right and left parietal and temporal bones. This suture is named for its upside-down "V" shape, which resembles the capital letter version of the Greek letter lambda (Λ). The squamous suture is located on the lateral skull. It unites the squamous portion of the temporal bone with the parietal bone (see Figure 7.5). At the intersection of four bones is the pterion, a small, capital-H-shaped suture line region that unites the frontal bone, parietal bone, squamous portion of the temporal bone, and greater wing of the sphenoid bone. It is the weakest part of the skull. The pterion is located approximately two finger widths above the zygomatic arch and a thumb’s width posterior to the upward portion of the zygomatic bone.
DISORDERS OF THE...
Skeletal System
Head and traumatic brain injuries are major causes of immediate death and disability, with bleeding and infections as possible additional complications. According to the Centers for Disease Control and Prevention (2010), approximately 30 percent of all injury-related deaths in the United States are caused by head injuries. The majority of head injuries involve falls. They are most common among young children (ages 0–4 years), adolescents (15–19 years), and the elderly (over 65 years). Additional causes vary, but prominent among these are automobile and motorcycle accidents.
Strong blows to the brain-case portion of the skull can produce fractures. These may result in bleeding inside the skull with subsequent injury to the brain. The most common is a linear skull fracture, in which fracture lines radiate from the point of impact. Other fracture types include a comminuted fracture, in which the bone is broken into several pieces at the point of impact, or a depressed fracture, in which the fractured bone is pushed inward. In a contrecoup (counterblow) fracture, the bone at the point of impact is not broken, but instead a fracture occurs on the opposite side of the skull. Fractures of the occipital bone at the base of the skull can occur in this manner, producing a basilar fracture that can damage the artery that passes through the carotid canal.
A blow to the lateral side of the head may fracture the bones of the pterion. The pterion is an important clinical landmark because located immediately deep to it on the inside of the skull is a major branch of an artery that supplies the skull and covering layers of the brain. A strong blow to this region can fracture the bones around the pterion. If the underlying artery is damaged, bleeding can cause the formation of a hematoma (collection of blood) between the brain and interior of the skull. As blood accumulates, it will put pressure on the brain. Symptoms associated with a hematoma may not be apparent immediately following the injury, but if untreated, blood accumulation will exert increasing pressure on the brain and can result in death within a few hours.
INTERACTIVE LINK
View this animation to see how a blow to the head may produce a contrecoup (counterblow) fracture of the basilar portion of the occipital bone on the base of the skull. Why may a basilar fracture be life threatening?
Facial Bones of the Skull
The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones, with six paired bones and two unpaired bones. The paired bones are the maxilla, palatine, zygomatic, nasal, lacrimal, and inferior nasal conchae bones. The unpaired bones are the vomer and mandible bones. Although classified with the brain-case bones, the ethmoid bone also contributes to the nasal septum and the walls of the nasal cavity and orbit.
Maxillary Bone
The maxillary bone, often referred to simply as the maxilla (plural = maxillae), is one of a pair that together form the upper jaw, much of the hard palate, the medial floor of the orbit, and the lateral base of the nose (see Figure 7.4). The curved, inferior margin of the maxillary bone that forms the upper jaw and contains the upper teeth is the alveolar process of the maxilla(Figure 7.14). Each tooth is anchored into a deep socket called an alveolus. On the anterior maxilla, just below the orbit, is the infraorbital foramen. This is the point of exit for a sensory nerve that supplies the nose, upper lip, and anterior cheek. On the inferior skull, the palatine process from each maxillary bone can be seen joining together at the midline to form the anterior three-quarters of the hard palate (see Figure 7.8a). The hard palate is the bony plate that forms the roof of the mouth and floor of the nasal cavity, separating the oral and nasal cavities.
Figure 7.14 Maxillary Bone The maxillary bone forms the upper jaw and supports the upper teeth. Each maxilla also forms the lateral floor of each orbit and the majority of the hard palate.
Palatine Bone
The palatine bone is one of a pair of irregularly shaped bones that contribute small areas to the lateral walls of the nasal cavity and the medial wall of each orbit. The largest region of each of the palatine bone is the horizontal plate. The plates from the right and left palatine bones join together at the midline to form the posterior quarter of the hard palate (see Figure 7.8a). Thus, the palatine bones are best seen in an inferior view of the skull and hard palate.
HOMEOSTATIC IMBALANCES
Cleft Lip and Cleft Palate
During embryonic development, the right and left maxilla bones come together at the midline to form the upper jaw. At the same time, the muscle and skin overlying these bones join together to form the upper lip. Inside the mouth, the palatine processes of the maxilla bones, along with the horizontal plates of the right and left palatine bones, join together to form the hard palate. If an error occurs in these developmental processes, a birth defect of cleft lip or cleft palate may result.
Cleft lip is a common development defect that affects approximately 1:1000 births, most of which are male. This defect involves a partial or complete failure of the right and left portions of the upper lip to fuse together, leaving a cleft (gap).
A more severe developmental defect is cleft palate, which affects the hard palate. The hard palate is the bony structure that separates the nasal cavity from the oral cavity. It is formed during embryonic development by the midline fusion of the horizontal plates from the right and left palatine bones and the palatine processes of the maxilla bones. Cleft palate affects approximately 1:2500 births and is more common in females. It results from a failure of the two halves of the hard palate to completely come together and fuse at the midline, thus leaving a gap between them. This gap allows for communication between the nasal and oral cavities. In severe cases, the bony gap continues into the anterior upper jaw where the alveolar processes of the maxilla bones also do not properly join together above the front teeth. If this occurs, a cleft lip will also be seen. Because of the communication between the oral and nasal cavities, a cleft palate makes it very difficult for an infant to generate the suckling needed for nursing, thus leaving the infant at risk for malnutrition. Surgical repair is required to correct cleft palate defects.
Zygomatic Bone
The zygomatic bone is also known as the cheekbone. Each of the paired zygomatic bones forms much of the lateral wall of the orbit and the lateral-inferior margins of the anterior orbital opening (see Figure 7.4). The short temporal process of the zygomatic bone projects posteriorly, where it forms the anterior portion of the zygomatic arch (see Figure 7.5).
Nasal Bone
The nasal bone is one of two small bones that articulate (join) with each other to form the bony base (bridge) of the nose. They also support the cartilages that form the lateral walls of the nose (see Figure 7.11). These are the bones that are damaged when the nose is broken.
Lacrimal Bone
Each lacrimal bone is a small, rectangular bone that forms the anterior, medial wall of the orbit (see Figure 7.4 and Figure 7.5). The anterior portion of the lacrimal bone forms a shallow depression called the lacrimal fossa, and extending inferiorly from this is the nasolacrimal canal. The lacrimal fluid (tears of the eye), which serves to maintain the moist surface of the eye, drains at the medial corner of the eye into the nasolacrimal canal. This duct then extends downward to open into the nasal cavity, behind the inferior nasal concha. In the nasal cavity, the lacrimal fluid normally drains posteriorly, but with an increased flow of tears due to crying or eye irritation, some fluid will also drain anteriorly, thus causing a runny nose.
Inferior Nasal Conchae
The right and left inferior nasal conchae form a curved bony plate that projects into the nasal cavity space from the lower lateral wall (see Figure 7.13). The inferior concha is the largest of the nasal conchae and can easily be seen when looking into the anterior opening of the nasal cavity.
Vomer Bone
The unpaired vomer bone, often referred to simply as the vomer, is triangular-shaped and forms the posterior-inferior part of the nasal septum (see Figure 7.11). The vomer is best seen when looking from behind into the posterior openings of the nasal cavity (see Figure 7.8a). In this view, the vomer is seen to form the entire height of the nasal septum. A much smaller portion of the vomer can also be seen when looking into the anterior opening of the nasal cavity.
Mandible
The mandible forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull. Each side of the mandible consists of a horizontal body and posteriorly, a vertically oriented ramus of the mandible (ramus = “branch”). The outside margin of the mandible, where the body and ramus come together is called the angle of the mandible(Figure 7.15).
The ramus on each side of the mandible has two upward-going bony projections. The more anterior projection is the flattened coronoid process of the mandible, which provides attachment for one of the biting muscles. The posterior projection is the condylar process of the mandible, which is topped by the oval-shaped condyle. The condyle of the mandible articulates (joins) with the mandibular fossa and articular tubercle of the temporal bone. Together these articulations form the temporomandibular joint, which allows for opening and closing of the mouth (see Figure 7.5). The broad U-shaped curve located between the coronoid and condylar processes is the mandibular notch.
Important landmarks for the mandible include the following:
- Alveolar process of the mandible—This is the upper border of the mandibular body and serves to anchor the lower teeth.
- Mental protuberance—The forward projection from the inferior margin of the anterior mandible that forms the chin (mental = “chin”).
- Mental foramen—The opening located on each side of the anterior-lateral mandible, which is the exit site for a sensory nerve that supplies the chin.
- Mylohyoid line—This bony ridge extends along the inner aspect of the mandibular body (see Figure 7.11). The muscle that forms the floor of the oral cavity attaches to the mylohyoid lines on both sides of the mandible.
- Mandibular foramen—This opening is located on the medial side of the ramus of the mandible. The opening leads into a tunnel that runs down the length of the mandibular body. The sensory nerve and blood vessels that supply the lower teeth enter the mandibular foramen and then follow this tunnel. Thus, to numb the lower teeth prior to dental work, the dentist must inject anesthesia into the lateral wall of the oral cavity at a point prior to where this sensory nerve enters the mandibular foramen.
- Lingula—This small flap of bone is named for its shape (lingula = “little tongue”). It is located immediately next to the mandibular foramen, on the medial side of the ramus. A ligament that anchors the mandible during opening and closing of the mouth extends down from the base of the skull and attaches to the lingula.
Figure 7.15 Isolated Mandible The mandible is the only moveable bone of the skull.
The Orbit
The orbit is the bony socket that houses the eyeball and contains the muscles that move the eyeball or open the upper eyelid. Each orbit is cone-shaped, with a narrow posterior region that widens toward the large anterior opening. To help protect the eye, the bony margins of the anterior opening are thickened and somewhat constricted. The medial walls of the two orbits are parallel to each other but each lateral wall diverges away from the midline at a 45° angle. This divergence provides greater lateral peripheral vision.
The walls of each orbit include contributions from seven skull bones (Figure 7.16). The frontal bone forms the roof and the zygomatic bone forms the lateral wall and lateral floor. The medial floor is primarily formed by the maxilla, with a small contribution from the palatine bone. The ethmoid bone and lacrimal bone make up much of the medial wall and the sphenoid bone forms the posterior orbit.
At the posterior apex of the orbit is the opening of the optic canal, which allows for passage of the optic nerve from the retina to the brain. Lateral to this is the elongated and irregularly shaped superior orbital fissure, which provides passage for the artery that supplies the eyeball, sensory nerves, and the nerves that supply the muscles involved in eye movements.
Figure 7.16 Bones of the Orbit Seven skull bones contribute to the walls of the orbit. Opening into the posterior orbit from the cranial cavity are the optic canal and superior orbital fissure.
The Nasal Septum and Nasal Conchae
The nasal septum consists of both bone and cartilage components (Figure 7.17; see also Figure 7.11). The upper portion of the septum is formed by the perpendicular plate of the ethmoid bone. The lower and posterior parts of the septum are formed by the triangular-shaped vomer bone. In an anterior view of the skull, the perpendicular plate of the ethmoid bone is easily seen inside the nasal opening as the upper nasal septum, but only a small portion of the vomer is seen as the inferior septum. A better view of the vomer bone is seen when looking into the posterior nasal cavity with an inferior view of the skull, where the vomer forms the full height of the nasal septum. The anterior nasal septum is formed by the septal cartilage, a flexible plate that fills in the gap between the perpendicular plate of the ethmoid and vomer bones. This cartilage also extends outward into the nose where it separates the right and left nostrils. The septal cartilage is not found in the dry skull.
Attached to the lateral wall on each side of the nasal cavity are the superior, middle, and inferior nasal conchae (singular = concha), which are named for their positions (see Figure 7.13). These are bony plates that curve downward as they project into the space of the nasal cavity. They serve to swirl the incoming air, which helps to warm and moisturize it before the air moves into the delicate air sacs of the lungs. This also allows mucus, secreted by the tissue lining the nasal cavity, to trap incoming dust, pollen, bacteria, and viruses. The largest of the conchae is the inferior nasal concha, which is an independent bone of the skull. The middle concha and the superior conchae, which is the smallest, are both formed by the ethmoid bone. When looking into the anterior nasal opening of the skull, only the inferior and middle conchae can be seen. The small superior nasal concha is well hidden above and behind the middle concha.
Figure 7.17 Nasal Septum The nasal septum is formed by the perpendicular plate of the ethmoid bone and the vomer bone. The septal cartilage fills the gap between these bones and extends into the nose.
Cranial Fossae
Inside the skull, the floor of the cranial cavity is subdivided into three cranial fossae (spaces), which increase in depth from anterior to posterior (see Figure 7.6, Figure 7.8b, and Figure 7.11). Since the brain occupies these areas, the shape of each conforms to the shape of the brain regions that it contains. Each cranial fossa has anterior and posterior boundaries and is divided at the midline into right and left areas by a significant bony structure or opening.
Anterior Cranial Fossa
The anterior cranial fossa is the most anterior and the shallowest of the three cranial fossae. It overlies the orbits and contains the frontal lobes of the brain. Anteriorly, the anterior fossa is bounded by the frontal bone, which also forms the majority of the floor for this space. The lesser wings of the sphenoid bone form the prominent ledge that marks the boundary between the anterior and middle cranial fossae. Located in the floor of the anterior cranial fossa at the midline is a portion of the ethmoid bone, consisting of the upward projecting crista galli and to either side of this, the cribriform plates.
Middle Cranial Fossa
The middle cranial fossa is deeper and situated posterior to the anterior fossa. It extends from the lesser wings of the sphenoid bone anteriorly, to the petrous ridges (petrous portion of the temporal bones) posteriorly. The large, diagonally positioned petrous ridges give the middle cranial fossa a butterfly shape, making it narrow at the midline and broad laterally. The temporal lobes of the brain occupy this fossa. The middle cranial fossa is divided at the midline by the upward bony prominence of the sella turcica, a part of the sphenoid bone. The middle cranial fossa has several openings for the passage of blood vessels and cranial nerves (see Figure 7.8).
Openings in the middle cranial fossa are as follows:
- Optic canal—This opening is located at the anterior lateral corner of the sella turcica. It provides for passage of the optic nerve into the orbit.
- Superior orbital fissure—This large, irregular opening into the posterior orbit is located on the anterior wall of the middle cranial fossa, lateral to the optic canal and under the projecting margin of the lesser wing of the sphenoid bone. Nerves to the eyeball and associated muscles, and sensory nerves to the forehead pass through this opening.
- Foramen rotundum—This rounded opening (rotundum = “round”) is located in the floor of the middle cranial fossa, just inferior to the superior orbital fissure. It is the exit point for a major sensory nerve that supplies the cheek, nose, and upper teeth.
- Foramen ovale of the middle cranial fossa—This large, oval-shaped opening in the floor of the middle cranial fossa provides passage for a major sensory nerve to the lateral head, cheek, chin, and lower teeth.
- Foramen spinosum—This small opening, located posterior-lateral to the foramen ovale, is the entry point for an important artery that supplies the covering layers surrounding the brain. The branching pattern of this artery forms readily visible grooves on the internal surface of the skull and these grooves can be traced back to their origin at the foramen spinosum.
- Carotid canal—This is the zig-zag passageway through which a major artery to the brain enters the skull. The entrance to the carotid canal is located on the inferior aspect of the skull, anteromedial to the styloid process (see Figure 7.8a). From here, the canal runs anteromedially within the bony base of the skull. Just above the foramen lacerum, the carotid canal opens into the middle cranial cavity, near the posterior-lateral base of the sella turcica.
- Foramen lacerum—This irregular opening is located in the base of the skull, immediately inferior to the exit of the carotid canal. This opening is an artifact of the dry skull, because in life it is completely filled with cartilage. All the openings of the skull that provide for passage of nerves or blood vessels have smooth margins; the word lacerum (“ragged” or “torn”) tells us that this opening has ragged edges and thus nothing passes through it.
Posterior Cranial Fossa
The posterior cranial fossa is the most posterior and deepest portion of the cranial cavity. It contains the cerebellum of the brain. The posterior fossa is bounded anteriorly by the petrous ridges, while the occipital bone forms the floor and posterior wall. It is divided at the midline by the large foramen magnum (“great aperture”), the opening that provides for passage of the spinal cord.
Located on the medial wall of the petrous ridge in the posterior cranial fossa is the internal acoustic meatus (see Figure 7.11). This opening provides for passage of the nerve from the hearing and equilibrium organs of the inner ear, and the nerve that supplies the muscles of the face. Located at the anterior-lateral margin of the foramen magnum is the hypoglossal canal. These emerge on the inferior aspect of the skull at the base of the occipital condyle and provide passage for an important nerve to the tongue.
Immediately inferior to the internal acoustic meatus is the large, irregularly shaped jugular foramen (see Figure 7.8a). Several cranial nerves from the brain exit the skull via this opening. It is also the exit point through the base of the skull for all the venous return blood leaving the brain. The venous structures that carry blood inside the skull form large, curved grooves on the inner walls of the posterior cranial fossa, which terminate at each jugular foramen.
Paranasal Sinuses
The paranasal sinuses are hollow, air-filled spaces located within certain bones of the skull (Figure 7.18). All of the sinuses communicate with the nasal cavity (paranasal = “next to nasal cavity”) and are lined with nasal mucosa. They serve to reduce bone mass and thus lighten the skull, and they also add resonance to the voice. This second feature is most obvious when you have a cold or sinus congestion. These produce swelling of the mucosa and excess mucus production, which can obstruct the narrow passageways between the sinuses and the nasal cavity, causing your voice to sound different to yourself and others. This blockage can also allow the sinuses to fill with fluid, with the resulting pressure producing pain and discomfort.
The paranasal sinuses are named for the skull bone that each occupies. The frontal sinus is located just above the eyebrows, within the frontal bone (see Figure 7.17). This irregular space may be divided at the midline into bilateral spaces, or these may be fused into a single sinus space. The frontal sinus is the most anterior of the paranasal sinuses. The largest sinus is the maxillary sinus. These are paired and located within the right and left maxillary bones, where they occupy the area just below the orbits. The maxillary sinuses are most commonly involved during sinus infections. Because their connection to the nasal cavity is located high on their medial wall, they are difficult to drain. The sphenoid sinus is a single, midline sinus. It is located within the body of the sphenoid bone, just anterior and inferior to the sella turcica, thus making it the most posterior of the paranasal sinuses. The lateral aspects of the ethmoid bone contain multiple small spaces separated by very thin bony walls. Each of these spaces is called an ethmoid air cell. These are located on both sides of the ethmoid bone, between the upper nasal cavity and medial orbit, just behind the superior nasal conchae.
Figure 7.18 Paranasal Sinuses The paranasal sinuses are hollow, air-filled spaces named for the skull bone that each occupies. The most anterior is the frontal sinus, located in the frontal bone above the eyebrows. The largest are the maxillary sinuses, located in the right and left maxillary bones below the orbits. The most posterior is the sphenoid sinus, located in the body of the sphenoid bone, under the sella turcica. The ethmoid air cells are multiple small spaces located in the right and left sides of the ethmoid bone, between the medial wall of the orbit and lateral wall of the upper nasal cavity.
Hyoid Bone
The hyoid bone is an independent bone that does not contact any other bone and thus is not part of the skull (Figure 7.19). It is a small U-shaped bone located in the upper neck near the level of the inferior mandible, with the tips of the “U” pointing posteriorly. The hyoid serves as the base for the tongue above, and is attached to the larynx below and the pharynx posteriorly. The hyoid is held in position by a series of small muscles that attach to it either from above or below. These muscles act to move the hyoid up/down or forward/back. Movements of the hyoid are coordinated with movements of the tongue, larynx, and pharynx during swallowing and speaking.
Figure 7.19 Hyoid Bone The hyoid bone is located in the upper neck and does not join with any other bone. It provides attachments for muscles that act on the tongue, larynx, and pharynx.
The Vertebral Column
- Describe each region of the vertebral column and the number of bones in each region
- Discuss the curves of the vertebral column and how these change after birth
- Describe a typical vertebra and determine the distinguishing characteristics for vertebrae in each vertebral region and features of the sacrum and the coccyx
- Define the structure of an intervertebral disc
- Determine the location of the ligaments that provide support for the vertebral column
The vertebral column is also known as the spinal column or spine (Figure 7.20). It consists of a sequence of vertebrae (singular = vertebra), each of which is separated and united by an intervertebral disc. Together, the vertebrae and intervertebral discs form the vertebral column. It is a flexible column that supports the head, neck, and body and allows for their movements. It also protects the spinal cord, which passes down the back through openings in the vertebrae.
Figure 7.20 Vertebral Column The adult vertebral column consists of 24 vertebrae, plus the sacrum and coccyx. The vertebrae are divided into three regions: cervical C1–C7 vertebrae, thoracic T1–T12 vertebrae, and lumbar L1–L5 vertebrae. The vertebral column is curved, with two primary curvatures (thoracic and sacrococcygeal curves) and two secondary curvatures (cervical and lumbar curves).
Regions of the Vertebral Column
The vertebral column originally develops as a series of 33 vertebrae, but this number is eventually reduced to 24 vertebrae, plus the sacrum and coccyx. The vertebral column is subdivided into five regions, with the vertebrae in each area named for that region and numbered in descending order. In the neck, there are seven cervical vertebrae, each designated with the letter “C” followed by its number. Superiorly, the C1 vertebra articulates (forms a joint) with the occipital condyles of the skull. Inferiorly, C1 articulates with the C2 vertebra, and so on. Below these are the 12 thoracic vertebrae, designated T1–T12. The lower back contains the L1–L5 lumbar vertebrae. The single sacrum, which is also part of the pelvis, is formed by the fusion of five sacral vertebrae. Similarly, the coccyx, or tailbone, results from the fusion of four small coccygeal vertebrae. However, the sacral and coccygeal fusions do not start until age 20 and are not completed until middle age.
An interesting anatomical fact is that almost all mammals have seven cervical vertebrae, regardless of body size. This means that there are large variations in the size of cervical vertebrae, ranging from the very small cervical vertebrae of a shrew to the greatly elongated vertebrae in the neck of a giraffe. In a full-grown giraffe, each cervical vertebra is 11 inches tall.
Curvatures of the Vertebral Column
The adult vertebral column does not form a straight line, but instead has four curvatures along its length (see Figure 7.20). These curves increase the vertebral column’s strength, flexibility, and ability to absorb shock. When the load on the spine is increased, by carrying a heavy backpack for example, the curvatures increase in depth (become more curved) to accommodate the extra weight. They then spring back when the weight is removed. The four adult curvatures are classified as either primary or secondary curvatures. Primary curves are retained from the original fetal curvature, while secondary curvatures develop after birth.
During fetal development, the body is flexed anteriorly into the fetal position, giving the entire vertebral column a single curvature that is concave anteriorly. In the adult, this fetal curvature is retained in two regions of the vertebral column as the thoracic curve, which involves the thoracic vertebrae, and the sacrococcygeal curve, formed by the sacrum and coccyx. Each of these is thus called a primary curve because they are retained from the original fetal curvature of the vertebral column.
A secondary curve develops gradually after birth as the child learns to sit upright, stand, and walk. Secondary curves are concave posteriorly, opposite in direction to the original fetal curvature. The cervical curve of the neck region develops as the infant begins to hold their head upright when sitting. Later, as the child begins to stand and then to walk, the lumbar curve of the lower back develops. In adults, the lumbar curve is generally deeper in females.
Disorders associated with the curvature of the spine include kyphosis (an excessive posterior curvature of the thoracic region), lordosis (an excessive anterior curvature of the lumbar region), and scoliosis (an abnormal, lateral curvature, accompanied by twisting of the vertebral column).
DISORDERS OF THE...
Vertebral Column
Developmental anomalies, pathological changes, or obesity can enhance the normal vertebral column curves, resulting in the development of abnormal or excessive curvatures (Figure 7.21). Kyphosis, also referred to as humpback or hunchback, is an excessive posterior curvature of the thoracic region. This can develop when osteoporosis causes weakening and erosion of the anterior portions of the upper thoracic vertebrae, resulting in their gradual collapse (Figure 7.22). Lordosis, or swayback, is an excessive anterior curvature of the lumbar region and is most commonly associated with obesity or late pregnancy. The accumulation of body weight in the abdominal region results an anterior shift in the line of gravity that carries the weight of the body. This causes in an anterior tilt of the pelvis and a pronounced enhancement of the lumbar curve.
Scoliosis is an abnormal, lateral curvature, accompanied by twisting of the vertebral column. Compensatory curves may also develop in other areas of the vertebral column to help maintain the head positioned over the feet. Scoliosis is the most common vertebral abnormality among girls. The cause is usually unknown, but it may result from weakness of the back muscles, defects such as differential growth rates in the right and left sides of the vertebral column, or differences in the length of the lower limbs. When present, scoliosis tends to get worse during adolescent growth spurts. Although most individuals do not require treatment, a back brace may be recommended for growing children. In extreme cases, surgery may be required.
Excessive vertebral curves can be identified while an individual stands in the anatomical position. Observe the vertebral profile from the side and then from behind to check for kyphosis or lordosis. Then have the person bend forward. If scoliosis is present, an individual will have difficulty in bending directly forward, and the right and left sides of the back will not be level with each other in the bent position.
Figure 7.21 Abnormal Curvatures of the Vertebral Column (a) Scoliosis is an abnormal lateral bending of the vertebral column. (b) An excessive curvature of the upper thoracic vertebral column is called kyphosis. (c) Lordosis is an excessive curvature in the lumbar region of the vertebral column.
Figure 7.22 Osteoporosis Osteoporosis is an age-related disorder that causes the gradual loss of bone density and strength. When the thoracic vertebrae are affected, there can be a gradual collapse of the vertebrae. This results in kyphosis, an excessive curvature of the thoracic region.
INTERACTIVE LINK
Osteoporosis is a common age-related bone disease in which bone density and strength is decreased. Watch this video to get a better understanding of how thoracic vertebrae may become weakened and may fracture due to this disease. How may vertebral osteoporosis contribute to kyphosis?
General Structure of a Vertebra
Within the different regions of the vertebral column, vertebrae vary in size and shape, but they all follow a similar structural pattern. A typical vertebra will consist of a body, a vertebral arch, and seven processes (Figure 7.23).
The body is the anterior portion of each vertebra and is the part that supports the body weight. Because of this, the vertebral bodies progressively increase in size and thickness going down the vertebral column. The bodies of adjacent vertebrae are separated and strongly united by an intervertebral disc.
The vertebral arch forms the posterior portion of each vertebra. It consists of four parts, the right and left pedicles and the right and left laminae. Each pedicle forms one of the lateral sides of the vertebral arch. The pedicles are anchored to the posterior side of the vertebral body. Each lamina forms part of the posterior roof of the vertebral arch. The large opening between the vertebral arch and body is the vertebral foramen, which contains the spinal cord. In the intact vertebral column, the vertebral foramina of all of the vertebrae align to form the vertebral (spinal) canal, which serves as the bony protection and passageway for the spinal cord down the back. When the vertebrae are aligned together in the vertebral column, notches in the margins of the pedicles of adjacent vertebrae together form an intervertebral foramen, the opening through which a spinal nerve exits from the vertebral column (Figure 7.24).
Seven processes arise from the vertebral arch. Each paired transverse process projects laterally and arises from the junction point between the pedicle and lamina. The single spinous process (vertebral spine) projects posteriorly at the midline of the back. The vertebral spines can easily be felt as a series of bumps just under the skin down the middle of the back. The transverse and spinous processes serve as important muscle attachment sites. A superior articular process extends or faces upward, and an inferior articular process faces or projects downward on each side of a vertebrae. The paired superior articular processes of one vertebra join with the corresponding paired inferior articular processes from the next higher vertebra. These junctions form slightly moveable joints between the adjacent vertebrae. The shape and orientation of the articular processes vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region.
Figure 7.23 Parts of a Typical Vertebra A typical vertebra consists of a body and a vertebral arch. The arch is formed by the paired pedicles and paired laminae. Arising from the vertebral arch are the transverse, spinous, superior articular, and inferior articular processes. The vertebral foramen provides for passage of the spinal cord. Each spinal nerve exits through an intervertebral foramen, located between adjacent vertebrae. Intervertebral discs unite the bodies of adjacent vertebrae.
Figure 7.24 Intervertebral Disc The bodies of adjacent vertebrae are separated and united by an intervertebral disc, which provides padding and allows for movements between adjacent vertebrae. The disc consists of a fibrous outer layer called the anulus fibrosus and a gel-like center called the nucleus pulposus. The intervertebral foramen is the opening formed between adjacent vertebrae for the exit of a spinal nerve.
Regional Modifications of Vertebrae
In addition to the general characteristics of a typical vertebra described above, vertebrae also display characteristic size and structural features that vary between the different vertebral column regions. Thus, cervical vertebrae are smaller than lumbar vertebrae due to differences in the proportion of body weight that each supports. Thoracic vertebrae have sites for rib attachment, and the vertebrae that give rise to the sacrum and coccyx have fused together into single bones.
Cervical Vertebrae
Typical cervical vertebrae, such as C4 or C5, have several characteristic features that differentiate them from thoracic or lumbar vertebrae (Figure 7.25). Cervical vertebrae have a small body, reflecting the fact that they carry the least amount of body weight. Cervical vertebrae usually have a bifid (Y-shaped) spinous process. The spinous processes of the C3–C6 vertebrae are short, but the spine of C7 is much longer. You can find these vertebrae by running your finger down the midline of the posterior neck until you encounter the prominent C7 spine located at the base of the neck. The transverse processes of the cervical vertebrae are sharply curved (U-shaped) to allow for passage of the cervical spinal nerves. Each transverse process also has an opening called the transverse foramen. An important artery that supplies the brain ascends up the neck by passing through these openings. The superior and inferior articular processes of the cervical vertebrae are flattened and largely face upward or downward, respectively.
The first and second cervical vertebrae are further modified, giving each a distinctive appearance. The first cervical (C1) vertebra is also called the atlas, because this is the vertebra that supports the skull on top of the vertebral column (in Greek mythology, Atlas was the god who supported the heavens on his shoulders). The C1 vertebra does not have a body or spinous process. Instead, it is ring-shaped, consisting of an anterior arch and a posterior arch. The transverse processes of the atlas are longer and extend more laterally than do the transverse processes of any other cervical vertebrae. The superior articular processes face upward and are deeply curved for articulation with the occipital condyles on the base of the skull. The inferior articular processes are flat and face downward to join with the superior articular processes of the C2 vertebra.
The second cervical (C2) vertebra is called the axis, because it serves as the axis for rotation when turning the head toward the right or left. The axis resembles typical cervical vertebrae in most respects, but is easily distinguished by the dens (odontoid process), a bony projection that extends upward from the vertebral body. The dens joins with the inner aspect of the anterior arch of the atlas, where it is held in place by transverse ligament.
Figure 7.25 Cervical Vertebrae A typical cervical vertebra has a small body, a bifid spinous process, transverse processes that have a transverse foramen and are curved for spinal nerve passage. The atlas (C1 vertebra) does not have a body or spinous process. It consists of an anterior and a posterior arch and elongated transverse processes. The axis (C2 vertebra) has the upward projecting dens, which articulates with the anterior arch of the atlas.
Thoracic Vertebrae
The bodies of the thoracic vertebrae are larger than those of cervical vertebrae (Figure 7.26). The characteristic feature for a typical midthoracic vertebra is the spinous process, which is long and has a pronounced downward angle that causes it to overlap the next inferior vertebra. The superior articular processes of thoracic vertebrae face anteriorly and the inferior processes face posteriorly. These orientations are important determinants for the type and range of movements available to the thoracic region of the vertebral column.
Thoracic vertebrae have several additional articulation sites, each of which is called a facet, where a rib is attached. Most thoracic vertebrae have two facets located on the lateral sides of the body, each of which is called a costal facet (costal = “rib”). These are for articulation with the head (end) of a rib. An additional facet is located on the transverse process for articulation with the tubercle of a rib.
Figure 7.26 Thoracic Vertebrae A typical thoracic vertebra is distinguished by the spinous process, which is long and projects downward to overlap the next inferior vertebra. It also has articulation sites (facets) on the vertebral body and a transverse process for rib attachment.
Figure 7.27 Rib Articulation in Thoracic Vertebrae Thoracic vertebrae have superior and inferior articular facets on the vertebral body for articulation with the head of a rib, and a transverse process facet for articulation with the rib tubercle.
Lumbar Vertebrae
Lumbar vertebrae carry the greatest amount of body weight and are thus characterized by the large size and thickness of the vertebral body (Figure 7.28). They have short transverse processes and a short, blunt spinous process that projects posteriorly. The articular processes are large, with the superior process facing backward and the inferior facing forward.
Figure 7.28 Lumbar Vertebrae Lumbar vertebrae are characterized by having a large, thick body and a short, rounded spinous process.
Sacrum and Coccyx
The sacrum is a triangular-shaped bone that is thick and wide across its superior base where it is weight bearing and then tapers down to an inferior, non-weight bearing apex (Figure 7.29). It is formed by the fusion of five sacral vertebrae, a process that does not begin until after the age of 20. On the anterior surface of the older adult sacrum, the lines of vertebral fusion can be seen as four transverse ridges. On the posterior surface, running down the midline, is the median sacral crest, a bumpy ridge that is the remnant of the fused spinous processes (median = “midline”; while medial = “toward, but not necessarily at, the midline”). Similarly, the fused transverse processes of the sacral vertebrae form the lateral sacral crest.
The sacral promontory is the anterior lip of the superior base of the sacrum. Lateral to this is the roughened auricular surface, which joins with the ilium portion of the hipbone to form the immobile sacroiliac joints of the pelvis. Passing inferiorly through the sacrum is a bony tunnel called the sacral canal, which terminates at the sacral hiatus near the inferior tip of the sacrum. The anterior and posterior surfaces of the sacrum have a series of paired openings called sacral foramina (singular = foramen) that connect to the sacral canal. Each of these openings is called a posterior (dorsal) sacral foramen or anterior (ventral) sacral foramen. These openings allow for the anterior and posterior branches of the sacral spinal nerves to exit the sacrum. The superior articular process of the sacrum, one of which is found on either side of the superior opening of the sacral canal, articulates with the inferior articular processes from the L5 vertebra.
The coccyx, or tailbone, is derived from the fusion of four very small coccygeal vertebrae (see Figure 7.29). It articulates with the inferior tip of the sacrum. It is not weight bearing in the standing position, but may receive some body weight when sitting.
Figure 7.29 Sacrum and Coccyx The sacrum is formed from the fusion of five sacral vertebrae, whose lines of fusion are indicated by the transverse ridges. The fused spinous processes form the median sacral crest, while the lateral sacral crest arises from the fused transverse processes. The coccyx is formed by the fusion of four small coccygeal vertebrae.
Intervertebral Discs and Ligaments of the Vertebral Column
The bodies of adjacent vertebrae are strongly anchored to each other by an intervertebral disc. This structure provides padding between the bones during weight bearing, and because it can change shape, also allows for movement between the vertebrae. Although the total amount of movement available between any two adjacent vertebrae is small, when these movements are summed together along the entire length of the vertebral column, large body movements can be produced. Ligaments that extend along the length of the vertebral column also contribute to its overall support and stability.
Intervertebral Disc
An intervertebral disc is a fibrocartilaginous pad that fills the gap between adjacent vertebral bodies (see Figure 7.24). Each disc is anchored to the bodies of its adjacent vertebrae, thus strongly uniting these. The discs also provide padding between vertebrae during weight bearing. Because of this, intervertebral discs are thin in the cervical region and thickest in the lumbar region, which carries the most body weight. In total, the intervertebral discs account for approximately 25 percent of your body height between the top of the pelvis and the base of the skull. Intervertebral discs are also flexible and can change shape to allow for movements of the vertebral column.
Each intervertebral disc consists of two parts. The anulus fibrosus is the tough, fibrous outer layer of the disc. It forms a circle (anulus = “ring” or “circle”) and is firmly anchored to the outer margins of the adjacent vertebral bodies. Inside is the nucleus pulposus, consisting of a softer, more gel-like material. It has a high water content that serves to resist compression and thus is important for weight bearing. With increasing age, the water content of the nucleus pulposus gradually declines. This causes the disc to become thinner, decreasing total body height somewhat, and reduces the flexibility and range of motion of the disc, making bending more difficult.
The gel-like nature of the nucleus pulposus also allows the intervertebral disc to change shape as one vertebra rocks side to side or forward and back in relation to its neighbors during movements of the vertebral column. Thus, bending forward causes compression of the anterior portion of the disc but expansion of the posterior disc. If the posterior anulus fibrosus is weakened due to injury or increasing age, the pressure exerted on the disc when bending forward and lifting a heavy object can cause the nucleus pulposus to protrude posteriorly through the anulus fibrosus, resulting in a herniated disc (“ruptured” or “slipped” disc) (Figure 7.30). The posterior bulging of the nucleus pulposus can cause compression of a spinal nerve at the point where it exits through the intervertebral foramen, with resulting pain and/or muscle weakness in those body regions supplied by that nerve. The most common sites for disc herniation are the L4/L5 or L5/S1 intervertebral discs, which can cause sciatica, a widespread pain that radiates from the lower back down the thigh and into the leg. Similar injuries of the C5/C6 or C6/C7 intervertebral discs, following forcible hyperflexion of the neck from a collision accident or football injury, can produce pain in the neck, shoulder, and upper limb.
Figure 7.30 Herniated Intervertebral Disc Weakening of the anulus fibrosus can result in herniation (protrusion) of the nucleus pulposus and compression of a spinal nerve, resulting in pain and/or muscle weakness in the body regions supplied by that nerve.
INTERACTIVE LINK
Watch this animation to see what it means to “slip” a disk. Watch this second animation to see one possible treatment for a herniated disc, removing and replacing the damaged disc with an artificial one that allows for movement between the adjacent certebrae. How could lifting a heavy object produce pain in a lower limb?
Ligaments of the Vertebral Column
Adjacent vertebrae are united by ligaments that run the length of the vertebral column along both its posterior and anterior aspects (Figure 7.31). These serve to resist excess forward or backward bending movements of the vertebral column, respectively.
The anterior longitudinal ligament runs down the anterior side of the entire vertebral column, uniting the vertebral bodies. It serves to resist excess backward bending of the vertebral column. Protection against this movement is particularly important in the neck, where extreme posterior bending of the head and neck can stretch or tear this ligament, resulting in a painful whiplash injury. Prior to the mandatory installation of seat headrests, whiplash injuries were common for passengers involved in a rear-end automobile collision.
The supraspinous ligament is located on the posterior side of the vertebral column, where it interconnects the spinous processes of the thoracic and lumbar vertebrae. This strong ligament supports the vertebral column during forward bending motions. In the posterior neck, where the cervical spinous processes are short, the supraspinous ligament expands to become the nuchal ligament (nuchae = “nape” or “back of the neck”). The nuchal ligament is attached to the cervical spinous processes and extends upward and posteriorly to attach to the midline base of the skull, out to the external occipital protuberance. It supports the skull and prevents it from falling forward. This ligament is much larger and stronger in four-legged animals such as cows, where the large skull hangs off the front end of the vertebral column. You can easily feel this ligament by first extending your head backward and pressing down on the posterior midline of your neck. Then tilt your head forward and you will fill the nuchal ligament popping out as it tightens to limit anterior bending of the head and neck.
Additional ligaments are located inside the vertebral canal, next to the spinal cord, along the length of the vertebral column. The posterior longitudinal ligament is found anterior to the spinal cord, where it is attached to the posterior sides of the vertebral bodies. Posterior to the spinal cord is the ligamentum flavum (“yellow ligament”). This consists of a series of short, paired ligaments, each of which interconnects the lamina regions of adjacent vertebrae. The ligamentum flavum has large numbers of elastic fibers, which have a yellowish color, allowing it to stretch and then pull back. Both of these ligaments provide important support for the vertebral column when bending forward.
Figure 7.31 Ligaments of Vertebral Column The anterior longitudinal ligament runs the length of the vertebral column, uniting the anterior sides of the vertebral bodies. The supraspinous ligament connects the spinous processes of the thoracic and lumbar vertebrae. In the posterior neck, the supraspinous ligament enlarges to form the nuchal ligament, which attaches to the cervical spinous processes and to the base of the skull.
INTERACTIVE LINK
Use this tool to identify the bones, intervertebral discs, and ligaments of the vertebral column. The thickest portions of the anterior longitudinal ligament and the supraspinous ligament are found in which regions of the vertebral column?
CAREER CONNECTION
Chiropractor
Chiropractors are health professionals who use nonsurgical techniques to help patients with musculoskeletal system problems that involve the bones, muscles, ligaments, tendons, or nervous system. They treat problems such as neck pain, back pain, joint pain, or headaches. Chiropractors focus on the patient’s overall health and can also provide counseling related to lifestyle issues, such as diet, exercise, or sleep problems. If needed, they will refer the patient to other medical specialists.
Chiropractors use a drug-free, hands-on approach for patient diagnosis and treatment. They will perform a physical exam, assess the patient’s posture and spine, and may perform additional diagnostic tests, including taking X-ray images. They primarily use manual techniques, such as spinal manipulation, to adjust the patient’s spine or other joints. They can recommend therapeutic or rehabilitative exercises, and some also include acupuncture, massage therapy, or ultrasound as part of the treatment program. In addition to those in general practice, some chiropractors specialize in sport injuries, neurology, orthopaedics, pediatrics, nutrition, internal disorders, or diagnostic imaging.
To become a chiropractor, students must have 3–4 years of undergraduate education, attend an accredited, four-year Doctor of Chiropractic (D.C.) degree program, and pass a licensure examination to be licensed for practice in their state. With the aging of the baby-boom generation, employment for chiropractors is expected to increase.
The Thoracic Cage
- Discuss the components that make up the thoracic cage
- Identify the parts of the sternum and define the sternal angle
- Discuss the parts of a rib and rib classifications
The thoracic cage (rib cage) forms the thorax (chest) portion of the body. It consists of the 12 pairs of ribs with their costal cartilages and the sternum (Figure 7.32). The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1–T12). The thoracic cage protects the heart and lungs.
Figure 7.32 Thoracic Cage The thoracic cage is formed by the (a) sternum and (b) 12 pairs of ribs with their costal cartilages. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The ribs are classified as true ribs (1–7) and false ribs (8–12). The last two pairs of false ribs are also known as floating ribs (11–12).
Sternum
The sternum is the elongated bony structure that anchors the anterior thoracic cage. It consists of three parts: the manubrium, body, and xiphoid process. The manubrium is the wider, superior portion of the sternum. The top of the manubrium has a shallow, U-shaped border called the jugular (suprasternal) notch. This can be easily felt at the anterior base of the neck, between the medial ends of the clavicles. The clavicular notch is the shallow depression located on either side at the superior-lateral margins of the manubrium. This is the site of the sternoclavicular joint, between the sternum and clavicle. The first ribs also attach to the manubrium.
The elongated, central portion of the sternum is the body. The manubrium and body join together at the sternal angle, so called because the junction between these two components is not flat, but forms a slight bend. The second rib attaches to the sternum at the sternal angle. Since the first rib is hidden behind the clavicle, the second rib is the highest rib that can be identified by palpation. Thus, the sternal angle and second rib are important landmarks for the identification and counting of the lower ribs. Ribs 3–7 attach to the sternal body.
The inferior tip of the sternum is the xiphoid process. This small structure is cartilaginous early in life, but gradually becomes ossified starting during middle age.
Ribs
Each rib is a curved, flattened bone that contributes to the wall of the thorax. The ribs articulate posteriorly with the T1–T12 thoracic vertebrae, and most attach anteriorly via their costal cartilages to the sternum. There are 12 pairs of ribs. The ribs are numbered 1–12 in accordance with the thoracic vertebrae.
Parts of a Typical Rib
The posterior end of a typical rib is called the head of the rib (see Figure 7.27). This region articulates primarily with the costal facet located on the body of the same numbered thoracic vertebra and to a lesser degree, with the costal facet located on the body of the next higher vertebra. Lateral to the head is the narrowed neck of the rib. A small bump on the posterior rib surface is the tubercle of the rib, which articulates with the facet located on the transverse process of the same numbered vertebra. The remainder of the rib is the body of the rib (shaft). Just lateral to the tubercle is the angle of the rib, the point at which the rib has its greatest degree of curvature. The angles of the ribs form the most posterior extent of the thoracic cage. In the anatomical position, the angles align with the medial border of the scapula. A shallow costal groove for the passage of blood vessels and a nerve is found along the inferior margin of each rib.
Rib Classifications
The bony ribs do not extend anteriorly completely around to the sternum. Instead, each rib ends in a costal cartilage. These cartilages are made of hyaline cartilage and can extend for several inches. Most ribs are then attached, either directly or indirectly, to the sternum via their costal cartilage (see Figure 7.32). The ribs are classified into three groups based on their relationship to the sternum.
Ribs 1–7 are classified as true ribs (vertebrosternal ribs). The costal cartilage from each of these ribs attaches directly to the sternum. Ribs 8–12 are called false ribs (vertebrochondral ribs). The costal cartilages from these ribs do not attach directly to the sternum. For ribs 8–10, the costal cartilages are attached to the cartilage of the next higher rib. Thus, the cartilage of rib 10 attaches to the cartilage of rib 9, rib 9 then attaches to rib 8, and rib 8 is attached to rib 7. The last two false ribs (11–12) are also called floating ribs (vertebral ribs). These are short ribs that do not attach to the sternum at all. Instead, their small costal cartilages terminate within the musculature of the lateral abdominal wall.
Embryonic Development of the Axial Skeleton
- Discuss the two types of embryonic bone development within the skull
- Describe the development of the vertebral column and thoracic cage
The axial skeleton begins to form during early embryonic development. However, growth, remodeling, and ossification (bone formation) continue for several decades after birth before the adult skeleton is fully formed. Knowledge of the developmental processes that give rise to the skeleton is important for understanding the abnormalities that may arise in skeletal structures.
Development of the Skull
During the third week of embryonic development, a rod-like structure called the notochord develops dorsally along the length of the embryo. The tissue overlying the notochord enlarges and forms the neural tube, which will give rise to the brain and spinal cord. By the fourth week, mesoderm tissue located on either side of the notochord thickens and separates into a repeating series of block-like tissue structures, each of which is called a somite. As the somites enlarge, each one will split into several parts. The most medial of these parts is called a sclerotome. The sclerotomes consist of an embryonic tissue called mesenchyme, which will give rise to the fibrous connective tissues, cartilages, and bones of the body.
The bones of the skull arise from mesenchyme during embryonic development in two different ways. The first mechanism produces the bones that form the top and sides of the brain case. This involves the local accumulation of mesenchymal cells at the site of the future bone. These cells then differentiate directly into bone producing cells, which form the skull bones through the process of intramembranous ossification. As the brain case bones grow in the fetal skull, they remain separated from each other by large areas of dense connective tissue, each of which is called a fontanelle (Figure 7.33). The fontanelles are the soft spots on an infant’s head. They are important during birth because these areas allow the skull to change shape as it squeezes through the birth canal. After birth, the fontanelles allow for continued growth and expansion of the skull as the brain enlarges. The largest fontanelle is located on the anterior head, at the junction of the frontal and parietal bones. The fontanelles decrease in size and disappear by age 2. However, the skull bones remained separated from each other at the sutures, which contain dense fibrous connective tissue that unites the adjacent bones. The connective tissue of the sutures allows for continued growth of the skull bones as the brain enlarges during childhood growth.
The second mechanism for bone development in the skull produces the facial bones and floor of the brain case. This also begins with the localized accumulation of mesenchymal cells. However, these cells differentiate into cartilage cells, which produce a hyaline cartilage model of the future bone. As this cartilage model grows, it is gradually converted into bone through the process of endochondral ossification. This is a slow process and the cartilage is not completely converted to bone until the skull achieves its full adult size.
At birth, the brain case and orbits of the skull are disproportionally large compared to the bones of the jaws and lower face. This reflects the relative underdevelopment of the maxilla and mandible, which lack teeth, and the small sizes of the paranasal sinuses and nasal cavity. During early childhood, the mastoid process enlarges, the two halves of the mandible and frontal bone fuse together to form single bones, and the paranasal sinuses enlarge. The jaws also expand as the teeth begin to appear. These changes all contribute to the rapid growth and enlargement of the face during childhood.
Figure 7.33 Newborn Skull The bones of the newborn skull are not fully ossified and are separated by large areas called fontanelles, which are filled with fibrous connective tissue. The fontanelles allow for continued growth of the skull after birth. At the time of birth, the facial bones are small and underdeveloped, and the mastoid process has not yet formed.
Development of the Vertebral Column and Thoracic cage
Development of the vertebrae begins with the accumulation of mesenchyme cells from each sclerotome around the notochord. These cells differentiate into a hyaline cartilage model for each vertebra, which then grow and eventually ossify into bone through the process of endochondral ossification. As the developing vertebrae grow, the notochord largely disappears. However, small areas of notochord tissue persist between the adjacent vertebrae and this contributes to the formation of each intervertebral disc.
The ribs and sternum also develop from mesenchyme. The ribs initially develop as part of the cartilage model for each vertebra, but in the thorax region, the rib portion separates from the vertebra by the eighth week. The cartilage model of the rib then ossifies, except for the anterior portion, which remains as the costal cartilage. The sternum initially forms as paired hyaline cartilage models on either side of the anterior midline, beginning during the fifth week of development. The cartilage models of the ribs become attached to the lateral sides of the developing sternum. Eventually, the two halves of the cartilaginous sternum fuse together along the midline and then ossify into bone. The manubrium and body of the sternum are converted into bone first, with the xiphoid process remaining as cartilage until late in life.
INTERACTIVE LINK
View this video to review the two processes that give rise to the bones of the skull and body. What are the two mechanisms by which the bones of the body are formed and which bones are formed by each mechanism?
HOMEOSTATIC IMBALANCES
Craniosynostosis
The premature closure (fusion) of a suture line is a condition called craniosynostosis. This error in the normal developmental process results in abnormal growth of the skull and deformity of the head. It is produced either by defects in the ossification process of the skull bones or failure of the brain to properly enlarge. Genetic factors are involved, but the underlying cause is unknown. It is a relatively common condition, occurring in approximately 1:2000 births, with males being more commonly affected. Primary craniosynostosis involves the early fusion of one cranial suture, whereas complex craniosynostosis results from the premature fusion of several sutures.
The early fusion of a suture in primary craniosynostosis prevents any additional enlargement of the cranial bones and skull along this line. Continued growth of the brain and skull is therefore diverted to other areas of the head, causing an abnormal enlargement of these regions. For example, the early disappearance of the anterior fontanelle and premature closure of the sagittal suture prevents growth across the top of the head. This is compensated by upward growth by the bones of the lateral skull, resulting in a long, narrow, wedge-shaped head. This condition, known as scaphocephaly, accounts for approximately 50 percent of craniosynostosis abnormalities. Although the skull is misshapen, the brain still has adequate room to grow and thus there is no accompanying abnormal neurological development.
In cases of complex craniosynostosis, several sutures close prematurely. The amount and degree of skull deformity is determined by the location and extent of the sutures involved. This results in more severe constraints on skull growth, which can alter or impede proper brain growth and development.
Cases of craniosynostosis are usually treated with surgery. A team of physicians will open the skull along the fused suture, which will then allow the skull bones to resume their growth in this area. In some cases, parts of the skull will be removed and replaced with an artificial plate. The earlier after birth that surgery is performed, the better the outcome. After treatment, most children continue to grow and develop normally and do not exhibit any neurological problems.
Key Terms
- alveolar process of the mandible
- upper border of mandibular body that contains the lower teeth
- alveolar process of the maxilla
- curved, inferior margin of the maxilla that supports and anchors the upper teeth
- angle of the mandible
- rounded corner located at outside margin of the body and ramus junction
- angle of the rib
- portion of rib with greatest curvature; together, the rib angles form the most posterior extent of the thoracic cage
- anterior (ventral) sacral foramen
- one of the series of paired openings located on the anterior (ventral) side of the sacrum
- anterior arch
- anterior portion of the ring-like C1 (atlas) vertebra
- anterior cranial fossa
- shallowest and most anterior cranial fossa of the cranial base that extends from the frontal bone to the lesser wing of the sphenoid bone
- anterior longitudinal ligament
- ligament that runs the length of the vertebral column, uniting the anterior aspects of the vertebral bodies
- anulus fibrosus
- tough, fibrous outer portion of an intervertebral disc, which is strongly anchored to the bodies of the adjacent vertebrae
- appendicular skeleton
- all bones of the upper and lower limbs, plus the girdle bones that attach each limb to the axial skeleton
- articular tubercle
- smooth ridge located on the inferior skull, immediately anterior to the mandibular fossa
- atlas
- first cervical (C1) vertebra
- axial skeleton
- central, vertical axis of the body, including the skull, vertebral column, and thoracic cage
- axis
- second cervical (C2) vertebra
- body of the rib
- shaft portion of a rib
- brain case
- portion of the skull that contains and protects the brain, consisting of the eight bones that form the cranial base and rounded upper skull
- calvaria
- (also, skullcap) rounded top of the skull
- carotid canal
- zig-zag tunnel providing passage through the base of the skull for the internal carotid artery to the brain; begins anteromedial to the styloid process and terminates in the middle cranial cavity, near the posterior-lateral base of the sella turcica
- cervical curve
- posteriorly concave curvature of the cervical vertebral column region; a secondary curve of the vertebral column
- cervical vertebrae
- seven vertebrae numbered as C1–C7 that are located in the neck region of the vertebral column
- clavicular notch
- paired notches located on the superior-lateral sides of the sternal manubrium, for articulation with the clavicle
- coccyx
- small bone located at inferior end of the adult vertebral column that is formed by the fusion of four coccygeal vertebrae; also referred to as the “tailbone”
- condylar process of the mandible
- thickened upward projection from posterior margin of mandibular ramus
- condyle
- oval-shaped process located at the top of the condylar process of the mandible
- coronal suture
- joint that unites the frontal bone to the right and left parietal bones across the top of the skull
- coronoid process of the mandible
- flattened upward projection from the anterior margin of the mandibular ramus
- costal cartilage
- hyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternum
- costal facet
- site on the lateral sides of a thoracic vertebra for articulation with the head of a rib
- costal groove
- shallow groove along the inferior margin of a rib that provides passage for blood vessels and a nerve
- cranial cavity
- interior space of the skull that houses the brain
- cranium
- skull
- cribriform plate
- small, flattened areas with numerous small openings, located to either side of the midline in the floor of the anterior cranial fossa; formed by the ethmoid bone
- crista galli
- small upward projection located at the midline in the floor of the anterior cranial fossa; formed by the ethmoid bone
- dens
- bony projection (odontoid process) that extends upward from the body of the C2 (axis) vertebra
- ear ossicles
- three small bones located in the middle ear cavity that serve to transmit sound vibrations to the inner ear
- ethmoid air cell
- one of several small, air-filled spaces located within the lateral sides of the ethmoid bone, between the orbit and upper nasal cavity
- ethmoid bone
- unpaired bone that forms the roof and upper, lateral walls of the nasal cavity, portions of the floor of the anterior cranial fossa and medial wall of orbit, and the upper portion of the nasal septum
- external acoustic meatus
- ear canal opening located on the lateral side of the skull
- external occipital protuberance
- small bump located at the midline on the posterior skull
- facet
- small, flattened area on a bone for an articulation (joint) with another bone, or for muscle attachment
- facial bones
- fourteen bones that support the facial structures and form the upper and lower jaws and the hard palate
- false ribs
- vertebrochondral ribs 8–12 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at all
- floating ribs
- vertebral ribs 11–12 that do not attach to the sternum or to the costal cartilage of another rib
- fontanelle
- expanded area of fibrous connective tissue that separates the brain case bones of the skull prior to birth and during the first year after birth
- foramen lacerum
- irregular opening in the base of the skull, located inferior to the exit of carotid canal
- foramen magnum
- large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium
- foramen ovale of the middle cranial fossa
- oval-shaped opening in the floor of the middle cranial fossa
- foramen rotundum
- round opening in the floor of the middle cranial fossa, located between the superior orbital fissure and foramen ovale
- foramen spinosum
- small opening in the floor of the middle cranial fossa, located lateral to the foramen ovale
- frontal bone
- unpaired bone that forms forehead, roof of orbit, and floor of anterior cranial fossa
- frontal sinus
- air-filled space within the frontal bone; most anterior of the paranasal sinuses
- glabella
- slight depression of frontal bone, located at the midline between the eyebrows
- greater wings of sphenoid bone
- lateral projections of the sphenoid bone that form the anterior wall of the middle cranial fossa and an area of the lateral skull
- hard palate
- bony structure that forms the roof of the mouth and floor of the nasal cavity, formed by the palatine process of the maxillary bones and the horizontal plate of the palatine bones
- head of the rib
- posterior end of a rib that articulates with the bodies of thoracic vertebrae
- horizontal plate
- medial extension from the palatine bone that forms the posterior quarter of the hard palate
- hyoid bone
- small, U-shaped bone located in upper neck that does not contact any other bone
- hypoglossal canal
- paired openings that pass anteriorly from the anterior-lateral margins of the foramen magnum deep to the occipital condyles
- hypophyseal (pituitary) fossa
- shallow depression on top of the sella turcica that houses the pituitary (hypophyseal) gland
- inferior articular process
- bony process that extends downward from the vertebral arch of a vertebra that articulates with the superior articular process of the next lower vertebra
- inferior nasal concha
- one of the paired bones that project from the lateral walls of the nasal cavity to form the largest and most inferior of the nasal conchae
- infraorbital foramen
- opening located on anterior skull, below the orbit
- infratemporal fossa
- space on lateral side of skull, below the level of the zygomatic arch and deep (medial) to the ramus of the mandible
- internal acoustic meatus
- opening into petrous ridge, located on the lateral wall of the posterior cranial fossa
- intervertebral disc
- structure located between the bodies of adjacent vertebrae that strongly joins the vertebrae; provides padding, weight bearing ability, and enables vertebral column movements
- intervertebral foramen
- opening located between adjacent vertebrae for exit of a spinal nerve
- jugular (suprasternal) notch
- shallow notch located on superior surface of sternal manubrium
- jugular foramen
- irregularly shaped opening located in the lateral floor of the posterior cranial cavity
- kyphosis
- (also, humpback or hunchback) excessive posterior curvature of the thoracic vertebral column region
- lacrimal bone
- paired bones that contribute to the anterior-medial wall of each orbit
- lacrimal fossa
- shallow depression in the anterior-medial wall of the orbit, formed by the lacrimal bone that gives rise to the nasolacrimal canal
- lambdoid suture
- inverted V-shaped joint that unites the occipital bone to the right and left parietal bones on the posterior skull
- lamina
- portion of the vertebral arch on each vertebra that extends between the transverse and spinous process
- lateral pterygoid plate
- paired, flattened bony projections of the sphenoid bone located on the inferior skull, lateral to the medial pterygoid plate
- lateral sacral crest
- paired irregular ridges running down the lateral sides of the posterior sacrum that was formed by the fusion of the transverse processes from the five sacral vertebrae
- lesser wings of the sphenoid bone
- lateral extensions of the sphenoid bone that form the bony lip separating the anterior and middle cranial fossae
- ligamentum flavum
- series of short ligaments that unite the lamina of adjacent vertebrae
- lingula
- small flap of bone located on the inner (medial) surface of mandibular ramus, next to the mandibular foramen
- lordosis
- (also, swayback) excessive anterior curvature of the lumbar vertebral column region
- lumbar curve
- posteriorly concave curvature of the lumbar vertebral column region; a secondary curve of the vertebral column
- lumbar vertebrae
- five vertebrae numbered as L1–L5 that are located in lumbar region (lower back) of the vertebral column
- mandible
- unpaired bone that forms the lower jaw bone; the only moveable bone of the skull
- mandibular foramen
- opening located on the inner (medial) surface of the mandibular ramus
- mandibular fossa
- oval depression located on the inferior surface of the skull
- mandibular notch
- large U-shaped notch located between the condylar process and coronoid process of the mandible
- manubrium
- expanded, superior portion of the sternum
- mastoid process
- large bony prominence on the inferior, lateral skull, just behind the earlobe
- maxillary bone
- (also, maxilla) paired bones that form the upper jaw and anterior portion of the hard palate
- maxillary sinus
- air-filled space located with each maxillary bone; largest of the paranasal sinuses
- medial pterygoid plate
- paired, flattened bony projections of the sphenoid bone located on the inferior skull medial to the lateral pterygoid plate; form the posterior portion of the nasal cavity lateral wall
- median sacral crest
- irregular ridge running down the midline of the posterior sacrum that was formed from the fusion of the spinous processes of the five sacral vertebrae
- mental foramen
- opening located on the anterior-lateral side of the mandibular body
- mental protuberance
- inferior margin of anterior mandible that forms the chin
- middle cranial fossa
- centrally located cranial fossa that extends from the lesser wings of the sphenoid bone to the petrous ridge
- middle nasal concha
- nasal concha formed by the ethmoid bone that is located between the superior and inferior conchae
- mylohyoid line
- bony ridge located along the inner (medial) surface of the mandibular body
- nasal bone
- paired bones that form the base of the nose
- nasal cavity
- opening through skull for passage of air
- nasal conchae
- curved bony plates that project from the lateral walls of the nasal cavity; include the superior and middle nasal conchae, which are parts of the ethmoid bone, and the independent inferior nasal conchae bone
- nasal septum
- flat, midline structure that divides the nasal cavity into halves, formed by the perpendicular plate of the ethmoid bone, vomer bone, and septal cartilage
- nasolacrimal canal
- passage for drainage of tears that extends downward from the medial-anterior orbit to the nasal cavity, terminating behind the inferior nasal conchae
- neck of the rib
- narrowed region of a rib, next to the rib head
- notochord
- rod-like structure along dorsal side of the early embryo; largely disappears during later development but does contribute to formation of the intervertebral discs
- nuchal ligament
- expanded portion of the supraspinous ligament within the posterior neck; interconnects the spinous processes of the cervical vertebrae and attaches to the base of the skull
- nucleus pulposus
- gel-like central region of an intervertebral disc; provides for padding, weight-bearing, and movement between adjacent vertebrae
- occipital bone
- unpaired bone that forms the posterior portions of the brain case and base of the skull
- occipital condyle
- paired, oval-shaped bony knobs located on the inferior skull, to either side of the foramen magnum
- optic canal
- opening spanning between middle cranial fossa and posterior orbit
- orbit
- bony socket that contains the eyeball and associated muscles
- palatine bone
- paired bones that form the posterior quarter of the hard palate and a small area in floor of the orbit
- palatine process
- medial projection from the maxilla bone that forms the anterior three quarters of the hard palate
- paranasal sinuses
- cavities within the skull that are connected to the conchae that serve to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consist of frontal, maxillary, sphenoidal, and ethmoidal sinuses
- parietal bone
- paired bones that form the upper, lateral sides of the skull
- pedicle
- portion of the vertebral arch that extends from the vertebral body to the transverse process
- perpendicular plate of the ethmoid bone
- downward, midline extension of the ethmoid bone that forms the superior portion of the nasal septum
- petrous ridge
- petrous portion of the temporal bone that forms a large, triangular ridge in the floor of the cranial cavity, separating the middle and posterior cranial fossae; houses the middle and inner ear structures
- posterior (dorsal) sacral foramen
- one of the series of paired openings located on the posterior (dorsal) side of the sacrum
- posterior arch
- posterior portion of the ring-like C1 (atlas) vertebra
- posterior cranial fossa
- deepest and most posterior cranial fossa; extends from the petrous ridge to the occipital bone
- posterior longitudinal ligament
- ligament that runs the length of the vertebral column, uniting the posterior sides of the vertebral bodies
- primary curve
- anteriorly concave curvatures of the thoracic and sacrococcygeal regions that are retained from the original fetal curvature of the vertebral column
- pterion
- H-shaped suture junction region that unites the frontal, parietal, temporal, and sphenoid bones on the lateral side of the skull
- ramus of the mandible
- vertical portion of the mandible
- ribs
- thin, curved bones of the chest wall
- sacral canal
- bony tunnel that runs through the sacrum
- sacral foramina
- series of paired openings for nerve exit located on both the anterior (ventral) and posterior (dorsal) aspects of the sacrum
- sacral hiatus
- inferior opening and termination of the sacral canal
- sacral promontory
- anterior lip of the base (superior end) of the sacrum
- sacrococcygeal curve
- anteriorly concave curvature formed by the sacrum and coccyx; a primary curve of the vertebral column
- sacrum
- single bone located near the inferior end of the adult vertebral column that is formed by the fusion of five sacral vertebrae; forms the posterior portion of the pelvis
- sagittal suture
- joint that unites the right and left parietal bones at the midline along the top of the skull
- sclerotome
- medial portion of a somite consisting of mesenchyme tissue that will give rise to bone, cartilage, and fibrous connective tissues
- scoliosis
- abnormal lateral curvature of the vertebral column
- secondary curve
- posteriorly concave curvatures of the cervical and lumbar regions of the vertebral column that develop after the time of birth
- sella turcica
- elevated area of sphenoid bone located at midline of the middle cranial fossa
- septal cartilage
- flat cartilage structure that forms the anterior portion of the nasal septum
- skeleton
- bones of the body
- skull
- bony structure that forms the head, face, and jaws, and protects the brain; consists of 22 bones
- somite
- one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo
- sphenoid bone
- unpaired bone that forms the central base of skull
- sphenoid sinus
- air-filled space located within the sphenoid bone; most posterior of the paranasal sinuses
- spinous process
- unpaired bony process that extends posteriorly from the vertebral arch of a vertebra
- squamous suture
- joint that unites the parietal bone to the squamous portion of the temporal bone on the lateral side of the skull
- sternal angle
- junction line between manubrium and body of the sternum and the site for attachment of the second rib to the sternum
- sternum
- flattened bone located at the center of the anterior chest
- styloid process
- downward projecting, elongated bony process located on the inferior aspect of the skull
- stylomastoid foramen
- opening located on inferior skull, between the styloid process and mastoid process
- superior articular process
- bony process that extends upward from the vertebral arch of a vertebra that articulates with the inferior articular process of the next higher vertebra
- superior articular process of the sacrum
- paired processes that extend upward from the sacrum to articulate (join) with the inferior articular processes from the L5 vertebra
- superior nasal concha
- smallest and most superiorly located of the nasal conchae; formed by the ethmoid bone
- superior nuchal line
- paired bony lines on the posterior skull that extend laterally from the external occipital protuberance
- superior orbital fissure
- irregularly shaped opening between the middle cranial fossa and the posterior orbit
- supraorbital foramen
- opening located on anterior skull, at the superior margin of the orbit
- supraorbital margin
- superior margin of the orbit
- supraspinous ligament
- ligament that interconnects the spinous processes of the thoracic and lumbar vertebrae
- suture
- junction line at which adjacent bones of the skull are united by fibrous connective tissue
- temporal bone
- paired bones that form the lateral, inferior portions of the skull, with squamous, mastoid, and petrous portions
- temporal fossa
- shallow space on the lateral side of the skull, above the level of the zygomatic arch
- temporal process of the zygomatic bone
- short extension from the zygomatic bone that forms the anterior portion of the zygomatic arch
- thoracic cage
- consists of 12 pairs of ribs and sternum
- thoracic curve
- anteriorly concave curvature of the thoracic vertebral column region; a primary curve of the vertebral column
- thoracic vertebrae
- twelve vertebrae numbered as T1–T12 that are located in the thoracic region (upper back) of the vertebral column
- transverse foramen
- opening found only in the transverse processes of cervical vertebrae
- transverse process
- paired bony processes that extends laterally from the vertebral arch of a vertebra
- true ribs
- vertebrosternal ribs 1–7 that attach via their costal cartilage directly to the sternum
- tubercle of the rib
- small bump on the posterior side of a rib for articulation with the transverse process of a thoracic vertebra
- vertebra
- individual bone in the neck and back regions of the vertebral column
- vertebral (spinal) canal
- bony passageway within the vertebral column for the spinal cord that is formed by the series of individual vertebral foramina
- vertebral arch
- bony arch formed by the posterior portion of each vertebra that surrounds and protects the spinal cord
- vertebral column
- entire sequence of bones that extend from the skull to the tailbone
- vertebral foramen
- opening associated with each vertebra defined by the vertebral arch that provides passage for the spinal cord
- vomer bone
- unpaired bone that forms the inferior and posterior portions of the nasal septum
- xiphoid process
- small process that forms the inferior tip of the sternum
- zygomatic arch
- elongated, free-standing arch on the lateral skull, formed anteriorly by the temporal process of the zygomatic bone and posteriorly by the zygomatic process of the temporal bone
- zygomatic bone
- cheekbone; paired bones that contribute to the lateral orbit and anterior zygomatic arch
- zygomatic process of the temporal bone
- extension from the temporal bone that forms the posterior portion of the zygomatic arch
Chapter Review
7.1 Divisions of the Skeletal System
The skeletal system includes all of the bones, cartilages, and ligaments of the body. It serves to support the body, protect the brain and other internal organs, and provides a rigid structure upon which muscles can pull to generate body movements. It also stores fat and the tissue responsible for the production of blood cells. The skeleton is subdivided into two parts. The axial skeleton forms a vertical axis that includes the head, neck, back, and chest. It has 80 bones and consists of the skull, vertebral column, and thoracic cage. The adult vertebral column consists of 24 vertebrae plus the sacrum and coccyx. The thoracic cage is formed by 12 pairs of ribs and the sternum. The appendicular skeleton consists of 126 bones in the adult and includes all of the bones of the upper and lower limbs plus the bones that anchor each limb to the axial skeleton.
7.2 The Skull
The skull consists of the brain case and the facial bones. The brain case surrounds and protects the brain, which occupies the cranial cavity inside the skull. It consists of the rounded calvaria and a complex base. The brain case is formed by eight bones, the paired parietal and temporal bones plus the unpaired frontal, occipital, sphenoid, and ethmoid bones. The narrow gap between the bones is filled with dense, fibrous connective tissue that unites the bones. The sagittal suture joins the right and left parietal bones. The coronal suture joins the parietal bones to the frontal bone, the lamboid suture joins them to the occipital bone, and the squamous suture joins them to the temporal bone.
The facial bones support the facial structures and form the upper and lower jaws. These consist of 14 bones, with the paired maxillary, palatine, zygomatic, nasal, lacrimal, and inferior conchae bones and the unpaired vomer and mandible bones. The ethmoid bone also contributes to the formation of facial structures. The maxilla forms the upper jaw and the mandible forms the lower jaw. The maxilla also forms the larger anterior portion of the hard palate, which is completed by the smaller palatine bones that form the posterior portion of the hard palate.
The floor of the cranial cavity increases in depth from front to back and is divided into three cranial fossae. The anterior cranial fossa is located between the frontal bone and lesser wing of the sphenoid bone. A small area of the ethmoid bone, consisting of the crista galli and cribriform plates, is located at the midline of this fossa. The middle cranial fossa extends from the lesser wing of the sphenoid bone to the petrous ridge (petrous portion of temporal bone). The right and left sides are separated at the midline by the sella turcica, which surrounds the shallow hypophyseal fossa. Openings through the skull in the floor of the middle fossa include the optic canal and superior orbital fissure, which open into the posterior orbit, the foramen rotundum, foramen ovale, and foramen spinosum, and the exit of the carotid canal with its underlying foramen lacerum. The deep posterior cranial fossa extends from the petrous ridge to the occipital bone. Openings here include the large foramen magnum, plus the internal acoustic meatus, jugular foramina, and hypoglossal canals. Additional openings located on the external base of the skull include the stylomastoid foramen and the entrance to the carotid canal.
The anterior skull has the orbits that house the eyeballs and associated muscles. The walls of the orbit are formed by contributions from seven bones: the frontal, zygomatic, maxillary, palatine, ethmoid, lacrimal, and sphenoid. Located at the superior margin of the orbit is the supraorbital foramen, and below the orbit is the infraorbital foramen. The mandible has two openings, the mandibular foramen on its inner surface and the mental foramen on its external surface near the chin. The nasal conchae are bony projections from the lateral walls of the nasal cavity. The large inferior nasal concha is an independent bone, while the middle and superior conchae are parts of the ethmoid bone. The nasal septum is formed by the perpendicular plate of the ethmoid bone, the vomer bone, and the septal cartilage. The paranasal sinuses are air-filled spaces located within the frontal, maxillary, sphenoid, and ethmoid bones.
On the lateral skull, the zygomatic arch consists of two parts, the temporal process of the zygomatic bone anteriorly and the zygomatic process of the temporal bone posteriorly. The temporal fossa is the shallow space located on the lateral skull above the level of the zygomatic arch. The infratemporal fossa is located below the zygomatic arch and deep to the ramus of the mandible.
The hyoid bone is located in the upper neck and does not join with any other bone. It is held in position by muscles and serves to support the tongue above, the larynx below, and the pharynx posteriorly.
7.3 The Vertebral Column
The vertebral column forms the neck and back. The vertebral column originally develops as 33 vertebrae, but is eventually reduced to 24 vertebrae, plus the sacrum and coccyx. The vertebrae are divided into the cervical region (C1–C7 vertebrae), the thoracic region (T1–T12 vertebrae), and the lumbar region (L1–L5 vertebrae). The sacrum arises from the fusion of five sacral vertebrae and the coccyx from the fusion of four small coccygeal vertebrae. The vertebral column has four curvatures, the cervical, thoracic, lumbar, and sacrococcygeal curves. The thoracic and sacrococcygeal curves are primary curves retained from the original fetal curvature. The cervical and lumbar curves develop after birth and thus are secondary curves. The cervical curve develops as the infant begins to hold up the head, and the lumbar curve appears with standing and walking.
A typical vertebra consists of an enlarged anterior portion called the body, which provides weight-bearing support. Attached posteriorly to the body is a vertebral arch, which surrounds and defines the vertebral foramen for passage of the spinal cord. The vertebral arch consists of the pedicles, which attach to the vertebral body, and the laminae, which come together to form the roof of the arch. Arising from the vertebral arch are the laterally projecting transverse processes and the posteriorly oriented spinous process. The superior articular processes project upward, where they articulate with the downward projecting inferior articular processes of the next higher vertebrae.
A typical cervical vertebra has a small body, a bifid (Y-shaped) spinous process, and U-shaped transverse processes with a transverse foramen. In addition to these characteristics, the axis (C2 vertebra) also has the dens projecting upward from the vertebral body. The atlas (C1 vertebra) differs from the other cervical vertebrae in that it does not have a body, but instead consists of bony ring formed by the anterior and posterior arches. The atlas articulates with the dens from the axis. A typical thoracic vertebra is distinguished by its long, downward projecting spinous process. Thoracic vertebrae also have articulation facets on the body and transverse processes for attachment of the ribs. Lumbar vertebrae support the greatest amount of body weight and thus have a large, thick body. They also have a short, blunt spinous process. The sacrum is triangular in shape. The median sacral crest is formed by the fused vertebral spinous processes and the lateral sacral crest is derived from the fused transverse processes. Anterior (ventral) and posterior (dorsal) sacral foramina allow branches of the sacral spinal nerves to exit the sacrum. The auricular surfaces are articulation sites on the lateral sacrum that anchor the sacrum to the hipbones to form the pelvis. The coccyx is small and derived from the fusion of four small vertebrae.
The intervertebral discs fill in the gaps between the bodies of adjacent vertebrae. They provide strong attachments and padding between the vertebrae. The outer, fibrous layer of a disc is called the anulus fibrosus. The gel-like interior is called the nucleus pulposus. The disc can change shape to allow for movement between vertebrae. If the anulus fibrosus is weakened or damaged, the nucleus pulposus can protrude outward, resulting in a herniated disc.
The anterior longitudinal ligament runs along the full length of the anterior vertebral column, uniting the vertebral bodies. The supraspinous ligament is located posteriorly and interconnects the spinous processes of the thoracic and lumbar vertebrae. In the neck, this ligament expands to become the nuchal ligament. The nuchal ligament is attached to the cervical spinous processes and superiorly to the base of the skull, out to the external occipital protuberance. The posterior longitudinal ligament runs within the vertebral canal and unites the posterior sides of the vertebral bodies. The ligamentum flavum unites the lamina of adjacent vertebrae.
7.4 The Thoracic Cage
The thoracic cage protects the heart and lungs. It is composed of 12 pairs of ribs with their costal cartilages and the sternum. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The manubrium and body are joined at the sternal angle, which is also the site for attachment of the second ribs.
Ribs are flattened, curved bones and are numbered 1–12. Posteriorly, the head of the rib articulates with the costal facets located on the bodies of thoracic vertebrae and the rib tubercle articulates with the facet located on the vertebral transverse process. The angle of the ribs forms the most posterior portion of the thoracic cage. The costal groove in the inferior margin of each rib carries blood vessels and a nerve. Anteriorly, each rib ends in a costal cartilage. True ribs (1–7) attach directly to the sternum via their costal cartilage. The false ribs (8–12) either attach to the sternum indirectly or not at all. Ribs 8–10 have their costal cartilages attached to the cartilage of the next higher rib. The floating ribs (11–12) are short and do not attach to the sternum or to another rib.
7.5 Embryonic Development of the Axial Skeleton
Formation of the axial skeleton begins during early embryonic development with the appearance of the rod-like notochord along the dorsal length of the early embryo. Repeating, paired blocks of tissue called somites then appear along either side of notochord. As the somites grow, they split into parts, one of which is called a sclerotome. This consists of mesenchyme, the embryonic tissue that will become the bones, cartilages, and connective tissues of the body.
Mesenchyme in the head region will produce the bones of the skull via two different mechanisms. The bones of the brain case arise via intramembranous ossification in which embryonic mesenchyme tissue converts directly into bone. At the time of birth, these bones are separated by fontanelles, wide areas of fibrous connective tissue. As the bones grow, the fontanelles are reduced to sutures, which allow for continued growth of the skull throughout childhood. In contrast, the cranial base and facial bones are produced by the process of endochondral ossification, in which mesenchyme tissue initially produces a hyaline cartilage model of the future bone. The cartilage model allows for growth of the bone and is gradually converted into bone over a period of many years.
The vertebrae, ribs, and sternum also develop via endochondral ossification. Mesenchyme accumulates around the notochord and produces hyaline cartilage models of the vertebrae. The notochord largely disappears, but remnants of the notochord contribute to formation of the intervertebral discs. In the thorax region, a portion of the vertebral cartilage model splits off to form the ribs. These then become attached anteriorly to the developing cartilage model of the sternum. Growth of the cartilage models for the vertebrae, ribs, and sternum allow for enlargement of the thoracic cage during childhood and adolescence. The cartilage models gradually undergo ossification and are converted into bone.
Interactive Link Questions
Watch this video to view a rotating and exploded skull with color-coded bones. Which bone (yellow) is centrally located and joins with most of the other bones of the skull?
2.View this animation to see how a blow to the head may produce a contrecoup (counterblow) fracture of the basilar portion of the occipital bone on the base of the skull. Why may a basilar fracture be life threatening?
3.Osteoporosis is a common age-related bone disease in which bone density and strength is decreased. Watch this videoto get a better understanding of how thoracic vertebrae may become weakened and may fractured due to this disease. How may vertebral osteoporosis contribute to kyphosis?
4.Watch this animation to see what it means to “slip” a disk. Watch this second animation to see one possible treatment for a herniated disc, removing and replacing the damaged disc with an artificial one that allows for movement between the adjacent certebrae. How could lifting a heavy object produce pain in a lower limb?
5.Use this tool to identify the bones, intervertebral discs, and ligaments of the vertebral column. The thickest portions of the anterior longitudinal ligament and the supraspinous ligament are found in which regions of the vertebral column?
6.View this video to review the two processes that give rise to the bones of the skull and body. What are the two mechanisms by which the bones of the body are formed and which bones are formed by each mechanism?
Review Questions
Which of the following is part of the axial skeleton?
- shoulder bones
- thigh bone
- foot bones
- vertebral column
Which of the following is a function of the axial skeleton?
- allows for movement of the wrist and hand
- protects nerves and blood vessels at the elbow
- supports trunk of body
- allows for movements of the ankle and foot
The axial skeleton ________.
- consists of 126 bones
- forms the vertical axis of the body
- includes all bones of the body trunk and limbs
- includes only the bones of the lower limbs
Which of the following is a bone of the brain case?
- parietal bone
- zygomatic bone
- maxillary bone
- lacrimal bone
The lambdoid suture joins the parietal bone to the ________.
- frontal bone
- occipital bone
- other parietal bone
- temporal bone
The middle cranial fossa ________.
- is bounded anteriorly by the petrous ridge
- is bounded posteriorly by the lesser wing of the sphenoid bone
- is divided at the midline by a small area of the ethmoid bone
- has the foramen rotundum, foramen ovale, and foramen spinosum
The paranasal sinuses are ________.
- air-filled spaces found within the frontal, maxilla, sphenoid, and ethmoid bones only
- air-filled spaces found within all bones of the skull
- not connected to the nasal cavity
- divided at the midline by the nasal septum
Parts of the sphenoid bone include the ________.
- sella turcica
- squamous portion
- glabella
- zygomatic process
The bony openings of the skull include the ________.
- carotid canal, which is located in the anterior cranial fossa
- superior orbital fissure, which is located at the superior margin of the anterior orbit
- mental foramen, which is located just below the orbit
- hypoglossal canal, which is located in the posterior cranial fossa
The cervical region of the vertebral column consists of ________.
- seven vertebrae
- 12 vertebrae
- five vertebrae
- a single bone derived from the fusion of five vertebrae
The primary curvatures of the vertebral column ________.
- include the lumbar curve
- are remnants of the original fetal curvature
- include the cervical curve
- develop after the time of birth
A typical vertebra has ________.
- a vertebral foramen that passes through the body
- a superior articular process that projects downward to articulate with the superior portion of the next lower vertebra
- lamina that spans between the transverse process and spinous process
- a pair of laterally projecting spinous processes
A typical lumbar vertebra has ________.
- a short, rounded spinous process
- a bifid spinous process
- articulation sites for ribs
- a transverse foramen
Which is found only in the cervical region of the vertebral column?
- nuchal ligament
- ligamentum flavum
- supraspinous ligament
- anterior longitudinal ligament
The sternum ________.
- consists of only two parts, the manubrium and xiphoid process
- has the sternal angle located between the manubrium and body
- receives direct attachments from the costal cartilages of all 12 pairs of ribs
- articulates directly with the thoracic vertebrae
The sternal angle is the ________.
- junction between the body and xiphoid process
- site for attachment of the clavicle
- site for attachment of the floating ribs
- junction between the manubrium and body
The tubercle of a rib ________.
- is for articulation with the transverse process of a thoracic vertebra
- is for articulation with the body of a thoracic vertebra
- provides for passage of blood vessels and a nerve
- is the area of greatest rib curvature
True ribs are ________.
- ribs 8–12
- attached via their costal cartilage to the next higher rib
- made entirely of bone, and thus do not have a costal cartilage
- attached via their costal cartilage directly to the sternum
Embryonic development of the axial skeleton involves ________.
- intramembranous ossification, which forms the facial bones.
- endochondral ossification, which forms the ribs and sternum
- the notochord, which produces the cartilage models for the vertebrae
- the formation of hyaline cartilage models, which give rise to the flat bones of the skull
A fontanelle ________.
- is the cartilage model for a vertebra that later is converted into bone
- gives rise to the facial bones and vertebrae
- is the rod-like structure that runs the length of the early embryo
- is the area of fibrous connective tissue found at birth between the brain case bones
Critical Thinking Questions
Define the two divisions of the skeleton.
28.Discuss the functions of the axial skeleton.
29.Define and list the bones that form the brain case or support the facial structures.
30.Identify the major sutures of the skull, their locations, and the bones united by each.
31.Describe the anterior, middle, and posterior cranial fossae and their boundaries, and give the midline structure that divides each into right and left areas.
32.Describe the parts of the nasal septum in both the dry and living skull.
33.Describe the vertebral column and define each region.
34.Describe a typical vertebra.
35.Describe the sacrum.
36.Describe the structure and function of an intervertebral disc.
37.Define the ligaments of the vertebral column.
38.Define the parts and functions of the thoracic cage.
39.Describe the parts of the sternum.
40.Discuss the parts of a typical rib.
41.Define the classes of ribs.
42.Discuss the processes by which the brain-case bones of the skull are formed and grow during skull enlargement.
43.Discuss the process that gives rise to the base and facial bones of the skull.
44.Discuss the development of the vertebrae, ribs, and sternum.
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2025-03-18T00:38:17.808009
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https://oercommons.org/courseware/lesson/56367/overview
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The Appendicular Skeleton
Introduction
Figure 8.1 Dancer The appendicular skeleton consists of the upper and lower limb bones, the bones of the hands and feet, and the bones that anchor the limbs to the axial skeleton. (credit: Melissa Dooley/flickr)
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Discuss the bones of the pectoral and pelvic girdles, and describe how these unite the limbs with the axial skeleton
- Describe the bones of the upper limb, including the bones of the arm, forearm, wrist, and hand
- Identify the features of the pelvis and explain how these differ between the adult male and female pelvis
- Describe the bones of the lower limb, including the bones of the thigh, leg, ankle, and foot
- Describe the embryonic formation and growth of the limb bones
Your skeleton provides the internal supporting structure of the body. The adult axial skeleton consists of 80 bones that form the head and body trunk. Attached to this are the limbs, whose 126 bones constitute the appendicular skeleton. These bones are divided into two groups: the bones that are located within the limbs themselves, and the girdle bones that attach the limbs to the axial skeleton. The bones of the shoulder region form the pectoral girdle, which anchors the upper limb to the thoracic cage of the axial skeleton. The lower limb is attached to the vertebral column by the pelvic girdle.
Because of our upright stance, different functional demands are placed upon the upper and lower limbs. Thus, the bones of the lower limbs are adapted for weight-bearing support and stability, as well as for body locomotion via walking or running. In contrast, our upper limbs are not required for these functions. Instead, our upper limbs are highly mobile and can be utilized for a wide variety of activities. The large range of upper limb movements, coupled with the ability to easily manipulate objects with our hands and opposable thumbs, has allowed humans to construct the modern world in which we live.
The Pectoral Girdle
- Describe the bones that form the pectoral girdle
- List the functions of the pectoral girdle
The appendicular skeleton includes all of the limb bones, plus the bones that unite each limb with the axial skeleton (Figure 8.2). The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). This consists of two bones, the scapula and clavicle (Figure 8.3). The clavicle (collarbone) is an S-shaped bone located on the anterior side of the shoulder. It is attached on its medial end to the sternum of the thoracic cage, which is part of the axial skeleton. The lateral end of the clavicle articulates (joins) with the scapula just above the shoulder joint. You can easily palpate, or feel with your fingers, the entire length of your clavicle.
Figure 8.2 Axial and Appendicular Skeletons The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and thoracic cage. The appendicular skeleton consists of the pectoral and pelvic girdles, the limb bones, and the bones of the hands and feet.
Figure 8.3 Pectoral Girdle The pectoral girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial skeleton.
The scapula (shoulder blade) lies on the posterior aspect of the shoulder. It is supported by the clavicle and articulates with the humerus (arm bone) to form the shoulder joint. The scapula is a flat, triangular-shaped bone with a prominent ridge running across its posterior surface. This ridge extends out laterally, where it forms the bony tip of the shoulder and joins with the lateral end of the clavicle. By following along the clavicle, you can palpate out to the bony tip of the shoulder, and from there, you can move back across your posterior shoulder to follow the ridge of the scapula. Move your shoulder around and feel how the clavicle and scapula move together as a unit. Both of these bones serve as important attachment sites for muscles that aid with movements of the shoulder and arm.
The right and left pectoral girdles are not joined to each other, allowing each to operate independently. In addition, the clavicle of each pectoral girdle is anchored to the axial skeleton by a single, highly mobile joint. This allows for the extensive mobility of the entire pectoral girdle, which in turn enhances movements of the shoulder and upper limb.
Clavicle
The clavicle is the only long bone that lies in a horizontal position in the body (see Figure 8.3). The clavicle has several important functions. First, anchored by muscles from above, it serves as a strut that extends laterally to support the scapula. This in turn holds the shoulder joint superiorly and laterally from the body trunk, allowing for maximal freedom of motion for the upper limb. The clavicle also transmits forces acting on the upper limb to the sternum and axial skeleton. Finally, it serves to protect the underlying nerves and blood vessels as they pass between the trunk of the body and the upper limb.
The clavicle has three regions: the medial end, the lateral end, and the shaft. The medial end, known as the sternal end of the clavicle, has a triangular shape and articulates with the manubrium portion of the sternum. This forms the sternoclavicular joint, which is the only bony articulation between the pectoral girdle of the upper limb and the axial skeleton. This joint allows considerable mobility, enabling the clavicle and scapula to move in upward/downward and anterior/posterior directions during shoulder movements. The sternoclavicular joint is indirectly supported by the costoclavicular ligament (costo- = “rib”), which spans the sternal end of the clavicle and the underlying first rib. The lateral or acromial end of the clavicle articulates with the acromion of the scapula, the portion of the scapula that forms the bony tip of the shoulder. There are some sex differences in the morphology of the clavicle. In women, the clavicle tends to be shorter, thinner, and less curved. In men, the clavicle is heavier and longer, and has a greater curvature and rougher surfaces where muscles attach, features that are more pronounced in manual workers.
The clavicle is the most commonly fractured bone in the body. Such breaks often occur because of the force exerted on the clavicle when a person falls onto his or her outstretched arms, or when the lateral shoulder receives a strong blow. Because the sternoclavicular joint is strong and rarely dislocated, excessive force results in the breaking of the clavicle, usually between the middle and lateral portions of the bone. If the fracture is complete, the shoulder and lateral clavicle fragment will drop due to the weight of the upper limb, causing the person to support the sagging limb with their other hand. Muscles acting across the shoulder will also pull the shoulder and lateral clavicle anteriorly and medially, causing the clavicle fragments to override. The clavicle overlies many important blood vessels and nerves for the upper limb, but fortunately, due to the anterior displacement of a broken clavicle, these structures are rarely affected when the clavicle is fractured.
Scapula
The scapula is also part of the pectoral girdle and thus plays an important role in anchoring the upper limb to the body. The scapula is located on the posterior side of the shoulder. It is surrounded by muscles on both its anterior (deep) and posterior (superficial) sides, and thus does not articulate with the ribs of the thoracic cage.
The scapula has several important landmarks (Figure 8.4). The three margins or borders of the scapula, named for their positions within the body, are the superior border of the scapula, the medial border of the scapula, and the lateral border of the scapula. The suprascapular notch is located lateral to the midpoint of the superior border. The corners of the triangular scapula, at either end of the medial border, are the superior angle of the scapula, located between the medial and superior borders, and the inferior angle of the scapula, located between the medial and lateral borders. The inferior angle is the most inferior portion of the scapula, and is particularly important because it serves as the attachment point for several powerful muscles involved in shoulder and upper limb movements. The remaining corner of the scapula, between the superior and lateral borders, is the location of the glenoid cavity (glenoid fossa). This shallow depression articulates with the humerus bone of the arm to form the glenohumeral joint (shoulder joint). The small bony bumps located immediately above and below the glenoid cavity are the supraglenoid tubercle and the infraglenoid tubercle, respectively. These provide attachments for muscles of the arm.
Figure 8.4 Scapula The isolated scapula is shown here from its anterior (deep) side and its posterior (superficial) side.
The scapula also has two prominent projections. Toward the lateral end of the superior border, between the suprascapular notch and glenoid cavity, is the hook-like coracoid process (coracoid = “shaped like a crow’s beak”). This process projects anteriorly and curves laterally. At the shoulder, the coracoid process is located inferior to the lateral end of the clavicle. It is anchored to the clavicle by a strong ligament, and serves as the attachment site for muscles of the anterior chest and arm. On the posterior aspect, the spine of the scapula is a long and prominent ridge that runs across its upper portion. Extending laterally from the spine is a flattened and expanded region called the acromion or acromial process. The acromion forms the bony tip of the superior shoulder region and articulates with the lateral end of the clavicle, forming the acromioclavicular joint (see Figure 8.3). Together, the clavicle, acromion, and spine of the scapula form a V-shaped bony line that provides for the attachment of neck and back muscles that act on the shoulder, as well as muscles that pass across the shoulder joint to act on the arm.
The scapula has three depressions, each of which is called a fossa (plural = fossae). Two of these are found on the posterior scapula, above and below the scapular spine. Superior to the spine is the narrow supraspinous fossa, and inferior to the spine is the broad infraspinous fossa. The anterior (deep) surface of the scapula forms the broad subscapular fossa. All of these fossae provide large surface areas for the attachment of muscles that cross the shoulder joint to act on the humerus.
The acromioclavicular joint transmits forces from the upper limb to the clavicle. The ligaments around this joint are relatively weak. A hard fall onto the elbow or outstretched hand can stretch or tear the acromioclavicular ligaments, resulting in a moderate injury to the joint. However, the primary support for the acromioclavicular joint comes from a very strong ligament called the coracoclavicular ligament (see Figure 8.3). This connective tissue band anchors the coracoid process of the scapula to the inferior surface of the acromial end of the clavicle and thus provides important indirect support for the acromioclavicular joint. Following a strong blow to the lateral shoulder, such as when a hockey player is driven into the boards, a complete dislocation of the acromioclavicular joint can result. In this case, the acromion is thrust under the acromial end of the clavicle, resulting in ruptures of both the acromioclavicular and coracoclavicular ligaments. The scapula then separates from the clavicle, with the weight of the upper limb pulling the shoulder downward. This dislocation injury of the acromioclavicular joint is known as a “shoulder separation” and is common in contact sports such as hockey, football, or martial arts.
Bones of the Upper Limb
- Identify the divisions of the upper limb and describe the bones in each region
- List the bones and bony landmarks that articulate at each joint of the upper limb
The upper limb is divided into three regions. These consist of the arm, located between the shoulder and elbow joints; the forearm, which is between the elbow and wrist joints; and the hand, which is located distal to the wrist. There are 30 bones in each upper limb (see Figure 8.2). The humerus is the single bone of the upper arm, and the ulna (medially) and the radius(laterally) are the paired bones of the forearm. The base of the hand contains eight bones, each called a carpal bone, and the palm of the hand is formed by five bones, each called a metacarpal bone. The fingers and thumb contain a total of 14 bones, each of which is a phalanx bone of the hand.
Humerus
The humerus is the single bone of the upper arm region (Figure 8.5). At its proximal end is the head of the humerus. This is the large, round, smooth region that faces medially. The head articulates with the glenoid cavity of the scapula to form the glenohumeral (shoulder) joint. The margin of the smooth area of the head is the anatomical neck of the humerus. Located on the lateral side of the proximal humerus is an expanded bony area called the greater tubercle. The smaller lesser tubercle of the humerus is found on the anterior aspect of the humerus. Both the greater and lesser tubercles serve as attachment sites for muscles that act across the shoulder joint. Passing between the greater and lesser tubercles is the narrow intertubercular groove (sulcus), which is also known as the bicipital groove because it provides passage for a tendon of the biceps brachii muscle. The surgical neck is located at the base of the expanded, proximal end of the humerus, where it joins the narrow shaft of the humerus. The surgical neck is a common site of arm fractures. The deltoid tuberosity is a roughened, V-shaped region located on the lateral side in the middle of the humerus shaft. As its name indicates, it is the site of attachment for the deltoid muscle.
Figure 8.5 Humerus and Elbow Joint The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint.
Distally, the humerus becomes flattened. The prominent bony projection on the medial side is the medial epicondyle of the humerus. The much smaller lateral epicondyle of the humerus is found on the lateral side of the distal humerus. The roughened ridge of bone above the lateral epicondyle is the lateral supracondylar ridge. All of these areas are attachment points for muscles that act on the forearm, wrist, and hand. The powerful grasping muscles of the anterior forearm arise from the medial epicondyle, which is thus larger and more robust than the lateral epicondyle that gives rise to the weaker posterior forearm muscles.
The distal end of the humerus has two articulation areas, which join the ulna and radius bones of the forearm to form the elbow joint. The more medial of these areas is the trochlea, a spindle- or pulley-shaped region (trochlea = “pulley”), which articulates with the ulna bone. Immediately lateral to the trochlea is the capitulum (“small head”), a knob-like structure located on the anterior surface of the distal humerus. The capitulum articulates with the radius bone of the forearm. Just above these bony areas are two small depressions. These spaces accommodate the forearm bones when the elbow is fully bent (flexed). Superior to the trochlea is the coronoid fossa, which receives the coronoid process of the ulna, and above the capitulum is the radial fossa, which receives the head of the radius when the elbow is flexed. Similarly, the posterior humerus has the olecranon fossa, a larger depression that receives the olecranon process of the ulna when the forearm is fully extended.
Ulna
The ulna is the medial bone of the forearm. It runs parallel to the radius, which is the lateral bone of the forearm (Figure 8.6). The proximal end of the ulna resembles a crescent wrench with its large, C-shaped trochlear notch. This region articulates with the trochlea of the humerus as part of the elbow joint. The inferior margin of the trochlear notch is formed by a prominent lip of bone called the coronoid process of the ulna. Just below this on the anterior ulna is a roughened area called the ulnar tuberosity. To the lateral side and slightly inferior to the trochlear notch is a small, smooth area called the radial notch of the ulna. This area is the site of articulation between the proximal radius and the ulna, forming the proximal radioulnar joint. The posterior and superior portions of the proximal ulna make up the olecranon process, which forms the bony tip of the elbow.
Figure 8.6 Ulna and Radius The ulna is located on the medial side of the forearm, and the radius is on the lateral side. These bones are attached to each other by an interosseous membrane.
More distal is the shaft of the ulna. The lateral side of the shaft forms a ridge called the interosseous border of the ulna. This is the line of attachment for the interosseous membrane of the forearm, a sheet of dense connective tissue that unites the ulna and radius bones. The small, rounded area that forms the distal end is the head of the ulna. Projecting from the posterior side of the ulnar head is the styloid process of the ulna, a short bony projection. This serves as an attachment point for a connective tissue structure that unites the distal ends of the ulna and radius.
In the anatomical position, with the elbow fully extended and the palms facing forward, the arm and forearm do not form a straight line. Instead, the forearm deviates laterally by 5–15 degrees from the line of the arm. This deviation is called the carrying angle. It allows the forearm and hand to swing freely or to carry an object without hitting the hip. The carrying angle is larger in females to accommodate their wider pelvis.
Radius
The radius runs parallel to the ulna, on the lateral (thumb) side of the forearm (see Figure 8.6). The head of the radius is a disc-shaped structure that forms the proximal end. The small depression on the surface of the head articulates with the capitulum of the humerus as part of the elbow joint, whereas the smooth, outer margin of the head articulates with the radial notch of the ulna at the proximal radioulnar joint. The neck of the radius is the narrowed region immediately below the expanded head. Inferior to this point on the medial side is the radial tuberosity, an oval-shaped, bony protuberance that serves as a muscle attachment point. The shaft of the radius is slightly curved and has a small ridge along its medial side. This ridge forms the interosseous border of the radius, which, like the similar border of the ulna, is the line of attachment for the interosseous membrane that unites the two forearm bones. The distal end of the radius has a smooth surface for articulation with two carpal bones to form the radiocarpal joint or wrist joint (Figure 8.7 and Figure 8.8). On the medial side of the distal radius is the ulnar notch of the radius. This shallow depression articulates with the head of the ulna, which together form the distal radioulnar joint. The lateral end of the radius has a pointed projection called the styloid process of the radius. This provides attachment for ligaments that support the lateral side of the wrist joint. Compared to the styloid process of the ulna, the styloid process of the radius projects more distally, thereby limiting the range of movement for lateral deviations of the hand at the wrist joint.
INTERACTIVE LINK
Watch this video to see how fractures of the distal radius bone can affect the wrist joint. Explain the problems that may occur if a fracture of the distal radius involves the joint surface of the radiocarpal joint of the wrist.
Carpal Bones
The wrist and base of the hand are formed by a series of eight small carpal bones (see Figure 8.7). The carpal bones are arranged in two rows, forming a proximal row of four carpal bones and a distal row of four carpal bones. The bones in the proximal row, running from the lateral (thumb) side to the medial side, are the scaphoid (“boat-shaped”), lunate (“moon-shaped”), triquetrum (“three-cornered”), and pisiform (“pea-shaped”) bones. The small, rounded pisiform bone articulates with the anterior surface of the triquetrum bone. The pisiform thus projects anteriorly, where it forms the bony bump that can be felt at the medial base of your hand. The distal bones (lateral to medial) are the trapezium (“table”), trapezoid (“resembles a table”), capitate (“head-shaped”), and hamate (“hooked bone”) bones. The hamate bone is characterized by a prominent bony extension on its anterior side called the hook of the hamate bone.
A helpful mnemonic for remembering the arrangement of the carpal bones is “So Long To Pinky, Here Comes The Thumb.” This mnemonic starts on the lateral side and names the proximal bones from lateral to medial (scaphoid, lunate, triquetrum, pisiform), then makes a U-turn to name the distal bones from medial to lateral (hamate, capitate, trapezoid, trapezium). Thus, it starts and finishes on the lateral side.
Figure 8.7 Bones of the Wrist and Hand The eight carpal bones form the base of the hand. These are arranged into proximal and distal rows of four bones each. The metacarpal bones form the palm of the hand. The thumb and fingers consist of the phalanx bones.
The carpal bones form the base of the hand. This can be seen in the radiograph (X-ray image) of the hand that shows the relationships of the hand bones to the skin creases of the hand (see Figure 8.8). Within the carpal bones, the four proximal bones are united to each other by ligaments to form a unit. Only three of these bones, the scaphoid, lunate, and triquetrum, contribute to the radiocarpal joint. The scaphoid and lunate bones articulate directly with the distal end of the radius, whereas the triquetrum bone articulates with a fibrocartilaginous pad that spans the radius and styloid process of the ulna. The distal end of the ulna thus does not directly articulate with any of the carpal bones.
The four distal carpal bones are also held together as a group by ligaments. The proximal and distal rows of carpal bones articulate with each other to form the midcarpal joint (see Figure 8.8). Together, the radiocarpal and midcarpal joints are responsible for all movements of the hand at the wrist. The distal carpal bones also articulate with the metacarpal bones of the hand.
Figure 8.8 Bones of the Hand This radiograph shows the position of the bones within the hand. Note the carpal bones that form the base of the hand. (credit: modification of work by Trace Meek)
In the articulated hand, the carpal bones form a U-shaped grouping. A strong ligament called the flexor retinaculum spans the top of this U-shaped area to maintain this grouping of the carpal bones. The flexor retinaculum is attached laterally to the trapezium and scaphoid bones, and medially to the hamate and pisiform bones. Together, the carpal bones and the flexor retinaculum form a passageway called the carpal tunnel, with the carpal bones forming the walls and floor, and the flexor retinaculum forming the roof of this space (Figure 8.9). The tendons of nine muscles of the anterior forearm and an important nerve pass through this narrow tunnel to enter the hand. Overuse of the muscle tendons or wrist injury can produce inflammation and swelling within this space. This produces compression of the nerve, resulting in carpal tunnel syndrome, which is characterized by pain or numbness, and muscle weakness in those areas of the hand supplied by this nerve.
Figure 8.9 Carpal Tunnel The carpal tunnel is the passageway by which nine muscle tendons and a major nerve enter the hand from the anterior forearm. The walls and floor of the carpal tunnel are formed by the U-shaped grouping of the carpal bones, and the roof is formed by the flexor retinaculum, a strong ligament that anteriorly unites the bones.
Metacarpal Bones
The palm of the hand contains five elongated metacarpal bones. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb (see Figure 8.7). The proximal end of each metacarpal bone articulates with one of the distal carpal bones. Each of these articulations is a carpometacarpal joint (see Figure 8.8). The expanded distal end of each metacarpal bone articulates at the metacarpophalangeal joint with the proximal phalanx bone of the thumb or one of the fingers. The distal end also forms the knuckles of the hand, at the base of the fingers. The metacarpal bones are numbered 1–5, beginning at the thumb.
The first metacarpal bone, at the base of the thumb, is separated from the other metacarpal bones. This allows it a freedom of motion that is independent of the other metacarpal bones, which is very important for thumb mobility. The remaining metacarpal bones are united together to form the palm of the hand. The second and third metacarpal bones are firmly anchored in place and are immobile. However, the fourth and fifth metacarpal bones have limited anterior-posterior mobility, a motion that is greater for the fifth bone. This mobility is important during power gripping with the hand (Figure 8.10). The anterior movement of these bones, particularly the fifth metacarpal bone, increases the strength of contact for the medial hand during gripping actions.
Figure 8.10 Hand During Gripping During tight gripping—compare (b) to (a)—the fourth and, particularly, the fifth metatarsal bones are pulled anteriorly. This increases the contact between the object and the medial side of the hand, thus improving the firmness of the grip.
Phalanx Bones
The fingers and thumb contain 14 bones, each of which is called a phalanx bone (plural = phalanges), named after the ancient Greek phalanx (a rectangular block of soldiers). The thumb (pollex) is digit number 1 and has two phalanges, a proximal phalanx, and a distal phalanx bone (see Figure 8.7). Digits 2 (index finger) through 5 (little finger) have three phalanges each, called the proximal, middle, and distal phalanx bones. An interphalangeal joint is one of the articulations between adjacent phalanges of the digits (see Figure 8.8).
INTERACTIVE LINK
Visit this site to explore the bones and joints of the hand. What are the three arches of the hand, and what is the importance of these during the gripping of an object?
DISORDERS OF THE...
Appendicular System: Fractures of Upper Limb Bones
Due to our constant use of the hands and the rest of our upper limbs, an injury to any of these areas will cause a significant loss of functional ability. Many fractures result from a hard fall onto an outstretched hand. The resulting transmission of force up the limb may result in a fracture of the humerus, radius, or scaphoid bones. These injuries are especially common in elderly people whose bones are weakened due to osteoporosis.
Falls onto the hand or elbow, or direct blows to the arm, can result in fractures of the humerus (Figure 8.11). Following a fall, fractures at the surgical neck, the region at which the expanded proximal end of the humerus joins with the shaft, can result in an impacted fracture, in which the distal portion of the humerus is driven into the proximal portion. Falls or blows to the arm can also produce transverse or spiral fractures of the humeral shaft.
In children, a fall onto the tip of the elbow frequently results in a distal humerus fracture. In these, the olecranon of the ulna is driven upward, resulting in a fracture across the distal humerus, above both epicondyles (supracondylar fracture), or a fracture between the epicondyles, thus separating one or both of the epicondyles from the body of the humerus (intercondylar fracture). With these injuries, the immediate concern is possible compression of the artery to the forearm due to swelling of the surrounding tissues. If compression occurs, the resulting ischemia (lack of oxygen) due to reduced blood flow can quickly produce irreparable damage to the forearm muscles. In addition, four major nerves for shoulder and upper limb muscles are closely associated with different regions of the humerus, and thus, humeral fractures may also damage these nerves.
Another frequent injury following a fall onto an outstretched hand is a Colles fracture (“col-lees”) of the distal radius (see Figure 8.11). This involves a complete transverse fracture across the distal radius that drives the separated distal fragment of the radius posteriorly and superiorly. This injury results in a characteristic “dinner fork” bend of the forearm just above the wrist due to the posterior displacement of the hand. This is the most frequent forearm fracture and is a common injury in persons over the age of 50, particularly in older women with osteoporosis. It also commonly occurs following a high-speed fall onto the hand during activities such as snowboarding or skating.
The most commonly fractured carpal bone is the scaphoid, often resulting from a fall onto the hand. Deep pain at the lateral wrist may yield an initial diagnosis of a wrist sprain, but a radiograph taken several weeks after the injury, after tissue swelling has subsided, will reveal the fracture. Due to the poor blood supply to the scaphoid bone, healing will be slow and there is the danger of bone necrosis and subsequent degenerative joint disease of the wrist.
Figure 8.11 Fractures of the Humerus and Radius Falls or direct blows can result in fractures of the surgical neck or shaft of the humerus. Falls onto the elbow can fracture the distal humerus. A Colles fracture of the distal radius is the most common forearm fracture.
INTERACTIVE LINK
Watch this video to learn about a Colles fracture, a break of the distal radius, usually caused by falling onto an outstretched hand. When would surgery be required and how would the fracture be repaired in this case?
The Pelvic Girdle and Pelvis
- Define the pelvic girdle and describe the bones and ligaments of the pelvis
- Explain the three regions of the hip bone and identify their bony landmarks
- Describe the openings of the pelvis and the boundaries of the greater and lesser pelvis
The pelvic girdle (hip girdle) is formed by a single bone, the hip bone or coxal bone (coxal = “hip”), which serves as the attachment point for each lower limb. Each hip bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony pelvis is the entire structure formed by the two hip bones, the sacrum, and, attached inferiorly to the sacrum, the coccyx (Figure 8.12).
Unlike the bones of the pectoral girdle, which are highly mobile to enhance the range of upper limb movements, the bones of the pelvis are strongly united to each other to form a largely immobile, weight-bearing structure. This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs.
Figure 8.12 Pelvis The pelvic girdle is formed by a single hip bone. The hip bone attaches the lower limb to the axial skeleton through its articulation with the sacrum. The right and left hip bones, plus the sacrum and the coccyx, together form the pelvis.
Hip Bone
The hip bone, or coxal bone, forms the pelvic girdle portion of the pelvis. The paired hip bones are the large, curved bones that form the lateral and anterior aspects of the pelvis. Each adult hip bone is formed by three separate bones that fuse together during the late teenage years. These bony components are the ilium, ischium, and pubis (Figure 8.13). These names are retained and used to define the three regions of the adult hip bone.
Figure 8.13 The Hip Bone The adult hip bone consists of three regions. The ilium forms the large, fan-shaped superior portion, the ischium forms the posteroinferior portion, and the pubis forms the anteromedial portion.
The ilium is the fan-like, superior region that forms the largest part of the hip bone. It is firmly united to the sacrum at the largely immobile sacroiliac joint (see Figure 8.12). The ischium forms the posteroinferior region of each hip bone. It supports the body when sitting. The pubis forms the anterior portion of the hip bone. The pubis curves medially, where it joins to the pubis of the opposite hip bone at a specialized joint called the pubic symphysis.
Ilium
When you place your hands on your waist, you can feel the arching, superior margin of the ilium along your waistline (see Figure 8.13). This curved, superior margin of the ilium is the iliac crest. The rounded, anterior termination of the iliac crest is the anterior superior iliac spine. This important bony landmark can be felt at your anterolateral hip. Inferior to the anterior superior iliac spine is a rounded protuberance called the anterior inferior iliac spine. Both of these iliac spines serve as attachment points for muscles of the thigh. Posteriorly, the iliac crest curves downward to terminate as the posterior superior iliac spine. Muscles and ligaments surround but do not cover this bony landmark, thus sometimes producing a depression seen as a “dimple” located on the lower back. More inferiorly is the posterior inferior iliac spine. This is located at the inferior end of a large, roughened area called the auricular surface of the ilium. The auricular surface articulates with the auricular surface of the sacrum to form the sacroiliac joint. Both the posterior superior and posterior inferior iliac spines serve as attachment points for the muscles and very strong ligaments that support the sacroiliac joint.
The shallow depression located on the anteromedial (internal) surface of the upper ilium is called the iliac fossa. The inferior margin of this space is formed by the arcuate line of the ilium, the ridge formed by the pronounced change in curvature between the upper and lower portions of the ilium. The large, inverted U-shaped indentation located on the posterior margin of the lower ilium is called the greater sciatic notch.
Ischium
The ischium forms the posterolateral portion of the hip bone (see Figure 8.13). The large, roughened area of the inferior ischium is the ischial tuberosity. This serves as the attachment for the posterior thigh muscles and also carries the weight of the body when sitting. You can feel the ischial tuberosity if you wiggle your pelvis against the seat of a chair. Projecting superiorly and anteriorly from the ischial tuberosity is a narrow segment of bone called the ischial ramus. The slightly curved posterior margin of the ischium above the ischial tuberosity is the lesser sciatic notch. The bony projection separating the lesser sciatic notch and greater sciatic notch is the ischial spine.
Pubis
The pubis forms the anterior portion of the hip bone (see Figure 8.13). The enlarged medial portion of the pubis is the pubic body. Located superiorly on the pubic body is a small bump called the pubic tubercle. The superior pubic ramus is the segment of bone that passes laterally from the pubic body to join the ilium. The narrow ridge running along the superior margin of the superior pubic ramus is the pectineal line of the pubis.
The pubic body is joined to the pubic body of the opposite hip bone by the pubic symphysis. Extending downward and laterally from the body is the inferior pubic ramus. The pubic arch is the bony structure formed by the pubic symphysis, and the bodies and inferior pubic rami of the adjacent pubic bones. The inferior pubic ramus extends downward to join the ischial ramus. Together, these form the single ischiopubic ramus, which extends from the pubic body to the ischial tuberosity. The inverted V-shape formed as the ischiopubic rami from both sides come together at the pubic symphysis is called the subpubic angle.
Pelvis
The pelvis consists of four bones: the right and left hip bones, the sacrum, and the coccyx (see Figure 8.12). The pelvis has several important functions. Its primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. It serves as an attachment point for trunk and lower limb muscles, and also protects the internal pelvic organs. When standing in the anatomical position, the pelvis is tilted anteriorly. In this position, the anterior superior iliac spines and the pubic tubercles lie in the same vertical plane, and the anterior (internal) surface of the sacrum faces forward and downward.
The three areas of each hip bone, the ilium, pubis, and ischium, converge centrally to form a deep, cup-shaped cavity called the acetabulum. This is located on the lateral side of the hip bone and is part of the hip joint. The large opening in the anteroinferior hip bone between the ischium and pubis is the obturator foramen. This space is largely filled in by a layer of connective tissue and serves for the attachment of muscles on both its internal and external surfaces.
Several ligaments unite the bones of the pelvis (Figure 8.14). The largely immobile sacroiliac joint is supported by a pair of strong ligaments that are attached between the sacrum and ilium portions of the hip bone. These are the anterior sacroiliac ligamenton the anterior side of the joint and the posterior sacroiliac ligament on the posterior side. Also spanning the sacrum and hip bone are two additional ligaments. The sacrospinous ligament runs from the sacrum to the ischial spine, and the sacrotuberous ligament runs from the sacrum to the ischial tuberosity. These ligaments help to support and immobilize the sacrum as it carries the weight of the body.
Figure 8.14 Ligaments of the Pelvis The posterior sacroiliac ligament supports the sacroiliac joint. The sacrospinous ligament spans the sacrum to the ischial spine, and the sacrotuberous ligament spans the sacrum to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramens.
INTERACTIVE LINK
Watch this video for a 3-D view of the pelvis and its associated ligaments. What is the large opening in the bony pelvis, located between the ischium and pubic regions, and what two parts of the pubis contribute to the formation of this opening?
The sacrospinous and sacrotuberous ligaments also help to define two openings on the posterolateral sides of the pelvis through which muscles, nerves, and blood vessels for the lower limb exit. The superior opening is the greater sciatic foramen. This large opening is formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous ligament. The smaller, more inferior lesser sciatic foramen is formed by the lesser sciatic notch of the hip bone, together with the sacrospinous and sacrotuberous ligaments.
The space enclosed by the bony pelvis is divided into two regions (Figure 8.15). The broad, superior region, defined laterally by the large, fan-like portion of the upper hip bone, is called the greater pelvis (greater pelvic cavity; false pelvis). This broad area is occupied by portions of the small and large intestines, and because it is more closely associated with the abdominal cavity, it is sometimes referred to as the false pelvis. More inferiorly, the narrow, rounded space of the lesser pelvis (lesser pelvic cavity; true pelvis) contains the bladder and other pelvic organs, and thus is also known as the true pelvis. The pelvic brim (also known as the pelvic inlet) forms the superior margin of the lesser pelvis, separating it from the greater pelvis. The pelvic brim is defined by a line formed by the upper margin of the pubic symphysis anteriorly, and the pectineal line of the pubis, the arcuate line of the ilium, and the sacral promontory (the anterior margin of the superior sacrum) posteriorly. The inferior limit of the lesser pelvic cavity is called the pelvic outlet. This large opening is defined by the inferior margin of the pubic symphysis anteriorly, and the ischiopubic ramus, the ischial tuberosity, the sacrotuberous ligament, and the inferior tip of the coccyx posteriorly. Because of the anterior tilt of the pelvis, the lesser pelvis is also angled, giving it an anterosuperior (pelvic inlet) to posteroinferior (pelvic outlet) orientation.
Figure 8.15 Male and Female Pelvis The female pelvis is adapted for childbirth and is broader, with a larger subpubic angle, a rounder pelvic brim, and a wider and more shallow lesser pelvic cavity than the male pelvis.
Comparison of the Female and Male Pelvis
The differences between the adult female and male pelvis relate to function and body size. In general, the bones of the male pelvis are thicker and heavier, adapted for support of the male’s heavier physical build and stronger muscles. The greater sciatic notch of the male hip bone is narrower and deeper than the broader notch of females. Because the female pelvis is adapted for childbirth, it is wider than the male pelvis, as evidenced by the distance between the anterior superior iliac spines (see Figure 8.15). The ischial tuberosities of females are also farther apart, which increases the size of the pelvic outlet. Because of this increased pelvic width, the subpubic angle is larger in females (greater than 80 degrees) than it is in males (less than 70 degrees). The female sacrum is wider, shorter, and less curved, and the sacral promontory projects less into the pelvic cavity, thus giving the female pelvic inlet (pelvic brim) a more rounded or oval shape compared to males. The lesser pelvic cavity of females is also wider and more shallow than the narrower, deeper, and tapering lesser pelvis of males. Because of the obvious differences between female and male hip bones, this is the one bone of the body that allows for the most accurate sex determination. Table 8.1 provides an overview of the general differences between the female and male pelvis.
Overview of Differences between the Female and Male Pelvis
| Female pelvis | Male pelvis | |
|---|---|---|
| Pelvic weight | Bones of the pelvis are lighter and thinner | Bones of the pelvis are thicker and heavier |
| Pelvic inlet shape | Pelvic inlet has a round or oval shape | Pelvic inlet is heart-shaped |
| Lesser pelvic cavity shape | Lesser pelvic cavity is shorter and wider | Lesser pelvic cavity is longer and narrower |
| Subpubic angle | Subpubic angle is greater than 80 degrees | Subpubic angle is less than 70 degrees |
| Pelvic outlet shape | Pelvic outlet is rounded and larger | Pelvic outlet is smaller |
Table 8.1
CAREER CONNECTION
Forensic Pathology and Forensic Anthropology
A forensic pathologist (also known as a medical examiner) is a medically trained physician who has been specifically trained in pathology to examine the bodies of the deceased to determine the cause of death. A forensic pathologist applies his or her understanding of disease as well as toxins, blood and DNA analysis, firearms and ballistics, and other factors to assess the cause and manner of death. At times, a forensic pathologist will be called to testify under oath in situations that involve a possible crime. Forensic pathology is a field that has received much media attention on television shows or following a high-profile death.
While forensic pathologists are responsible for determining whether the cause of someone’s death was natural, a suicide, accidental, or a homicide, there are times when uncovering the cause of death is more complex, and other skills are needed. Forensic anthropology brings the tools and knowledge of physical anthropology and human osteology (the study of the skeleton) to the task of investigating a death. A forensic anthropologist assists medical and legal professionals in identifying human remains. The science behind forensic anthropology involves the study of archaeological excavation; the examination of hair; an understanding of plants, insects, and footprints; the ability to determine how much time has elapsed since the person died; the analysis of past medical history and toxicology; the ability to determine whether there are any postmortem injuries or alterations of the skeleton; and the identification of the decedent (deceased person) using skeletal and dental evidence.
Due to the extensive knowledge and understanding of excavation techniques, a forensic anthropologist is an integral and invaluable team member to have on-site when investigating a crime scene, especially when the recovery of human skeletal remains is involved. When remains are bought to a forensic anthropologist for examination, he or she must first determine whether the remains are in fact human. Once the remains have been identified as belonging to a person and not to an animal, the next step is to approximate the individual’s age, sex, race, and height. The forensic anthropologist does not determine the cause of death, but rather provides information to the forensic pathologist, who will use all of the data collected to make a final determination regarding the cause of death.
Bones of the Lower Limb
- Identify the divisions of the lower limb and describe the bones of each region
- Describe the bones and bony landmarks that articulate at each joint of the lower limb
Like the upper limb, the lower limb is divided into three regions. The thigh is that portion of the lower limb located between the hip joint and knee joint. The leg is specifically the region between the knee joint and the ankle joint. Distal to the ankle is the foot. The lower limb contains 30 bones. These are the femur, patella, tibia, fibula, tarsal bones, metatarsal bones, and phalanges (see Figure 8.2). The femur is the single bone of the thigh. The patella is the kneecap and articulates with the distal femur. The tibia is the larger, weight-bearing bone located on the medial side of the leg, and the fibula is the thin bone of the lateral leg. The bones of the foot are divided into three groups. The posterior portion of the foot is formed by a group of seven bones, each of which is known as a tarsal bone, whereas the mid-foot contains five elongated bones, each of which is a metatarsal bone. The toes contain 14 small bones, each of which is a phalanx bone of the foot.
Femur
The femur, or thigh bone, is the single bone of the thigh region (Figure 8.16). It is the longest and strongest bone of the body, and accounts for approximately one-quarter of a person’s total height. The rounded, proximal end is the head of the femur, which articulates with the acetabulum of the hip bone to form the hip joint. The fovea capitis is a minor indentation on the medial side of the femoral head that serves as the site of attachment for the ligament of the head of the femur. This ligament spans the femur and acetabulum, but is weak and provides little support for the hip joint. It does, however, carry an important artery that supplies the head of the femur.
Figure 8.16 Femur and Patella The femur is the single bone of the thigh region. It articulates superiorly with the hip bone at the hip joint, and inferiorly with the tibia at the knee joint. The patella only articulates with the distal end of the femur.
The narrowed region below the head is the neck of the femur. This is a common area for fractures of the femur. The greater trochanter is the large, upward, bony projection located above the base of the neck. Multiple muscles that act across the hip joint attach to the greater trochanter, which, because of its projection from the femur, gives additional leverage to these muscles. The greater trochanter can be felt just under the skin on the lateral side of your upper thigh. The lesser trochanter is a small, bony prominence that lies on the medial aspect of the femur, just below the neck. A single, powerful muscle attaches to the lesser trochanter. Running between the greater and lesser trochanters on the anterior side of the femur is the roughened intertrochanteric line. The trochanters are also connected on the posterior side of the femur by the larger intertrochanteric crest.
The elongated shaft of the femur has a slight anterior bowing or curvature. At its proximal end, the posterior shaft has the gluteal tuberosity, a roughened area extending inferiorly from the greater trochanter. More inferiorly, the gluteal tuberosity becomes continuous with the linea aspera (“rough line”). This is the roughened ridge that passes distally along the posterior side of the mid-femur. Multiple muscles of the hip and thigh regions make long, thin attachments to the femur along the linea aspera.
The distal end of the femur has medial and lateral bony expansions. On the lateral side, the smooth portion that covers the distal and posterior aspects of the lateral expansion is the lateral condyle of the femur. The roughened area on the outer, lateral side of the condyle is the lateral epicondyle of the femur. Similarly, the smooth region of the distal and posterior medial femur is the medial condyle of the femur, and the irregular outer, medial side of this is the medial epicondyle of the femur. The lateral and medial condyles articulate with the tibia to form the knee joint. The epicondyles provide attachment for muscles and supporting ligaments of the knee. The adductor tubercle is a small bump located at the superior margin of the medial epicondyle. Posteriorly, the medial and lateral condyles are separated by a deep depression called the intercondylar fossa. Anteriorly, the smooth surfaces of the condyles join together to form a wide groove called the patellar surface, which provides for articulation with the patella bone. The combination of the medial and lateral condyles with the patellar surface gives the distal end of the femur a horseshoe (U) shape.
INTERACTIVE LINK
Watch this video to view how a fracture of the mid-femur is surgically repaired. How are the two portions of the broken femur stabilized during surgical repair of a fractured femur?
Patella
The patella (kneecap) is largest sesamoid bone of the body (see Figure 8.16). A sesamoid bone is a bone that is incorporated into the tendon of a muscle where that tendon crosses a joint. The sesamoid bone articulates with the underlying bones to prevent damage to the muscle tendon due to rubbing against the bones during movements of the joint. The patella is found in the tendon of the quadriceps femoris muscle, the large muscle of the anterior thigh that passes across the anterior knee to attach to the tibia. The patella articulates with the patellar surface of the femur and thus prevents rubbing of the muscle tendon against the distal femur. The patella also lifts the tendon away from the knee joint, which increases the leverage power of the quadriceps femoris muscle as it acts across the knee. The patella does not articulate with the tibia.
INTERACTIVE LINK
Visit this site to perform a virtual knee replacement surgery. The prosthetic knee components must be properly aligned to function properly. How is this alignment ensured?
HOMEOSTATIC IMBALANCES
Runner’s Knee
Runner’s knee, also known as patellofemoral syndrome, is the most common overuse injury among runners. It is most frequent in adolescents and young adults, and is more common in females. It often results from excessive running, particularly downhill, but may also occur in athletes who do a lot of knee bending, such as jumpers, skiers, cyclists, weight lifters, and soccer players. It is felt as a dull, aching pain around the front of the knee and deep to the patella. The pain may be felt when walking or running, going up or down stairs, kneeling or squatting, or after sitting with the knee bent for an extended period.
Patellofemoral syndrome may be initiated by a variety of causes, including individual variations in the shape and movement of the patella, a direct blow to the patella, or flat feet or improper shoes that cause excessive turning in or out of the feet or leg. These factors may cause in an imbalance in the muscle pull that acts on the patella, resulting in an abnormal tracking of the patella that allows it to deviate too far toward the lateral side of the patellar surface on the distal femur.
Because the hips are wider than the knee region, the femur has a diagonal orientation within the thigh, in contrast to the vertically oriented tibia of the leg (Figure 8.17). The Q-angle is a measure of how far the femur is angled laterally away from vertical. The Q-angle is normally 10–15 degrees, with females typically having a larger Q-angle due to their wider pelvis. During extension of the knee, the quadriceps femoris muscle pulls the patella both superiorly and laterally, with the lateral pull greater in women due to their large Q-angle. This makes women more vulnerable to developing patellofemoral syndrome than men. Normally, the large lip on the lateral side of the patellar surface of the femur compensates for the lateral pull on the patella, and thus helps to maintain its proper tracking.
However, if the pull produced by the medial and lateral sides of the quadriceps femoris muscle is not properly balanced, abnormal tracking of the patella toward the lateral side may occur. With continued use, this produces pain and could result in damage to the articulating surfaces of the patella and femur, and the possible future development of arthritis. Treatment generally involves stopping the activity that produces knee pain for a period of time, followed by a gradual resumption of activity. Proper strengthening of the quadriceps femoris muscle to correct for imbalances is also important to help prevent reoccurrence.
Figure 8.17 The Q-Angle The Q-angle is a measure of the amount of lateral deviation of the femur from the vertical line of the tibia. Adult females have a larger Q-angle due to their wider pelvis than adult males.
Tibia
The tibia (shin bone) is the medial bone of the leg and is larger than the fibula, with which it is paired (Figure 8.18). The tibia is the main weight-bearing bone of the lower leg and the second longest bone of the body, after the femur. The medial side of the tibia is located immediately under the skin, allowing it to be easily palpated down the entire length of the medial leg.
Figure 8.18 Tibia and Fibula The tibia is the larger, weight-bearing bone located on the medial side of the leg. The fibula is the slender bone of the lateral side of the leg and does not bear weight.
The proximal end of the tibia is greatly expanded. The two sides of this expansion form the medial condyle of the tibia and the lateral condyle of the tibia. The tibia does not have epicondyles. The top surface of each condyle is smooth and flattened. These areas articulate with the medial and lateral condyles of the femur to form the knee joint. Between the articulating surfaces of the tibial condyles is the intercondylar eminence, an irregular, elevated area that serves as the inferior attachment point for two supporting ligaments of the knee.
The tibial tuberosity is an elevated area on the anterior side of the tibia, near its proximal end. It is the final site of attachment for the muscle tendon associated with the patella. More inferiorly, the shaft of the tibia becomes triangular in shape. The anterior apex of
MH this triangle forms the anterior border of the tibia, which begins at the tibial tuberosity and runs inferiorly along the length of the tibia. Both the anterior border and the medial side of the triangular shaft are located immediately under the skin and can be easily palpated along the entire length of the tibia. A small ridge running down the lateral side of the tibial shaft is the interosseous border of the tibia. This is for the attachment of the interosseous membrane of the leg, the sheet of dense connective tissue that unites the tibia and fibula bones. Located on the posterior side of the tibia is the soleal line, a diagonally running, roughened ridge that begins below the base of the lateral condyle, and runs down and medially across the proximal third of the posterior tibia. Muscles of the posterior leg attach to this line.
The large expansion found on the medial side of the distal tibia is the medial malleolus (“little hammer”). This forms the large bony bump found on the medial side of the ankle region. Both the smooth surface on the inside of the medial malleolus and the smooth area at the distal end of the tibia articulate with the talus bone of the foot as part of the ankle joint. On the lateral side of the distal tibia is a wide groove called the fibular notch. This area articulates with the distal end of the fibula, forming the distal tibiofibular joint.
Fibula
The fibula is the slender bone located on the lateral side of the leg (see Figure 8.18). The fibula does not bear weight. It serves primarily for muscle attachments and thus is largely surrounded by muscles. Only the proximal and distal ends of the fibula can be palpated.
The head of the fibula is the small, knob-like, proximal end of the fibula. It articulates with the inferior aspect of the lateral tibial condyle, forming the proximal tibiofibular joint. The thin shaft of the fibula has the interosseous border of the fibula, a narrow ridge running down its medial side for the attachment of the interosseous membrane that spans the fibula and tibia. The distal end of the fibula forms the lateral malleolus, which forms the easily palpated bony bump on the lateral side of the ankle. The deep (medial) side of the lateral malleolus articulates with the talus bone of the foot as part of the ankle joint. The distal fibula also articulates with the fibular notch of the tibia.
Tarsal Bones
The posterior half of the foot is formed by seven tarsal bones (Figure 8.19). The most superior bone is the talus. This has a relatively square-shaped, upper surface that articulates with the tibia and fibula to form the ankle joint. Three areas of articulation form the ankle joint: The superomedial surface of the talus bone articulates with the medial malleolus of the tibia, the top of the talus articulates with the distal end of the tibia, and the lateral side of the talus articulates with the lateral malleolus of the fibula. Inferiorly, the talus articulates with the calcaneus (heel bone), the largest bone of the foot, which forms the heel. Body weight is transferred from the tibia to the talus to the calcaneus, which rests on the ground. The medial calcaneus has a prominent bony extension called the sustentaculum tali (“support for the talus”) that supports the medial side of the talus bone.
Figure 8.19 Bones of the Foot The bones of the foot are divided into three groups. The posterior foot is formed by the seven tarsal bones. The mid-foot has the five metatarsal bones. The toes contain the phalanges.
The cuboid bone articulates with the anterior end of the calcaneus bone. The cuboid has a deep groove running across its inferior surface, which provides passage for a muscle tendon. The talus bone articulates anteriorly with the navicular bone, which in turn articulates anteriorly with the three cuneiform (“wedge-shaped”) bones. These bones are the medial cuneiform, the intermediate cuneiform, and the lateral cuneiform. Each of these bones has a broad superior surface and a narrow inferior surface, which together produce the transverse (medial-lateral) curvature of the foot. The navicular and lateral cuneiform bones also articulate with the medial side of the cuboid bone.
INTERACTIVE LINK
Use this tutorial to review the bones of the foot. Which tarsal bones are in the proximal, intermediate, and distal groups?
Metatarsal Bones
The anterior half of the foot is formed by the five metatarsal bones, which are located between the tarsal bones of the posterior foot and the phalanges of the toes (see Figure 8.19). These elongated bones are numbered 1–5, starting with the medial side of the foot. The first metatarsal bone is shorter and thicker than the others. The second metatarsal is the longest. The base of the metatarsal bone is the proximal end of each metatarsal bone. These articulate with the cuboid or cuneiform bones. The base of the fifth metatarsal has a large, lateral expansion that provides for muscle attachments. This expanded base of the fifth metatarsal can be felt as a bony bump at the midpoint along the lateral border of the foot. The expanded distal end of each metatarsal is the head of the metatarsal bone. Each metatarsal bone articulates with the proximal phalanx of a toe to form a metatarsophalangeal joint. The heads of the metatarsal bones also rest on the ground and form the ball (anterior end) of the foot.
Phalanges
The toes contain a total of 14 phalanx bones (phalanges), arranged in a similar manner as the phalanges of the fingers (see Figure 8.19). The toes are numbered 1–5, starting with the big toe (hallux). The big toe has two phalanx bones, the proximal and distal phalanges. The remaining toes all have proximal, middle, and distal phalanges. A joint between adjacent phalanx bones is called an interphalangeal joint.
INTERACTIVE LINK
View this link to learn about a bunion, a localized swelling on the medial side of the foot, next to the first metatarsophalangeal joint, at the base of the big toe. What is a bunion and what type of shoe is most likely to cause this to develop?
Arches of the Foot
When the foot comes into contact with the ground during walking, running, or jumping activities, the impact of the body weight puts a tremendous amount of pressure and force on the foot. During running, the force applied to each foot as it contacts the ground can be up to 2.5 times your body weight. The bones, joints, ligaments, and muscles of the foot absorb this force, thus greatly reducing the amount of shock that is passed superiorly into the lower limb and body. The arches of the foot play an important role in this shock-absorbing ability. When weight is applied to the foot, these arches will flatten somewhat, thus absorbing energy. When the weight is removed, the arch rebounds, giving “spring” to the step. The arches also serve to distribute body weight side to side and to either end of the foot.
The foot has a transverse arch, a medial longitudinal arch, and a lateral longitudinal arch (see Figure 8.19). The transverse arch forms the medial-lateral curvature of the mid-foot. It is formed by the wedge shapes of the cuneiform bones and bases (proximal ends) of the first to fourth metatarsal bones. This arch helps to distribute body weight from side to side within the foot, thus allowing the foot to accommodate uneven terrain.
The longitudinal arches run down the length of the foot. The lateral longitudinal arch is relatively flat, whereas the medial longitudinal arch is larger (taller). The longitudinal arches are formed by the tarsal bones posteriorly and the metatarsal bones anteriorly. These arches are supported at either end, where they contact the ground. Posteriorly, this support is provided by the calcaneus bone and anteriorly by the heads (distal ends) of the metatarsal bones. The talus bone, which receives the weight of the body, is located at the top of the longitudinal arches. Body weight is then conveyed from the talus to the ground by the anterior and posterior ends of these arches. Strong ligaments unite the adjacent foot bones to prevent disruption of the arches during weight bearing. On the bottom of the foot, additional ligaments tie together the anterior and posterior ends of the arches. These ligaments have elasticity, which allows them to stretch somewhat during weight bearing, thus allowing the longitudinal arches to spread. The stretching of these ligaments stores energy within the foot, rather than passing these forces into the leg. Contraction of the foot muscles also plays an important role in this energy absorption. When the weight is removed, the elastic ligaments recoil and pull the ends of the arches closer together. This recovery of the arches releases the stored energy and improves the energy efficiency of walking.
Stretching of the ligaments that support the longitudinal arches can lead to pain. This can occur in overweight individuals, with people who have jobs that involve standing for long periods of time (such as a waitress), or walking or running long distances. If stretching of the ligaments is prolonged, excessive, or repeated, it can result in a gradual lengthening of the supporting ligaments, with subsequent depression or collapse of the longitudinal arches, particularly on the medial side of the foot. This condition is called pes planus (“flat foot” or “fallen arches”).
Development of the Appendicular Skeleton
- Describe the growth and development of the embryonic limb buds
- Discuss the appearance of primary and secondary ossification centers
Embryologically, the appendicular skeleton arises from mesenchyme, a type of embryonic tissue that can differentiate into many types of tissues, including bone or muscle tissue. Mesenchyme gives rise to the bones of the upper and lower limbs, as well as to the pectoral and pelvic girdles. Development of the limbs begins near the end of the fourth embryonic week, with the upper limbs appearing first. Thereafter, the development of the upper and lower limbs follows similar patterns, with the lower limbs lagging behind the upper limbs by a few days.
Limb Growth
Each upper and lower limb initially develops as a small bulge called a limb bud, which appears on the lateral side of the early embryo. The upper limb bud appears near the end of the fourth week of development, with the lower limb bud appearing shortly after (Figure 8.20).
Figure 8.20 Embryo at Seven Weeks Limb buds are visible in an embryo at the end of the seventh week of development (embryo derived from an ectopic pregnancy). (credit: Ed Uthman/flickr)
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying mesenchyme to rapidly proliferate, producing the outgrowth of the developing limb. As the limb bud elongates, cells located farther from the apical ectodermal ridge slow their rates of cell division and begin to differentiate. In this way, the limb develops along a proximal-to-distal axis.
During the sixth week of development, the distal ends of the upper and lower limb buds expand and flatten into a paddle shape. This region will become the hand or foot. The wrist or ankle areas then appear as a constriction that develops at the base of the paddle. Shortly after this, a second constriction on the limb bud appears at the future site of the elbow or knee. Within the paddle, areas of tissue undergo cell death, producing separations between the growing fingers and toes. Also during the sixth week of development, mesenchyme within the limb buds begins to differentiate into hyaline cartilage that will form models of the future limb bones.
The early outgrowth of the upper and lower limb buds initially has the limbs positioned so that the regions that will become the palm of the hand or the bottom of the foot are facing medially toward the body, with the future thumb or big toe both oriented toward the head. During the seventh week of development, the upper limb rotates laterally by 90 degrees, so that the palm of the hand faces anteriorly and the thumb points laterally. In contrast, the lower limb undergoes a 90-degree medial rotation, thus bringing the big toe to the medial side of the foot.
INTERACTIVE LINK
Watch this animation to follow the development and growth of the upper and lower limb buds. On what days of embryonic development do these events occur: (a) first appearance of the upper limb bud (limb ridge); (b) the flattening of the distal limb to form the handplate or footplate; and (c) the beginning of limb rotation?
Ossification of Appendicular Bones
All of the girdle and limb bones, except for the clavicle, develop by the process of endochondral ossification. This process begins as the mesenchyme within the limb bud differentiates into hyaline cartilage to form cartilage models for future bones. By the twelfth week, a primary ossification center will have appeared in the diaphysis (shaft) region of the long bones, initiating the process that converts the cartilage model into bone. A secondary ossification center will appear in each epiphysis (expanded end) of these bones at a later time, usually after birth. The primary and secondary ossification centers are separated by the epiphyseal plate, a layer of growing hyaline cartilage. This plate is located between the diaphysis and each epiphysis. It continues to grow and is responsible for the lengthening of the bone. The epiphyseal plate is retained for many years, until the bone reaches its final, adult size, at which time the epiphyseal plate disappears and the epiphysis fuses to the diaphysis. (Seek additional content on ossification in the chapter on bone tissue.)
Small bones, such as the phalanges, will develop only one secondary ossification center and will thus have only a single epiphyseal plate. Large bones, such as the femur, will develop several secondary ossification centers, with an epiphyseal plate associated with each secondary center. Thus, ossification of the femur begins at the end of the seventh week with the appearance of the primary ossification center in the diaphysis, which rapidly expands to ossify the shaft of the bone prior to birth. Secondary ossification centers develop at later times. Ossification of the distal end of the femur, to form the condyles and epicondyles, begins shortly before birth. Secondary ossification centers also appear in the femoral head late in the first year after birth, in the greater trochanter during the fourth year, and in the lesser trochanter between the ages of 9 and 10 years. Once these areas have ossified, their fusion to the diaphysis and the disappearance of each epiphyseal plate follow a reversed sequence. Thus, the lesser trochanter is the first to fuse, doing so at the onset of puberty (around 11 years of age), followed by the greater trochanter approximately 1 year later. The femoral head fuses between the ages of 14–17 years, whereas the distal condyles of the femur are the last to fuse, between the ages of 16–19 years. Knowledge of the age at which different epiphyseal plates disappear is important when interpreting radiographs taken of children. Since the cartilage of an epiphyseal plate is less dense than bone, the plate will appear dark in a radiograph image. Thus, a normal epiphyseal plate may be mistaken for a bone fracture.
The clavicle is the one appendicular skeleton bone that does not develop via endochondral ossification. Instead, the clavicle develops through the process of intramembranous ossification. During this process, mesenchymal cells differentiate directly into bone-producing cells, which produce the clavicle directly, without first making a cartilage model. Because of this early production of bone, the clavicle is the first bone of the body to begin ossification, with ossification centers appearing during the fifth week of development. However, ossification of the clavicle is not complete until age 25.
DISORDERS OF THE...
Appendicular System: Congenital Clubfoot
Clubfoot, also known as talipes, is a congenital (present at birth) disorder of unknown cause and is the most common deformity of the lower limb. It affects the foot and ankle, causing the foot to be twisted inward at a sharp angle, like the head of a golf club (Figure 8.21). Clubfoot has a frequency of about 1 out of every 1,000 births, and is twice as likely to occur in a male child as in a female child. In 50 percent of cases, both feet are affected.
Figure 8.21 Clubfoot Clubfoot is a common deformity of the ankle and foot that is present at birth. Most cases are corrected without surgery, and affected individuals will grow up to lead normal, active lives. (credit: James W. Hanson)
At birth, children with a clubfoot have the heel turned inward and the anterior foot twisted so that the lateral side of the foot is facing inferiorly, commonly due to ligaments or leg muscles attached to the foot that are shortened or abnormally tight. These pull the foot into an abnormal position, resulting in bone deformities. Other symptoms may include bending of the ankle that lifts the heel of the foot and an extremely high foot arch. Due to the limited range of motion in the affected foot, it is difficult to place the foot into the correct position. Additionally, the affected foot may be shorter than normal, and the calf muscles are usually underdeveloped on the affected side. Despite the appearance, this is not a painful condition for newborns. However, it must be treated early to avoid future pain and impaired walking ability.
Although the cause of clubfoot is idiopathic (unknown), evidence indicates that fetal position within the uterus is not a contributing factor. Genetic factors are involved, because clubfoot tends to run within families. Cigarette smoking during pregnancy has been linked to the development of clubfoot, particularly in families with a history of clubfoot.
Previously, clubfoot required extensive surgery. Today, 90 percent of cases are successfully treated without surgery using new corrective casting techniques. The best chance for a full recovery requires that clubfoot treatment begin during the first 2 weeks after birth. Corrective casting gently stretches the foot, which is followed by the application of a holding cast to keep the foot in the proper position. This stretching and casting is repeated weekly for several weeks. In severe cases, surgery may also be required, after which the foot typically remains in a cast for 6 to 8 weeks. After the cast is removed following either surgical or nonsurgical treatment, the child will be required to wear a brace part-time (at night) for up to 4 years. In addition, special exercises will be prescribed, and the child must also wear special shoes. Close monitoring by the parents and adherence to postoperative instructions are imperative in minimizing the risk of relapse.
Despite these difficulties, treatment for clubfoot is usually successful, and the child will grow up to lead a normal, active life. Numerous examples of individuals born with a clubfoot who went on to successful careers include Dudley Moore (comedian and actor), Damon Wayans (comedian and actor), Troy Aikman (three-time Super Bowl-winning quarterback), Kristi Yamaguchi (Olympic gold medalist in figure skating), Mia Hamm (two-time Olympic gold medalist in soccer), and Charles Woodson (Heisman trophy and Super Bowl winner).
Key Terms
- acetabulum
- large, cup-shaped cavity located on the lateral side of the hip bone; formed by the junction of the ilium, pubis, and ischium portions of the hip bone
- acromial end of the clavicle
- lateral end of the clavicle that articulates with the acromion of the scapula
- acromial process
- acromion of the scapula
- acromioclavicular joint
- articulation between the acromion of the scapula and the acromial end of the clavicle
- acromion
- flattened bony process that extends laterally from the scapular spine to form the bony tip of the shoulder
- adductor tubercle
- small, bony bump located on the superior aspect of the medial epicondyle of the femur
- anatomical neck
- line on the humerus located around the outside margin of the humeral head
- ankle joint
- joint that separates the leg and foot portions of the lower limb; formed by the articulations between the talus bone of the foot inferiorly, and the distal end of the tibia, medial malleolus of the tibia, and lateral malleolus of the fibula superiorly
- anterior border of the tibia
- narrow, anterior margin of the tibia that extends inferiorly from the tibial tuberosity
- anterior inferior iliac spine
- small, bony projection located on the anterior margin of the ilium, below the anterior superior iliac spine
- anterior sacroiliac ligament
- strong ligament between the sacrum and the ilium portions of the hip bone that supports the anterior side of the sacroiliac joint
- anterior superior iliac spine
- rounded, anterior end of the iliac crest
- apical ectodermal ridge
- enlarged ridge of ectoderm at the distal end of a limb bud that stimulates growth and elongation of the limb
- arcuate line of the ilium
- smooth ridge located at the inferior margin of the iliac fossa; forms the lateral portion of the pelvic brim
- arm
- region of the upper limb located between the shoulder and elbow joints; contains the humerus bone
- auricular surface of the ilium
- roughened area located on the posterior, medial side of the ilium of the hip bone; articulates with the auricular surface of the sacrum to form the sacroiliac joint
- base of the metatarsal bone
- expanded, proximal end of each metatarsal bone
- bicipital groove
- intertubercular groove; narrow groove located between the greater and lesser tubercles of the humerus
- calcaneus
- heel bone; posterior, inferior tarsal bone that forms the heel of the foot
- capitate
- from the lateral side, the third of the four distal carpal bones; articulates with the scaphoid and lunate proximally, the trapezoid laterally, the hamate medially, and primarily with the third metacarpal distally
- capitulum
- knob-like bony structure located anteriorly on the lateral, distal end of the humerus
- carpal bone
- one of the eight small bones that form the wrist and base of the hand; these are grouped as a proximal row consisting of (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones, and a distal row containing (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones
- carpal tunnel
- passageway between the anterior forearm and hand formed by the carpal bones and flexor retinaculum
- carpometacarpal joint
- articulation between one of the carpal bones in the distal row and a metacarpal bone of the hand
- clavicle
- collarbone; elongated bone that articulates with the manubrium of the sternum medially and the acromion of the scapula laterally
- coracoclavicular ligament
- strong band of connective tissue that anchors the coracoid process of the scapula to the lateral clavicle; provides important indirect support for the acromioclavicular joint
- coracoid process
- short, hook-like process that projects anteriorly and laterally from the superior margin of the scapula
- coronoid fossa
- depression on the anterior surface of the humerus above the trochlea; this space receives the coronoid process of the ulna when the elbow is maximally flexed
- coronoid process of the ulna
- projecting bony lip located on the anterior, proximal ulna; forms the inferior margin of the trochlear notch
- costoclavicular ligament
- band of connective tissue that unites the medial clavicle with the first rib
- coxal bone
- hip bone
- cuboid
- tarsal bone that articulates posteriorly with the calcaneus bone, medially with the lateral cuneiform bone, and anteriorly with the fourth and fifth metatarsal bones
- deltoid tuberosity
- roughened, V-shaped region located laterally on the mid-shaft of the humerus
- distal radioulnar joint
- articulation between the head of the ulna and the ulnar notch of the radius
- distal tibiofibular joint
- articulation between the distal fibula and the fibular notch of the tibia
- elbow joint
- joint located between the upper arm and forearm regions of the upper limb; formed by the articulations between the trochlea of the humerus and the trochlear notch of the ulna, and the capitulum of the humerus and the head of the radius
- femur
- thigh bone; the single bone of the thigh
- fibula
- thin, non-weight-bearing bone found on the lateral side of the leg
- fibular notch
- wide groove on the lateral side of the distal tibia for articulation with the fibula at the distal tibiofibular joint
- flexor retinaculum
- strong band of connective tissue at the anterior wrist that spans the top of the U-shaped grouping of the carpal bones to form the roof of the carpal tunnel
- foot
- portion of the lower limb located distal to the ankle joint
- forearm
- region of the upper limb located between the elbow and wrist joints; contains the radius and ulna bones
- fossa
- (plural = fossae) shallow depression on the surface of a bone
- fovea capitis
- minor indentation on the head of the femur that serves as the site of attachment for the ligament to the head of the femur
- glenohumeral joint
- shoulder joint; formed by the articulation between the glenoid cavity of the scapula and the head of the humerus
- glenoid cavity
- (also, glenoid fossa) shallow depression located on the lateral scapula, between the superior and lateral borders
- gluteal tuberosity
- roughened area on the posterior side of the proximal femur, extending inferiorly from the base of the greater trochanter
- greater pelvis
- (also, greater pelvic cavity or false pelvis) broad space above the pelvic brim defined laterally by the fan-like portion of the upper ilium
- greater sciatic foramen
- pelvic opening formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous ligament
- greater sciatic notch
- large, U-shaped indentation located on the posterior margin of the ilium, superior to the ischial spine
- greater trochanter
- large, bony expansion of the femur that projects superiorly from the base of the femoral neck
- greater tubercle
- enlarged prominence located on the lateral side of the proximal humerus
- hallux
- big toe; digit 1 of the foot
- hamate
- from the lateral side, the fourth of the four distal carpal bones; articulates with the lunate and triquetrum proximally, the fourth and fifth metacarpals distally, and the capitate laterally
- hand
- region of the upper limb distal to the wrist joint
- head of the femur
- rounded, proximal end of the femur that articulates with the acetabulum of the hip bone to form the hip joint
- head of the fibula
- small, knob-like, proximal end of the fibula; articulates with the inferior aspect of the lateral condyle of the tibia
- head of the humerus
- smooth, rounded region on the medial side of the proximal humerus; articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint
- head of the metatarsal bone
- expanded, distal end of each metatarsal bone
- head of the radius
- disc-shaped structure that forms the proximal end of the radius; articulates with the capitulum of the humerus as part of the elbow joint, and with the radial notch of the ulna as part of the proximal radioulnar joint
- head of the ulna
- small, rounded distal end of the ulna; articulates with the ulnar notch of the distal radius, forming the distal radioulnar joint
- hip bone
- coxal bone; single bone that forms the pelvic girdle; consists of three areas, the ilium, ischium, and pubis
- hip joint
- joint located at the proximal end of the lower limb; formed by the articulation between the acetabulum of the hip bone and the head of the femur
- hook of the hamate bone
- bony extension located on the anterior side of the hamate carpal bone
- humerus
- single bone of the upper arm
- iliac crest
- curved, superior margin of the ilium
- iliac fossa
- shallow depression found on the anterior and medial surfaces of the upper ilium
- ilium
- superior portion of the hip bone
- inferior angle of the scapula
- inferior corner of the scapula located where the medial and lateral borders meet
- inferior pubic ramus
- narrow segment of bone that passes inferiorly and laterally from the pubic body; joins with the ischial ramus to form the ischiopubic ramus
- infraglenoid tubercle
- small bump or roughened area located on the lateral border of the scapula, near the inferior margin of the glenoid cavity
- infraspinous fossa
- broad depression located on the posterior scapula, inferior to the spine
- intercondylar eminence
- irregular elevation on the superior end of the tibia, between the articulating surfaces of the medial and lateral condyles
- intercondylar fossa
- deep depression on the posterior side of the distal femur that separates the medial and lateral condyles
- intermediate cuneiform
- middle of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the medial cuneiform bone, laterally with the lateral cuneiform bone, and anteriorly with the second metatarsal bone
- interosseous border of the fibula
- small ridge running down the medial side of the fibular shaft; for attachment of the interosseous membrane between the fibula and tibia
- interosseous border of the radius
- narrow ridge located on the medial side of the radial shaft; for attachment of the interosseous membrane between the ulna and radius bones
- interosseous border of the tibia
- small ridge running down the lateral side of the tibial shaft; for attachment of the interosseous membrane between the tibia and fibula
- interosseous border of the ulna
- narrow ridge located on the lateral side of the ulnar shaft; for attachment of the interosseous membrane between the ulna and radius
- interosseous membrane of the forearm
- sheet of dense connective tissue that unites the radius and ulna bones
- interosseous membrane of the leg
- sheet of dense connective tissue that unites the shafts of the tibia and fibula bones
- interphalangeal joint
- articulation between adjacent phalanx bones of the hand or foot digits
- intertrochanteric crest
- short, prominent ridge running between the greater and lesser trochanters on the posterior side of the proximal femur
- intertrochanteric line
- small ridge running between the greater and lesser trochanters on the anterior side of the proximal femur
- intertubercular groove (sulcus)
- bicipital groove; narrow groove located between the greater and lesser tubercles of the humerus
- ischial ramus
- bony extension projecting anteriorly and superiorly from the ischial tuberosity; joins with the inferior pubic ramus to form the ischiopubic ramus
- ischial spine
- pointed, bony projection from the posterior margin of the ischium that separates the greater sciatic notch and lesser sciatic notch
- ischial tuberosity
- large, roughened protuberance that forms the posteroinferior portion of the hip bone; weight-bearing region of the pelvis when sitting
- ischiopubic ramus
- narrow extension of bone that connects the ischial tuberosity to the pubic body; formed by the junction of the ischial ramus and inferior pubic ramus
- ischium
- posteroinferior portion of the hip bone
- knee joint
- joint that separates the thigh and leg portions of the lower limb; formed by the articulations between the medial and lateral condyles of the femur, and the medial and lateral condyles of the tibia
- lateral border of the scapula
- diagonally oriented lateral margin of the scapula
- lateral condyle of the femur
- smooth, articulating surface that forms the distal and posterior sides of the lateral expansion of the distal femur
- lateral condyle of the tibia
- lateral, expanded region of the proximal tibia that includes the smooth surface that articulates with the lateral condyle of the femur as part of the knee joint
- lateral cuneiform
- most lateral of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the intermediate cuneiform bone, laterally with the cuboid bone, and anteriorly with the third metatarsal bone
- lateral epicondyle of the femur
- roughened area of the femur located on the lateral side of the lateral condyle
- lateral epicondyle of the humerus
- small projection located on the lateral side of the distal humerus
- lateral malleolus
- expanded distal end of the fibula
- lateral supracondylar ridge
- narrow, bony ridge located along the lateral side of the distal humerus, superior to the lateral epicondyle
- leg
- portion of the lower limb located between the knee and ankle joints
- lesser pelvis
- (also, lesser pelvic cavity or true pelvis) narrow space located within the pelvis, defined superiorly by the pelvic brim (pelvic inlet) and inferiorly by the pelvic outlet
- lesser sciatic foramen
- pelvic opening formed by the lesser sciatic notch of the hip bone, the sacrospinous ligament, and the sacrotuberous ligament
- lesser sciatic notch
- shallow indentation along the posterior margin of the ischium, inferior to the ischial spine
- lesser trochanter
- small, bony projection on the medial side of the proximal femur, at the base of the femoral neck
- lesser tubercle
- small, bony prominence located on anterior side of the proximal humerus
- ligament of the head of the femur
- ligament that spans the acetabulum of the hip bone and the fovea capitis of the femoral head
- limb bud
- small elevation that appears on the lateral side of the embryo during the fourth or fifth week of development, which gives rise to an upper or lower limb
- linea aspera
- longitudinally running bony ridge located in the middle third of the posterior femur
- lunate
- from the lateral side, the second of the four proximal carpal bones; articulates with the radius proximally, the capitate and hamate distally, the scaphoid laterally, and the triquetrum medially
- medial border of the scapula
- elongated, medial margin of the scapula
- medial condyle of the femur
- smooth, articulating surface that forms the distal and posterior sides of the medial expansion of the distal femur
- medial condyle of the tibia
- medial, expanded region of the proximal tibia that includes the smooth surface that articulates with the medial condyle of the femur as part of the knee joint
- medial cuneiform
- most medial of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, laterally with the intermediate cuneiform bone, and anteriorly with the first and second metatarsal bones
- medial epicondyle of the femur
- roughened area of the distal femur located on the medial side of the medial condyle
- medial epicondyle of the humerus
- enlarged projection located on the medial side of the distal humerus
- medial malleolus
- bony expansion located on the medial side of the distal tibia
- metacarpal bone
- one of the five long bones that form the palm of the hand; numbered 1–5, starting on the lateral (thumb) side of the hand
- metacarpophalangeal joint
- articulation between the distal end of a metacarpal bone of the hand and a proximal phalanx bone of the thumb or a finger
- metatarsal bone
- one of the five elongated bones that forms the anterior half of the foot; numbered 1–5, starting on the medial side of the foot
- metatarsophalangeal joint
- articulation between a metatarsal bone of the foot and the proximal phalanx bone of a toe
- midcarpal joint
- articulation between the proximal and distal rows of the carpal bones; contributes to movements of the hand at the wrist
- navicular
- tarsal bone that articulates posteriorly with the talus bone, laterally with the cuboid bone, and anteriorly with the medial, intermediate, and lateral cuneiform bones
- neck of the femur
- narrowed region located inferior to the head of the femur
- neck of the radius
- narrowed region immediately distal to the head of the radius
- obturator foramen
- large opening located in the anterior hip bone, between the pubis and ischium regions
- olecranon fossa
- large depression located on the posterior side of the distal humerus; this space receives the olecranon process of the ulna when the elbow is fully extended
- olecranon process
- expanded posterior and superior portions of the proximal ulna; forms the bony tip of the elbow
- patella
- kneecap; the largest sesamoid bone of the body; articulates with the distal femur
- patellar surface
- smooth groove located on the anterior side of the distal femur, between the medial and lateral condyles; site of articulation for the patella
- pectineal line
- narrow ridge located on the superior surface of the superior pubic ramus
- pectoral girdle
- shoulder girdle; the set of bones, consisting of the scapula and clavicle, which attaches each upper limb to the axial skeleton
- pelvic brim
- pelvic inlet; the dividing line between the greater and lesser pelvic regions; formed by the superior margin of the pubic symphysis, the pectineal lines of each pubis, the arcuate lines of each ilium, and the sacral promontory
- pelvic girdle
- hip girdle; consists of a single hip bone, which attaches a lower limb to the sacrum of the axial skeleton
- pelvic inlet
- pelvic brim
- pelvic outlet
- inferior opening of the lesser pelvis; formed by the inferior margin of the pubic symphysis, right and left ischiopubic rami and sacrotuberous ligaments, and the tip of the coccyx
- pelvis
- ring of bone consisting of the right and left hip bones, the sacrum, and the coccyx
- phalanx bone of the foot
- (plural = phalanges) one of the 14 bones that form the toes; these include the proximal and distal phalanges of the big toe, and the proximal, middle, and distal phalanx bones of toes two through five
- phalanx bone of the hand
- (plural = phalanges) one of the 14 bones that form the thumb and fingers; these include the proximal and distal phalanges of the thumb, and the proximal, middle, and distal phalanx bones of the fingers two through five
- pisiform
- from the lateral side, the fourth of the four proximal carpal bones; articulates with the anterior surface of the triquetrum
- pollex
- (also, thumb) digit 1 of the hand
- posterior inferior iliac spine
- small, bony projection located at the inferior margin of the auricular surface on the posterior ilium
- posterior sacroiliac ligament
- strong ligament spanning the sacrum and ilium of the hip bone that supports the posterior side of the sacroiliac joint
- posterior superior iliac spine
- rounded, posterior end of the iliac crest
- proximal radioulnar joint
- articulation formed by the radial notch of the ulna and the head of the radius
- proximal tibiofibular joint
- articulation between the head of the fibula and the inferior aspect of the lateral condyle of the tibia
- pubic arch
- bony structure formed by the pubic symphysis, and the bodies and inferior pubic rami of the right and left pubic bones
- pubic body
- enlarged, medial portion of the pubis region of the hip bone
- pubic symphysis
- joint formed by the articulation between the pubic bodies of the right and left hip bones
- pubic tubercle
- small bump located on the superior aspect of the pubic body
- pubis
- anterior portion of the hip bone
- radial fossa
- small depression located on the anterior humerus above the capitulum; this space receives the head of the radius when the elbow is maximally flexed
- radial notch of the ulna
- small, smooth area on the lateral side of the proximal ulna; articulates with the head of the radius as part of the proximal radioulnar joint
- radial tuberosity
- oval-shaped, roughened protuberance located on the medial side of the proximal radius
- radiocarpal joint
- wrist joint, located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones
- radius
- bone located on the lateral side of the forearm
- sacroiliac joint
- joint formed by the articulation between the auricular surfaces of the sacrum and ilium
- sacrospinous ligament
- ligament that spans the sacrum to the ischial spine of the hip bone
- sacrotuberous ligament
- ligament that spans the sacrum to the ischial tuberosity of the hip bone
- scaphoid
- from the lateral side, the first of the four proximal carpal bones; articulates with the radius proximally, the trapezoid, trapezium, and capitate distally, and the lunate medially
- scapula
- shoulder blade bone located on the posterior side of the shoulder
- shaft of the femur
- cylindrically shaped region that forms the central portion of the femur
- shaft of the fibula
- elongated, slender portion located between the expanded ends of the fibula
- shaft of the humerus
- narrow, elongated, central region of the humerus
- shaft of the radius
- narrow, elongated, central region of the radius
- shaft of the tibia
- triangular-shaped, central portion of the tibia
- shaft of the ulna
- narrow, elongated, central region of the ulna
- soleal line
- small, diagonally running ridge located on the posterior side of the proximal tibia
- spine of the scapula
- prominent ridge passing mediolaterally across the upper portion of the posterior scapular surface
- sternal end of the clavicle
- medial end of the clavicle that articulates with the manubrium of the sternum
- sternoclavicular joint
- articulation between the manubrium of the sternum and the sternal end of the clavicle; forms the only bony attachment between the pectoral girdle of the upper limb and the axial skeleton
- styloid process of the radius
- pointed projection located on the lateral end of the distal radius
- styloid process of the ulna
- short, bony projection located on the medial end of the distal ulna
- subpubic angle
- inverted V-shape formed by the convergence of the right and left ischiopubic rami; this angle is greater than 80 degrees in females and less than 70 degrees in males
- subscapular fossa
- broad depression located on the anterior (deep) surface of the scapula
- superior angle of the scapula
- corner of the scapula between the superior and medial borders of the scapula
- superior border of the scapula
- superior margin of the scapula
- superior pubic ramus
- narrow segment of bone that passes laterally from the pubic body to join the ilium
- supraglenoid tubercle
- small bump located at the superior margin of the glenoid cavity
- suprascapular notch
- small notch located along the superior border of the scapula, medial to the coracoid process
- supraspinous fossa
- narrow depression located on the posterior scapula, superior to the spine
- surgical neck
- region of the humerus where the expanded, proximal end joins with the narrower shaft
- sustentaculum tali
- bony ledge extending from the medial side of the calcaneus bone
- talus
- tarsal bone that articulates superiorly with the tibia and fibula at the ankle joint; also articulates inferiorly with the calcaneus bone and anteriorly with the navicular bone
- tarsal bone
- one of the seven bones that make up the posterior foot; includes the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform bones
- thigh
- portion of the lower limb located between the hip and knee joints
- tibia
- shin bone; the large, weight-bearing bone located on the medial side of the leg
- tibial tuberosity
- elevated area on the anterior surface of the proximal tibia
- trapezium
- from the lateral side, the first of the four distal carpal bones; articulates with the scaphoid proximally, the first and second metacarpals distally, and the trapezoid medially
- trapezoid
- from the lateral side, the second of the four distal carpal bones; articulates with the scaphoid proximally, the second metacarpal distally, the trapezium laterally, and the capitate medially
- triquetrum
- from the lateral side, the third of the four proximal carpal bones; articulates with the lunate laterally, the hamate distally, and has a facet for the pisiform
- trochlea
- pulley-shaped region located medially at the distal end of the humerus; articulates at the elbow with the trochlear notch of the ulna
- trochlear notch
- large, C-shaped depression located on the anterior side of the proximal ulna; articulates at the elbow with the trochlea of the humerus
- ulna
- bone located on the medial side of the forearm
- ulnar notch of the radius
- shallow, smooth area located on the medial side of the distal radius; articulates with the head of the ulna at the distal radioulnar joint
- ulnar tuberosity
- roughened area located on the anterior, proximal ulna inferior to the coronoid process
Chapter Review
8.1 The Pectoral Girdle
The pectoral girdle, consisting of the clavicle and the scapula, attaches each upper limb to the axial skeleton. The clavicle is an anterior bone whose sternal end articulates with the manubrium of the sternum at the sternoclavicular joint. The sternal end is also anchored to the first rib by the costoclavicular ligament. The acromial end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint. This end is also anchored to the coracoid process of the scapula by the coracoclavicular ligament, which provides indirect support for the acromioclavicular joint. The clavicle supports the scapula, transmits the weight and forces from the upper limb to the body trunk, and protects the underlying nerves and blood vessels.
The scapula lies on the posterior aspect of the pectoral girdle. It mediates the attachment of the upper limb to the clavicle, and contributes to the formation of the glenohumeral (shoulder) joint. This triangular bone has three sides called the medial, lateral, and superior borders. The suprascapular notch is located on the superior border. The scapula also has three corners, two of which are the superior and inferior angles. The third corner is occupied by the glenoid cavity. Posteriorly, the spine separates the supraspinous and infraspinous fossae, and then extends laterally as the acromion. The subscapular fossa is located on the anterior surface of the scapula. The coracoid process projects anteriorly, passing inferior to the lateral end of the clavicle.
8.2 Bones of the Upper Limb
Each upper limb is divided into three regions and contains a total of 30 bones. The upper arm is the region located between the shoulder and elbow joints. This area contains the humerus. The proximal humerus consists of the head, which articulates with the scapula at the glenohumeral joint, the greater and lesser tubercles separated by the intertubercular (bicipital) groove, and the anatomical and surgical necks. The humeral shaft has the roughened area of the deltoid tuberosity on its lateral side. The distal humerus is flattened, forming a lateral supracondylar ridge that terminates at the small lateral epicondyle. The medial side of the distal humerus has the large, medial epicondyle. The articulating surfaces of the distal humerus consist of the trochlea medially and the capitulum laterally. Depressions on the humerus that accommodate the forearm bones during bending (flexing) and straightening (extending) of the elbow include the coronoid fossa, the radial fossa, and the olecranon fossa.
The forearm is the region of the upper limb located between the elbow and wrist joints. This region contains two bones, the ulna medially and the radius on the lateral (thumb) side. The elbow joint is formed by the articulation between the trochlea of the humerus and the trochlear notch of the ulna, plus the articulation between the capitulum of the humerus and the head of the radius. The proximal radioulnar joint is the articulation between the head of the radius and the radial notch of the ulna. The proximal ulna also has the olecranon process, forming an expanded posterior region, and the coronoid process and ulnar tuberosity on its anterior aspect. On the proximal radius, the narrowed region below the head is the neck; distal to this is the radial tuberosity. The shaft portions of both the ulna and radius have an interosseous border, whereas the distal ends of each bone have a pointed styloid process. The distal radioulnar joint is found between the head of the ulna and the ulnar notch of the radius. The distal end of the radius articulates with the proximal carpal bones, but the ulna does not.
The base of the hand is formed by eight carpal bones. The carpal bones are united into two rows of bones. The proximal row contains (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones. The scaphoid, lunate, and triquetrum bones contribute to the formation of the radiocarpal joint. The distal row of carpal bones contains (from medial to lateral) the hamate, capitate, trapezoid, and trapezium bones (“So Long To Pinky, Here Comes The Thumb”). The anterior hamate has a prominent bony hook. The proximal and distal carpal rows articulate with each other at the midcarpal joint. The carpal bones, together with the flexor retinaculum, also form the carpal tunnel of the wrist.
The five metacarpal bones form the palm of the hand. The metacarpal bones are numbered 1–5, starting with the thumb side. The first metacarpal bone is freely mobile, but the other bones are united as a group. The digits are also numbered 1–5, with the thumb being number 1. The fingers and thumb contain a total of 14 phalanges (phalanx bones). The thumb contains a proximal and a distal phalanx, whereas the remaining digits each contain proximal, middle, and distal phalanges.
8.3 The Pelvic Girdle and Pelvis
The pelvic girdle, consisting of a hip bone, serves to attach a lower limb to the axial skeleton. The hip bone articulates posteriorly at the sacroiliac joint with the sacrum, which is part of the axial skeleton. The right and left hip bones converge anteriorly and articulate with each other at the pubic symphysis. The combination of the hip bone, the sacrum, and the coccyx forms the pelvis. The pelvis has a pronounced anterior tilt. The primary function of the pelvis is to support the upper body and transfer body weight to the lower limbs. It also serves as the site of attachment for multiple muscles.
The hip bone consists of three regions: the ilium, ischium, and pubis. The ilium forms the large, fan-like region of the hip bone. The superior margin of this area is the iliac crest. Located at either end of the iliac crest are the anterior superior and posterior superior iliac spines. Inferior to these are the anterior inferior and posterior inferior iliac spines. The auricular surface of the ilium articulates with the sacrum to form the sacroiliac joint. The medial surface of the upper ilium forms the iliac fossa, with the arcuate line marking the inferior limit of this area. The posterior margin of the ilium has the large greater sciatic notch.
The posterolateral portion of the hip bone is the ischium. It has the expanded ischial tuberosity, which supports body weight when sitting. The ischial ramus projects anteriorly and superiorly. The posterior margin of the ischium has the shallow lesser sciatic notch and the ischial spine, which separates the greater and lesser sciatic notches.
The pubis forms the anterior portion of the hip bone. The body of the pubis articulates with the pubis of the opposite hip bone at the pubic symphysis. The superior margin of the pubic body has the pubic tubercle. The pubis is joined to the ilium by the superior pubic ramus, the superior surface of which forms the pectineal line. The inferior pubic ramus projects inferiorly and laterally. The pubic arch is formed by the pubic symphysis, the bodies of the adjacent pubic bones, and the two inferior pubic rami. The inferior pubic ramus joins the ischial ramus to form the ischiopubic ramus. The subpubic angle is formed by the medial convergence of the right and left ischiopubic rami.
The lateral side of the hip bone has the cup-like acetabulum, which is part of the hip joint. The large anterior opening is the obturator foramen. The sacroiliac joint is supported by the anterior and posterior sacroiliac ligaments. The sacrum is also joined to the hip bone by the sacrospinous ligament, which attaches to the ischial spine, and the sacrotuberous ligament, which attaches to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramina.
The broad space of the upper pelvis is the greater pelvis, and the narrow, inferior space is the lesser pelvis. These areas are separated by the pelvic brim (pelvic inlet). The inferior opening of the pelvis is the pelvic outlet. Compared to the male, the female pelvis is wider to accommodate childbirth, has a larger subpubic angle, and a broader greater sciatic notch.
8.4 Bones of the Lower Limb
The lower limb is divided into three regions. These are the thigh, located between the hip and knee joints; the leg, located between the knee and ankle joints; and distal to the ankle, the foot. There are 30 bones in each lower limb. These are the femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and 14 phalanges.
The femur is the single bone of the thigh. Its rounded head articulates with the acetabulum of the hip bone to form the hip joint. The head has the fovea capitis for attachment of the ligament of the head of the femur. The narrow neck joins inferiorly with the greater and lesser trochanters. Passing between these bony expansions are the intertrochanteric line on the anterior femur and the larger intertrochanteric crest on the posterior femur. On the posterior shaft of the femur is the gluteal tuberosity proximally and the linea aspera in the mid-shaft region. The expanded distal end consists of three articulating surfaces: the medial and lateral condyles, and the patellar surface. The outside margins of the condyles are the medial and lateral epicondyles. The adductor tubercle is on the superior aspect of the medial epicondyle.
The patella is a sesamoid bone located within a muscle tendon. It articulates with the patellar surface on the anterior side of the distal femur, thereby protecting the muscle tendon from rubbing against the femur.
The leg contains the large tibia on the medial side and the slender fibula on the lateral side. The tibia bears the weight of the body, whereas the fibula does not bear weight. The interosseous border of each bone is the attachment site for the interosseous membrane of the leg, the connective tissue sheet that unites the tibia and fibula.
The proximal tibia consists of the expanded medial and lateral condyles, which articulate with the medial and lateral condyles of the femur to form the knee joint. Between the tibial condyles is the intercondylar eminence. On the anterior side of the proximal tibia is the tibial tuberosity, which is continuous inferiorly with the anterior border of the tibia. On the posterior side, the proximal tibia has the curved soleal line. The bony expansion on the medial side of the distal tibia is the medial malleolus. The groove on the lateral side of the distal tibia is the fibular notch.
The head of the fibula forms the proximal end and articulates with the underside of the lateral condyle of the tibia. The distal fibula articulates with the fibular notch of the tibia. The expanded distal end of the fibula is the lateral malleolus.
The posterior foot is formed by the seven tarsal bones. The talus articulates superiorly with the distal tibia, the medial malleolus of the tibia, and the lateral malleolus of the fibula to form the ankle joint. The talus articulates inferiorly with the calcaneus bone. The sustentaculum tali of the calcaneus helps to support the talus. Anterior to the talus is the navicular bone, and anterior to this are the medial, intermediate, and lateral cuneiform bones. The cuboid bone is anterior to the calcaneus.
The five metatarsal bones form the anterior foot. The base of these bones articulate with the cuboid or cuneiform bones. The metatarsal heads, at their distal ends, articulate with the proximal phalanges of the toes. The big toe (toe number 1) has proximal and distal phalanx bones. The remaining toes have proximal, middle, and distal phalanges.
8.5 Development of the Appendicular Skeleton
The bones of the appendicular skeleton arise from embryonic mesenchyme. Limb buds appear at the end of the fourth week. The apical ectodermal ridge, located at the end of the limb bud, stimulates growth and elongation of the limb. During the sixth week, the distal end of the limb bud becomes paddle-shaped, and selective cell death separates the developing fingers and toes. At the same time, mesenchyme within the limb bud begins to differentiate into hyaline cartilage, forming models for future bones. During the seventh week, the upper limbs rotate laterally and the lower limbs rotate medially, bringing the limbs into their final positions.
Endochondral ossification, the process that converts the hyaline cartilage model into bone, begins in most appendicular bones by the twelfth fetal week. This begins as a primary ossification center in the diaphysis, followed by the later appearance of one or more secondary ossifications centers in the regions of the epiphyses. Each secondary ossification center is separated from the primary ossification center by an epiphyseal plate. Continued growth of the epiphyseal plate cartilage provides for bone lengthening. Disappearance of the epiphyseal plate is followed by fusion of the bony components to form a single, adult bone.
The clavicle develops via intramembranous ossification, in which mesenchyme is converted directly into bone tissue. Ossification within the clavicle begins during the fifth week of development and continues until 25 years of age.
Interactive Link Questions
Watch this video to see how fractures of the distal radius bone can affect the wrist joint. Explain the problems that may occur if a fracture of the distal radius involves the joint surface of the radiocarpal joint of the wrist.
2.Visit this site to explore the bones and joints of the hand. What are the three arches of the hand, and what is the importance of these during the gripping of an object?
3.Watch this video to learn about a Colles fracture, a break of the distal radius, usually caused by falling onto an outstretched hand. When would surgery be required and how would the fracture be repaired in this case?
4.Watch this video for a 3-D view of the pelvis and its associated ligaments. What is the large opening in the bony pelvis, located between the ischium and pubic regions, and what two parts of the pubis contribute to the formation of this opening?
5.Watch this video to view how a fracture of the mid-femur is surgically repaired. How are the two portions of the broken femur stabilized during surgical repair of a fractured femur?
6.Visit this site to perform a virtual knee replacement surgery. The prosthetic knee components must be properly aligned to function properly. How is this alignment ensured?
7.Use this tutorial to review the bones of the foot. Which tarsal bones are in the proximal, intermediate, and distal groups?
8.View this link to learn about a bunion, a localized swelling on the medial side of the foot, next to the first metatarsophalangeal joint, at the base of the big toe. What is a bunion and what type of shoe is most likely to cause this to develop?
9.Watch this animation to follow the development and growth of the upper and lower limb buds. On what days of embryonic development do these events occur: (a) first appearance of the upper limb bud (limb ridge); (b) the flattening of the distal limb to form the handplate or footplate; and (c) the beginning of limb rotation?
Review Questions
Which part of the clavicle articulates with the manubrium?
- shaft
- sternal end
- acromial end
- coracoid process
A shoulder separation results from injury to the ________.
- glenohumeral joint
- costoclavicular joint
- acromioclavicular joint
- sternoclavicular joint
Which feature lies between the spine and superior border of the scapula?
- suprascapular notch
- glenoid cavity
- superior angle
- supraspinous fossa
What structure is an extension of the spine of the scapula?
- acromion
- coracoid process
- supraglenoid tubercle
- glenoid cavity
Name the short, hook-like bony process of the scapula that projects anteriorly.
- acromial process
- clavicle
- coracoid process
- glenoid fossa
How many bones are there in the upper limbs combined?
- 20
- 30
- 40
- 60
Which bony landmark is located on the lateral side of the proximal humerus?
- greater tubercle
- trochlea
- lateral epicondyle
- lesser tubercle
Which region of the humerus articulates with the radius as part of the elbow joint?
- trochlea
- styloid process
- capitulum
- olecranon process
Which is the lateral-most carpal bone of the proximal row?
- trapezium
- hamate
- pisiform
- scaphoid
The radius bone ________.
- is found on the medial side of the forearm
- has a head that articulates with the radial notch of the ulna
- does not articulate with any of the carpal bones
- has the radial tuberosity located near its distal end
How many bones fuse in adulthood to form the hip bone?
- 2
- 3
- 4
- 5
Which component forms the superior part of the hip bone?
- ilium
- pubis
- ischium
- sacrum
Which of the following supports body weight when sitting?
- iliac crest
- ischial tuberosity
- ischiopubic ramus
- pubic body
The ischial spine is found between which of the following structures?
- inferior pubic ramus and ischial ramus
- pectineal line and arcuate line
- lesser sciatic notch and greater sciatic notch
- anterior superior iliac spine and posterior superior iliac spine
The pelvis ________.
- has a subpubic angle that is larger in females
- consists of the two hip bones, but does not include the sacrum or coccyx
- has an obturator foramen, an opening that is defined in part by the sacrospinous and sacrotuberous ligaments
- has a space located inferior to the pelvic brim called the greater pelvis
Which bony landmark of the femur serves as a site for muscle attachments?
- fovea capitis
- lesser trochanter
- head
- medial condyle
What structure contributes to the knee joint?
- lateral malleolus of the fibula
- tibial tuberosity
- medial condyle of the tibia
- lateral epicondyle of the femur
Which tarsal bone articulates with the tibia and fibula?
- calcaneus
- cuboid
- navicular
- talus
What is the total number of bones found in the foot and toes?
- 7
- 14
- 26
- 30
The tibia ________.
- has an expanded distal end called the lateral malleolus
- is not a weight-bearing bone
- is firmly anchored to the fibula by an interosseous membrane
- can be palpated (felt) under the skin only at its proximal and distal ends
Which event takes place during the seventh week of development?
- appearance of the upper and lower limb buds
- flattening of the distal limb bud into a paddle shape
- the first appearance of hyaline cartilage models of future bones
- the rotation of the limbs
During endochondral ossification of a long bone, ________.
- a primary ossification center will develop within the epiphysis
- mesenchyme will differentiate directly into bone tissue
- growth of the epiphyseal plate will produce bone lengthening
- all epiphyseal plates will disappear before birth
The clavicle ________.
- develops via intramembranous ossification
- develops via endochondral ossification
- is the last bone of the body to begin ossification
- is fully ossified at the time of birth
Critical Thinking Questions
Describe the shape and palpable line formed by the clavicle and scapula.
34.Discuss two possible injuries of the pectoral girdle that may occur following a strong blow to the shoulder or a hard fall onto an outstretched hand.
35.Your friend runs out of gas and you have to help push his car. Discuss the sequence of bones and joints that convey the forces passing from your hand, through your upper limb and your pectoral girdle, and to your axial skeleton.
36.Name the bones in the wrist and hand, and describe or sketch out their locations and articulations.
37.Describe the articulations and ligaments that unite the four bones of the pelvis to each other.
38.Discuss the ways in which the female pelvis is adapted for childbirth.
39.Define the regions of the lower limb, name the bones found in each region, and describe the bony landmarks that articulate together to form the hip, knee, and ankle joints.
40.The talus bone of the foot receives the weight of the body from the tibia. The talus bone then distributes this weight toward the ground in two directions: one-half of the body weight is passed in a posterior direction and one-half of the weight is passed in an anterior direction. Describe the arrangement of the tarsal and metatarsal bones that are involved in both the posterior and anterior distribution of body weight.
41.How can a radiograph of a child’s femur be used to determine the approximate age of that child?
42.How does the development of the clavicle differ from the development of other appendicular skeleton bones?
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oercommons
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2025-03-18T00:38:17.940721
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/56367/overview",
"title": "Anatomy and Physiology, Support and Movement",
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https://oercommons.org/courseware/lesson/56368/overview
|
Joints
Introduction
Figure 9.1 Girl Kayaking Without joints, body movements would be impossible. (credit: Graham Richardson/flickr.com)
CHAPTER OBJECTIVES
After this chapter, you will be able to:
- Discuss both functional and structural classifications for body joints
- Describe the characteristic features for fibrous, cartilaginous, and synovial joints and give examples of each
- Define and identify the different body movements
- Discuss the structure of specific body joints and the movements allowed by each
- Explain the development of body joints
The adult human body has 206 bones, and with the exception of the hyoid bone in the neck, each bone is connected to at least one other bone. Joints are the location where bones come together. Many joints allow for movement between the bones. At these joints, the articulating surfaces of the adjacent bones can move smoothly against each other. However, the bones of other joints may be joined to each other by connective tissue or cartilage. These joints are designed for stability and provide for little or no movement. Importantly, joint stability and movement are related to each other. This means that stable joints allow for little or no mobility between the adjacent bones. Conversely, joints that provide the most movement between bones are the least stable. Understanding the relationship between joint structure and function will help to explain why particular types of joints are found in certain areas of the body.
The articulating surfaces of bones at stable types of joints, with little or no mobility, are strongly united to each other. For example, most of the joints of the skull are held together by fibrous connective tissue and do not allow for movement between the adjacent bones. This lack of mobility is important, because the skull bones serve to protect the brain. Similarly, other joints united by fibrous connective tissue allow for very little movement, which provides stability and weight-bearing support for the body. For example, the tibia and fibula of the leg are tightly united to give stability to the body when standing. At other joints, the bones are held together by cartilage, which permits limited movements between the bones. Thus, the joints of the vertebral column only allow for small movements between adjacent vertebrae, but when added together, these movements provide the flexibility that allows your body to twist, or bend to the front, back, or side. In contrast, at joints that allow for wide ranges of motion, the articulating surfaces of the bones are not directly united to each other. Instead, these surfaces are enclosed within a space filled with lubricating fluid, which allows the bones to move smoothly against each other. These joints provide greater mobility, but since the bones are free to move in relation to each other, the joint is less stable. Most of the joints between the bones of the appendicular skeleton are this freely moveable type of joint. These joints allow the muscles of the body to pull on a bone and thereby produce movement of that body region. Your ability to kick a soccer ball, pick up a fork, and dance the tango depend on mobility at these types of joints.
Classification of Joints
- Distinguish between the functional and structural classifications for joints
- Describe the three functional types of joints and give an example of each
- List the three types of diarthrodial joints
A joint, also called an articulation, is any place where adjacent bones or bone and cartilage come together (articulate with each other) to form a connection. Joints are classified both structurally and functionally. Structural classifications of joints take into account whether the adjacent bones are strongly anchored to each other by fibrous connective tissue or cartilage, or whether the adjacent bones articulate with each other within a fluid-filled space called a joint cavity. Functional classifications describe the degree of movement available between the bones, ranging from immobile, to slightly mobile, to freely moveable joints. The amount of movement available at a particular joint of the body is related to the functional requirements for that joint. Thus immobile or slightly moveable joints serve to protect internal organs, give stability to the body, and allow for limited body movement. In contrast, freely moveable joints allow for much more extensive movements of the body and limbs.
Structural Classification of Joints
The structural classification of joints is based on whether the articulating surfaces of the adjacent bones are directly connected by fibrous connective tissue or cartilage, or whether the articulating surfaces contact each other within a fluid-filled joint cavity. These differences serve to divide the joints of the body into three structural classifications. A fibrous joint is where the adjacent bones are united by fibrous connective tissue. At a cartilaginous joint, the bones are joined by hyaline cartilage or fibrocartilage. At a synovial joint, the articulating surfaces of the bones are not directly connected, but instead come into contact with each other within a joint cavity that is filled with a lubricating fluid. Synovial joints allow for free movement between the bones and are the most common joints of the body.
Functional Classification of Joints
The functional classification of joints is determined by the amount of mobility found between the adjacent bones. Joints are thus functionally classified as a synarthrosis or immobile joint, an amphiarthrosis or slightly moveable joint, or as a diarthrosis, which is a freely moveable joint (arthroun = “to fasten by a joint”). Depending on their location, fibrous joints may be functionally classified as a synarthrosis (immobile joint) or an amphiarthrosis (slightly mobile joint). Cartilaginous joints are also functionally classified as either a synarthrosis or an amphiarthrosis joint. All synovial joints are functionally classified as a diarthrosis joint.
Synarthrosis
An immobile or nearly immobile joint is called a synarthrosis. The immobile nature of these joints provide for a strong union between the articulating bones. This is important at locations where the bones provide protection for internal organs. Examples include sutures, the fibrous joints between the bones of the skull that surround and protect the brain (Figure 9.2), and the manubriosternal joint, the cartilaginous joint that unites the manubrium and body of the sternum for protection of the heart.
Figure 9.2 Suture Joints of Skull The suture joints of the skull are an example of a synarthrosis, an immobile or essentially immobile joint.
Amphiarthrosis
An amphiarthrosis is a joint that has limited mobility. An example of this type of joint is the cartilaginous joint that unites the bodies of adjacent vertebrae. Filling the gap between the vertebrae is a thick pad of fibrocartilage called an intervertebral disc (Figure 9.3). Each intervertebral disc strongly unites the vertebrae but still allows for a limited amount of movement between them. However, the small movements available between adjacent vertebrae can sum together along the length of the vertebral column to provide for large ranges of body movements.
Another example of an amphiarthrosis is the pubic symphysis of the pelvis. This is a cartilaginous joint in which the pubic regions of the right and left hip bones are strongly anchored to each other by fibrocartilage. This joint normally has very little mobility. The strength of the pubic symphysis is important in conferring weight-bearing stability to the pelvis.
Figure 9.3 Intervertebral Disc An intervertebral disc unites the bodies of adjacent vertebrae within the vertebral column. Each disc allows for limited movement between the vertebrae and thus functionally forms an amphiarthrosis type of joint. Intervertebral discs are made of fibrocartilage and thereby structurally form a symphysis type of cartilaginous joint.
Diarthrosis
A freely mobile joint is classified as a diarthrosis. These types of joints include all synovial joints of the body, which provide the majority of body movements. Most diarthrotic joints are found in the appendicular skeleton and thus give the limbs a wide range of motion. These joints are divided into three categories, based on the number of axes of motion provided by each. An axis in anatomy is described as the movements in reference to the three anatomical planes: transverse, frontal, and sagittal. Thus, diarthroses are classified as uniaxial (for movement in one plane), biaxial (for movement in two planes), or multiaxial joints (for movement in all three anatomical planes).
A uniaxial joint only allows for a motion in a single plane (around a single axis). The elbow joint, which only allows for bending or straightening, is an example of a uniaxial joint. A biaxial joint allows for motions within two planes. An example of a biaxial joint is a metacarpophalangeal joint (knuckle joint) of the hand. The joint allows for movement along one axis to produce bending or straightening of the finger, and movement along a second axis, which allows for spreading of the fingers away from each other and bringing them together. A joint that allows for the several directions of movement is called a multiaxial joint(polyaxial or triaxial joint). This type of diarthrotic joint allows for movement along three axes (Figure 9.4). The shoulder and hip joints are multiaxial joints. They allow the upper or lower limb to move in an anterior-posterior direction and a medial-lateral direction. In addition, the limb can also be rotated around its long axis. This third movement results in rotation of the limb so that its anterior surface is moved either toward or away from the midline of the body.
Figure 9.4 Multiaxial Joint A multiaxial joint, such as the hip joint, allows for three types of movement: anterior-posterior, medial-lateral, and rotational.
Fibrous Joints
- Describe the structural features of fibrous joints
- Distinguish between a suture, syndesmosis, and gomphosis
- Give an example of each type of fibrous joint
At a fibrous joint, the adjacent bones are directly connected to each other by fibrous connective tissue, and thus the bones do not have a joint cavity between them (Figure 9.5). The gap between the bones may be narrow or wide. There are three types of fibrous joints. A suture is the narrow fibrous joint found between most bones of the skull. At a syndesmosis joint, the bones are more widely separated but are held together by a narrow band of fibrous connective tissue called a ligament or a wide sheet of connective tissue called an interosseous membrane. This type of fibrous joint is found between the shaft regions of the long bones in the forearm and in the leg. Lastly, a gomphosis is the narrow fibrous joint between the roots of a tooth and the bony socket in the jaw into which the tooth fits.
Figure 9.5 Fibrous Joints Fibrous joints form strong connections between bones. (a) Sutures join most bones of the skull. (b) An interosseous membrane forms a syndesmosis between the radius and ulna bones of the forearm. (c) A gomphosis is a specialized fibrous joint that anchors a tooth to its socket in the jaw.
Suture
All the bones of the skull, except for the mandible, are joined to each other by a fibrous joint called a suture. The fibrous connective tissue found at a suture (“to bind or sew”) strongly unites the adjacent skull bones and thus helps to protect the brain and form the face. In adults, the skull bones are closely opposed and fibrous connective tissue fills the narrow gap between the bones. The suture is frequently convoluted, forming a tight union that prevents most movement between the bones. (See Figure 9.5a.) Thus, skull sutures are functionally classified as a synarthrosis, although some sutures may allow for slight movements between the cranial bones.
In newborns and infants, the areas of connective tissue between the bones are much wider, especially in those areas on the top and sides of the skull that will become the sagittal, coronal, squamous, and lambdoid sutures. These broad areas of connective tissue are called fontanelles (Figure 9.6). During birth, the fontanelles provide flexibility to the skull, allowing the bones to push closer together or to overlap slightly, thus aiding movement of the infant’s head through the birth canal. After birth, these expanded regions of connective tissue allow for rapid growth of the skull and enlargement of the brain. The fontanelles greatly decrease in width during the first year after birth as the skull bones enlarge. When the connective tissue between the adjacent bones is reduced to a narrow layer, these fibrous joints are now called sutures. At some sutures, the connective tissue will ossify and be converted into bone, causing the adjacent bones to fuse to each other. This fusion between bones is called a synostosis (“joined by bone”). Examples of synostosis fusions between cranial bones are found both early and late in life. At the time of birth, the frontal and maxillary bones consist of right and left halves joined together by sutures, which disappear by the eighth year as the halves fuse together to form a single bone. Late in life, the sagittal, coronal, and lambdoid sutures of the skull will begin to ossify and fuse, causing the suture line to gradually disappear.
Figure 9.6 The Newborn Skull The fontanelles of a newborn’s skull are broad areas of fibrous connective tissue that form fibrous joints between the bones of the skull.
Syndesmosis
A syndesmosis (“fastened with a band”) is a type of fibrous joint in which two parallel bones are united to each other by fibrous connective tissue. The gap between the bones may be narrow, with the bones joined by ligaments, or the gap may be wide and filled in by a broad sheet of connective tissue called an interosseous membrane.
In the forearm, the wide gap between the shaft portions of the radius and ulna bones are strongly united by an interosseous membrane (see Figure 9.5b). Similarly, in the leg, the shafts of the tibia and fibula are also united by an interosseous membrane. In addition, at the distal tibiofibular joint, the articulating surfaces of the bones lack cartilage and the narrow gap between the bones is anchored by fibrous connective tissue and ligaments on both the anterior and posterior aspects of the joint. Together, the interosseous membrane and these ligaments form the tibiofibular syndesmosis.
The syndesmoses found in the forearm and leg serve to unite parallel bones and prevent their separation. However, a syndesmosis does not prevent all movement between the bones, and thus this type of fibrous joint is functionally classified as an amphiarthrosis. In the leg, the syndesmosis between the tibia and fibula strongly unites the bones, allows for little movement, and firmly locks the talus bone in place between the tibia and fibula at the ankle joint. This provides strength and stability to the leg and ankle, which are important during weight bearing. In the forearm, the interosseous membrane is flexible enough to allow for rotation of the radius bone during forearm movements. Thus in contrast to the stability provided by the tibiofibular syndesmosis, the flexibility of the antebrachial interosseous membrane allows for the much greater mobility of the forearm.
The interosseous membranes of the leg and forearm also provide areas for muscle attachment. Damage to a syndesmotic joint, which usually results from a fracture of the bone with an accompanying tear of the interosseous membrane, will produce pain, loss of stability of the bones, and may damage the muscles attached to the interosseous membrane. If the fracture site is not properly immobilized with a cast or splint, contractile activity by these muscles can cause improper alignment of the broken bones during healing.
Gomphosis
A gomphosis (“fastened with bolts”) is the specialized fibrous joint that anchors the root of a tooth into its bony socket within the maxillary bone (upper jaw) or mandible bone (lower jaw) of the skull. A gomphosis is also known as a peg-and-socket joint. Spanning between the bony walls of the socket and the root of the tooth are numerous short bands of dense connective tissue, each of which is called a periodontal ligament (see Figure 9.5c). Due to the immobility of a gomphosis, this type of joint is functionally classified as a synarthrosis.
Cartilaginous Joints
- Describe the structural features of cartilaginous joints
- Distinguish between a synchondrosis and symphysis
- Give an example of each type of cartilaginous joint
As the name indicates, at a cartilaginous joint, the adjacent bones are united by cartilage, a tough but flexible type of connective tissue. These types of joints lack a joint cavity and involve bones that are joined together by either hyaline cartilage or fibrocartilage (Figure 9.7). There are two types of cartilaginous joints. A synchondrosis is a cartilaginous joint where the bones are joined by hyaline cartilage. Also classified as a synchondrosis are places where bone is united to a cartilage structure, such as between the anterior end of a rib and the costal cartilage of the thoracic cage. The second type of cartilaginous joint is a symphysis, where the bones are joined by fibrocartilage.
Figure 9.7 Cartiliginous Joints At cartilaginous joints, bones are united by hyaline cartilage to form a synchondrosis or by fibrocartilage to form a symphysis. (a) The hyaline cartilage of the epiphyseal plate (growth plate) forms a synchondrosis that unites the shaft (diaphysis) and end (epiphysis) of a long bone and allows the bone to grow in length. (b) The pubic portions of the right and left hip bones of the pelvis are joined together by fibrocartilage, forming the pubic symphysis.
Synchondrosis
A synchondrosis (“joined by cartilage”) is a cartilaginous joint where bones are joined together by hyaline cartilage, or where bone is united to hyaline cartilage. A synchondrosis may be temporary or permanent. A temporary synchondrosis is the epiphyseal plate (growth plate) of a growing long bone. The epiphyseal plate is the region of growing hyaline cartilage that unites the diaphysis (shaft) of the bone to the epiphysis (end of the bone). Bone lengthening involves growth of the epiphyseal plate cartilage and its replacement by bone, which adds to the diaphysis. For many years during childhood growth, the rates of cartilage growth and bone formation are equal and thus the epiphyseal plate does not change in overall thickness as the bone lengthens. During the late teens and early 20s, growth of the cartilage slows and eventually stops. The epiphyseal plate is then completely replaced by bone, and the diaphysis and epiphysis portions of the bone fuse together to form a single adult bone. This fusion of the diaphysis and epiphysis is a synostosis. Once this occurs, bone lengthening ceases. For this reason, the epiphyseal plate is considered to be a temporary synchondrosis. Because cartilage is softer than bone tissue, injury to a growing long bone can damage the epiphyseal plate cartilage, thus stopping bone growth and preventing additional bone lengthening.
Growing layers of cartilage also form synchondroses that join together the ilium, ischium, and pubic portions of the hip bone during childhood and adolescence. When body growth stops, the cartilage disappears and is replaced by bone, forming synostoses and fusing the bony components together into the single hip bone of the adult. Similarly, synostoses unite the sacral vertebrae that fuse together to form the adult sacrum.
INTERACTIVE LINK
Visit this website to view a radiograph (X-ray image) of a child’s hand and wrist. The growing bones of child have an epiphyseal plate that forms a synchondrosis between the shaft and end of a long bone. Being less dense than bone, the area of epiphyseal cartilage is seen on this radiograph as the dark epiphyseal gaps located near the ends of the long bones, including the radius, ulna, metacarpal, and phalanx bones. Which of the bones in this image do not show an epiphyseal plate (epiphyseal gap)?
Examples of permanent synchondroses are found in the thoracic cage. One example is the first sternocostal joint, where the first rib is anchored to the manubrium by its costal cartilage. (The articulations of the remaining costal cartilages to the sternum are all synovial joints.) Additional synchondroses are formed where the anterior end of the other 11 ribs is joined to its costal cartilage. Unlike the temporary synchondroses of the epiphyseal plate, these permanent synchondroses retain their hyaline cartilage and thus do not ossify with age. Due to the lack of movement between the bone and cartilage, both temporary and permanent synchondroses are functionally classified as a synarthrosis.
Symphysis
A cartilaginous joint where the bones are joined by fibrocartilage is called a symphysis (“growing together”). Fibrocartilage is very strong because it contains numerous bundles of thick collagen fibers, thus giving it a much greater ability to resist pulling and bending forces when compared with hyaline cartilage. This gives symphyses the ability to strongly unite the adjacent bones, but can still allow for limited movement to occur. Thus, a symphysis is functionally classified as an amphiarthrosis.
The gap separating the bones at a symphysis may be narrow or wide. Examples in which the gap between the bones is narrow include the pubic symphysis and the manubriosternal joint. At the pubic symphysis, the pubic portions of the right and left hip bones of the pelvis are joined together by fibrocartilage across a narrow gap. Similarly, at the manubriosternal joint, fibrocartilage unites the manubrium and body portions of the sternum.
The intervertebral symphysis is a wide symphysis located between the bodies of adjacent vertebrae of the vertebral column. Here a thick pad of fibrocartilage called an intervertebral disc strongly unites the adjacent vertebrae by filling the gap between them. The width of the intervertebral symphysis is important because it allows for small movements between the adjacent vertebrae. In addition, the thick intervertebral disc provides cushioning between the vertebrae, which is important when carrying heavy objects or during high-impact activities such as running or jumping.
Synovial Joints
- Describe the structural features of a synovial joint
- Discuss the function of additional structures associated with synovial joints
- List the six types of synovial joints and give an example of each
Synovial joints are the most common type of joint in the body (Figure 9.8). A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity. This fluid-filled space is the site at which the articulating surfaces of the bones contact each other. Also unlike fibrous or cartilaginous joints, the articulating bone surfaces at a synovial joint are not directly connected to each other with fibrous connective tissue or cartilage. This gives the bones of a synovial joint the ability to move smoothly against each other, allowing for increased joint mobility.
Figure 9.8 Synovial Joints Synovial joints allow for smooth movements between the adjacent bones. The joint is surrounded by an articular capsule that defines a joint cavity filled with synovial fluid. The articulating surfaces of the bones are covered by a thin layer of articular cartilage. Ligaments support the joint by holding the bones together and resisting excess or abnormal joint motions.
Structural Features of Synovial Joints
Synovial joints are characterized by the presence of a joint cavity. The walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. The bones of the joint articulate with each other within the joint cavity.
Friction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. However, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. Instead, the articular cartilage acts like a Teflon® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. Lining the inner surface of the articular capsule is a thin synovial membrane. The cells of this membrane secrete synovial fluid(synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. This fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. The ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.
Outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. These strengthen and support the joint by anchoring the bones together and preventing their separation. Ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. Ligaments are classified based on their relationship to the fibrous articular capsule. An extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.
At many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. A tendon is the dense connective tissue structure that attaches a muscle to bone. As forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. This type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.
Additional Structures Associated with Synovial Joints
A few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and C-shaped. These structures can serve several functions, depending on the specific joint. In some places, an articular disc may act to strongly unite the bones of the joint to each other. Examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. At other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. Finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. Some synovial joints also have a fat pad, which can serve as a cushion between the bones.
Additional structures located outside of a synovial joint serve to prevent friction between the bones of the joint and the overlying muscle tendons or skin. A bursa (plural = bursae) is a thin connective tissue sac filled with lubricating liquid. They are located in regions where skin, ligaments, muscles, or muscle tendons can rub against each other, usually near a body joint (Figure 9.9). Bursae reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other. Bursae are classified by their location. A subcutaneous bursa is located between the skin and an underlying bone. It allows skin to move smoothly over the bone. Examples include the prepatellar bursa located over the kneecap and the olecranon bursa at the tip of the elbow. A submuscular bursa is found between a muscle and an underlying bone, or between adjacent muscles. These prevent rubbing of the muscle during movements. A large submuscular bursa, the trochanteric bursa, is found at the lateral hip, between the greater trochanter of the femur and the overlying gluteus maximus muscle. A subtendinous bursa is found between a tendon and a bone. Examples include the subacromial bursa that protects the tendon of shoulder muscle as it passes under the acromion of the scapula, and the suprapatellar bursa that separates the tendon of the large anterior thigh muscle from the distal femur just above the knee.
Figure 9.9 Bursae Bursae are fluid-filled sacs that serve to prevent friction between skin, muscle, or tendon and an underlying bone. Three major bursae and a fat pad are part of the complex joint that unites the femur and tibia of the leg.
A tendon sheath is similar in structure to a bursa, but smaller. It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements.
HOMEOSTATIC IMBALANCES
Bursitis
Bursitis is the inflammation of a bursa near a joint. This will cause pain, swelling, or tenderness of the bursa and surrounding area, and may also result in joint stiffness. Bursitis is most commonly associated with the bursae found at or near the shoulder, hip, knee, or elbow joints. At the shoulder, subacromial bursitis may occur in the bursa that separates the acromion of the scapula from the tendon of a shoulder muscle as it passes deep to the acromion. In the hip region, trochanteric bursitis can occur in the bursa that overlies the greater trochanter of the femur, just below the lateral side of the hip. Ischial bursitis occurs in the bursa that separates the skin from the ischial tuberosity of the pelvis, the bony structure that is weight bearing when sitting. At the knee, inflammation and swelling of the bursa located between the skin and patella bone is prepatellar bursitis (“housemaid’s knee”), a condition more commonly seen today in roofers or floor and carpet installers who do not use knee pads. At the elbow, olecranon bursitis is inflammation of the bursa between the skin and olecranon process of the ulna. The olecranon forms the bony tip of the elbow, and bursitis here is also known as “student’s elbow.”
Bursitis can be either acute (lasting only a few days) or chronic. It can arise from muscle overuse, trauma, excessive or prolonged pressure on the skin, rheumatoid arthritis, gout, or infection of the joint. Repeated acute episodes of bursitis can result in a chronic condition. Treatments for the disorder include antibiotics if the bursitis is caused by an infection, or anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids if the bursitis is due to trauma or overuse. Chronic bursitis may require that fluid be drained, but additional surgery is usually not required.
Types of Synovial Joints
Synovial joints are subdivided based on the shapes of the articulating surfaces of the bones that form each joint. The six types of synovial joints are pivot, hinge, condyloid, saddle, plane, and ball-and socket-joints (Figure 9.10).
Figure 9.10 Types of Synovial Joints The six types of synovial joints allow the body to move in a variety of ways. (a) Pivot joints allow for rotation around an axis, such as between the first and second cervical vertebrae, which allows for side-to-side rotation of the head. (b) The hinge joint of the elbow works like a door hinge. (c) The articulation between the trapezium carpal bone and the first metacarpal bone at the base of the thumb is a saddle joint. (d) Plane joints, such as those between the tarsal bones of the foot, allow for limited gliding movements between bones. (e) The radiocarpal joint of the wrist is a condyloid joint. (f) The hip and shoulder joints are the only ball-and-socket joints of the body.
Pivot Joint
At a pivot joint, a rounded portion of a bone is enclosed within a ring formed partially by the articulation with another bone and partially by a ligament (see Figure 9.10a). The bone rotates within this ring. Since the rotation is around a single axis, pivot joints are functionally classified as a uniaxial diarthrosis type of joint. An example of a pivot joint is the atlantoaxial joint, found between the C1 (atlas) and C2 (axis) vertebrae. Here, the upward projecting dens of the axis articulates with the inner aspect of the atlas, where it is held in place by a ligament. Rotation at this joint allows you to turn your head from side to side. A second pivot joint is found at the proximal radioulnar joint. Here, the head of the radius is largely encircled by a ligament that holds it in place as it articulates with the radial notch of the ulna. Rotation of the radius allows for forearm movements.
Hinge Joint
In a hinge joint, the convex end of one bone articulates with the concave end of the adjoining bone (see Figure 9.10b). This type of joint allows only for bending and straightening motions along a single axis, and thus hinge joints are functionally classified as uniaxial joints. A good example is the elbow joint, with the articulation between the trochlea of the humerus and the trochlear notch of the ulna. Other hinge joints of the body include the knee, ankle, and interphalangeal joints between the phalanx bones of the fingers and toes.
Condyloid Joint
At a condyloid joint (ellipsoid joint), the shallow depression at the end of one bone articulates with a rounded structure from an adjacent bone or bones (see Figure 9.10e). The knuckle (metacarpophalangeal) joints of the hand between the distal end of a metacarpal bone and the proximal phalanx bone are condyloid joints. Another example is the radiocarpal joint of the wrist, between the shallow depression at the distal end of the radius bone and the rounded scaphoid, lunate, and triquetrum carpal bones. In this case, the articulation area has a more oval (elliptical) shape. Functionally, condyloid joints are biaxial joints that allow for two planes of movement. One movement involves the bending and straightening of the fingers or the anterior-posterior movements of the hand. The second movement is a side-to-side movement, which allows you to spread your fingers apart and bring them together, or to move your hand in a medial-going or lateral-going direction.
Saddle Joint
At a saddle joint, both of the articulating surfaces for the bones have a saddle shape, which is concave in one direction and convex in the other (see Figure 9.10c). This allows the two bones to fit together like a rider sitting on a saddle. Saddle joints are functionally classified as biaxial joints. The primary example is the first carpometacarpal joint, between the trapezium (a carpal bone) and the first metacarpal bone at the base of the thumb. This joint provides the thumb the ability to move away from the palm of the hand along two planes. Thus, the thumb can move within the same plane as the palm of the hand, or it can jut out anteriorly, perpendicular to the palm. This movement of the first carpometacarpal joint is what gives humans their distinctive “opposable” thumbs. The sternoclavicular joint is also classified as a saddle joint.
Plane Joint
At a plane joint (gliding joint), the articulating surfaces of the bones are flat or slightly curved and of approximately the same size, which allows the bones to slide against each other (see Figure 9.10d). The motion at this type of joint is usually small and tightly constrained by surrounding ligaments. Based only on their shape, plane joints can allow multiple movements, including rotation. Thus plane joints can be functionally classified as a multiaxial joint. However, not all of these movements are available to every plane joint due to limitations placed on it by ligaments or neighboring bones. Thus, depending upon the specific joint of the body, a plane joint may exhibit only a single type of movement or several movements. Plane joints are found between the carpal bones (intercarpal joints) of the wrist or tarsal bones (intertarsal joints) of the foot, between the clavicle and acromion of the scapula (acromioclavicular joint), and between the superior and inferior articular processes of adjacent vertebrae (zygapophysial joints).
Ball-and-Socket Joint
The joint with the greatest range of motion is the ball-and-socket joint. At these joints, the rounded head of one bone (the ball) fits into the concave articulation (the socket) of the adjacent bone (see Figure 9.10f). The hip joint and the glenohumeral (shoulder) joint are the only ball-and-socket joints of the body. At the hip joint, the head of the femur articulates with the acetabulum of the hip bone, and at the shoulder joint, the head of the humerus articulates with the glenoid cavity of the scapula.
Ball-and-socket joints are classified functionally as multiaxial joints. The femur and the humerus are able to move in both anterior-posterior and medial-lateral directions and they can also rotate around their long axis. The shallow socket formed by the glenoid cavity allows the shoulder joint an extensive range of motion. In contrast, the deep socket of the acetabulum and the strong supporting ligaments of the hip joint serve to constrain movements of the femur, reflecting the need for stability and weight-bearing ability at the hip.
INTERACTIVE LINK
Watch this video to see an animation of synovial joints in action. Synovial joints are places where bones articulate with each other inside of a joint cavity. The different types of synovial joints are the ball-and-socket joint (shoulder joint), hinge joint (knee), pivot joint (atlantoaxial joint, between C1 and C2 vertebrae of the neck), condyloid joint (radiocarpal joint of the wrist), saddle joint (first carpometacarpal joint, between the trapezium carpal bone and the first metacarpal bone, at the base of the thumb), and plane joint (facet joints of vertebral column, between superior and inferior articular processes). Which type of synovial joint allows for the widest range of motion?
AGING AND THE...
Joints
Arthritis is a common disorder of synovial joints that involves inflammation of the joint. This often results in significant joint pain, along with swelling, stiffness, and reduced joint mobility. There are more than 100 different forms of arthritis. Arthritis may arise from aging, damage to the articular cartilage, autoimmune diseases, bacterial or viral infections, or unknown (probably genetic) causes.
The most common type of arthritis is osteoarthritis, which is associated with aging and “wear and tear” of the articular cartilage (Figure 9.11). Risk factors that may lead to osteoarthritis later in life include injury to a joint; jobs that involve physical labor; sports with running, twisting, or throwing actions; and being overweight. These factors put stress on the articular cartilage that covers the surfaces of bones at synovial joints, causing the cartilage to gradually become thinner. As the articular cartilage layer wears down, more pressure is placed on the bones. The joint responds by increasing production of the lubricating synovial fluid, but this can lead to swelling of the joint cavity, causing pain and joint stiffness as the articular capsule is stretched. The bone tissue underlying the damaged articular cartilage also responds by thickening, producing irregularities and causing the articulating surface of the bone to become rough or bumpy. Joint movement then results in pain and inflammation. In its early stages, symptoms of osteoarthritis may be reduced by mild activity that “warms up” the joint, but the symptoms may worsen following exercise. In individuals with more advanced osteoarthritis, the affected joints can become more painful and therefore are difficult to use effectively, resulting in increased immobility. There is no cure for osteoarthritis, but several treatments can help alleviate the pain. Treatments may include lifestyle changes, such as weight loss and low-impact exercise, and over-the-counter or prescription medications that help to alleviate the pain and inflammation. For severe cases, joint replacement surgery (arthroplasty) may be required.
Joint replacement is a very invasive procedure, so other treatments are always tried before surgery. However arthroplasty can provide relief from chronic pain and can enhance mobility within a few months following the surgery. This type of surgery involves replacing the articular surfaces of the bones with prosthesis (artificial components). For example, in hip arthroplasty, the worn or damaged parts of the hip joint, including the head and neck of the femur and the acetabulum of the pelvis, are removed and replaced with artificial joint components. The replacement head for the femur consists of a rounded ball attached to the end of a shaft that is inserted inside the diaphysis of the femur. The acetabulum of the pelvis is reshaped and a replacement socket is fitted into its place. The parts, which are always built in advance of the surgery, are sometimes custom made to produce the best possible fit for a patient.
Gout is a form of arthritis that results from the deposition of uric acid crystals within a body joint. Usually only one or a few joints are affected, such as the big toe, knee, or ankle. The attack may only last a few days, but may return to the same or another joint. Gout occurs when the body makes too much uric acid or the kidneys do not properly excrete it. A diet with excessive fructose has been implicated in raising the chances of a susceptible individual developing gout.
Other forms of arthritis are associated with various autoimmune diseases, bacterial infections of the joint, or unknown genetic causes. Autoimmune diseases, including rheumatoid arthritis, scleroderma, or systemic lupus erythematosus, produce arthritis because the immune system of the body attacks the body joints. In rheumatoid arthritis, the joint capsule and synovial membrane become inflamed. As the disease progresses, the articular cartilage is severely damaged or destroyed, resulting in joint deformation, loss of movement, and severe disability. The most commonly involved joints are the hands, feet, and cervical spine, with corresponding joints on both sides of the body usually affected, though not always to the same extent. Rheumatoid arthritis is also associated with lung fibrosis, vasculitis (inflammation of blood vessels), coronary heart disease, and premature mortality. With no known cure, treatments are aimed at alleviating symptoms. Exercise, anti-inflammatory and pain medications, various specific disease-modifying anti-rheumatic drugs, or surgery are used to treat rheumatoid arthritis.
Figure 9.11 Osteoarthritis Osteoarthritis of a synovial joint results from aging or prolonged joint wear and tear. These cause erosion and loss of the articular cartilage covering the surfaces of the bones, resulting in inflammation that causes joint stiffness and pain.
INTERACTIVE LINK
Visit this website to learn about a patient who arrives at the hospital with joint pain and weakness in his legs. What caused this patient’s weakness?
INTERACTIVE LINK
Watch this animation to observe hip replacement surgery (total hip arthroplasty), which can be used to alleviate the pain and loss of joint mobility associated with osteoarthritis of the hip joint. What is the most common cause of hip disability?
INTERACTIVE LINK
Watch this video to learn about the symptoms and treatments for rheumatoid arthritis. Which system of the body malfunctions in rheumatoid arthritis and what does this cause?
Types of Body Movements
- Define the different types of body movements
- Identify the joints that allow for these motions
Synovial joints allow the body a tremendous range of movements. Each movement at a synovial joint results from the contraction or relaxation of the muscles that are attached to the bones on either side of the articulation. The type of movement that can be produced at a synovial joint is determined by its structural type. While the ball-and-socket joint gives the greatest range of movement at an individual joint, in other regions of the body, several joints may work together to produce a particular movement. Overall, each type of synovial joint is necessary to provide the body with its great flexibility and mobility. There are many types of movement that can occur at synovial joints (Table 9.1). Movement types are generally paired, with one being the opposite of the other. Body movements are always described in relation to the anatomical position of the body: upright stance, with upper limbs to the side of body and palms facing forward. Refer to Figure 9.12 as you go through this section.
INTERACTIVE LINK
Watch this video to learn about anatomical motions. What motions involve increasing or decreasing the angle of the foot at the ankle?
Figure 9.12 Movements of the Body, Part 1 Synovial joints give the body many ways in which to move. (a)–(b) Flexion and extension motions are in the sagittal (anterior–posterior) plane of motion. These movements take place at the shoulder, hip, elbow, knee, wrist, metacarpophalangeal, metatarsophalangeal, and interphalangeal joints. (c)–(d) Anterior bending of the head or vertebral column is flexion, while any posterior-going movement is extension. (e) Abduction and adduction are motions of the limbs, hand, fingers, or toes in the coronal (medial–lateral) plane of movement. Moving the limb or hand laterally away from the body, or spreading the fingers or toes, is abduction. Adduction brings the limb or hand toward or across the midline of the body, or brings the fingers or toes together. Circumduction is the movement of the limb, hand, or fingers in a circular pattern, using the sequential combination of flexion, adduction, extension, and abduction motions. Adduction/abduction and circumduction take place at the shoulder, hip, wrist, metacarpophalangeal, and metatarsophalangeal joints. (f) Turning of the head side to side or twisting of the body is rotation. Medial and lateral rotation of the upper limb at the shoulder or lower limb at the hip involves turning the anterior surface of the limb toward the midline of the body (medial or internal rotation) or away from the midline (lateral or external rotation).
Figure 9.13 Movements of the Body, Part 2 (g) Supination of the forearm turns the hand to the palm forward position in which the radius and ulna are parallel, while forearm pronation turns the hand to the palm backward position in which the radius crosses over the ulna to form an "X." (h) Dorsiflexion of the foot at the ankle joint moves the top of the foot toward the leg, while plantar flexion lifts the heel and points the toes. (i) Eversion of the foot moves the bottom (sole) of the foot away from the midline of the body, while foot inversion faces the sole toward the midline. (j) Protraction of the mandible pushes the chin forward, and retraction pulls the chin back. (k) Depression of the mandible opens the mouth, while elevation closes it. (l) Opposition of the thumb brings the tip of the thumb into contact with the tip of the fingers of the same hand and reposition brings the thumb back next to the index finger.
Flexion and Extension
Flexion and extension are typically movements that take place within the sagittal plane and involve anterior or posterior movements of the neck, trunk, or limbs. For the vertebral column, flexion (anterior flexion) is an anterior (forward) bending of the neck or trunk, while extension involves a posterior-directed motion, such as straightening from a flexed position or bending backward. Lateral flexion of the vertebral column occurs in the coronal plane and is defined as the bending of the neck or trunk toward the right or left side.. These movements of the vertebral column involve both the symphysis joint formed by each intervertebral disc, as well as the plane type of synovial joint formed between the inferior articular processes of one vertebra and the superior articular processes of the next lower vertebra.
In the limbs, flexion decreases the angle between the bones (bending of the joint), while extension increases the angle and straightens the joint. For the upper limb, all anterior-going motions are flexion and all posterior-going motions are extension. These include anterior-posterior movements of the arm at the shoulder, the forearm at the elbow, the hand at the wrist, and the fingers at the metacarpophalangeal and interphalangeal joints. For the thumb, extension moves the thumb away from the palm of the hand, within the same plane as the palm, while flexion brings the thumb back against the index finger or into the palm. These motions take place at the first carpometacarpal joint. In the lower limb, bringing the thigh forward and upward is flexion at the hip joint, while any posterior-going motion of the thigh is extension. Note that extension of the thigh beyond the anatomical (standing) position is greatly limited by the ligaments that support the hip joint. Knee flexion is the bending of the knee to bring the foot toward the posterior thigh, and extension is the straightening of the knee. Flexion and extension movements are seen at the hinge, condyloid, saddle, and ball-and-socket joints of the limbs (see Figure 9.12a-d).
Hyperextension is the abnormal or excessive extension of a joint beyond its normal range of motion, thus resulting in injury. Similarly, hyperflexion is excessive flexion at a joint. Hyperextension injuries are common at hinge joints such as the knee or elbow. In cases of “whiplash” in which the head is suddenly moved backward and then forward, a patient may experience both hyperextension and hyperflexion of the cervical region.
Abduction and Adduction
Abduction and adduction motions occur within the coronal plane and involve medial-lateral motions of the limbs, fingers, toes, or thumb. Abduction moves the limb laterally away from the midline of the body, while adduction is the opposing movement that brings the limb toward the body or across the midline. For example, abduction is raising the arm at the shoulder joint, moving it laterally away from the body, while adduction brings the arm down to the side of the body. Similarly, abduction and adduction at the wrist moves the hand away from or toward the midline of the body. Spreading the fingers or toes apart is also abduction, while bringing the fingers or toes together is adduction. For the thumb, abduction is the anterior movement that brings the thumb to a 90° perpendicular position, pointing straight out from the palm. Adduction moves the thumb back to the anatomical position, next to the index finger. Abduction and adduction movements are seen at condyloid, saddle, and ball-and-socket joints (see Figure 9.12e).
Circumduction
Circumduction is the movement of a body region in a circular manner, in which one end of the body region being moved stays relatively stationary while the other end describes a circle. It involves the sequential combination of flexion, adduction, extension, and abduction at a joint. This type of motion is found at biaxial condyloid and saddle joints, and at multiaxial ball-and-sockets joints (see Figure 9.12e).
Rotation
Rotation can occur within the vertebral column, at a pivot joint, or at a ball-and-socket joint. Rotation of the neck or body is the twisting movement produced by the summation of the small rotational movements available between adjacent vertebrae. At a pivot joint, one bone rotates in relation to another bone. This is a uniaxial joint, and thus rotation is the only motion allowed at a pivot joint. For example, at the atlantoaxial joint, the first cervical (C1) vertebra (atlas) rotates around the dens, the upward projection from the second cervical (C2) vertebra (axis). This allows the head to rotate from side to side as when shaking the head “no.” The proximal radioulnar joint is a pivot joint formed by the head of the radius and its articulation with the ulna. This joint allows for the radius to rotate along its length during pronation and supination movements of the forearm.
Rotation can also occur at the ball-and-socket joints of the shoulder and hip. Here, the humerus and femur rotate around their long axis, which moves the anterior surface of the arm or thigh either toward or away from the midline of the body. Movement that brings the anterior surface of the limb toward the midline of the body is called medial (internal) rotation. Conversely, rotation of the limb so that the anterior surface moves away from the midline is lateral (external) rotation (see Figure 9.12f). Be sure to distinguish medial and lateral rotation, which can only occur at the multiaxial shoulder and hip joints, from circumduction, which can occur at either biaxial or multiaxial joints.
Supination and Pronation
Supination and pronation are movements of the forearm. In the anatomical position, the upper limb is held next to the body with the palm facing forward. This is the supinated position of the forearm. In this position, the radius and ulna are parallel to each other. When the palm of the hand faces backward, the forearm is in the pronated position, and the radius and ulna form an X-shape.
Supination and pronation are the movements of the forearm that go between these two positions. Pronation is the motion that moves the forearm from the supinated (anatomical) position to the pronated (palm backward) position. This motion is produced by rotation of the radius at the proximal radioulnar joint, accompanied by movement of the radius at the distal radioulnar joint. The proximal radioulnar joint is a pivot joint that allows for rotation of the head of the radius. Because of the slight curvature of the shaft of the radius, this rotation causes the distal end of the radius to cross over the distal ulna at the distal radioulnar joint. This crossing over brings the radius and ulna into an X-shape position. Supination is the opposite motion, in which rotation of the radius returns the bones to their parallel positions and moves the palm to the anterior facing (supinated) position. It helps to remember that supination is the motion you use when scooping up soup with a spoon (see Figure 9.13g).
Dorsiflexion and Plantar Flexion
Dorsiflexion and plantar flexion are movements at the ankle joint, which is a hinge joint. Lifting the front of the foot, so that the top of the foot moves toward the anterior leg is dorsiflexion, while lifting the heel of the foot from the ground or pointing the toes downward is plantar flexion. These are the only movements available at the ankle joint (see Figure 9.13h).
Inversion and Eversion
Inversion and eversion are complex movements that involve the multiple plane joints among the tarsal bones of the posterior foot (intertarsal joints) and thus are not motions that take place at the ankle joint. Inversion is the turning of the foot to angle the bottom of the foot toward the midline, while eversion turns the bottom of the foot away from the midline. The foot has a greater range of inversion than eversion motion. These are important motions that help to stabilize the foot when walking or running on an uneven surface and aid in the quick side-to-side changes in direction used during active sports such as basketball, racquetball, or soccer (see Figure 9.13i).
Protraction and Retraction
Protraction and retraction are anterior-posterior movements of the scapula or mandible. Protraction of the scapula occurs when the shoulder is moved forward, as when pushing against something or throwing a ball. Retraction is the opposite motion, with the scapula being pulled posteriorly and medially, toward the vertebral column. For the mandible, protraction occurs when the lower jaw is pushed forward, to stick out the chin, while retraction pulls the lower jaw backward. (See Figure 9.13j.)
Depression and Elevation
Depression and elevation are downward and upward movements of the scapula or mandible. The upward movement of the scapula and shoulder is elevation, while a downward movement is depression. These movements are used to shrug your shoulders. Similarly, elevation of the mandible is the upward movement of the lower jaw used to close the mouth or bite on something, and depression is the downward movement that produces opening of the mouth (see Figure 9.13k).
Excursion
Excursion is the side to side movement of the mandible. Lateral excursion moves the mandible away from the midline, toward either the right or left side. Medial excursion returns the mandible to its resting position at the midline.
Superior Rotation and Inferior Rotation
Superior and inferior rotation are movements of the scapula and are defined by the direction of movement of the glenoid cavity. These motions involve rotation of the scapula around a point inferior to the scapular spine and are produced by combinations of muscles acting on the scapula. During superior rotation, the glenoid cavity moves upward as the medial end of the scapular spine moves downward. This is a very important motion that contributes to upper limb abduction. Without superior rotation of the scapula, the greater tubercle of the humerus would hit the acromion of the scapula, thus preventing any abduction of the arm above shoulder height. Superior rotation of the scapula is thus required for full abduction of the upper limb. Superior rotation is also used without arm abduction when carrying a heavy load with your hand or on your shoulder. You can feel this rotation when you pick up a load, such as a heavy book bag and carry it on only one shoulder. To increase its weight-bearing support for the bag, the shoulder lifts as the scapula superiorly rotates. Inferior rotation occurs during limb adduction and involves the downward motion of the glenoid cavity with upward movement of the medial end of the scapular spine.
Opposition and Reposition
Opposition is the thumb movement that brings the tip of the thumb in contact with the tip of a finger. This movement is produced at the first carpometacarpal joint, which is a saddle joint formed between the trapezium carpal bone and the first metacarpal bone. Thumb opposition is produced by a combination of flexion and abduction of the thumb at this joint. Returning the thumb to its anatomical position next to the index finger is called reposition (see Figure 9.13l).
Movements of the Joints
| Type of Joint | Movement | Example |
|---|---|---|
| Pivot | Uniaxial joint; allows rotational movement | Atlantoaxial joint (C1–C2 vertebrae articulation); proximal radioulnar joint |
| Hinge | Uniaxial joint; allows flexion/extension movements | Knee; elbow; ankle; interphalangeal joints of fingers and toes |
| Condyloid | Biaxial joint; allows flexion/extension, abduction/adduction, and circumduction movements | Metacarpophalangeal (knuckle) joints of fingers; radiocarpal joint of wrist; metatarsophalangeal joints for toes |
| Saddle | Biaxial joint; allows flexion/extension, abduction/adduction, and circumduction movements | First carpometacarpal joint of the thumb; sternoclavicular joint |
| Plane | Multiaxial joint; allows inversion and eversion of foot, or flexion, extension, and lateral flexion of the vertebral column | Intertarsal joints of foot; superior-inferior articular process articulations between vertebrae |
| Ball-and-socket | Multiaxial joint; allows flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation movements | Shoulder and hip joints |
Table 9.1
Anatomy of Selected Synovial Joints
- Describe the bones that articulate together to form selected synovial joints
- Discuss the movements available at each joint
- Describe the structures that support and prevent excess movements at each joint
Each synovial joint of the body is specialized to perform certain movements. The movements that are allowed are determined by the structural classification for each joint. For example, a multiaxial ball-and-socket joint has much more mobility than a uniaxial hinge joint. However, the ligaments and muscles that support a joint may place restrictions on the total range of motion available. Thus, the ball-and-socket joint of the shoulder has little in the way of ligament support, which gives the shoulder a very large range of motion. In contrast, movements at the hip joint are restricted by strong ligaments, which reduce its range of motion but confer stability during standing and weight bearing.
This section will examine the anatomy of selected synovial joints of the body. Anatomical names for most joints are derived from the names of the bones that articulate at that joint, although some joints, such as the elbow, hip, and knee joints are exceptions to this general naming scheme.
Articulations of the Vertebral Column
In addition to being held together by the intervertebral discs, adjacent vertebrae also articulate with each other at synovial joints formed between the superior and inferior articular processes called zygapophysial joints (facet joints) (see Figure 9.3). These are plane joints that provide for only limited motions between the vertebrae. The orientation of the articular processes at these joints varies in different regions of the vertebral column and serves to determine the types of motions available in each vertebral region. The cervical and lumbar regions have the greatest ranges of motions.
In the neck, the articular processes of cervical vertebrae are flattened and generally face upward or downward. This orientation provides the cervical vertebral column with extensive ranges of motion for flexion, extension, lateral flexion, and rotation. In the thoracic region, the downward projecting and overlapping spinous processes, along with the attached thoracic cage, greatly limit flexion, extension, and lateral flexion. However, the flattened and vertically positioned thoracic articular processes allow for the greatest range of rotation within the vertebral column. The lumbar region allows for considerable extension, flexion, and lateral flexion, but the orientation of the articular processes largely prohibits rotation.
The articulations formed between the skull, the atlas (C1 vertebra), and the axis (C2 vertebra) differ from the articulations in other vertebral areas and play important roles in movement of the head. The atlanto-occipital joint is formed by the articulations between the superior articular processes of the atlas and the occipital condyles on the base of the skull. This articulation has a pronounced U-shaped curvature, oriented along the anterior-posterior axis. This allows the skull to rock forward and backward, producing flexion and extension of the head. This moves the head up and down, as when shaking your head “yes.”
The atlantoaxial joint, between the atlas and axis, consists of three articulations. The paired superior articular processes of the axis articulate with the inferior articular processes of the atlas. These articulating surfaces are relatively flat and oriented horizontally. The third articulation is the pivot joint formed between the dens, which projects upward from the body of the axis, and the inner aspect of the anterior arch of the atlas (Figure 9.14). A strong ligament passes posterior to the dens to hold it in position against the anterior arch. These articulations allow the atlas to rotate on top of the axis, moving the head toward the right or left, as when shaking your head “no.”
Figure 9.14 Atlantoaxial Joint The atlantoaxial joint is a pivot type of joint between the dens portion of the axis (C2 vertebra) and the anterior arch of the atlas (C1 vertebra), with the dens held in place by a ligament.
Temporomandibular Joint
The temporomandibular joint (TMJ) is the joint that allows for opening (mandibular depression) and closing (mandibular elevation) of the mouth, as well as side-to-side and protraction/retraction motions of the lower jaw. This joint involves the articulation between the mandibular fossa and articular tubercle of the temporal bone, with the condyle (head) of the mandible. Located between these bony structures, filling the gap between the skull and mandible, is a flexible articular disc (Figure 9.15). This disc serves to smooth the movements between the temporal bone and mandibular condyle.
Movement at the TMJ during opening and closing of the mouth involves both gliding and hinge motions of the mandible. With the mouth closed, the mandibular condyle and articular disc are located within the mandibular fossa of the temporal bone. During opening of the mouth, the mandible hinges downward and at the same time is pulled anteriorly, causing both the condyle and the articular disc to glide forward from the mandibular fossa onto the downward projecting articular tubercle. The net result is a forward and downward motion of the condyle and mandibular depression. The temporomandibular joint is supported by an extrinsic ligament that anchors the mandible to the skull. This ligament spans the distance between the base of the skull and the lingula on the medial side of the mandibular ramus.
Dislocation of the TMJ may occur when opening the mouth too wide (such as when taking a large bite) or following a blow to the jaw, resulting in the mandibular condyle moving beyond (anterior to) the articular tubercle. In this case, the individual would not be able to close his or her mouth. Temporomandibular joint disorder is a painful condition that may arise due to arthritis, wearing of the articular cartilage covering the bony surfaces of the joint, muscle fatigue from overuse or grinding of the teeth, damage to the articular disc within the joint, or jaw injury. Temporomandibular joint disorders can also cause headache, difficulty chewing, or even the inability to move the jaw (lock jaw). Pharmacologic agents for pain or other therapies, including bite guards, are used as treatments.
Figure 9.15 Temporomandibular Joint The temporomandibular joint is the articulation between the temporal bone of the skull and the condyle of the mandible, with an articular disc located between these bones. During depression of the mandible (opening of the mouth), the mandibular condyle moves both forward and hinges downward as it travels from the mandibular fossa onto the articular tubercle.
INTERACTIVE LINK
Watch this video to learn about TMJ. Opening of the mouth requires the combination of two motions at the temporomandibular joint, an anterior gliding motion of the articular disc and mandible and the downward hinging of the mandible. What is the initial movement of the mandible during opening and how much mouth opening does this produce?
Shoulder Joint
The shoulder joint is called the glenohumeral joint. This is a ball-and-socket joint formed by the articulation between the head of the humerus and the glenoid cavity of the scapula (Figure 9.16). This joint has the largest range of motion of any joint in the body. However, this freedom of movement is due to the lack of structural support and thus the enhanced mobility is offset by a loss of stability.
Figure 9.16 Glenohumeral Joint The glenohumeral (shoulder) joint is a ball-and-socket joint that provides the widest range of motions. It has a loose articular capsule and is supported by ligaments and the rotator cuff muscles.
The large range of motions at the shoulder joint is provided by the articulation of the large, rounded humeral head with the small and shallow glenoid cavity, which is only about one third of the size of the humeral head. The socket formed by the glenoid cavity is deepened slightly by a small lip of fibrocartilage called the glenoid labrum, which extends around the outer margin of the cavity. The articular capsule that surrounds the glenohumeral joint is relatively thin and loose to allow for large motions of the upper limb. Some structural support for the joint is provided by thickenings of the articular capsule wall that form weak intrinsic ligaments. These include the coracohumeral ligament, running from the coracoid process of the scapula to the anterior humerus, and three ligaments, each called a glenohumeral ligament, located on the anterior side of the articular capsule. These ligaments help to strengthen the superior and anterior capsule walls.
However, the primary support for the shoulder joint is provided by muscles crossing the joint, particularly the four rotator cuff muscles. These muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) arise from the scapula and attach to the greater or lesser tubercles of the humerus. As these muscles cross the shoulder joint, their tendons encircle the head of the humerus and become fused to the anterior, superior, and posterior walls of the articular capsule. The thickening of the capsule formed by the fusion of these four muscle tendons is called the rotator cuff. Two bursae, the subacromial bursa and the subscapular bursa, help to prevent friction between the rotator cuff muscle tendons and the scapula as these tendons cross the glenohumeral joint. In addition to their individual actions of moving the upper limb, the rotator cuff muscles also serve to hold the head of the humerus in position within the glenoid cavity. By constantly adjusting their strength of contraction to resist forces acting on the shoulder, these muscles serve as “dynamic ligaments” and thus provide the primary structural support for the glenohumeral joint.
Injuries to the shoulder joint are common. Repetitive use of the upper limb, particularly in abduction such as during throwing, swimming, or racquet sports, may lead to acute or chronic inflammation of the bursa or muscle tendons, a tear of the glenoid labrum, or degeneration or tears of the rotator cuff. Because the humeral head is strongly supported by muscles and ligaments around its anterior, superior, and posterior aspects, most dislocations of the humerus occur in an inferior direction. This can occur when force is applied to the humerus when the upper limb is fully abducted, as when diving to catch a baseball and landing on your hand or elbow. Inflammatory responses to any shoulder injury can lead to the formation of scar tissue between the articular capsule and surrounding structures, thus reducing shoulder mobility, a condition called adhesive capsulitis (“frozen shoulder”).
INTERACTIVE LINK
Watch this video for a tutorial on the anatomy of the shoulder joint. What movements are available at the shoulder joint?
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Watch this video to learn more about the anatomy of the shoulder joint, including bones, joints, muscles, nerves, and blood vessels. What is the shape of the glenoid labrum in cross-section, and what is the importance of this shape?
Elbow Joint
The elbow joint is a uniaxial hinge joint formed by the humeroulnar joint, the articulation between the trochlea of the humerus and the trochlear notch of the ulna. Also associated with the elbow are the humeroradial joint and the proximal radioulnar joint. All three of these joints are enclosed within a single articular capsule (Figure 9.17).
The articular capsule of the elbow is thin on its anterior and posterior aspects, but is thickened along its outside margins by strong intrinsic ligaments. These ligaments prevent side-to-side movements and hyperextension. On the medial side is the triangular ulnar collateral ligament. This arises from the medial epicondyle of the humerus and attaches to the medial side of the proximal ulna. The strongest part of this ligament is the anterior portion, which resists hyperextension of the elbow. The ulnar collateral ligament may be injured by frequent, forceful extensions of the forearm, as is seen in baseball pitchers. Reconstructive surgical repair of this ligament is referred to as Tommy John surgery, named for the former major league pitcher who was the first person to have this treatment.
The lateral side of the elbow is supported by the radial collateral ligament. This arises from the lateral epicondyle of the humerus and then blends into the lateral side of the annular ligament. The annular ligament encircles the head of the radius. This ligament supports the head of the radius as it articulates with the radial notch of the ulna at the proximal radioulnar joint. This is a pivot joint that allows for rotation of the radius during supination and pronation of the forearm.
Figure 9.17 Elbow Joint (a) The elbow is a hinge joint that allows only for flexion and extension of the forearm. (b) It is supported by the ulnar and radial collateral ligaments. (c) The annular ligament supports the head of the radius at the proximal radioulnar joint, the pivot joint that allows for rotation of the radius.
INTERACTIVE LINK
Watch this animation to learn more about the anatomy of the elbow joint. Which structures provide the main stability for the elbow?
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Watch this video to learn more about the anatomy of the elbow joint, including bones, joints, muscles, nerves, and blood vessels. What are the functions of the articular cartilage?
Hip Joint
The hip joint is a multiaxial ball-and-socket joint between the head of the femur and the acetabulum of the hip bone (Figure 9.18). The hip carries the weight of the body and thus requires strength and stability during standing and walking. For these reasons, its range of motion is more limited than at the shoulder joint.
The acetabulum is the socket portion of the hip joint. This space is deep and has a large articulation area for the femoral head, thus giving stability and weight bearing ability to the joint. The acetabulum is further deepened by the acetabular labrum, a fibrocartilage lip attached to the outer margin of the acetabulum. The surrounding articular capsule is strong, with several thickened areas forming intrinsic ligaments. These ligaments arise from the hip bone, at the margins of the acetabulum, and attach to the femur at the base of the neck. The ligaments are the iliofemoral ligament, pubofemoral ligament, and ischiofemoral ligament, all of which spiral around the head and neck of the femur. The ligaments are tightened by extension at the hip, thus pulling the head of the femur tightly into the acetabulum when in the upright, standing position. Very little additional extension of the thigh is permitted beyond this vertical position. These ligaments thus stabilize the hip joint and allow you to maintain an upright standing position with only minimal muscle contraction. Inside of the articular capsule, the ligament of the head of the femur (ligamentum teres) spans between the acetabulum and femoral head. This intracapsular ligament is normally slack and does not provide any significant joint support, but it does provide a pathway for an important artery that supplies the head of the femur.
The hip is prone to osteoarthritis, and thus was the first joint for which a replacement prosthesis was developed. A common injury in elderly individuals, particularly those with weakened bones due to osteoporosis, is a “broken hip,” which is actually a fracture of the femoral neck. This may result from a fall, or it may cause the fall. This can happen as one lower limb is taking a step and all of the body weight is placed on the other limb, causing the femoral neck to break and producing a fall. Any accompanying disruption of the blood supply to the femoral neck or head can lead to necrosis of these areas, resulting in bone and cartilage death. Femoral fractures usually require surgical treatment, after which the patient will need mobility assistance for a prolonged period, either from family members or in a long-term care facility. Consequentially, the associated health care costs of “broken hips” are substantial. In addition, hip fractures are associated with increased rates of morbidity (incidences of disease) and mortality (death). Surgery for a hip fracture followed by prolonged bed rest may lead to life-threatening complications, including pneumonia, infection of pressure ulcers (bedsores), and thrombophlebitis (deep vein thrombosis; blood clot formation) that can result in a pulmonary embolism (blood clot within the lung).
Figure 9.18 Hip Joint (a) The ball-and-socket joint of the hip is a multiaxial joint that provides both stability and a wide range of motion. (b–c) When standing, the supporting ligaments are tight, pulling the head of the femur into the acetabulum.
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Watch this video for a tutorial on the anatomy of the hip joint. What is a possible consequence following a fracture of the femoral neck within the capsule of the hip joint?
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Watch this video to learn more about the anatomy of the hip joint, including bones, joints, muscles, nerves, and blood vessels. Where is the articular cartilage thickest within the hip joint?
Knee Joint
The knee joint is the largest joint of the body (Figure 9.19). It actually consists of three articulations. The femoropatellar joint is found between the patella and the distal femur. The medial tibiofemoral joint and lateral tibiofemoral joint are located between the medial and lateral condyles of the femur and the medial and lateral condyles of the tibia. All of these articulations are enclosed within a single articular capsule. The knee functions as a hinge joint, allowing flexion and extension of the leg. This action is generated by both rolling and gliding motions of the femur on the tibia. In addition, some rotation of the leg is available when the knee is flexed, but not when extended. The knee is well constructed for weight bearing in its extended position, but is vulnerable to injuries associated with hyperextension, twisting, or blows to the medial or lateral side of the joint, particularly while weight bearing.
At the femoropatellar joint, the patella slides vertically within a groove on the distal femur. The patella is a sesamoid bone incorporated into the tendon of the quadriceps femoris muscle, the large muscle of the anterior thigh. The patella serves to protect the quadriceps tendon from friction against the distal femur. Continuing from the patella to the anterior tibia just below the knee is the patellar ligament. Acting via the patella and patellar ligament, the quadriceps femoris is a powerful muscle that acts to extend the leg at the knee. It also serves as a “dynamic ligament” to provide very important support and stabilization for the knee joint.
The medial and lateral tibiofemoral joints are the articulations between the rounded condyles of the femur and the relatively flat condyles of the tibia. During flexion and extension motions, the condyles of the femur both roll and glide over the surfaces of the tibia. The rolling action produces flexion or extension, while the gliding action serves to maintain the femoral condyles centered over the tibial condyles, thus ensuring maximal bony, weight-bearing support for the femur in all knee positions. As the knee comes into full extension, the femur undergoes a slight medial rotation in relation to tibia. The rotation results because the lateral condyle of the femur is slightly smaller than the medial condyle. Thus, the lateral condyle finishes its rolling motion first, followed by the medial condyle. The resulting small medial rotation of the femur serves to “lock” the knee into its fully extended and most stable position. Flexion of the knee is initiated by a slight lateral rotation of the femur on the tibia, which “unlocks” the knee. This lateral rotation motion is produced by the popliteus muscle of the posterior leg.
Located between the articulating surfaces of the femur and tibia are two articular discs, the medial meniscus and lateral meniscus (see Figure 9.19b). Each is a C-shaped fibrocartilage structure that is thin along its inside margin and thick along the outer margin. They are attached to their tibial condyles, but do not attach to the femur. While both menisci are free to move during knee motions, the medial meniscus shows less movement because it is anchored at its outer margin to the articular capsule and tibial collateral ligament. The menisci provide padding between the bones and help to fill the gap between the round femoral condyles and flattened tibial condyles. Some areas of each meniscus lack an arterial blood supply and thus these areas heal poorly if damaged.
The knee joint has multiple ligaments that provide support, particularly in the extended position (see Figure 9.19c). Outside of the articular capsule, located at the sides of the knee, are two extrinsic ligaments. The fibular collateral ligament (lateral collateral ligament) is on the lateral side and spans from the lateral epicondyle of the femur to the head of the fibula. The tibial collateral ligament (medial collateral ligament) of the medial knee runs from the medial epicondyle of the femur to the medial tibia. As it crosses the knee, the tibial collateral ligament is firmly attached on its deep side to the articular capsule and to the medial meniscus, an important factor when considering knee injuries. In the fully extended knee position, both collateral ligaments are taut (tight), thus serving to stabilize and support the extended knee and preventing side-to-side or rotational motions between the femur and tibia.
The articular capsule of the posterior knee is thickened by intrinsic ligaments that help to resist knee hyperextension. Inside the knee are two intracapsular ligaments, the anterior cruciate ligament and posterior cruciate ligament. These ligaments are anchored inferiorly to the tibia at the intercondylar eminence, the roughened area between the tibial condyles. The cruciate ligaments are named for whether they are attached anteriorly or posteriorly to this tibial region. Each ligament runs diagonally upward to attach to the inner aspect of a femoral condyle. The cruciate ligaments are named for the X-shape formed as they pass each other (cruciate means “cross”). The posterior cruciate ligament is the stronger ligament. It serves to support the knee when it is flexed and weight bearing, as when walking downhill. In this position, the posterior cruciate ligament prevents the femur from sliding anteriorly off the top of the tibia. The anterior cruciate ligament becomes tight when the knee is extended, and thus resists hyperextension.
Figure 9.19 Knee Joint (a) The knee joint is the largest joint of the body. (b)–(c) It is supported by the tibial and fibular collateral ligaments located on the sides of the knee outside of the articular capsule, and the anterior and posterior cruciate ligaments found inside the capsule. The medial and lateral menisci provide padding and support between the femoral condyles and tibial condyles.
INTERACTIVE LINK
Watch this video to learn more about the flexion and extension of the knee, as the femur both rolls and glides on the tibia to maintain stable contact between the bones in all knee positions. The patella glides along a groove on the anterior side of the distal femur. The collateral ligaments on the sides of the knee become tight in the fully extended position to help stabilize the knee. The posterior cruciate ligament supports the knee when flexed and the anterior cruciate ligament becomes tight when the knee comes into full extension to resist hyperextension. What are the ligaments that support the knee joint?
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Watch this video to learn more about the anatomy of the knee joint, including bones, joints, muscles, nerves, and blood vessels. Which ligament of the knee keeps the tibia from sliding too far forward in relation to the femur and which ligament keeps the tibia from sliding too far backward?
DISORDERS OF THE...
Joints
Injuries to the knee are common. Since this joint is primarily supported by muscles and ligaments, injuries to any of these structures will result in pain or knee instability. Injury to the posterior cruciate ligament occurs when the knee is flexed and the tibia is driven posteriorly, such as falling and landing on the tibial tuberosity or hitting the tibia on the dashboard when not wearing a seatbelt during an automobile accident. More commonly, injuries occur when forces are applied to the extended knee, particularly when the foot is planted and unable to move. Anterior cruciate ligament injuries can result with a forceful blow to the anterior knee, producing hyperextension, or when a runner makes a quick change of direction that produces both twisting and hyperextension of the knee.
A worse combination of injuries can occur with a hit to the lateral side of the extended knee (Figure 9.20). A moderate blow to the lateral knee will cause the medial side of the joint to open, resulting in stretching or damage to the tibial collateral ligament. Because the medial meniscus is attached to the tibial collateral ligament, a stronger blow can tear the ligament and also damage the medial meniscus. This is one reason that the medial meniscus is 20 times more likely to be injured than the lateral meniscus. A powerful blow to the lateral knee produces a “terrible triad” injury, in which there is a sequential injury to the tibial collateral ligament, medial meniscus, and anterior cruciate ligament.
Arthroscopic surgery has greatly improved the surgical treatment of knee injuries and reduced subsequent recovery times. This procedure involves a small incision and the insertion into the joint of an arthroscope, a pencil-thin instrument that allows for visualization of the joint interior. Small surgical instruments are also inserted via additional incisions. These tools allow a surgeon to remove or repair a torn meniscus or to reconstruct a ruptured cruciate ligament. The current method for anterior cruciate ligament replacement involves using a portion of the patellar ligament. Holes are drilled into the cruciate ligament attachment points on the tibia and femur, and the patellar ligament graft, with small areas of attached bone still intact at each end, is inserted into these holes. The bone-to-bone sites at each end of the graft heal rapidly and strongly, thus enabling a rapid recovery.
Figure 9.20 Knee Injury A strong blow to the lateral side of the extended knee will cause three injuries, in sequence: tearing of the tibial collateral ligament, damage to the medial meniscus, and rupture of the anterior cruciate ligament.
INTERACTIVE LINK
Watch this video to learn more about different knee injuries and diagnostic testing of the knee. What are the most common causes of anterior cruciate ligament injury?
Ankle and Foot Joints
The ankle is formed by the talocrural joint (Figure 9.21). It consists of the articulations between the talus bone of the foot and the distal ends of the tibia and fibula of the leg (crural = “leg”). The superior aspect of the talus bone is square-shaped and has three areas of articulation. The top of the talus articulates with the inferior tibia. This is the portion of the ankle joint that carries the body weight between the leg and foot. The sides of the talus are firmly held in position by the articulations with the medial malleolus of the tibia and the lateral malleolus of the fibula, which prevent any side-to-side motion of the talus. The ankle is thus a uniaxial hinge joint that allows only for dorsiflexion and plantar flexion of the foot.
Additional joints between the tarsal bones of the posterior foot allow for the movements of foot inversion and eversion. Most important for these movements is the subtalar joint, located between the talus and calcaneus bones. The joints between the talus and navicular bones and the calcaneus and cuboid bones are also important contributors to these movements. All of the joints between tarsal bones are plane joints. Together, the small motions that take place at these joints all contribute to the production of inversion and eversion foot motions.
Like the hinge joints of the elbow and knee, the talocrural joint of the ankle is supported by several strong ligaments located on the sides of the joint. These ligaments extend from the medial malleolus of the tibia or lateral malleolus of the fibula and anchor to the talus and calcaneus bones. Since they are located on the sides of the ankle joint, they allow for dorsiflexion and plantar flexion of the foot. They also prevent abnormal side-to-side and twisting movements of the talus and calcaneus bones during eversion and inversion of the foot. On the medial side is the broad deltoid ligament. The deltoid ligament supports the ankle joint and also resists excessive eversion of the foot. The lateral side of the ankle has several smaller ligaments. These include the anterior talofibular ligament and the posterior talofibular ligament, both of which span between the talus bone and the lateral malleolus of the fibula, and the calcaneofibular ligament, located between the calcaneus bone and fibula. These ligaments support the ankle and also resist excess inversion of the foot.
Figure 9.21 Ankle Joint The talocrural (ankle) joint is a uniaxial hinge joint that only allows for dorsiflexion or plantar flexion of the foot. Movements at the subtalar joint, between the talus and calcaneus bones, combined with motions at other intertarsal joints, enables eversion/inversion movements of the foot. Ligaments that unite the medial or lateral malleolus with the talus and calcaneus bones serve to support the talocrural joint and to resist excess eversion or inversion of the foot.
INTERACTIVE LINK
Watch this video for a tutorial on the anatomy of the ankle joint. What are the three ligaments found on the lateral side of the ankle joint?
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Watch this video to learn more about the anatomy of the ankle joint, including bones, joints, muscles, nerves, and blood vessels. Which type of joint used in woodworking does the ankle joint resemble?
DISORDERS OF THE...
Joints
The ankle is the most frequently injured joint in the body, with the most common injury being an inversion ankle sprain. A sprain is the stretching or tearing of the supporting ligaments. Excess inversion causes the talus bone to tilt laterally, thus damaging the ligaments on the lateral side of the ankle. The anterior talofibular ligament is most commonly injured, followed by the calcaneofibular ligament. In severe inversion injuries, the forceful lateral movement of the talus not only ruptures the lateral ankle ligaments, but also fractures the distal fibula.
Less common are eversion sprains of the ankle, which involve stretching of the deltoid ligament on the medial side of the ankle. Forcible eversion of the foot, for example, with an awkward landing from a jump or when a football player has a foot planted and is hit on the lateral ankle, can result in a Pott’s fracture and dislocation of the ankle joint. In this injury, the very strong deltoid ligament does not tear, but instead shears off the medial malleolus of the tibia. This frees the talus, which moves laterally and fractures the distal fibula. In extreme cases, the posterior margin of the tibia may also be sheared off.
Above the ankle, the distal ends of the tibia and fibula are united by a strong syndesmosis formed by the interosseous membrane and ligaments at the distal tibiofibular joint. These connections prevent separation between the distal ends of the tibia and fibula and maintain the talus locked into position between the medial malleolus and lateral malleolus. Injuries that produce a lateral twisting of the leg on top of the planted foot can result in stretching or tearing of the tibiofibular ligaments, producing a syndesmotic ankle sprain or “high ankle sprain.”
Most ankle sprains can be treated using the RICE technique: Rest, Ice, Compression, and Elevation. Reducing joint mobility using a brace or cast may be required for a period of time. More severe injuries involving ligament tears or bone fractures may require surgery.
INTERACTIVE LINK
Watch this video to learn more about the ligaments of the ankle joint, ankle sprains, and treatment. During an inversion ankle sprain injury, all three ligaments that resist excessive inversion of the foot may be injured. What is the sequence in which these three ligaments are injured?
Development of Joints
- Describe the two processes by which mesenchyme can give rise to bone
- Discuss the process by which joints of the limbs are formed
Joints form during embryonic development in conjunction with the formation and growth of the associated bones. The embryonic tissue that gives rise to all bones, cartilages, and connective tissues of the body is called mesenchyme. In the head, mesenchyme will accumulate at those areas that will become the bones that form the top and sides of the skull. The mesenchyme in these areas will develop directly into bone through the process of intramembranous ossification, in which mesenchymal cells differentiate into bone-producing cells that then generate bone tissue. The mesenchyme between the areas of bone production will become the fibrous connective tissue that fills the spaces between the developing bones. Initially, the connective tissue-filled gaps between the bones are wide, and are called fontanelles. After birth, as the skull bones grow and enlarge, the gaps between them decrease in width and the fontanelles are reduced to suture joints in which the bones are united by a narrow layer of fibrous connective tissue.
The bones that form the base and facial regions of the skull develop through the process of endochondral ossification. In this process, mesenchyme accumulates and differentiates into hyaline cartilage, which forms a model of the future bone. The hyaline cartilage model is then gradually, over a period of many years, displaced by bone. The mesenchyme between these developing bones becomes the fibrous connective tissue of the suture joints between the bones in these regions of the skull.
A similar process of endochondral ossification gives rises to the bones and joints of the limbs. The limbs initially develop as small limb buds that appear on the sides of the embryo around the end of the fourth week of development. Starting during the sixth week, as each limb bud continues to grow and elongate, areas of mesenchyme within the bud begin to differentiate into the hyaline cartilage that will form models for of each of the future bones. The synovial joints will form between the adjacent cartilage models, in an area called the joint interzone. Cells at the center of this interzone region undergo cell death to form the joint cavity, while surrounding mesenchyme cells will form the articular capsule and supporting ligaments. The process of endochondral ossification, which converts the cartilage models into bone, begins by the twelfth week of embryonic development. At birth, ossification of much of the bone has occurred, but the hyaline cartilage of the epiphyseal plate will remain throughout childhood and adolescence to allow for bone lengthening. Hyaline cartilage is also retained as the articular cartilage that covers the surfaces of the bones at synovial joints.
Key Terms
- abduction
- movement in the coronal plane that moves a limb laterally away from the body; spreading of the fingers
- acetabular labrum
- lip of fibrocartilage that surrounds outer margin of the acetabulum on the hip bone
- adduction
- movement in the coronal plane that moves a limb medially toward or across the midline of the body; bringing fingers together
- amphiarthrosis
- slightly mobile joint
- annular ligament
- intrinsic ligament of the elbow articular capsule that surrounds and supports the head of the radius at the proximal radioulnar joint
- anterior cruciate ligament
- intracapsular ligament of the knee; extends from anterior, superior surface of the tibia to the inner aspect of the lateral condyle of the femur; resists hyperextension of knee
- anterior talofibular ligament
- intrinsic ligament located on the lateral side of the ankle joint, between talus bone and lateral malleolus of fibula; supports talus at the talocrural joint and resists excess inversion of the foot
- articular capsule
- connective tissue structure that encloses the joint cavity of a synovial joint
- articular cartilage
- thin layer of hyaline cartilage that covers the articulating surfaces of bones at a synovial joint
- articular disc
- meniscus; a fibrocartilage structure found between the bones of some synovial joints; provides padding or smooths movements between the bones; strongly unites the bones together
- articulation
- joint of the body
- atlanto-occipital joint
- articulation between the occipital condyles of the skull and the superior articular processes of the atlas (C1 vertebra)
- atlantoaxial joint
- series of three articulations between the atlas (C1) vertebra and the axis (C2) vertebra, consisting of the joints between the inferior articular processes of C1 and the superior articular processes of C2, and the articulation between the dens of C2 and the anterior arch of C1
- ball-and-socket joint
- synovial joint formed between the spherical end of one bone (the ball) that fits into the depression of a second bone (the socket); found at the hip and shoulder joints; functionally classified as a multiaxial joint
- biaxial joint
- type of diarthrosis; a joint that allows for movements within two planes (two axes)
- bursa
- connective tissue sac containing lubricating fluid that prevents friction between adjacent structures, such as skin and bone, tendons and bone, or between muscles
- calcaneofibular ligament
- intrinsic ligament located on the lateral side of the ankle joint, between the calcaneus bone and lateral malleolus of the fibula; supports the talus bone at the ankle joint and resists excess inversion of the foot
- cartilaginous joint
- joint at which the bones are united by hyaline cartilage (synchondrosis) or fibrocartilage (symphysis)
- circumduction
- circular motion of the arm, thigh, hand, thumb, or finger that is produced by the sequential combination of flexion, abduction, extension, and adduction
- condyloid joint
- synovial joint in which the shallow depression at the end of one bone receives a rounded end from a second bone or a rounded structure formed by two bones; found at the metacarpophalangeal joints of the fingers or the radiocarpal joint of the wrist; functionally classified as a biaxial joint
- coracohumeral ligament
- intrinsic ligament of the shoulder joint; runs from the coracoid process of the scapula to the anterior humerus
- deltoid ligament
- broad intrinsic ligament located on the medial side of the ankle joint; supports the talus at the talocrural joint and resists excess eversion of the foot
- depression
- downward (inferior) motion of the scapula or mandible
- diarthrosis
- freely mobile joint
- dorsiflexion
- movement at the ankle that brings the top of the foot toward the anterior leg
- elbow joint
- humeroulnar joint
- elevation
- upward (superior) motion of the scapula or mandible
- eversion
- foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned laterally, away from the midline
- extension
- movement in the sagittal plane that increases the angle of a joint (straightens the joint); motion involving posterior bending of the vertebral column or returning to the upright position from a flexed position
- extrinsic ligament
- ligament located outside of the articular capsule of a synovial joint
- femoropatellar joint
- portion of the knee joint consisting of the articulation between the distal femur and the patella
- fibrous joint
- joint where the articulating areas of the adjacent bones are connected by fibrous connective tissue
- fibular collateral ligament
- extrinsic ligament of the knee joint that spans from the lateral epicondyle of the femur to the head of the fibula; resists hyperextension and rotation of the extended knee
- flexion
- movement in the sagittal plane that decreases the angle of a joint (bends the joint); motion involving anterior bending of the vertebral column
- fontanelles
- expanded areas of fibrous connective tissue that separate the braincase bones of the skull prior to birth and during the first year after birth
- glenohumeral joint
- shoulder joint; articulation between the glenoid cavity of the scapula and head of the humerus; multiaxial ball-and-socket joint that allows for flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation of the humerus
- glenohumeral ligament
- one of the three intrinsic ligaments of the shoulder joint that strengthen the anterior articular capsule
- glenoid labrum
- lip of fibrocartilage located around the outside margin of the glenoid cavity of the scapula
- gomphosis
- type of fibrous joint in which the root of a tooth is anchored into its bony jaw socket by strong periodontal ligaments
- hinge joint
- synovial joint at which the convex surface of one bone articulates with the concave surface of a second bone; includes the elbow, knee, ankle, and interphalangeal joints; functionally classified as a uniaxial joint
- humeroradial joint
- articulation between the capitulum of the humerus and head of the radius
- humeroulnar joint
- articulation between the trochlea of humerus and the trochlear notch of the ulna; uniaxial hinge joint that allows for flexion/extension of the forearm
- hyperextension
- excessive extension of joint, beyond the normal range of movement
- hyperflexion
- excessive flexion of joint, beyond the normal range of movement
- iliofemoral ligament
- intrinsic ligament spanning from the ilium of the hip bone to the femur, on the superior-anterior aspect of the hip joint
- inferior rotation
- movement of the scapula during upper limb adduction in which the glenoid cavity of the scapula moves in a downward direction as the medial end of the scapular spine moves in an upward direction
- interosseous membrane
- wide sheet of fibrous connective tissue that fills the gap between two parallel bones, forming a syndesmosis; found between the radius and ulna of the forearm and between the tibia and fibula of the leg
- intracapsular ligament
- ligament that is located within the articular capsule of a synovial joint
- intrinsic ligament
- ligament that is fused to or incorporated into the wall of the articular capsule of a synovial joint
- inversion
- foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned toward the midline
- ischiofemoral ligament
- intrinsic ligament spanning from the ischium of the hip bone to the femur, on the posterior aspect of the hip joint
- joint
- site at which two or more bones or bone and cartilage come together (articulate)
- joint cavity
- space enclosed by the articular capsule of a synovial joint that is filled with synovial fluid and contains the articulating surfaces of the adjacent bones
- joint interzone
- site within a growing embryonic limb bud that will become a synovial joint
- lateral (external) rotation
- movement of the arm at the shoulder joint or the thigh at the hip joint that moves the anterior surface of the limb away from the midline of the body
- lateral excursion
- side-to-side movement of the mandible away from the midline, toward either the right or left side
- lateral flexion
- bending of the neck or body toward the right or left side
- lateral meniscus
- C-shaped fibrocartilage articular disc located at the knee, between the lateral condyle of the femur and the lateral condyle of the tibia
- lateral tibiofemoral joint
- portion of the knee consisting of the articulation between the lateral condyle of the tibia and the lateral condyle of the femur; allows for flexion/extension at the knee
- ligament
- strong band of dense connective tissue spanning between bones
- ligament of the head of the femur
- intracapsular ligament that runs from the acetabulum of the hip bone to the head of the femur
- medial (internal) rotation
- movement of the arm at the shoulder joint or the thigh at the hip joint that brings the anterior surface of the limb toward the midline of the body
- medial excursion
- side-to-side movement that returns the mandible to the midline
- medial meniscus
- C-shaped fibrocartilage articular disc located at the knee, between the medial condyle of the femur and medial condyle of the tibia
- medial tibiofemoral joint
- portion of the knee consisting of the articulation between the medial condyle of the tibia and the medial condyle of the femur; allows for flexion/extension at the knee
- meniscus
- articular disc
- multiaxial joint
- type of diarthrosis; a joint that allows for movements within three planes (three axes)
- opposition
- thumb movement that brings the tip of the thumb in contact with the tip of a finger
- patellar ligament
- ligament spanning from the patella to the anterior tibia; serves as the final attachment for the quadriceps femoris muscle
- periodontal ligament
- band of dense connective tissue that anchors the root of a tooth into the bony jaw socket
- pivot joint
- synovial joint at which the rounded portion of a bone rotates within a ring formed by a ligament and an articulating bone; functionally classified as uniaxial joint
- plane joint
- synovial joint formed between the flattened articulating surfaces of adjacent bones; functionally classified as a multiaxial joint
- plantar flexion
- foot movement at the ankle in which the heel is lifted off of the ground
- posterior cruciate ligament
- intracapsular ligament of the knee; extends from the posterior, superior surface of the tibia to the inner aspect of the medial condyle of the femur; prevents anterior displacement of the femur when the knee is flexed and weight bearing
- posterior talofibular ligament
- intrinsic ligament located on the lateral side of the ankle joint, between the talus bone and lateral malleolus of the fibula; supports the talus at the talocrural joint and resists excess inversion of the foot
- pronated position
- forearm position in which the palm faces backward
- pronation
- forearm motion that moves the palm of the hand from the palm forward to the palm backward position
- protraction
- anterior motion of the scapula or mandible
- proximal radioulnar joint
- articulation between head of radius and radial notch of ulna; uniaxial pivot joint that allows for rotation of radius during pronation/supination of forearm
- pubofemoral ligament
- intrinsic ligament spanning from the pubis of the hip bone to the femur, on the anterior-inferior aspect of the hip joint
- radial collateral ligament
- intrinsic ligament on the lateral side of the elbow joint; runs from the lateral epicondyle of humerus to merge with the annular ligament
- reposition
- movement of the thumb from opposition back to the anatomical position (next to index finger)
- retraction
- posterior motion of the scapula or mandible
- rotation
- movement of a bone around a central axis (atlantoaxial joint) or around its long axis (proximal radioulnar joint; shoulder or hip joint); twisting of the vertebral column resulting from the summation of small motions between adjacent vertebrae
- rotator cuff
- strong connective tissue structure formed by the fusion of four rotator cuff muscle tendons to the articular capsule of the shoulder joint; surrounds and supports superior, anterior, lateral, and posterior sides of the humeral head
- saddle joint
- synovial joint in which the articulating ends of both bones are convex and concave in shape, such as at the first carpometacarpal joint at the base of the thumb; functionally classified as a biaxial joint
- subacromial bursa
- bursa that protects the supraspinatus muscle tendon and superior end of the humerus from rubbing against the acromion of the scapula
- subcutaneous bursa
- bursa that prevents friction between skin and an underlying bone
- submuscular bursa
- bursa that prevents friction between bone and a muscle or between adjacent muscles
- subscapular bursa
- bursa that prevents rubbing of the subscapularis muscle tendon against the scapula
- subtalar joint
- articulation between the talus and calcaneus bones of the foot; allows motions that contribute to inversion/eversion of the foot
- subtendinous bursa
- bursa that prevents friction between bone and a muscle tendon
- superior rotation
- movement of the scapula during upper limb abduction in which the glenoid cavity of the scapula moves in an upward direction as the medial end of the scapular spine moves in a downward direction
- supinated position
- forearm position in which the palm faces anteriorly (anatomical position)
- supination
- forearm motion that moves the palm of the hand from the palm backward to the palm forward position
- suture
- fibrous joint that connects the bones of the skull (except the mandible); an immobile joint (synarthrosis)
- symphysis
- type of cartilaginous joint where the bones are joined by fibrocartilage
- synarthrosis
- immobile or nearly immobile joint
- synchondrosis
- type of cartilaginous joint where the bones are joined by hyaline cartilage
- syndesmosis
- type of fibrous joint in which two separated, parallel bones are connected by an interosseous membrane
- synostosis
- site at which adjacent bones or bony components have fused together
- synovial fluid
- thick, lubricating fluid that fills the interior of a synovial joint
- synovial joint
- joint at which the articulating surfaces of the bones are located within a joint cavity formed by an articular capsule
- synovial membrane
- thin layer that lines the inner surface of the joint cavity at a synovial joint; produces the synovial fluid
- talocrural joint
- ankle joint; articulation between the talus bone of the foot and medial malleolus of the tibia, distal tibia, and lateral malleolus of the fibula; a uniaxial hinge joint that allows only for dorsiflexion and plantar flexion of the foot
- temporomandibular joint (TMJ)
- articulation between the condyle of the mandible and the mandibular fossa and articular tubercle of the temporal bone of the skull; allows for depression/elevation (opening/closing of mouth), protraction/retraction, and side-to-side motions of the mandible
- tendon
- dense connective tissue structure that anchors a muscle to bone
- tendon sheath
- connective tissue that surrounds a tendon at places where the tendon crosses a joint; contains a lubricating fluid to prevent friction and allow smooth movements of the tendon
- tibial collateral ligament
- extrinsic ligament of knee joint that spans from the medial epicondyle of the femur to the medial tibia; resists hyperextension and rotation of extended knee
- ulnar collateral ligament
- intrinsic ligament on the medial side of the elbow joint; spans from the medial epicondyle of the humerus to the medial ulna
- uniaxial joint
- type of diarthrosis; joint that allows for motion within only one plane (one axis)
- zygapophysial joints
- facet joints; plane joints between the superior and inferior articular processes of adjacent vertebrae that provide for only limited motions between the vertebrae
Chapter Review
9.1 Classification of Joints
Structural classifications of the body joints are based on how the bones are held together and articulate with each other. At fibrous joints, the adjacent bones are directly united to each other by fibrous connective tissue. Similarly, at a cartilaginous joint, the adjacent bones are united by cartilage. In contrast, at a synovial joint, the articulating bone surfaces are not directly united to each other, but come together within a fluid-filled joint cavity.
The functional classification of body joints is based on the degree of movement found at each joint. A synarthrosis is a joint that is essentially immobile. This type of joint provides for a strong connection between the adjacent bones, which serves to protect internal structures such as the brain or heart. Examples include the fibrous joints of the skull sutures and the cartilaginous manubriosternal joint. A joint that allows for limited movement is an amphiarthrosis. An example is the pubic symphysis of the pelvis, the cartilaginous joint that strongly unites the right and left hip bones of the pelvis. The cartilaginous joints in which vertebrae are united by intervertebral discs provide for small movements between the adjacent vertebrae and are also an amphiarthrosis type of joint. Thus, based on their movement ability, both fibrous and cartilaginous joints are functionally classified as a synarthrosis or amphiarthrosis.
The most common type of joint is the diarthrosis, which is a freely moveable joint. All synovial joints are functionally classified as diarthroses. A uniaxial diarthrosis, such as the elbow, is a joint that only allows for movement within a single anatomical plane. Joints that allow for movements in two planes are biaxial joints, such as the metacarpophalangeal joints of the fingers. A multiaxial joint, such as the shoulder or hip joint, allows for three planes of motions.
9.2 Fibrous Joints
Fibrous joints are where adjacent bones are strongly united by fibrous connective tissue. The gap filled by connective tissue may be narrow or wide. The three types of fibrous joints are sutures, gomphoses, and syndesmoses. A suture is the narrow fibrous joint that unites most bones of the skull. At a gomphosis, the root of a tooth is anchored across a narrow gap by periodontal ligaments to the walls of its socket in the bony jaw. A syndesmosis is the type of fibrous joint found between parallel bones. The gap between the bones may be wide and filled with a fibrous interosseous membrane, or it may narrow with ligaments spanning between the bones. Syndesmoses are found between the bones of the forearm (radius and ulna) and the leg (tibia and fibula). Fibrous joints strongly unite adjacent bones and thus serve to provide protection for internal organs, strength to body regions, or weight-bearing stability.
9.3 Cartilaginous Joints
There are two types of cartilaginous joints. A synchondrosis is formed when the adjacent bones are united by hyaline cartilage. A temporary synchondrosis is formed by the epiphyseal plate of a growing long bone, which is lost when the epiphyseal plate ossifies as the bone reaches maturity. The synchondrosis is thus replaced by a synostosis. Permanent synchondroses that do not ossify are found at the first sternocostal joint and between the anterior ends of the bony ribs and the junction with their costal cartilage. A symphysis is where the bones are joined by fibrocartilage and the gap between the bones may be narrow or wide. A narrow symphysis is found at the manubriosternal joint and at the pubic symphysis. A wide symphysis is the intervertebral symphysis in which the bodies of adjacent vertebrae are united by an intervertebral disc.
9.4 Synovial Joints
Synovial joints are the most common type of joints in the body. They are characterized by the presence of a joint cavity, inside of which the bones of the joint articulate with each other. The articulating surfaces of the bones at a synovial joint are not directly connected to each other by connective tissue or cartilage, which allows the bones to move freely against each other. The walls of the joint cavity are formed by the articular capsule. Friction between the bones is reduced by a thin layer of articular cartilage covering the surfaces of the bones, and by a lubricating synovial fluid, which is secreted by the synovial membrane.
Synovial joints are strengthened by the presence of ligaments, which hold the bones together and resist excessive or abnormal movements of the joint. Ligaments are classified as extrinsic ligaments if they are located outside of the articular capsule, intrinsic ligaments if they are fused to the wall of the articular capsule, or intracapsular ligaments if they are located inside the articular capsule. Some synovial joints also have an articular disc (meniscus), which can provide padding between the bones, smooth their movements, or strongly join the bones together to strengthen the joint. Muscles and their tendons acting across a joint can also increase their contractile strength when needed, thus providing indirect support for the joint.
Bursae contain a lubricating fluid that serves to reduce friction between structures. Subcutaneous bursae prevent friction between the skin and an underlying bone, submuscular bursae protect muscles from rubbing against a bone or another muscle, and a subtendinous bursa prevents friction between bone and a muscle tendon. Tendon sheaths contain a lubricating fluid and surround tendons to allow for smooth movement of the tendon as it crosses a joint.
Based on the shape of the articulating bone surfaces and the types of movement allowed, synovial joints are classified into six types. At a pivot joint, one bone is held within a ring by a ligament and its articulation with a second bone. Pivot joints only allow for rotation around a single axis. These are found at the articulation between the C1 (atlas) and the dens of the C2 (axis) vertebrae, which provides the side-to-side rotation of the head, or at the proximal radioulnar joint between the head of the radius and the radial notch of the ulna, which allows for rotation of the radius during forearm movements. Hinge joints, such as at the elbow, knee, ankle, or interphalangeal joints between phalanx bones of the fingers and toes, allow only for bending and straightening of the joint. Pivot and hinge joints are functionally classified as uniaxial joints.
Condyloid joints are found where the shallow depression of one bone receives a rounded bony area formed by one or two bones. Condyloid joints are found at the base of the fingers (metacarpophalangeal joints) and at the wrist (radiocarpal joint). At a saddle joint, the articulating bones fit together like a rider and a saddle. An example is the first carpometacarpal joint located at the base of the thumb. Both condyloid and saddle joints are functionally classified as biaxial joints.
Plane joints are formed between the small, flattened surfaces of adjacent bones. These joints allow the bones to slide or rotate against each other, but the range of motion is usually slight and tightly limited by ligaments or surrounding bones. This type of joint is found between the articular processes of adjacent vertebrae, at the acromioclavicular joint, or at the intercarpal joints of the hand and intertarsal joints of the foot. Ball-and-socket joints, in which the rounded head of a bone fits into a large depression or socket, are found at the shoulder and hip joints. Both plane and ball-and-sockets joints are classified functionally as multiaxial joints. However, ball-and-socket joints allow for large movements, while the motions between bones at a plane joint are small.
9.5 Types of Body Movements
The variety of movements provided by the different types of synovial joints allows for a large range of body motions and gives you tremendous mobility. These movements allow you to flex or extend your body or limbs, medially rotate and adduct your arms and flex your elbows to hold a heavy object against your chest, raise your arms above your head, rotate or shake your head, and bend to touch the toes (with or without bending your knees).
Each of the different structural types of synovial joints also allow for specific motions. The atlantoaxial pivot joint provides side-to-side rotation of the head, while the proximal radioulnar articulation allows for rotation of the radius during pronation and supination of the forearm. Hinge joints, such as at the knee and elbow, allow only for flexion and extension. Similarly, the hinge joint of the ankle only allows for dorsiflexion and plantar flexion of the foot.
Condyloid and saddle joints are biaxial. These allow for flexion and extension, and abduction and adduction. The sequential combination of flexion, adduction, extension, and abduction produces circumduction. Multiaxial plane joints provide for only small motions, but these can add together over several adjacent joints to produce body movement, such as inversion and eversion of the foot. Similarly, plane joints allow for flexion, extension, and lateral flexion movements of the vertebral column. The multiaxial ball and socket joints allow for flexion-extension, abduction-adduction, and circumduction. In addition, these also allow for medial (internal) and lateral (external) rotation. Ball-and-socket joints have the greatest range of motion of all synovial joints.
9.6 Anatomy of Selected Synovial Joints
Although synovial joints share many common features, each joint of the body is specialized for certain movements and activities. The joints of the upper limb provide for large ranges of motion, which give the upper limb great mobility, thus enabling actions such as the throwing of a ball or typing on a keyboard. The joints of the lower limb are more robust, giving them greater strength and the stability needed to support the body weight during running, jumping, or kicking activities.
The joints of the vertebral column include the symphysis joints formed by each intervertebral disc and the plane synovial joints between the superior and inferior articular processes of adjacent vertebrae. Each of these joints provide for limited motions, but these sum together to produce flexion, extension, lateral flexion, and rotation of the neck and body. The range of motions available in each region of the vertebral column varies, with all of these motions available in the cervical region. Only rotation is allowed in the thoracic region, while the lumbar region has considerable extension, flexion, and lateral flexion, but rotation is prevented. The atlanto-occipital joint allows for flexion and extension of the head, while the atlantoaxial joint is a pivot joint that provides for rotation of the head.
The temporomandibular joint is the articulation between the condyle of the mandible and the mandibular fossa and articular tubercle of the skull temporal bone. An articular disc is located between the bony components of this joint. A combination of gliding and hinge motions of the mandibular condyle allows for elevation/depression, protraction/retraction, and side-to-side motions of the lower jaw.
The glenohumeral (shoulder) joint is a multiaxial ball-and-socket joint that provides flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation of the humerus. The head of the humerus articulates with the glenoid cavity of the scapula. The glenoid labrum extends around the margin of the glenoid cavity. Intrinsic ligaments, including the coracohumeral ligament and glenohumeral ligaments, provide some support for the shoulder joint. However, the primary support comes from muscles crossing the joint whose tendons form the rotator cuff. These muscle tendons are protected from friction against the scapula by the subacromial bursa and subscapular bursa.
The elbow is a uniaxial hinge joint that allows for flexion/extension of the forearm. It includes the humeroulnar joint and the humeroradial joint. The medial elbow is supported by the ulnar collateral ligament and the radial collateral ligament supports the lateral side. These ligaments prevent side-to-side movements and resist hyperextension of the elbow. The proximal radioulnar joint is a pivot joint that allows for rotation of the radius during pronation/supination of the forearm. The annular ligament surrounds the head of the radius to hold it in place at this joint.
The hip joint is a ball-and-socket joint whose motions are more restricted than at the shoulder to provide greater stability during weight bearing. The hip joint is the articulation between the head of the femur and the acetabulum of the hip bone. The acetabulum is deepened by the acetabular labrum. The iliofemoral, pubofemoral, and ischiofemoral ligaments strongly support the hip joint in the upright, standing position. The ligament of the head of the femur provides little support but carries an important artery that supplies the femur.
The knee includes three articulations. The femoropatellar joint is between the patella and distal femur. The patella, a sesamoid bone incorporated into the tendon of the quadriceps femoris muscle of the anterior thigh, serves to protect this tendon from rubbing against the distal femur during knee movements. The medial and lateral tibiofemoral joints, between the condyles of the femur and condyles of the tibia, are modified hinge joints that allow for knee extension and flexion. During these movements, the condyles of the femur both roll and glide over the surface of the tibia. As the knee comes into full extension, a slight medial rotation of the femur serves to “lock” the knee into its most stable, weight-bearing position. The reverse motion, a small lateral rotation of the femur, is required to initiate knee flexion. When the knee is flexed, some rotation of the leg is available.
Two extrinsic ligaments, the tibial collateral ligament on the medial side and the fibular collateral ligament on the lateral side, serve to resist hyperextension or rotation of the extended knee joint. Two intracapsular ligaments, the anterior cruciate ligament and posterior cruciate ligament, span between the tibia and the inner aspects of the femoral condyles. The anterior cruciate ligament resists hyperextension of the knee, while the posterior cruciate ligament prevents anterior sliding of the femur, thus supporting the knee when it is flexed and weight bearing. The medial and lateral menisci, located between the femoral and tibial condyles, are articular discs that provide padding and improve the fit between the bones.
The talocrural joint forms the ankle. It consists of the articulation between the talus bone and the medial malleolus of the tibia, the distal end of the tibia, and the lateral malleolus of the fibula. This is a uniaxial hinge joint that allows only dorsiflexion and plantar flexion of the foot. Gliding motions at the subtalar and intertarsal joints of the foot allow for inversion/eversion of the foot. The ankle joint is supported on the medial side by the deltoid ligament, which prevents side-to-side motions of the talus at the talocrural joint and resists excessive eversion of the foot. The lateral ankle is supported by the anterior and posterior talofibular ligaments and the calcaneofibular ligament. These support the ankle joint and also resist excess inversion of the foot. An inversion ankle sprain, a common injury, will result in injury to one or more of these lateral ankle ligaments.
9.7 Development of Joints
During embryonic growth, bones and joints develop from mesenchyme, an embryonic tissue that gives rise to bone, cartilage, and fibrous connective tissues. In the skull, the bones develop either directly from mesenchyme through the process of intramembranous ossification, or indirectly through endochondral ossification, which initially forms a hyaline cartilage model of the future bone, which is later converted into bone. In both cases, the mesenchyme between the developing bones differentiates into fibrous connective tissue that will unite the skull bones at suture joints. In the limbs, mesenchyme accumulations within the growing limb bud will become a hyaline cartilage model for each of the limb bones. A joint interzone will develop between these areas of cartilage. Mesenchyme cells at the margins of the interzone will give rise to the articular capsule, while cell death at the center forms the space that will become the joint cavity of the future synovial joint. The hyaline cartilage model of each limb bone will eventually be converted into bone via the process of endochondral ossification. However, hyaline cartilage will remain, covering the ends of the adult bone as the articular cartilage.
Interactive Link Questions
Go to this website to view a radiograph (X-ray image) of a child’s hand and wrist. The growing bones of child have an epiphyseal plate that forms a synchondrosis between the shaft and end of a long bone. Being less dense than bone, the area of epiphyseal cartilage is seen on this radiograph as the dark epiphyseal gaps located near the ends of the long bones, including the radius, ulna, metacarpal, and phalanx bones. Which of the bones in this image do not show an epiphyseal plate (epiphyseal gap)?
2.Watch this video to see an animation of synovial joints in action. Synovial joints are places where bones articulate with each other inside of a joint cavity. The different types of synovial joints are the ball-and-socket joint (shoulder joint), hinge joint (knee), pivot joint (atlantoaxial joint, between C1 and C2 vertebrae of the neck), condyloid joint (radiocarpal joint of the wrist), saddle joint (first carpometacarpal joint, between the trapezium carpal bone and the first metacarpal bone, at the base of the thumb), and plane joint (facet joints of vertebral column, between superior and inferior articular processes). Which type of synovial joint allows for the widest ranges of motion?
3.Visit this website to read about a patient who arrives at the hospital with joint pain and weakness in his legs. What caused this patient’s weakness?
4.Watch this animation to observe hip replacement surgery (total hip arthroplasty), which can be used to alleviate the pain and loss of joint mobility associated with osteoarthritis of the hip joint. What is the most common cause of hip disability?
5.Watch this video to learn about the symptoms and treatments for rheumatoid arthritis. Which system of the body malfunctions in rheumatoid arthritis and what does this cause?
6.Watch this video to learn about anatomical motions. What motions involve increasing or decreasing the angle of the foot at the ankle?
7.Watch this video to learn about TMJ. Opening of the mouth requires the combination of two motions at the temporomandibular joint, an anterior gliding motion of the articular disc and mandible and the downward hinging of the mandible. What is the initial movement of the mandible during opening and how much mouth opening does this produce?
8.Watch this video for a tutorial on the anatomy of the shoulder joint. What movements are available at the shoulder joint?
9.Watch this video to learn about the anatomy of the shoulder joint, including bones, joints, muscles, nerves, and blood vessels. What is the shape of the glenoid labrum in cross-section, and what is the importance of this shape?
10.Watch this animation to learn more about the anatomy of the elbow joint. What structures provide the main stability for the elbow?
11.Watch this video to learn more about the anatomy of the elbow joint, including bones, joints, muscles, nerves, and blood vessels. What are the functions of the articular cartilage?
12.Watch this video for a tutorial on the anatomy of the hip joint. What is a possible consequence following a fracture of the femoral neck within the capsule of the hip joint?
13.Watch this video to learn more about the anatomy of the hip joint, including bones, joints, muscles, nerves, and blood vessels. Where is the articular cartilage thickest within the hip joint?
14.Watch this video to learn more about the flexion and extension of the knee, as the femur both rolls and glides on the tibia to maintain stable contact between the bones in all knee positions. The patella glides along a groove on the anterior side of the distal femur. The collateral ligaments on the sides of the knee become tight in the fully extended position to help stabilize the knee. The posterior cruciate ligament supports the knee when flexed and the anterior cruciate ligament becomes tight when the knee comes into full extension to resist hyperextension. What are the ligaments that support the knee joint?
15.Watch this video to learn more about the anatomy of the knee joint, including bones, joints, muscles, nerves, and blood vessels. Which ligament of the knee keeps the tibia from sliding too far forward in relation to the femur and which ligament keeps the tibia from sliding too far backward?
16.Watch this video to learn more about different knee injuries and diagnostic testing of the knee. What are the most causes of anterior cruciate ligament injury?
17.Watch this video for a tutorial on the anatomy of the ankle joint. What are the three ligaments found on the lateral side of the ankle joint?
18.Watch this video to learn more about the anatomy of the ankle joint, including bones, joints, muscles, nerves, and blood vessels. The ankle joint resembles what type of joint used in woodworking?
19.Watch this video to learn about the ligaments of the ankle joint, ankle sprains, and treatment. During an inversion ankle sprain injury, all three ligaments that resist excessive inversion of the foot may be injured. What is the sequence in which these three ligaments are injured?
Review Questions
The joint between adjacent vertebrae that includes an invertebral disc is classified as which type of joint?
- diarthrosis
- multiaxial
- amphiarthrosis
- synarthrosis
Which of these joints is classified as a synarthrosis?
- the pubic symphysis
- the manubriosternal joint
- an invertebral disc
- the shoulder joint
Which of these joints is classified as a biaxial diarthrosis?
- the metacarpophalangeal joint
- the hip joint
- the elbow joint
- the pubic symphysis
Synovial joints ________.
- may be functionally classified as a synarthrosis
- are joints where the bones are connected to each other by hyaline cartilage
- may be functionally classified as a amphiarthrosis
- are joints where the bones articulate with each other within a fluid-filled joint cavity
Which type of fibrous joint connects the tibia and fibula?
- syndesmosis
- symphysis
- suture
- gomphosis
An example of a wide fibrous joint is ________.
- the interosseous membrane of the forearm
- a gomphosis
- a suture joint
- a synostosis
A gomphosis ________.
- is formed by an interosseous membrane
- connects the tibia and fibula bones of the leg
- contains a joint cavity
- anchors a tooth to the jaw
A syndesmosis is ________.
- a narrow fibrous joint
- the type of joint that unites bones of the skull
- a fibrous joint that unites parallel bones
- the type of joint that anchors the teeth in the jaws
A cartilaginous joint ________.
- has a joint cavity
- is called a symphysis when the bones are united by fibrocartilage
- anchors the teeth to the jaws
- is formed by a wide sheet of fibrous connective tissue
A synchondrosis is ________.
- found at the pubic symphysis
- where bones are connected together with fibrocartilage
- a type of fibrous joint
- found at the first sternocostal joint of the thoracic cage
Which of the following are joined by a symphysis?
- adjacent vertebrae
- the first rib and the sternum
- the end and shaft of a long bone
- the radius and ulna bones
The epiphyseal plate of a growing long bone in a child is classified as a ________.
- synchondrosis
- synostosis
- symphysis
- syndesmosis
Which type of joint provides the greatest range of motion?
- ball-and-socket
- hinge
- condyloid
- plane
Which type of joint allows for only uniaxial movement?
- saddle joint
- hinge joint
- condyloid joint
- ball-and-socket joint
Which of the following is a type of synovial joint?
- a synostosis
- a suture
- a plane joint
- a synchondrosis
A bursa ________.
- surrounds a tendon at the point where the tendon crosses a joint
- secretes the lubricating fluid for a synovial joint
- prevents friction between skin and bone, or a muscle tendon and bone
- is the strong band of connective tissue that holds bones together at a synovial joint
At synovial joints, ________.
- the articulating ends of the bones are directly connected by fibrous connective tissue
- the ends of the bones are enclosed within a space called a subcutaneous bursa
- intrinsic ligaments are located entirely inside of the articular capsule
- the joint cavity is filled with a thick, lubricating fluid
At a synovial joint, the synovial membrane ________.
- forms the fibrous connective walls of the joint cavity
- is the layer of cartilage that covers the articulating surfaces of the bones
- forms the intracapsular ligaments
- secretes the lubricating synovial fluid
Condyloid joints ________.
- are a type of ball-and-socket joint
- include the radiocarpal joint
- are a uniaxial diarthrosis joint
- are found at the proximal radioulnar joint
A meniscus is ________.
- a fibrocartilage pad that provides padding between bones
- a fluid-filled space that prevents friction between a muscle tendon and underlying bone
- the articular cartilage that covers the ends of a bone at a synovial joint
- the lubricating fluid within a synovial joint
The joints between the articular processes of adjacent vertebrae can contribute to which movement?
- lateral flexion
- circumduction
- dorsiflexion
- abduction
Which motion moves the bottom of the foot away from the midline of the body?
- elevation
- dorsiflexion
- eversion
- plantar flexion
Movement of a body region in a circular movement at a condyloid joint is what type of motion?
- rotation
- elevation
- abduction
- circumduction
Supination is the motion that moves the ________.
- hand from the palm backward position to the palm forward position
- foot so that the bottom of the foot faces the midline of the body
- hand from the palm forward position to the palm backward position
- scapula in an upward direction
Movement at the shoulder joint that moves the upper limb laterally away from the body is called ________.
- elevation
- eversion
- abduction
- lateral rotation
The primary support for the glenohumeral joint is provided by the ________.
- coracohumeral ligament
- glenoid labrum
- rotator cuff muscles
- subacromial bursa
The proximal radioulnar joint ________.
- is supported by the annular ligament
- contains an articular disc that strongly unites the bones
- is supported by the ulnar collateral ligament
- is a hinge joint that allows for flexion/extension of the forearm
Which statement is true concerning the knee joint?
- The lateral meniscus is an intrinsic ligament located on the lateral side of the knee joint.
- Hyperextension is resisted by the posterior cruciate ligament.
- The anterior cruciate ligament supports the knee when it is flexed and weight bearing.
- The medial meniscus is attached to the tibial collateral ligament.
The ankle joint ________.
- is also called the subtalar joint
- allows for gliding movements that produce inversion/eversion of the foot
- is a uniaxial hinge joint
- is supported by the tibial collateral ligament on the lateral side
Which region of the vertebral column has the greatest range of motion for rotation?
- cervical
- thoracic
- lumbar
- sacral
Intramembranous ossification ________.
- gives rise to the bones of the limbs
- produces the bones of the top and sides of the skull
- produces the bones of the face and base of the skull
- involves the conversion of a hyaline cartilage model into bone
Synovial joints ________.
- are derived from fontanelles
- are produced by intramembranous ossification
- develop at an interzone site
- are produced by endochondral ossification
Endochondral ossification is ________.
- the process that replaces hyaline cartilage with bone tissue
- the process by which mesenchyme differentiates directly into bone tissue
- completed before birth
- the process that gives rise to the joint interzone and future joint cavity
Critical Thinking Questions
Define how joints are classified based on function. Describe and give an example for each functional type of joint.
54.Explain the reasons for why joints differ in their degree of mobility.
55.Distinguish between a narrow and wide fibrous joint and give an example of each.
56.The periodontal ligaments are made of collagen fibers and are responsible for connecting the roots of the teeth to the jaws. Describe how scurvy, a disease that inhibits collagen production, can affect the teeth.
57.Describe the two types of cartilaginous joints and give examples of each.
58.Both functional and structural classifications can be used to describe an individual joint. Define the first sternocostal joint and the pubic symphysis using both functional and structural characteristics.
59.Describe the characteristic structures found at all synovial joints.
60.Describe the structures that provide direct and indirect support for a synovial joint.
61.Briefly define the types of joint movements available at a ball-and-socket joint.
62.Discuss the joints involved and movements required for you to cross your arms together in front of your chest.
63.Discuss the structures that contribute to support of the shoulder joint.
64.Describe the sequence of injuries that may occur if the extended, weight-bearing knee receives a very strong blow to the lateral side of the knee.
65.Describe how synovial joints develop within the embryonic limb.
66.Differentiate between endochondral and intramembranous ossification.
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oercommons
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2025-03-18T00:38:18.072621
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/56368/overview",
"title": "Anatomy and Physiology, Support and Movement",
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https://oercommons.org/courseware/lesson/56369/overview
|
Muscle Tissue
Introduction
Figure 10.1 Tennis Player Athletes rely on toned skeletal muscles to supply the force required for movement. (credit: Emmanuel Huybrechts/flickr)
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Explain the organization of muscle tissue
- Describe the function and structure of skeletal, cardiac muscle, and smooth muscle
- Explain how muscles work with tendons to move the body
- Describe how muscles contract and relax
- Define the process of muscle metabolism
- Explain how the nervous system controls muscle tension
- Relate the connections between exercise and muscle performance
- Explain the development and regeneration of muscle tissue
When most people think of muscles, they think of the muscles that are visible just under the skin, particularly of the limbs. These are skeletal muscles, so-named because most of them move the skeleton. But there are two other types of muscle in the body, with distinctly different jobs. Cardiac muscle, found in the heart, is concerned with pumping blood through the circulatory system. Smooth muscle is concerned with various involuntary movements, such as having one’s hair stand on end when cold or frightened, or moving food through the digestive system. This chapter will examine the structure and function of these three types of muscles.
Overview of Muscle Tissues
- Describe the different types of muscle
- Explain contractibility and extensibility
Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle (Figure 10.2). All three muscle tissues have some properties in common; they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from polarized to depolarized) and send an electrical wave called an action potential along the entire length of the membrane. While the nervous system can influence the excitability of cardiac and smooth muscle to some degree, skeletal muscle completely depends on signaling from the nervous system to work properly. On the other hand, both cardiac muscle and smooth muscle can respond to other stimuli, such as hormones and local stimuli.
Figure 10.2 The Three Types of Muscle Tissue The body contains three types of muscle tissue: (a) skeletal muscle, (b) smooth muscle, and (c) cardiac muscle. From top, LM × 1600, LM × 1600, LM × 1600. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)
The muscles all begin the actual process of contracting (shortening) when a protein called actin is pulled by a protein called myosin. This occurs in striated muscle (skeletal and cardiac) after specific binding sites on the actin have been exposed in response to the interaction between calcium ions (Ca++) and proteins (troponin and tropomyosin) that “shield” the actin-binding sites. Ca++ also is required for the contraction of smooth muscle, although its role is different: here Ca++ activates enzymes, which in turn activate myosin heads. All muscles require adenosine triphosphate (ATP) to continue the process of contracting, and they all relax when the Ca++ is removed and the actin-binding sites are re-shielded.
A muscle can return to its original length when relaxed due to a quality of muscle tissue called elasticity. It can recoil back to its original length due to elastic fibers. Muscle tissue also has the quality of extensibility; it can stretch or extend. Contractilityallows muscle tissue to pull on its attachment points and shorten with force.
Differences among the three muscle types include the microscopic organization of their contractile proteins—actin and myosin. The actin and myosin proteins are arranged very regularly in the cytoplasm of individual muscle cells (referred to as fibers) in both skeletal muscle and cardiac muscle, which creates a pattern, or stripes, called striations. The striations are visible with a light microscope under high magnification (see Figure 10.2). Skeletal muscle fibers are multinucleated structures that compose the skeletal muscle. Cardiac muscle fibers each have one to two nuclei and are physically and electrically connected to each other so that the entire heart contracts as one unit (called a syncytium).
Because the actin and myosin are not arranged in such regular fashion in smooth muscle, the cytoplasm of a smooth muscle fiber (which has only a single nucleus) has a uniform, nonstriated appearance (resulting in the name smooth muscle). However, the less organized appearance of smooth muscle should not be interpreted as less efficient. Smooth muscle in the walls of arteries is a critical component that regulates blood pressure necessary to push blood through the circulatory system; and smooth muscle in the skin, visceral organs, and internal passageways is essential for moving all materials through the body.
Skeletal Muscle
- Describe the layers of connective tissues packaging skeletal muscle
- Explain how muscles work with tendons to move the body
- Identify areas of the skeletal muscle fibers
- Describe excitation-contraction coupling
The best-known feature of skeletal muscle is its ability to contract and cause movement. Skeletal muscles act not only to produce movement but also to stop movement, such as resisting gravity to maintain posture. Small, constant adjustments of the skeletal muscles are needed to hold a body upright or balanced in any position. Muscles also prevent excess movement of the bones and joints, maintaining skeletal stability and preventing skeletal structure damage or deformation. Joints can become misaligned or dislocated entirely by pulling on the associated bones; muscles work to keep joints stable. Skeletal muscles are located throughout the body at the openings of internal tracts to control the movement of various substances. These muscles allow functions, such as swallowing, urination, and defecation, to be under voluntary control. Skeletal muscles also protect internal organs (particularly abdominal and pelvic organs) by acting as an external barrier or shield to external trauma and by supporting the weight of the organs.
Skeletal muscles contribute to the maintenance of homeostasis in the body by generating heat. Muscle contraction requires energy, and when ATP is broken down, heat is produced. This heat is very noticeable during exercise, when sustained muscle movement causes body temperature to rise, and in cases of extreme cold, when shivering produces random skeletal muscle contractions to generate heat.
Each skeletal muscle is an organ that consists of various integrated tissues. These tissues include the skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Each skeletal muscle has three layers of connective tissue (called “mysia”) that enclose it and provide structure to the muscle as a whole, and also compartmentalize the muscle fibers within the muscle (Figure 10.3). Each muscle is wrapped in a sheath of dense, irregular connective tissue called the epimysium, which allows a muscle to contract and move powerfully while maintaining its structural integrity. The epimysium also separates muscle from other tissues and organs in the area, allowing the muscle to move independently.
Figure 10.3 The Three Connective Tissue Layers Bundles of muscle fibers, called fascicles, are covered by the perimysium. Muscle fibers are covered by the endomysium.
Inside each skeletal muscle, muscle fibers are organized into individual bundles, each called a fascicle, by a middle layer of connective tissue called the perimysium. This fascicular organization is common in muscles of the limbs; it allows the nervous system to trigger a specific movement of a muscle by activating a subset of muscle fibers within a bundle, or fascicle of the muscle. Inside each fascicle, each muscle fiber is encased in a thin connective tissue layer of collagen and reticular fibers called the endomysium. The endomysium contains the extracellular fluid and nutrients to support the muscle fiber. These nutrients are supplied via blood to the muscle tissue.
In skeletal muscles that work with tendons to pull on bones, the collagen in the three tissue layers (the mysia) intertwines with the collagen of a tendon. At the other end of the tendon, it fuses with the periosteum coating the bone. The tension created by contraction of the muscle fibers is then transferred though the mysia, to the tendon, and then to the periosteum to pull on the bone for movement of the skeleton. In other places, the mysia may fuse with a broad, tendon-like sheet called an aponeurosis, or to fascia, the connective tissue between skin and bones. The broad sheet of connective tissue in the lower back that the latissimus dorsi muscles (the “lats”) fuse into is an example of an aponeurosis.
Every skeletal muscle is also richly supplied by blood vessels for nourishment, oxygen delivery, and waste removal. In addition, every muscle fiber in a skeletal muscle is supplied by the axon branch of a somatic motor neuron, which signals the fiber to contract. Unlike cardiac and smooth muscle, the only way to functionally contract a skeletal muscle is through signaling from the nervous system.
Skeletal Muscle Fibers
Because skeletal muscle cells are long and cylindrical, they are commonly referred to as muscle fibers. Skeletal muscle fibers can be quite large for human cells, with diameters up to 100 μm and lengths up to 30 cm (11.8 in) in the Sartorius of the upper leg. During early development, embryonic myoblasts, each with its own nucleus, fuse with up to hundreds of other myoblasts to form the multinucleated skeletal muscle fibers. Multiple nuclei mean multiple copies of genes, permitting the production of the large amounts of proteins and enzymes needed for muscle contraction.
Some other terminology associated with muscle fibers is rooted in the Greek sarco, which means “flesh.” The plasma membrane of muscle fibers is called the sarcolemma, the cytoplasm is referred to as sarcoplasm, and the specialized smooth endoplasmic reticulum, which stores, releases, and retrieves calcium ions (Ca++) is called the sarcoplasmic reticulum (SR)(Figure 10.4). As will soon be described, the functional unit of a skeletal muscle fiber is the sarcomere, a highly organized arrangement of the contractile myofilaments actin (thin filament) and myosin (thick filament), along with other support proteins.
Figure 10.4 Muscle Fiber A skeletal muscle fiber is surrounded by a plasma membrane called the sarcolemma, which contains sarcoplasm, the cytoplasm of muscle cells. A muscle fiber is composed of many fibrils, which give the cell its striated appearance.
The Sarcomere
The striated appearance of skeletal muscle fibers is due to the arrangement of the myofilaments of actin and myosin in sequential order from one end of the muscle fiber to the other. Each packet of these microfilaments and their regulatory proteins, troponin and tropomyosin (along with other proteins) is called a sarcomere.
INTERACTIVE LINK
Watch this video to learn more about macro- and microstructures of skeletal muscles. (a) What are the names of the “junction points” between sarcomeres? (b) What are the names of the “subunits” within the myofibrils that run the length of skeletal muscle fibers? (c) What is the “double strand of pearls” described in the video? (d) What gives a skeletal muscle fiber its striated appearance?
The sarcomere is the functional unit of the muscle fiber. The sarcomere itself is bundled within the myofibril that runs the entire length of the muscle fiber and attaches to the sarcolemma at its end. As myofibrils contract, the entire muscle cell contracts. Because myofibrils are only approximately 1.2 μm in diameter, hundreds to thousands (each with thousands of sarcomeres) can be found inside one muscle fiber. Each sarcomere is approximately 2 μm in length with a three-dimensional cylinder-like arrangement and is bordered by structures called Z-discs (also called Z-lines, because pictures are two-dimensional), to which the actin myofilaments are anchored (Figure 10.5). Because the actin and its troponin-tropomyosin complex (projecting from the Z-discs toward the center of the sarcomere) form strands that are thinner than the myosin, it is called the thin filament of the sarcomere. Likewise, because the myosin strands and their multiple heads (projecting from the center of the sarcomere, toward but not all to way to, the Z-discs) have more mass and are thicker, they are called the thick filament of the sarcomere.
Figure 10.5 The Sarcomere The sarcomere, the region from one Z-line to the next Z-line, is the functional unit of a skeletal muscle fiber.
The Neuromuscular Junction
Another specialization of the skeletal muscle is the site where a motor neuron’s terminal meets the muscle fiber—called the neuromuscular junction (NMJ). This is where the muscle fiber first responds to signaling by the motor neuron. Every skeletal muscle fiber in every skeletal muscle is innervated by a motor neuron at the NMJ. Excitation signals from the neuron are the only way to functionally activate the fiber to contract.
INTERACTIVE LINK
Every skeletal muscle fiber is supplied by a motor neuron at the NMJ. Watch this video to learn more about what happens at the NMJ. (a) What is the definition of a motor unit? (b) What is the structural and functional difference between a large motor unit and a small motor unit? (c) Can you give an example of each? (d) Why is the neurotransmitter acetylcholine degraded after binding to its receptor?
Excitation-Contraction Coupling
All living cells have membrane potentials, or electrical gradients across their membranes. The inside of the membrane is usually around -60 to -90 mV, relative to the outside. This is referred to as a cell’s membrane potential. Neurons and muscle cells can use their membrane potentials to generate electrical signals. They do this by controlling the movement of charged particles, called ions, across their membranes to create electrical currents. This is achieved by opening and closing specialized proteins in the membrane called ion channels. Although the currents generated by ions moving through these channel proteins are very small, they form the basis of both neural signaling and muscle contraction.
Both neurons and skeletal muscle cells are electrically excitable, meaning that they are able to generate action potentials. An action potential is a special type of electrical signal that can travel along a cell membrane as a wave. This allows a signal to be transmitted quickly and faithfully over long distances.
Although the term excitation-contraction coupling confuses or scares some students, it comes down to this: for a skeletal muscle fiber to contract, its membrane must first be “excited”—in other words, it must be stimulated to fire an action potential. The muscle fiber action potential, which sweeps along the sarcolemma as a wave, is “coupled” to the actual contraction through the release of calcium ions (Ca++) from the SR. Once released, the Ca++ interacts with the shielding proteins, forcing them to move aside so that the actin-binding sites are available for attachment by myosin heads. The myosin then pulls the actin filaments toward the center, shortening the muscle fiber.
In skeletal muscle, this sequence begins with signals from the somatic motor division of the nervous system. In other words, the “excitation” step in skeletal muscles is always triggered by signaling from the nervous system (Figure 10.6).
Figure 10.6 Motor End-Plate and Innervation At the NMJ, the axon terminal releases ACh. The motor end-plate is the location of the ACh-receptors in the muscle fiber sarcolemma. When ACh molecules are released, they diffuse across a minute space called the synaptic cleft and bind to the receptors.
The motor neurons that tell the skeletal muscle fibers to contract originate in the spinal cord, with a smaller number located in the brainstem for activation of skeletal muscles of the face, head, and neck. These neurons have long processes, called axons, which are specialized to transmit action potentials long distances— in this case, all the way from the spinal cord to the muscle itself (which may be up to three feet away). The axons of multiple neurons bundle together to form nerves, like wires bundled together in a cable.
Signaling begins when a neuronal action potential travels along the axon of a motor neuron, and then along the individual branches to terminate at the NMJ. At the NMJ, the axon terminal releases a chemical messenger, or neurotransmitter, called acetylcholine (ACh). The ACh molecules diffuse across a minute space called the synaptic cleft and bind to ACh receptors located within the motor end-plate of the sarcolemma on the other side of the synapse. Once ACh binds, a channel in the ACh receptor opens and positively charged ions can pass through into the muscle fiber, causing it to depolarize, meaning that the membrane potential of the muscle fiber becomes less negative (closer to zero.)
As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered to open. Sodium ions enter the muscle fiber, and an action potential rapidly spreads (or “fires”) along the entire membrane to initiate excitation-contraction coupling.
Things happen very quickly in the world of excitable membranes (just think about how quickly you can snap your fingers as soon as you decide to do it). Immediately following depolarization of the membrane, it repolarizes, re-establishing the negative membrane potential. Meanwhile, the ACh in the synaptic cleft is degraded by the enzyme acetylcholinesterase (AChE) so that the ACh cannot rebind to a receptor and reopen its channel, which would cause unwanted extended muscle excitation and contraction.
Propagation of an action potential along the sarcolemma is the excitation portion of excitation-contraction coupling. Recall that this excitation actually triggers the release of calcium ions (Ca++) from its storage in the cell’s SR. For the action potential to reach the membrane of the SR, there are periodic invaginations in the sarcolemma, called T-tubules (“T” stands for “transverse”). You will recall that the diameter of a muscle fiber can be up to 100 μm, so these T-tubules ensure that the membrane can get close to the SR in the sarcoplasm. The arrangement of a T-tubule with the membranes of SR on either side is called a triad (Figure 10.7). The triad surrounds the cylindrical structure called a myofibril, which contains actin and myosin.
Figure 10.7 The T-tubule Narrow T-tubules permit the conduction of electrical impulses. The SR functions to regulate intracellular levels of calcium. Two terminal cisternae (where enlarged SR connects to the T-tubule) and one T-tubule comprise a triad—a “threesome” of membranes, with those of SR on two sides and the T-tubule sandwiched between them.
The T-tubules carry the action potential into the interior of the cell, which triggers the opening of calcium channels in the membrane of the adjacent SR, causing Ca++ to diffuse out of the SR and into the sarcoplasm. It is the arrival of Ca++ in the sarcoplasm that initiates contraction of the muscle fiber by its contractile units, or sarcomeres.
Muscle Fiber Contraction and Relaxation
- Describe the components involved in a muscle contraction
- Explain how muscles contract and relax
- Describe the sliding filament model of muscle contraction
The sequence of events that result in the contraction of an individual muscle fiber begins with a signal—the neurotransmitter, ACh—from the motor neuron innervating that fiber. The local membrane of the fiber will depolarize as positively charged sodium ions (Na+) enter, triggering an action potential that spreads to the rest of the membrane which will depolarize, including the T-tubules. This triggers the release of calcium ions (Ca++) from storage in the sarcoplasmic reticulum (SR). The Ca++ then initiates contraction, which is sustained by ATP (Figure 10.8). As long as Ca++ ions remain in the sarcoplasm to bind to troponin, which keeps the actin-binding sites “unshielded,” and as long as ATP is available to drive the cross-bridge cycling and the pulling of actin strands by myosin, the muscle fiber will continue to shorten to an anatomical limit.
Figure 10.8 Contraction of a Muscle Fiber A cross-bridge forms between actin and the myosin heads triggering contraction. As long as Ca++ ions remain in the sarcoplasm to bind to troponin, and as long as ATP is available, the muscle fiber will continue to shorten.
Muscle contraction usually stops when signaling from the motor neuron ends, which repolarizes the sarcolemma and T-tubules, and closes the voltage-gated calcium channels in the SR. Ca++ ions are then pumped back into the SR, which causes the tropomyosin to reshield (or re-cover) the binding sites on the actin strands. A muscle also can stop contracting when it runs out of ATP and becomes fatigued (Figure 10.9).
Figure 10.9 Relaxation of a Muscle Fiber Ca++ ions are pumped back into the SR, which causes the tropomyosin to reshield the binding sites on the actin strands. A muscle may also stop contracting when it runs out of ATP and becomes fatigued.
INTERACTIVE LINK
The release of calcium ions initiates muscle contractions. Watch this video to learn more about the role of calcium. (a) What are “T-tubules” and what is their role? (b) Please describe how actin-binding sites are made available for cross-bridging with myosin heads during contraction.
The molecular events of muscle fiber shortening occur within the fiber’s sarcomeres (see Figure 10.10). The contraction of a striated muscle fiber occurs as the sarcomeres, linearly arranged within myofibrils, shorten as myosin heads pull on the actin filaments.
The region where thick and thin filaments overlap has a dense appearance, as there is little space between the filaments. This zone where thin and thick filaments overlap is very important to muscle contraction, as it is the site where filament movement starts. Thin filaments, anchored at their ends by the Z-discs, do not extend completely into the central region that only contains thick filaments, anchored at their bases at a spot called the M-line. A myofibril is composed of many sarcomeres running along its length; thus, myofibrils and muscle cells contract as the sarcomeres contract.
The Sliding Filament Model of Contraction
When signaled by a motor neuron, a skeletal muscle fiber contracts as the thin filaments are pulled and then slide past the thick filaments within the fiber’s sarcomeres. This process is known as the sliding filament model of muscle contraction (Figure 10.10). The sliding can only occur when myosin-binding sites on the actin filaments are exposed by a series of steps that begins with Ca++ entry into the sarcoplasm.
Figure 10.10 The Sliding Filament Model of Muscle Contraction When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap completely.
Tropomyosin is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin. Tropomyosin binds to troponin to form a troponin-tropomyosin complex. The troponin-tropomyosin complex prevents the myosin “heads” from binding to the active sites on the actin microfilaments. Troponin also has a binding site for Ca++ ions.
To initiate muscle contraction, tropomyosin has to expose the myosin-binding site on an actin filament to allow cross-bridge formation between the actin and myosin microfilaments. The first step in the process of contraction is for Ca++ to bind to troponin so that tropomyosin can slide away from the binding sites on the actin strands. This allows the myosin heads to bind to these exposed binding sites and form cross-bridges. The thin filaments are then pulled by the myosin heads to slide past the thick filaments toward the center of the sarcomere. But each head can only pull a very short distance before it has reached its limit and must be “re-cocked” before it can pull again, a step that requires ATP.
ATP and Muscle Contraction
For thin filaments to continue to slide past thick filaments during muscle contraction, myosin heads must pull the actin at the binding sites, detach, re-cock, attach to more binding sites, pull, detach, re-cock, etc. This repeated movement is known as the cross-bridge cycle. This motion of the myosin heads is similar to the oars when an individual rows a boat: The paddle of the oars (the myosin heads) pull, are lifted from the water (detach), repositioned (re-cocked) and then immersed again to pull (Figure 10.11). Each cycle requires energy, and the action of the myosin heads in the sarcomeres repetitively pulling on the thin filaments also requires energy, which is provided by ATP.
Figure 10.11 Skeletal Muscle Contraction (a) The active site on actin is exposed as calcium binds to troponin. (b) The myosin head is attracted to actin, and myosin binds actin at its actin-binding site, forming the cross-bridge. (c) During the power stroke, the phosphate generated in the previous contraction cycle is released. This results in the myosin head pivoting toward the center of the sarcomere, after which the attached ADP and phosphate group are released. (d) A new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach. (e) The myosin head hydrolyzes ATP to ADP and phosphate, which returns the myosin to the cocked position.
Cross-bridge formation occurs when the myosin head attaches to the actin while adenosine diphosphate (ADP) and inorganic phosphate (Pi) are still bound to myosin (Figure 10.11a,b). Pi is then released, causing myosin to form a stronger attachment to the actin, after which the myosin head moves toward the M-line, pulling the actin along with it. As actin is pulled, the filaments move approximately 10 nm toward the M-line. This movement is called the power stroke, as movement of the thin filament occurs at this step (Figure 10.11c). In the absence of ATP, the myosin head will not detach from actin.
One part of the myosin head attaches to the binding site on the actin, but the head has another binding site for ATP. ATP binding causes the myosin head to detach from the actin (Figure 10.11d). After this occurs, ATP is converted to ADP and Pi by the intrinsic ATPase activity of myosin. The energy released during ATP hydrolysis changes the angle of the myosin head into a cocked position (Figure 10.11e). The myosin head is now in position for further movement.
When the myosin head is cocked, myosin is in a high-energy configuration. This energy is expended as the myosin head moves through the power stroke, and at the end of the power stroke, the myosin head is in a low-energy position. After the power stroke, ADP is released; however, the formed cross-bridge is still in place, and actin and myosin are bound together. As long as ATP is available, it readily attaches to myosin, the cross-bridge cycle can recur, and muscle contraction can continue.
Note that each thick filament of roughly 300 myosin molecules has multiple myosin heads, and many cross-bridges form and break continuously during muscle contraction. Multiply this by all of the sarcomeres in one myofibril, all the myofibrils in one muscle fiber, and all of the muscle fibers in one skeletal muscle, and you can understand why so much energy (ATP) is needed to keep skeletal muscles working. In fact, it is the loss of ATP that results in the rigor mortis observed soon after someone dies. With no further ATP production possible, there is no ATP available for myosin heads to detach from the actin-binding sites, so the cross-bridges stay in place, causing the rigidity in the skeletal muscles.
Sources of ATP
ATP supplies the energy for muscle contraction to take place. In addition to its direct role in the cross-bridge cycle, ATP also provides the energy for the active-transport Ca++ pumps in the SR. Muscle contraction does not occur without sufficient amounts of ATP. The amount of ATP stored in muscle is very low, only sufficient to power a few seconds worth of contractions. As it is broken down, ATP must therefore be regenerated and replaced quickly to allow for sustained contraction. There are three mechanisms by which ATP can be regenerated: creatine phosphate metabolism, anaerobic glycolysis, and fermentation and aerobic respiration.
Creatine phosphate is a molecule that can store energy in its phosphate bonds. In a resting muscle, excess ATP transfers its energy to creatine, producing ADP and creatine phosphate. This acts as an energy reserve that can be used to quickly create more ATP. When the muscle starts to contract and needs energy, creatine phosphate transfers its phosphate back to ADP to form ATP and creatine. This reaction is catalyzed by the enzyme creatine kinase and occurs very quickly; thus, creatine phosphate-derived ATP powers the first few seconds of muscle contraction. However, creatine phosphate can only provide approximately 15 seconds worth of energy, at which point another energy source has to be used (Figure 10.12).
Figure 10.12 Muscle Metabolism (a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.
As the ATP produced by creatine phosphate is depleted, muscles turn to glycolysis as an ATP source. Glycolysis is an anaerobic (non-oxygen-dependent) process that breaks down glucose (sugar) to produce ATP; however, glycolysis cannot generate ATP as quickly as creatine phosphate. Thus, the switch to glycolysis results in a slower rate of ATP availability to the muscle. The sugar used in glycolysis can be provided by blood glucose or by metabolizing glycogen that is stored in the muscle. The breakdown of one glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or when oxygen levels are low, converted to lactic acid (Figure 10.12b).
If oxygen is available, pyruvic acid is used in aerobic respiration. However, if oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This conversion allows the recycling of the enzyme NAD+ from NADH, which is needed for glycolysis to continue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. Glycolysis itself cannot be sustained for very long (approximately 1 minute of muscle activity), but it is useful in facilitating short bursts of high-intensity output. This is because glycolysis does not utilize glucose very efficiently, producing a net gain of two ATPs per molecule of glucose, and the end product of lactic acid, which may contribute to muscle fatigue as it accumulates.
Aerobic respiration is the breakdown of glucose or other nutrients in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria. The inputs for aerobic respiration include glucose circulating in the bloodstream, pyruvic acid, and fatty acids. Aerobic respiration is much more efficient than anaerobic glycolysis, producing approximately 36 ATPs per molecule of glucose versus four from glycolysis. However, aerobic respiration cannot be sustained without a steady supply of O2 to the skeletal muscle and is much slower (Figure 10.12c). To compensate, muscles store small amount of excess oxygen in proteins call myoglobin, allowing for more efficient muscle contractions and less fatigue. Aerobic training also increases the efficiency of the circulatory system so that O2 can be supplied to the muscles for longer periods of time.
Muscle fatigue occurs when a muscle can no longer contract in response to signals from the nervous system. The exact causes of muscle fatigue are not fully known, although certain factors have been correlated with the decreased muscle contraction that occurs during fatigue. ATP is needed for normal muscle contraction, and as ATP reserves are reduced, muscle function may decline. This may be more of a factor in brief, intense muscle output rather than sustained, lower intensity efforts. Lactic acid buildup may lower intracellular pH, affecting enzyme and protein activity. Imbalances in Na+ and K+ levels as a result of membrane depolarization may disrupt Ca++ flow out of the SR. Long periods of sustained exercise may damage the SR and the sarcolemma, resulting in impaired Ca++ regulation.
Intense muscle activity results in an oxygen debt, which is the amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction. Oxygen is required to restore ATP and creatine phosphate levels, convert lactic acid to pyruvic acid, and, in the liver, to convert lactic acid into glucose or glycogen. Other systems used during exercise also require oxygen, and all of these combined processes result in the increased breathing rate that occurs after exercise. Until the oxygen debt has been met, oxygen intake is elevated, even after exercise has stopped.
Relaxation of a Skeletal Muscle
Relaxing skeletal muscle fibers, and ultimately, the skeletal muscle, begins with the motor neuron, which stops releasing its chemical signal, ACh, into the synapse at the NMJ. The muscle fiber will repolarize, which closes the gates in the SR where Ca++ was being released. ATP-driven pumps will move Ca++ out of the sarcoplasm back into the SR. This results in the “reshielding” of the actin-binding sites on the thin filaments. Without the ability to form cross-bridges between the thin and thick filaments, the muscle fiber loses its tension and relaxes.
Muscle Strength
The number of skeletal muscle fibers in a given muscle is genetically determined and does not change. Muscle strength is directly related to the amount of myofibrils and sarcomeres within each fiber. Factors, such as hormones and stress (and artificial anabolic steroids), acting on the muscle can increase the production of sarcomeres and myofibrils within the muscle fibers, a change called hypertrophy, which results in the increased mass and bulk in a skeletal muscle. Likewise, decreased use of a skeletal muscle results in atrophy, where the number of sarcomeres and myofibrils disappear (but not the number of muscle fibers). It is common for a limb in a cast to show atrophied muscles when the cast is removed, and certain diseases, such as polio, show atrophied muscles.
DISORDERS OF THE...
Muscular System
Duchenne muscular dystrophy (DMD) is a progressive weakening of the skeletal muscles. It is one of several diseases collectively referred to as “muscular dystrophy.” DMD is caused by a lack of the protein dystrophin, which helps the thin filaments of myofibrils bind to the sarcolemma. Without sufficient dystrophin, muscle contractions cause the sarcolemma to tear, causing an influx of Ca++, leading to cellular damage and muscle fiber degradation. Over time, as muscle damage accumulates, muscle mass is lost, and greater functional impairments develop.
DMD is an inherited disorder caused by an abnormal X chromosome. It primarily affects males, and it is usually diagnosed in early childhood. DMD usually first appears as difficulty with balance and motion, and then progresses to an inability to walk. It continues progressing upward in the body from the lower extremities to the upper body, where it affects the muscles responsible for breathing and circulation. It ultimately causes death due to respiratory failure, and those afflicted do not usually live past their 20s.
Because DMD is caused by a mutation in the gene that codes for dystrophin, it was thought that introducing healthy myoblasts into patients might be an effective treatment. Myoblasts are the embryonic cells responsible for muscle development, and ideally, they would carry healthy genes that could produce the dystrophin needed for normal muscle contraction. This approach has been largely unsuccessful in humans. A recent approach has involved attempting to boost the muscle’s production of utrophin, a protein similar to dystrophin that may be able to assume the role of dystrophin and prevent cellular damage from occurring.
Nervous System Control of Muscle Tension
- Explain concentric, isotonic, and eccentric contractions
- Describe the length-tension relationship
- Describe the three phases of a muscle twitch
- Define wave summation, tetanus, and treppe
To move an object, referred to as load, the sarcomeres in the muscle fibers of the skeletal muscle must shorten. The force generated by the contraction of the muscle (or shortening of the sarcomeres) is called muscle tension. However, muscle tension also is generated when the muscle is contracting against a load that does not move, resulting in two main types of skeletal muscle contractions: isotonic contractions and isometric contractions.
In isotonic contractions, where the tension in the muscle stays constant, a load is moved as the length of the muscle changes (shortens). There are two types of isotonic contractions: concentric and eccentric. A concentric contraction involves the muscle shortening to move a load. An example of this is the biceps brachii muscle contracting when a hand weight is brought upward with increasing muscle tension. As the biceps brachii contract, the angle of the elbow joint decreases as the forearm is brought toward the body. Here, the biceps brachii contracts as sarcomeres in its muscle fibers are shortening and cross-bridges form; the myosin heads pull the actin. An eccentric contraction occurs as the muscle tension diminishes and the muscle lengthens. In this case, the hand weight is lowered in a slow and controlled manner as the amount of cross-bridges being activated by nervous system stimulation decreases. In this case, as tension is released from the biceps brachii, the angle of the elbow joint increases. Eccentric contractions are also used for movement and balance of the body.
An isometric contraction occurs as the muscle produces tension without changing the angle of a skeletal joint. Isometric contractions involve sarcomere shortening and increasing muscle tension, but do not move a load, as the force produced cannot overcome the resistance provided by the load. For example, if one attempts to lift a hand weight that is too heavy, there will be sarcomere activation and shortening to a point, and ever-increasing muscle tension, but no change in the angle of the elbow joint. In everyday living, isometric contractions are active in maintaining posture and maintaining bone and joint stability. However, holding your head in an upright position occurs not because the muscles cannot move the head, but because the goal is to remain stationary and not produce movement. Most actions of the body are the result of a combination of isotonic and isometric contractions working together to produce a wide range of outcomes (Figure 10.13).
Figure 10.13 Types of Muscle Contractions During isotonic contractions, muscle length changes to move a load. During isometric contractions, muscle length does not change because the load exceeds the tension the muscle can generate.
All of these muscle activities are under the exquisite control of the nervous system. Neural control regulates concentric, eccentric and isometric contractions, muscle fiber recruitment, and muscle tone. A crucial aspect of nervous system control of skeletal muscles is the role of motor units.
Motor Units
As you have learned, every skeletal muscle fiber must be innervated by the axon terminal of a motor neuron in order to contract. Each muscle fiber is innervated by only one motor neuron. The actual group of muscle fibers in a muscle innervated by a single motor neuron is called a motor unit. The size of a motor unit is variable depending on the nature of the muscle.
A small motor unit is an arrangement where a single motor neuron supplies a small number of muscle fibers in a muscle. Small motor units permit very fine motor control of the muscle. The best example in humans is the small motor units of the extraocular eye muscles that move the eyeballs. There are thousands of muscle fibers in each muscle, but every six or so fibers are supplied by a single motor neuron, as the axons branch to form synaptic connections at their individual NMJs. This allows for exquisite control of eye movements so that both eyes can quickly focus on the same object. Small motor units are also involved in the many fine movements of the fingers and thumb of the hand for grasping, texting, etc.
A large motor unit is an arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle. Large motor units are concerned with simple, or “gross,” movements, such as powerfully extending the knee joint. The best example is the large motor units of the thigh muscles or back muscles, where a single motor neuron will supply thousands of muscle fibers in a muscle, as its axon splits into thousands of branches.
There is a wide range of motor units within many skeletal muscles, which gives the nervous system a wide range of control over the muscle. The small motor units in the muscle will have smaller, lower-threshold motor neurons that are more excitable, firing first to their skeletal muscle fibers, which also tend to be the smallest. Activation of these smaller motor units, results in a relatively small degree of contractile strength (tension) generated in the muscle. As more strength is needed, larger motor units, with bigger, higher-threshold motor neurons are enlisted to activate larger muscle fibers. This increasing activation of motor units produces an increase in muscle contraction known as recruitment. As more motor units are recruited, the muscle contraction grows progressively stronger. In some muscles, the largest motor units may generate a contractile force of 50 times more than the smallest motor units in the muscle. This allows a feather to be picked up using the biceps brachii arm muscle with minimal force, and a heavy weight to be lifted by the same muscle by recruiting the largest motor units.
When necessary, the maximal number of motor units in a muscle can be recruited simultaneously, producing the maximum force of contraction for that muscle, but this cannot last for very long because of the energy requirements to sustain the contraction. To prevent complete muscle fatigue, motor units are generally not all simultaneously active, but instead some motor units rest while others are active, which allows for longer muscle contractions. The nervous system uses recruitment as a mechanism to efficiently utilize a skeletal muscle.
The Length-Tension Range of a Sarcomere
When a skeletal muscle fiber contracts, myosin heads attach to actin to form cross-bridges followed by the thin filaments sliding over the thick filaments as the heads pull the actin, and this results in sarcomere shortening, creating the tension of the muscle contraction. The cross-bridges can only form where thin and thick filaments already overlap, so that the length of the sarcomere has a direct influence on the force generated when the sarcomere shortens. This is called the length-tension relationship.
The ideal length of a sarcomere to produce maximal tension occurs at 80 percent to 120 percent of its resting length, with 100 percent being the state where the medial edges of the thin filaments are just at the most-medial myosin heads of the thick filaments (Figure 10.14). This length maximizes the overlap of actin-binding sites and myosin heads. If a sarcomere is stretched past this ideal length (beyond 120 percent), thick and thin filaments do not overlap sufficiently, which results in less tension produced. If a sarcomere is shortened beyond 80 percent, the zone of overlap is reduced with the thin filaments jutting beyond the last of the myosin heads and shrinks the H zone, which is normally composed of myosin tails. Eventually, there is nowhere else for the thin filaments to go and the amount of tension is diminished. If the muscle is stretched to the point where thick and thin filaments do not overlap at all, no cross-bridges can be formed, and no tension is produced in that sarcomere. This amount of stretching does not usually occur, as accessory proteins and connective tissue oppose extreme stretching.
Figure 10.14 The Ideal Length of a Sarcomere Sarcomeres produce maximal tension when thick and thin filaments overlap between about 80 percent to 120 percent.
The Frequency of Motor Neuron Stimulation
A single action potential from a motor neuron will produce a single contraction in the muscle fibers of its motor unit. This isolated contraction is called a twitch. A twitch can last for a few milliseconds or 100 milliseconds, depending on the muscle type. The tension produced by a single twitch can be measured by a myogram, an instrument that measures the amount of tension produced over time (Figure 10.15). Each twitch undergoes three phases. The first phase is the latent period, during which the action potential is being propagated along the sarcolemma and Ca++ ions are released from the SR. This is the phase during which excitation and contraction are being coupled but contraction has yet to occur. The contraction phase occurs next. The Ca++ ions in the sarcoplasm have bound to troponin, tropomyosin has shifted away from actin-binding sites, cross-bridges formed, and sarcomeres are actively shortening to the point of peak tension. The last phase is the relaxation phase, when tension decreases as contraction stops. Ca++ ions are pumped out of the sarcoplasm into the SR, and cross-bridge cycling stops, returning the muscle fibers to their resting state.
Figure 10.15 A Myogram of a Muscle Twitch A single muscle twitch has a latent period, a contraction phase when tension increases, and a relaxation phase when tension decreases. During the latent period, the action potential is being propagated along the sarcolemma. During the contraction phase, Ca++ ions in the sarcoplasm bind to troponin, tropomyosin moves from actin-binding sites, cross-bridges form, and sarcomeres shorten. During the relaxation phase, tension decreases as Ca++ ions are pumped out of the sarcoplasm and cross-bridge cycling stops.
Although a person can experience a muscle “twitch,” a single twitch does not produce any significant muscle activity in a living body. A series of action potentials to the muscle fibers is necessary to produce a muscle contraction that can produce work. Normal muscle contraction is more sustained, and it can be modified by input from the nervous system to produce varying amounts of force; this is called a graded muscle response. The frequency of action potentials (nerve impulses) from a motor neuron and the number of motor neurons transmitting action potentials both affect the tension produced in skeletal muscle.
The rate at which a motor neuron fires action potentials affects the tension produced in the skeletal muscle. If the fibers are stimulated while a previous twitch is still occurring, the second twitch will be stronger. This response is called wave summation, because the excitation-contraction coupling effects of successive motor neuron signaling is summed, or added together (Figure 10.16a). At the molecular level, summation occurs because the second stimulus triggers the release of more Ca++ ions, which become available to activate additional sarcomeres while the muscle is still contracting from the first stimulus. Summation results in greater contraction of the motor unit.
Figure 10.16 Wave Summation and Tetanus (a) The excitation-contraction coupling effects of successive motor neuron signaling is added together which is referred to as wave summation. The bottom of each wave, the end of the relaxation phase, represents the point of stimulus. (b) When the stimulus frequency is so high that the relaxation phase disappears completely, the contractions become continuous; this is called tetanus.
If the frequency of motor neuron signaling increases, summation and subsequent muscle tension in the motor unit continues to rise until it reaches a peak point. The tension at this point is about three to four times greater than the tension of a single twitch, a state referred to as incomplete tetanus. During incomplete tetanus, the muscle goes through quick cycles of contraction with a short relaxation phase for each. If the stimulus frequency is so high that the relaxation phase disappears completely, contractions become continuous in a process called complete tetanus (Figure 10.16b).
During tetanus, the concentration of Ca++ ions in the sarcoplasm allows virtually all of the sarcomeres to form cross-bridges and shorten, so that a contraction can continue uninterrupted (until the muscle fatigues and can no longer produce tension).
Treppe
When a skeletal muscle has been dormant for an extended period and then activated to contract, with all other things being equal, the initial contractions generate about one-half the force of later contractions. The muscle tension increases in a graded manner that to some looks like a set of stairs. This tension increase is called treppe, a condition where muscle contractions become more efficient. It’s also known as the “staircase effect” (Figure 10.17).
Figure 10.17 Treppe When muscle tension increases in a graded manner that looks like a set of stairs, it is called treppe. The bottom of each wave represents the point of stimulus.
It is believed that treppe results from a higher concentration of Ca++ in the sarcoplasm resulting from the steady stream of signals from the motor neuron. It can only be maintained with adequate ATP.
Muscle Tone
Skeletal muscles are rarely completely relaxed, or flaccid. Even if a muscle is not producing movement, it is contracted a small amount to maintain its contractile proteins and produce muscle tone. The tension produced by muscle tone allows muscles to continually stabilize joints and maintain posture.
Muscle tone is accomplished by a complex interaction between the nervous system and skeletal muscles that results in the activation of a few motor units at a time, most likely in a cyclical manner. In this manner, muscles never fatigue completely, as some motor units can recover while others are active.
The absence of the low-level contractions that lead to muscle tone is referred to as hypotonia, and can result from damage to parts of the central nervous system (CNS), such as the cerebellum, or from loss of innervations to a skeletal muscle, as in poliomyelitis. Hypotonic muscles have a flaccid appearance and display functional impairments, such as weak reflexes. Conversely, excessive muscle tone is referred to as hypertonia, accompanied by hyperreflexia (excessive reflex responses), often the result of damage to upper motor neurons in the CNS. Hypertonia can present with muscle rigidity (as seen in Parkinson’s disease) or spasticity, a phasic change in muscle tone, where a limb will “snap” back from passive stretching (as seen in some strokes).
Types of Muscle Fibers
- Describe the types of skeletal muscle fibers
- Explain fast and slow muscle fibers
Two criteria to consider when classifying the types of muscle fibers are how fast some fibers contract relative to others, and how fibers produce ATP. Using these criteria, there are three main types of skeletal muscle fibers. Slow oxidative (SO) fibers contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP. Fast oxidative (FO) fibers have fast contractions and primarily use aerobic respiration, but because they may switch to anaerobic respiration (glycolysis), can fatigue more quickly than SO fibers. Lastly, fast glycolytic (FG) fibers have fast contractions and primarily use anaerobic glycolysis. The FG fibers fatigue more quickly than the others. Most skeletal muscles in a human contain(s) all three types, although in varying proportions.
The speed of contraction is dependent on how quickly myosin’s ATPase hydrolyzes ATP to produce cross-bridge action. Fast fibers hydrolyze ATP approximately twice as quickly as slow fibers, resulting in much quicker cross-bridge cycling (which pulls the thin filaments toward the center of the sarcomeres at a faster rate). The primary metabolic pathway used by a muscle fiber determines whether the fiber is classified as oxidative or glycolytic. If a fiber primarily produces ATP through aerobic pathways it is oxidative. More ATP can be produced during each metabolic cycle, making the fiber more resistant to fatigue. Glycolytic fibers primarily create ATP through anaerobic glycolysis, which produces less ATP per cycle. As a result, glycolytic fibers fatigue at a quicker rate.
The oxidative fibers contain many more mitochondria than the glycolytic fibers, because aerobic metabolism, which uses oxygen (O2) in the metabolic pathway, occurs in the mitochondria. The SO fibers possess a large number of mitochondria and are capable of contracting for longer periods because of the large amount of ATP they can produce, but they have a relatively small diameter and do not produce a large amount of tension. SO fibers are extensively supplied with blood capillaries to supply O2 from the red blood cells in the bloodstream. The SO fibers also possess myoglobin, an O2-carrying molecule similar to O2-carrying hemoglobin in the red blood cells. The myoglobin stores some of the needed O2 within the fibers themselves (and gives SO fibers their red color). All of these features allow SO fibers to produce large quantities of ATP, which can sustain muscle activity without fatiguing for long periods of time.
The fact that SO fibers can function for long periods without fatiguing makes them useful in maintaining posture, producing isometric contractions, stabilizing bones and joints, and making small movements that happen often but do not require large amounts of energy. They do not produce high tension, and thus they are not used for powerful, fast movements that require high amounts of energy and rapid cross-bridge cycling.
FO fibers are sometimes called intermediate fibers because they possess characteristics that are intermediate between fast fibers and slow fibers. They produce ATP relatively quickly, more quickly than SO fibers, and thus can produce relatively high amounts of tension. They are oxidative because they produce ATP aerobically, possess high amounts of mitochondria, and do not fatigue quickly. However, FO fibers do not possess significant myoglobin, giving them a lighter color than the red SO fibers. FO fibers are used primarily for movements, such as walking, that require more energy than postural control but less energy than an explosive movement, such as sprinting. FO fibers are useful for this type of movement because they produce more tension than SO fibers but they are more fatigue-resistant than FG fibers.
FG fibers primarily use anaerobic glycolysis as their ATP source. They have a large diameter and possess high amounts of glycogen, which is used in glycolysis to generate ATP quickly to produce high levels of tension. Because they do not primarily use aerobic metabolism, they do not possess substantial numbers of mitochondria or significant amounts of myoglobin and therefore have a white color. FG fibers are used to produce rapid, forceful contractions to make quick, powerful movements. These fibers fatigue quickly, permitting them to only be used for short periods. Most muscles possess a mixture of each fiber type. The predominant fiber type in a muscle is determined by the primary function of the muscle.
Exercise and Muscle Performance
- Describe hypertrophy and atrophy
- Explain how resistance exercise builds muscle
- Explain how performance-enhancing substances affect muscle
Physical training alters the appearance of skeletal muscles and can produce changes in muscle performance. Conversely, a lack of use can result in decreased performance and muscle appearance. Although muscle cells can change in size, new cells are not formed when muscles grow. Instead, structural proteins are added to muscle fibers in a process called hypertrophy, so cell diameter increases. The reverse, when structural proteins are lost and muscle mass decreases, is called atrophy. Age-related muscle atrophy is called sarcopenia. Cellular components of muscles can also undergo changes in response to changes in muscle use.
Endurance Exercise
Slow fibers are predominantly used in endurance exercises that require little force but involve numerous repetitions. The aerobic metabolism used by slow-twitch fibers allows them to maintain contractions over long periods. Endurance training modifies these slow fibers to make them even more efficient by producing more mitochondria to enable more aerobic metabolism and more ATP production. Endurance exercise can also increase the amount of myoglobin in a cell, as increased aerobic respiration increases the need for oxygen. Myoglobin is found in the sarcoplasm and acts as an oxygen storage supply for the mitochondria.
The training can trigger the formation of more extensive capillary networks around the fiber, a process called angiogenesis, to supply oxygen and remove metabolic waste. To allow these capillary networks to supply the deep portions of the muscle, muscle mass does not greatly increase in order to maintain a smaller area for the diffusion of nutrients and gases. All of these cellular changes result in the ability to sustain low levels of muscle contractions for greater periods without fatiguing.
The proportion of SO muscle fibers in muscle determines the suitability of that muscle for endurance, and may benefit those participating in endurance activities. Postural muscles have a large number of SO fibers and relatively few FO and FG fibers, to keep the back straight (Figure 10.18). Endurance athletes, like marathon-runners also would benefit from a larger proportion of SO fibers, but it is unclear if the most-successful marathoners are those with naturally high numbers of SO fibers, or whether the most successful marathon runners develop high numbers of SO fibers with repetitive training. Endurance training can result in overuse injuries such as stress fractures and joint and tendon inflammation.
Figure 10.18 Marathoners Long-distance runners have a large number of SO fibers and relatively few FO and FG fibers. (credit: “Tseo2”/Wikimedia Commons)
Resistance Exercise
Resistance exercises, as opposed to endurance exercise, require large amounts of FG fibers to produce short, powerful movements that are not repeated over long periods. The high rates of ATP hydrolysis and cross-bridge formation in FG fibers result in powerful muscle contractions. Muscles used for power have a higher ratio of FG to SO/FO fibers, and trained athletes possess even higher levels of FG fibers in their muscles. Resistance exercise affects muscles by increasing the formation of myofibrils, thereby increasing the thickness of muscle fibers. This added structure causes hypertrophy, or the enlargement of muscles, exemplified by the large skeletal muscles seen in body builders and other athletes (Figure 10.19). Because this muscular enlargement is achieved by the addition of structural proteins, athletes trying to build muscle mass often ingest large amounts of protein.
Figure 10.19 Hypertrophy Body builders have a large number of FG fibers and relatively few FO and SO fibers. (credit: Lin Mei/flickr)
Except for the hypertrophy that follows an increase in the number of sarcomeres and myofibrils in a skeletal muscle, the cellular changes observed during endurance training do not usually occur with resistance training. There is usually no significant increase in mitochondria or capillary density. However, resistance training does increase the development of connective tissue, which adds to the overall mass of the muscle and helps to contain muscles as they produce increasingly powerful contractions. Tendons also become stronger to prevent tendon damage, as the force produced by muscles is transferred to tendons that attach the muscle to bone.
For effective strength training, the intensity of the exercise must continually be increased. For instance, continued weight lifting without increasing the weight of the load does not increase muscle size. To produce ever-greater results, the weights lifted must become increasingly heavier, making it more difficult for muscles to move the load. The muscle then adapts to this heavier load, and an even heavier load must be used if even greater muscle mass is desired.
If done improperly, resistance training can lead to overuse injuries of the muscle, tendon, or bone. These injuries can occur if the load is too heavy or if the muscles are not given sufficient time between workouts to recover or if joints are not aligned properly during the exercises. Cellular damage to muscle fibers that occurs after intense exercise includes damage to the sarcolemma and myofibrils. This muscle damage contributes to the feeling of soreness after strenuous exercise, but muscles gain mass as this damage is repaired, and additional structural proteins are added to replace the damaged ones. Overworking skeletal muscles can also lead to tendon damage and even skeletal damage if the load is too great for the muscles to bear.
Performance-Enhancing Substances
Some athletes attempt to boost their performance by using various agents that may enhance muscle performance. Anabolic steroids are one of the more widely known agents used to boost muscle mass and increase power output. Anabolic steroids are a form of testosterone, a male sex hormone that stimulates muscle formation, leading to increased muscle mass.
Endurance athletes may also try to boost the availability of oxygen to muscles to increase aerobic respiration by using substances such as erythropoietin (EPO), a hormone normally produced in the kidneys, which triggers the production of red blood cells. The extra oxygen carried by these blood cells can then be used by muscles for aerobic respiration. Human growth hormone (hGH) is another supplement, and although it can facilitate building muscle mass, its main role is to promote the healing of muscle and other tissues after strenuous exercise. Increased hGH may allow for faster recovery after muscle damage, reducing the rest required after exercise, and allowing for more sustained high-level performance.
Although performance-enhancing substances often do improve performance, most are banned by governing bodies in sports and are illegal for nonmedical purposes. Their use to enhance performance raises ethical issues of cheating because they give users an unfair advantage over nonusers. A greater concern, however, is that their use carries serious health risks. The side effects of these substances are often significant, nonreversible, and in some cases fatal. The physiological strain caused by these substances is often greater than what the body can handle, leading to effects that are unpredictable and dangerous. Anabolic steroid use has been linked to infertility, aggressive behavior, cardiovascular disease, and brain cancer.
Similarly, some athletes have used creatine to increase power output. Creatine phosphate provides quick bursts of ATP to muscles in the initial stages of contraction. Increasing the amount of creatine available to cells is thought to produce more ATP and therefore increase explosive power output, although its effectiveness as a supplement has been questioned.
EVERYDAY CONNECTION
Aging and Muscle Tissue
Although atrophy due to disuse can often be reversed with exercise, muscle atrophy with age, referred to as sarcopenia, is irreversible. This is a primary reason why even highly trained athletes succumb to declining performance with age. This decline is noticeable in athletes whose sports require strength and powerful movements, such as sprinting, whereas the effects of age are less noticeable in endurance athletes such as marathon runners or long-distance cyclists. As muscles age, muscle fibers die, and they are replaced by connective tissue and adipose tissue (Figure 10.20). Because those tissues cannot contract and generate force as muscle can, muscles lose the ability to produce powerful contractions. The decline in muscle mass causes a loss of strength, including the strength required for posture and mobility. This may be caused by a reduction in FG fibers that hydrolyze ATP quickly to produce short, powerful contractions. Muscles in older people sometimes possess greater numbers of SO fibers, which are responsible for longer contractions and do not produce powerful movements. There may also be a reduction in the size of motor units, resulting in fewer fibers being stimulated and less muscle tension being produced.
Figure 10.20 Atrophy Muscle mass is reduced as muscles atrophy with disuse.
Sarcopenia can be delayed to some extent by exercise, as training adds structural proteins and causes cellular changes that can offset the effects of atrophy. Increased exercise can produce greater numbers of cellular mitochondria, increase capillary density, and increase the mass and strength of connective tissue. The effects of age-related atrophy are especially pronounced in people who are sedentary, as the loss of muscle cells is displayed as functional impairments such as trouble with locomotion, balance, and posture. This can lead to a decrease in quality of life and medical problems, such as joint problems because the muscles that stabilize bones and joints are weakened. Problems with locomotion and balance can also cause various injuries due to falls.
Cardiac Muscle Tissue
- Describe intercalated discs and gap junctions
- Describe a desmosome
Cardiac muscle tissue is only found in the heart. Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Similar to skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle (Figure 10.21). However, cardiac muscle fibers are shorter than skeletal muscle fibers and usually contain only one nucleus, which is located in the central region of the cell. Cardiac muscle fibers also possess many mitochondria and myoglobin, as ATP is produced primarily through aerobic metabolism. Cardiac muscle fibers cells also are extensively branched and are connected to one another at their ends by intercalated discs. An intercalated disc allows the cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump.
Figure 10.21 Cardiac Muscle Tissue Cardiac muscle tissue is only found in the heart. LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
INTERACTIVE LINK
View the University of Michigan WebScope to explore the tissue sample in greater detail.
Intercalated discs are part of the sarcolemma and contain two structures important in cardiac muscle contraction: gap junctions and desmosomes. A gap junction forms channels between adjacent cardiac muscle fibers that allow the depolarizing current produced by cations to flow from one cardiac muscle cell to the next. This joining is called electric coupling, and in cardiac muscle it allows the quick transmission of action potentials and the coordinated contraction of the entire heart. This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium. The remainder of the intercalated disc is composed of desmosomes. A desmosome is a cell structure that anchors the ends of cardiac muscle fibers together so the cells do not pull apart during the stress of individual fibers contracting (Figure 10.22).
Figure 10.22 Cardiac Muscle Intercalated discs are part of the cardiac muscle sarcolemma and they contain gap junctions and desmosomes.
Contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate. Although cardiac muscle cannot be consciously controlled, the pacemaker cells respond to signals from the autonomic nervous system (ANS) to speed up or slow down the heart rate. The pacemaker cells can also respond to various hormones that modulate heart rate to control blood pressure.
The wave of contraction that allows the heart to work as a unit, called a functional syncytium, begins with the pacemaker cells. This group of cells is self-excitable and able to depolarize to threshold and fire action potentials on their own, a feature called autorhythmicity; they do this at set intervals which determine heart rate. Because they are connected with gap junctions to surrounding muscle fibers and the specialized fibers of the heart’s conduction system, the pacemaker cells are able to transfer the depolarization to the other cardiac muscle fibers in a manner that allows the heart to contract in a coordinated manner.
Another feature of cardiac muscle is its relatively long action potentials in its fibers, having a sustained depolarization “plateau.” The plateau is produced by Ca++ entry though voltage-gated calcium channels in the sarcolemma of cardiac muscle fibers. This sustained depolarization (and Ca++ entry) provides for a longer contraction than is produced by an action potential in skeletal muscle. Unlike skeletal muscle, a large percentage of the Ca++ that initiates contraction in cardiac muscles comes from outside the cell rather than from the SR.
Smooth Muscle
- Describe a dense body
- Explain how smooth muscle works with internal organs and passageways through the body
- Explain how smooth muscles differ from skeletal and cardiac muscles
- Explain the difference between single-unit and multi-unit smooth muscle
Smooth muscle (so-named because the cells do not have striations) is present in the walls of hollow organs like the urinary bladder, uterus, stomach, intestines, and in the walls of passageways, such as the arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive systems (Figure 10.23ab). Smooth muscle is also present in the eyes, where it functions to change the size of the iris and alter the shape of the lens; and in the skin where it causes hair to stand erect in response to cold temperature or fear.
Figure 10.23 Smooth Muscle Tissue Smooth muscle tissue is found around organs in the digestive, respiratory, reproductive tracts and the iris of the eye. LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
INTERACTIVE LINK
View the University of Michigan WebScope to explore the tissue sample in greater detail.
Smooth muscle fibers are spindle-shaped (wide in the middle and tapered at both ends, somewhat like a football) and have a single nucleus; they range from about 30 to 200 μm (thousands of times shorter than skeletal muscle fibers), and they produce their own connective tissue, endomysium. Although they do not have striations and sarcomeres, smooth muscle fibers do have actin and myosin contractile proteins, and thick and thin filaments. These thin filaments are anchored by dense bodies. A dense body is analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma. Calcium ions are supplied by the SR in the fibers and by sequestration from the extracellular fluid through membrane indentations called calveoli.
Because smooth muscle cells do not contain troponin, cross-bridge formation is not regulated by the troponin-tropomyosin complex but instead by the regulatory protein calmodulin. In a smooth muscle fiber, external Ca++ ions passing through opened calcium channels in the sarcolemma, and additional Ca++ released from SR, bind to calmodulin. The Ca++-calmodulin complex then activates an enzyme called myosin (light chain) kinase, which, in turn, activates the myosin heads by phosphorylating them (converting ATP to ADP and Pi, with the Pi attaching to the head). The heads can then attach to actin-binding sites and pull on the thin filaments. The thin filaments also are anchored to the dense bodies; the structures invested in the inner membrane of the sarcolemma (at adherens junctions) that also have cord-like intermediate filaments attached to them. When the thin filaments slide past the thick filaments, they pull on the dense bodies, structures tethered to the sarcolemma, which then pull on the intermediate filaments networks throughout the sarcoplasm. This arrangement causes the entire muscle fiber to contract in a manner whereby the ends are pulled toward the center, causing the midsection to bulge in a corkscrew motion (Figure 10.24).
Figure 10.24 Muscle Contraction The dense bodies and intermediate filaments are networked through the sarcoplasm, which cause the muscle fiber to contract.
Although smooth muscle contraction relies on the presence of Ca++ ions, smooth muscle fibers have a much smaller diameter than skeletal muscle cells. T-tubules are not required to reach the interior of the cell and therefore not necessary to transmit an action potential deep into the fiber. Smooth muscle fibers have a limited calcium-storing SR but have calcium channels in the sarcolemma (similar to cardiac muscle fibers) that open during the action potential along the sarcolemma. The influx of extracellular Ca++ ions, which diffuse into the sarcoplasm to reach the calmodulin, accounts for most of the Ca++ that triggers contraction of a smooth muscle cell.
Muscle contraction continues until ATP-dependent calcium pumps actively transport Ca++ ions back into the SR and out of the cell. However, a low concentration of calcium remains in the sarcoplasm to maintain muscle tone. This remaining calcium keeps the muscle slightly contracted, which is important in certain tracts and around blood vessels.
Because most smooth muscles must function for long periods without rest, their power output is relatively low, but contractions can continue without using large amounts of energy. Some smooth muscle can also maintain contractions even as Ca++ is removed and myosin kinase is inactivated/dephosphorylated. This can happen as a subset of cross-bridges between myosin heads and actin, called latch-bridges, keep the thick and thin filaments linked together for a prolonged period, and without the need for ATP. This allows for the maintaining of muscle “tone” in smooth muscle that lines arterioles and other visceral organs with very little energy expenditure.
Smooth muscle is not under voluntary control; thus, it is called involuntary muscle. The triggers for smooth muscle contraction include hormones, neural stimulation by the ANS, and local factors. In certain locations, such as the walls of visceral organs, stretching the muscle can trigger its contraction (the stress-relaxation response).
Axons of neurons in the ANS do not form the highly organized NMJs with smooth muscle, as seen between motor neurons and skeletal muscle fibers. Instead, there is a series of neurotransmitter-filled bulges called varicosities as an axon courses through smooth muscle, loosely forming motor units (Figure 10.25). A varicosity releases neurotransmitters into the synaptic cleft. Also, visceral muscle in the walls of the hollow organs (except the heart) contains pacesetter cells. A pacesetter cell can spontaneously trigger action potentials and contractions in the muscle.
Figure 10.25 Motor Units A series of axon-like swelling, called varicosities or “boutons,” from autonomic neurons form motor units through the smooth muscle.
Smooth muscle is organized in two ways: as single-unit smooth muscle, which is much more common; and as multiunit smooth muscle. The two types have different locations in the body and have different characteristics. Single-unit muscle has its muscle fibers joined by gap junctions so that the muscle contracts as a single unit. This type of smooth muscle is found in the walls of all visceral organs except the heart (which has cardiac muscle in its walls), and so it is commonly called visceral muscle. Because the muscle fibers are not constrained by the organization and stretchability limits of sarcomeres, visceral smooth muscle has a stress-relaxation response. This means that as the muscle of a hollow organ is stretched when it fills, the mechanical stress of the stretching will trigger contraction, but this is immediately followed by relaxation so that the organ does not empty its contents prematurely. This is important for hollow organs, such as the stomach or urinary bladder, which continuously expand as they fill. The smooth muscle around these organs also can maintain a muscle tone when the organ empties and shrinks, a feature that prevents “flabbiness” in the empty organ. In general, visceral smooth muscle produces slow, steady contractions that allow substances, such as food in the digestive tract, to move through the body.
Multiunit smooth muscle cells rarely possess gap junctions, and thus are not electrically coupled. As a result, contraction does not spread from one cell to the next, but is instead confined to the cell that was originally stimulated. Stimuli for multiunit smooth muscles come from autonomic nerves or hormones but not from stretching. This type of tissue is found around large blood vessels, in the respiratory airways, and in the eyes.
Hyperplasia in Smooth Muscle
Similar to skeletal and cardiac muscle cells, smooth muscle can undergo hypertrophy to increase in size. Unlike other muscle, smooth muscle can also divide to produce more cells, a process called hyperplasia. This can most evidently be observed in the uterus at puberty, which responds to increased estrogen levels by producing more uterine smooth muscle fibers, and greatly increases the size of the myometrium.
Development and Regeneration of Muscle Tissue
- Describe the function of satellite cells
- Define fibrosis
- Explain which muscle has the greatest regeneration ability
Most muscle tissue of the body arises from embryonic mesoderm. Paraxial mesodermal cells adjacent to the neural tube form blocks of cells called somites. Skeletal muscles, excluding those of the head and limbs, develop from mesodermal somites, whereas skeletal muscle in the head and limbs develop from general mesoderm. Somites give rise to myoblasts. A myoblast is a muscle-forming stem cell that migrates to different regions in the body and then fuse(s) to form a syncytium, or myotube. As a myotube is formed from many different myoblast cells, it contains many nuclei, but has a continuous cytoplasm. This is why skeletal muscle cells are multinucleate, as the nucleus of each contributing myoblast remains intact in the mature skeletal muscle cell. However, cardiac and smooth muscle cells are not multinucleate because the myoblasts that form their cells do not fuse.
Gap junctions develop in the cardiac and single-unit smooth muscle in the early stages of development. In skeletal muscles, ACh receptors are initially present along most of the surface of the myoblasts, but spinal nerve innervation causes the release of growth factors that stimulate the formation of motor end-plates and NMJs. As neurons become active, electrical signals that are sent through the muscle influence the distribution of slow and fast fibers in the muscle.
Although the number of muscle cells is set during development, satellite cells help to repair skeletal muscle cells. A satellite cellis similar to a myoblast because it is a type of stem cell; however, satellite cells are incorporated into muscle cells and facilitate the protein synthesis required for repair and growth. These cells are located outside the sarcolemma and are stimulated to grow and fuse with muscle cells by growth factors that are released by muscle fibers under certain forms of stress. Satellite cells can regenerate muscle fibers to a very limited extent, but they primarily help to repair damage in living cells. If a cell is damaged to a greater extent than can be repaired by satellite cells, the muscle fibers are replaced by scar tissue in a process called fibrosis. Because scar tissue cannot contract, muscle that has sustained significant damage loses strength and cannot produce the same amount of power or endurance as it could before being damaged.
Smooth muscle tissue can regenerate from a type of stem cell called a pericyte, which is found in some small blood vessels. Pericytes allow smooth muscle cells to regenerate and repair much more readily than skeletal and cardiac muscle tissue. Similar to skeletal muscle tissue, cardiac muscle does not regenerate to a great extent. Dead cardiac muscle tissue is replaced by scar tissue, which cannot contract. As scar tissue accumulates, the heart loses its ability to pump because of the loss of contractile power. However, some minor regeneration may occur due to stem cells found in the blood that occasionally enter cardiac tissue.
CAREER CONNECTION
Physical Therapist
As muscle cells die, they are not regenerated but instead are replaced by connective tissue and adipose tissue, which do not possess the contractile abilities of muscle tissue. Muscles atrophy when they are not used, and over time if atrophy is prolonged, muscle cells die. It is therefore important that those who are susceptible to muscle atrophy exercise to maintain muscle function and prevent the complete loss of muscle tissue. In extreme cases, when movement is not possible, electrical stimulation can be introduced to a muscle from an external source. This acts as a substitute for endogenous neural stimulation, stimulating the muscle to contract and preventing the loss of proteins that occurs with a lack of use.
Physiotherapists work with patients to maintain muscles. They are trained to target muscles susceptible to atrophy, and to prescribe and monitor exercises designed to stimulate those muscles. There are various causes of atrophy, including mechanical injury, disease, and age. After breaking a limb or undergoing surgery, muscle use is impaired and can lead to disuse atrophy. If the muscles are not exercised, this atrophy can lead to long-term muscle weakness. A stroke can also cause muscle impairment by interrupting neural stimulation to certain muscles. Without neural inputs, these muscles do not contract and thus begin to lose structural proteins. Exercising these muscles can help to restore muscle function and minimize functional impairments. Age-related muscle loss is also a target of physical therapy, as exercise can reduce the effects of age-related atrophy and improve muscle function.
The goal of a physiotherapist is to improve physical functioning and reduce functional impairments; this is achieved by understanding the cause of muscle impairment and assessing the capabilities of a patient, after which a program to enhance these capabilities is designed. Some factors that are assessed include strength, balance, and endurance, which are continually monitored as exercises are introduced to track improvements in muscle function. Physiotherapists can also instruct patients on the proper use of equipment, such as crutches, and assess whether someone has sufficient strength to use the equipment and when they can function without it.
Key Terms
- acetylcholine (ACh)
- neurotransmitter that binds at a motor end-plate to trigger depolarization
- actin
- protein that makes up most of the thin myofilaments in a sarcomere muscle fiber
- action potential
- change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
- aerobic respiration
- production of ATP in the presence of oxygen
- angiogenesis
- formation of blood capillary networks
- aponeurosis
- broad, tendon-like sheet of connective tissue that attaches a skeletal muscle to another skeletal muscle or to a bone
- ATPase
- enzyme that hydrolyzes ATP to ADP
- atrophy
- loss of structural proteins from muscle fibers
- autorhythmicity
- heart’s ability to control its own contractions
- calmodulin
- regulatory protein that facilitates contraction in smooth muscles
- cardiac muscle
- striated muscle found in the heart; joined to one another at intercalated discs and under the regulation of pacemaker cells, which contract as one unit to pump blood through the circulatory system. Cardiac muscle is under involuntary control.
- concentric contraction
- muscle contraction that shortens the muscle to move a load
- contractility
- ability to shorten (contract) forcibly
- contraction phase
- twitch contraction phase when tension increases
- creatine phosphate
- phosphagen used to store energy from ATP and transfer it to muscle
- dense body
- sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments
- depolarize
- to reduce the voltage difference between the inside and outside of a cell’s plasma membrane (the sarcolemma for a muscle fiber), making the inside less negative than at rest
- desmosome
- cell structure that anchors the ends of cardiac muscle fibers to allow contraction to occur
- eccentric contraction
- muscle contraction that lengthens the muscle as the tension is diminished
- elasticity
- ability to stretch and rebound
- endomysium
- loose, and well-hydrated connective tissue covering each muscle fiber in a skeletal muscle
- epimysium
- outer layer of connective tissue around a skeletal muscle
- excitability
- ability to undergo neural stimulation
- excitation-contraction coupling
- sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber’s sarcomeres
- extensibility
- ability to lengthen (extend)
- fascicle
- bundle of muscle fibers within a skeletal muscle
- fast glycolytic (FG)
- muscle fiber that primarily uses anaerobic glycolysis
- fast oxidative (FO)
- intermediate muscle fiber that is between slow oxidative and fast glycolytic fibers
- fibrosis
- replacement of muscle fibers by scar tissue
- glycolysis
- anaerobic breakdown of glucose to ATP
- graded muscle response
- modification of contraction strength
- hyperplasia
- process in which one cell splits to produce new cells
- hypertonia
- abnormally high muscle tone
- hypertrophy
- addition of structural proteins to muscle fibers
- hypotonia
- abnormally low muscle tone caused by the absence of low-level contractions
- intercalated disc
- part of the sarcolemma that connects cardiac tissue, and contains gap junctions and desmosomes
- isometric contraction
- muscle contraction that occurs with no change in muscle length
- isotonic contraction
- muscle contraction that involves changes in muscle length
- lactic acid
- product of anaerobic glycolysis
- latch-bridges
- subset of a cross-bridge in which actin and myosin remain locked together
- latent period
- the time when a twitch does not produce contraction
- motor end-plate
- sarcolemma of muscle fiber at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine
- motor unit
- motor neuron and the group of muscle fibers it innervates
- muscle tension
- force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions
- muscle tone
- low levels of muscle contraction that occur when a muscle is not producing movement
- myoblast
- muscle-forming stem cell
- myofibril
- long, cylindrical organelle that runs parallel within the muscle fiber and contains the sarcomeres
- myogram
- instrument used to measure twitch tension
- myosin
- protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fiber
- myotube
- fusion of many myoblast cells
- neuromuscular junction (NMJ)
- synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal
- neurotransmitter
- signaling chemical released by nerve terminals that bind to and activate receptors on target cells
- oxygen debt
- amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction
- pacesetter cell
- cell that triggers action potentials in smooth muscle
- pericyte
- stem cell that regenerates smooth muscle cells
- perimysium
- connective tissue that bundles skeletal muscle fibers into fascicles within a skeletal muscle
- power stroke
- action of myosin pulling actin inward (toward the M line)
- pyruvic acid
- product of glycolysis that can be used in aerobic respiration or converted to lactic acid
- recruitment
- increase in the number of motor units involved in contraction
- relaxation phase
- period after twitch contraction when tension decreases
- sarcolemma
- plasma membrane of a skeletal muscle fiber
- sarcomere
- longitudinally, repeating functional unit of skeletal muscle, with all of the contractile and associated proteins involved in contraction
- sarcopenia
- age-related muscle atrophy
- sarcoplasm
- cytoplasm of a muscle cell
- sarcoplasmic reticulum (SR)
- specialized smooth endoplasmic reticulum, which stores, releases, and retrieves Ca++
- satellite cell
- stem cell that helps to repair muscle cells
- skeletal muscle
- striated, multinucleated muscle that requires signaling from the nervous system to trigger contraction; most skeletal muscles are referred to as voluntary muscles that move bones and produce movement
- slow oxidative (SO)
- muscle fiber that primarily uses aerobic respiration
- smooth muscle
- nonstriated, mononucleated muscle in the skin that is associated with hair follicles; assists in moving materials in the walls of internal organs, blood vessels, and internal passageways
- somites
- blocks of paraxial mesoderm cells
- stress-relaxation response
- relaxation of smooth muscle tissue after being stretched
- synaptic cleft
- space between a nerve (axon) terminal and a motor end-plate
- T-tubule
- projection of the sarcolemma into the interior of the cell
- tetanus
- a continuous fused contraction
- thick filament
- the thick myosin strands and their multiple heads projecting from the center of the sarcomere toward, but not all to way to, the Z-discs
- thin filament
- thin strands of actin and its troponin-tropomyosin complex projecting from the Z-discs toward the center of the sarcomere
- treppe
- stepwise increase in contraction tension
- triad
- the grouping of one T-tubule and two terminal cisternae
- tropomyosin
- regulatory protein that covers myosin-binding sites to prevent actin from binding to myosin
- troponin
- regulatory protein that binds to actin, tropomyosin, and calcium
- twitch
- single contraction produced by one action potential
- varicosity
- enlargement of neurons that release neurotransmitters into synaptic clefts
- visceral muscle
- smooth muscle found in the walls of visceral organs
- voltage-gated sodium channels
- membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na+ enters through the channel
- wave summation
- addition of successive neural stimuli to produce greater contraction
Chapter Review
10.1 Overview of Muscle Tissues
Muscle is the tissue in animals that allows for active movement of the body or materials within the body. There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Most of the body’s skeletal muscle produces movement by acting on the skeleton. Cardiac muscle is found in the wall of the heart and pumps blood through the circulatory system.
Smooth muscle is found in the skin, where it is associated with hair follicles; it also is found in the walls of internal organs, blood vessels, and internal passageways, where it assists in moving materials.
10.2 Skeletal Muscle
Skeletal muscles contain connective tissue, blood vessels, and nerves. There are three layers of connective tissue: epimysium, perimysium, and endomysium. Skeletal muscle fibers are organized into groups called fascicles. Blood vessels and nerves enter the connective tissue and branch in the cell. Muscles attach to bones directly or through tendons or aponeuroses. Skeletal muscles maintain posture, stabilize bones and joints, control internal movement, and generate heat.
Skeletal muscle fibers are long, multinucleated cells. The membrane of the cell is the sarcolemma; the cytoplasm of the cell is the sarcoplasm. The sarcoplasmic reticulum (SR) is a form of endoplasmic reticulum. Muscle fibers are composed of myofibrils. The striations are created by the organization of actin and myosin resulting in the banding pattern of myofibrils.
10.3 Muscle Fiber Contraction and Relaxation
A sarcomere is the smallest contractile portion of a muscle. Myofibrils are composed of thick and thin filaments. Thick filaments are composed of the protein myosin; thin filaments are composed of the protein actin. Troponin and tropomyosin are regulatory proteins.
Muscle contraction is described by the sliding filament model of contraction. ACh is the neurotransmitter that binds at the neuromuscular junction (NMJ) to trigger depolarization, and an action potential travels along the sarcolemma to trigger calcium release from SR. The actin sites are exposed after Ca++ enters the sarcoplasm from its SR storage to activate the troponin-tropomyosin complex so that the tropomyosin shifts away from the sites. The cross-bridging of myposin heads docking into actin-binding sites is followed by the “power stroke”—the sliding of the thin filaments by thick filaments. The power strokes are powered by ATP. Ultimately, the sarcomeres, myofibrils, and muscle fibers shorten to produce movement.
10.4 Nervous System Control of Muscle Tension
The number of cross-bridges formed between actin and myosin determines the amount of tension produced by a muscle. The length of a sarcomere is optimal when the zone of overlap between thin and thick filaments is greatest. Muscles that are stretched or compressed too greatly do not produce maximal amounts of power. A motor unit is formed by a motor neuron and all of the muscle fibers that are innervated by that same motor neuron. A single contraction is called a twitch. A muscle twitch has a latent period, a contraction phase, and a relaxation phase. A graded muscle response allows variation in muscle tension. Summation occurs as successive stimuli are added together to produce a stronger muscle contraction. Tetanus is the fusion of contractions to produce a continuous contraction. Increasing the number of motor neurons involved increases the amount of motor units activated in a muscle, which is called recruitment. Muscle tone is the constant low-level contractions that allow for posture and stability.
10.5 Types of Muscle Fibers
ATP provides the energy for muscle contraction. The three mechanisms for ATP regeneration are creatine phosphate, anaerobic glycolysis, and aerobic metabolism. Creatine phosphate provides about the first 15 seconds of ATP at the beginning of muscle contraction. Anaerobic glycolysis produces small amounts of ATP in the absence of oxygen for a short period. Aerobic metabolism utilizes oxygen to produce much more ATP, allowing a muscle to work for longer periods. Muscle fatigue, which has many contributing factors, occurs when muscle can no longer contract. An oxygen debt is created as a result of muscle use. The three types of muscle fiber are slow oxidative (SO), fast oxidative (FO) and fast glycolytic (FG). SO fibers use aerobic metabolism to produce low power contractions over long periods and are slow to fatigue. FO fibers use aerobic metabolism to produce ATP but produce higher tension contractions than SO fibers. FG fibers use anaerobic metabolism to produce powerful, high-tension contractions but fatigue quickly.
10.6 Exercise and Muscle Performance
Hypertrophy is an increase in muscle mass due to the addition of structural proteins. The opposite of hypertrophy is atrophy, the loss of muscle mass due to the breakdown of structural proteins. Endurance exercise causes an increase in cellular mitochondria, myoglobin, and capillary networks in SO fibers. Endurance athletes have a high level of SO fibers relative to the other fiber types. Resistance exercise causes hypertrophy. Power-producing muscles have a higher number of FG fibers than of slow fibers. Strenuous exercise causes muscle cell damage that requires time to heal. Some athletes use performance-enhancing substances to enhance muscle performance. Muscle atrophy due to age is called sarcopenia and occurs as muscle fibers die and are replaced by connective and adipose tissue.
10.7 Cardiac Muscle Tissue
Cardiac muscle is striated muscle that is present only in the heart. Cardiac muscle fibers have a single nucleus, are branched, and joined to one another by intercalated discs that contain gap junctions for depolarization between cells and desmosomes to hold the fibers together when the heart contracts. Contraction in each cardiac muscle fiber is triggered by Ca++ ions in a similar manner as skeletal muscle, but here the Ca++ ions come from SR and through voltage-gated calcium channels in the sarcolemma. Pacemaker cells stimulate the spontaneous contraction of cardiac muscle as a functional unit, called a syncytium.
10.8 Smooth Muscle
Smooth muscle is found throughout the body around various organs and tracts. Smooth muscle cells have a single nucleus, and are spindle-shaped. Smooth muscle cells can undergo hyperplasia, mitotically dividing to produce new cells. The smooth cells are nonstriated, but their sarcoplasm is filled with actin and myosin, along with dense bodies in the sarcolemma to anchor the thin filaments and a network of intermediate filaments involved in pulling the sarcolemma toward the fiber’s middle, shortening it in the process. Ca++ ions trigger contraction when they are released from SR and enter through opened voltage-gated calcium channels. Smooth muscle contraction is initiated when the Ca++ binds to intracellular calmodulin, which then activates an enzyme called myosin kinase that phosphorylates myosin heads so they can form the cross-bridges with actin and then pull on the thin filaments. Smooth muscle can be stimulated by pacesetter cells, by the autonomic nervous system, by hormones, spontaneously, or by stretching. The fibers in some smooth muscle have latch-bridges, cross-bridges that cycle slowly without the need for ATP; these muscles can maintain low-level contractions for long periods. Single-unit smooth muscle tissue contains gap junctions to synchronize membrane depolarization and contractions so that the muscle contracts as a single unit. Single-unit smooth muscle in the walls of the viscera, called visceral muscle, has a stress-relaxation response that permits muscle to stretch, contract, and relax as the organ expands. Multiunit smooth muscle cells do not possess gap junctions, and contraction does not spread from one cell to the next.
10.9 Development and Regeneration of Muscle Tissue
Muscle tissue arises from embryonic mesoderm. Somites give rise to myoblasts and fuse to form a myotube. The nucleus of each contributing myoblast remains intact in the mature skeletal muscle cell, resulting in a mature, multinucleate cell. Satellite cells help to repair skeletal muscle cells. Smooth muscle tissue can regenerate from stem cells called pericytes, whereas dead cardiac muscle tissue is replaced by scar tissue. Aging causes muscle mass to decrease and be replaced by noncontractile connective tissue and adipose tissue.
Interactive Link Questions
Watch this video to learn more about macro- and microstructures of skeletal muscles. (a) What are the names of the “junction points” between sarcomeres? (b) What are the names of the “subunits” within the myofibrils that run the length of skeletal muscle fibers? (c) What is the “double strand of pearls” described in the video? (d) What gives a skeletal muscle fiber its striated appearance?
2.Every skeletal muscle fiber is supplied by a motor neuron at the NMJ. Watch this video to learn more about what happens at the neuromuscular junction. (a) What is the definition of a motor unit? (b) What is the structural and functional difference between a large motor unit and a small motor unit? Can you give an example of each? (c) Why is the neurotransmitter acetylcholine degraded after binding to its receptor?
3.The release of calcium ions initiates muscle contractions. Watch this video to learn more about the role of calcium. (a) What are “T-tubules” and what is their role? (b) Please also describe how actin-binding sites are made available for cross-bridging with myosin heads during contraction.
Review Questions
Muscle that has a striped appearance is described as being ________.
- elastic
- nonstriated
- excitable
- striated
Which element is important in directly triggering contraction?
- sodium (Na+)
- calcium (Ca++)
- potassium (K+)
- chloride (Cl-)
Which of the following properties is not common to all three muscle tissues?
- excitability
- the need for ATP
- at rest, uses shielding proteins to cover actin-binding sites
- elasticity
The correct order for the smallest to the largest unit of organization in muscle tissue is ________.
- fascicle, filament, muscle fiber, myofibril
- filament, myofibril, muscle fiber, fascicle
- muscle fiber, fascicle, filament, myofibril
- myofibril, muscle fiber, filament, fascicle
Depolarization of the sarcolemma means ________.
- the inside of the membrane has become less negative as sodium ions accumulate
- the outside of the membrane has become less negative as sodium ions accumulate
- the inside of the membrane has become more negative as sodium ions accumulate
- the sarcolemma has completely lost any electrical charge
In relaxed muscle, the myosin-binding site on actin is blocked by ________.
- titin
- troponin
- myoglobin
- tropomyosin
According to the sliding filament model, binding sites on actin open when ________.
- creatine phosphate levels rise
- ATP levels rise
- acetylcholine levels rise
- calcium ion levels rise
The cell membrane of a muscle fiber is called ________.
- myofibril
- sarcolemma
- sarcoplasm
- myofilament
Muscle relaxation occurs when ________.
- calcium ions are actively transported out of the sarcoplasmic reticulum
- calcium ions diffuse out of the sarcoplasmic reticulum
- calcium ions are actively transported into the sarcoplasmic reticulum
- calcium ions diffuse into the sarcoplasmic reticulum
During muscle contraction, the cross-bridge detaches when ________.
- the myosin head binds to an ADP molecule
- the myosin head binds to an ATP molecule
- calcium ions bind to troponin
- calcium ions bind to actin
Thin and thick filaments are organized into functional units called ________.
- myofibrils
- myofilaments
- T-tubules
- sarcomeres
During which phase of a twitch in a muscle fiber is tension the greatest?
- resting phase
- repolarization phase
- contraction phase
- relaxation phase
Muscle fatigue is caused by ________.
- buildup of ATP and lactic acid levels
- exhaustion of energy reserves and buildup of lactic acid levels
- buildup of ATP and pyruvic acid levels
- exhaustion of energy reserves and buildup of pyruvic acid levels
A sprinter would experience muscle fatigue sooner than a marathon runner due to ________.
- anaerobic metabolism in the muscles of the sprinter
- anaerobic metabolism in the muscles of the marathon runner
- aerobic metabolism in the muscles of the sprinter
- glycolysis in the muscles of the marathon runner
What aspect of creatine phosphate allows it to supply energy to muscles?
- ATPase activity
- phosphate bonds
- carbon bonds
- hydrogen bonds
Drug X blocks ATP regeneration from ADP and phosphate. How will muscle cells respond to this drug?
- by absorbing ATP from the bloodstream
- by using ADP as an energy source
- by using glycogen as an energy source
- none of the above
The muscles of a professional sprinter are most likely to have ________.
- 80 percent fast-twitch muscle fibers and 20 percent slow-twitch muscle fibers
- 20 percent fast-twitch muscle fibers and 80 percent slow-twitch muscle fibers
- 50 percent fast-twitch muscle fibers and 50 percent slow-twitch muscle fibers
- 40 percent fast-twitch muscle fibers and 60 percent slow-twitch muscle fibers
The muscles of a professional marathon runner are most likely to have ________.
- 80 percent fast-twitch muscle fibers and 20 percent slow-twitch muscle fibers
- 20 percent fast-twitch muscle fibers and 80 percent slow-twitch muscle fibers
- 50 percent fast-twitch muscle fibers and 50 percent slow-twitch muscle fibers
- 40 percent fast-twitch muscle fibers and 60 percent slow-twitch muscle fibers
Which of the following statements is true?
- Fast fibers have a small diameter.
- Fast fibers contain loosely packed myofibrils.
- Fast fibers have large glycogen reserves.
- Fast fibers have many mitochondria.
Which of the following statements is false?
- Slow fibers have a small network of capillaries.
- Slow fibers contain the pigment myoglobin.
- Slow fibers contain a large number of mitochondria.
- Slow fibers contract for extended periods.
Cardiac muscles differ from skeletal muscles in that they ________.
- are striated
- utilize aerobic metabolism
- contain myofibrils
- contain intercalated discs
If cardiac muscle cells were prevented from undergoing aerobic metabolism, they ultimately would ________.
- undergo glycolysis
- synthesize ATP
- stop contracting
- start contracting
Smooth muscles differ from skeletal and cardiac muscles in that they ________.
- lack myofibrils
- are under voluntary control
- lack myosin
- lack actin
Which of the following statements describes smooth muscle cells?
- They are resistant to fatigue.
- They have a rapid onset of contractions.
- They cannot exhibit tetanus.
- They primarily use anaerobic metabolism.
From which embryonic cell type does muscle tissue develop?
- ganglion cells
- myotube cells
- myoblast cells
- satellite cells
Which cell type helps to repair injured muscle fibers?
- ganglion cells
- myotube cells
- myoblast cells
- satellite cells
Critical Thinking Questions
Why is elasticity an important quality of muscle tissue?
31.What would happen to skeletal muscle if the epimysium were destroyed?
32.Describe how tendons facilitate body movement.
33.What are the five primary functions of skeletal muscle?
34.What are the opposite roles of voltage-gated sodium channels and voltage-gated potassium channels?
35.How would muscle contractions be affected if skeletal muscle fibers did not have T-tubules?
36.What causes the striated appearance of skeletal muscle tissue?
37.How would muscle contractions be affected if ATP was completely depleted in a muscle fiber?
38.Why does a motor unit of the eye have few muscle fibers compared to a motor unit of the leg?
39.What factors contribute to the amount of tension produced in an individual muscle fiber?
40.Why do muscle cells use creatine phosphate instead of glycolysis to supply ATP for the first few seconds of muscle contraction?
41.Is aerobic respiration more or less efficient than glycolysis? Explain your answer.
42.What changes occur at the cellular level in response to endurance training?
43.What changes occur at the cellular level in response to resistance training?
44.What would be the drawback of cardiac contractions being the same duration as skeletal muscle contractions?
45.How are cardiac muscle cells similar to and different from skeletal muscle cells?
46.Why can smooth muscles contract over a wider range of resting lengths than skeletal and cardiac muscle?
47.Describe the differences between single-unit smooth muscle and multiunit smooth muscle.
48.Why is muscle that has sustained significant damage unable to produce the same amount of power as it could before being damaged?
49.Which muscle type(s) (skeletal, smooth, or cardiac) can regenerate new muscle cells/fibers? Explain your answer.
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2025-03-18T00:38:18.186442
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/56369/overview",
"title": "Anatomy and Physiology, Support and Movement",
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https://oercommons.org/courseware/lesson/56370/overview
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The Muscular System
Introduction
Figure 11.1 A Body in Motion The muscular system allows us to move, flex and contort our bodies. Practicing yoga, as pictured here, is a good example of the voluntary use of the muscular system. (credit: Dmitry Yanchylenko)
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Describe the actions and roles of agonists and antagonists
- Explain the structure and organization of muscle fascicles and their role in generating force
- Explain the criteria used to name skeletal muscles
- Identify the skeletal muscles and their actions on the skeleton and soft tissues of the body
- Identify the origins and insertions of skeletal muscles and the prime movements
Think about the things that you do each day—talking, walking, sitting, standing, and running—all of these activities require movement of particular skeletal muscles. Skeletal muscles are even used during sleep. The diaphragm is a sheet of skeletal muscle that has to contract and relax for you to breathe day and night. If you recall from your study of the skeletal system and joints, body movement occurs around the joints in the body. The focus of this chapter is on skeletal muscle organization. The system to name skeletal muscles will be explained; in some cases, the muscle is named by its shape, and in other cases it is named by its location or attachments to the skeleton. If you understand the meaning of the name of the muscle, often it will help you remember its location and/or what it does. This chapter also will describe how skeletal muscles are arranged to accomplish movement, and how other muscles may assist, or be arranged on the skeleton to resist or carry out the opposite movement. The actions of the skeletal muscles will be covered in a regional manner, working from the head down to the toes.
Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems
- Compare and contrast agonist and antagonist muscles
- Describe how fascicles are arranged within a skeletal muscle
- Explain the major events of a skeletal muscle contraction within a muscle in generating force
To move the skeleton, the tension created by the contraction of the fibers in most skeletal muscles is transferred to the tendons. The tendons are strong bands of dense, regular connective tissue that connect muscles to bones. The bone connection is why this muscle tissue is called skeletal muscle.
Interactions of Skeletal Muscles in the Body
To pull on a bone, that is, to change the angle at its synovial joint, which essentially moves the skeleton, a skeletal muscle must also be attached to a fixed part of the skeleton. The moveable end of the muscle that attaches to the bone being pulled is called the muscle’s insertion, and the end of the muscle attached to a fixed (stabilized) bone is called the origin. During forearm flexion—bending the elbow—the brachioradialis assists the brachialis.
Although a number of muscles may be involved in an action, the principal muscle involved is called the prime mover, or agonist. To lift a cup, a muscle called the biceps brachii is actually the prime mover; however, because it can be assisted by the brachialis, the brachialis is called a synergist in this action (Figure 11.2). A synergist can also be a fixator that stabilizes the bone that is the attachment for the prime mover’s origin.
Figure 11.2 Prime Movers and Synergists The biceps brachii flex the lower arm. The brachoradialis, in the forearm, and brachialis, located deep to the biceps in the upper arm, are both synergists that aid in this motion.
A muscle with the opposite action of the prime mover is called an antagonist. Antagonists play two important roles in muscle function: (1) they maintain body or limb position, such as holding the arm out or standing erect; and (2) they control rapid movement, as in shadow boxing without landing a punch or the ability to check the motion of a limb.
For example, to extend the knee, a group of four muscles called the quadriceps femoris in the anterior compartment of the thigh are activated (and would be called the agonists of knee extension). However, to flex the knee joint, an opposite or antagonistic set of muscles called the hamstrings is activated.
As you can see, these terms would also be reversed for the opposing action. If you consider the first action as the knee bending, the hamstrings would be called the agonists and the quadriceps femoris would then be called the antagonists. See Table 11.1 for a list of some agonists and antagonists.
Agonist and Antagonist Skeletal Muscle Pairs
| Agonist | Antagonist | Movement |
|---|---|---|
| Biceps brachii: in the anterior compartment of the arm | Triceps brachii: in the posterior compartment of the arm | The biceps brachii flexes the forearm, whereas the triceps brachii extends it. |
| Hamstrings: group of three muscles in the posterior compartment of the thigh | Quadriceps femoris: group of four muscles in the anterior compartment of the thigh | The hamstrings flex the leg, whereas the quadriceps femoris extend it. |
| Flexor digitorum superficialis and flexor digitorum profundus: in the anterior compartment of the forearm | Extensor digitorum: in the posterior compartment of the forearm | The flexor digitorum superficialis and flexor digitorum profundus flex the fingers and the hand at the wrist, whereas the extensor digitorum extends the fingers and the hand at the wrist. |
Table 11.1
There are also skeletal muscles that do not pull against the skeleton for movements. For example, there are the muscles that produce facial expressions. The insertions and origins of facial muscles are in the skin, so that certain individual muscles contract to form a smile or frown, form sounds or words, and raise the eyebrows. There also are skeletal muscles in the tongue, and the external urinary and anal sphincters that allow for voluntary regulation of urination and defecation, respectively. In addition, the diaphragm contracts and relaxes to change the volume of the pleural cavities but it does not move the skeleton to do this.
EVERYDAY CONNECTION
Exercise and Stretching
When exercising, it is important to first warm up the muscles. Stretching pulls on the muscle fibers and it also results in an increased blood flow to the muscles being worked. Without a proper warm-up, it is possible that you may either damage some of the muscle fibers or pull a tendon. A pulled tendon, regardless of location, results in pain, swelling, and diminished function; if it is moderate to severe, the injury could immobilize you for an extended period.
Recall the discussion about muscles crossing joints to create movement. Most of the joints you use during exercise are synovial joints, which have synovial fluid in the joint space between two bones. Exercise and stretching may also have a beneficial effect on synovial joints. Synovial fluid is a thin, but viscous film with the consistency of egg whites. When you first get up and start moving, your joints feel stiff for a number of reasons. After proper stretching and warm-up, the synovial fluid may become less viscous, allowing for better joint function.
Patterns of Fascicle Organization
Skeletal muscle is enclosed in connective tissue scaffolding at three levels. Each muscle fiber (cell) is covered by endomysium and the entire muscle is covered by epimysium. When a group of muscle fibers is “bundled” as a unit within the whole muscle by an additional covering of a connective tissue called perimysium, that bundled group of muscle fibers is called a fascicle. Fascicle arrangement by perimysia is correlated to the force generated by a muscle; it also affects the range of motion of the muscle. Based on the patterns of fascicle arrangement, skeletal muscles can be classified in several ways. What follows are the most common fascicle arrangements.
Parallel muscles have fascicles that are arranged in the same direction as the long axis of the muscle (Figure 11.3). The majority of skeletal muscles in the body have this type of organization. Some parallel muscles are flat sheets that expand at the ends to make broad attachments. Other parallel muscles are rotund with tendons at one or both ends. Muscles that seem to be plump have a large mass of tissue located in the middle of the muscle, between the insertion and the origin, which is known as the central body. A more common name for this muscle is belly. When a muscle contracts, the contractile fibers shorten it to an even larger bulge. For example, extend and then flex your biceps brachii muscle; the large, middle section is the belly (Figure 11.4). When a parallel muscle has a central, large belly that is spindle-shaped, meaning it tapers as it extends to its origin and insertion, it sometimes is called fusiform.
Figure 11.3 Muscle Shapes and Fiber Alignment The skeletal muscles of the body typically come in seven different general shapes.
Figure 11.4 Biceps Brachii Muscle Contraction The large mass at the center of a muscle is called the belly. Tendons emerge from both ends of the belly and connect the muscle to the bones, allowing the skeleton to move. The tendons of the bicep connect to the upper arm and the forearm. (credit: Victoria Garcia)
Circular muscles are also called sphincters (see Figure 11.3). When they relax, the sphincters’ concentrically arranged bundles of muscle fibers increase the size of the opening, and when they contract, the size of the opening shrinks to the point of closure. The orbicularis oris muscle is a circular muscle that goes around the mouth. When it contracts, the oral opening becomes smaller, as when puckering the lips for whistling. Another example is the orbicularis oculi, one of which surrounds each eye. Consider, for example, the names of the two orbicularis muscles (orbicularis oris and oribicularis oculi), where part of the first name of both muscles is the same. The first part of orbicularis, orb (orb = “circular”), is a reference to a round or circular structure; it may also make one think of orbit, such as the moon’s path around the earth. The word oris (oris = “oral”) refers to the oral cavity, or the mouth. The word oculi (ocular = “eye”) refers to the eye.
There are other muscles throughout the body named by their shape or location. The deltoid is a large, triangular-shaped muscle that covers the shoulder. It is so-named because the Greek letter delta looks like a triangle. The rectus abdomis (rector = “straight”) is the straight muscle in the anterior wall of the abdomen, while the rectus femoris is the straight muscle in the anterior compartment of the thigh.
When a muscle has a widespread expansion over a sizable area, but then the fascicles come to a single, common attachment point, the muscle is called convergent. The attachment point for a convergent muscle could be a tendon, an aponeurosis (a flat, broad tendon), or a raphe (a very slender tendon). The large muscle on the chest, the pectoralis major, is an example of a convergent muscle because it converges on the greater tubercle of the humerus via a tendon. The temporalis muscle of the cranium is another.
Pennate muscles (penna = “feathers”) blend into a tendon that runs through the central region of the muscle for its whole length, somewhat like the quill of a feather with the muscle arranged similar to the feathers. Due to this design, the muscle fibers in a pennate muscle can only pull at an angle, and as a result, contracting pennate muscles do not move their tendons very far. However, because a pennate muscle generally can hold more muscle fibers within it, it can produce relatively more tension for its size. There are three subtypes of pennate muscles.
In a unipennate muscle, the fascicles are located on one side of the tendon. The extensor digitorum of the forearm is an example of a unipennate muscle. A bipennate muscle has fascicles on both sides of the tendon. In some pennate muscles, the muscle fibers wrap around the tendon, sometimes forming individual fascicles in the process. This arrangement is referred to as multipennate. A common example is the deltoid muscle of the shoulder, which covers the shoulder but has a single tendon that inserts on the deltoid tuberosity of the humerus.
Because of fascicles, a portion of a multipennate muscle like the deltoid can be stimulated by the nervous system to change the direction of the pull. For example, when the deltoid muscle contracts, the arm abducts (moves away from midline in the sagittal plane), but when only the anterior fascicle is stimulated, the arm will abduct and flex (move anteriorly at the shoulder joint).
The Lever System of Muscle and Bone Interactions
Skeletal muscles do not work by themselves. Muscles are arranged in pairs based on their functions. For muscles attached to the bones of the skeleton, the connection determines the force, speed, and range of movement. These characteristics depend on each other and can explain the general organization of the muscular and skeletal systems.
The skeleton and muscles act together to move the body. Have you ever used the back of a hammer to remove a nail from wood? The handle acts as a lever and the head of the hammer acts as a fulcrum, the fixed point that the force is applied to when you pull back or push down on the handle. The effort applied to this system is the pulling or pushing on the handle to remove the nail, which is the load, or “resistance” to the movement of the handle in the system. Our musculoskeletal system works in a similar manner, with bones being stiff levers and the articular endings of the bones—encased in synovial joints—acting as fulcrums. The load would be an object being lifted or any resistance to a movement (your head is a load when you are lifting it), and the effort, or applied force, comes from contracting skeletal muscle.
Naming Skeletal Muscles
- Describe the criteria used to name skeletal muscles
- Explain how understanding the muscle names helps describe shapes, location, and actions of various muscles
The Greeks and Romans conducted the first studies done on the human body in Western culture. The educated class of subsequent societies studied Latin and Greek, and therefore the early pioneers of anatomy continued to apply Latin and Greek terminology or roots when they named the skeletal muscles. The large number of muscles in the body and unfamiliar words can make learning the names of the muscles in the body seem daunting, but understanding the etymology can help. Etymology is the study of how the root of a particular word entered a language and how the use of the word evolved over time. Taking the time to learn the root of the words is crucial to understanding the vocabulary of anatomy and physiology. When you understand the names of muscles it will help you remember where the muscles are located and what they do (Figure 11.5, Figure 11.6, and Table 11.2). Pronunciation of words and terms will take a bit of time to master, but after you have some basic information; the correct names and pronunciations will become easier.
Figure 11.5 Overview of the Muscular System On the anterior and posterior views of the muscular system above, superficial muscles (those at the surface) are shown on the right side of the body while deep muscles (those underneath the superficial muscles) are shown on the left half of the body. For the legs, superficial muscles are shown in the anterior view while the posterior view shows both superficial and deep muscles.
Figure 11.6 Understanding a Muscle Name from the Latin
Mnemonic Device for Latin Roots
| Example | Latin or Greek Translation | Mnemonic Device |
|---|---|---|
| ad | to; toward | ADvance toward your goal |
| ab | away from | n/a |
| sub | under | SUBmarines move under water. |
| ductor | something that moves | A conDUCTOR makes a train move. |
| anti | against | If you are antisocial, you are against engaging in social activities. |
| epi | on top of | n/a |
| apo | to the side of | n/a |
| longissimus | longest | “Longissimus” is longer than the word “long.” |
| longus | long | long |
| brevis | short | brief |
| maximus | large | max |
| medius | medium | “Medius” and “medium” both begin with “med.” |
| minimus | tiny; little | mini |
| rectus | straight | To RECTify a situation is to straighten it out. |
| multi | many | If something is MULTIcolored, it has many colors. |
| uni | one | A UNIcorn has one horn. |
| bi/di | two | If a ring is DIcast, it is made of two metals. |
| tri | three | TRIple the amount of money is three times as much. |
| quad | four | QUADruplets are four children born at one birth. |
| externus | outside | EXternal |
| internus | inside | INternal |
Table 11.2
Anatomists name the skeletal muscles according to a number of criteria, each of which describes the muscle in some way. These include naming the muscle after its shape, its size compared to other muscles in the area, its location in the body or the location of its attachments to the skeleton, how many origins it has, or its action.
The skeletal muscle’s anatomical location or its relationship to a particular bone often determines its name. For example, the frontalis muscle is located on top of the frontal bone of the skull. Similarly, the shapes of some muscles are very distinctive and the names, such as orbicularis, reflect the shape. For the buttocks, the size of the muscles influences the names: gluteus maximus (largest), gluteus medius (medium), and the gluteus minimus (smallest). Names were given to indicate length—brevis(short), longus (long)—and to identify position relative to the midline: lateralis (to the outside away from the midline), and medialis (toward the midline). The direction of the muscle fibers and fascicles are used to describe muscles relative to the midline, such as the rectus (straight) abdominis, or the oblique (at an angle) muscles of the abdomen.
Some muscle names indicate the number of muscles in a group. One example of this is the quadriceps, a group of four muscles located on the anterior (front) thigh. Other muscle names can provide information as to how many origins a particular muscle has, such as the biceps brachii. The prefix bi indicates that the muscle has two origins and tri indicates three origins.
The location of a muscle’s attachment can also appear in its name. When the name of a muscle is based on the attachments, the origin is always named first. For instance, the sternocleidomastoid muscle of the neck has a dual origin on the sternum (sterno) and clavicle (cleido), and it inserts on the mastoid process of the temporal bone. The last feature by which to name a muscle is its action. When muscles are named for the movement they produce, one can find action words in their name. Some examples are flexor (decreases the angle at the joint), extensor (increases the angle at the joint), abductor (moves the bone away from the midline), or adductor (moves the bone toward the midline).
Axial Muscles of the Head, Neck, and Back
- Identify the axial muscles of the face, head, and neck
- Identify the movement and function of the face, head, and neck muscles
The skeletal muscles are divided into axial (muscles of the trunk and head) and appendicular (muscles of the arms and legs) categories. This system reflects the bones of the skeleton system, which are also arranged in this manner. The axial muscles are grouped based on location, function, or both. Some of the axial muscles may seem to blur the boundaries because they cross over to the appendicular skeleton. The first grouping of the axial muscles you will review includes the muscles of the head and neck, then you will review the muscles of the vertebral column, and finally you will review the oblique and rectus muscles.
Muscles That Create Facial Expression
The origins of the muscles of facial expression are on the surface of the skull (remember, the origin of a muscle does not move). The insertions of these muscles have fibers intertwined with connective tissue and the dermis of the skin. Because the muscles insert in the skin rather than on bone, when they contract, the skin moves to create facial expression (Figure 11.7).
Figure 11.7 Muscles of Facial Expression Many of the muscles of facial expression insert into the skin surrounding the eyelids, nose and mouth, producing facial expressions by moving the skin rather than bones.
The orbicularis oris is a circular muscle that moves the lips, and the orbicularis oculi is a circular muscle that closes the eye. The occipitofrontalis muscle moves up the scalp and eyebrows. The muscle has a frontal belly and an occipital (near the occipital bone on the posterior part of the skull) belly. In other words, there is a muscle on the forehead (frontalis) and one on the back of the head (occipitalis), but there is no muscle across the top of the head. Instead, the two bellies are connected by a broad tendon called the epicranial aponeurosis, or galea aponeurosis (galea = “helmet”). The physicians originally studying human anatomy thought the skull looked like an helmet.
A large portion of the face is composed of the buccinator muscle, which compresses the cheek. This muscle allows you to whistle, blow, and suck; and it contributes to the action of chewing. There are several small facial muscles, one of which is the corrugator supercilii, which is the prime mover of the eyebrows. Place your finger on your eyebrows at the point of the bridge of the nose. Raise your eyebrows as if you were surprised and lower your eyebrows as if you were frowning. With these movements, you can feel the action of the corrugator supercilli. Additional muscles of facial expression are presented in Figure 11.8.
Figure 11.8 Muscles in Facial Expression
Muscles That Move the Eyes
The movement of the eyeball is under the control of the extrinsic eye muscles, which originate outside the eye and insert onto the outer surface of the white of the eye. These muscles are located inside the eye socket and cannot be seen on any part of the visible eyeball (Figure 11.9 and Table 11.3). If you have ever been to a doctor who held up a finger and asked you to follow it up, down, and to both sides, he or she is checking to make sure your eye muscles are acting in a coordinated pattern.
Figure 11.9 Muscles of the Eyes (a) The extrinsic eye muscles originate outside of the eye on the skull. (b) Each muscle inserts onto the eyeball.
Muscles of the Eyes
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|
| Moves eyes up and toward nose; rotates eyes from 1 o’clock to 3 o’clock | Eyeballs | Superior (elevates); medial (adducts) | Superior rectus | Common tendinous ring (ring attaches to optic foramen) | Superior surface of eyeball |
| Moves eyes down and toward nose; rotates eyes from 6 o’clock to 3 o’clock | Eyeballs | Inferior (depresses); medial (adducts) | Inferior rectus | Common tendinous ring (ring attaches to optic foramen) | Inferior surface of eyeball |
| Moves eyes away from nose | Eyeballs | Lateral (abducts) | Lateral rectus | Common tendinous ring (ring attaches to optic foramen) | Lateral surface of eyeball |
| Moves eyes toward nose | Eyeballs | Medial (adducts) | Medial rectus | Common tendinous ring (ring attaches to optic foramen) | Medial surface of eyeball |
| Moves eyes up and away from nose; rotates eyeball from 12 o’clock to 9 o’clock | Eyeballs | Superior (elevates); lateral (abducts) | Inferior oblique | Floor of orbit (maxilla) | Surface of eyeball between inferior rectus and lateral rectus |
| Moves eyes down and away from nose; rotates eyeball from 6 o’clock to 9 o’clock | Eyeballs | Superior (elevates); lateral (abducts) | Superior oblique | Sphenoid bone | Suface of eyeball between superior rectus and lateral rectus |
| Opens eyes | Upper eyelid | Superior (elevates) | Levator palpabrae superioris | Roof of orbit (sphenoid bone) | Skin of upper eyelids |
| Closes eyelids | Eyelid skin | Compression along superior–inferior axis | Orbicularis oculi | Medial bones composing the orbit | Circumference of orbit |
Table 11.3
Muscles That Move the Lower Jaw
In anatomical terminology, chewing is called mastication. Muscles involved in chewing must be able to exert enough pressure to bite through and then chew food before it is swallowed (Figure 11.10 and Table 11.4). The masseter muscle is the main muscle used for chewing because it elevates the mandible (lower jaw) to close the mouth, and it is assisted by the temporalismuscle, which retracts the mandible. You can feel the temporalis move by putting your fingers to your temple as you chew.
Figure 11.10 Muscles That Move the Lower Jaw The muscles that move the lower jaw are typically located within the cheek and originate from processes in the skull. This provides the jaw muscles with the large amount of leverage needed for chewing.
Muscles of the Lower Jaw
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|
| Closes mouth; aids chewing | Mandible | Superior (elevates) | Masseter | Maxilla arch; zygomatic arch (for masseter) | Mandible |
| Closes mouth; pulls lower jaw in under upper jaw | Mandible | Superior (elevates); posterior (retracts) | Temporalis | Temporal bone | Mandible |
| Opens mouth; pushes lower jaw out under upper jaw; moves lower jaw side-to-side | Mandible | Inferior (depresses); posterior (protracts); lateral (abducts); medial (adducts) | Lateral pterygoid | Pterygoid process of sphenoid bone | Mandible |
| Closes mouth; pushes lower jaw out under upper jaw; moves lower jaw side-to-side | Mandible | Superior (elevates); posterior (protracts); lateral (abducts); medial (adducts) | Medial pterygoid | Sphenoid bone; maxilla | Mandible; temporo-mandibular joint |
Table 11.4
Although the masseter and temporalis are responsible for elevating and closing the jaw to break food into digestible pieces, the medial pterygoid and lateral pterygoid muscles provide assistance in chewing and moving food within the mouth.
Muscles That Move the Tongue
Although the tongue is obviously important for tasting food, it is also necessary for mastication, deglutition (swallowing), and speech (Figure 11.11 and Figure 11.12). Because it is so moveable, the tongue facilitates complex speech patterns and sounds.
Figure 11.11 Muscles that Move the Tongue
Figure 11.12 Muscles for Tongue Movement, Swallowing, and Speech
Tongue muscles can be extrinsic or intrinsic. Extrinsic tongue muscles insert into the tongue from outside origins, and the intrinsic tongue muscles insert into the tongue from origins within it. The extrinsic muscles move the whole tongue in different directions, whereas the intrinsic muscles allow the tongue to change its shape (such as, curling the tongue in a loop or flattening it).
The extrinsic muscles all include the word root glossus (glossus = “tongue”), and the muscle names are derived from where the muscle originates. The genioglossus (genio = “chin”) originates on the mandible and allows the tongue to move downward and forward. The styloglossus originates on the styloid bone, and allows upward and backward motion. The palatoglossusoriginates on the soft palate to elevate the back of the tongue, and the hyoglossus originates on the hyoid bone to move the tongue downward and flatten it.
EVERYDAY CONNECTION
Anesthesia and the Tongue Muscles
Before surgery, a patient must be made ready for general anesthesia. The normal homeostatic controls of the body are put “on hold” so that the patient can be prepped for surgery. Control of respiration must be switched from the patient’s homeostatic control to the control of the anesthesiologist. The drugs used for anesthesia relax a majority of the body’s muscles.
Among the muscles affected during general anesthesia are those that are necessary for breathing and moving the tongue. Under anesthesia, the tongue can relax and partially or fully block the airway, and the muscles of respiration may not move the diaphragm or chest wall. To avoid possible complications, the safest procedure to use on a patient is called endotracheal intubation. Placing a tube into the trachea allows the doctors to maintain a patient’s (open) airway to the lungs and seal the airway off from the oropharynx. Post-surgery, the anesthesiologist gradually changes the mixture of the gases that keep the patient unconscious, and when the muscles of respiration begin to function, the tube is removed. It still takes about 30 minutes for a patient to wake up, and for breathing muscles to regain control of respiration. After surgery, most people have a sore or scratchy throat for a few days.
Muscles of the Anterior Neck
The muscles of the anterior neck assist in deglutition (swallowing) and speech by controlling the positions of the larynx (voice box), and the hyoid bone, a horseshoe-shaped bone that functions as a solid foundation on which the tongue can move. The muscles of the neck are categorized according to their position relative to the hyoid bone (Figure 11.13). Suprahyoid musclesare superior to it, and the infrahyoid muscles are located inferiorly.
Figure 11.13 Muscles of the Anterior Neck The anterior muscles of the neck facilitate swallowing and speech. The suprahyoid muscles originate from above the hyoid bone in the chin region. The infrahyoid muscles originate below the hyoid bone in the lower neck.
The suprahyoid muscles raise the hyoid bone, the floor of the mouth, and the larynx during deglutition. These include the digastric muscle, which has anterior and posterior bellies that work to elevate the hyoid bone and larynx when one swallows; it also depresses the mandible. The stylohyoid muscle moves the hyoid bone posteriorly, elevating the larynx, and the mylohyoidmuscle lifts it and helps press the tongue to the top of the mouth. The geniohyoid depresses the mandible in addition to raising and pulling the hyoid bone anteriorly.
The strap-like infrahyoid muscles generally depress the hyoid bone and control the position of the larynx. The omohyoidmuscle, which has superior and inferior bellies, depresses the hyoid bone in conjunction with the sternohyoid and thyrohyoidmuscles. The thyrohyoid muscle also elevates the larynx’s thyroid cartilage, whereas the sternothyroid depresses it to create different tones of voice.
Muscles That Move the Head
The head, attached to the top of the vertebral column, is balanced, moved, and rotated by the neck muscles (Table 11.5). When these muscles act unilaterally, the head rotates. When they contract bilaterally, the head flexes or extends. The major muscle that laterally flexes and rotates the head is the sternocleidomastoid. In addition, both muscles working together are the flexors of the head. Place your fingers on both sides of the neck and turn your head to the left and to the right. You will feel the movement originate there. This muscle divides the neck into anterior and posterior triangles when viewed from the side (Figure 11.14).
Figure 11.14 Posterior and Lateral Views of the Neck The superficial and deep muscles of the neck are responsible for moving the head, cervical vertebrae, and scapulas.
Muscles That Move the Head
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|
| Rotates and tilts head to the side; tilts head forward | Skull; vertebrae | Individually: rotates head to opposite side; bilaterally: flexion | Sternocleidomastoid | Sternum; clavicle | Temporal bone (mastoid process); occipital bone |
| Rotates and tilts head backward | Skull; vertebrae | Individually: laterally flexes and rotates head to same side; bilaterally: extension | Semispinalis capitis | Transverse and articular processes of cervical and thoracic vertebra | Occipital bone |
| Rotates and tilts head to the side; tilts head backward | Skull; vertebrae | Individually: laterally flexes and rotates head to same side; bilaterally: extension | Splenius capitis | Spinous processes of cervical and thoracic vertebra | Temporal bone (mastoid process); occipital bone |
| Rotates and tilts head to the side; tilts head backward | Skull; vertebrae | Individually: laterally flexes and rotates head to same side; bilaterally: extension | Longissimus capitis | Transverse and articular processes of cervical and thoracic vertebra | Temporal bone (mastoid process) |
Table 11.5
Muscles of the Posterior Neck and the Back
The posterior muscles of the neck are primarily concerned with head movements, like extension. The back muscles stabilize and move the vertebral column, and are grouped according to the lengths and direction of the fascicles.
The splenius muscles originate at the midline and run laterally and superiorly to their insertions. From the sides and the back of the neck, the splenius capitis inserts onto the head region, and the splenius cervicis extends onto the cervical region. These muscles can extend the head, laterally flex it, and rotate it (Figure 11.15).
Figure 11.15 Muscles of the Neck and Back The large, complex muscles of the neck and back move the head, shoulders, and vertebral column.
The erector spinae group forms the majority of the muscle mass of the back and it is the primary extensor of the vertebral column. It controls flexion, lateral flexion, and rotation of the vertebral column, and maintains the lumbar curve. The erector spinae comprises the iliocostalis (laterally placed) group, the longissimus (intermediately placed) group, and the spinalis (medially placed) group.
The iliocostalis group includes the iliocostalis cervicis, associated with the cervical region; the iliocostalis thoracis, associated with the thoracic region; and the iliocostalis lumborum, associated with the lumbar region. The three muscles of the longissimus group are the longissimus capitis, associated with the head region; the longissimus cervicis, associated with the cervical region; and the longissimus thoracis, associated with the thoracic region. The third group, the spinalis group, comprises the spinalis capitis (head region), the spinalis cervicis (cervical region), and the spinalis thoracis (thoracic region).
The transversospinales muscles run from the transverse processes to the spinous processes of the vertebrae. Similar to the erector spinae muscles, the semispinalis muscles in this group are named for the areas of the body with which they are associated. The semispinalis muscles include the semispinalis capitis, the semispinalis cervicis, and the semispinalis thoracis. The multifidus muscle of the lumbar region helps extend and laterally flex the vertebral column.
Important in the stabilization of the vertebral column is the segmental muscle group, which includes the interspinales and intertransversarii muscles. These muscles bring together the spinous and transverse processes of each consecutive vertebra. Finally, the scalene muscles work together to flex, laterally flex, and rotate the head. They also contribute to deep inhalation. The scalene muscles include the anterior scalene muscle (anterior to the middle scalene), the middle scalene muscle (the longest, intermediate between the anterior and posterior scalenes), and the posterior scalene muscle (the smallest, posterior to the middle scalene).
Axial Muscles of the Abdominal Wall, and Thorax
- Identify the intrinsic skeletal muscles of the back and neck, and the skeletal muscles of the abdominal wall and thorax
- Identify the movement and function of the intrinsic skeletal muscles of the back and neck, and the skeletal muscles of the abdominal wall and thorax
It is a complex job to balance the body on two feet and walk upright. The muscles of the vertebral column, thorax, and abdominal wall extend, flex, and stabilize different parts of the body’s trunk. The deep muscles of the core of the body help maintain posture as well as carry out other functions. The brain sends out electrical impulses to these various muscle groups to control posture by alternate contraction and relaxation. This is necessary so that no single muscle group becomes fatigued too quickly. If any one group fails to function, body posture will be compromised.
Muscles of the Abdomen
There are four pairs of abdominal muscles that cover the anterior and lateral abdominal region and meet at the anterior midline. These muscles of the anterolateral abdominal wall can be divided into four groups: the external obliques, the internal obliques, the transversus abdominis, and the rectus abdominis (Figure 11.16 and Table 11.6).
Figure 11.16 Muscles of the Abdomen (a) The anterior abdominal muscles include the medially located rectus abdominis, which is covered by a sheet of connective tissue called the rectus sheath. On the flanks of the body, medial to the rectus abdominis, the abdominal wall is composed of three layers. The external oblique muscles form the superficial layer, while the internal oblique muscles form the middle layer, and the transverses abdominus forms the deepest layer. (b) The muscles of the lower back move the lumbar spine but also assist in femur movements.
Muscles of the Abdomen
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|
| Twisting at waist; also bending to the side | Vertebral column | Supination; lateral flexion | External obliques; internal obliques | Ribs 5–12; ilium | Ribs 7–10; linea alba; ilium |
| Squeezing abdomen during forceful exhalations, defecation, urination, and childbirth | Abdominal cavity | Compression | Transversus abdominus | Ilium; ribs 5–10 | Sternum; linea alba; pubis |
| Sitting up | Vertebral column | Flexion | Rectus abdominis | Pubis | Sternum; ribs 5 and 7 |
| Bending to the side | Vertebral column | Lateral flexion | Quadratus lumborum | Ilium; ribs 5–10 | Rib 12; vertebrae L1–L4 |
Table 11.6
There are three flat skeletal muscles in the antero-lateral wall of the abdomen. The external oblique, closest to the surface, extend inferiorly and medially, in the direction of sliding one’s four fingers into pants pockets. Perpendicular to it is the intermediate internal oblique, extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. The deep muscle, the transversus abdominis, is arranged transversely around the abdomen, similar to the front of a belt on a pair of pants. This arrangement of three bands of muscles in different orientations allows various movements and rotations of the trunk. The three layers of muscle also help to protect the internal abdominal organs in an area where there is no bone.
The linea alba is a white, fibrous band that is made of the bilateral rectus sheaths that join at the anterior midline of the body. These enclose the rectus abdominis muscles (a pair of long, linear muscles, commonly called the “sit-up” muscles) that originate at the pubic crest and symphysis, and extend the length of the body’s trunk. Each muscle is segmented by three transverse bands of collagen fibers called the tendinous intersections. This results in the look of “six-pack abs,” as each segment hypertrophies on individuals at the gym who do many sit-ups.
The posterior abdominal wall is formed by the lumbar vertebrae, parts of the ilia of the hip bones, psoas major and iliacus muscles, and quadratus lumborum muscle. This part of the core plays a key role in stabilizing the rest of the body and maintaining posture.
CAREER CONNECTION
Physical Therapists
Those who have a muscle or joint injury will most likely be sent to a physical therapist (PT) after seeing their regular doctor. PTs have a master’s degree or doctorate, and are highly trained experts in the mechanics of body movements. Many PTs also specialize in sports injuries.
If you injured your shoulder while you were kayaking, the first thing a physical therapist would do during your first visit is to assess the functionality of the joint. The range of motion of a particular joint refers to the normal movements the joint performs. The PT will ask you to abduct and adduct, circumduct, and flex and extend the arm. The PT will note the shoulder’s degree of function, and based on the assessment of the injury, will create an appropriate physical therapy plan.
The first step in physical therapy will probably be applying a heat pack to the injured site, which acts much like a warm-up to draw blood to the area, to enhance healing. You will be instructed to do a series of exercises to continue the therapy at home, followed by icing, to decrease inflammation and swelling, which will continue for several weeks. When physical therapy is complete, the PT will do an exit exam and send a detailed report on the improved range of motion and return of normal limb function to your doctor. Gradually, as the injury heals, the shoulder will begin to function correctly. A PT works closely with patients to help them get back to their normal level of physical activity.
Muscles of the Thorax
The muscles of the chest serve to facilitate breathing by changing the size of the thoracic cavity (Table 11.7). When you inhale, your chest rises because the cavity expands. Alternately, when you exhale, your chest falls because the thoracic cavity decreases in size.
Muscles of the Thorax
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|
| Inhalation; exhalation | Thoracic cavity | Compression; expansion | Diaphragm | Sternum; ribs 6–12; lumbar vertebrae | Central tendon |
| Inhalation;exhalation | Ribs | Elevation (expands thoracic cavity) | External intercostals | Rib superior to each intercostal muscle | Rib inferior to each intercostal muscle |
| Forced exhalation | Ribs | Movement along superior/inferior axis to bring ribs closer together | Internal intercostals | Rib inferior to each intercostal muscle | Rib superior to each intercostal muscle |
Table 11.7
The Diaphragm
The change in volume of the thoracic cavity during breathing is due to the alternate contraction and relaxation of the diaphragm(Figure 11.17). It separates the thoracic and abdominal cavities, and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.
Figure 11.17 Muscles of the Diaphragm The diaphragm separates the thoracic and abdominal cavities.
Defecating, urination, and even childbirth involve cooperation between the diaphragm and abdominal muscles (this cooperation is referred to as the “Valsalva maneuver”). You hold your breath by a steady contraction of the diaphragm; this stabilizes the volume and pressure of the peritoneal cavity. When the abdominal muscles contract, the pressure cannot push the diaphragm up, so it increases pressure on the intestinal tract (defecation), urinary tract (urination), or reproductive tract (childbirth).
The inferior surface of the pericardial sac and the inferior surfaces of the pleural membranes (parietal pleura) fuse onto the central tendon of the diaphragm. To the sides of the tendon are the skeletal muscle portions of the diaphragm, which insert into the tendon while having a number of origins including the xiphoid process of the sternum anteriorly, the inferior six ribs and their cartilages laterally, and the lumbar vertebrae and 12th ribs posteriorly.
The diaphragm also includes three openings for the passage of structures between the thorax and the abdomen. The inferior vena cava passes through the caval opening, and the esophagus and attached nerves pass through the esophageal hiatus. The aorta, thoracic duct, and azygous vein pass through the aortic hiatus of the posterior diaphragm.
The Intercostal Muscles
There are three sets of muscles, called intercostal muscles, which span each of the intercostal spaces. The principal role of the intercostal muscles is to assist in breathing by changing the dimensions of the rib cage (Figure 11.18).
Figure 11.18 Intercostal Muscles The external intercostals are located laterally on the sides of the body. The internal intercostals are located medially near the sternum. The innermost intercostals are located deep to both the internal and external intercostals.
The 11 pairs of superficial external intercostal muscles aid in inspiration of air during breathing because when they contract, they raise the rib cage, which expands it. The 11 pairs of internal intercostal muscles, just under the externals, are used for expiration because they draw the ribs together to constrict the rib cage. The innermost intercostal muscles are the deepest, and they act as synergists for the action of the internal intercostals.
Muscles of the Pelvic Floor and Perineum
The pelvic floor is a muscular sheet that defines the inferior portion of the pelvic cavity. The pelvic diaphragm, spanning anteriorly to posteriorly from the pubis to the coccyx, comprises the levator ani and the ischiococcygeus. Its openings include the anal canal and urethra, and the vagina in women.
The large levator ani consists of two skeletal muscles, the pubococcygeus and the iliococcygeus (Figure 11.19). The levator ani is considered the most important muscle of the pelvic floor because it supports the pelvic viscera. It resists the pressure produced by contraction of the abdominal muscles so that the pressure is applied to the colon to aid in defecation and to the uterus to aid in childbirth (assisted by the ischiococcygeus, which pulls the coccyx anteriorly). This muscle also creates skeletal muscle sphincters at the urethra and anus.
Figure 11.19 Muscles of the Pelvic Floor The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.
The perineum is the diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and coccygeus). Divided transversely into triangles, the anterior is the urogenital triangle, which includes the external genitals. The posterior is the anal triangle, which contains the anus (Figure 11.20). The perineum is also divided into superficial and deep layers with some of the muscles common to men and women (Figure 11.21). Women also have the compressor urethrae and the sphincter urethrovaginalis, which function to close the vagina. In men, there is the deep transverse perineal muscle that plays a role in ejaculation.
Figure 11.20 Muscles of the Perineum The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women.
Figure 11.21 Muscles of the Perineum Common to Men and Women
Muscles of the Pectoral Girdle and Upper Limbs
- Identify the muscles of the pectoral girdle and upper limbs
- Identify the movement and function of the pectoral girdle and upper limbs
Muscles of the shoulder and upper limb can be divided into four groups: muscles that stabilize and position the pectoral girdle, muscles that move the arm, muscles that move the forearm, and muscles that move the wrists, hands, and fingers. The pectoral girdle, or shoulder girdle, consists of the lateral ends of the clavicle and scapula, along with the proximal end of the humerus, and the muscles covering these three bones to stabilize the shoulder joint. The girdle creates a base from which the head of the humerus, in its ball-and-socket joint with the glenoid fossa of the scapula, can move the arm in multiple directions.
Muscles That Position the Pectoral Girdle
Muscles that position the pectoral girdle are located either on the anterior thorax or on the posterior thorax (Figure 11.22 and Table 11.8). The anterior muscles include the subclavius, pectoralis minor, and serratus anterior. The posterior muscles include the trapezius, rhomboid major, and rhomboid minor. When the rhomboids are contracted, your scapula moves medially, which can pull the shoulder and upper limb posteriorly.
Figure 11.22 Muscles That Position the Pectoral Girdle The muscles that stabilize the pectoral girdle make it a steady base on which other muscles can move the arm. Note that the pectoralis major and deltoid, which move the humerus, are cut here to show the deeper positioning muscles.
Muscles that Position the Pectoral girdle
| Position in the thorax | Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|---|
| Anterior thorax | Stabilizes clavicle during movement by depressing it | Clavicle | Depression | Subclavius | First rib | Inferior surface of clavicle |
| Anterior thorax | Rotates shoulder anteriorly (throwing motion); assists with inhalation | Scapula; ribs | Scapula: depresses; ribs: elevates | Pectoralis minor | Anterior surfaces of certain ribs (2–4 or 3–5) | Coracoid process of scapula |
| Anterior thorax | Moves arm from side of body to front of body; assists with inhalation | Scapula; ribs | Scapula: protracts; ribs: elevates | Serratus anterior | Muscle slips from certain ribs (1–8 or 1–9) | Anterior surface of vertebral border of scapula |
| Posterior thorax | Elevates shoulders (shrugging); pulls shoulder blades together; tilts head backwards | Scapula; cervical spine | Scapula: rotests inferiorly, retracts, elevates, and depresses; spine: extends | Trapezius | Skull; vertebral column | Acromion and spine of scapula; clavicle |
| Posterior thorax | Stabilizes scapula during pectoral girdle movement | Scapula | Retracts; rotates inferiorly | Rhomboid major | Thoracic vertebrae (T2–T5) | Medial border of scapula |
| Posterior thorax | Stabilizes scapula during pectoral girdle movement | Scapula | Retracts; rotates inferiorly | Rhomboid minor | Cervical and thoracic vertebrae (C7 and T1) | Medial border of scapula |
Table 11.8
Muscles That Move the Humerus
Similar to the muscles that position the pectoral girdle, muscles that cross the shoulder joint and move the humerus bone of the arm include both axial and scapular muscles (Figure 11.23 and Figure 11.24). The two axial muscles are the pectoralis major and the latissimus dorsi. The pectoralis major is thick and fan-shaped, covering much of the superior portion of the anterior thorax. The broad, triangular latissimus dorsi is located on the inferior part of the back, where it inserts into a thick connective tissue shealth called an aponeurosis.
Figure 11.23 Muscles That Move the Humerus (a, c) The muscles that move the humerus anteriorly are generally located on the anterior side of the body and originate from the sternum (e.g., pectoralis major) or the anterior side of the scapula (e.g., subscapularis). (b) The muscles that move the humerus superiorly generally originate from the superior surfaces of the scapula and/or the clavicle (e.g., deltoids). The muscles that move the humerus inferiorly generally originate from middle or lower back (e.g., latissiumus dorsi). (d) The muscles that move the humerus posteriorly are generally located on the posterior side of the body and insert into the scapula (e.g., infraspinatus).
Figure 11.24 Muscles That Move the Humerus
The rest of the shoulder muscles originate on the scapula. The anatomical and ligamental structure of the shoulder joint and the arrangements of the muscles covering it, allows the arm to carry out different types of movements. The deltoid, the thick muscle that creates the rounded lines of the shoulder is the major abductor of the arm, but it also facilitates flexing and medial rotation, as well as extension and lateral rotation. The subscapularis originates on the anterior scapula and medially rotates the arm. Named for their locations, the supraspinatus (superior to the spine of the scapula) and the infraspinatus (inferior to the spine of the scapula) abduct the arm, and laterally rotate the arm, respectively. The thick and flat teres major is inferior to the teres minor and extends the arm, and assists in adduction and medial rotation of it. The long teres minor laterally rotates and extends the arm. Finally, the coracobrachialis flexes and adducts the arm.
The tendons of the deep subscapularis, supraspinatus, infraspinatus, and teres minor connect the scapula to the humerus, forming the rotator cuff (musculotendinous cuff), the circle of tendons around the shoulder joint. When baseball pitchers undergo shoulder surgery it is usually on the rotator cuff, which becomes pinched and inflamed, and may tear away from the bone due to the repetitive motion of bring the arm overhead to throw a fast pitch.
Muscles That Move the Forearm
The forearm, made of the radius and ulna bones, has four main types of action at the hinge of the elbow joint: flexion, extension, pronation, and supination. The forearm flexors include the biceps brachii, brachialis, and brachioradialis. The extensors are the triceps brachii and anconeus. The pronators are the pronator teres and the pronator quadratus, and the supinator is the only one that turns the forearm anteriorly. When the forearm faces anteriorly, it is supinated. When the forearm faces posteriorly, it is pronated.
The biceps brachii, brachialis, and brachioradialis flex the forearm. The two-headed biceps brachii crosses the shoulder and elbow joints to flex the forearm, also taking part in supinating the forearm at the radioulnar joints and flexing the arm at the shoulder joint. Deep to the biceps brachii, the brachialis provides additional power in flexing the forearm. Finally, the brachioradialis can flex the forearm quickly or help lift a load slowly. These muscles and their associated blood vessels and nerves form the anterior compartment of the arm (anterior flexor compartment of the arm) (Figure 11.25 and Figure 11.26).
Figure 11.25 Muscles That Move the Forearm The muscles originating in the upper arm flex, extend, pronate, and supinate the forearm. The muscles originating in the forearm move the wrists, hands, and fingers.
Figure 11.26 Muscles That Move the Forearm
Muscles That Move the Wrist, Hand, and Fingers
Wrist, hand, and finger movements are facilitated by two groups of muscles. The forearm is the origin of the extrinsic muscles of the hand. The palm is the origin of the intrinsic muscles of the hand.
Muscles of the Arm That Move the Wrists, Hands, and Fingers
The muscles in the anterior compartment of the forearm (anterior flexor compartment of the forearm) originate on the humerus and insert onto different parts of the hand. These make up the bulk of the forearm. From lateral to medial, the superficial anterior compartment of the forearm includes the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis. The flexor digitorum superficialis flexes the hand as well as the digits at the knuckles, which allows for rapid finger movements, as in typing or playing a musical instrument (see Figure 11.27 and Table 11.9). However, poor ergonomics can irritate the tendons of these muscles as they slide back and forth with the carpal tunnel of the anterior wrist and pinch the median nerve, which also travels through the tunnel, causing Carpal Tunnel Syndrome. The deep anterior compartment produces flexion and bends fingers to make a fist. These are the flexor pollicis longus and the flexor digitorum profundus.
The muscles in the superficial posterior compartment of the forearm (superficial posterior extensor compartment of the forearm) originate on the humerus. These are the extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and the extensor carpi ulnaris.
The muscles of the deep posterior compartment of the forearm (deep posterior extensor compartment of the forearm) originate on the radius and ulna. These include the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis (see Figure 11.27).
Figure 11.27 Muscles That Move the Wrist, Hands, and Forearm
The tendons of the forearm muscles attach to the wrist and extend into the hand. Fibrous bands called retinacula sheath the tendons at the wrist. The flexor retinaculum extends over the palmar surface of the hand while the extensor retinaculumextends over the dorsal surface of the hand.
Intrinsic Muscles of the Hand
The intrinsic muscles of the hand both originate and insert within it (Figure 11.28). These muscles allow your fingers to also make precise movements for actions, such as typing or writing. These muscles are divided into three groups. The thenarmuscles are on the radial aspect of the palm. The hypothenar muscles are on the medial aspect of the palm, and the intermediate muscles are midpalmar.
The thenar muscles include the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and the adductor pollicis. These muscles form the thenar eminence, the rounded contour of the base of the thumb, and all act on the thumb. The movements of the thumb play an integral role in most precise movements of the hand.
The hypothenar muscles include the abductor digiti minimi, flexor digiti minimi brevis, and the opponens digiti minimi. These muscles form the hypothenar eminence, the rounded contour of the little finger, and as such, they all act on the little finger. Finally, the intermediate muscles act on all the fingers and include the lumbrical, the palmar interossei, and the dorsal interossei.
Figure 11.28 Intrinsic Muscles of the Hand The intrinsic muscles of the hand both originate and insert within the hand. These muscles provide the fine motor control of the fingers by flexing, extending, abducting, and adducting the more distal finger and thumb segments.
Intrinsic Muscles of the Hand
| Muscle | Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|---|
| Thenar muscles | Moves thumb toward body | Thumb | Abduction | Abductor pollicis brevis | Flexor retinaculum; and nearby carpals | Lateral base of proximal phalanx of thumb |
| Thenar muscles | Moves thumb across palm to touch other fingers | Thumb | Opposition | Opponens pollicis | Flexor retinaculum; trapezium | Anterior of first metacarpal |
| Thenar muscles | Flexes thumb | Thumb | Flexion | Flexor pollicis brevis | Flexor retinaculum; trapezium | Lateral base of proximal phalanx of thumb |
| Thenar muscles | Moves thumb away from body | Thumb | Adduction | Adductor pollicis | Capitate bone; bases of metacarpals 2–4; front of metacarpal 3 | Medial base of proximal phalanx of thumb |
| Hypothenar muscles | Moves little finger toward body | Little finger | Abduction | Abductor digiti minimi | Pisiform bone | Medial side of proximal phalanx of little finger |
| Hypothenar muscles | Flexes little finger | Little finger | Flexion | Flexor digiti minimi brevis | Hamate bone; flexor retinaculum | Medial side of proximal phalanx of little finger |
| Hypothenar muscles | Moves little finger across palm to touch thumb | Little finger | Opposition | Opponens digiti minimi | Hamate bone; flexor retinaculum | Medial side of fifth metacarpal |
| Intermediate muscles | Flexes each finger at metacarpo-phalangeal joints; extends each finger at interphalangeal joints | Fingers | Flexion | Lumbricals | Palm (lateral sides of tendons in flexor digitorum profundus) | Fingers 2–5 (lateral edges of extensional expansions on first phalanges) |
| Intermediate muscles | Adducts and flexes each finger at metacarpo-phalangeal joints; extends each finger at interphalangeal joints | Fingers | Adduction; flexion; extension | Palmar interossei | Side of each metacarpal that faces metacarpal 3 (absent from metacarpal 3) | Extensor expansion on first phalanx of each finger (except finger 3) on side facing finger 3 |
| Intermediate muscles | Abducts and flexes the three middle fingers at metacarpo-phalangeal joints; extends the three middle fingers at interphalangeal joints | Fingers | Abduction; flexion; extension | Dorsal interossei | Sides of metacarpals | Both sides of finger 3; for each other finger, extensor expansion over first phalanx on side opposite finger 3 |
Table 11.9
Appendicular Muscles of the Pelvic Girdle and Lower Limbs
- Identify the appendicular muscles of the pelvic girdle and lower limb
- Identify the movement and function of the pelvic girdle and lower limb
The appendicular muscles of the lower body position and stabilize the pelvic girdle, which serves as a foundation for the lower limbs. Comparatively, there is much more movement at the pectoral girdle than at the pelvic girdle. There is very little movement of the pelvic girdle because of its connection with the sacrum at the base of the axial skeleton. The pelvic girdle is less range of motion because it was designed to stabilize and support the body.
Muscles of the Thigh
What would happen if the pelvic girdle, which attaches the lower limbs to the torso, were capable of the same range of motion as the pectoral girdle? For one thing, walking would expend more energy if the heads of the femurs were not secured in the acetabula of the pelvis. The body’s center of gravity is in the area of the pelvis. If the center of gravity were not to remain fixed, standing up would be difficult as well. Therefore, what the leg muscles lack in range of motion and versatility, they make up for in size and power, facilitating the body’s stabilization, posture, and movement.
Gluteal Region Muscles That Move the Femur
Most muscles that insert on the femur (the thigh bone) and move it, originate on the pelvic girdle. The psoas major and iliacusmake up the iliopsoas group. Some of the largest and most powerful muscles in the body are the gluteal muscles or gluteal group. The gluteus maximus is the largest; deep to the gluteus maximus is the gluteus medius, and deep to the gluteus medius is the gluteus minimus, the smallest of the trio (Figure 11.29 and Figure 11.30).
Figure 11.29 Hip and Thigh Muscles The large and powerful muscles of the hip that move the femur generally originate on the pelvic girdle and insert into the femur. The muscles that move the lower leg typically originate on the femur and insert into the bones of the knee joint. The anterior muscles of the femur extend the lower leg but also aid in flexing the thigh. The posterior muscles of the femur flex the lower leg but also aid in extending the thigh. A combination of gluteal and thigh muscles also adduct, abduct, and rotate the thigh and lower leg.
Figure 11.30 Gluteal Region Muscles That Move the Femur
The tensor fascia latae is a thick, squarish muscle in the superior aspect of the lateral thigh. It acts as a synergist of the gluteus medius and iliopsoas in flexing and abducting the thigh. It also helps stabilize the lateral aspect of the knee by pulling on the iliotibial tract (band), making it taut. Deep to the gluteus maximus, the piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris laterally rotate the femur at the hip.
The adductor longus, adductor brevis, and adductor magnus can both medially and laterally rotate the thigh depending on the placement of the foot. The adductor longus flexes the thigh, whereas the adductor magnus extends it. The pectineusadducts and flexes the femur at the hip as well. The pectineus is located in the femoral triangle, which is formed at the junction between the hip and the leg and also includes the femoral nerve, the femoral artery, the femoral vein, and the deep inguinal lymph nodes.
Thigh Muscles That Move the Femur, Tibia, and Fibula
Deep fascia in the thigh separates it into medial, anterior, and posterior compartments (see Figure 11.29 and Figure 11.31). The muscles in the medial compartment of the thigh are responsible for adducting the femur at the hip. Along with the adductor longus, adductor brevis, adductor magnus, and pectineus, the strap-like gracilis adducts the thigh in addition to flexing the leg at the knee.
Figure 11.31 Thigh Muscles That Move the Femur, Tibia, and Fibula
The muscles of the anterior compartment of the thigh flex the thigh and extend the leg. This compartment contains the quadriceps femoris group, which actually comprises four muscles that extend and stabilize the knee. The rectus femoris is on the anterior aspect of the thigh, the vastus lateralis is on the lateral aspect of the thigh, the vastus medialis is on the medial aspect of the thigh, and the vastus intermedius is between the vastus lateralis and vastus medialis and deep to the rectus femoris. The tendon common to all four is the quadriceps tendon (patellar tendon), which inserts into the patella and continues below it as the patellar ligament. The patellar ligament attaches to the tibial tuberosity. In addition to the quadriceps femoris, the sartorius is a band-like muscle that extends from the anterior superior iliac spine to the medial side of the proximal tibia. This versatile muscle flexes the leg at the knee and flexes, abducts, and laterally rotates the leg at the hip. This muscle allows us to sit cross-legged.
The posterior compartment of the thigh includes muscles that flex the leg and extend the thigh. The three long muscles on the back of the knee are the hamstring group, which flexes the knee. These are the biceps femoris, semitendinosus, and semimembranosus. The tendons of these muscles form the popliteal fossa, the diamond-shaped space at the back of the knee.
Muscles That Move the Feet and Toes
Similar to the thigh muscles, the muscles of the leg are divided by deep fascia into compartments, although the leg has three: anterior, lateral, and posterior (Figure 11.32 and Figure 11.33).
Figure 11.32 Muscles of the Lower Leg The muscles of the anterior compartment of the lower leg are generally responsible for dorsiflexion, and the muscles of the posterior compartment of the lower leg are generally responsible for plantar flexion. The lateral and medial muscles in both compartments invert, evert, and rotate the foot.
Figure 11.33 Muscles That Move the Feet and Toes
The muscles in the anterior compartment of the leg: the tibialis anterior, a long and thick muscle on the lateral surface of the tibia, the extensor hallucis longus, deep under it, and the extensor digitorum longus, lateral to it, all contribute to raising the front of the foot when they contract. The fibularis tertius, a small muscle that originates on the anterior surface of the fibula, is associated with the extensor digitorum longus and sometimes fused to it, but is not present in all people. Thick bands of connective tissue called the superior extensor retinaculum (transverse ligament of the ankle) and the inferior extensor retinaculum, hold the tendons of these muscles in place during dorsiflexion.
The lateral compartment of the leg includes two muscles: the fibularis longus (peroneus longus) and the fibularis brevis(peroneus brevis). The superficial muscles in the posterior compartment of the leg all insert onto the calcaneal tendon(Achilles tendon), a strong tendon that inserts into the calcaneal bone of the ankle. The muscles in this compartment are large and strong and keep humans upright. The most superficial and visible muscle of the calf is the gastrocnemius. Deep to the gastrocnemius is the wide, flat soleus. The plantaris runs obliquely between the two; some people may have two of these muscles, whereas no plantaris is observed in about seven percent of other cadaver dissections. The plantaris tendon is a desirable substitute for the fascia lata in hernia repair, tendon transplants, and repair of ligaments. There are four deep muscles in the posterior compartment of the leg as well: the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior.
The foot also has intrinsic muscles, which originate and insert within it (similar to the intrinsic muscles of the hand). These muscles primarily provide support for the foot and its arch, and contribute to movements of the toes (Figure 11.34 and Figure 11.35). The principal support for the longitudinal arch of the foot is a deep fascia called plantar aponeurosis, which runs from the calcaneus bone to the toes (inflammation of this tissue is the cause of “plantar fasciitis,” which can affect runners. The intrinsic muscles of the foot consist of two groups. The dorsal group includes only one muscle, the extensor digitorum brevis. The second group is the plantar group, which consists of four layers, starting with the most superficial.
Figure 11.34 Intrinsic Muscles of the Foot The muscles along the dorsal side of the foot (a) generally extend the toes while the muscles of the plantar side of the foot (b, c, d) generally flex the toes. The plantar muscles exist in three layers, providing the foot the strength to counterbalance the weight of the body. In this diagram, these three layers are shown from a plantar view beginning with the bottom-most layer just under the plantar skin of the foot (b) and ending with the top-most layer (d) located just inferior to the foot and toe bones.
Figure 11.35 Intrinsic Muscles in the Foot
Key Terms
- abduct
- move away from midline in the sagittal plane
- abductor
- moves the bone away from the midline
- abductor digiti minimi
- muscle that abducts the little finger
- abductor pollicis brevis
- muscle that abducts the thumb
- abductor pollicis longus
- muscle that inserts into the first metacarpal
- adductor
- moves the bone toward the midline
- adductor brevis
- muscle that adducts and medially rotates the thigh
- adductor longus
- muscle that adducts, medially rotates, and flexes the thigh
- adductor magnus
- muscle with an anterior fascicle that adducts, medially rotates and flexes the thigh, and a posterior fascicle that assists in thigh extension
- adductor pollicis
- muscle that adducts the thumb
- agonist
- (also, prime mover) muscle whose contraction is responsible for producing a particular motion
- anal triangle
- posterior triangle of the perineum that includes the anus
- anconeus
- small muscle on the lateral posterior elbow that extends the forearm
- antagonist
- muscle that opposes the action of an agonist
- anterior compartment of the arm
- (anterior flexor compartment of the arm) the biceps brachii, brachialis, brachioradialis, and their associated blood vessels and nerves
- anterior compartment of the forearm
- (anterior flexor compartment of the forearm) deep and superficial muscles that originate on the humerus and insert into the hand
- anterior compartment of the leg
- region that includes muscles that dorsiflex the foot
- anterior compartment of the thigh
- region that includes muscles that flex the thigh and extend the leg
- anterior scalene
- a muscle anterior to the middle scalene
- appendicular
- of the arms and legs
- axial
- of the trunk and head
- belly
- bulky central body of a muscle
- bi
- two
- biceps brachii
- two-headed muscle that crosses the shoulder and elbow joints to flex the forearm while assisting in supinating it and flexing the arm at the shoulder
- biceps femoris
- hamstring muscle
- bipennate
- pennate muscle that has fascicles that are located on both sides of the tendon
- brachialis
- muscle deep to the biceps brachii that provides power in flexing the forearm.
- brachioradialis
- muscle that can flex the forearm quickly or help lift a load slowly
- brevis
- short
- buccinator
- muscle that compresses the cheek
- calcaneal tendon
- (also, Achilles tendon) strong tendon that inserts into the calcaneal bone of the ankle
- caval opening
- opening in the diaphragm that allows the inferior vena cava to pass through; foramen for the vena cava
- circular
- (also, sphincter) fascicles that are concentrically arranged around an opening
- compressor urethrae
- deep perineal muscle in women
- convergent
- fascicles that extend over a broad area and converge on a common attachment site
- coracobrachialis
- muscle that flexes and adducts the arm
- corrugator supercilii
- prime mover of the eyebrows
- deep anterior compartment
- flexor pollicis longus, flexor digitorum profundus, and their associated blood vessels and nerves
- deep posterior compartment of the forearm
- (deep posterior extensor compartment of the forearm) the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, and their associated blood vessels and nerves
- deep transverse perineal
- deep perineal muscle in men
- deglutition
- swallowing
- deltoid
- shoulder muscle that abducts the arm as well as flexes and medially rotates it, and extends and laterally rotates it
- diaphragm
- skeletal muscle that separates the thoracic and abdominal cavities and is dome-shaped at rest
- digastric
- muscle that has anterior and posterior bellies and elevates the hyoid bone and larynx when one swallows; it also depresses the mandible
- dorsal group
- region that includes the extensor digitorum brevis
- dorsal interossei
- muscles that abduct and flex the three middle fingers at the metacarpophalangeal joints and extend them at the interphalangeal joints
- epicranial aponeurosis
- (also, galea aponeurosis) flat broad tendon that connects the frontalis and occipitalis
- erector spinae group
- large muscle mass of the back; primary extensor of the vertebral column
- extensor
- muscle that increases the angle at the joint
- extensor carpi radialis brevis
- muscle that extends and abducts the hand at the wrist
- extensor carpi ulnaris
- muscle that extends and adducts the hand
- extensor digiti minimi
- muscle that extends the little finger
- extensor digitorum
- muscle that extends the hand at the wrist and the phalanges
- extensor digitorum brevis
- muscle that extends the toes
- extensor digitorum longus
- muscle that is lateral to the tibialis anterior
- extensor hallucis longus
- muscle that is partly deep to the tibialis anterior and extensor digitorum longus
- extensor indicis
- muscle that inserts onto the tendon of the extensor digitorum of the index finger
- extensor pollicis brevis
- muscle that inserts onto the base of the proximal phalanx of the thumb
- extensor pollicis longus
- muscle that inserts onto the base of the distal phalanx of the thumb
- extensor radialis longus
- muscle that extends and abducts the hand at the wrist
- extensor retinaculum
- band of connective tissue that extends over the dorsal surface of the hand
- external intercostal
- superficial intercostal muscles that raise the rib cage
- external oblique
- superficial abdominal muscle with fascicles that extend inferiorly and medially
- extrinsic eye muscles
- originate outside the eye and insert onto the outer surface of the white of the eye, and create eyeball movement
- extrinsic muscles of the hand
- muscles that move the wrists, hands, and fingers and originate on the arm
- fascicle
- muscle fibers bundled by perimysium into a unit
- femoral triangle
- region formed at the junction between the hip and the leg and includes the pectineus, femoral nerve, femoral artery, femoral vein, and deep inguinal lymph nodes
- fibularis brevis
- (also, peroneus brevis) muscle that plantar flexes the foot at the ankle and everts it at the intertarsal joints
- fibularis longus
- (also, peroneus longus) muscle that plantar flexes the foot at the ankle and everts it at the intertarsal joints
- fibularis tertius
- small muscle that is associated with the extensor digitorum longus
- fixator
- synergist that assists an agonist by preventing or reducing movement at another joint, thereby stabilizing the origin of the agonist
- flexion
- movement that decreases the angle of a joint
- flexor
- muscle that decreases the angle at the joint
- flexor carpi radialis
- muscle that flexes and abducts the hand at the wrist
- flexor carpi ulnaris
- muscle that flexes and adducts the hand at the wrist
- flexor digiti minimi brevis
- muscle that flexes the little finger
- flexor digitorum longus
- muscle that flexes the four small toes
- flexor digitorum profundus
- muscle that flexes the phalanges of the fingers and the hand at the wrist
- flexor digitorum superficialis
- muscle that flexes the hand and the digits
- flexor hallucis longus
- muscle that flexes the big toe
- flexor pollicis brevis
- muscle that flexes the thumb
- flexor pollicis longus
- muscle that flexes the distal phalanx of the thumb
- flexor retinaculum
- band of connective tissue that extends over the palmar surface of the hand
- frontalis
- front part of the occipitofrontalis muscle
- fusiform
- muscle that has fascicles that are spindle-shaped to create large bellies
- gastrocnemius
- most superficial muscle of the calf
- genioglossus
- muscle that originates on the mandible and allows the tongue to move downward and forward
- geniohyoid
- muscle that depresses the mandible, and raises and pulls the hyoid bone anteriorly
- gluteal group
- muscle group that extends, flexes, rotates, adducts, and abducts the femur
- gluteus maximus
- largest of the gluteus muscles that extends the femur
- gluteus medius
- muscle deep to the gluteus maximus that abducts the femur at the hip
- gluteus minimus
- smallest of the gluteal muscles and deep to the gluteus medius
- gracilis
- muscle that adducts the thigh and flexes the leg at the knee
- hamstring group
- three long muscles on the back of the leg
- hyoglossus
- muscle that originates on the hyoid bone to move the tongue downward and flatten it
- hypothenar
- group of muscles on the medial aspect of the palm
- hypothenar eminence
- rounded contour of muscle at the base of the little finger
- iliacus
- muscle that, along with the psoas major, makes up the iliopsoas
- iliococcygeus
- muscle that makes up the levator ani along with the pubococcygeus
- iliocostalis cervicis
- muscle of the iliocostalis group associated with the cervical region
- iliocostalis group
- laterally placed muscles of the erector spinae
- iliocostalis lumborum
- muscle of the iliocostalis group associated with the lumbar region
- iliocostalis thoracis
- muscle of the iliocostalis group associated with the thoracic region
- iliopsoas group
- muscle group consisting of iliacus and psoas major muscles, that flexes the thigh at the hip, rotates it laterally, and flexes the trunk of the body onto the hip
- iliotibial tract
- muscle that inserts onto the tibia; made up of the gluteus maximus and connective tissues of the tensor fasciae latae
- inferior extensor retinaculum
- cruciate ligament of the ankle
- inferior gemellus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- infrahyoid muscles
- anterior neck muscles that are attached to, and inferior to the hyoid bone
- infraspinatus
- muscle that laterally rotates the arm
- innermost intercostal
- the deepest intercostal muscles that draw the ribs together
- insertion
- end of a skeletal muscle that is attached to the structure (usually a bone) that is moved when the muscle contracts
- intercostal muscles
- muscles that span the spaces between the ribs
- intermediate
- group of midpalmar muscles
- internal intercostal
- muscles the intermediate intercostal muscles that draw the ribs together
- internal oblique
- flat, intermediate abdominal muscle with fascicles that run perpendicular to those of the external oblique
- intrinsic muscles of the hand
- muscles that move the wrists, hands, and fingers and originate in the palm
- ischiococcygeus
- muscle that assists the levator ani and pulls the coccyx anteriorly
- lateral compartment of the leg
- region that includes the fibularis (peroneus) longus and the fibularis (peroneus) brevis and their associated blood vessels and nerves
- lateral pterygoid
- muscle that moves the mandible from side to side
- lateralis
- to the outside
- latissimus dorsi
- broad, triangular axial muscle located on the inferior part of the back
- levator ani
- pelvic muscle that resists intra-abdominal pressure and supports the pelvic viscera
- linea alba
- white, fibrous band that runs along the midline of the trunk
- longissimus capitis
- muscle of the longissimus group associated with the head region
- longissimus cervicis
- muscle of the longissimus group associated with the cervical region
- longissimus group
- intermediately placed muscles of the erector spinae
- longissimus thoracis
- muscle of the longissimus group associated with the thoracic region
- longus
- long
- lumbrical
- muscle that flexes each finger at the metacarpophalangeal joints and extend each finger at the interphalangeal joints
- masseter
- main muscle for chewing that elevates the mandible to close the mouth
- mastication
- chewing
- maximus
- largest
- medial compartment of the thigh
- a region that includes the adductor longus, adductor brevis, adductor magnus, pectineus, gracilis, and their associated blood vessels and nerves
- medial pterygoid
- muscle that moves the mandible from side to side
- medialis
- to the inside
- medius
- medium
- middle scalene
- longest scalene muscle, located between the anterior and posterior scalenes
- minimus
- smallest
- multifidus
- muscle of the lumbar region that helps extend and laterally flex the vertebral column
- multipennate
- pennate muscle that has a tendon branching within it
- mylohyoid
- muscle that lifts the hyoid bone and helps press the tongue to the top of the mouth
- oblique
- at an angle
- obturator externus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- obturator internus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- occipitalis
- posterior part of the occipitofrontalis muscle
- occipitofrontalis
- muscle that makes up the scalp with a frontal belly and an occipital belly
- omohyoid
- muscle that has superior and inferior bellies and depresses the hyoid bone
- opponens digiti minimi
- muscle that brings the little finger across the palm to meet the thumb
- opponens pollicis
- muscle that moves the thumb across the palm to meet another finger
- orbicularis oculi
- circular muscle that closes the eye
- orbicularis oris
- circular muscle that moves the lips
- origin
- end of a skeletal muscle that is attached to another structure (usually a bone) in a fixed position
- palatoglossus
- muscle that originates on the soft palate to elevate the back of the tongue
- palmar interossei
- muscles that abduct and flex each finger at the metacarpophalangeal joints and extend each finger at the interphalangeal joints
- palmaris longus
- muscle that provides weak flexion of the hand at the wrist
- parallel
- fascicles that extend in the same direction as the long axis of the muscle
- patellar ligament
- extension of the quadriceps tendon below the patella
- pectineus
- muscle that abducts and flexes the femur at the hip
- pectoral girdle
- shoulder girdle, made up of the clavicle and scapula
- pectoralis major
- thick, fan-shaped axial muscle that covers much of the superior thorax
- pectoralis minor
- muscle that moves the scapula and assists in inhalation
- pelvic diaphragm
- muscular sheet that comprises the levator ani and the ischiococcygeus
- pelvic girdle
- hips, a foundation for the lower limb
- pennate
- fascicles that are arranged differently based on their angles to the tendon
- perineum
- diamond-shaped region between the pubic symphysis, coccyx, and ischial tuberosities
- piriformis
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- plantar aponeurosis
- muscle that supports the longitudinal arch of the foot
- plantar group
- four-layered group of intrinsic foot muscles
- plantaris
- muscle that runs obliquely between the gastrocnemius and the soleus
- popliteal fossa
- diamond-shaped space at the back of the knee
- popliteus
- muscle that flexes the leg at the knee and creates the floor of the popliteal fossa
- posterior compartment of the leg
- region that includes the superficial gastrocnemius, soleus, and plantaris, and the deep popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior
- posterior compartment of the thigh
- region that includes muscles that flex the leg and extend the thigh
- posterior scalene
- smallest scalene muscle, located posterior to the middle scalene
- prime mover
- (also, agonist) principle muscle involved in an action
- pronator quadratus
- pronator that originates on the ulna and inserts on the radius
- pronator teres
- pronator that originates on the humerus and inserts on the radius
- psoas major
- muscle that, along with the iliacus, makes up the iliopsoas
- pubococcygeus
- muscle that makes up the levator ani along with the iliococcygeus
- quadratus femoris
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- quadratus lumborum
- posterior part of the abdominal wall that helps with posture and stabilization of the body
- quadriceps femoris group
- four muscles, that extend and stabilize the knee
- quadriceps tendon
- (also, patellar tendon) tendon common to all four quadriceps muscles, inserts into the patella
- rectus
- straight
- rectus abdominis
- long, linear muscle that extends along the middle of the trunk
- rectus femoris
- quadricep muscle on the anterior aspect of the thigh
- rectus sheaths
- tissue that makes up the linea alba
- retinacula
- fibrous bands that sheath the tendons at the wrist
- rhomboid major
- muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae
- rhomboid minor
- muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae
- rotator cuff
- (also, musculotendinous cuff) the circle of tendons around the shoulder joint
- sartorius
- band-like muscle that flexes, abducts, and laterally rotates the leg at the hip
- scalene muscles
- flex, laterally flex, and rotate the head; contribute to deep inhalation
- segmental muscle group
- interspinales and intertransversarii muscles that bring together the spinous and transverse processes of each consecutive vertebra
- semimembranosus
- hamstring muscle
- semispinalis capitis
- transversospinales muscle associated with the head region
- semispinalis cervicis
- transversospinales muscle associated with the cervical region
- semispinalis thoracis
- transversospinales muscle associated with the thoracic region
- semitendinosus
- hamstring muscle
- serratus anterior
- large and flat muscle that originates on the ribs and inserts onto the scapula
- soleus
- wide, flat muscle deep to the gastrocnemius
- sphincter urethrovaginalis
- deep perineal muscle in women
- spinalis capitis
- muscle of the spinalis group associated with the head region
- spinalis cervicis
- muscle of the spinalis group associated with the cervical region
- spinalis group
- medially placed muscles of the erector spinae
- spinalis thoracis
- muscle of the spinalis group associated with the thoracic region
- splenius
- posterior neck muscles; includes the splenius capitis and splenius cervicis
- splenius capitis
- neck muscle that inserts into the head region
- splenius cervicis
- neck muscle that inserts into the cervical region
- sternocleidomastoid
- major muscle that laterally flexes and rotates the head
- sternohyoid
- muscle that depresses the hyoid bone
- sternothyroid
- muscle that depresses the larynx’s thyroid cartilage
- styloglossus
- muscle that originates on the styloid bone, and allows upward and backward motion of the tongue
- stylohyoid
- muscle that elevates the hyoid bone posteriorly
- subclavius
- muscle that stabilizes the clavicle during movement
- subscapularis
- muscle that originates on the anterior scapula and medially rotates the arm
- superficial anterior compartment of the forearm
- flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis, and their associated blood vessels and nerves
- superficial posterior compartment of the forearm
- extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and their associated blood vessels and nerves
- superior extensor retinaculum
- transverse ligament of the ankle
- superior gemellus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- supinator
- muscle that moves the palm and forearm anteriorly
- suprahyoid muscles
- neck muscles that are superior to the hyoid bone
- supraspinatus
- muscle that abducts the arm
- synergist
- muscle whose contraction helps a prime mover in an action
- temporalis
- muscle that retracts the mandible
- tendinous intersections
- three transverse bands of collagen fibers that divide the rectus abdominis into segments
- tensor fascia lata
- muscle that flexes and abducts the thigh
- teres major
- muscle that extends the arm and assists in adduction and medial rotation of it
- teres minor
- muscle that laterally rotates and extends the arm
- thenar
- group of muscles on the lateral aspect of the palm
- thenar eminence
- rounded contour of muscle at the base of the thumb
- thyrohyoid
- muscle that depresses the hyoid bone and elevates the larynx’s thyroid cartilage
- tibialis anterior
- muscle located on the lateral surface of the tibia
- tibialis posterior
- muscle that plantar flexes and inverts the foot
- transversospinales
- muscles that originate at the transverse processes and insert at the spinous processes of the vertebrae
- transversus abdominis
- deep layer of the abdomen that has fascicles arranged transversely around the abdomen
- trapezius
- muscle that stabilizes the upper part of the back
- tri
- three
- triceps brachii
- three-headed muscle that extends the forearm
- unipennate
- pennate muscle that has fascicles located on one side of the tendon
- urogenital triangle
- anterior triangle of the perineum that includes the external genitals
- vastus intermedius
- quadricep muscle that is between the vastus lateralis and vastus medialis and is deep to the rectus femoris
- vastus lateralis
- quadricep muscle on the lateral aspect of the thigh
- vastus medialis
- quadricep muscle on the medial aspect of the thigh
Chapter Review
11.1 Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems
Skeletal muscles each have an origin and an insertion. The end of the muscle that attaches to the bone being pulled is called the muscle’s insertion and the end of the muscle attached to a fixed, or stabilized, bone is called the origin. The muscle primarily responsible for a movement is called the prime mover, and muscles that assist in this action are called synergists. A synergist that makes the insertion site more stable is called a fixator. Meanwhile, a muscle with the opposite action of the prime mover is called an antagonist. Several factors contribute to the force generated by a skeletal muscle. One is the arrangement of the fascicles in the skeletal muscle. Fascicles can be parallel, circular, convergent, pennate, fusiform, or triangular. Each arrangement has its own range of motion and ability to do work.
11.2 Naming Skeletal Muscles
Muscle names are based on many characteristics. The location of a muscle in the body is important. Some muscles are named based on their size and location, such as the gluteal muscles of the buttocks. Other muscle names can indicate the location in the body or bones with which the muscle is associated, such as the tibialis anterior. The shapes of some muscles are distinctive; for example, the direction of the muscle fibers is used to describe muscles of the body midline. The origin and/or insertion can also be features used to name a muscle; examples are the biceps brachii, triceps brachii, and the pectoralis major.
11.3 Axial Muscles of the Head, Neck, and Back
Muscles are either axial muscles or appendicular. The axial muscles are grouped based on location, function, or both. Some axial muscles cross over to the appendicular skeleton. The muscles of the head and neck are all axial. The muscles in the face create facial expression by inserting into the skin rather than onto bone. Muscles that move the eyeballs are extrinsic, meaning they originate outside of the eye and insert onto it. Tongue muscles are both extrinsic and intrinsic. The genioglossus depresses the tongue and moves it anteriorly; the styloglossus lifts the tongue and retracts it; the palatoglossus elevates the back of the tongue; and the hyoglossus depresses and flattens it. The muscles of the anterior neck facilitate swallowing and speech, stabilize the hyoid bone and position the larynx. The muscles of the neck stabilize and move the head. The sternocleidomastoid divides the neck into anterior and posterior triangles.
The muscles of the back and neck that move the vertebral column are complex, overlapping, and can be divided into five groups. The splenius group includes the splenius capitis and the splenius cervicis. The erector spinae has three subgroups. The iliocostalis group includes the iliocostalis cervicis, the iliocostalis thoracis, and the iliocostalis lumborum. The longissimus group includes the longissimus capitis, the longissimus cervicis, and the longissimus thoracis. The spinalis group includes the spinalis capitis, the spinalis cervicis, and the spinalis thoracis. The transversospinales include the semispinalis capitis, semispinalis cervicis, semispinalis thoracis, multifidus, and rotatores. The segmental muscles include the interspinales and intertransversarii. Finally, the scalenes include the anterior scalene, middle scalene, and posterior scalene.
11.4 Axial Muscles of the Abdominal Wall, and Thorax
Made of skin, fascia, and four pairs of muscle, the anterior abdominal wall protects the organs located in the abdomen and moves the vertebral column. These muscles include the rectus abdominis, which extends through the entire length of the trunk, the external oblique, the internal oblique, and the transversus abdominus. The quadratus lumborum forms the posterior abdominal wall.
The muscles of the thorax play a large role in breathing, especially the dome-shaped diaphragm. When it contracts and flattens, the volume inside the pleural cavities increases, which decreases the pressure within them. As a result, air will flow into the lungs. The external and internal intercostal muscles span the space between the ribs and help change the shape of the rib cage and the volume-pressure ratio inside the pleural cavities during inspiration and expiration.
The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women. The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.
11.5 Muscles of the Pectoral Girdle and Upper Limbs
The clavicle and scapula make up the pectoral girdle, which provides a stable origin for the muscles that move the humerus. The muscles that position and stabilize the pectoral girdle are located on the thorax. The anterior thoracic muscles are the subclavius, pectoralis minor, and the serratus anterior. The posterior thoracic muscles are the trapezius, levator scapulae, rhomboid major, and rhomboid minor. Nine muscles cross the shoulder joint to move the humerus. The ones that originate on the axial skeleton are the pectoralis major and the latissimus dorsi. The deltoid, subscapularis, supraspinatus, infraspinatus, teres major, teres minor, and coracobrachialis originate on the scapula.
The forearm flexors include the biceps brachii, brachialis, and brachioradialis. The extensors are the triceps brachii and anconeus. The pronators are the pronator teres and the pronator quadratus. The supinator is the only one that turns the forearm anteriorly.
The extrinsic muscles of the hands originate along the forearm and insert into the hand in order to facilitate crude movements of the wrists, hands, and fingers. The superficial anterior compartment of the forearm produces flexion. These muscles are the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and the flexor digitorum superficialis. The deep anterior compartment produces flexion as well. These are the flexor pollicis longus and the flexor digitorum profundus. The rest of the compartments produce extension. The extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris are the muscles found in the superficial posterior compartment. The deep posterior compartment includes the abductor longus, extensor pollicis brevis, extensor pollicis longus, and the extensor indicis.
Finally, the intrinsic muscles of the hands allow our fingers to make precise movements, such as typing and writing. They both originate and insert within the hand. The thenar muscles, which are located on the lateral part of the palm, are the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and adductor pollicis. The hypothenar muscles, which are located on the medial part of the palm, are the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi. The intermediate muscles, located in the middle of the palm, are the lumbricals, palmar interossei, and dorsal interossei.
11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs
The pelvic girdle attaches the legs to the axial skeleton. The hip joint is where the pelvic girdle and the leg come together. The hip is joined to the pelvic girdle by many muscles. In the gluteal region, the psoas major and iliacus form the iliopsoas. The large and strong gluteus maximus, gluteus medius, and gluteus minimus extend and abduct the femur. Along with the gluteus maximus, the tensor fascia lata muscle forms the iliotibial tract. The lateral rotators of the femur at the hip are the piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris. On the medial part of the thigh, the adductor longus, adductor brevis, and adductor magnus adduct the thigh and medially rotate it. The pectineus muscle adducts and flexes the femur at the hip.
The thigh muscles that move the femur, tibia, and fibula are divided into medial, anterior, and posterior compartments. The medial compartment includes the adductors, pectineus, and the gracilis. The anterior compartment comprises the quadriceps femoris, quadriceps tendon, patellar ligament, and the sartorius. The quadriceps femoris is made of four muscles: the rectus femoris, the vastus lateralis, the vastus medius, and the vastus intermedius, which together extend the knee. The posterior compartment of the thigh includes the hamstrings: the biceps femoris, semitendinosus, and the semimembranosus, which all flex the knee.
The muscles of the leg that move the foot and toes are divided into anterior, lateral, superficial- and deep-posterior compartments. The anterior compartment includes the tibialis anterior, the extensor hallucis longus, the extensor digitorum longus, and the fibularis (peroneus) tertius. The lateral compartment houses the fibularis (peroneus) longus and the fibularis (peroneus) brevis. The superficial posterior compartment has the gastrocnemius, soleus, and plantaris; and the deep posterior compartment has the popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus.
Review Questions
Which of the following is unique to the muscles of facial expression?
- They all originate from the scalp musculature.
- They insert onto the cartilage found around the face.
- They only insert onto the facial bones.
- They insert into the skin.
Which of the following helps an agonist work?
- a synergist
- a fixator
- an insertion
- an antagonist
Which of the following statements is correct about what happens during flexion?
- The angle between bones is increased.
- The angle between bones is decreased.
- The bone moves away from the body.
- The bone moves toward the center of the body.
Which is moved the least during muscle contraction?
- the origin
- the insertion
- the ligaments
- the joints
Which muscle has a convergent pattern of fascicles?
- biceps brachii
- gluteus maximus
- pectoralis major
- rectus femoris
A muscle that has a pattern of fascicles running along the long axis of the muscle has which of the following fascicle arrangements?
- circular
- pennate
- parallel
- rectus
Which arrangement best describes a bipennate muscle?
- The muscle fibers feed in on an angle to a long tendon from both sides.
- The muscle fibers feed in on an angle to a long tendon from all directions.
- The muscle fibers feed in on an angle to a long tendon from one side.
- The muscle fibers on one side of a tendon feed into it at a certain angle and muscle fibers on the other side of the tendon feed into it at the opposite angle.
The location of a muscle’s insertion and origin can determine ________.
- action
- the force of contraction
- muscle name
- the load a muscle can carry
Where is the temporalis muscle located?
- on the forehead
- in the neck
- on the side of the head
- on the chin
Which muscle name does not make sense?
- extensor digitorum
- gluteus minimus
- biceps femoris
- extensor minimus longus
Which of the following terms would be used in the name of a muscle that moves the leg away from the body?
- flexor
- adductor
- extensor
- abductor
Which of the following is a prime mover in head flexion?
- occipitofrontalis
- corrugator supercilii
- sternocleidomastoid
- masseter
Where is the inferior oblique muscle located?
- in the abdomen
- in the eye socket
- in the anterior neck
- in the face
What is the action of the masseter?
- swallowing
- chewing
- moving the lips
- closing the eye
The names of the extrinsic tongue muscles commonly end in ________.
- -glottis
- -glossus
- -gluteus
- -hyoid
What is the function of the erector spinae?
- movement of the arms
- stabilization of the pelvic girdle
- postural support
- rotating of the vertebral column
Which of the following abdominal muscles is not a part of the anterior abdominal wall?
- quadratus lumborum
- rectus abdominis
- interior oblique
- exterior oblique
Which muscle pair plays a role in respiration?
- intertransversarii, interspinales
- semispinalis cervicis, semispinalis thoracis
- trapezius, rhomboids
- diaphragm, scalene
What is the linea alba?
- a small muscle that helps with compression of the abdominal organs
- a long tendon that runs down the middle of the rectus abdominis
- a long band of collagen fibers that connects the hip to the knee
- another name for the tendinous inscription
The rhomboid major and minor muscles are deep to the ________.
- rectus abdominis
- scalene muscles
- trapezius
- ligamentum nuchae
Which muscle extends the forearm?
- biceps brachii
- triceps brachii
- brachialis
- deltoid
What is the origin of the wrist flexors?
- the lateral epicondyle of the humerus
- the medial epicondyle of the humerus
- the carpal bones of the wrist
- the deltoid tuberosity of the humerus
Which muscles stabilize the pectoral girdle?
- axial and scapular
- axial
- appendicular
- axial and appendicular
The large muscle group that attaches the leg to the pelvic girdle and produces extension of the hip joint is the ________ group.
- gluteal
- obturator
- adductor
- abductor
Which muscle produces movement that allows you to cross your legs?
- the gluteus maximus
- the piriformis
- the gracilis
- the sartorius
What is the largest muscle in the lower leg?
- soleus
- gastrocnemius
- tibialis anterior
- tibialis posterior
The vastus intermedius muscle is deep to which of the following muscles?
- biceps femoris
- rectus femoris
- vastus medialis
- vastus lateralis
Critical Thinking Questions
What effect does fascicle arrangement have on a muscle’s action?
29.Movements of the body occur at joints. Describe how muscles are arranged around the joints of the body.
30.Explain how a synergist assists an agonist by being a fixator.
31.Describe the different criteria that contribute to how skeletal muscles are named.
32.Explain the difference between axial and appendicular muscles.
33.Describe the muscles of the anterior neck.
34.Why are the muscles of the face different from typical skeletal muscle?
35.Describe the fascicle arrangement in the muscles of the abdominal wall. How do they relate to each other?
36.What are some similarities and differences between the diaphragm and the pelvic diaphragm?
37.The tendons of which muscles form the rotator cuff? Why is the rotator cuff important?
38.List the general muscle groups of the shoulders and upper limbs as well as their subgroups.
39.Which muscles form the hamstrings? How do they function together?
40.Which muscles form the quadriceps? How do they function together?
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2025-03-18T00:38:18.342539
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
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"title": "Anatomy and Physiology, Support and Movement",
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https://oercommons.org/courseware/lesson/58765/overview
|
The Cardiovascular System: The Heart
Overview
The Cardiovascular System: The Heart
Introduction
Figure 19.1 Human Heart This artist’s conception of the human heart suggests a powerful engine—not inappropriate for a muscular pump that keeps the body continually supplied with blood. (credit: Patrick J. Lynch)
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Identify and describe the interior and exterior parts of the human heart
- Describe the path of blood through the cardiac circuits
- Describe the size, shape, and location of the heart
- Compare cardiac muscle to skeletal and smooth muscle
- Explain the cardiac conduction system
- Describe the process and purpose of an electrocardiogram
- Explain the cardiac cycle
- Calculate cardiac output
- Describe the effects of exercise on cardiac output and heart rate
- Name the centers of the brain that control heart rate and describe their function
- Identify other factors affecting heart rate
- Describe fetal heart development
In this chapter, you will explore the remarkable pump that propels the blood into the vessels. There is no single better word to describe the function of the heart other than “pump,” since its contraction develops the pressure that ejects blood into the major vessels: the aorta and pulmonary trunk. From these vessels, the blood is distributed to the remainder of the body. Although the connotation of the term “pump” suggests a mechanical device made of steel and plastic, the anatomical structure is a living, sophisticated muscle. As you read this chapter, try to keep these twin concepts in mind: pump and muscle.
Although the term “heart” is an English word, cardiac (heart-related) terminology can be traced back to the Latin term, “kardia.” Cardiology is the study of the heart, and cardiologists are the physicians who deal primarily with the heart.
Heart Anatomy
- Describe the location and position of the heart within the body cavity
- Describe the internal and external anatomy of the heart
- Identify the tissue layers of the heart
- Relate the structure of the heart to its function as a pump
- Compare systemic circulation to pulmonary circulation
- Identify the veins and arteries of the coronary circulation system
- Trace the pathway of oxygenated and deoxygenated blood thorough the chambers of the heart
The vital importance of the heart is obvious. If one assumes an average rate of contraction of 75 contractions per minute, a human heart would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Each of the major pumping chambers of the heart ejects approximately 70 mL blood per contraction in a resting adult. This would be equal to 5.25 liters of fluid per minute and approximately 14,000 liters per day. Over one year, that would equal 10,000,000 liters or 2.6 million gallons of blood sent through roughly 60,000 miles of vessels. In order to understand how that happens, it is necessary to understand the anatomy and physiology of the heart.
Location of the Heart
The human heart is located within the thoracic cavity, medially between the lungs in the space known as the mediastinum. Figure 19.2 shows the position of the heart within the thoracic cavity. Within the mediastinum, the heart is separated from the other mediastinal structures by a tough membrane known as the pericardium, or pericardial sac, and sits in its own space called the pericardial cavity. The dorsal surface of the heart lies near the bodies of the vertebrae, and its anterior surface sits deep to the sternum and costal cartilages. The great veins, the superior and inferior venae cavae, and the great arteries, the aorta and pulmonary trunk, are attached to the superior surface of the heart, called the base. The base of the heart is located at the level of the third costal cartilage, as seen in Figure 19.2. The inferior tip of the heart, the apex, lies just to the left of the sternum between the junction of the fourth and fifth ribs near their articulation with the costal cartilages. The right side of the heart is deflected anteriorly, and the left side is deflected posteriorly. It is important to remember the position and orientation of the heart when placing a stethoscope on the chest of a patient and listening for heart sounds, and also when looking at images taken from a midsagittal perspective. The slight deviation of the apex to the left is reflected in a depression in the medial surface of the inferior lobe of the left lung, called the cardiac notch.
Figure 19.2 Position of the Heart in the Thorax The heart is located within the thoracic cavity, medially between the lungs in the mediastinum. It is about the size of a fist, is broad at the top, and tapers toward the base.
EVERYDAY CONNECTION
CPR
The position of the heart in the torso between the vertebrae and sternum (see Figure 19.2 for the position of the heart within the thorax) allows for individuals to apply an emergency technique known as cardiopulmonary resuscitation (CPR) if the heart of a patient should stop. By applying pressure with the flat portion of one hand on the sternum in the area between the line at T4 and T9 (Figure 19.3), it is possible to manually compress the blood within the heart enough to push some of the blood within it into the pulmonary and systemic circuits. This is particularly critical for the brain, as irreversible damage and death of neurons occur within minutes of loss of blood flow. Current standards call for compression of the chest at least 5 cm deep and at a rate of 100 compressions per minute, a rate equal to the beat in “Staying Alive,” recorded in 1977 by the Bee Gees. If you are unfamiliar with this song, a version is available on www.youtube.com. At this stage, the emphasis is on performing high-quality chest compressions, rather than providing artificial respiration. CPR is generally performed until the patient regains spontaneous contraction or is declared dead by an experienced healthcare professional.
When performed by untrained or overzealous individuals, CPR can result in broken ribs or a broken sternum, and can inflict additional severe damage on the patient. It is also possible, if the hands are placed too low on the sternum, to manually drive the xiphoid process into the liver, a consequence that may prove fatal for the patient. Proper training is essential. This proven life-sustaining technique is so valuable that virtually all medical personnel as well as concerned members of the public should be certified and routinely recertified in its application. CPR courses are offered at a variety of locations, including colleges, hospitals, the American Red Cross, and some commercial companies. They normally include practice of the compression technique on a mannequin.
Figure 19.3 CPR Technique If the heart should stop, CPR can maintain the flow of blood until the heart resumes beating. By applying pressure to the sternum, the blood within the heart will be squeezed out of the heart and into the circulation. Proper positioning of the hands on the sternum to perform CPR would be between the lines at T4 and T9.
INTERACTIVE LINK
Visit the American Heart Association website to help locate a course near your home in the United States. There are also many other national and regional heart associations that offer the same service, depending upon the location.
Shape and Size of the Heart
The shape of the heart is similar to a pinecone, rather broad at the superior surface and tapering to the apex (see Figure 19.2). A typical heart is approximately the size of your fist: 12 cm (5 in) in length, 8 cm (3.5 in) wide, and 6 cm (2.5 in) in thickness. Given the size difference between most members of the sexes, the weight of a female heart is approximately 250–300 grams (9 to 11 ounces), and the weight of a male heart is approximately 300–350 grams (11 to 12 ounces). The heart of a well-trained athlete, especially one specializing in aerobic sports, can be considerably larger than this. Cardiac muscle responds to exercise in a manner similar to that of skeletal muscle. That is, exercise results in the addition of protein myofilaments that increase the size of the individual cells without increasing their numbers, a concept called hypertrophy. Hearts of athletes can pump blood more effectively at lower rates than those of nonathletes. Enlarged hearts are not always a result of exercise; they can result from pathologies, such as hypertrophic cardiomyopathy. The cause of an abnormally enlarged heart muscle is unknown, but the condition is often undiagnosed and can cause sudden death in apparently otherwise healthy young people.
Chambers and Circulation through the Heart
The human heart consists of four chambers: The left side and the right side each have one atrium and one ventricle. Each of the upper chambers, the right atrium (plural = atria) and the left atrium, acts as a receiving chamber and contracts to push blood into the lower chambers, the right ventricle and the left ventricle. The ventricles serve as the primary pumping chambers of the heart, propelling blood to the lungs or to the rest of the body.
There are two distinct but linked circuits in the human circulation called the pulmonary and systemic circuits. Although both circuits transport blood and everything it carries, we can initially view the circuits from the point of view of gases. The pulmonary circuit transports blood to and from the lungs, where it picks up oxygen and delivers carbon dioxide for exhalation. The systemic circuit transports oxygenated blood to virtually all of the tissues of the body and returns relatively deoxygenated blood and carbon dioxide to the heart to be sent back to the pulmonary circulation.
The right ventricle pumps deoxygenated blood into the pulmonary trunk, which leads toward the lungs and bifurcates into the left and right pulmonary arteries. These vessels in turn branch many times before reaching the pulmonary capillaries, where gas exchange occurs: Carbon dioxide exits the blood and oxygen enters. The pulmonary trunk arteries and their branches are the only arteries in the post-natal body that carry relatively deoxygenated blood. Highly oxygenated blood returning from the pulmonary capillaries in the lungs passes through a series of vessels that join together to form the pulmonary veins—the only post-natal veins in the body that carry highly oxygenated blood. The pulmonary veins conduct blood into the left atrium, which pumps the blood into the left ventricle, which in turn pumps oxygenated blood into the aorta and on to the many branches of the systemic circuit. Eventually, these vessels will lead to the systemic capillaries, where exchange with the tissue fluid and cells of the body occurs. In this case, oxygen and nutrients exit the systemic capillaries to be used by the cells in their metabolic processes, and carbon dioxide and waste products will enter the blood.
The blood exiting the systemic capillaries is lower in oxygen concentration than when it entered. The capillaries will ultimately unite to form venules, joining to form ever-larger veins, eventually flowing into the two major systemic veins, the superior vena cava and the inferior vena cava, which return blood to the right atrium. The blood in the superior and inferior venae cavae flows into the right atrium, which pumps blood into the right ventricle. This process of blood circulation continues as long as the individual remains alive. Understanding the flow of blood through the pulmonary and systemic circuits is critical to all health professions (Figure 19.4).
Figure 19.4 Dual System of the Human Blood Circulation Blood flows from the right atrium to the right ventricle, where it is pumped into the pulmonary circuit. The blood in the pulmonary artery branches is low in oxygen but relatively high in carbon dioxide. Gas exchange occurs in the pulmonary capillaries (oxygen into the blood, carbon dioxide out), and blood high in oxygen and low in carbon dioxide is returned to the left atrium. From here, blood enters the left ventricle, which pumps it into the systemic circuit. Following exchange in the systemic capillaries (oxygen and nutrients out of the capillaries and carbon dioxide and wastes in), blood returns to the right atrium and the cycle is repeated.
Membranes, Surface Features, and Layers
Our exploration of more in-depth heart structures begins by examining the membrane that surrounds the heart, the prominent surface features of the heart, and the layers that form the wall of the heart. Each of these components plays its own unique role in terms of function.
Membranes
The membrane that directly surrounds the heart and defines the pericardial cavity is called the pericardium or pericardial sac. It also surrounds the “roots” of the major vessels, or the areas of closest proximity to the heart. The pericardium, which literally translates as “around the heart,” consists of two distinct sublayers: the sturdy outer fibrous pericardium and the inner serous pericardium. The fibrous pericardium is made of tough, dense connective tissue that protects the heart and maintains its position in the thorax. The more delicate serous pericardium consists of two layers: the parietal pericardium, which is fused to the fibrous pericardium, and an inner visceral pericardium, or epicardium, which is fused to the heart and is part of the heart wall. The pericardial cavity, filled with lubricating serous fluid, lies between the epicardium and the pericardium.
In most organs within the body, visceral serous membranes such as the epicardium are microscopic. However, in the case of the heart, it is not a microscopic layer but rather a macroscopic layer, consisting of a simple squamous epithelium called a mesothelium, reinforced with loose, irregular, or areolar connective tissue that attaches to the pericardium. This mesothelium secretes the lubricating serous fluid that fills the pericardial cavity and reduces friction as the heart contracts. Figure 19.5illustrates the pericardial membrane and the layers of the heart.
Figure 19.5 Pericardial Membranes and Layers of the Heart Wall The pericardial membrane that surrounds the heart consists of three layers and the pericardial cavity. The heart wall also consists of three layers. The pericardial membrane and the heart wall share the epicardium.
DISORDERS OF THE...
Heart: Cardiac Tamponade
If excess fluid builds within the pericardial space, it can lead to a condition called cardiac tamponade, or pericardial tamponade. With each contraction of the heart, more fluid—in most instances, blood—accumulates within the pericardial cavity. In order to fill with blood for the next contraction, the heart must relax. However, the excess fluid in the pericardial cavity puts pressure on the heart and prevents full relaxation, so the chambers within the heart contain slightly less blood as they begin each heart cycle. Over time, less and less blood is ejected from the heart. If the fluid builds up slowly, as in hypothyroidism, the pericardial cavity may be able to expand gradually to accommodate this extra volume. Some cases of fluid in excess of one liter within the pericardial cavity have been reported. Rapid accumulation of as little as 100 mL of fluid following trauma may trigger cardiac tamponade. Other common causes include myocardial rupture, pericarditis, cancer, or even cardiac surgery. Removal of this excess fluid requires insertion of drainage tubes into the pericardial cavity. Premature removal of these drainage tubes, for example, following cardiac surgery, or clot formation within these tubes are causes of this condition. Untreated, cardiac tamponade can lead to death.
Surface Features of the Heart
Inside the pericardium, the surface features of the heart are visible, including the four chambers. There is a superficial leaf-like extension of the atria near the superior surface of the heart, one on each side, called an auricle—a name that means “ear like”—because its shape resembles the external ear of a human (Figure 19.6). Auricles are relatively thin-walled structures that can fill with blood and empty into the atria or upper chambers of the heart. You may also hear them referred to as atrial appendages. Also prominent is a series of fat-filled grooves, each of which is known as a sulcus (plural = sulci), along the superior surfaces of the heart. Major coronary blood vessels are located in these sulci. The deep coronary sulcus is located between the atria and ventricles. Located between the left and right ventricles are two additional sulci that are not as deep as the coronary sulcus. The anterior interventricular sulcus is visible on the anterior surface of the heart, whereas the posterior interventricular sulcus is visible on the posterior surface of the heart. Figure 19.6 illustrates anterior and posterior views of the surface of the heart.
Figure 19.6 External Anatomy of the Heart Inside the pericardium, the surface features of the heart are visible.
Layers
The wall of the heart is composed of three layers of unequal thickness. From superficial to deep, these are the epicardium, the myocardium, and the endocardium (see Figure 19.5). The outermost layer of the wall of the heart is also the innermost layer of the pericardium, the epicardium, or the visceral pericardium discussed earlier.
The middle and thickest layer is the myocardium, made largely of cardiac muscle cells. It is built upon a framework of collagenous fibers, plus the blood vessels that supply the myocardium and the nerve fibers that help regulate the heart. It is the contraction of the myocardium that pumps blood through the heart and into the major arteries. The muscle pattern is elegant and complex, as the muscle cells swirl and spiral around the chambers of the heart. They form a figure 8 pattern around the atria and around the bases of the great vessels. Deeper ventricular muscles also form a figure 8 around the two ventricles and proceed toward the apex. More superficial layers of ventricular muscle wrap around both ventricles. This complex swirling pattern allows the heart to pump blood more effectively than a simple linear pattern would. Figure 19.7 illustrates the arrangement of muscle cells.
Figure 19.7 Heart Musculature The swirling pattern of cardiac muscle tissue contributes significantly to the heart’s ability to pump blood effectively.
Although the ventricles on the right and left sides pump the same amount of blood per contraction, the muscle of the left ventricle is much thicker and better developed than that of the right ventricle. In order to overcome the high resistance required to pump blood into the long systemic circuit, the left ventricle must generate a great amount of pressure. The right ventricle does not need to generate as much pressure, since the pulmonary circuit is shorter and provides less resistance. Figure 19.8illustrates the differences in muscular thickness needed for each of the ventricles.
Figure 19.8 Differences in Ventricular Muscle Thickness The myocardium in the left ventricle is significantly thicker than that of the right ventricle. Both ventricles pump the same amount of blood, but the left ventricle must generate a much greater pressure to overcome greater resistance in the systemic circuit. The ventricles are shown in both relaxed and contracting states. Note the differences in the relative size of the lumens, the region inside each ventricle where the blood is contained.
The innermost layer of the heart wall, the endocardium, is joined to the myocardium with a thin layer of connective tissue. The endocardium lines the chambers where the blood circulates and covers the heart valves. It is made of simple squamous epithelium called endothelium, which is continuous with the endothelial lining of the blood vessels (see Figure 19.5).
Once regarded as a simple lining layer, recent evidence indicates that the endothelium of the endocardium and the coronary capillaries may play active roles in regulating the contraction of the muscle within the myocardium. The endothelium may also regulate the growth patterns of the cardiac muscle cells throughout life, and the endothelins it secretes create an environment in the surrounding tissue fluids that regulates ionic concentrations and states of contractility. Endothelins are potent vasoconstrictors and, in a normal individual, establish a homeostatic balance with other vasoconstrictors and vasodilators.
Internal Structure of the Heart
Recall that the heart’s contraction cycle follows a dual pattern of circulation—the pulmonary and systemic circuits—because of the pairs of chambers that pump blood into the circulation. In order to develop a more precise understanding of cardiac function, it is first necessary to explore the internal anatomical structures in more detail.
Septa of the Heart
The word septum is derived from the Latin for “something that encloses;” in this case, a septum (plural = septa) refers to a wall or partition that divides the heart into chambers. The septa are physical extensions of the myocardium lined with endocardium. Located between the two atria is the interatrial septum. Normally in an adult heart, the interatrial septum bears an oval-shaped depression known as the fossa ovalis, a remnant of an opening in the fetal heart known as the foramen ovale. The foramen ovale allowed blood in the fetal heart to pass directly from the right atrium to the left atrium, allowing some blood to bypass the pulmonary circuit. Within seconds after birth, a flap of tissue known as the septum primum that previously acted as a valve closes the foramen ovale and establishes the typical cardiac circulation pattern.
Between the two ventricles is a second septum known as the interventricular septum. Unlike the interatrial septum, the interventricular septum is normally intact after its formation during fetal development. It is substantially thicker than the interatrial septum, since the ventricles generate far greater pressure when they contract.
The septum between the atria and ventricles is known as the atrioventricular septum. It is marked by the presence of four openings that allow blood to move from the atria into the ventricles and from the ventricles into the pulmonary trunk and aorta. Located in each of these openings between the atria and ventricles is a valve, a specialized structure that ensures one-way flow of blood. The valves between the atria and ventricles are known generically as atrioventricular valves. The valves at the openings that lead to the pulmonary trunk and aorta are known generically as semilunar valves. The interventricular septum is visible in Figure 19.9. In this figure, the atrioventricular septum has been removed to better show the bicupid and tricuspid valves; the interatrial septum is not visible, since its location is covered by the aorta and pulmonary trunk. Since these openings and valves structurally weaken the atrioventricular septum, the remaining tissue is heavily reinforced with dense connective tissue called the cardiac skeleton, or skeleton of the heart. It includes four rings that surround the openings between the atria and ventricles, and the openings to the pulmonary trunk and aorta, and serve as the point of attachment for the heart valves. The cardiac skeleton also provides an important boundary in the heart electrical conduction system.
Figure 19.9 Internal Structures of the Heart This anterior view of the heart shows the four chambers, the major vessels and their early branches, as well as the valves. The presence of the pulmonary trunk and aorta covers the interatrial septum, and the atrioventricular septum is cut away to show the atrioventricular valves.
DISORDERS OF THE...
Heart: Heart Defects
One very common form of interatrial septum pathology is patent foramen ovale, which occurs when the septum primum does not close at birth, and the fossa ovalis is unable to fuse. The word patent is from the Latin root patens for “open.” It may be benign or asymptomatic, perhaps never being diagnosed, or in extreme cases, it may require surgical repair to close the opening permanently. As much as 20–25 percent of the general population may have a patent foramen ovale, but fortunately, most have the benign, asymptomatic version. Patent foramen ovale is normally detected by auscultation of a heart murmur (an abnormal heart sound) and confirmed by imaging with an echocardiogram. Despite its prevalence in the general population, the causes of patent ovale are unknown, and there are no known risk factors. In nonlife-threatening cases, it is better to monitor the condition than to risk heart surgery to repair and seal the opening.
Coarctation of the aorta is a congenital abnormal narrowing of the aorta that is normally located at the insertion of the ligamentum arteriosum, the remnant of the fetal shunt called the ductus arteriosus. If severe, this condition drastically restricts blood flow through the primary systemic artery, which is life threatening. In some individuals, the condition may be fairly benign and not detected until later in life. Detectable symptoms in an infant include difficulty breathing, poor appetite, trouble feeding, or failure to thrive. In older individuals, symptoms include dizziness, fainting, shortness of breath, chest pain, fatigue, headache, and nosebleeds. Treatment involves surgery to resect (remove) the affected region or angioplasty to open the abnormally narrow passageway. Studies have shown that the earlier the surgery is performed, the better the chance of survival.
A patent ductus arteriosus is a congenital condition in which the ductus arteriosus fails to close. The condition may range from severe to benign. Failure of the ductus arteriosus to close results in blood flowing from the higher pressure aorta into the lower pressure pulmonary trunk. This additional fluid moving toward the lungs increases pulmonary pressure and makes respiration difficult. Symptoms include shortness of breath (dyspnea), tachycardia, enlarged heart, a widened pulse pressure, and poor weight gain in infants. Treatments include surgical closure (ligation), manual closure using platinum coils or specialized mesh inserted via the femoral artery or vein, or nonsteroidal anti-inflammatory drugs to block the synthesis of prostaglandin E2, which maintains the vessel in an open position. If untreated, the condition can result in congestive heart failure.
Septal defects are not uncommon in individuals and may be congenital or caused by various disease processes. Tetralogy of Fallot is a congenital condition that may also occur from exposure to unknown environmental factors; it occurs when there is an opening in the interventricular septum caused by blockage of the pulmonary trunk, normally at the pulmonary semilunar valve. This allows blood that is relatively low in oxygen from the right ventricle to flow into the left ventricle and mix with the blood that is relatively high in oxygen. Symptoms include a distinct heart murmur, low blood oxygen percent saturation, dyspnea or difficulty in breathing, polycythemia, broadening (clubbing) of the fingers and toes, and in children, difficulty in feeding or failure to grow and develop. It is the most common cause of cyanosis following birth. The term “tetralogy” is derived from the four components of the condition, although only three may be present in an individual patient: pulmonary infundibular stenosis (rigidity of the pulmonary valve), overriding aorta (the aorta is shifted above both ventricles), ventricular septal defect (opening), and right ventricular hypertrophy (enlargement of the right ventricle). Other heart defects may also accompany this condition, which is typically confirmed by echocardiography imaging. Tetralogy of Fallot occurs in approximately 400 out of one million live births. Normal treatment involves extensive surgical repair, including the use of stents to redirect blood flow and replacement of valves and patches to repair the septal defect, but the condition has a relatively high mortality. Survival rates are currently 75 percent during the first year of life; 60 percent by 4 years of age; 30 percent by 10 years; and 5 percent by 40 years.
In the case of severe septal defects, including both tetralogy of Fallot and patent foramen ovale, failure of the heart to develop properly can lead to a condition commonly known as a “blue baby.” Regardless of normal skin pigmentation, individuals with this condition have an insufficient supply of oxygenated blood, which leads to cyanosis, a blue or purple coloration of the skin, especially when active.
Septal defects are commonly first detected through auscultation, listening to the chest using a stethoscope. In this case, instead of hearing normal heart sounds attributed to the flow of blood and closing of heart valves, unusual heart sounds may be detected. This is often followed by medical imaging to confirm or rule out a diagnosis. In many cases, treatment may not be needed. Some common congenital heart defects are illustrated in Figure 19.10.
Figure 19.10 Congenital Heart Defects (a) A patent foramen ovale defect is an abnormal opening in the interatrial septum, or more commonly, a failure of the foramen ovale to close. (b) Coarctation of the aorta is an abnormal narrowing of the aorta. (c) A patent ductus arteriosus is the failure of the ductus arteriosus to close. (d) Tetralogy of Fallot includes an abnormal opening in the interventricular septum.
Right Atrium
The right atrium serves as the receiving chamber for blood returning to the heart from the systemic circulation. The two major systemic veins, the superior and inferior venae cavae, and the large coronary vein called the coronary sinus that drains the heart myocardium empty into the right atrium. The superior vena cava drains blood from regions superior to the diaphragm: the head, neck, upper limbs, and the thoracic region. It empties into the superior and posterior portions of the right atrium. The inferior vena cava drains blood from areas inferior to the diaphragm: the lower limbs and abdominopelvic region of the body. It, too, empties into the posterior portion of the atria, but inferior to the opening of the superior vena cava. Immediately superior and slightly medial to the opening of the inferior vena cava on the posterior surface of the atrium is the opening of the coronary sinus. This thin-walled vessel drains most of the coronary veins that return systemic blood from the heart. The majority of the internal heart structures discussed in this and subsequent sections are illustrated in Figure 19.9.
While the bulk of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface demonstrates prominent ridges of muscle called the pectinate muscles. The right auricle also has pectinate muscles. The left atrium does not have pectinate muscles except in the auricle.
The atria receive venous blood on a nearly continuous basis, preventing venous flow from stopping while the ventricles are contracting. While most ventricular filling occurs while the atria are relaxed, they do demonstrate a contractile phase and actively pump blood into the ventricles just prior to ventricular contraction. The opening between the atrium and ventricle is guarded by the tricuspid valve.
Right Ventricle
The right ventricle receives blood from the right atrium through the tricuspid valve. Each flap of the valve is attached to strong strands of connective tissue, the chordae tendineae, literally “tendinous cords,” or sometimes more poetically referred to as “heart strings.” There are several chordae tendineae associated with each of the flaps. They are composed of approximately 80 percent collagenous fibers with the remainder consisting of elastic fibers and endothelium. They connect each of the flaps to a papillary muscle that extends from the inferior ventricular surface. There are three papillary muscles in the right ventricle, called the anterior, posterior, and septal muscles, which correspond to the three sections of the valves.
When the myocardium of the ventricle contracts, pressure within the ventricular chamber rises. Blood, like any fluid, flows from higher pressure to lower pressure areas, in this case, toward the pulmonary trunk and the atrium. To prevent any potential backflow, the papillary muscles also contract, generating tension on the chordae tendineae. This prevents the flaps of the valves from being forced into the atria and regurgitation of the blood back into the atria during ventricular contraction. Figure 19.11shows papillary muscles and chordae tendineae attached to the tricuspid valve.
Figure 19.11 Chordae Tendineae and Papillary Muscles In this frontal section, you can see papillary muscles attached to the tricuspid valve on the right as well as the mitral valve on the left via chordae tendineae. (credit: modification of work by “PV KS”/flickr.com)
The walls of the ventricle are lined with trabeculae carneae, ridges of cardiac muscle covered by endocardium. In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band (see Figure 19.9) reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction. It arises from the inferior portion of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.
When the right ventricle contracts, it ejects blood into the pulmonary trunk, which branches into the left and right pulmonary arteries that carry it to each lung. The superior surface of the right ventricle begins to taper as it approaches the pulmonary trunk. At the base of the pulmonary trunk is the pulmonary semilunar valve that prevents backflow from the pulmonary trunk.
Left Atrium
After exchange of gases in the pulmonary capillaries, blood returns to the left atrium high in oxygen via one of the four pulmonary veins. While the left atrium does not contain pectinate muscles, it does have an auricle that includes these pectinate ridges. Blood flows nearly continuously from the pulmonary veins back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period, the left atrium will contract, pumping blood into the ventricle. This atrial contraction accounts for approximately 20 percent of ventricular filling. The opening between the left atrium and ventricle is guarded by the mitral valve.
Left Ventricle
Recall that, although both sides of the heart will pump the same amount of blood, the muscular layer is much thicker in the left ventricle compared to the right (see Figure 19.8). Like the right ventricle, the left also has trabeculae carneae, but there is no moderator band. The mitral valve is connected to papillary muscles via chordae tendineae. There are two papillary muscles on the left—the anterior and posterior—as opposed to three on the right.
The left ventricle is the major pumping chamber for the systemic circuit; it ejects blood into the aorta through the aortic semilunar valve.
Heart Valve Structure and Function
A transverse section through the heart slightly above the level of the atrioventricular septum reveals all four heart valves along the same plane (Figure 19.12). The valves ensure unidirectional blood flow through the heart. Between the right atrium and the right ventricle is the right atrioventricular valve, or tricuspid valve. It typically consists of three flaps, or leaflets, made of endocardium reinforced with additional connective tissue. The flaps are connected by chordae tendineae to the papillary muscles, which control the opening and closing of the valves.
Figure 19.12 Heart Valves With the atria and major vessels removed, all four valves are clearly visible, although it is difficult to distinguish the three separate cusps of the tricuspid valve.
Emerging from the right ventricle at the base of the pulmonary trunk is the pulmonary semilunar valve, or the pulmonary valve; it is also known as the pulmonic valve or the right semilunar valve. The pulmonary valve is comprised of three small flaps of endothelium reinforced with connective tissue. When the ventricle relaxes, the pressure differential causes blood to flow back into the ventricle from the pulmonary trunk. This flow of blood fills the pocket-like flaps of the pulmonary valve, causing the valve to close and producing an audible sound. Unlike the atrioventricular valves, there are no papillary muscles or chordae tendineae associated with the pulmonary valve.
Located at the opening between the left atrium and left ventricle is the mitral valve, also called the bicuspid valve or the left atrioventricular valve. Structurally, this valve consists of two cusps, known as the anterior medial cusp and the posterior medial cusp, compared to the three cusps of the tricuspid valve. In a clinical setting, the valve is referred to as the mitral valve, rather than the bicuspid valve. The two cusps of the mitral valve are attached by chordae tendineae to two papillary muscles that project from the wall of the ventricle.
At the base of the aorta is the aortic semilunar valve, or the aortic valve, which prevents backflow from the aorta. It normally is composed of three flaps. When the ventricle relaxes and blood attempts to flow back into the ventricle from the aorta, blood will fill the cusps of the valve, causing it to close and producing an audible sound.
In Figure 19.13a, the two atrioventricular valves are open and the two semilunar valves are closed. This occurs when both atria and ventricles are relaxed and when the atria contract to pump blood into the ventricles. Figure 19.13b shows a frontal view. Although only the left side of the heart is illustrated, the process is virtually identical on the right.
Figure 19.13 Blood Flow from the Left Atrium to the Left Ventricle (a) A transverse section through the heart illustrates the four heart valves. The two atrioventricular valves are open; the two semilunar valves are closed. The atria and vessels have been removed. (b) A frontal section through the heart illustrates blood flow through the mitral valve. When the mitral valve is open, it allows blood to move from the left atrium to the left ventricle. The aortic semilunar valve is closed to prevent backflow of blood from the aorta to the left ventricle.
Figure 19.14a shows the atrioventricular valves closed while the two semilunar valves are open. This occurs when the ventricles contract to eject blood into the pulmonary trunk and aorta. Closure of the two atrioventricular valves prevents blood from being forced back into the atria. This stage can be seen from a frontal view in Figure 19.14b.
Figure 19.14 Blood Flow from the Left Ventricle into the Great Vessels (a) A transverse section through the heart illustrates the four heart valves during ventricular contraction. The two atrioventricular valves are closed, but the two semilunar valves are open. The atria and vessels have been removed. (b) A frontal view shows the closed mitral (bicuspid) valve that prevents backflow of blood into the left atrium. The aortic semilunar valve is open to allow blood to be ejected into the aorta.
When the ventricles begin to contract, pressure within the ventricles rises and blood flows toward the area of lowest pressure, which is initially in the atria. This backflow causes the cusps of the tricuspid and mitral (bicuspid) valves to close. These valves are tied down to the papillary muscles by chordae tendineae. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight (see Figure 19.13b). However, as the myocardium of the ventricle contracts, so do the papillary muscles. This creates tension on the chordae tendineae (see Figure 19.14b), helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.
The aortic and pulmonary semilunar valves lack the chordae tendineae and papillary muscles associated with the atrioventricular valves. Instead, they consist of pocket-like folds of endocardium reinforced with additional connective tissue. When the ventricles relax and the change in pressure forces the blood toward the ventricles, the blood presses against these cusps and seals the openings.
INTERACTIVE LINK
Visit this site to observe an echocardiogram of actual heart valves opening and closing. Although much of the heart has been “removed” from this gif loop so the chordae tendineae are not visible, why is their presence more critical for the atrioventricular valves (tricuspid and mitral) than the semilunar (aortic and pulmonary) valves?
DISORDERS OF THE...
Heart Valves
When heart valves do not function properly, they are often described as incompetent and result in valvular heart disease, which can range from benign to lethal. Some of these conditions are congenital, that is, the individual was born with the defect, whereas others may be attributed to disease processes or trauma. Some malfunctions are treated with medications, others require surgery, and still others may be mild enough that the condition is merely monitored since treatment might trigger more serious consequences.
Valvular disorders are often caused by carditis, or inflammation of the heart. One common trigger for this inflammation is rheumatic fever, or scarlet fever, an autoimmune response to the presence of a bacterium, Streptococcus pyogenes, normally a disease of childhood.
While any of the heart valves may be involved in valve disorders, mitral regurgitation is the most common, detected in approximately 2 percent of the population, and the pulmonary semilunar valve is the least frequently involved. When a valve malfunctions, the flow of blood to a region will often be disrupted. The resulting inadequate flow of blood to this region will be described in general terms as an insufficiency. The specific type of insufficiency is named for the valve involved: aortic insufficiency, mitral insufficiency, tricuspid insufficiency, or pulmonary insufficiency.
If one of the cusps of the valve is forced backward by the force of the blood, the condition is referred to as a prolapsed valve. Prolapse may occur if the chordae tendineae are damaged or broken, causing the closure mechanism to fail. The failure of the valve to close properly disrupts the normal one-way flow of blood and results in regurgitation, when the blood flows backward from its normal path. Using a stethoscope, the disruption to the normal flow of blood produces a heart murmur.
Stenosis is a condition in which the heart valves become rigid and may calcify over time. The loss of flexibility of the valve interferes with normal function and may cause the heart to work harder to propel blood through the valve, which eventually weakens the heart. Aortic stenosis affects approximately 2 percent of the population over 65 years of age, and the percentage increases to approximately 4 percent in individuals over 85 years. Occasionally, one or more of the chordae tendineae will tear or the papillary muscle itself may die as a component of a myocardial infarction (heart attack). In this case, the patient’s condition will deteriorate dramatically and rapidly, and immediate surgical intervention may be required.
Auscultation, or listening to a patient’s heart sounds, is one of the most useful diagnostic tools, since it is proven, safe, and inexpensive. The term auscultation is derived from the Latin for “to listen,” and the technique has been used for diagnostic purposes as far back as the ancient Egyptians. Valve and septal disorders will trigger abnormal heart sounds. If a valvular disorder is detected or suspected, a test called an echocardiogram, or simply an “echo,” may be ordered. Echocardiograms are sonograms of the heart and can help in the diagnosis of valve disorders as well as a wide variety of heart pathologies.
INTERACTIVE LINK
Visit this site for a free download, including excellent animations and audio of heart sounds.
CAREER CONNECTION
Cardiologist
Cardiologists are medical doctors that specialize in the diagnosis and treatment of diseases of the heart. After completing 4 years of medical school, cardiologists complete a three-year residency in internal medicine followed by an additional three or more years in cardiology. Following this 10-year period of medical training and clinical experience, they qualify for a rigorous two-day examination administered by the Board of Internal Medicine that tests their academic training and clinical abilities, including diagnostics and treatment. After successful completion of this examination, a physician becomes a board-certified cardiologist. Some board-certified cardiologists may be invited to become a Fellow of the American College of Cardiology (FACC). This professional recognition is awarded to outstanding physicians based upon merit, including outstanding credentials, achievements, and community contributions to cardiovascular medicine.
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CAREER CONNECTION
Cardiovascular Technologist/Technician
Cardiovascular technologists/technicians are trained professionals who perform a variety of imaging techniques, such as sonograms or echocardiograms, used by physicians to diagnose and treat diseases of the heart. Nearly all of these positions require an associate degree, and these technicians earn a median salary of $49,410 as of May 2010, according to the U.S. Bureau of Labor Statistics. Growth within the field is fast, projected at 29 percent from 2010 to 2020.
There is a considerable overlap and complementary skills between cardiac technicians and vascular technicians, and so the term cardiovascular technician is often used. Special certifications within the field require documenting appropriate experience and completing additional and often expensive certification examinations. These subspecialties include Certified Rhythm Analysis Technician (CRAT), Certified Cardiographic Technician (CCT), Registered Congenital Cardiac Sonographer (RCCS), Registered Cardiac Electrophysiology Specialist (RCES), Registered Cardiovascular Invasive Specialist (RCIS), Registered Cardiac Sonographer (RCS), Registered Vascular Specialist (RVS), and Registered Phlebology Sonographer (RPhS).
INTERACTIVE LINK
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Coronary Circulation
You will recall that the heart is a remarkable pump composed largely of cardiac muscle cells that are incredibly active throughout life. Like all other cells, a cardiomyocyte requires a reliable supply of oxygen and nutrients, and a way to remove wastes, so it needs a dedicated, complex, and extensive coronary circulation. And because of the critical and nearly ceaseless activity of the heart throughout life, this need for a blood supply is even greater than for a typical cell. However, coronary circulation is not continuous; rather, it cycles, reaching a peak when the heart muscle is relaxed and nearly ceasing while it is contracting.
Coronary Arteries
Coronary arteries supply blood to the myocardium and other components of the heart. The first portion of the aorta after it arises from the left ventricle gives rise to the coronary arteries. There are three dilations in the wall of the aorta just superior to the aortic semilunar valve. Two of these, the left posterior aortic sinus and anterior aortic sinus, give rise to the left and right coronary arteries, respectively. The third sinus, the right posterior aortic sinus, typically does not give rise to a vessel. Coronary vessel branches that remain on the surface of the artery and follow the sulci are called epicardial coronary arteries.
The left coronary artery distributes blood to the left side of the heart, the left atrium and ventricle, and the interventricular septum. The circumflex artery arises from the left coronary artery and follows the coronary sulcus to the left. Eventually, it will fuse with the small branches of the right coronary artery. The larger anterior interventricular artery, also known as the left anterior descending artery (LAD), is the second major branch arising from the left coronary artery. It follows the anterior interventricular sulcus around the pulmonary trunk. Along the way it gives rise to numerous smaller branches that interconnect with the branches of the posterior interventricular artery, forming anastomoses. An anastomosis is an area where vessels unite to form interconnections that normally allow blood to circulate to a region even if there may be partial blockage in another branch. The anastomoses in the heart are very small. Therefore, this ability is somewhat restricted in the heart so a coronary artery blockage often results in death of the cells (myocardial infarction) supplied by the particular vessel.
The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and the heart conduction system. Normally, one or more marginal arteries arise from the right coronary artery inferior to the right atrium. The marginal arteries supply blood to the superficial portions of the right ventricle. On the posterior surface of the heart, the right coronary artery gives rise to the posterior interventricular artery, also known as the posterior descending artery. It runs along the posterior portion of the interventricular sulcus toward the apex of the heart, giving rise to branches that supply the interventricular septum and portions of both ventricles. Figure 19.15 presents views of the coronary circulation from both the anterior and posterior views.
Figure 19.15 Coronary Circulation The anterior view of the heart shows the prominent coronary surface vessels. The posterior view of the heart shows the prominent coronary surface vessels.
DISEASES OF THE...
Heart: Myocardial Infarction
Myocardial infarction (MI) is the formal term for what is commonly referred to as a heart attack. It normally results from a lack of blood flow (ischemia) and oxygen (hypoxia) to a region of the heart, resulting in death of the cardiac muscle cells. An MI often occurs when a coronary artery is blocked by the buildup of atherosclerotic plaque consisting of lipids, cholesterol and fatty acids, and white blood cells, primarily macrophages. It can also occur when a portion of an unstable atherosclerotic plaque travels through the coronary arterial system and lodges in one of the smaller vessels. The resulting blockage restricts the flow of blood and oxygen to the myocardium and causes death of the tissue. MIs may be triggered by excessive exercise, in which the partially occluded artery is no longer able to pump sufficient quantities of blood, or severe stress, which may induce spasm of the smooth muscle in the walls of the vessel.
In the case of acute MI, there is often sudden pain beneath the sternum (retrosternal pain) called angina pectoris, often radiating down the left arm in males but not in female patients. Until this anomaly between the sexes was discovered, many female patients suffering MIs were misdiagnosed and sent home. In addition, patients typically present with difficulty breathing and shortness of breath (dyspnea), irregular heartbeat (palpations), nausea and vomiting, sweating (diaphoresis), anxiety, and fainting (syncope), although not all of these symptoms may be present. Many of the symptoms are shared with other medical conditions, including anxiety attacks and simple indigestion, so differential diagnosis is critical. It is estimated that between 22 and 64 percent of MIs present without any symptoms.
An MI can be confirmed by examining the patient’s ECG, which frequently reveals alterations in the ST and Q components. Some classification schemes of MI are referred to as ST-elevated MI (STEMI) and non-elevated MI (non-STEMI). In addition, echocardiography or cardiac magnetic resonance imaging may be employed. Common blood tests indicating an MI include elevated levels of creatine kinase MB (an enzyme that catalyzes the conversion of creatine to phosphocreatine, consuming ATP) and cardiac troponin (the regulatory protein for muscle contraction), both of which are released by damaged cardiac muscle cells.
Immediate treatments for MI are essential and include administering supplemental oxygen, aspirin that helps to break up clots, and nitroglycerine administered sublingually (under the tongue) to facilitate its absorption. Despite its unquestioned success in treatments and use since the 1880s, the mechanism of nitroglycerine is still incompletely understood but is believed to involve the release of nitric oxide, a known vasodilator, and endothelium-derived releasing factor, which also relaxes the smooth muscle in the tunica media of coronary vessels. Longer-term treatments include injections of thrombolytic agents such as streptokinase that dissolve the clot, the anticoagulant heparin, balloon angioplasty and stents to open blocked vessels, and bypass surgery to allow blood to pass around the site of blockage. If the damage is extensive, coronary replacement with a donor heart or coronary assist device, a sophisticated mechanical device that supplements the pumping activity of the heart, may be employed. Despite the attention, development of artificial hearts to augment the severely limited supply of heart donors has proven less than satisfactory but will likely improve in the future.
MIs may trigger cardiac arrest, but the two are not synonymous. Important risk factors for MI include cardiovascular disease, age, smoking, high blood levels of the low-density lipoprotein (LDL, often referred to as “bad” cholesterol), low levels of high-density lipoprotein (HDL, or “good” cholesterol), hypertension, diabetes mellitus, obesity, lack of physical exercise, chronic kidney disease, excessive alcohol consumption, and use of illegal drugs.
Coronary Veins
Coronary veins drain the heart and generally parallel the large surface arteries (see Figure 19.15). The great cardiac vein can be seen initially on the surface of the heart following the interventricular sulcus, but it eventually flows along the coronary sulcus into the coronary sinus on the posterior surface. The great cardiac vein initially parallels the anterior interventricular artery and drains the areas supplied by this vessel. It receives several major branches, including the posterior cardiac vein, the middle cardiac vein, and the small cardiac vein. The posterior cardiac vein parallels and drains the areas supplied by the marginal artery branch of the circumflex artery. The middle cardiac vein parallels and drains the areas supplied by the posterior interventricular artery. The small cardiac vein parallels the right coronary artery and drains the blood from the posterior surfaces of the right atrium and ventricle. The coronary sinus is a large, thin-walled vein on the posterior surface of the heart lying within the atrioventricular sulcus and emptying directly into the right atrium. The anterior cardiac veins parallel the small cardiac arteries and drain the anterior surface of the right ventricle. Unlike these other cardiac veins, it bypasses the coronary sinus and drains directly into the right atrium.
DISORDERS OF THE...
Heart: Coronary Artery Disease
Coronary artery disease is the leading cause of death worldwide. It occurs when the buildup of plaque—a fatty material including cholesterol, connective tissue, white blood cells, and some smooth muscle cells—within the walls of the arteries obstructs the flow of blood and decreases the flexibility or compliance of the vessels. This condition is called atherosclerosis, a hardening of the arteries that involves the accumulation of plaque. As the coronary blood vessels become occluded, the flow of blood to the tissues will be restricted, a condition called ischemia that causes the cells to receive insufficient amounts of oxygen, called hypoxia. Figure 19.16 shows the blockage of coronary arteries highlighted by the injection of dye. Some individuals with coronary artery disease report pain radiating from the chest called angina pectoris, but others remain asymptomatic. If untreated, coronary artery disease can lead to MI or a heart attack.
Figure 19.16 Atherosclerotic Coronary Arteries In this coronary angiogram (X-ray), the dye makes visible two occluded coronary arteries. Such blockages can lead to decreased blood flow (ischemia) and insufficient oxygen (hypoxia) delivered to the cardiac tissues. If uncorrected, this can lead to cardiac muscle death (myocardial infarction).
The disease progresses slowly and often begins in children and can be seen as fatty “streaks” in the vessels. It then gradually progresses throughout life. Well-documented risk factors include smoking, family history, hypertension, obesity, diabetes, high alcohol consumption, lack of exercise, stress, and hyperlipidemia or high circulating levels of lipids in the blood. Treatments may include medication, changes to diet and exercise, angioplasty with a balloon catheter, insertion of a stent, or coronary bypass procedure.
Angioplasty is a procedure in which the occlusion is mechanically widened with a balloon. A specialized catheter with an expandable tip is inserted into a superficial vessel, normally in the leg, and then directed to the site of the occlusion. At this point, the balloon is inflated to compress the plaque material and to open the vessel to increase blood flow. Then, the balloon is deflated and retracted. A stent consisting of a specialized mesh is typically inserted at the site of occlusion to reinforce the weakened and damaged walls. Stent insertions have been routine in cardiology for more than 40 years.
Coronary bypass surgery may also be performed. This surgical procedure grafts a replacement vessel obtained from another, less vital portion of the body to bypass the occluded area. This procedure is clearly effective in treating patients experiencing a MI, but overall does not increase longevity. Nor does it seem advisable in patients with stable although diminished cardiac capacity since frequently loss of mental acuity occurs following the procedure. Long-term changes to behavior, emphasizing diet and exercise plus a medicine regime tailored to lower blood pressure, lower cholesterol and lipids, and reduce clotting are equally as effective.
Cardiac Muscle and Electrical Activity
- Describe the structure of cardiac muscle
- Identify and describe the components of the conducting system that distributes electrical impulses through the heart
- Compare the effect of ion movement on membrane potential of cardiac conductive and contractile cells
- Relate characteristics of an electrocardiogram to events in the cardiac cycle
- Identify blocks that can interrupt the cardiac cycle
Recall that cardiac muscle shares a few characteristics with both skeletal muscle and smooth muscle, but it has some unique properties of its own. Not the least of these exceptional properties is its ability to initiate an electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger the contractile mechanism. This property is known as autorhythmicity. Neither smooth nor skeletal muscle can do this. Even though cardiac muscle has autorhythmicity, heart rate is modulated by the endocrine and nervous systems.
There are two major types of cardiac muscle cells: myocardial contractile cells and myocardial conducting cells. The myocardial contractile cells constitute the bulk (99 percent) of the cells in the atria and ventricles. Contractile cells conduct impulses and are responsible for contractions that pump blood through the body. The myocardial conducting cells (1 percent of the cells) form the conduction system of the heart. Except for Purkinje cells, they are generally much smaller than the contractile cells and have few of the myofibrils or filaments needed for contraction. Their function is similar in many respects to neurons, although they are specialized muscle cells. Myocardial conduction cells initiate and propagate the action potential (the electrical impulse) that travels throughout the heart and triggers the contractions that propel the blood.
Structure of Cardiac Muscle
Compared to the giant cylinders of skeletal muscle, cardiac muscle cells, or cardiomyocytes, are considerably shorter with much smaller diameters. Cardiac muscle also demonstrates striations, the alternating pattern of dark A bands and light I bands attributed to the precise arrangement of the myofilaments and fibrils that are organized in sarcomeres along the length of the cell (Figure 19.17a). These contractile elements are virtually identical to skeletal muscle. T (transverse) tubules penetrate from the surface plasma membrane, the sarcolemma, to the interior of the cell, allowing the electrical impulse to reach the interior. The T tubules are only found at the Z discs, whereas in skeletal muscle, they are found at the junction of the A and I bands. Therefore, there are one-half as many T tubules in cardiac muscle as in skeletal muscle. In addition, the sarcoplasmic reticulum stores few calcium ions, so most of the calcium ions must come from outside the cells. The result is a slower onset of contraction. Mitochondria are plentiful, providing energy for the contractions of the heart. Typically, cardiomyocytes have a single, central nucleus, but two or more nuclei may be found in some cells.
Cardiac muscle cells branch freely. A junction between two adjoining cells is marked by a critical structure called an intercalated disc, which helps support the synchronized contraction of the muscle (Figure 19.17b). The sarcolemmas from adjacent cells bind together at the intercalated discs. They consist of desmosomes, specialized linking proteoglycans, tight junctions, and large numbers of gap junctions that allow the passage of ions between the cells and help to synchronize the contraction (Figure 19.17c). Intercellular connective tissue also helps to bind the cells together. The importance of strongly binding these cells together is necessitated by the forces exerted by contraction.
Figure 19.17 Cardiac Muscle (a) Cardiac muscle cells have myofibrils composed of myofilaments arranged in sarcomeres, T tubules to transmit the impulse from the sarcolemma to the interior of the cell, numerous mitochondria for energy, and intercalated discs that are found at the junction of different cardiac muscle cells. (b) A photomicrograph of cardiac muscle cells shows the nuclei and intercalated discs. (c) An intercalated disc connects cardiac muscle cells and consists of desmosomes and gap junctions. LM × 1600. (Micrograph provided by the Regents of the University of Michigan Medical School © 2012)
Cardiac muscle undergoes aerobic respiration patterns, primarily metabolizing lipids and carbohydrates. Myoglobin, lipids, and glycogen are all stored within the cytoplasm. Cardiac muscle cells undergo twitch-type contractions with long refractory periods followed by brief relaxation periods. The relaxation is essential so the heart can fill with blood for the next cycle. The refractory period is very long to prevent the possibility of tetany, a condition in which muscle remains involuntarily contracted. In the heart, tetany is not compatible with life, since it would prevent the heart from pumping blood.
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Repair and Replacement
Damaged cardiac muscle cells have extremely limited abilities to repair themselves or to replace dead cells via mitosis. Recent evidence indicates that at least some stem cells remain within the heart that continue to divide and at least potentially replace these dead cells. However, newly formed or repaired cells are rarely as functional as the original cells, and cardiac function is reduced. In the event of a heart attack or MI, dead cells are often replaced by patches of scar tissue. Autopsies performed on individuals who had successfully received heart transplants show some proliferation of original cells. If researchers can unlock the mechanism that generates new cells and restore full mitotic capabilities to heart muscle, the prognosis for heart attack survivors will be greatly enhanced. To date, myocardial cells produced within the patient (in situ) by cardiac stem cells seem to be nonfunctional, although those grown in Petri dishes (in vitro) do beat. Perhaps soon this mystery will be solved, and new advances in treatment will be commonplace.
Conduction System of the Heart
If embryonic heart cells are separated into a Petri dish and kept alive, each is capable of generating its own electrical impulse followed by contraction. When two independently beating embryonic cardiac muscle cells are placed together, the cell with the higher inherent rate sets the pace, and the impulse spreads from the faster to the slower cell to trigger a contraction. As more cells are joined together, the fastest cell continues to assume control of the rate. A fully developed adult heart maintains the capability of generating its own electrical impulse, triggered by the fastest cells, as part of the cardiac conduction system. The components of the cardiac conduction system include the sinoatrial node, the atrioventricular node, the atrioventricular bundle, the atrioventricular bundle branches, and the Purkinje cells (Figure 19.18).
Figure 19.18 Conduction System of the Heart Specialized conducting components of the heart include the sinoatrial node, the internodal pathways, the atrioventricular node, the atrioventricular bundle, the right and left bundle branches, and the Purkinje fibers.
Sinoatrial (SA) Node
Normal cardiac rhythm is established by the sinoatrial (SA) node, a specialized clump of myocardial conducting cells located in the superior and posterior walls of the right atrium in close proximity to the orifice of the superior vena cava. The SA node has the highest inherent rate of depolarization and is known as the pacemaker of the heart. It initiates the sinus rhythm, or normal electrical pattern followed by contraction of the heart.
This impulse spreads from its initiation in the SA node throughout the atria through specialized internodal pathways, to the atrial myocardial contractile cells and the atrioventricular node. The internodal pathways consist of three bands (anterior, middle, and posterior) that lead directly from the SA node to the next node in the conduction system, the atrioventricular node (see Figure 19.18). The impulse takes approximately 50 ms (milliseconds) to travel between these two nodes. The relative importance of this pathway has been debated since the impulse would reach the atrioventricular node simply following the cell-by-cell pathway through the contractile cells of the myocardium in the atria. In addition, there is a specialized pathway called Bachmann’s bundle or the interatrial band that conducts the impulse directly from the right atrium to the left atrium. Regardless of the pathway, as the impulse reaches the atrioventricular septum, the connective tissue of the cardiac skeleton prevents the impulse from spreading into the myocardial cells in the ventricles except at the atrioventricular node. Figure 19.19illustrates the initiation of the impulse in the SA node that then spreads the impulse throughout the atria to the atrioventricular node.
Figure 19.19 Cardiac Conduction (1) The sinoatrial (SA) node and the remainder of the conduction system are at rest. (2) The SA node initiates the action potential, which sweeps across the atria. (3) After reaching the atrioventricular node, there is a delay of approximately 100 ms that allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle. (4) Following the delay, the impulse travels through the atrioventricular bundle and bundle branches to the Purkinje fibers, and also reaches the right papillary muscle via the moderator band. (5) The impulse spreads to the contractile fibers of the ventricle. (6) Ventricular contraction begins.
The electrical event, the wave of depolarization, is the trigger for muscular contraction. The wave of depolarization begins in the right atrium, and the impulse spreads across the superior portions of both atria and then down through the contractile cells. The contractile cells then begin contraction from the superior to the inferior portions of the atria, efficiently pumping blood into the ventricles.
Atrioventricular (AV) Node
The atrioventricular (AV) node is a second clump of specialized myocardial conductive cells, located in the inferior portion of the right atrium within the atrioventricular septum. The septum prevents the impulse from spreading directly to the ventricles without passing through the AV node. There is a critical pause before the AV node depolarizes and transmits the impulse to the atrioventricular bundle (see Figure 19.19, step 3). This delay in transmission is partially attributable to the small diameter of the cells of the node, which slow the impulse. Also, conduction between nodal cells is less efficient than between conducting cells. These factors mean that it takes the impulse approximately 100 ms to pass through the node. This pause is critical to heart function, as it allows the atrial cardiomyocytes to complete their contraction that pumps blood into the ventricles before the impulse is transmitted to the cells of the ventricle itself. With extreme stimulation by the SA node, the AV node can transmit impulses maximally at 220 per minute. This establishes the typical maximum heart rate in a healthy young individual. Damaged hearts or those stimulated by drugs can contract at higher rates, but at these rates, the heart can no longer effectively pump blood.
Atrioventricular Bundle (Bundle of His), Bundle Branches, and Purkinje Fibers
Arising from the AV node, the atrioventricular bundle, or bundle of His, proceeds through the interventricular septum before dividing into two atrioventricular bundle branches, commonly called the left and right bundle branches. The left bundle branch has two fascicles. The left bundle branch supplies the left ventricle, and the right bundle branch the right ventricle. Since the left ventricle is much larger than the right, the left bundle branch is also considerably larger than the right. Portions of the right bundle branch are found in the moderator band and supply the right papillary muscles. Because of this connection, each papillary muscle receives the impulse at approximately the same time, so they begin to contract simultaneously just prior to the remainder of the myocardial contractile cells of the ventricles. This is believed to allow tension to develop on the chordae tendineae prior to right ventricular contraction. There is no corresponding moderator band on the left. Both bundle branches descend and reach the apex of the heart where they connect with the Purkinje fibers (see Figure 19.19, step 4). This passage takes approximately 25 ms.
The Purkinje fibers are additional myocardial conductive fibers that spread the impulse to the myocardial contractile cells in the ventricles. They extend throughout the myocardium from the apex of the heart toward the atrioventricular septum and the base of the heart. The Purkinje fibers have a fast inherent conduction rate, and the electrical impulse reaches all of the ventricular muscle cells in about 75 ms (see Figure 19.19, step 5). Since the electrical stimulus begins at the apex, the contraction also begins at the apex and travels toward the base of the heart, similar to squeezing a tube of toothpaste from the bottom. This allows the blood to be pumped out of the ventricles and into the aorta and pulmonary trunk. The total time elapsed from the initiation of the impulse in the SA node until depolarization of the ventricles is approximately 225 ms.
Membrane Potentials and Ion Movement in Cardiac Conductive Cells
Action potentials are considerably different between cardiac conductive cells and cardiac contractive cells. While Na+ and K+play essential roles, Ca2+ is also critical for both types of cells. Unlike skeletal muscles and neurons, cardiac conductive cells do not have a stable resting potential. Conductive cells contain a series of sodium ion channels that allow a normal and slow influx of sodium ions that causes the membrane potential to rise slowly from an initial value of −60 mV up to about –40 mV. The resulting movement of sodium ions creates spontaneous depolarization (or prepotential depolarization). At this point, calcium ion channels open and Ca2+ enters the cell, further depolarizing it at a more rapid rate until it reaches a value of approximately +15 mV. At this point, the calcium ion channels close and K+ channels open, allowing outflux of K+ and resulting in repolarization. When the membrane potential reaches approximately −60 mV, the K+ channels close and Na+ channels open, and the prepotential phase begins again. This phenomenon explains the autorhythmicity properties of cardiac muscle (Figure 19.20).
Figure 19.20 Action Potential at the SA Node The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarization and repolarization. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell. Note the lack of a resting potential.
Membrane Potentials and Ion Movement in Cardiac Contractile Cells
There is a distinctly different electrical pattern involving the contractile cells. In this case, there is a rapid depolarization, followed by a plateau phase and then repolarization. This phenomenon accounts for the long refractory periods required for the cardiac muscle cells to pump blood effectively before they are capable of firing for a second time. These cardiac myocytes normally do not initiate their own electrical potential but rather wait for an impulse to reach them.
Contractile cells demonstrate a much more stable resting phase than conductive cells at approximately −80 mV for cells in the atria and −90 mV for cells in the ventricles. Despite this initial difference, the other components of their action potentials are virtually identical. In both cases, when stimulated by an action potential, voltage-gated channels rapidly open, beginning the positive-feedback mechanism of depolarization. This rapid influx of positively charged ions raises the membrane potential to approximately +30 mV, at which point the sodium channels close. The rapid depolarization period typically lasts 3–5 ms. Depolarization is followed by the plateau phase, in which membrane potential declines relatively slowly. This is due in large part to the opening of the slow Ca2+ channels, allowing Ca2+ to enter the cell while few K+ channels are open, allowing K+ to exit the cell. The relatively long plateau phase lasts approximately 175 ms. Once the membrane potential reaches approximately zero, the Ca2+ channels close and K+ channels open, allowing K+ to exit the cell. The repolarization lasts approximately 75 ms. At this point, membrane potential drops until it reaches resting levels once more and the cycle repeats. The entire event lasts between 250 and 300 ms (Figure 19.21).
The absolute refractory period for cardiac contractile muscle lasts approximately 200 ms, and the relative refractory period lasts approximately 50 ms, for a total of 250 ms. This extended period is critical, since the heart muscle must contract to pump blood effectively and the contraction must follow the electrical events. Without extended refractory periods, premature contractions would occur in the heart and would not be compatible with life.
Figure 19.21 Action Potential in Cardiac Contractile Cells (a) Note the long plateau phase due to the influx of calcium ions. The extended refractory period allows the cell to fully contract before another electrical event can occur. (b) The action potential for heart muscle is compared to that of skeletal muscle.
Calcium Ions
Calcium ions play two critical roles in the physiology of cardiac muscle. Their influx through slow calcium channels accounts for the prolonged plateau phase and absolute refractory period that enable cardiac muscle to function properly. Calcium ions also combine with the regulatory protein troponin in the troponin-tropomyosin complex; this complex removes the inhibition that prevents the heads of the myosin molecules from forming cross bridges with the active sites on actin that provide the power stroke of contraction. This mechanism is virtually identical to that of skeletal muscle. Approximately 20 percent of the calcium required for contraction is supplied by the influx of Ca2+ during the plateau phase. The remaining Ca2+ for contraction is released from storage in the sarcoplasmic reticulum.
Comparative Rates of Conduction System Firing
The pattern of prepotential or spontaneous depolarization, followed by rapid depolarization and repolarization just described, are seen in the SA node and a few other conductive cells in the heart. Since the SA node is the pacemaker, it reaches threshold faster than any other component of the conduction system. It will initiate the impulses spreading to the other conducting cells. The SA node, without nervous or endocrine control, would initiate a heart impulse approximately 80–100 times per minute. Although each component of the conduction system is capable of generating its own impulse, the rate progressively slows as you proceed from the SA node to the Purkinje fibers. Without the SA node, the AV node would generate a heart rate of 40–60 beats per minute. If the AV node were blocked, the atrioventricular bundle would fire at a rate of approximately 30–40 impulses per minute. The bundle branches would have an inherent rate of 20–30 impulses per minute, and the Purkinje fibers would fire at 15–20 impulses per minute. While a few exceptionally trained aerobic athletes demonstrate resting heart rates in the range of 30–40 beats per minute (the lowest recorded figure is 28 beats per minute for Miguel Indurain, a cyclist), for most individuals, rates lower than 50 beats per minute would indicate a condition called bradycardia. Depending upon the specific individual, as rates fall much below this level, the heart would be unable to maintain adequate flow of blood to vital tissues, initially resulting in decreasing loss of function across the systems, unconsciousness, and ultimately death.
Electrocardiogram
By careful placement of surface electrodes on the body, it is possible to record the complex, compound electrical signal of the heart. This tracing of the electrical signal is the electrocardiogram (ECG), also commonly abbreviated EKG (K coming kardiology, from the German term for cardiology). Careful analysis of the ECG reveals a detailed picture of both normal and abnormal heart function, and is an indispensable clinical diagnostic tool. The standard electrocardiograph (the instrument that generates an ECG) uses 3, 5, or 12 leads. The greater the number of leads an electrocardiograph uses, the more information the ECG provides. The term “lead” may be used to refer to the cable from the electrode to the electrical recorder, but it typically describes the voltage difference between two of the electrodes. The 12-lead electrocardiograph uses 10 electrodes placed in standard locations on the patient’s skin (Figure 19.22). In continuous ambulatory electrocardiographs, the patient wears a small, portable, battery-operated device known as a Holter monitor, or simply a Holter, that continuously monitors heart electrical activity, typically for a period of 24 hours during the patient’s normal routine.
Figure 19.22 Standard Placement of ECG Leads In a 12-lead ECG, six electrodes are placed on the chest, and four electrodes are placed on the limbs.
A normal ECG tracing is presented in Figure 19.23. Each component, segment, and interval is labeled and corresponds to important electrical events, demonstrating the relationship between these events and contraction in the heart.
There are five prominent points on the ECG: the P wave, the QRS complex, and the T wave. The small P wave represents the depolarization of the atria. The atria begin contracting approximately 25 ms after the start of the P wave. The large QRS complex represents the depolarization of the ventricles, which requires a much stronger electrical signal because of the larger size of the ventricular cardiac muscle. The ventricles begin to contract as the QRS reaches the peak of the R wave. Lastly, the T wave represents the repolarization of the ventricles. The repolarization of the atria occurs during the QRS complex, which masks it on an ECG.
The major segments and intervals of an ECG tracing are indicated in Figure 19.23. Segments are defined as the regions between two waves. Intervals include one segment plus one or more waves. For example, the PR segment begins at the end of the P wave and ends at the beginning of the QRS complex. The PR interval starts at the beginning of the P wave and ends with the beginning of the QRS complex. The PR interval is more clinically relevant, as it measures the duration from the beginning of atrial depolarization (the P wave) to the initiation of the QRS complex. Since the Q wave may be difficult to view in some tracings, the measurement is often extended to the R that is more easily visible. Should there be a delay in passage of the impulse from the SA node to the AV node, it would be visible in the PR interval. Figure 19.24 correlates events of heart contraction to the corresponding segments and intervals of an ECG.
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Figure 19.23 Electrocardiogram A normal tracing shows the P wave, QRS complex, and T wave. Also indicated are the PR, QT, QRS, and ST intervals, plus the P-R and S-T segments.
Figure 19.24 ECG Tracing Correlated to the Cardiac Cycle This diagram correlates an ECG tracing with the electrical and mechanical events of a heart contraction. Each segment of an ECG tracing corresponds to one event in the cardiac cycle.
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ECG Abnormalities
Occassionally, an area of the heart other than the SA node will initiate an impulse that will be followed by a premature contraction. Such an area, which may actually be a component of the conduction system or some other contractile cells, is known as an ectopic focus or ectopic pacemaker. An ectopic focus may be stimulated by localized ischemia; exposure to certain drugs, including caffeine, digitalis, or acetylcholine; elevated stimulation by both sympathetic or parasympathetic divisions of the autonomic nervous system; or a number of disease or pathological conditions. Occasional occurances are generally transitory and nonlife threatening, but if the condition becomes chronic, it may lead to either an arrhythmia, a deviation from the normal pattern of impulse conduction and contraction, or to fibrillation, an uncoordinated beating of the heart.
While interpretation of an ECG is possible and extremely valuable after some training, a full understanding of the complexities and intricacies generally requires several years of experience. In general, the size of the electrical variations, the duration of the events, and detailed vector analysis provide the most comprehensive picture of cardiac function. For example, an amplified P wave may indicate enlargement of the atria, an enlarged Q wave may indicate a MI, and an enlarged suppressed or inverted Q wave often indicates enlarged ventricles. T waves often appear flatter when insufficient oxygen is being delivered to the myocardium. An elevation of the ST segment above baseline is often seen in patients with an acute MI, and may appear depressed below the baseline when hypoxia is occurring.
As useful as analyzing these electrical recordings may be, there are limitations. For example, not all areas suffering a MI may be obvious on the ECG. Additionally, it will not reveal the effectiveness of the pumping, which requires further testing, such as an ultrasound test called an echocardiogram or nuclear medicine imaging. It is also possible for there to be pulseless electrical activity, which will show up on an ECG tracing, although there is no corresponding pumping action. Common abnormalities that may be detected by the ECGs are shown in Figure 19.25.
Figure 19.25 Common ECG Abnormalities (a) In a second-degree or partial block, one-half of the P waves are not followed by the QRS complex and T waves while the other half are. (b) In atrial fibrillation, the electrical pattern is abnormal prior to the QRS complex, and the frequency between the QRS complexes has increased. (c) In ventricular tachycardia, the shape of the QRS complex is abnormal. (d) In ventricular fibrillation, there is no normal electrical activity. (e) In a third-degree block, there is no correlation between atrial activity (the P wave) and ventricular activity (the QRS complex).
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External Automated Defibrillators
In the event that the electrical activity of the heart is severely disrupted, cessation of electrical activity or fibrillation may occur. In fibrillation, the heart beats in a wild, uncontrolled manner, which prevents it from being able to pump effectively. Atrial fibrillation (see Figure 19.25b) is a serious condition, but as long as the ventricles continue to pump blood, the patient’s life may not be in immediate danger. Ventricular fibrillation (see Figure 19.25d) is a medical emergency that requires life support, because the ventricles are not effectively pumping blood. In a hospital setting, it is often described as “code blue.” If untreated for as little as a few minutes, ventricular fibrillation may lead to brain death. The most common treatment is defibrillation, which uses special paddles to apply a charge to the heart from an external electrical source in an attempt to establish a normal sinus rhythm (Figure 19.26). A defibrillator effectively stops the heart so that the SA node can trigger a normal conduction cycle. Because of their effectiveness in reestablishing a normal sinus rhythm, external automated defibrillators (EADs) are being placed in areas frequented by large numbers of people, such as schools, restaurants, and airports. These devices contain simple and direct verbal instructions that can be followed by nonmedical personnel in an attempt to save a life.
Figure 19.26 Defibrillators (a) An external automatic defibrillator can be used by nonmedical personnel to reestablish a normal sinus rhythm in a person with fibrillation. (b) Defibrillator paddles are more commonly used in hospital settings. (credit b: “widerider107”/flickr.com)
A heart block refers to an interruption in the normal conduction pathway. The nomenclature for these is very straightforward. SA nodal blocks occur within the SA node. AV nodal blocks occur within the AV node. Infra-Hisian blocks involve the bundle of His. Bundle branch blocks occur within either the left or right atrioventricular bundle branches. Hemiblocks are partial and occur within one or more fascicles of the atrioventricular bundle branch. Clinically, the most common types are the AV nodal and infra-Hisian blocks.
AV blocks are often described by degrees. A first-degree or partial block indicates a delay in conduction between the SA and AV nodes. This can be recognized on the ECG as an abnormally long PR interval. A second-degree or incomplete block occurs when some impulses from the SA node reach the AV node and continue, while others do not. In this instance, the ECG would reveal some P waves not followed by a QRS complex, while others would appear normal. In the third-degree or complete block, there is no correlation between atrial activity (the P wave) and ventricular activity (the QRS complex). Even in the event of a total SA block, the AV node will assume the role of pacemaker and continue initiating contractions at 40–60 contractions per minute, which is adequate to maintain consciousness. Second- and third-degree blocks are demonstrated on the ECG presented in Figure 19.25.
When arrhythmias become a chronic problem, the heart maintains a junctional rhythm, which originates in the AV node. In order to speed up the heart rate and restore full sinus rhythm, a cardiologist can implant an artificial pacemaker, which delivers electrical impulses to the heart muscle to ensure that the heart continues to contract and pump blood effectively. These artificial pacemakers are programmable by the cardiologists and can either provide stimulation temporarily upon demand or on a continuous basis. Some devices also contain built-in defibrillators.
Cardiac Muscle Metabolism
Normally, cardiac muscle metabolism is entirely aerobic. Oxygen from the lungs is brought to the heart, and every other organ, attached to the hemoglobin molecules within the erythrocytes. Heart cells also store appreciable amounts of oxygen in myoglobin. Normally, these two mechanisms, circulating oxygen and oxygen attached to myoglobin, can supply sufficient oxygen to the heart, even during peak performance.
Fatty acids and glucose from the circulation are broken down within the mitochondria to release energy in the form of ATP. Both fatty acid droplets and glycogen are stored within the sarcoplasm and provide additional nutrient supply. (Seek additional content for more detail about metabolism.)
Cardiac Cycle
- Describe the relationship between blood pressure and blood flow
- Summarize the events of the cardiac cycle
- Compare atrial and ventricular systole and diastole
- Relate heart sounds detected by auscultation to action of heart’s valves
The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle(Figure 19.27). The period of contraction that the heart undergoes while it pumps blood into circulation is called systole. The period of relaxation that occurs as the chambers fill with blood is called diastole. Both the atria and ventricles undergo systole and diastole, and it is essential that these components be carefully regulated and coordinated to ensure blood is pumped efficiently to the body.
Figure 19.27 Overview of the Cardiac Cycle The cardiac cycle begins with atrial systole and progresses to ventricular systole, atrial diastole, and ventricular diastole, when the cycle begins again. Correlations to the ECG are highlighted.
Pressures and Flow
Fluids, whether gases or liquids, are materials that flow according to pressure gradients—that is, they move from regions that are higher in pressure to regions that are lower in pressure. Accordingly, when the heart chambers are relaxed (diastole), blood will flow into the atria from the veins, which are higher in pressure. As blood flows into the atria, the pressure will rise, so the blood will initially move passively from the atria into the ventricles. When the action potential triggers the muscles in the atria to contract (atrial systole), the pressure within the atria rises further, pumping blood into the ventricles. During ventricular systole, pressure rises in the ventricles, pumping blood into the pulmonary trunk from the right ventricle and into the aorta from the left ventricle. Again, as you consider this flow and relate it to the conduction pathway, the elegance of the system should become apparent.
Phases of the Cardiac Cycle
At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). Blood is flowing into the right atrium from the superior and inferior venae cavae and the coronary sinus. Blood flows into the left atrium from the four pulmonary veins. The two atrioventricular valves, the tricuspid and mitral valves, are both open, so blood flows unimpeded from the atria and into the ventricles. Approximately 70–80 percent of ventricular filling occurs by this method. The two semilunar valves, the pulmonary and aortic valves, are closed, preventing backflow of blood into the right and left ventricles from the pulmonary trunk on the right and the aorta on the left.
Atrial Systole and Diastole
Contraction of the atria follows depolarization, represented by the P wave of the ECG. As the atrial muscles contract from the superior portion of the atria toward the atrioventricular septum, pressure rises within the atria and blood is pumped into the ventricles through the open atrioventricular (tricuspid, and mitral or bicuspid) valves. At the start of atrial systole, the ventricles are normally filled with approximately 70–80 percent of their capacity due to inflow during diastole. Atrial contraction, also referred to as the “atrial kick,” contributes the remaining 20–30 percent of filling (see Figure 19.27). Atrial systole lasts approximately 100 ms and ends prior to ventricular systole, as the atrial muscle returns to diastole.
Ventricular Systole
Ventricular systole (see Figure 19.27) follows the depolarization of the ventricles and is represented by the QRS complex in the ECG. It may be conveniently divided into two phases, lasting a total of 270 ms. At the end of atrial systole and just prior to atrial contraction, the ventricles contain approximately 130 mL blood in a resting adult in a standing position. This volume is known as the end diastolic volume (EDV) or preload.
Initially, as the muscles in the ventricle contract, the pressure of the blood within the chamber rises, but it is not yet high enough to open the semilunar (pulmonary and aortic) valves and be ejected from the heart. However, blood pressure quickly rises above that of the atria that are now relaxed and in diastole. This increase in pressure causes blood to flow back toward the atria, closing the tricuspid and mitral valves. Since blood is not being ejected from the ventricles at this early stage, the volume of blood within the chamber remains constant. Consequently, this initial phase of ventricular systole is known as isovolumic contraction, also called isovolumetric contraction (see Figure 19.27).
In the second phase of ventricular systole, the ventricular ejection phase, the contraction of the ventricular muscle has raised the pressure within the ventricle to the point that it is greater than the pressures in the pulmonary trunk and the aorta. Blood is pumped from the heart, pushing open the pulmonary and aortic semilunar valves. Pressure generated by the left ventricle will be appreciably greater than the pressure generated by the right ventricle, since the existing pressure in the aorta will be so much higher. Nevertheless, both ventricles pump the same amount of blood. This quantity is referred to as stroke volume. Stroke volume will normally be in the range of 70–80 mL. Since ventricular systole began with an EDV of approximately 130 mL of blood, this means that there is still 50–60 mL of blood remaining in the ventricle following contraction. This volume of blood is known as the end systolic volume (ESV).
Ventricular Diastole
Ventricular relaxation, or diastole, follows repolarization of the ventricles and is represented by the T wave of the ECG. It too is divided into two distinct phases and lasts approximately 430 ms.
During the early phase of ventricular diastole, as the ventricular muscle relaxes, pressure on the remaining blood within the ventricle begins to fall. When pressure within the ventricles drops below pressure in both the pulmonary trunk and aorta, blood flows back toward the heart, producing the dicrotic notch (small dip) seen in blood pressure tracings. The semilunar valves close to prevent backflow into the heart. Since the atrioventricular valves remain closed at this point, there is no change in the volume of blood in the ventricle, so the early phase of ventricular diastole is called the isovolumic ventricular relaxation phase, also called isovolumetric ventricular relaxation phase (see Figure 19.27).
In the second phase of ventricular diastole, called late ventricular diastole, as the ventricular muscle relaxes, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria. When this occurs, blood flows from the atria into the ventricles, pushing open the tricuspid and mitral valves. As pressure drops within the ventricles, blood flows from the major veins into the relaxed atria and from there into the ventricles. Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves remain closed (see Figure 19.27). The cardiac cycle is complete.
Figure 19.28 illustrates the relationship between the cardiac cycle and the ECG.
Figure 19.28 Relationship between the Cardiac Cycle and ECG Initially, both the atria and ventricles are relaxed (diastole). The P wave represents depolarization of the atria and is followed by atrial contraction (systole). Atrial systole extends until the QRS complex, at which point, the atria relax. The QRS complex represents depolarization of the ventricles and is followed by ventricular contraction. The T wave represents the repolarization of the ventricles and marks the beginning of ventricular relaxation.
Heart Sounds
One of the simplest, yet effective, diagnostic techniques applied to assess the state of a patient’s heart is auscultation using a stethoscope.
In a normal, healthy heart, there are only two audible heart sounds: S1 and S2. S1 is the sound created by the closing of the atrioventricular valves during ventricular contraction and is normally described as a “lub,” or first heart sound. The second heart sound, S2, is the sound of the closing of the semilunar valves during ventricular diastole and is described as a “dub” (Figure 19.29). In both cases, as the valves close, the openings within the atrioventricular septum guarded by the valves will become reduced, and blood flow through the opening will become more turbulent until the valves are fully closed. There is a third heart sound, S3, but it is rarely heard in healthy individuals. It may be the sound of blood flowing into the atria, or blood sloshing back and forth in the ventricle, or even tensing of the chordae tendineae. S3 may be heard in youth, some athletes, and pregnant women. If the sound is heard later in life, it may indicate congestive heart failure, warranting further tests. Some cardiologists refer to the collective S1, S2, and S3 sounds as the “Kentucky gallop,” because they mimic those produced by a galloping horse. The fourth heart sound, S4, results from the contraction of the atria pushing blood into a stiff or hypertrophic ventricle, indicating failure of the left ventricle. S4 occurs prior to S1 and the collective sounds S4, S1, and S2 are referred to by some cardiologists as the “Tennessee gallop,” because of their similarity to the sound produced by a galloping horse with a different gait. A few individuals may have both S3 and S4, and this combined sound is referred to as S7.
Figure 19.29 Heart Sounds and the Cardiac Cycle In this illustration, the x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.
The term murmur is used to describe an unusual sound coming from the heart that is caused by the turbulent flow of blood. Murmurs are graded on a scale of 1 to 6, with 1 being the most common, the most difficult sound to detect, and the least serious. The most severe is a 6. Phonocardiograms or auscultograms can be used to record both normal and abnormal sounds using specialized electronic stethoscopes.
During auscultation, it is common practice for the clinician to ask the patient to breathe deeply. This procedure not only allows for listening to airflow, but it may also amplify heart murmurs. Inhalation increases blood flow into the right side of the heart and may increase the amplitude of right-sided heart murmurs. Expiration partially restricts blood flow into the left side of the heart and may amplify left-sided heart murmurs. Figure 19.30 indicates proper placement of the bell of the stethoscope to facilitate auscultation.
Figure 19.30 Stethoscope Placement for Auscultation Proper placement of the bell of the stethoscope facilitates auscultation. At each of the four locations on the chest, a different valve can be heard.
Cardiac Physiology
- Relate heart rate to cardiac output
- Describe the effect of exercise on heart rate
- Identify cardiovascular centers and cardiac reflexes that regulate heart function
- Describe factors affecting heart rate
- Distinguish between positive and negative factors that affect heart contractility
- Summarize factors affecting stroke volume and cardiac output
- Describe the cardiac response to variations in blood flow and pressure
The autorhythmicity inherent in cardiac cells keeps the heart beating at a regular pace; however, the heart is regulated by and responds to outside influences as well. Neural and endocrine controls are vital to the regulation of cardiac function. In addition, the heart is sensitive to several environmental factors, including electrolytes.
Resting Cardiac Output
Cardiac output (CO) is a measurement of the amount of blood pumped by each ventricle in one minute. To calculate this value, multiply stroke volume (SV), the amount of blood pumped by each ventricle, by heart rate (HR), in contractions per minute (or beats per minute, bpm). It can be represented mathematically by the following equation:
CO = HR × SV
SV is normally measured using an echocardiogram to record EDV and ESV, and calculating the difference: SV = EDV – ESV. SV can also be measured using a specialized catheter, but this is an invasive procedure and far more dangerous to the patient. A mean SV for a resting 70-kg (150-lb) individual would be approximately 70 mL. There are several important variables, including size of the heart, physical and mental condition of the individual, sex, contractility, duration of contraction, preload or EDV, and afterload or resistance. Normal range for SV would be 55–100 mL. An average resting HR would be approximately 75 bpm but could range from 60–100 in some individuals.
Using these numbers, the mean CO is 5.25 L/min, with a range of 4.0–8.0 L/min. Remember, however, that these numbers refer to CO from each ventricle separately, not the total for the heart. Factors influencing CO are summarized in Figure 19.31.
Figure 19.31 Major Factors Influencing Cardiac Output Cardiac output is influenced by heart rate and stroke volume, both of which are also variable.
SVs are also used to calculate ejection fraction, which is the portion of the blood that is pumped or ejected from the heart with each contraction. To calculate ejection fraction, SV is divided by EDV. Despite the name, the ejection fraction is normally expressed as a percentage. Ejection fractions range from approximately 55–70 percent, with a mean of 58 percent.
Exercise and Maximum Cardiac Output
In healthy young individuals, HR may increase to 150 bpm during exercise. SV can also increase from 70 to approximately 130 mL due to increased strength of contraction. This would increase CO to approximately 19.5 L/min, 4–5 times the resting rate. Top cardiovascular athletes can achieve even higher levels. At their peak performance, they may increase resting CO by 7–8 times.
Since the heart is a muscle, exercising it increases its efficiency. The difference between maximum and resting CO is known as the cardiac reserve. It measures the residual capacity of the heart to pump blood.
Heart Rates
HRs vary considerably, not only with exercise and fitness levels, but also with age. Newborn resting HRs may be 120 bpm. HR gradually decreases until young adulthood and then gradually increases again with age.
Maximum HRs are normally in the range of 200–220 bpm, although there are some extreme cases in which they may reach higher levels. As one ages, the ability to generate maximum rates decreases. This may be estimated by taking the maximal value of 220 bpm and subtracting the individual’s age. So a 40-year-old individual would be expected to hit a maximum rate of approximately 180, and a 60-year-old person would achieve a HR of 160.
DISORDERS OF THE...
Heart: Abnormal Heart Rates
For an adult, normal resting HR will be in the range of 60–100 bpm. Bradycardia is the condition in which resting rate drops below 60 bpm, and tachycardia is the condition in which the resting rate is above 100 bpm. Trained athletes typically have very low HRs. If the patient is not exhibiting other symptoms, such as weakness, fatigue, dizziness, fainting, chest discomfort, palpitations, or respiratory distress, bradycardia is not considered clinically significant. However, if any of these symptoms are present, they may indicate that the heart is not providing sufficient oxygenated blood to the tissues. The term relative bradycardia may be used with a patient who has a HR in the normal range but is still suffering from these symptoms. Most patients remain asymptomatic as long as the HR remains above 50 bpm.
Bradycardia may be caused by either inherent factors or causes external to the heart. While the condition may be inherited, typically it is acquired in older individuals. Inherent causes include abnormalities in either the SA or AV node. If the condition is serious, a pacemaker may be required. Other causes include ischemia to the heart muscle or diseases of the heart vessels or valves. External causes include metabolic disorders, pathologies of the endocrine system often involving the thyroid, electrolyte imbalances, neurological disorders including inappropriate autonomic responses, autoimmune pathologies, over-prescription of beta blocker drugs that reduce HR, recreational drug use, or even prolonged bed rest. Treatment relies upon establishing the underlying cause of the disorder and may necessitate supplemental oxygen.
Tachycardia is not normal in a resting patient but may be detected in pregnant women or individuals experiencing extreme stress. In the latter case, it would likely be triggered by stimulation from the limbic system or disorders of the autonomic nervous system. In some cases, tachycardia may involve only the atria. Some individuals may remain asymptomatic, but when present, symptoms may include dizziness, shortness of breath, lightheadedness, rapid pulse, heart palpations, chest pain, or fainting (syncope). While tachycardia is defined as a HR above 100 bpm, there is considerable variation among people. Further, the normal resting HRs of children are often above 100 bpm, but this is not considered to be tachycardia Many causes of tachycardia may be benign, but the condition may also be correlated with fever, anemia, hypoxia, hyperthyroidism, hypersecretion of catecholamines, some cardiomyopathies, some disorders of the valves, and acute exposure to radiation. Elevated rates in an exercising or resting patient are normal and expected. Resting rate should always be taken after recovery from exercise. Treatment depends upon the underlying cause but may include medications, implantable cardioverter defibrillators, ablation, or surgery.
Correlation Between Heart Rates and Cardiac Output
Initially, physiological conditions that cause HR to increase also trigger an increase in SV. During exercise, the rate of blood returning to the heart increases. However as the HR rises, there is less time spent in diastole and consequently less time for the ventricles to fill with blood. Even though there is less filling time, SV will initially remain high. However, as HR continues to increase, SV gradually decreases due to decreased filling time. CO will initially stabilize as the increasing HR compensates for the decreasing SV, but at very high rates, CO will eventually decrease as increasing rates are no longer able to compensate for the decreasing SV. Consider this phenomenon in a healthy young individual. Initially, as HR increases from resting to approximately 120 bpm, CO will rise. As HR increases from 120 to 160 bpm, CO remains stable, since the increase in rate is offset by decreasing ventricular filling time and, consequently, SV. As HR continues to rise above 160 bpm, CO actually decreases as SV falls faster than HR increases. So although aerobic exercises are critical to maintain the health of the heart, individuals are cautioned to monitor their HR to ensure they stay within the target heart rate range of between 120 and 160 bpm, so CO is maintained. The target HR is loosely defined as the range in which both the heart and lungs receive the maximum benefit from the aerobic workout and is dependent upon age.
Cardiovascular Centers
Nervous control over HR is centralized within the two paired cardiovascular centers of the medulla oblongata (Figure 19.32). The cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, and the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve, cranial nerve X. During rest, both centers provide slight stimulation to the heart, contributing to autonomic tone. This is a similar concept to tone in skeletal muscles. Normally, vagal stimulation predominates as, left unregulated, the SA node would initiate a sinus rhythm of approximately 100 bpm.
Both sympathetic and parasympathetic stimulations flow through a paired complex network of nerve fibers known as the cardiac plexus near the base of the heart. The cardioaccelerator center also sends additional fibers, forming the cardiac nerves via sympathetic ganglia (the cervical ganglia plus superior thoracic ganglia T1–T4) to both the SA and AV nodes, plus additional fibers to the atria and ventricles. The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes the release of the neurotransmitter norepinephrine (NE) at the neuromuscular junction of the cardiac nerves. NE shortens the repolarization period, thus speeding the rate of depolarization and contraction, which results in an increase in HR. It opens chemical- or ligand-gated sodium and calcium ion channels, allowing an influx of positively charged ions.
NE binds to the beta-1 receptor. Some cardiac medications (for example, beta blockers) work by blocking these receptors, thereby slowing HR and are one possible treatment for hypertension. Overprescription of these drugs may lead to bradycardia and even stoppage of the heart.
Figure 19.32 Autonomic Innervation of the Heart Cardioaccelerator and cardioinhibitory areas are components of the paired cardiac centers located in the medulla oblongata of the brain. They innervate the heart via sympathetic cardiac nerves that increase cardiac activity and vagus (parasympathetic) nerves that slow cardiac activity.
Parasympathetic stimulation originates from the cardioinhibitory region with impulses traveling via the vagus nerve (cranial nerve X). The vagus nerve sends branches to both the SA and AV nodes, and to portions of both the atria and ventricles. Parasympathetic stimulation releases the neurotransmitter acetylcholine (ACh) at the neuromuscular junction. ACh slows HR by opening chemical- or ligand-gated potassium ion channels to slow the rate of spontaneous depolarization, which extends repolarization and increases the time before the next spontaneous depolarization occurs. Without any nervous stimulation, the SA node would establish a sinus rhythm of approximately 100 bpm. Since resting rates are considerably less than this, it becomes evident that parasympathetic stimulation normally slows HR. This is similar to an individual driving a car with one foot on the brake pedal. To speed up, one need merely remove one’s foot from the break and let the engine increase speed. In the case of the heart, decreasing parasympathetic stimulation decreases the release of ACh, which allows HR to increase up to approximately 100 bpm. Any increases beyond this rate would require sympathetic stimulation. Figure 19.33 illustrates the effects of parasympathetic and sympathetic stimulation on the normal sinus rhythm.
Figure 19.33 Effects of Parasympathetic and Sympathetic Stimulation on Normal Sinus Rhythm The wave of depolarization in a normal sinus rhythm shows a stable resting HR. Following parasympathetic stimulation, HR slows. Following sympathetic stimulation, HR increases.
Input to the Cardiovascular Center
The cardiovascular center receives input from a series of visceral receptors with impulses traveling through visceral sensory fibers within the vagus and sympathetic nerves via the cardiac plexus. Among these receptors are various proprioreceptors, baroreceptors, and chemoreceptors, plus stimuli from the limbic system. Collectively, these inputs normally enable the cardiovascular centers to regulate heart function precisely, a process known as cardiac reflexes. Increased physical activity results in increased rates of firing by various proprioreceptors located in muscles, joint capsules, and tendons. Any such increase in physical activity would logically warrant increased blood flow. The cardiac centers monitor these increased rates of firing, and suppress parasympathetic stimulation and increase sympathetic stimulation as needed in order to increase blood flow.
Similarly, baroreceptors are stretch receptors located in the aortic sinus, carotid bodies, the venae cavae, and other locations, including pulmonary vessels and the right side of the heart itself. Rates of firing from the baroreceptors represent blood pressure, level of physical activity, and the relative distribution of blood. The cardiac centers monitor baroreceptor firing to maintain cardiac homeostasis, a mechanism called the baroreceptor reflex. With increased pressure and stretch, the rate of baroreceptor firing increases, and the cardiac centers decrease sympathetic stimulation and increase parasympathetic stimulation. As pressure and stretch decrease, the rate of baroreceptor firing decreases, and the cardiac centers increase sympathetic stimulation and decrease parasympathetic stimulation.
There is a similar reflex, called the atrial reflex or Bainbridge reflex, associated with varying rates of blood flow to the atria. Increased venous return stretches the walls of the atria where specialized baroreceptors are located. However, as the atrial baroreceptors increase their rate of firing and as they stretch due to the increased blood pressure, the cardiac center responds by increasing sympathetic stimulation and inhibiting parasympathetic stimulation to increase HR. The opposite is also true.
Increased metabolic byproducts associated with increased activity, such as carbon dioxide, hydrogen ions, and lactic acid, plus falling oxygen levels, are detected by a suite of chemoreceptors innervated by the glossopharyngeal and vagus nerves. These chemoreceptors provide feedback to the cardiovascular centers about the need for increased or decreased blood flow, based on the relative levels of these substances.
The limbic system can also significantly impact HR related to emotional state. During periods of stress, it is not unusual to identify higher than normal HRs, often accompanied by a surge in the stress hormone cortisol. Individuals experiencing extreme anxiety may manifest panic attacks with symptoms that resemble those of heart attacks. These events are typically transient and treatable. Meditation techniques have been developed to ease anxiety and have been shown to lower HR effectively. Doing simple deep and slow breathing exercises with one’s eyes closed can also significantly reduce this anxiety and HR.
DISORDERS OF THE...
Heart: Broken Heart Syndrome
Extreme stress from such life events as the death of a loved one, an emotional break up, loss of income, or foreclosure of a home may lead to a condition commonly referred to as broken heart syndrome. This condition may also be called Takotsubo cardiomyopathy, transient apical ballooning syndrome, apical ballooning cardiomyopathy, stress-induced cardiomyopathy, Gebrochenes-Herz syndrome, and stress cardiomyopathy. The recognized effects on the heart include congestive heart failure due to a profound weakening of the myocardium not related to lack of oxygen. This may lead to acute heart failure, lethal arrhythmias, or even the rupture of a ventricle. The exact etiology is not known, but several factors have been suggested, including transient vasospasm, dysfunction of the cardiac capillaries, or thickening of the myocardium—particularly in the left ventricle—that may lead to the critical circulation of blood to this region. While many patients survive the initial acute event with treatment to restore normal function, there is a strong correlation with death. Careful statistical analysis by the Cass Business School, a prestigious institution located in London, published in 2008, revealed that within one year of the death of a loved one, women are more than twice as likely to die and males are six times as likely to die as would otherwise be expected.
Other Factors Influencing Heart Rate
Using a combination of autorhythmicity and innervation, the cardiovascular center is able to provide relatively precise control over HR. However, there are a number of other factors that have an impact on HR as well, including epinephrine, NE, and thyroid hormones; levels of various ions including calcium, potassium, and sodium; body temperature; hypoxia; and pH balance (Table 19.1 and Table 19.2). After reading this section, the importance of maintaining homeostasis should become even more apparent.
Major Factors Increasing Heart Rate and Force of Contraction
| Factor | Effect |
|---|---|
| Cardioaccelerator nerves | Release of norepinephrine by cardioinhibitory nerves |
| Proprioreceptors | Increased firing rates of proprioreceptors (e.g. during exercise) |
| Chemoreceptors | Chemoreceptors sensing decreased levels of O2 or increased levels of H+, CO2 and lactic acid |
| Baroreceptors | Decreased firing rates of baroreceptors (indicating falling blood volume/pressure) |
| Limbic system | Anticipation of physical exercise or strong emotions by the limbic system |
| Catecholamines | Increased epinephrine and norepinephrine release by the adrenal glands |
| Thyroid hormones | Increased T3 and T4 in the blood (released by thyroid) |
| Calcium | Increase in calcium ions in the blood |
| Potassium | Decrease in potassium ions in the blood |
| Sodium | Decrease in sodium ions in the blood |
| Body temperature | Increase in body temperature |
| Nicotine and caffeine | Presence of nicotine, caffeine or other stimulants |
Table 19.1
Factors Decreasing Heart Rate and Force of Contraction
| Factor | Effect |
|---|---|
| Cardioinhibitor nerves (vagus) | Release of acetylcholine by cardioaccelerator nerves |
| Proprioreceptors | Decreased firing rates of proprioreceptors (e.g. during rest) |
| Chemoreceptors | Chemoreceptors sensing increased levels of O2 or decreased levels of H+, CO2 and lactic acid |
| Baroreceptors | Increased firing rates of baroreceptors (indicating rising blood volume/pressure) |
| Limbic system | Anticipation of relaxation by the limbic system |
| Catecholamines | Increased epinephrine and norepinephrine release by the adrenal glands |
| Thyroid hormones | Decreased T3 and T4 in the blood (released by thyroid) |
| Calcium | Increase in calcium ions in the blood |
| Potassium | Increase in potassium ions in the blood |
| Sodium | Increase in sodium ions in the blood |
| Body temperature | Decrease in body temperature |
| Opiates and tranquilizers | Presence of opiates (heroin), tranquilizers or other depressants |
Table 19.2
Epinephrine and Norepinephrine
The catecholamines, epinephrine and NE, secreted by the adrenal medulla form one component of the extended fight-or-flight mechanism. The other component is sympathetic stimulation. Epinephrine and NE have similar effects: binding to the beta-1 receptors, and opening sodium and calcium ion chemical- or ligand-gated channels. The rate of depolarization is increased by this additional influx of positively charged ions, so the threshold is reached more quickly and the period of repolarization is shortened. However, massive releases of these hormones coupled with sympathetic stimulation may actually lead to arrhythmias. There is no parasympathetic stimulation to the adrenal medulla.
Thyroid Hormones
In general, increased levels of thyroid hormone, or thyroxin, increase cardiac rate and contractility. The impact of thyroid hormone is typically of a much longer duration than that of the catecholamines. The physiologically active form of thyroid hormone, T3 or triiodothyronine, has been shown to directly enter cardiomyocytes and alter activity at the level of the genome. It also impacts the beta adrenergic response similar to epinephrine and NE described above. Excessive levels of thyroxin may trigger tachycardia.
Calcium
Calcium ion levels have great impacts upon both HR and contractility; as the levels of calcium ions increase, so do HR and contractility. High levels of calcium ions (hypercalcemia) may be implicated in a short QT interval and a widened T wave in the ECG. The QT interval represents the time from the start of depolarization to repolarization of the ventricles, and includes the period of ventricular systole. Extremely high levels of calcium may induce cardiac arrest. Drugs known as calcium channel blockers slow HR by binding to these channels and blocking or slowing the inward movement of calcium ions.
Caffeine and Nicotine
Caffeine and nicotine are not found naturally within the body. Both of these nonregulated drugs have an excitatory effect on membranes of neurons in general and have a stimulatory effect on the cardiac centers specifically, causing an increase in HR. Caffeine works by increasing the rates of depolarization at the SA node, whereas nicotine stimulates the activity of the sympathetic neurons that deliver impulses to the heart.
Although it is the world’s most widely consumed psychoactive drug, caffeine is legal and not regulated. While precise quantities have not been established, “normal” consumption is not considered harmful to most people, although it may cause disruptions to sleep and acts as a diuretic. Its consumption by pregnant women is cautioned against, although no evidence of negative effects has been confirmed. Tolerance and even physical and mental addiction to the drug result in individuals who routinely consume the substance.
Nicotine, too, is a stimulant and produces addiction. While legal and nonregulated, concerns about nicotine’s safety and documented links to respiratory and cardiac disease have resulted in warning labels on cigarette packages.
Factors Decreasing Heart Rate
HR can be slowed when a person experiences altered sodium and potassium levels, hypoxia, acidosis, alkalosis, and hypothermia (see Table 19.1). The relationship between electrolytes and HR is complex, but maintaining electrolyte balance is critical to the normal wave of depolarization. Of the two ions, potassium has the greater clinical significance. Initially, both hyponatremia (low sodium levels) and hypernatremia (high sodium levels) may lead to tachycardia. Severely high hypernatremia may lead to fibrillation, which may cause CO to cease. Severe hyponatremia leads to both bradycardia and other arrhythmias. Hypokalemia (low potassium levels) also leads to arrhythmias, whereas hyperkalemia (high potassium levels) causes the heart to become weak and flaccid, and ultimately to fail.
Acidosis is a condition in which excess hydrogen ions are present, and the patient’s blood expresses a low pH value. Alkalosis is a condition in which there are too few hydrogen ions, and the patient’s blood has an elevated pH. Normal blood pH falls in the range of 7.35–7.45, so a number lower than this range represents acidosis and a higher number represents alkalosis. Recall that enzymes are the regulators or catalysts of virtually all biochemical reactions; they are sensitive to pH and will change shape slightly with values outside their normal range. These variations in pH and accompanying slight physical changes to the active site on the enzyme decrease the rate of formation of the enzyme-substrate complex, subsequently decreasing the rate of many enzymatic reactions, which can have complex effects on HR. Severe changes in pH will lead to denaturation of the enzyme.
The last variable is body temperature. Elevated body temperature is called hyperthermia, and suppressed body temperature is called hypothermia. Slight hyperthermia results in increasing HR and strength of contraction. Hypothermia slows the rate and strength of heart contractions. This distinct slowing of the heart is one component of the larger diving reflex that diverts blood to essential organs while submerged. If sufficiently chilled, the heart will stop beating, a technique that may be employed during open heart surgery. In this case, the patient’s blood is normally diverted to an artificial heart-lung machine to maintain the body’s blood supply and gas exchange until the surgery is complete, and sinus rhythm can be restored. Excessive hyperthermia and hypothermia will both result in death, as enzymes drive the body systems to cease normal function, beginning with the central nervous system.
Stroke Volume
Many of the same factors that regulate HR also impact cardiac function by altering SV. While a number of variables are involved, SV is ultimately dependent upon the difference between EDV and ESV. The three primary factors to consider are preload, or the stretch on the ventricles prior to contraction; the contractility, or the force or strength of the contraction itself; and afterload, the force the ventricles must generate to pump blood against the resistance in the vessels. These factors are summarized in Table 19.1 and Table 19.2.
Preload
Preload is another way of expressing EDV. Therefore, the greater the EDV is, the greater the preload is. One of the primary factors to consider is filling time, or the duration of ventricular diastole during which filling occurs. The more rapidly the heart contracts, the shorter the filling time becomes, and the lower the EDV and preload are. This effect can be partially overcome by increasing the second variable, contractility, and raising SV, but over time, the heart is unable to compensate for decreased filling time, and preload also decreases.
With increasing ventricular filling, both EDV or preload increase, and the cardiac muscle itself is stretched to a greater degree. At rest, there is little stretch of the ventricular muscle, and the sarcomeres remain short. With increased ventricular filling, the ventricular muscle is increasingly stretched and the sarcomere length increases. As the sarcomeres reach their optimal lengths, they will contract more powerfully, because more of the myosin heads can bind to the actin on the thin filaments, forming cross bridges and increasing the strength of contraction and SV. If this process were to continue and the sarcomeres stretched beyond their optimal lengths, the force of contraction would decrease. However, due to the physical constraints of the location of the heart, this excessive stretch is not a concern.
The relationship between ventricular stretch and contraction has been stated in the well-known Frank-Starling mechanism or simply Starling’s Law of the Heart. This principle states that, within physiological limits, the force of heart contraction is directly proportional to the initial length of the muscle fiber. This means that the greater the stretch of the ventricular muscle (within limits), the more powerful the contraction is, which in turn increases SV. Therefore, by increasing preload, you increase the second variable, contractility.
Otto Frank (1865–1944) was a German physiologist; among his many published works are detailed studies of this important heart relationship. Ernest Starling (1866–1927) was an important English physiologist who also studied the heart. Although they worked largely independently, their combined efforts and similar conclusions have been recognized in the name “Frank-Starling mechanism.”
Any sympathetic stimulation to the venous system will increase venous return to the heart, which contributes to ventricular filling, and EDV and preload. While much of the ventricular filling occurs while both atria and ventricles are in diastole, the contraction of the atria, the atrial kick, plays a crucial role by providing the last 20–30 percent of ventricular filling.
Contractility
It is virtually impossible to consider preload or ESV without including an early mention of the concept of contractility. Indeed, the two parameters are intimately linked. Contractility refers to the force of the contraction of the heart muscle, which controls SV, and is the primary parameter for impacting ESV. The more forceful the contraction is, the greater the SV and smaller the ESV are. Less forceful contractions result in smaller SVs and larger ESVs. Factors that increase contractility are described as positive inotropic factors, and those that decrease contractility are described as negative inotropic factors (ino- = “fiber;” -tropic = “turning toward”).
Not surprisingly, sympathetic stimulation is a positive inotrope, whereas parasympathetic stimulation is a negative inotrope. Sympathetic stimulation triggers the release of NE at the neuromuscular junction from the cardiac nerves and also stimulates the adrenal cortex to secrete epinephrine and NE. In addition to their stimulatory effects on HR, they also bind to both alpha and beta receptors on the cardiac muscle cell membrane to increase metabolic rate and the force of contraction. This combination of actions has the net effect of increasing SV and leaving a smaller residual ESV in the ventricles. In comparison, parasympathetic stimulation releases ACh at the neuromuscular junction from the vagus nerve. The membrane hyperpolarizes and inhibits contraction to decrease the strength of contraction and SV, and to raise ESV. Since parasympathetic fibers are more widespread in the atria than in the ventricles, the primary site of action is in the upper chambers. Parasympathetic stimulation in the atria decreases the atrial kick and reduces EDV, which decreases ventricular stretch and preload, thereby further limiting the force of ventricular contraction. Stronger parasympathetic stimulation also directly decreases the force of contraction of the ventricles.
Several synthetic drugs, including dopamine and isoproterenol, have been developed that mimic the effects of epinephrine and NE by stimulating the influx of calcium ions from the extracellular fluid. Higher concentrations of intracellular calcium ions increase the strength of contraction. Excess calcium (hypercalcemia) also acts as a positive inotropic agent. The drug digitalis lowers HR and increases the strength of the contraction, acting as a positive inotropic agent by blocking the sequestering of calcium ions into the sarcoplasmic reticulum. This leads to higher intracellular calcium levels and greater strength of contraction. In addition to the catecholamines from the adrenal medulla, other hormones also demonstrate positive inotropic effects. These include thyroid hormones and glucagon from the pancreas.
Negative inotropic agents include hypoxia, acidosis, hyperkalemia, and a variety of synthetic drugs. These include numerous beta blockers and calcium channel blockers. Early beta blocker drugs include propranolol and pronethalol, and are credited with revolutionizing treatment of cardiac patients experiencing angina pectoris. There is also a large class of dihydropyridine, phenylalkylamine, and benzothiazepine calcium channel blockers that may be administered decreasing the strength of contraction and SV.
Afterload
Afterload refers to the tension that the ventricles must develop to pump blood effectively against the resistance in the vascular system. Any condition that increases resistance requires a greater afterload to force open the semilunar valves and pump the blood. Damage to the valves, such as stenosis, which makes them harder to open will also increase afterload. Any decrease in resistance decreases the afterload. Figure 19.34 summarizes the major factors influencing SV, Figure 19.35 summarizes the major factors influencing CO, and Table 19.3 and Table 19.4 summarize cardiac responses to increased and decreased blood flow and pressure in order to restore homeostasis.
Figure 19.34 Major Factors Influencing Stroke Volume Multiple factors impact preload, afterload, and contractility, and are the major considerations influencing SV.
Figure 19.35 Summary of Major Factors Influencing Cardiac Output The primary factors influencing HR include autonomic innervation plus endocrine control. Not shown are environmental factors, such as electrolytes, metabolic products, and temperature. The primary factors controlling SV include preload, contractility, and afterload. Other factors such as electrolytes may be classified as either positive or negative inotropic agents.
Cardiac Response to Decreasing Blood Flow and Pressure Due to Decreasing Cardiac Output
| Baroreceptors (aorta, carotid arteries, venae cavae, and atria) | Chemoreceptors (both central nervous system and in proximity to baroreceptors) | |
|---|---|---|
| Sensitive to | Decreasing stretch | Decreasing O2 and increasing CO2, H+, and lactic acid |
| Target | Parasympathetic stimulation suppressed | Sympathetic stimulation increased |
| Response of heart | Increasing heart rate and increasing stroke volume | Increasing heart rate and increasing stroke volume |
| Overall effect | Increasing blood flow and pressure due to increasing cardiac output; homeostasis restored | Increasing blood flow and pressure due to increasing cardiac output; homeostasis restored |
Table 19.3
Cardiac Response to Increasing Blood Flow and Pressure Due to Increasing Cardiac Output
| Baroreceptors (aorta, carotid arteries, venae cavae, and atria) | Chemoreceptors (both central nervous system and in proximity to baroreceptors) | |
|---|---|---|
| Sensitive to | Increasing stretch | Increasing O2 and decreasing CO2, H+, and lactic acid |
| Target | Parasympathetic stimulation increased | Sympathetic stimulation suppressed |
| Response of heart | Decreasing heart rate and decreasing stroke volume | Decreasing heart rate and decreasing stroke volume |
| Overall effect | Decreasing blood flow and pressure due to decreasing cardiac output; homeostasis restored | Decreasing blood flow and pressure due to decreasing cardiac output; homeostasis restored |
Table 19.4
Development of the Heart
- Describe the embryological development of heart structures
- Identify five regions of the fetal heart
- Relate fetal heart structures to adult counterparts
The human heart is the first functional organ to develop. It begins beating and pumping blood around day 21 or 22, a mere three weeks after fertilization. This emphasizes the critical nature of the heart in distributing blood through the vessels and the vital exchange of nutrients, oxygen, and wastes both to and from the developing baby. The critical early development of the heart is reflected by the prominent heart bulge that appears on the anterior surface of the embryo.
The heart forms from an embryonic tissue called mesoderm around 18 to 19 days after fertilization. Mesoderm is one of the three primary germ layers that differentiates early in development that collectively gives rise to all subsequent tissues and organs. The heart begins to develop near the head of the embryo in a region known as the cardiogenic area. Following chemical signals called factors from the underlying endoderm (another of the three primary germ layers), the cardiogenic area begins to form two strands called the cardiogenic cords (Figure 19.36). As the cardiogenic cords develop, a lumen rapidly develops within them. At this point, they are referred to as endocardial tubes. The two tubes migrate together and fuse to form a single primitive heart tube. The primitive heart tube quickly forms five distinct regions. From head to tail, these include the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus. Initially, all venous blood flows into the sinus venosus, and contractions propel the blood from tail to head, or from the sinus venosus to the truncus arteriosus. This is a very different pattern from that of an adult.
Figure 19.36 Development of the Human Heart This diagram outlines the embryological development of the human heart during the first eight weeks and the subsequent formation of the four heart chambers.
The five regions of the primitive heart tube develop into recognizable structures in a fully developed heart. The truncus arteriosus will eventually divide and give rise to the ascending aorta and pulmonary trunk. The bulbus cordis develops into the right ventricle. The primitive ventricle forms the left ventricle. The primitive atrium becomes the anterior portions of both the right and left atria, and the two auricles. The sinus venosus develops into the posterior portion of the right atrium, the SA node, and the coronary sinus.
As the primitive heart tube elongates, it begins to fold within the pericardium, eventually forming an S shape, which places the chambers and major vessels into an alignment similar to the adult heart. This process occurs between days 23 and 28. The remainder of the heart development pattern includes development of septa and valves, and remodeling of the actual chambers. Partitioning of the atria and ventricles by the interatrial septum, interventricular septum, and atrioventricular septum is complete by the end of the fifth week, although the fetal blood shunts remain until birth or shortly after. The atrioventricular valves form between weeks five and eight, and the semilunar valves form between weeks five and nine.
Key Terms
- afterload
- force the ventricles must develop to effectively pump blood against the resistance in the vessels
- anastomosis
- (plural = anastomoses) area where vessels unite to allow blood to circulate even if there may be partial blockage in another branch
- anterior cardiac veins
- vessels that parallel the small cardiac arteries and drain the anterior surface of the right ventricle; bypass the coronary sinus and drain directly into the right atrium
- anterior interventricular artery
- (also, left anterior descending artery or LAD) major branch of the left coronary artery that follows the anterior interventricular sulcus
- anterior interventricular sulcus
- sulcus located between the left and right ventricles on the anterior surface of the heart
- aortic valve
- (also, aortic semilunar valve) valve located at the base of the aorta
- artificial pacemaker
- medical device that transmits electrical signals to the heart to ensure that it contracts and pumps blood to the body
- atrial reflex
- (also, called Bainbridge reflex) autonomic reflex that responds to stretch receptors in the atria that send impulses to the cardioaccelerator area to increase HR when venous flow into the atria increases
- atrioventricular (AV) node
- clump of myocardial cells located in the inferior portion of the right atrium within the atrioventricular septum; receives the impulse from the SA node, pauses, and then transmits it into specialized conducting cells within the interventricular septum
- atrioventricular bundle
- (also, bundle of His) group of specialized myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches
- atrioventricular bundle branches
- (also, left or right bundle branches) specialized myocardial conductile cells that arise from the bifurcation of the atrioventricular bundle and pass through the interventricular septum; lead to the Purkinje fibers and also to the right papillary muscle via the moderator band
- atrioventricular septum
- cardiac septum located between the atria and ventricles; atrioventricular valves are located here
- atrioventricular valves
- one-way valves located between the atria and ventricles; the valve on the right is called the tricuspid valve, and the one on the left is the mitral or bicuspid valve
- atrium
- (plural = atria) upper or receiving chamber of the heart that pumps blood into the lower chambers just prior to their contraction; the right atrium receives blood from the systemic circuit that flows into the right ventricle; the left atrium receives blood from the pulmonary circuit that flows into the left ventricle
- auricle
- extension of an atrium visible on the superior surface of the heart
- autonomic tone
- contractile state during resting cardiac activity produced by mild sympathetic and parasympathetic stimulation
- autorhythmicity
- ability of cardiac muscle to initiate its own electrical impulse that triggers the mechanical contraction that pumps blood at a fixed pace without nervous or endocrine control
- Bachmann’s bundle
- (also, interatrial band) group of specialized conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium
- Bainbridge reflex
- (also, called atrial reflex) autonomic reflex that responds to stretch receptors in the atria that send impulses to the cardioaccelerator area to increase HR when venous flow into the atria increases
- baroreceptor reflex
- autonomic reflex in which the cardiac centers monitor signals from the baroreceptor stretch receptors and regulate heart function based on blood flow
- bicuspid valve
- (also, mitral valve or left atrioventricular valve) valve located between the left atrium and ventricle; consists of two flaps of tissue
- bulbus cordis
- portion of the primitive heart tube that will eventually develop into the right ventricle
- bundle of His
- (also, atrioventricular bundle) group of specialized myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches
- cardiac cycle
- period of time between the onset of atrial contraction (atrial systole) and ventricular relaxation (ventricular diastole)
- cardiac notch
- depression in the medial surface of the inferior lobe of the left lung where the apex of the heart is located
- cardiac output (CO)
- amount of blood pumped by each ventricle during one minute; equals HR multiplied by SV
- cardiac plexus
- paired complex network of nerve fibers near the base of the heart that receive sympathetic and parasympathetic stimulations to regulate HR
- cardiac reflexes
- series of autonomic reflexes that enable the cardiovascular centers to regulate heart function based upon sensory information from a variety of visceral sensors
- cardiac reserve
- difference between maximum and resting CO
- cardiac skeleton
- (also, skeleton of the heart) reinforced connective tissue located within the atrioventricular septum; includes four rings that surround the openings between the atria and ventricles, and the openings to the pulmonary trunk and aorta; the point of attachment for the heart valves
- cardiogenic area
- area near the head of the embryo where the heart begins to develop 18–19 days after fertilization
- cardiogenic cords
- two strands of tissue that form within the cardiogenic area
- cardiomyocyte
- muscle cell of the heart
- chordae tendineae
- string-like extensions of tough connective tissue that extend from the flaps of the atrioventricular valves to the papillary muscles
- circumflex artery
- branch of the left coronary artery that follows coronary sulcus
- coronary arteries
- branches of the ascending aorta that supply blood to the heart; the left coronary artery feeds the left side of the heart, the left atrium and ventricle, and the interventricular septum; the right coronary artery feeds the right atrium, portions of both ventricles, and the heart conduction system
- coronary sinus
- large, thin-walled vein on the posterior surface of the heart that lies within the atrioventricular sulcus and drains the heart myocardium directly into the right atrium
- coronary sulcus
- sulcus that marks the boundary between the atria and ventricles
- coronary veins
- vessels that drain the heart and generally parallel the large surface arteries
- diastole
- period of time when the heart muscle is relaxed and the chambers fill with blood
- ejection fraction
- portion of the blood that is pumped or ejected from the heart with each contraction; mathematically represented by SV divided by EDV
- electrocardiogram (ECG)
- surface recording of the electrical activity of the heart that can be used for diagnosis of irregular heart function; also abbreviated as EKG
- end diastolic volume (EDV)
- (also, preload) the amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction
- end systolic volume (ESV)
- amount of blood remaining in each ventricle following systole
- endocardial tubes
- stage in which lumens form within the expanding cardiogenic cords, forming hollow structures
- endocardium
- innermost layer of the heart lining the heart chambers and heart valves; composed of endothelium reinforced with a thin layer of connective tissue that binds to the myocardium
- endothelium
- layer of smooth, simple squamous epithelium that lines the endocardium and blood vessels
- epicardial coronary arteries
- surface arteries of the heart that generally follow the sulci
- epicardium
- innermost layer of the serous pericardium and the outermost layer of the heart wall
- filling time
- duration of ventricular diastole during which filling occurs
- foramen ovale
- opening in the fetal heart that allows blood to flow directly from the right atrium to the left atrium, bypassing the fetal pulmonary circuit
- fossa ovalis
- oval-shaped depression in the interatrial septum that marks the former location of the foramen ovale
- Frank-Starling mechanism
- relationship between ventricular stretch and contraction in which the force of heart contraction is directly proportional to the initial length of the muscle fiber
- great cardiac vein
- vessel that follows the interventricular sulcus on the anterior surface of the heart and flows along the coronary sulcus into the coronary sinus on the posterior surface; parallels the anterior interventricular artery and drains the areas supplied by this vessel
- heart block
- interruption in the normal conduction pathway
- heart bulge
- prominent feature on the anterior surface of the heart, reflecting early cardiac development
- heart rate (HR)
- number of times the heart contracts (beats) per minute
- heart sounds
- sounds heard via auscultation with a stethoscope of the closing of the atrioventricular valves (“lub”) and semilunar valves (“dub”)
- hypertrophic cardiomyopathy
- pathological enlargement of the heart, generally for no known reason
- inferior vena cava
- large systemic vein that returns blood to the heart from the inferior portion of the body
- interatrial band
- (also, Bachmann’s bundle) group of specialized conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium
- interatrial septum
- cardiac septum located between the two atria; contains the fossa ovalis after birth
- intercalated disc
- physical junction between adjacent cardiac muscle cells; consisting of desmosomes, specialized linking proteoglycans, and gap junctions that allow passage of ions between the two cells
- internodal pathways
- specialized conductile cells within the atria that transmit the impulse from the SA node throughout the myocardial cells of the atrium and to the AV node
- interventricular septum
- cardiac septum located between the two ventricles
- isovolumic contraction
- (also, isovolumetric contraction) initial phase of ventricular contraction in which tension and pressure in the ventricle increase, but no blood is pumped or ejected from the heart
- isovolumic ventricular relaxation phase
- initial phase of the ventricular diastole when pressure in the ventricles drops below pressure in the two major arteries, the pulmonary trunk, and the aorta, and blood attempts to flow back into the ventricles, producing the dicrotic notch of the ECG and closing the two semilunar valves
- left atrioventricular valve
- (also, mitral valve or bicuspid valve) valve located between the left atrium and ventricle; consists of two flaps of tissue
- marginal arteries
- branches of the right coronary artery that supply blood to the superficial portions of the right ventricle
- mesoderm
- one of the three primary germ layers that differentiate early in embryonic development
- mesothelium
- simple squamous epithelial portion of serous membranes, such as the superficial portion of the epicardium (the visceral pericardium) and the deepest portion of the pericardium (the parietal pericardium)
- middle cardiac vein
- vessel that parallels and drains the areas supplied by the posterior interventricular artery; drains into the great cardiac vein
- mitral valve
- (also, left atrioventricular valve or bicuspid valve) valve located between the left atrium and ventricle; consists of two flaps of tissue
- moderator band
- band of myocardium covered by endocardium that arises from the inferior portion of the interventricular septum in the right ventricle and crosses to the anterior papillary muscle; contains conductile fibers that carry electrical signals followed by contraction of the heart
- murmur
- unusual heart sound detected by auscultation; typically related to septal or valve defects
- myocardial conducting cells
- specialized cells that transmit electrical impulses throughout the heart and trigger contraction by the myocardial contractile cells
- myocardial contractile cells
- bulk of the cardiac muscle cells in the atria and ventricles that conduct impulses and contract to propel blood
- myocardium
- thickest layer of the heart composed of cardiac muscle cells built upon a framework of primarily collagenous fibers and blood vessels that supply it and the nervous fibers that help to regulate it
- negative inotropic factors
- factors that negatively impact or lower heart contractility
- P wave
- component of the electrocardiogram that represents the depolarization of the atria
- pacemaker
- cluster of specialized myocardial cells known as the SA node that initiates the sinus rhythm
- papillary muscle
- extension of the myocardium in the ventricles to which the chordae tendineae attach
- pectinate muscles
- muscular ridges seen on the anterior surface of the right atrium
- pericardial cavity
- cavity surrounding the heart filled with a lubricating serous fluid that reduces friction as the heart contracts
- pericardial sac
- (also, pericardium) membrane that separates the heart from other mediastinal structures; consists of two distinct, fused sublayers: the fibrous pericardium and the parietal pericardium
- pericardium
- (also, pericardial sac) membrane that separates the heart from other mediastinal structures; consists of two distinct, fused sublayers: the fibrous pericardium and the parietal pericardium
- positive inotropic factors
- factors that positively impact or increase heart contractility
- posterior cardiac vein
- vessel that parallels and drains the areas supplied by the marginal artery branch of the circumflex artery; drains into the great cardiac vein
- posterior interventricular artery
- (also, posterior descending artery) branch of the right coronary artery that runs along the posterior portion of the interventricular sulcus toward the apex of the heart and gives rise to branches that supply the interventricular septum and portions of both ventricles
- posterior interventricular sulcus
- sulcus located between the left and right ventricles on the anterior surface of the heart
- preload
- (also, end diastolic volume) amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction
- prepotential depolarization
- (also, spontaneous depolarization) mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise
- primitive atrium
- portion of the primitive heart tube that eventually becomes the anterior portions of both the right and left atria, and the two auricles
- primitive heart tube
- singular tubular structure that forms from the fusion of the two endocardial tubes
- primitive ventricle
- portion of the primitive heart tube that eventually forms the left ventricle
- pulmonary arteries
- left and right branches of the pulmonary trunk that carry deoxygenated blood from the heart to each of the lungs
- pulmonary capillaries
- capillaries surrounding the alveoli of the lungs where gas exchange occurs: carbon dioxide exits the blood and oxygen enters
- pulmonary circuit
- blood flow to and from the lungs
- pulmonary trunk
- large arterial vessel that carries blood ejected from the right ventricle; divides into the left and right pulmonary arteries
- pulmonary valve
- (also, pulmonary semilunar valve, the pulmonic valve, or the right semilunar valve) valve at the base of the pulmonary trunk that prevents backflow of blood into the right ventricle; consists of three flaps
- pulmonary veins
- veins that carry highly oxygenated blood into the left atrium, which pumps the blood into the left ventricle, which in turn pumps oxygenated blood into the aorta and to the many branches of the systemic circuit
- Purkinje fibers
- specialized myocardial conduction fibers that arise from the bundle branches and spread the impulse to the myocardial contraction fibers of the ventricles
- QRS complex
- component of the electrocardiogram that represents the depolarization of the ventricles and includes, as a component, the repolarization of the atria
- right atrioventricular valve
- (also, tricuspid valve) valve located between the right atrium and ventricle; consists of three flaps of tissue
- semilunar valves
- valves located at the base of the pulmonary trunk and at the base of the aorta
- septum
- (plural = septa) walls or partitions that divide the heart into chambers
- septum primum
- flap of tissue in the fetus that covers the foramen ovale within a few seconds after birth
- sinoatrial (SA) node
- known as the pacemaker, a specialized clump of myocardial conducting cells located in the superior portion of the right atrium that has the highest inherent rate of depolarization that then spreads throughout the heart
- sinus rhythm
- normal contractile pattern of the heart
- sinus venosus
- develops into the posterior portion of the right atrium, the SA node, and the coronary sinus
- small cardiac vein
- parallels the right coronary artery and drains blood from the posterior surfaces of the right atrium and ventricle; drains into the great cardiac vein
- spontaneous depolarization
- (also, prepotential depolarization) the mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise
- stroke volume (SV)
- amount of blood pumped by each ventricle per contraction; also, the difference between EDV and ESV
- sulcus
- (plural = sulci) fat-filled groove visible on the surface of the heart; coronary vessels are also located in these areas
- superior vena cava
- large systemic vein that returns blood to the heart from the superior portion of the body
- systemic circuit
- blood flow to and from virtually all of the tissues of the body
- systole
- period of time when the heart muscle is contracting
- T wave
- component of the electrocardiogram that represents the repolarization of the ventricles
- target heart rate
- range in which both the heart and lungs receive the maximum benefit from an aerobic workout
- trabeculae carneae
- ridges of muscle covered by endocardium located in the ventricles
- tricuspid valve
- term used most often in clinical settings for the right atrioventricular valve
- truncus arteriosus
- portion of the primitive heart that will eventually divide and give rise to the ascending aorta and pulmonary trunk
- valve
- in the cardiovascular system, a specialized structure located within the heart or vessels that ensures one-way flow of blood
- ventricle
- one of the primary pumping chambers of the heart located in the lower portion of the heart; the left ventricle is the major pumping chamber on the lower left side of the heart that ejects blood into the systemic circuit via the aorta and receives blood from the left atrium; the right ventricle is the major pumping chamber on the lower right side of the heart that ejects blood into the pulmonary circuit via the pulmonary trunk and receives blood from the right atrium
- ventricular ejection phase
- second phase of ventricular systole during which blood is pumped from the ventricle
Chapter Review
19.1 Heart Anatomy
The heart resides within the pericardial sac and is located in the mediastinal space within the thoracic cavity. The pericardial sac consists of two fused layers: an outer fibrous capsule and an inner parietal pericardium lined with a serous membrane. Between the pericardial sac and the heart is the pericardial cavity, which is filled with lubricating serous fluid. The walls of the heart are composed of an outer epicardium, a thick myocardium, and an inner lining layer of endocardium. The human heart consists of a pair of atria, which receive blood and pump it into a pair of ventricles, which pump blood into the vessels. The right atrium receives systemic blood relatively low in oxygen and pumps it into the right ventricle, which pumps it into the pulmonary circuit. Exchange of oxygen and carbon dioxide occurs in the lungs, and blood high in oxygen returns to the left atrium, which pumps blood into the left ventricle, which in turn pumps blood into the aorta and the remainder of the systemic circuit. The septa are the partitions that separate the chambers of the heart. They include the interatrial septum, the interventricular septum, and the atrioventricular septum. Two of these openings are guarded by the atrioventricular valves, the right tricuspid valve and the left mitral valve, which prevent the backflow of blood. Each is attached to chordae tendineae that extend to the papillary muscles, which are extensions of the myocardium, to prevent the valves from being blown back into the atria. The pulmonary valve is located at the base of the pulmonary trunk, and the left semilunar valve is located at the base of the aorta. The right and left coronary arteries are the first to branch off the aorta and arise from two of the three sinuses located near the base of the aorta and are generally located in the sulci. Cardiac veins parallel the small cardiac arteries and generally drain into the coronary sinus.
19.2 Cardiac Muscle and Electrical Activity
The heart is regulated by both neural and endocrine control, yet it is capable of initiating its own action potential followed by muscular contraction. The conductive cells within the heart establish the heart rate and transmit it through the myocardium. The contractile cells contract and propel the blood. The normal path of transmission for the conductive cells is the sinoatrial (SA) node, internodal pathways, atrioventricular (AV) node, atrioventricular (AV) bundle of His, bundle branches, and Purkinje fibers. The action potential for the conductive cells consists of a prepotential phase with a slow influx of Na+ followed by a rapid influx of Ca2+ and outflux of K+. Contractile cells have an action potential with an extended plateau phase that results in an extended refractory period to allow complete contraction for the heart to pump blood effectively. Recognizable points on the ECG include the P wave that corresponds to atrial depolarization, the QRS complex that corresponds to ventricular depolarization, and the T wave that corresponds to ventricular repolarization.
19.3 Cardiac Cycle
The cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0.8 seconds. Beginning with all chambers in diastole, blood flows passively from the veins into the atria and past the atrioventricular valves into the ventricles. The atria begin to contract (atrial systole), following depolarization of the atria, and pump blood into the ventricles. The ventricles begin to contract (ventricular systole), raising pressure within the ventricles. When ventricular pressure rises above the pressure in the atria, blood flows toward the atria, producing the first heart sound, S1 or lub. As pressure in the ventricles rises above two major arteries, blood pushes open the two semilunar valves and moves into the pulmonary trunk and aorta in the ventricular ejection phase. Following ventricular repolarization, the ventricles begin to relax (ventricular diastole), and pressure within the ventricles drops. As ventricular pressure drops, there is a tendency for blood to flow back into the atria from the major arteries, producing the dicrotic notch in the ECG and closing the two semilunar valves. The second heart sound, S2 or dub, occurs when the semilunar valves close. When the pressure falls below that of the atria, blood moves from the atria into the ventricles, opening the atrioventricular valves and marking one complete heart cycle. The valves prevent backflow of blood. Failure of the valves to operate properly produces turbulent blood flow within the heart; the resulting heart murmur can often be heard with a stethoscope.
19.4 Cardiac Physiology
Many factors affect HR and SV, and together, they contribute to cardiac function. HR is largely determined and regulated by autonomic stimulation and hormones. There are several feedback loops that contribute to maintaining homeostasis dependent upon activity levels, such as the atrial reflex, which is determined by venous return.
SV is regulated by autonomic innervation and hormones, but also by filling time and venous return. Venous return is determined by activity of the skeletal muscles, blood volume, and changes in peripheral circulation. Venous return determines preload and the atrial reflex. Filling time directly related to HR also determines preload. Preload then impacts both EDV and ESV. Autonomic innervation and hormones largely regulate contractility. Contractility impacts EDV as does afterload. CO is the product of HR multiplied by SV. SV is the difference between EDV and ESV.
19.5 Development of the Heart
The heart is the first organ to form and become functional, emphasizing the importance of transport of material to and from the developing infant. It originates about day 18 or 19 from the mesoderm and begins beating and pumping blood about day 21 or 22. It forms from the cardiogenic region near the head and is visible as a prominent heart bulge on the surface of the embryo. Originally, it consists of a pair of strands called cardiogenic cords that quickly form a hollow lumen and are referred to as endocardial tubes. These then fuse into a single heart tube and differentiate into the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus, starting about day 22. The primitive heart begins to form an S shape within the pericardium between days 23 and 28. The internal septa begin to form about day 28, separating the heart into the atria and ventricles, although the foramen ovale persists until shortly after birth. Between weeks five and eight, the atrioventricular valves form. The semilunar valves form between weeks five and nine.
Interactive Link Questions
1.
Visit this site to observe an echocardiogram of actual heart valves opening and closing. Although much of the heart has been “removed” from this gif loop so the chordae tendineae are not visible, why is their presence more critical for the atrioventricular valves (tricuspid and mitral) than the semilunar (aortic and pulmonary) valves?
Review Questions
Which of the following is not important in preventing backflow of blood?
- chordae tendineae
- papillary muscles
- AV valves
- endocardium
Which valve separates the left atrium from the left ventricle?
- mitral
- tricuspid
- pulmonary
- aortic
Which of the following lists the valves in the order through which the blood flows from the vena cava through the heart?
- tricuspid, pulmonary semilunar, bicuspid, aortic semilunar
- mitral, pulmonary semilunar, bicuspid, aortic semilunar
- aortic semilunar, pulmonary semilunar, tricuspid, bicuspid
- bicuspid, aortic semilunar, tricuspid, pulmonary semilunar
Which chamber initially receives blood from the systemic circuit?
- left atrium
- left ventricle
- right atrium
- right ventricle
The ________ layer secretes chemicals that help to regulate ionic environments and strength of contraction and serve as powerful vasoconstrictors.
- pericardial sac
- endocardium
- myocardium
- epicardium
The myocardium would be the thickest in the ________.
- left atrium
- left ventricle
- right atrium
- right ventricle
In which septum is it normal to find openings in the adult?
- interatrial septum
- interventricular septum
- atrioventricular septum
- all of the above
Which of the following is unique to cardiac muscle cells?
- Only cardiac muscle contains a sarcoplasmic reticulum.
- Only cardiac muscle has gap junctions.
- Only cardiac muscle is capable of autorhythmicity
- Only cardiac muscle has a high concentration of mitochondria.
The influx of which ion accounts for the plateau phase?
- sodium
- potassium
- chloride
- calcium
Which portion of the ECG corresponds to repolarization of the atria?
- P wave
- QRS complex
- T wave
- none of the above: atrial repolarization is masked by ventricular depolarization
Which component of the heart conduction system would have the slowest rate of firing?
- atrioventricular node
- atrioventricular bundle
- bundle branches
- Purkinje fibers
The cardiac cycle consists of a distinct relaxation and contraction phase. Which term is typically used to refer ventricular contraction while no blood is being ejected?
- systole
- diastole
- quiescent
- isovolumic contraction
Most blood enters the ventricle during ________.
- atrial systole
- atrial diastole
- ventricular systole
- isovolumic contraction
The first heart sound represents which portion of the cardiac cycle?
- atrial systole
- ventricular systole
- closing of the atrioventricular valves
- closing of the semilunar valves
Ventricular relaxation immediately follows ________.
- atrial depolarization
- ventricular repolarization
- ventricular depolarization
- atrial repolarization
The force the heart must overcome to pump blood is known as ________.
- preload
- afterload
- cardiac output
- stroke volume
The cardiovascular centers are located in which area of the brain?
- medulla oblongata
- pons
- mesencephalon (midbrain)
- cerebrum
In a healthy young adult, what happens to cardiac output when heart rate increases above 160 bpm?
- It increases.
- It decreases.
- It remains constant.
- There is no way to predict.
What happens to preload when there is venous constriction in the veins?
- It increases.
- It decreases.
- It remains constant.
- There is no way to predict.
Which of the following is a positive inotrope?
- Na+
- K+
- Ca2+
- both Na+ and K+
The earliest organ to form and begin function within the developing human is the ________.
- brain
- stomach
- lungs
- heart
Of the three germ layers that give rise to all adult tissues and organs, which gives rise to the heart?
- ectoderm
- endoderm
- mesoderm
- placenta
The two tubes that eventually fuse to form the heart are referred to as the ________.
- primitive heart tubes
- endocardial tubes
- cardiogenic region
- cardiogenic tubes
Which primitive area of the heart will give rise to the right ventricle?
- bulbus cordis
- primitive ventricle
- sinus venosus
- truncus arteriosus
The pulmonary trunk and aorta are derived from which primitive heart structure?
- bulbus cordis
- primitive ventricle
- sinus venosus
- truncus arteriosus
Critical Thinking Questions
Describe how the valves keep the blood moving in one direction.
28.Why is the pressure in the pulmonary circulation lower than in the systemic circulation?
29.Why is the plateau phase so critical to cardiac muscle function?
30.How does the delay of the impulse at the atrioventricular node contribute to cardiac function?
31.How do gap junctions and intercalated disks aid contraction of the heart?
32.Why do the cardiac muscles cells demonstrate autorhythmicity?
33.Describe one cardiac cycle, beginning with both atria and ventricles relaxed.
34.Why does increasing EDV increase contractility?
35.Why is afterload important to cardiac function?
36.Why is it so important for the human heart to develop early and begin functioning within the developing embryo?
37.Describe how the major pumping chambers, the ventricles, form within the developing heart.
|
oercommons
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2025-03-18T00:38:18.493779
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10/14/2019
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/58765/overview",
"title": "Anatomy and Physiology, Fluids and Transport, The Cardiovascular System: The Heart",
"author": null
}
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https://oercommons.org/courseware/lesson/56364/overview
|
The Integumentary System
Introduction
Figure 5.1 Your skin is a vital part of your life and appearance (a–d). Some people choose to embellish it with tattoos (a), makeup (b), and even piercings (c). (credit a: Steve Teo; credit b: “spaceodissey”/flickr; credit c: Mark/flickr; credit d: Lisa Schaffer)
CHAPTER OBJECTIVES
After studying the chapter, you will be able to:
- Describe the integumentary system and the role it plays in homeostasis
- Describe the layers of the skin and the functions of each layer
- Describe the accessory structures of the skin and the functions of each
- Describe the changes that occur in the integumentary system during the aging process
- Discuss several common diseases, disorders, and injuries that affect the integumentary system
- Explain treatments for some common diseases, disorders, and injuries of the integumentary system
What do you think when you look at your skin in the mirror? Do you think about covering it with makeup, adding a tattoo, or maybe a body piercing? Or do you think about the fact that the skin belongs to one of the body’s most essential and dynamic systems: the integumentary system? The integumentary system refers to the skin and its accessory structures, and it is responsible for much more than simply lending to your outward appearance. In the adult human body, the skin makes up about 16 percent of body weight and covers an area of 1.5 to 2 m2. In fact, the skin and accessory structures are the largest organ system in the human body. As such, the skin protects your inner organs and it is in need of daily care and protection to maintain its health. This chapter will introduce the structure and functions of the integumentary system, as well as some of the diseases, disorders, and injuries that can affect this system.
Layers of the Skin
- Identify the components of the integumentary system
- Describe the layers of the skin and the functions of each layer
- Identify and describe the hypodermis and deep fascia
- Describe the role of keratinocytes and their life cycle
- Describe the role of melanocytes in skin pigmentation
Although you may not typically think of the skin as an organ, it is in fact made of tissues that work together as a single structure to perform unique and critical functions. The skin and its accessory structures make up the integumentary system, which provides the body with overall protection. The skin is made of multiple layers of cells and tissues, which are held to underlying structures by connective tissue (Figure 5.2). The deeper layer of skin is well vascularized (has numerous blood vessels). It also has numerous sensory, and autonomic and sympathetic nerve fibers ensuring communication to and from the brain.
Figure 5.2 Layers of Skin The skin is composed of two main layers: the epidermis, made of closely packed epithelial cells, and the dermis, made of dense, irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures. Beneath the dermis lies the hypodermis, which is composed mainly of loose connective and fatty tissues.
INTERACTIVE LINK
The skin consists of two main layers and a closely associated layer. View this animation to learn more about layers of the skin. What are the basic functions of each of these layers?
The Epidermis
The epidermis is composed of keratinized, stratified squamous epithelium. It is made of four or five layers of epithelial cells, depending on its location in the body. It does not have any blood vessels within it (i.e., it is avascular). Skin that has four layers of cells is referred to as “thin skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Most of the skin can be classified as thin skin. “Thick skin” is found only on the palms of the hands and the soles of the feet. It has a fifth layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum (Figure 5.3).
Figure 5.3 Thin Skin versus Thick Skin These slides show cross-sections of the epidermis and dermis of (a) thin and (b) thick skin. Note the significant difference in the thickness of the epithelial layer of the thick skin. From top, LM × 40, LM × 40. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)
The cells in all of the layers except the stratum basale are called keratinocytes. A keratinocyte is a cell that manufactures and stores the protein keratin. Keratin is an intracellular fibrous protein that gives hair, nails, and skin their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced by cells from the deeper layers (Figure 5.4).
Figure 5.4 Epidermis The epidermis is epithelium composed of multiple layers of cells. The basal layer consists of cuboidal cells, whereas the outer layers are squamous, keratinized cells, so the whole epithelium is often described as being keratinized stratified squamous epithelium. LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
INTERACTIVE LINK
View the University of Michigan WebScope to explore the tissue sample in greater detail. If you zoom on the cells at the outermost layer of this section of skin, what do you notice about the cells?
Stratum Basale
The stratum basale (also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis. The cells in the stratum basale bond to the dermis via intertwining collagen fibers, referred to as the basement membrane. A finger-like projection, or fold, known as the dermal papilla (plural = dermal papillae) is found in the superficial portion of the dermis. Dermal papillae increase the strength of the connection between the epidermis and dermis; the greater the folding, the stronger the connections made (Figure 5.5).
Figure 5.5 Layers of the Epidermis The epidermis of thick skin has five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
The stratum basale is a single layer of cells primarily made of basal cells. A basal cell is a cuboidal-shaped stem cell that is a precursor of the keratinocytes of the epidermis. All of the keratinocytes are produced from this single layer of cells, which are constantly going through mitosis to produce new cells. As new cells are formed, the existing cells are pushed superficially away from the stratum basale. Two other cell types are found dispersed among the basal cells in the stratum basale. The first is a Merkel cell, which functions as a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. These cells are especially abundant on the surfaces of the hands and feet. The second is a melanocyte, a cell that produces the pigment melanin. Melanin gives hair and skin its color, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiation damage.
In a growing fetus, fingerprints form where the cells of the stratum basale meet the papillae of the underlying dermal layer (papillary layer), resulting in the formation of the ridges on your fingers that you recognize as fingerprints. Fingerprints are unique to each individual and are used for forensic analyses because the patterns do not change with the growth and aging processes.
Stratum Spinosum
As the name suggests, the stratum spinosum is spiny in appearance due to the protruding cell processes that join the cells via a structure called a desmosome. The desmosomes interlock with each other and strengthen the bond between the cells. It is interesting to note that the “spiny” nature of this layer is an artifact of the staining process. Unstained epidermis samples do not exhibit this characteristic appearance. The stratum spinosum is composed of eight to 10 layers of keratinocytes, formed as a result of cell division in the stratum basale (Figure 5.6). Interspersed among the keratinocytes of this layer is a type of dendritic cell called the Langerhans cell, which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer.
Figure 5.6 Cells of the Epidermis The cells in the different layers of the epidermis originate from basal cells located in the stratum basale, yet the cells of each layer are distinctively different. EM × 2700. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
INTERACTIVE LINK
View the University of Michigan WebScope to explore the tissue sample in greater detail. If you zoom on the cells at the outermost layer of this section of skin, what do you notice about the cells?
The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid that helps prevent water loss from the body, making the skin relatively waterproof. As new keratinocytes are produced atop the stratum basale, the keratinocytes of the stratum spinosum are pushed into the stratum granulosum.
Stratum Granulosum
The stratum granulosum has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum. The cells (three to five layers deep) become flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is fibrous, and keratohyalin, which accumulates as lamellar granules within the cells (see Figure 5.5). These two proteins make up the bulk of the keratinocyte mass in the stratum granulosum and give the layer its grainy appearance. The nuclei and other cell organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin, and cell membranes that will form the stratum lucidum, the stratum corneum, and the accessory structures of hair and nails.
Stratum Lucidum
The stratum lucidum is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer of cells is found only in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened (see Figure 5.5). These cells are densely packed with eleiden, a clear protein rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.e., lucid) appearance and provides a barrier to water.
Stratum Corneum
The stratum corneum is the most superficial layer of the epidermis and is the layer exposed to the outside environment (see Figure 5.5). The increased keratinization (also called cornification) of the cells in this layer gives it its name. There are usually 15 to 30 layers of cells in the stratum corneum. This dry, dead layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion for the more delicate, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed up from the stratum granulosum (or stratum lucidum in the case of the palms and soles of feet). The entire layer is replaced during a period of about 4 weeks. Cosmetic procedures, such as microdermabrasion, help remove some of the dry, upper layer and aim to keep the skin looking “fresh” and healthy.
Dermis
The dermis might be considered the “core” of the integumentary system (derma- = “skin”), as distinct from the epidermis (epi- = “upon” or “over”) and hypodermis (hypo- = “below”). It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands. The dermis is made of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts (Figure 5.7).
Figure 5.7 Layers of the Dermis This stained slide shows the two components of the dermis—the papillary layer and the reticular layer. Both are made of connective tissue with fibers of collagen extending from one to the other, making the border between the two somewhat indistinct. The dermal papillae extending into the epidermis belong to the papillary layer, whereas the dense collagen fiber bundles below belong to the reticular layer. LM × 10. (credit: modification of work by “kilbad”/Wikimedia Commons)
Papillary Layer
The papillary layer is made of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer form a loose mesh. This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae (see Figure 5.7). Within the papillary layer are fibroblasts, a small number of fat cells (adipocytes), and an abundance of small blood vessels. In addition, the papillary layer contains phagocytes, defensive cells that help fight bacteria or other infections that have breached the skin. This layer also contains lymphatic capillaries, nerve fibers, and touch receptors called the Meissner corpuscles.
Reticular Layer
Underlying the papillary layer is the much thicker reticular layer, composed of dense, irregular connective tissue. This layer is well vascularized and has a rich sensory and sympathetic nerve supply. The reticular layer appears reticulated (net-like) due to a tight meshwork of fibers. Elastin fibers provide some elasticity to the skin, enabling movement. Collagen fibers provide structure and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis. In addition, collagen binds water to keep the skin hydrated. Collagen injections and Retin-A creams help restore skin turgor by either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively.
Hypodermis
The hypodermis (also called the subcutaneous layer or superficial fascia) is a layer directly below the dermis and serves to connect the skin to the underlying fascia (fibrous tissue) of the bones and muscles. It is not strictly a part of the skin, although the border between the hypodermis and dermis can be difficult to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for the integument.
EVERYDAY CONNECTION
Lipid Storage
The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight under control. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes. This stored fat can serve as an energy reserve, insulate the body to prevent heat loss, and act as a cushion to protect underlying structures from trauma.
Where the fat is deposited and accumulates within the hypodermis depends on hormones (testosterone, estrogen, insulin, glucagon, leptin, and others), as well as genetic factors. Fat distribution changes as our bodies mature and age. Men tend to accumulate fat in different areas (neck, arms, lower back, and abdomen) than do women (breasts, hips, thighs, and buttocks). The body mass index (BMI) is often used as a measure of fat, although this measure is, in fact, derived from a mathematical formula that compares body weight (mass) to height. Therefore, its accuracy as a health indicator can be called into question in individuals who are extremely physically fit.
In many animals, there is a pattern of storing excess calories as fat to be used in times when food is not readily available. In much of the developed world, insufficient exercise coupled with the ready availability and consumption of high-calorie foods have resulted in unwanted accumulations of adipose tissue in many people. Although periodic accumulation of excess fat may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, it is now becoming chronic and considered a major health threat. Recent studies indicate that a distressing percentage of our population is overweight and/or clinically obese. Not only is this a problem for the individuals affected, but it also has a severe impact on our healthcare system. Changes in lifestyle, specifically in diet and exercise, are the best ways to control body fat accumulation, especially when it reaches levels that increase the risk of heart disease and diabetes.
Pigmentation
The color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred into the keratinocytes via a cellular vesicle called a melanosome (Figure 5.8).
Figure 5.8 Skin Pigmentation The relative coloration of the skin depends of the amount of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes.
Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red color. Dark-skinned individuals produce more melanin than those with pale skin. Exposure to the UV rays of the sun or a tanning salon causes melanin to be manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the DNA of epidermal cells from UV ray damage and the breakdown of folic acid, a nutrient necessary for our health and well-being. In contrast, too much melanin can interfere with the production of vitamin D, an important nutrient involved in calcium absorption. Thus, the amount of melanin present in our skin is dependent on a balance between available sunlight and folic acid destruction, and protection from UV radiation and vitamin D production.
It requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially. Dark-skinned individuals can also get sunburns, but are more protected than are pale-skinned individuals. Melanosomes are temporary structures that are eventually destroyed by fusion with lysosomes; this fact, along with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.
Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular structure of the skin, and in severe cases, can cause sufficient DNA damage to result in skin cancer. When there is an irregular accumulation of melanocytes in the skin, freckles appear. Moles are larger masses of melanocytes, and although most are benign, they should be monitored for changes that might indicate the presence of cancer (Figure 5.9).
Figure 5.9 Moles Moles range from benign accumulations of melanocytes to melanomas. These structures populate the landscape of our skin. (credit: the National Cancer Institute)
DISORDERS OF THE...
Integumentary System
The first thing a clinician sees is the skin, and so the examination of the skin should be part of any thorough physical examination. Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the skin and its accessory organs. Although neither is fatal, it would be hard to claim that they are benign, at least to the individuals so afflicted.
Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, hair, and eyes. The defect is primarily due to the inability of melanocytes to produce melanin. Individuals with albinism tend to appear white or very pale due to the lack of melanin in their skin and hair. Recall that melanin helps protect the skin from the harmful effects of UV radiation. Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and skin cancer. They also tend to be more sensitive to light and have vision problems due to the lack of pigmentation on the retinal wall. Treatment of this disorder usually involves addressing the symptoms, such as limiting UV light exposure to the skin and eyes. In vitiligo, the melanocytes in certain areas lose their ability to produce melanin, possibly due to an autoimmune reaction. This leads to a loss of color in patches (Figure 5.10). Neither albinism nor vitiligo directly affects the lifespan of an individual.
Figure 5.10 Vitiligo Individuals with vitiligo experience depigmentation that results in lighter colored patches of skin. The condition is especially noticeable on darker skin. (credit: Klaus D. Peter)
Other changes in the appearance of skin coloration can be indicative of diseases associated with other body systems. Liver disease or liver cancer can cause the accumulation of bile and the yellow pigment bilirubin, leading to the skin appearing yellow or jaundiced (jaune is the French word for “yellow”). Tumors of the pituitary gland can result in the secretion of large amounts of melanocyte-stimulating hormone (MSH), which results in a darkening of the skin. Similarly, Addison’s disease can stimulate the release of excess amounts of adrenocorticotropic hormone (ACTH), which can give the skin a deep bronze color. A sudden drop in oxygenation can affect skin color, causing the skin to initially turn ashen (white). With a prolonged reduction in oxygen levels, dark red deoxyhemoglobin becomes dominant in the blood, making the skin appear blue, a condition referred to as cyanosis (kyanos is the Greek word for “blue”). This happens when the oxygen supply is restricted, as when someone is experiencing difficulty in breathing because of asthma or a heart attack. However, in these cases the effect on skin color has nothing do with the skin’s pigmentation.
INTERACTIVE LINK
This ABC video follows the story of a pair of fraternal African-American twins, one of whom is albino. Watch this videoto learn about the challenges these children and their family face. Which ethnicities do you think are exempt from the possibility of albinism?
Accessory Structures of the Skin
- Identify the accessory structures of the skin
- Describe the structure and function of hair and nails
- Describe the structure and function of sweat glands and sebaceous glands
Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. These structures embryologically originate from the epidermis and can extend down through the dermis into the hypodermis.
Hair
Hair is a keratinous filament growing out of the epidermis. It is primarily made of dead, keratinized cells. Strands of hair originate in an epidermal penetration of the dermis called the hair follicle. The hair shaft is the part of the hair not anchored to the follicle, and much of this is exposed at the skin’s surface. The rest of the hair, which is anchored in the follicle, lies below the surface of the skin and is referred to as the hair root. The hair root ends deep in the dermis at the hair bulb, and includes a layer of mitotically active basal cells called the hair matrix. The hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis (Figure 5.11).
Figure 5.11 Hair Hair follicles originate in the epidermis and have many different parts.
Just as the basal layer of the epidermis forms the layers of epidermis that get pushed to the surface as the dead skin on the surface sheds, the basal cells of the hair bulb divide and push cells outward in the hair root and shaft as the hair grows. The medulla forms the central core of the hair, which is surrounded by the cortex, a layer of compressed, keratinized cells that is covered by an outer layer of very hard, keratinized cells known as the cuticle. These layers are depicted in a longitudinal cross-section of the hair follicle (Figure 5.12), although not all hair has a medullary layer. Hair texture (straight, curly) is determined by the shape and structure of the cortex, and to the extent that it is present, the medulla. The shape and structure of these layers are, in turn, determined by the shape of the hair follicle. Hair growth begins with the production of keratinocytes by the basal cells of the hair bulb. As new cells are deposited at the hair bulb, the hair shaft is pushed through the follicle toward the surface. Keratinization is completed as the cells are pushed to the skin surface to form the shaft of hair that is externally visible. The external hair is completely dead and composed entirely of keratin. For this reason, our hair does not have sensation. Furthermore, you can cut your hair or shave without damaging the hair structure because the cut is superficial. Most chemical hair removers also act superficially; however, electrolysis and yanking both attempt to destroy the hair bulb so hair cannot grow.
Figure 5.12 Hair Follicle The slide shows a cross-section of a hair follicle. Basal cells of the hair matrix in the center differentiate into cells of the inner root sheath. Basal cells at the base of the hair root form the outer root sheath. LM × 4. (credit: modification of work by “kilbad”/Wikimedia Commons)
The wall of the hair follicle is made of three concentric layers of cells. The cells of the internal root sheath surround the root of the growing hair and extend just up to the hair shaft. They are derived from the basal cells of the hair matrix. The external root sheath, which is an extension of the epidermis, encloses the hair root. It is made of basal cells at the base of the hair root and tends to be more keratinous in the upper regions. The glassy membrane is a thick, clear connective tissue sheath covering the hair root, connecting it to the tissue of the dermis.
INTERACTIVE LINK
The hair follicle is made of multiple layers of cells that form from basal cells in the hair matrix and the hair root. Cells of the hair matrix divide and differentiate to form the layers of the hair. Watch this video to learn more about hair follicles.
Hair serves a variety of functions, including protection, sensory input, thermoregulation, and communication. For example, hair on the head protects the skull from the sun. The hair in the nose and ears, and around the eyes (eyelashes) defends the body by trapping and excluding dust particles that may contain allergens and microbes. Hair of the eyebrows prevents sweat and other particles from dripping into and bothering the eyes. Hair also has a sensory function due to sensory innervation by a hair root plexus surrounding the base of each hair follicle. Hair is extremely sensitive to air movement or other disturbances in the environment, much more so than the skin surface. This feature is also useful for the detection of the presence of insects or other potentially damaging substances on the skin surface. Each hair root is connected to a smooth muscle called the arrector pilithat contracts in response to nerve signals from the sympathetic nervous system, making the external hair shaft “stand up.” The primary purpose for this is to trap a layer of air to add insulation. This is visible in humans as goose bumps and even more obvious in animals, such as when a frightened cat raises its fur. Of course, this is much more obvious in organisms with a heavier coat than most humans, such as dogs and cats.
Hair Growth
Hair grows and is eventually shed and replaced by new hair. This occurs in three phases. The first is the anagen phase, during which cells divide rapidly at the root of the hair, pushing the hair shaft up and out. The length of this phase is measured in years, typically from 2 to 7 years. The catagen phase lasts only 2 to 3 weeks, and marks a transition from the hair follicle’s active growth. Finally, during the telogen phase, the hair follicle is at rest and no new growth occurs. At the end of this phase, which lasts about 2 to 4 months, another anagen phase begins. The basal cells in the hair matrix then produce a new hair follicle, which pushes the old hair out as the growth cycle repeats itself. Hair typically grows at the rate of 0.3 mm per day during the anagen phase. On average, 50 hairs are lost and replaced per day. Hair loss occurs if there is more hair shed than what is replaced and can happen due to hormonal or dietary changes. Hair loss can also result from the aging process, or the influence of hormones.
Hair Color
Similar to the skin, hair gets its color from the pigment melanin, produced by melanocytes in the hair papilla. Different hair color results from differences in the type of melanin, which is genetically determined. As a person ages, the melanin production decreases, and hair tends to lose its color and becomes gray and/or white.
Nails
The nail bed is a specialized structure of the epidermis that is found at the tips of our fingers and toes. The nail body is formed on the nail bed, and protects the tips of our fingers and toes as they are the farthest extremities and the parts of the body that experience the maximum mechanical stress (Figure 5.13). In addition, the nail body forms a back-support for picking up small objects with the fingers. The nail body is composed of densely packed dead keratinocytes. The epidermis in this part of the body has evolved a specialized structure upon which nails can form. The nail body forms at the nail root, which has a matrix of proliferating cells from the stratum basale that enables the nail to grow continuously. The lateral nail fold overlaps the nail on the sides, helping to anchor the nail body. The nail fold that meets the proximal end of the nail body forms the nail cuticle, also called the eponychium. The nail bed is rich in blood vessels, making it appear pink, except at the base, where a thick layer of epithelium over the nail matrix forms a crescent-shaped region called the lunula (the “little moon”). The area beneath the free edge of the nail, furthest from the cuticle, is called the hyponychium. It consists of a thickened layer of stratum corneum.
Figure 5.13 Nails The nail is an accessory structure of the integumentary system.
INTERACTIVE LINK
Nails are accessory structures of the integumentary system. Visit this link to learn more about the origin and growth of fingernails.
Sweat Glands
When the body becomes warm, sudoriferous glands produce sweat to cool the body. Sweat glands develop from epidermal projections into the dermis and are classified as merocrine glands; that is, the secretions are excreted by exocytosis through a duct without affecting the cells of the gland. There are two types of sweat glands, each secreting slightly different products.
An eccrine sweat gland is type of gland that produces a hypotonic sweat for thermoregulation. These glands are found all over the skin’s surface, but are especially abundant on the palms of the hand, the soles of the feet, and the forehead (Figure 5.14). They are coiled glands lying deep in the dermis, with the duct rising up to a pore on the skin surface, where the sweat is released. This type of sweat, released by exocytosis, is hypotonic and composed mostly of water, with some salt, antibodies, traces of metabolic waste, and dermicidin, an antimicrobial peptide. Eccrine glands are a primary component of thermoregulation in humans and thus help to maintain homeostasis.
Figure 5.14 Eccrine Gland Eccrine glands are coiled glands in the dermis that release sweat that is mostly water.
An apocrine sweat gland is usually associated with hair follicles in densely hairy areas, such as armpits and genital regions. Apocrine sweat glands are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even reaching the hypodermis, with the duct normally emptying into the hair follicle. In addition to water and salts, apocrine sweat includes organic compounds that make the sweat thicker and subject to bacterial decomposition and subsequent smell. The release of this sweat is under both nervous and hormonal control, and plays a role in the poorly understood human pheromone response. Most commercial antiperspirants use an aluminum-based compound as their primary active ingredient to stop sweat. When the antiperspirant enters the sweat gland duct, the aluminum-based compounds precipitate due to a change in pH and form a physical block in the duct, which prevents sweat from coming out of the pore.
INTERACTIVE LINK
Sweating regulates body temperature. The composition of the sweat determines whether body odor is a byproduct of sweating. Visit this link to learn more about sweating and body odor.
Sebaceous Glands
A sebaceous gland is a type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair. Most sebaceous glands are associated with hair follicles. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the dry and dead layer of keratinized cells of the stratum corneum, keeping it pliable. The fatty acids of sebum also have antibacterial properties, and prevent water loss from the skin in low-humidity environments. The secretion of sebum is stimulated by hormones, many of which do not become active until puberty. Thus, sebaceous glands are relatively inactive during childhood.
Functions of the Integumentary System
- Describe the different functions of the skin and the structures that enable them
- Explain how the skin helps maintain body temperature
The skin and accessory structures perform a variety of essential functions, such as protecting the body from invasion by microorganisms, chemicals, and other environmental factors; preventing dehydration; acting as a sensory organ; modulating body temperature and electrolyte balance; and synthesizing vitamin D. The underlying hypodermis has important roles in storing fats, forming a “cushion” over underlying structures, and providing insulation from cold temperatures.
Protection
The skin protects the rest of the body from the basic elements of nature such as wind, water, and UV sunlight. It acts as a protective barrier against water loss, due to the presence of layers of keratin and glycolipids in the stratum corneum. It also is the first line of defense against abrasive activity due to contact with grit, microbes, or harmful chemicals. Sweat excreted from sweat glands deters microbes from over-colonizing the skin surface by generating dermicidin, which has antibiotic properties.
EVERYDAY CONNECTION
Tattoos and Piercings
The word “armor” evokes several images. You might think of a Roman centurion or a medieval knight in a suit of armor. The skin, in its own way, functions as a form of armor—body armor. It provides a barrier between your vital, life-sustaining organs and the influence of outside elements that could potentially damage them.
For any form of armor, a breach in the protective barrier poses a danger. The skin can be breached when a child skins a knee or an adult has blood drawn—one is accidental and the other medically necessary. However, you also breach this barrier when you choose to “accessorize” your skin with a tattoo or body piercing. Because the needles involved in producing body art and piercings must penetrate the skin, there are dangers associated with the practice. These include allergic reactions; skin infections; blood-borne diseases, such as tetanus, hepatitis C, and hepatitis D; and the growth of scar tissue. Despite the risk, the practice of piercing the skin for decorative purposes has become increasingly popular. According to the American Academy of Dermatology, 24 percent of people from ages 18 to 50 have a tattoo.
INTERACTIVE LINK
Tattooing has a long history, dating back thousands of years ago. The dyes used in tattooing typically derive from metals. A person with tattoos should be cautious when having a magnetic resonance imaging (MRI) scan because an MRI machine uses powerful magnets to create images of the soft tissues of the body, which could react with the metals contained in the tattoo dyes. Watch this video to learn more about tattooing.
Sensory Function
The fact that you can feel an ant crawling on your skin, allowing you to flick it off before it bites, is because the skin, and especially the hairs projecting from hair follicles in the skin, can sense changes in the environment. The hair root plexus surrounding the base of the hair follicle senses a disturbance, and then transmits the information to the central nervous system (brain and spinal cord), which can then respond by activating the skeletal muscles of your eyes to see the ant and the skeletal muscles of the body to act against the ant.
The skin acts as a sense organ because the epidermis, dermis, and the hypodermis contain specialized sensory nerve structures that detect touch, surface temperature, and pain. These receptors are more concentrated on the tips of the fingers, which are most sensitive to touch, especially the Meissner corpuscle (tactile corpuscle) (Figure 5.15), which responds to light touch, and the Pacinian corpuscle (lamellated corpuscle), which responds to vibration. Merkel cells, seen scattered in the stratum basale, are also touch receptors. In addition to these specialized receptors, there are sensory nerves connected to each hair follicle, pain and temperature receptors scattered throughout the skin, and motor nerves innervate the arrector pili muscles and glands. This rich innervation helps us sense our environment and react accordingly.
Figure 5.15 Light Micrograph of a Meissner Corpuscle In this micrograph of a skin cross-section, you can see a Meissner corpuscle (arrow), a type of touch receptor located in a dermal papilla adjacent to the basement membrane and stratum basale of the overlying epidermis. LM × 100. (credit: “Wbensmith”/Wikimedia Commons)
Thermoregulation
The integumentary system helps regulate body temperature through its tight association with the sympathetic nervous system, the division of the nervous system involved in our fight-or-flight responses. The sympathetic nervous system is continuously monitoring body temperature and initiating appropriate motor responses. Recall that sweat glands, accessory structures to the skin, secrete water, salt, and other substances to cool the body when it becomes warm. Even when the body does not appear to be noticeably sweating, approximately 500 mL of sweat (insensible perspiration) are secreted a day. If the body becomes excessively warm due to high temperatures, vigorous activity (Figure 5.16ac), or a combination of the two, sweat glands will be stimulated by the sympathetic nervous system to produce large amounts of sweat, as much as 0.7 to 1.5 L per hour for an active person. When the sweat evaporates from the skin surface, the body is cooled as body heat is dissipated.
In addition to sweating, arterioles in the dermis dilate so that excess heat carried by the blood can dissipate through the skin and into the surrounding environment (Figure 5.16b). This accounts for the skin redness that many people experience when exercising.
Figure 5.16 Thermoregulation During strenuous physical activities, such as skiing (a) or running (c), the dermal blood vessels dilate and sweat secretion increases (b). These mechanisms prevent the body from overheating. In contrast, the dermal blood vessels constrict to minimize heat loss in response to low temperatures (b). (credit a: “Trysil”/flickr; credit c: Ralph Daily)
When body temperatures drop, the arterioles constrict to minimize heat loss, particularly in the ends of the digits and tip of the nose. This reduced circulation can result in the skin taking on a whitish hue. Although the temperature of the skin drops as a result, passive heat loss is prevented, and internal organs and structures remain warm. If the temperature of the skin drops too much (such as environmental temperatures below freezing), the conservation of body core heat can result in the skin actually freezing, a condition called frostbite.
AGING AND THE...
Integumentary System
All systems in the body accumulate subtle and some not-so-subtle changes as a person ages. Among these changes are reductions in cell division, metabolic activity, blood circulation, hormonal levels, and muscle strength (Figure 5.17). In the skin, these changes are reflected in decreased mitosis in the stratum basale, leading to a thinner epidermis. The dermis, which is responsible for the elasticity and resilience of the skin, exhibits a reduced ability to regenerate, which leads to slower wound healing. The hypodermis, with its fat stores, loses structure due to the reduction and redistribution of fat, which in turn contributes to the thinning and sagging of skin.
Figure 5.17 Aging Generally, skin, especially on the face and hands, starts to display the first noticeable signs of aging, as it loses its elasticity over time. (credit: Janet Ramsden)
The accessory structures also have lowered activity, generating thinner hair and nails, and reduced amounts of sebum and sweat. A reduced sweating ability can cause some elderly to be intolerant to extreme heat. Other cells in the skin, such as melanocytes and dendritic cells, also become less active, leading to a paler skin tone and lowered immunity. Wrinkling of the skin occurs due to breakdown of its structure, which results from decreased collagen and elastin production in the dermis, weakening of muscles lying under the skin, and the inability of the skin to retain adequate moisture.
Many anti-aging products can be found in stores today. In general, these products try to rehydrate the skin and thereby fill out the wrinkles, and some stimulate skin growth using hormones and growth factors. Additionally, invasive techniques include collagen injections to plump the tissue and injections of BOTOX® (the name brand of the botulinum neurotoxin) that paralyze the muscles that crease the skin and cause wrinkling.
Vitamin D Synthesis
The epidermal layer of human skin synthesizes vitamin D when exposed to UV radiation. In the presence of sunlight, a form of vitamin D3 called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys. Vitamin D is essential for normal absorption of calcium and phosphorous, which are required for healthy bones. The absence of sun exposure can lead to a lack of vitamin D in the body, leading to a condition called rickets, a painful condition in children where the bones are misshapen due to a lack of calcium, causing bowleggedness. Elderly individuals who suffer from vitamin D deficiency can develop a condition called osteomalacia, a softening of the bones. In present day society, vitamin D is added as a supplement to many foods, including milk and orange juice, compensating for the need for sun exposure.
In addition to its essential role in bone health, vitamin D is essential for general immunity against bacterial, viral, and fungal infections. Recent studies are also finding a link between insufficient vitamin D and cancer.
Diseases, Disorders, and Injuries of the Integumentary System
- Describe several different diseases and disorders of the skin
- Describe the effect of injury to the skin and the process of healing
The integumentary system is susceptible to a variety of diseases, disorders, and injuries. These range from annoying but relatively benign bacterial or fungal infections that are categorized as disorders, to skin cancer and severe burns, which can be fatal. In this section, you will learn several of the most common skin conditions.
Diseases
One of the most talked about diseases is skin cancer. Cancer is a broad term that describes diseases caused by abnormal cells in the body dividing uncontrollably. Most cancers are identified by the organ or tissue in which the cancer originates. One common form of cancer is skin cancer. The Skin Cancer Foundation reports that one in five Americans will experience some type of skin cancer in their lifetime. The degradation of the ozone layer in the atmosphere and the resulting increase in exposure to UV radiation has contributed to its rise. Overexposure to UV radiation damages DNA, which can lead to the formation of cancerous lesions. Although melanin offers some protection against DNA damage from the sun, often it is not enough. The fact that cancers can also occur on areas of the body that are normally not exposed to UV radiation suggests that there are additional factors that can lead to cancerous lesions.
In general, cancers result from an accumulation of DNA mutations. These mutations can result in cell populations that do not die when they should and uncontrolled cell proliferation that leads to tumors. Although many tumors are benign (harmless), some produce cells that can mobilize and establish tumors in other organs of the body; this process is referred to as metastasis. Cancers are characterized by their ability to metastasize.
Basal Cell Carcinoma
Basal cell carcinoma is a form of cancer that affects the mitotically active stem cells in the stratum basale of the epidermis. It is the most common of all cancers that occur in the United States and is frequently found on the head, neck, arms, and back, which are areas that are most susceptible to long-term sun exposure. Although UV rays are the main culprit, exposure to other agents, such as radiation and arsenic, can also lead to this type of cancer. Wounds on the skin due to open sores, tattoos, burns, etc. may be predisposing factors as well. Basal cell carcinomas start in the stratum basale and usually spread along this boundary. At some point, they begin to grow toward the surface and become an uneven patch, bump, growth, or scar on the skin surface (Figure 5.18). Like most cancers, basal cell carcinomas respond best to treatment when caught early. Treatment options include surgery, freezing (cryosurgery), and topical ointments (Mayo Clinic 2012).
Figure 5.18 Basal Cell Carcinoma Basal cell carcinoma can take several different forms. Similar to other forms of skin cancer, it is readily cured if caught early and treated. (credit: John Hendrix, MD)
Squamous Cell Carcinoma
Squamous cell carcinoma is a cancer that affects the keratinocytes of the stratum spinosum and presents as lesions commonly found on the scalp, ears, and hands (Figure 5.19). It is the second most common skin cancer. The American Cancer Society reports that two of 10 skin cancers are squamous cell carcinomas, and it is more aggressive than basal cell carcinoma. If not removed, these carcinomas can metastasize. Surgery and radiation are used to cure squamous cell carcinoma.
Figure 5.19 Squamous Cell Carcinoma Squamous cell carcinoma presents here as a lesion on an individual’s nose. (credit: the National Cancer Institute)
Melanoma
A melanoma is a cancer characterized by the uncontrolled growth of melanocytes, the pigment-producing cells in the epidermis. Typically, a melanoma develops from a mole. It is the most fatal of all skin cancers, as it is highly metastatic and can be difficult to detect before it has spread to other organs. Melanomas usually appear as asymmetrical brown and black patches with uneven borders and a raised surface (Figure 5.20). Treatment typically involves surgical excision and immunotherapy.
Figure 5.20 Melanoma Melanomas typically present as large brown or black patches with uneven borders and a raised surface. (credit: the National Cancer Institute)
Doctors often give their patients the following ABCDE mnemonic to help with the diagnosis of early-stage melanoma. If you observe a mole on your body displaying these signs, consult a doctor.
- Asymmetry – the two sides are not symmetrical
- Borders – the edges are irregular in shape
- Color – the color is varied shades of brown or black
- Diameter – it is larger than 6 mm (0.24 in)
- Evolving – its shape has changed
Some specialists cite the following additional signs for the most serious form, nodular melanoma:
- Elevated – it is raised on the skin surface
- Firm – it feels hard to the touch
- Growing – it is getting larger
Skin Disorders
Two common skin disorders are eczema and acne. Eczema is an inflammatory condition and occurs in individuals of all ages. Acne involves the clogging of pores, which can lead to infection and inflammation, and is often seen in adolescents. Other disorders, not discussed here, include seborrheic dermatitis (on the scalp), psoriasis, cold sores, impetigo, scabies, hives, and warts.
Eczema
Eczema is an allergic reaction that manifests as dry, itchy patches of skin that resemble rashes (Figure 5.21). It may be accompanied by swelling of the skin, flaking, and in severe cases, bleeding. Many who suffer from eczema have antibodies against dust mites in their blood, but the link between eczema and allergy to dust mites has not been proven. Symptoms are usually managed with moisturizers, corticosteroid creams, and immunosuppressants.
Figure 5.21 Eczema Eczema is a common skin disorder that presents as a red, flaky rash. (credit: “Jambula”/Wikimedia Commons)
Acne
Acne is a skin disturbance that typically occurs on areas of the skin that are rich in sebaceous glands (face and back). It is most common along with the onset of puberty due to associated hormonal changes, but can also occur in infants and continue into adulthood. Hormones, such as androgens, stimulate the release of sebum. An overproduction and accumulation of sebum along with keratin can block hair follicles. This plug is initially white. The sebum, when oxidized by exposure to air, turns black. Acne results from infection by acne-causing bacteria (Propionibacterium and Staphylococcus), which can lead to redness and potential scarring due to the natural wound healing process (Figure 5.22).
Figure 5.22 Acne Acne is a result of over-productive sebaceous glands, which leads to formation of blackheads and inflammation of the skin.
CAREER CONNECTION
Dermatologist
Have you ever had a skin rash that did not respond to over-the-counter creams, or a mole that you were concerned about? Dermatologists help patients with these types of problems and more, on a daily basis. Dermatologists are medical doctors who specialize in diagnosing and treating skin disorders. Like all medical doctors, dermatologists earn a medical degree and then complete several years of residency training. In addition, dermatologists may then participate in a dermatology fellowship or complete additional, specialized training in a dermatology practice. If practicing in the United States, dermatologists must pass the United States Medical Licensing Exam (USMLE), become licensed in their state of practice, and be certified by the American Board of Dermatology.
Most dermatologists work in a medical office or private-practice setting. They diagnose skin conditions and rashes, prescribe oral and topical medications to treat skin conditions, and may perform simple procedures, such as mole or wart removal. In addition, they may refer patients to an oncologist if skin cancer that has metastasized is suspected. Recently, cosmetic procedures have also become a prominent part of dermatology. Botox injections, laser treatments, and collagen and dermal filler injections are popular among patients, hoping to reduce the appearance of skin aging.
Dermatology is a competitive specialty in medicine. Limited openings in dermatology residency programs mean that many medical students compete for a few select spots. Dermatology is an appealing specialty to many prospective doctors, because unlike emergency room physicians or surgeons, dermatologists generally do not have to work excessive hours or be “on-call” weekends and holidays. Moreover, the popularity of cosmetic dermatology has made it a growing field with many lucrative opportunities. It is not unusual for dermatology clinics to market themselves exclusively as cosmetic dermatology centers, and for dermatologists to specialize exclusively in these procedures.
Consider visiting a dermatologist to talk about why he or she entered the field and what the field of dermatology is like. Visit this site for additional information.
Injuries
Because the skin is the part of our bodies that meets the world most directly, it is especially vulnerable to injury. Injuries include burns and wounds, as well as scars and calluses. They can be caused by sharp objects, heat, or excessive pressure or friction to the skin.
Skin injuries set off a healing process that occurs in several overlapping stages. The first step to repairing damaged skin is the formation of a blood clot that helps stop the flow of blood and scabs over with time. Many different types of cells are involved in wound repair, especially if the surface area that needs repair is extensive. Before the basal stem cells of the stratum basale can recreate the epidermis, fibroblasts mobilize and divide rapidly to repair the damaged tissue by collagen deposition, forming granulation tissue. Blood capillaries follow the fibroblasts and help increase blood circulation and oxygen supply to the area. Immune cells, such as macrophages, roam the area and engulf any foreign matter to reduce the chance of infection.
Burns
A burn results when the skin is damaged by intense heat, radiation, electricity, or chemicals. The damage results in the death of skin cells, which can lead to a massive loss of fluid. Dehydration, electrolyte imbalance, and renal and circulatory failure follow, which can be fatal. Burn patients are treated with intravenous fluids to offset dehydration, as well as intravenous nutrients that enable the body to repair tissues and replace lost proteins. Another serious threat to the lives of burn patients is infection. Burned skin is extremely susceptible to bacteria and other pathogens, due to the loss of protection by intact layers of skin.
Burns are sometimes measured in terms of the size of the total surface area affected. This is referred to as the “rule of nines,” which associates specific anatomical areas with a percentage that is a factor of nine (Figure 5.23). Burns are also classified by the degree of their severity. A first-degree burn is a superficial burn that affects only the epidermis. Although the skin may be painful and swollen, these burns typically heal on their own within a few days. Mild sunburn fits into the category of a first-degree burn. A second-degree burn goes deeper and affects both the epidermis and a portion of the dermis. These burns result in swelling and a painful blistering of the skin. It is important to keep the burn site clean and sterile to prevent infection. If this is done, the burn will heal within several weeks. A third-degree burn fully extends into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function. These are serious burns that may appear white, red, or black; they require medical attention and will heal slowly without it. A fourth-degree burn is even more severe, affecting the underlying muscle and bone. Oddly, third and fourth-degree burns are usually not as painful because the nerve endings themselves are damaged. Full-thickness burns cannot be repaired by the body, because the local tissues used for repair are damaged and require excision (debridement), or amputation in severe cases, followed by grafting of the skin from an unaffected part of the body, or from skin grown in tissue culture for grafting purposes.
Figure 5.23 Calculating the Size of a Burn The size of a burn will guide decisions made about the need for specialized treatment. Specific parts of the body are associated with a percentage of body area.
INTERACTIVE LINK
Skin grafts are required when the damage from trauma or infection cannot be closed with sutures or staples. Watch this video to learn more about skin grafting procedures.
Scars and Keloids
Most cuts or wounds, with the exception of ones that only scratch the surface (the epidermis), lead to scar formation. A scar is collagen-rich skin formed after the process of wound healing that differs from normal skin. Scarring occurs in cases in which there is repair of skin damage, but the skin fails to regenerate the original skin structure. Fibroblasts generate scar tissue in the form of collagen, and the bulk of repair is due to the basket-weave pattern generated by collagen fibers and does not result in regeneration of the typical cellular structure of skin. Instead, the tissue is fibrous in nature and does not allow for the regeneration of accessory structures, such as hair follicles, sweat glands, or sebaceous glands.
Sometimes, there is an overproduction of scar tissue, because the process of collagen formation does not stop when the wound is healed; this results in the formation of a raised or hypertrophic scar called a keloid. In contrast, scars that result from acne and chickenpox have a sunken appearance and are called atrophic scars.
Scarring of skin after wound healing is a natural process and does not need to be treated further. Application of mineral oil and lotions may reduce the formation of scar tissue. However, modern cosmetic procedures, such as dermabrasion, laser treatments, and filler injections have been invented as remedies for severe scarring. All of these procedures try to reorganize the structure of the epidermis and underlying collagen tissue to make it look more natural.
Bedsores and Stretch Marks
Skin and its underlying tissue can be affected by excessive pressure. One example of this is called a bedsore. Bedsores, also called decubitis ulcers, are caused by constant, long-term, unrelieved pressure on certain body parts that are bony, reducing blood flow to the area and leading to necrosis (tissue death). Bedsores are most common in elderly patients who have debilitating conditions that cause them to be immobile. Most hospitals and long-term care facilities have the practice of turning the patients every few hours to prevent the incidence of bedsores. If left untreated by removal of necrotized tissue, bedsores can be fatal if they become infected.
The skin can also be affected by pressure associated with rapid growth. A stretch mark results when the dermis is stretched beyond its limits of elasticity, as the skin stretches to accommodate the excess pressure. Stretch marks usually accompany rapid weight gain during puberty and pregnancy. They initially have a reddish hue, but lighten over time. Other than for cosmetic reasons, treatment of stretch marks is not required. They occur most commonly over the hips and abdomen.
Calluses
When you wear shoes that do not fit well and are a constant source of abrasion on your toes, you tend to form a callus at the point of contact. This occurs because the basal stem cells in the stratum basale are triggered to divide more often to increase the thickness of the skin at the point of abrasion to protect the rest of the body from further damage. This is an example of a minor or local injury, and the skin manages to react and treat the problem independent of the rest of the body. Calluses can also form on your fingers if they are subject to constant mechanical stress, such as long periods of writing, playing string instruments, or video games. A corn is a specialized form of callus. Corns form from abrasions on the skin that result from an elliptical-type motion.
Key Terms
- acne
- skin condition due to infected sebaceous glands
- albinism
- genetic disorder that affects the skin, in which there is no melanin production
- anagen
- active phase of the hair growth cycle
- apocrine sweat gland
- type of sweat gland that is associated with hair follicles in the armpits and genital regions
- arrector pili
- smooth muscle that is activated in response to external stimuli that pull on hair follicles and make the hair “stand up”
- basal cell
- type of stem cell found in the stratum basale and in the hair matrix that continually undergoes cell division, producing the keratinocytes of the epidermis
- basal cell carcinoma
- cancer that originates from basal cells in the epidermis of the skin
- bedsore
- sore on the skin that develops when regions of the body start necrotizing due to constant pressure and lack of blood supply; also called decubitis ulcers
- callus
- thickened area of skin that arises due to constant abrasion
- catagen
- transitional phase marking the end of the anagen phase of the hair growth cycle
- corn
- type of callus that is named for its shape and the elliptical motion of the abrasive force
- cortex
- in hair, the second or middle layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb
- cuticle
- in hair, the outermost layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb
- dermal papilla
- (plural = dermal papillae) extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis
- dermis
- layer of skin between the epidermis and hypodermis, composed mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures
- desmosome
- structure that forms an impermeable junction between cells
- eccrine sweat gland
- type of sweat gland that is common throughout the skin surface; it produces a hypotonic sweat for thermoregulation
- eczema
- skin condition due to an allergic reaction, which resembles a rash
- elastin fibers
- fibers made of the protein elastin that increase the elasticity of the dermis
- eleiden
- clear protein-bound lipid found in the stratum lucidum that is derived from keratohyalin and helps to prevent water loss
- epidermis
- outermost tissue layer of the skin
- eponychium
- nail fold that meets the proximal end of the nail body, also called the cuticle
- external root sheath
- outer layer of the hair follicle that is an extension of the epidermis, which encloses the hair root
- first-degree burn
- superficial burn that injures only the epidermis
- fourth-degree burn
- burn in which full thickness of the skin and underlying muscle and bone is damaged
- glassy membrane
- layer of connective tissue that surrounds the base of the hair follicle, connecting it to the dermis
- hair
- keratinous filament growing out of the epidermis
- hair bulb
- structure at the base of the hair root that surrounds the dermal papilla
- hair follicle
- cavity or sac from which hair originates
- hair matrix
- layer of basal cells from which a strand of hair grows
- hair papilla
- mass of connective tissue, blood capillaries, and nerve endings at the base of the hair follicle
- hair root
- part of hair that is below the epidermis anchored to the follicle
- hair shaft
- part of hair that is above the epidermis but is not anchored to the follicle
- hypodermis
- connective tissue connecting the integument to the underlying bone and muscle
- hyponychium
- thickened layer of stratum corneum that lies below the free edge of the nail
- integumentary system
- skin and its accessory structures
- internal root sheath
- innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft
- keloid
- type of scar that has layers raised above the skin surface
- keratin
- type of structural protein that gives skin, hair, and nails its hard, water-resistant properties
- keratinocyte
- cell that produces keratin and is the most predominant type of cell found in the epidermis
- keratohyalin
- granulated protein found in the stratum granulosum
- Langerhans cell
- specialized dendritic cell found in the stratum spinosum that functions as a macrophage
- lunula
- basal part of the nail body that consists of a crescent-shaped layer of thick epithelium
- medulla
- in hair, the innermost layer of keratinocytes originating from the hair matrix
- Meissner corpuscle
- (also, tactile corpuscle) receptor in the skin that responds to light touch
- melanin
- pigment that determines the color of hair and skin
- melanocyte
- cell found in the stratum basale of the epidermis that produces the pigment melanin
- melanoma
- type of skin cancer that originates from the melanocytes of the skin
- melanosome
- intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis
- Merkel cell
- receptor cell in the stratum basale of the epidermis that responds to the sense of touch
- metastasis
- spread of cancer cells from a source to other parts of the body
- nail bed
- layer of epidermis upon which the nail body forms
- nail body
- main keratinous plate that forms the nail
- nail cuticle
- fold of epithelium that extends over the nail bed, also called the eponychium
- nail fold
- fold of epithelium at that extend over the sides of the nail body, holding it in place
- nail root
- part of the nail that is lodged deep in the epidermis from which the nail grows
- Pacinian corpuscle
- (also, lamellated corpuscle) receptor in the skin that responds to vibration
- papillary layer
- superficial layer of the dermis, made of loose, areolar connective tissue
- reticular layer
- deeper layer of the dermis; it has a reticulated appearance due to the presence of abundant collagen and elastin fibers
- rickets
- disease in children caused by vitamin D deficiency, which leads to the weakening of bones
- scar
- collagen-rich skin formed after the process of wound healing that is different from normal skin
- sebaceous gland
- type of oil gland found in the dermis all over the body and helps to lubricate and waterproof the skin and hair by secreting sebum
- sebum
- oily substance that is composed of a mixture of lipids that lubricates the skin and hair
- second-degree burn
- partial-thickness burn that injures the epidermis and a portion of the dermis
- squamous cell carcinoma
- type of skin cancer that originates from the stratum spinosum of the epidermis
- stratum basale
- deepest layer of the epidermis, made of epidermal stem cells
- stratum corneum
- most superficial layer of the epidermis
- stratum granulosum
- layer of the epidermis superficial to the stratum spinosum
- stratum lucidum
- layer of the epidermis between the stratum granulosum and stratum corneum, found only in thick skin covering the palms, soles of the feet, and digits
- stratum spinosum
- layer of the epidermis superficial to the stratum basale, characterized by the presence of desmosomes
- stretch mark
- mark formed on the skin due to a sudden growth spurt and expansion of the dermis beyond its elastic limits
- sudoriferous gland
- sweat gland
- telogen
- resting phase of the hair growth cycle initiated with catagen and terminated by the beginning of a new anagen phase of hair growth
- third-degree burn
- burn that penetrates and destroys the full thickness of the skin (epidermis and dermis)
- vitamin D
- compound that aids absorption of calcium and phosphates in the intestine to improve bone health
- vitiligo
- skin condition in which melanocytes in certain areas lose the ability to produce melanin, possibly due an autoimmune reaction that leads to loss of color in patches
Chapter Review
5.1 Layers of the Skin
The skin is composed of two major layers: a superficial epidermis and a deeper dermis. The epidermis consists of several layers beginning with the innermost (deepest) stratum basale (germinatum), followed by the stratum spinosum, stratum granulosum, stratum lucidum (when present), and ending with the outermost layer, the stratum corneum. The topmost layer, the stratum corneum, consists of dead cells that shed periodically and is progressively replaced by cells formed from the basal layer. The stratum basale also contains melanocytes, cells that produce melanin, the pigment primarily responsible for giving skin its color. Melanin is transferred to keratinocytes in the stratum spinosum to protect cells from UV rays.
The dermis connects the epidermis to the hypodermis, and provides strength and elasticity due to the presence of collagen and elastin fibers. It has only two layers: the papillary layer with papillae that extend into the epidermis and the lower, reticular layer composed of loose connective tissue. The hypodermis, deep to the dermis of skin, is the connective tissue that connects the dermis to underlying structures; it also harbors adipose tissue for fat storage and protection.
5.2 Accessory Structures of the Skin
Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. Hair is made of dead keratinized cells, and gets its color from melanin pigments. Nails, also made of dead keratinized cells, protect the extremities of our fingers and toes from mechanical damage. Sweat glands and sebaceous glands produce sweat and sebum, respectively. Each of these fluids has a role to play in maintaining homeostasis. Sweat cools the body surface when it gets overheated and helps excrete small amounts of metabolic waste. Sebum acts as a natural moisturizer and keeps the dead, flaky, outer keratin layer healthy.
5.3 Functions of the Integumentary System
The skin plays important roles in protection, sensing stimuli, thermoregulation, and vitamin D synthesis. It is the first layer of defense to prevent dehydration, infection, and injury to the rest of the body. Sweat glands in the skin allow the skin surface to cool when the body gets overheated. Thermoregulation is also accomplished by the dilation or constriction of heat-carrying blood vessels in the skin. Immune cells present among the skin layers patrol the areas to keep them free of foreign materials. Fat stores in the hypodermis aid in both thermoregulation and protection. Finally, the skin plays a role in the synthesis of vitamin D, which is necessary for our well-being but not easily available in natural foods.
5.4 Diseases, Disorders, and Injuries of the Integumentary System
Skin cancer is a result of damage to the DNA of skin cells, often due to excessive exposure to UV radiation. Basal cell carcinoma and squamous cell carcinoma are highly curable, and arise from cells in the stratum basale and stratum spinosum, respectively. Melanoma is the most dangerous form of skin cancer, affecting melanocytes, which can spread/metastasize to other organs. Burns are an injury to the skin that occur as a result of exposure to extreme heat, radiation, or chemicals. First-degree and second-degree burns usually heal quickly, but third-degree burns can be fatal because they penetrate the full thickness of the skin. Scars occur when there is repair of skin damage. Fibroblasts generate scar tissue in the form of collagen, which forms a basket-weave pattern that looks different from normal skin.
Bedsores and stretch marks are the result of excessive pressure on the skin and underlying tissue. Bedsores are characterized by necrosis of tissue due to immobility, whereas stretch marks result from rapid growth. Eczema is an allergic reaction that manifests as a rash, and acne results from clogged sebaceous glands. Eczema and acne are usually long-term skin conditions that may be treated successfully in mild cases. Calluses and corns are the result of abrasive pressure on the skin.
Interactive Link Questions
The skin consists of two layers and a closely associated layer. View this animation to learn more about layers of the skin. What are the basic functions of each of these layers?
2.Figure 5.4 If you zoom on the cells at the outermost layer of this section of skin, what do you notice about the cells?
3.Figure 5.6 If you zoom on the cells of the stratum spinosum, what is distinctive about them?
4.This ABC video follows the story of a pair of fraternal African-American twins, one of whom is albino. Watch this videoto learn about the challenges these children and their family face. Which ethnicities do you think are exempt from the possibility of albinism?
Review Questions
The papillary layer of the dermis is most closely associated with which layer of the epidermis?
- stratum spinosum
- stratum corneum
- stratum granulosum
- stratum basale
Langerhans cells are commonly found in the ________.
- stratum spinosum
- stratum corneum
- stratum granulosum
- stratum basale
The papillary and reticular layers of the dermis are composed mainly of ________.
- melanocytes
- keratinocytes
- connective tissue
- adipose tissue
Collagen lends ________ to the skin.
- elasticity
- structure
- color
- UV protection
Which of the following is not a function of the hypodermis?
- protects underlying organs
- helps maintain body temperature
- source of blood vessels in the epidermis
- a site to long-term energy storage
In response to stimuli from the sympathetic nervous system, the arrector pili ________.
- are glands on the skin surface
- can lead to excessive sweating
- are responsible for goose bumps
- secrete sebum
The hair matrix contains ________.
- the hair follicle
- the hair shaft
- the glassy membrane
- a layer of basal cells
Eccrine sweat glands ________.
- are present on hair
- are present in the skin throughout the body and produce watery sweat
- produce sebum
- act as a moisturizer
Sebaceous glands ________.
- are a type of sweat gland
- are associated with hair follicles
- may function in response to touch
- release a watery solution of salt and metabolic waste
Similar to the hair, nails grow continuously throughout our lives. Which of the following is furthest from the nail growth center?
- nail bed
- hyponychium
- nail root
- eponychium
In humans, exposure of the skin to sunlight is required for ________.
- vitamin D synthesis
- arteriole constriction
- folate production
- thermoregulation
One of the functions of the integumentary system is protection. Which of the following does not directly contribute to that function?
- stratum lucidum
- desmosomes
- folic acid synthesis
- Merkel cells
An individual using a sharp knife notices a small amount of blood where he just cut himself. Which of the following layers of skin did he have to cut into in order to bleed?
- stratum corneum
- stratum basale
- papillary dermis
- stratum granulosum
As you are walking down the beach, you see a dead, dry, shriveled-up fish. Which layer of your epidermis keeps you from drying out?
- stratum corneum
- stratum basale
- stratum spinosum
- stratum granulosum
If you cut yourself and bacteria enter the wound, which of the following cells would help get rid of the bacteria?
- Merkel cells
- keratinocytes
- Langerhans cells
- melanocytes
In general, skin cancers ________.
- are easily treatable and not a major health concern
- occur due to poor hygiene
- can be reduced by limiting exposure to the sun
- affect only the epidermis
Bedsores ________.
- can be treated with topical moisturizers
- can result from deep massages
- are preventable by eliminating pressure points
- are caused by dry skin
An individual has spent too much time sun bathing. Not only is his skin painful to touch, but small blisters have appeared in the affected area. This indicates that he has damaged which layers of his skin?
- epidermis only
- hypodermis only
- epidermis and hypodermis
- epidermis and dermis
After a skin injury, the body initiates a wound-healing response. The first step of this response is the formation of a blood clot to stop bleeding. Which of the following would be the next response?
- increased production of melanin by melanocytes
- increased production of connective tissue
- an increase in Pacinian corpuscles around the wound
- an increased activity in the stratum lucidum
Squamous cell carcinomas are the second most common of the skin cancers and are capable of metastasizing if not treated. This cancer affects which cells?
- basal cells of the stratum basale
- melanocytes of the stratum basale
- keratinocytes of the stratum spinosum
- Langerhans cells of the stratum lucidum
Critical Thinking Questions
What determines the color of skin, and what is the process that darkens skin when it is exposed to UV light?
26.Cells of the epidermis derive from stem cells of the stratum basale. Describe how the cells change as they become integrated into the different layers of the epidermis.
27.Explain the differences between eccrine and apocrine sweat glands.
28.Describe the structure and composition of nails.
29.Why do people sweat excessively when exercising outside on a hot day?
30.Explain your skin’s response to a drop in body core temperature.
31.Why do teenagers often experience acne?
32.Why do scars look different from surrounding skin?
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oercommons
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2025-03-18T00:38:18.587124
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07/23/2019
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"title": "Anatomy and Physiology, Support and Movement, The Integumentary System",
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https://oercommons.org/courseware/lesson/58775/overview
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The Reproductive System
Introduction
Figure 27.1 Ovulation Following a surge of luteinizing hormone (LH), an oocyte (immature egg cell) will be released into the uterine tube, where it will then be available to be fertilized by a male’s sperm. Ovulation marks the end of the follicular phase of the ovarian cycle and the start of the luteal phase.
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Describe the anatomy of the male and female reproductive systems, including their accessory structures
- Explain the role of hypothalamic and pituitary hormones in male and female reproductive function
- Trace the path of a sperm cell from its initial production through fertilization of an oocyte
- Explain the events in the ovary prior to ovulation
- Describe the development and maturation of the sex organs and the emergence of secondary sex characteristics during puberty
Small, uncoordinated, and slick with amniotic fluid, a newborn encounters the world outside of her mother’s womb. We do not often consider that a child’s birth is proof of the healthy functioning of both her mother’s and father’s reproductive systems. Moreover, her parents’ endocrine systems had to secrete the appropriate regulating hormones to induce the production and release of unique male and female gametes, reproductive cells containing the parents’ genetic material (one set of 23 chromosomes). Her parent’s reproductive behavior had to facilitate the transfer of male gametes—the sperm—to the female reproductive tract at just the right time to encounter the female gamete, an oocyte (egg). Finally, combination of the gametes (fertilization) had to occur, followed by implantation and development. In this chapter, you will explore the male and female reproductive systems, whose healthy functioning can culminate in the powerful sound of a newborn’s first cry.
Anatomy and Physiology of the Male Reproductive System
- Describe the structure and function of the organs of the male reproductive system
- Describe the structure and function of the sperm cell
- Explain the events during spermatogenesis that produce haploid sperm from diploid cells
- Identify the importance of testosterone in male reproductive function
Unique for its role in human reproduction, a gamete is a specialized sex cell carrying 23 chromosomes—one half the number in body cells. At fertilization, the chromosomes in one male gamete, called a sperm (or spermatozoon), combine with the chromosomes in one female gamete, called an oocyte. The function of the male reproductive system (Figure 27.2) is to produce sperm and transfer them to the female reproductive tract. The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology. In humans, the most important male androgen is testosterone. Several accessory organs and ducts aid the process of sperm maturation and transport the sperm and other seminal components to the penis, which delivers sperm to the female reproductive tract. In this section, we examine each of these different structures, and discuss the process of sperm production and transport.
Figure 27.2 Male Reproductive System The structures of the male reproductive system include the testes, the epididymides, the penis, and the ducts and glands that produce and carry semen. Sperm exit the scrotum through the ductus deferens, which is bundled in the spermatic cord. The seminal vesicles and prostate gland add fluids to the sperm to create semen.
Scrotum
The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis (see Figure 27.2). This location is important in sperm production, which occurs within the testes, and proceeds more efficiently when the testes are kept 2 to 4°C below core body temperature.
The dartos muscle makes up the subcutaneous muscle layer of the scrotum (Figure 27.3). It continues internally to make up the scrotal septum, a wall that divides the scrotum into two compartments, each housing one testis. Descending from the internal oblique muscle of the abdominal wall are the two cremaster muscles, which cover each testis like a muscular net. By contracting simultaneously, the dartos and cremaster muscles can elevate the testes in cold weather (or water), moving the testes closer to the body and decreasing the surface area of the scrotum to retain heat. Alternatively, as the environmental temperature increases, the scrotum relaxes, moving the testes farther from the body core and increasing scrotal surface area, which promotes heat loss. Externally, the scrotum has a raised medial thickening on the surface called the raphae.
Figure 27.3 The Scrotum and Testes This anterior view shows the structures of the scrotum and testes.
Testes
The testes (singular = testis) are the male gonads—that is, the male reproductive organs. They produce both sperm and androgens, such as testosterone, and are active throughout the reproductive lifespan of the male.
Paired ovals, the testes are each approximately 4 to 5 cm in length and are housed within the scrotum (see Figure 27.3). They are surrounded by two distinct layers of protective connective tissue (Figure 27.4). The outer tunica vaginalis is a serous membrane that has both a parietal and a thin visceral layer. Beneath the tunica vaginalis is the tunica albuginea, a tough, white, dense connective tissue layer covering the testis itself. Not only does the tunica albuginea cover the outside of the testis, it also invaginates to form septa that divide the testis into 300 to 400 structures called lobules. Within the lobules, sperm develop in structures called seminiferous tubules. During the seventh month of the developmental period of a male fetus, each testis moves through the abdominal musculature to descend into the scrotal cavity. This is called the “descent of the testis.” Cryptorchidism is the clinical term used when one or both of the testes fail to descend into the scrotum prior to birth.
Figure 27.4 Anatomy of the Testis This sagittal view shows the seminiferous tubules, the site of sperm production. Formed sperm are transferred to the epididymis, where they mature. They leave the epididymis during an ejaculation via the ductus deferens.
The tightly coiled seminiferous tubules form the bulk of each testis. They are composed of developing sperm cells surrounding a lumen, the hollow center of the tubule, where formed sperm are released into the duct system of the testis. Specifically, from the lumens of the seminiferous tubules, sperm move into the straight tubules (or tubuli recti), and from there into a fine meshwork of tubules called the rete testes. Sperm leave the rete testes, and the testis itself, through the 15 to 20 efferent ductules that cross the tunica albuginea.
Inside the seminiferous tubules are six different cell types. These include supporting cells called sustentacular cells, as well as five types of developing sperm cells called germ cells. Germ cell development progresses from the basement membrane—at the perimeter of the tubule—toward the lumen. Let’s look more closely at these cell types.
Sertoli Cells
Surrounding all stages of the developing sperm cells are elongate, branching Sertoli cells. Sertoli cells are a type of supporting cell called a sustentacular cell, or sustentocyte, that are typically found in epithelial tissue. Sertoli cells secrete signaling molecules that promote sperm production and can control whether germ cells live or die. They extend physically around the germ cells from the peripheral basement membrane of the seminiferous tubules to the lumen. Tight junctions between these sustentacular cells create the blood–testis barrier, which keeps bloodborne substances from reaching the germ cells and, at the same time, keeps surface antigens on developing germ cells from escaping into the bloodstream and prompting an autoimmune response.
Germ Cells
The least mature cells, the spermatogonia (singular = spermatogonium), line the basement membrane inside the tubule. Spermatogonia are the stem cells of the testis, which means that they are still able to differentiate into a variety of different cell types throughout adulthood. Spermatogonia divide to produce primary and secondary spermatocytes, then spermatids, which finally produce formed sperm. The process that begins with spermatogonia and concludes with the production of sperm is called spermatogenesis.
Spermatogenesis
As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis (see Figure 27.4). The process begins at puberty, after which time sperm are produced constantly throughout a man’s life. One production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new cycle starts approximately every 16 days, although this timing is not synchronous across the seminiferous tubules. Sperm counts—the total number of sperm a man produces—slowly decline after age 35, and some studies suggest that smoking can lower sperm counts irrespective of age.
The process of spermatogenesis begins with mitosis of the diploid spermatogonia (Figure 27.5). Because these cells are diploid (2n), they each have a complete copy of the father’s genetic material, or 46 chromosomes. However, mature gametes are haploid (1n), containing 23 chromosomes—meaning that daughter cells of spermatogonia must undergo a second cellular division through the process of meiosis.
Figure 27.5 Spermatogenesis (a) Mitosis of a spermatogonial stem cell involves a single cell division that results in two identical, diploid daughter cells (spermatogonia to primary spermatocyte). Meiosis has two rounds of cell division: primary spermatocyte to secondary spermatocyte, and then secondary spermatocyte to spermatid. This produces four haploid daughter cells (spermatids). (b) In this electron micrograph of a cross-section of a seminiferous tubule from a rat, the lumen is the light-shaded area in the center of the image. The location of the primary spermatocytes is near the basement membrane, and the early spermatids are approaching the lumen (tissue source: rat). EM × 900. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte, the next stage in the process of spermatogenesis. As in mitosis, DNA is replicated in a primary spermatocyte, before it undergoes a cell division called meiosis I. During meiosis I each of the 23 pairs of chromosomes separates. This results in two cells, called secondary spermatocytes, each with only half the number of chromosomes. Now a second round of cell division (meiosis II) occurs in both of the secondary spermatocytes. During meiosis II each of the 23 replicated chromosomes divides, similar to what happens during mitosis. Thus, meiosis results in separating the chromosome pairs. This second meiotic division results in a total of four cells with only half of the number of chromosomes. Each of these new cells is a spermatid. Although haploid, early spermatids look very similar to cells in the earlier stages of spermatogenesis, with a round shape, central nucleus, and large amount of cytoplasm. A process called spermiogenesis transforms these early spermatids, reducing the cytoplasm, and beginning the formation of the parts of a true sperm. The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the end result of this process, which occurs in the portion of the tubule nearest the lumen. Eventually, the sperm are released into the lumen and are moved along a series of ducts in the testis toward a structure called the epididymis for the next step of sperm maturation.
Structure of Formed Sperm
Sperm are smaller than most cells in the body; in fact, the volume of a sperm cell is 85,000 times less than that of the female gamete. Approximately 100 to 300 million sperm are produced each day, whereas women typically ovulate only one oocyte per month. As is true for most cells in the body, the structure of sperm cells speaks to their function. Sperm have a distinctive head, mid-piece, and tail region (Figure 27.6). The head of the sperm contains the extremely compact haploid nucleus with very little cytoplasm. These qualities contribute to the overall small size of the sperm (the head is only 5 μm long). A structure called the acrosome covers most of the head of the sperm cell as a “cap” that is filled with lysosomal enzymes important for preparing sperm to participate in fertilization. Tightly packed mitochondria fill the mid-piece of the sperm. ATP produced by these mitochondria will power the flagellum, which extends from the neck and the mid-piece through the tail of the sperm, enabling it to move the entire sperm cell. The central strand of the flagellum, the axial filament, is formed from one centriole inside the maturing sperm cell during the final stages of spermatogenesis.
Figure 27.6 Structure of Sperm Sperm cells are divided into a head, containing DNA; a mid-piece, containing mitochondria; and a tail, providing motility. The acrosome is oval and somewhat flattened.
Sperm Transport
To fertilize an egg, sperm must be moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female reproductive tract.
Role of the Epididymis
From the lumen of the seminiferous tubules, the immotile sperm are surrounded by testicular fluid and moved to the epididymis(plural = epididymides), a coiled tube attached to the testis where newly formed sperm continue to mature (see Figure 27.4). Though the epididymis does not take up much room in its tightly coiled state, it would be approximately 6 m (20 feet) long if straightened. It takes an average of 12 days for sperm to move through the coils of the epididymis, with the shortest recorded transit time in humans being one day. Sperm enter the head of the epididymis and are moved along predominantly by the contraction of smooth muscles lining the epididymal tubes. As they are moved along the length of the epididymis, the sperm further mature and acquire the ability to move under their own power. Once inside the female reproductive tract, they will use this ability to move independently toward the unfertilized egg. The more mature sperm are then stored in the tail of the epididymis (the final section) until ejaculation occurs.
Duct System
During ejaculation, sperm exit the tail of the epididymis and are pushed by smooth muscle contraction to the ductus deferens(also called the vas deferens). The ductus deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord (see Figure 27.2 and Figure 27.3). Because the ductus deferens is physically accessible within the scrotum, surgical sterilization to interrupt sperm delivery can be performed by cutting and sealing a small section of the ductus (vas) deferens. This procedure is called a vasectomy, and it is an effective form of male birth control. Although it may be possible to reverse a vasectomy, clinicians consider the procedure permanent, and advise men to undergo it only if they are certain they no longer wish to father children.
INTERACTIVE LINK
Watch this video to learn about a vasectomy. As described in this video, a vasectomy is a procedure in which a small section of the ductus (vas) deferens is removed from the scrotum. This interrupts the path taken by sperm through the ductus deferens. If sperm do not exit through the vas, either because the man has had a vasectomy or has not ejaculated, in what region of the testis do they remain?
From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the abdominal wall. From here, the ductus deferens continues posteriorly to the pelvic cavity, ending posterior to the bladder where it dilates in a region called the ampulla (meaning “flask”).
Sperm make up only 5 percent of the final volume of semen, the thick, milky fluid that the male ejaculates. The bulk of semen is produced by three critical accessory glands of the male reproductive system: the seminal vesicles, the prostate, and the bulbourethral glands.
Seminal Vesicles
As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated seminal vesicle (see Figure 27.2). The paired seminal vesicles are glands that contribute approximately 60 percent of the semen volume. Seminal vesicle fluid contains large amounts of fructose, which is used by the sperm mitochondria to generate ATP to allow movement through the female reproductive tract.
The fluid, now containing both sperm and seminal vesicle secretions, next moves into the associated ejaculatory duct, a short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory ducts transport the seminal fluid into the next structure, the prostate gland.
Prostate Gland
As shown in Figure 27.2, the centrally located prostate gland sits anterior to the rectum at the base of the bladder surrounding the prostatic urethra (the portion of the urethra that runs within the prostate). About the size of a walnut, the prostate is formed of both muscular and glandular tissues. It excretes an alkaline, milky fluid to the passing seminal fluid—now called semen—that is critical to first coagulate and then decoagulate the semen following ejaculation. The temporary thickening of semen helps retain it within the female reproductive tract, providing time for sperm to utilize the fructose provided by seminal vesicle secretions. When the semen regains its fluid state, sperm can then pass farther into the female reproductive tract.
The prostate normally doubles in size during puberty. At approximately age 25, it gradually begins to enlarge again. This enlargement does not usually cause problems; however, abnormal growth of the prostate, or benign prostatic hyperplasia (BPH), can cause constriction of the urethra as it passes through the middle of the prostate gland, leading to a number of lower urinary tract symptoms, such as a frequent and intense urge to urinate, a weak stream, and a sensation that the bladder has not emptied completely. By age 60, approximately 40 percent of men have some degree of BPH. By age 80, the number of affected individuals has jumped to as many as 80 percent. Treatments for BPH attempt to relieve the pressure on the urethra so that urine can flow more normally. Mild to moderate symptoms are treated with medication, whereas severe enlargement of the prostate is treated by surgery in which a portion of the prostate tissue is removed.
Another common disorder involving the prostate is prostate cancer. According to the Centers for Disease Control and Prevention (CDC), prostate cancer is the second most common cancer in men. However, some forms of prostate cancer grow very slowly and thus may not ever require treatment. Aggressive forms of prostate cancer, in contrast, involve metastasis to vulnerable organs like the lungs and brain. There is no link between BPH and prostate cancer, but the symptoms are similar. Prostate cancer is detected by a medical history, a blood test, and a rectal exam that allows physicians to palpate the prostate and check for unusual masses. If a mass is detected, the cancer diagnosis is confirmed by biopsy of the cells.
Bulbourethral Glands
The final addition to semen is made by two bulbourethral glands (or Cowper’s glands) that release a thick, salty fluid that lubricates the end of the urethra and the vagina, and helps to clean urine residues from the penile urethra. The fluid from these accessory glands is released after the male becomes sexually aroused, and shortly before the release of the semen. It is therefore sometimes called pre-ejaculate. It is important to note that, in addition to the lubricating proteins, it is possible for bulbourethral fluid to pick up sperm already present in the urethra, and therefore it may be able to cause pregnancy.
INTERACTIVE LINK
Watch this video to explore the structures of the male reproductive system and the path of sperm, which starts in the testes and ends as the sperm leave the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct?
The Penis
The penis is the male organ of copulation (sexual intercourse). It is flaccid for non-sexual actions, such as urination, and turgid and rod-like with sexual arousal. When erect, the stiffness of the organ allows it to penetrate into the vagina and deposit semen into the female reproductive tract.
Figure 27.7 Cross-Sectional Anatomy of the Penis Three columns of erectile tissue make up most of the volume of the penis.
The shaft of the penis surrounds the urethra (Figure 27.7). The shaft is composed of three column-like chambers of erectile tissue that span the length of the shaft. Each of the two larger lateral chambers is called a corpus cavernosum (plural = corpora cavernosa). Together, these make up the bulk of the penis. The corpus spongiosum, which can be felt as a raised ridge on the erect penis, is a smaller chamber that surrounds the spongy, or penile, urethra. The end of the penis, called the glans penis, has a high concentration of nerve endings, resulting in very sensitive skin that influences the likelihood of ejaculation (see Figure 27.2). The skin from the shaft extends down over the glans and forms a collar called the prepuce (or foreskin). The foreskin also contains a dense concentration of nerve endings, and both lubricate and protect the sensitive skin of the glans penis. A surgical procedure called circumcision, often performed for religious or social reasons, removes the prepuce, typically within days of birth.
Both sexual arousal and REM sleep (during which dreaming occurs) can induce an erection. Penile erections are the result of vasocongestion, or engorgement of the tissues because of more arterial blood flowing into the penis than is leaving in the veins. During sexual arousal, nitric oxide (NO) is released from nerve endings near blood vessels within the corpora cavernosa and spongiosum. Release of NO activates a signaling pathway that results in relaxation of the smooth muscles that surround the penile arteries, causing them to dilate. This dilation increases the amount of blood that can enter the penis and induces the endothelial cells in the penile arterial walls to also secrete NO and perpetuate the vasodilation. The rapid increase in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the thin-walled penile venules, preventing venous drainage of the penis. The result of this increased blood flow to the penis and reduced blood return from the penis is erection. Depending on the flaccid dimensions of a penis, it can increase in size slightly or greatly during erection, with the average length of an erect penis measuring approximately 15 cm.
DISORDERS OF THE...
Male Reproductive System
Erectile dysfunction (ED) is a condition in which a man has difficulty either initiating or maintaining an erection. The combined prevalence of minimal, moderate, and complete ED is approximately 40 percent in men at age 40, and reaches nearly 70 percent by 70 years of age. In addition to aging, ED is associated with diabetes, vascular disease, psychiatric disorders, prostate disorders, the use of some drugs such as certain antidepressants, and problems with the testes resulting in low testosterone concentrations. These physical and emotional conditions can lead to interruptions in the vasodilation pathway and result in an inability to achieve an erection.
Recall that the release of NO induces relaxation of the smooth muscles that surround the penile arteries, leading to the vasodilation necessary to achieve an erection. To reverse the process of vasodilation, an enzyme called phosphodiesterase (PDE) degrades a key component of the NO signaling pathway called cGMP. There are several different forms of this enzyme, and PDE type 5 is the type of PDE found in the tissues of the penis. Scientists discovered that inhibiting PDE5 increases blood flow, and allows vasodilation of the penis to occur.
PDEs and the vasodilation signaling pathway are found in the vasculature in other parts of the body. In the 1990s, clinical trials of a PDE5 inhibitor called sildenafil were initiated to treat hypertension and angina pectoris (chest pain caused by poor blood flow through the heart). The trial showed that the drug was not effective at treating heart conditions, but many men experienced erection and priapism (erection lasting longer than 4 hours). Because of this, a clinical trial was started to investigate the ability of sildenafil to promote erections in men suffering from ED. In 1998, the FDA approved the drug, marketed as Viagra®. Since approval of the drug, sildenafil and similar PDE inhibitors now generate over a billion dollars a year in sales, and are reported to be effective in treating approximately 70 to 85 percent of cases of ED. Importantly, men with health problems—especially those with cardiac disease taking nitrates—should avoid Viagra or talk to their physician to find out if they are a candidate for the use of this drug, as deaths have been reported for at-risk users.
Testosterone
Testosterone, an androgen, is a steroid hormone produced by Leydig cells. The alternate term for Leydig cells, interstitial cells, reflects their location between the seminiferous tubules in the testes. In male embryos, testosterone is secreted by Leydig cells by the seventh week of development, with peak concentrations reached in the second trimester. This early release of testosterone results in the anatomical differentiation of the male sexual organs. In childhood, testosterone concentrations are low. They increase during puberty, activating characteristic physical changes and initiating spermatogenesis.
Functions of Testosterone
The continued presence of testosterone is necessary to keep the male reproductive system working properly, and Leydig cells produce approximately 6 to 7 mg of testosterone per day. Testicular steroidogenesis (the manufacture of androgens, including testosterone) results in testosterone concentrations that are 100 times higher in the testes than in the circulation. Maintaining these normal concentrations of testosterone promotes spermatogenesis, whereas low levels of testosterone can lead to infertility. In addition to intratesticular secretion, testosterone is also released into the systemic circulation and plays an important role in muscle development, bone growth, the development of secondary sex characteristics, and maintaining libido (sex drive) in both males and females. In females, the ovaries secrete small amounts of testosterone, although most is converted to estradiol. A small amount of testosterone is also secreted by the adrenal glands in both sexes.
Control of Testosterone
The regulation of testosterone concentrations throughout the body is critical for male reproductive function. The intricate interplay between the endocrine system and the reproductive system is shown in Figure 27.8.
Figure 27.8 Regulation of Testosterone Production The hypothalamus and pituitary gland regulate the production of testosterone and the cells that assist in spermatogenesis. GnRH activates the anterior pituitary to produce LH and FSH, which in turn stimulate Leydig cells and Sertoli cells, respectively. The system is a negative feedback loop because the end products of the pathway, testosterone and inhibin, interact with the activity of GnRH to inhibit their own production.
The regulation of Leydig cell production of testosterone begins outside of the testes. The hypothalamus and the pituitary gland in the brain integrate external and internal signals to control testosterone synthesis and secretion. The regulation begins in the hypothalamus. Pulsatile release of a hormone called gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the endocrine release of hormones from the pituitary gland. Binding of GnRH to its receptors on the anterior pituitary gland stimulates release of the two gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These two hormones are critical for reproductive function in both men and women. In men, FSH binds predominantly to the Sertoli cells within the seminiferous tubules to promote spermatogenesis. FSH also stimulates the Sertoli cells to produce hormones called inhibins, which function to inhibit FSH release from the pituitary, thus reducing testosterone secretion. These polypeptide hormones correlate directly with Sertoli cell function and sperm number; inhibin B can be used as a marker of spermatogenic activity. In men, LH binds to receptors on Leydig cells in the testes and upregulates the production of testosterone.
A negative feedback loop predominantly controls the synthesis and secretion of both FSH and LH. Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the anterior pituitary to secrete LH into the bloodstream. In the testis, LH binds to LH receptors on Leydig cells and stimulates the release of testosterone. When concentrations of testosterone in the blood reach a critical threshold, testosterone itself will bind to androgen receptors on both the hypothalamus and the anterior pituitary, inhibiting the synthesis and secretion of GnRH and LH, respectively. When the blood concentrations of testosterone once again decline, testosterone no longer interacts with the receptors to the same degree and GnRH and LH are once again secreted, stimulating more testosterone production. This same process occurs with FSH and inhibin to control spermatogenesis.
AGING AND THE...
Male Reproductive System
Declines in Leydig cell activity can occur in men beginning at 40 to 50 years of age. The resulting reduction in circulating testosterone concentrations can lead to symptoms of andropause, also known as male menopause. While the reduction in sex steroids in men is akin to female menopause, there is no clear sign—such as a lack of a menstrual period—to denote the initiation of andropause. Instead, men report feelings of fatigue, reduced muscle mass, depression, anxiety, irritability, loss of libido, and insomnia. A reduction in spermatogenesis resulting in lowered fertility is also reported, and sexual dysfunction can also be associated with andropausal symptoms.
Whereas some researchers believe that certain aspects of andropause are difficult to tease apart from aging in general, testosterone replacement is sometimes prescribed to alleviate some symptoms. Recent studies have shown a benefit from androgen replacement therapy on the new onset of depression in elderly men; however, other studies caution against testosterone replacement for long-term treatment of andropause symptoms, showing that high doses can sharply increase the risk of both heart disease and prostate cancer.
Anatomy and Physiology of the Female Reproductive System
- Describe the structure and function of the organs of the female reproductive system
- List the steps of oogenesis
- Describe the hormonal changes that occur during the ovarian and menstrual cycles
- Trace the path of an oocyte from ovary to fertilization
The female reproductive system functions to produce gametes and reproductive hormones, just like the male reproductive system; however, it also has the additional task of supporting the developing fetus and delivering it to the outside world. Unlike its male counterpart, the female reproductive system is located primarily inside the pelvic cavity (Figure 27.9). Recall that the ovaries are the female gonads. The gamete they produce is called an oocyte. We’ll discuss the production of oocytes in detail shortly. First, let’s look at some of the structures of the female reproductive system.
Figure 27.9 Female Reproductive System The major organs of the female reproductive system are located inside the pelvic cavity.
External Female Genitals
The external female reproductive structures are referred to collectively as the vulva (Figure 27.10). The mons pubis is a pad of fat that is located at the anterior, over the pubic bone. After puberty, it becomes covered in pubic hair. The labia majora (labia = “lips”; majora = “larger”) are folds of hair-covered skin that begin just posterior to the mons pubis. The thinner and more pigmented labia minora (labia = “lips”; minora = “smaller”) extend medial to the labia majora. Although they naturally vary in shape and size from woman to woman, the labia minora serve to protect the female urethra and the entrance to the female reproductive tract.
The superior, anterior portions of the labia minora come together to encircle the clitoris (or glans clitoris), an organ that originates from the same cells as the glans penis and has abundant nerves that make it important in sexual sensation and orgasm. The hymen is a thin membrane that sometimes partially covers the entrance to the vagina. An intact hymen cannot be used as an indication of “virginity”; even at birth, this is only a partial membrane, as menstrual fluid and other secretions must be able to exit the body, regardless of penile–vaginal intercourse. The vaginal opening is located between the opening of the urethra and the anus. It is flanked by outlets to the Bartholin’s glands (or greater vestibular glands).
Figure 27.10 The Vulva The external female genitalia are referred to collectively as the vulva.
Vagina
The vagina, shown at the bottom of Figure 27.9 and Figure 27.9, is a muscular canal (approximately 10 cm long) that serves as the entrance to the reproductive tract. It also serves as the exit from the uterus during menses and childbirth. The outer walls of the anterior and posterior vagina are formed into longitudinal columns, or ridges, and the superior portion of the vagina—called the fornix—meets the protruding uterine cervix. The walls of the vagina are lined with an outer, fibrous adventitia; a middle layer of smooth muscle; and an inner mucous membrane with transverse folds called rugae. Together, the middle and inner layers allow the expansion of the vagina to accommodate intercourse and childbirth. The thin, perforated hymen can partially surround the opening to the vaginal orifice. The hymen can be ruptured with strenuous physical exercise, penile–vaginal intercourse, and childbirth. The Bartholin’s glands and the lesser vestibular glands (located near the clitoris) secrete mucus, which keeps the vestibular area moist.
The vagina is home to a normal population of microorganisms that help to protect against infection by pathogenic bacteria, yeast, or other organisms that can enter the vagina. In a healthy woman, the most predominant type of vaginal bacteria is from the genus Lactobacillus. This family of beneficial bacterial flora secretes lactic acid, and thus protects the vagina by maintaining an acidic pH (below 4.5). Potential pathogens are less likely to survive in these acidic conditions. Lactic acid, in combination with other vaginal secretions, makes the vagina a self-cleansing organ. However, douching—or washing out the vagina with fluid—can disrupt the normal balance of healthy microorganisms, and actually increase a woman’s risk for infections and irritation. Indeed, the American College of Obstetricians and Gynecologists recommend that women do not douche, and that they allow the vagina to maintain its normal healthy population of protective microbial flora.
Ovaries
The ovaries are the female gonads (see Figure 27.9). Paired ovals, they are each about 2 to 3 cm in length, about the size of an almond. The ovaries are located within the pelvic cavity, and are supported by the mesovarium, an extension of the peritoneum that connects the ovaries to the broad ligament. Extending from the mesovarium itself is the suspensory ligament that contains the ovarian blood and lymph vessels. Finally, the ovary itself is attached to the uterus via the ovarian ligament.
The ovary comprises an outer covering of cuboidal epithelium called the ovarian surface epithelium that is superficial to a dense connective tissue covering called the tunica albuginea. Beneath the tunica albuginea is the cortex, or outer portion, of the organ. The cortex is composed of a tissue framework called the ovarian stroma that forms the bulk of the adult ovary. Oocytes develop within the outer layer of this stroma, each surrounded by supporting cells. This grouping of an oocyte and its supporting cells is called a follicle. The growth and development of ovarian follicles will be described shortly. Beneath the cortex lies the inner ovarian medulla, the site of blood vessels, lymph vessels, and the nerves of the ovary. You will learn more about the overall anatomy of the female reproductive system at the end of this section.
The Ovarian Cycle
The ovarian cycle is a set of predictable changes in a female’s oocytes and ovarian follicles. During a woman’s reproductive years, it is a roughly 28-day cycle that can be correlated with, but is not the same as, the menstrual cycle (discussed shortly). The cycle includes two interrelated processes: oogenesis (the production of female gametes) and folliculogenesis (the growth and development of ovarian follicles).
Oogenesis
Gametogenesis in females is called oogenesis. The process begins with the ovarian stem cells, or oogonia (Figure 27.11). Oogonia are formed during fetal development, and divide via mitosis, much like spermatogonia in the testis. Unlike spermatogonia, however, oogonia form primary oocytes in the fetal ovary prior to birth. These primary oocytes are then arrested in this stage of meiosis I, only to resume it years later, beginning at puberty and continuing until the woman is near menopause (the cessation of a woman’s reproductive functions). The number of primary oocytes present in the ovaries declines from one to two million in an infant, to approximately 400,000 at puberty, to zero by the end of menopause.
The initiation of ovulation—the release of an oocyte from the ovary—marks the transition from puberty into reproductive maturity for women. From then on, throughout a woman’s reproductive years, ovulation occurs approximately once every 28 days. Just prior to ovulation, a surge of luteinizing hormone triggers the resumption of meiosis in a primary oocyte. This initiates the transition from primary to secondary oocyte. However, as you can see in Figure 27.11, this cell division does not result in two identical cells. Instead, the cytoplasm is divided unequally, and one daughter cell is much larger than the other. This larger cell, the secondary oocyte, eventually leaves the ovary during ovulation. The smaller cell, called the first polar body, may or may not complete meiosis and produce second polar bodies; in either case, it eventually disintegrates. Therefore, even though oogenesis produces up to four cells, only one survives.
Figure 27.11 Oogenesis The unequal cell division of oogenesis produces one to three polar bodies that later degrade, as well as a single haploid ovum, which is produced only if there is penetration of the secondary oocyte by a sperm cell.
How does the diploid secondary oocyte become an ovum—the haploid female gamete? Meiosis of a secondary oocyte is completed only if a sperm succeeds in penetrating its barriers. Meiosis II then resumes, producing one haploid ovum that, at the instant of fertilization by a (haploid) sperm, becomes the first diploid cell of the new offspring (a zygote). Thus, the ovum can be thought of as a brief, transitional, haploid stage between the diploid oocyte and diploid zygote.
The larger amount of cytoplasm contained in the female gamete is used to supply the developing zygote with nutrients during the period between fertilization and implantation into the uterus. Interestingly, sperm contribute only DNA at fertilization —not cytoplasm. Therefore, the cytoplasm and all of the cytoplasmic organelles in the developing embryo are of maternal origin. This includes mitochondria, which contain their own DNA. Scientific research in the 1980s determined that mitochondrial DNA was maternally inherited, meaning that you can trace your mitochondrial DNA directly to your mother, her mother, and so on back through your female ancestors.
EVERYDAY CONNECTION
Mapping Human History with Mitochondrial DNA
When we talk about human DNA, we’re usually referring to nuclear DNA; that is, the DNA coiled into chromosomal bundles in the nucleus of our cells. We inherit half of our nuclear DNA from our father, and half from our mother. However, mitochondrial DNA (mtDNA) comes only from the mitochondria in the cytoplasm of the fat ovum we inherit from our mother. She received her mtDNA from her mother, who got it from her mother, and so on. Each of our cells contains approximately 1700 mitochondria, with each mitochondrion packed with mtDNA containing approximately 37 genes.
Mutations (changes) in mtDNA occur spontaneously in a somewhat organized pattern at regular intervals in human history. By analyzing these mutational relationships, researchers have been able to determine that we can all trace our ancestry back to one woman who lived in Africa about 200,000 years ago. Scientists have given this woman the biblical name Eve, although she is not, of course, the first Homo sapiens female. More precisely, she is our most recent common ancestor through matrilineal descent.
This doesn’t mean that everyone’s mtDNA today looks exactly like that of our ancestral Eve. Because of the spontaneous mutations in mtDNA that have occurred over the centuries, researchers can map different “branches” off of the “main trunk” of our mtDNA family tree. Your mtDNA might have a pattern of mutations that aligns more closely with one branch, and your neighbor’s may align with another branch. Still, all branches eventually lead back to Eve.
But what happened to the mtDNA of all of the other Homo sapiens females who were living at the time of Eve? Researchers explain that, over the centuries, their female descendants died childless or with only male children, and thus, their maternal line—and its mtDNA—ended.
Folliculogenesis
Again, ovarian follicles are oocytes and their supporting cells. They grow and develop in a process called folliculogenesis, which typically leads to ovulation of one follicle approximately every 28 days, along with death to multiple other follicles. The death of ovarian follicles is called atresia, and can occur at any point during follicular development. Recall that, a female infant at birth will have one to two million oocytes within her ovarian follicles, and that this number declines throughout life until menopause, when no follicles remain. As you’ll see next, follicles progress from primordial, to primary, to secondary and tertiary stages prior to ovulation—with the oocyte inside the follicle remaining as a primary oocyte until right before ovulation.
Folliculogenesis begins with follicles in a resting state. These small primordial follicles are present in newborn females and are the prevailing follicle type in the adult ovary (Figure 27.12). Primordial follicles have only a single flat layer of support cells, called granulosa cells, that surround the oocyte, and they can stay in this resting state for years—some until right before menopause.
After puberty, a few primordial follicles will respond to a recruitment signal each day, and will join a pool of immature growing follicles called primary follicles. Primary follicles start with a single layer of granulosa cells, but the granulosa cells then become active and transition from a flat or squamous shape to a rounded, cuboidal shape as they increase in size and proliferate. As the granulosa cells divide, the follicles—now called secondary follicles (see Figure 27.12)—increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells—cells that work with the granulosa cells to produce estrogens.
Within the growing secondary follicle, the primary oocyte now secretes a thin acellular membrane called the zona pellucida that will play a critical role in fertilization. A thick fluid, called follicular fluid, that has formed between the granulosa cells also begins to collect into one large pool, or antrum. Follicles in which the antrum has become large and fully formed are considered tertiary follicles (or antral follicles). Several follicles reach the tertiary stage at the same time, and most of these will undergo atresia. The one that does not die will continue to grow and develop until ovulation, when it will expel its secondary oocyte surrounded by several layers of granulosa cells from the ovary. Keep in mind that most follicles don’t make it to this point. In fact, roughly 99 percent of the follicles in the ovary will undergo atresia, which can occur at any stage of folliculogenesis.
Figure 27.12 Folliculogenesis (a) The maturation of a follicle is shown in a clockwise direction proceeding from the primordial follicles. FSH stimulates the growth of a tertiary follicle, and LH stimulates the production of estrogen by granulosa and theca cells. Once the follicle is mature, it ruptures and releases the oocyte. Cells remaining in the follicle then develop into the corpus luteum. (b) In this electron micrograph of a secondary follicle, the oocyte, theca cells (thecae folliculi), and developing antrum are clearly visible. EM × 1100. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Hormonal Control of the Ovarian Cycle
The process of development that we have just described, from primordial follicle to early tertiary follicle, takes approximately two months in humans. The final stages of development of a small cohort of tertiary follicles, ending with ovulation of a secondary oocyte, occur over a course of approximately 28 days. These changes are regulated by many of the same hormones that regulate the male reproductive system, including GnRH, LH, and FSH.
As in men, the hypothalamus produces GnRH, a hormone that signals the anterior pituitary gland to produce the gonadotropins FSH and LH (Figure 27.13). These gonadotropins leave the pituitary and travel through the bloodstream to the ovaries, where they bind to receptors on the granulosa and theca cells of the follicles. FSH stimulates the follicles to grow (hence its name of follicle-stimulating hormone), and the five or six tertiary follicles expand in diameter. The release of LH also stimulates the granulosa and theca cells of the follicles to produce the sex steroid hormone estradiol, a type of estrogen. This phase of the ovarian cycle, when the tertiary follicles are growing and secreting estrogen, is known as the follicular phase.
The more granulosa and theca cells a follicle has (that is, the larger and more developed it is), the more estrogen it will produce in response to LH stimulation. As a result of these large follicles producing large amounts of estrogen, systemic plasma estrogen concentrations increase. Following a classic negative feedback loop, the high concentrations of estrogen will stimulate the hypothalamus and pituitary to reduce the production of GnRH, LH, and FSH. Because the large tertiary follicles require FSH to grow and survive at this point, this decline in FSH caused by negative feedback leads most of them to die (atresia). Typically only one follicle, now called the dominant follicle, will survive this reduction in FSH, and this follicle will be the one that releases an oocyte. Scientists have studied many factors that lead to a particular follicle becoming dominant: size, the number of granulosa cells, and the number of FSH receptors on those granulosa cells all contribute to a follicle becoming the one surviving dominant follicle.
Figure 27.13 Hormonal Regulation of Ovulation The hypothalamus and pituitary gland regulate the ovarian cycle and ovulation. GnRH activates the anterior pituitary to produce LH and FSH, which stimulate the production of estrogen and progesterone by the ovaries.
When only the one dominant follicle remains in the ovary, it again begins to secrete estrogen. It produces more estrogen than all of the developing follicles did together before the negative feedback occurred. It produces so much estrogen that the normal negative feedback doesn’t occur. Instead, these extremely high concentrations of systemic plasma estrogen trigger a regulatory switch in the anterior pituitary that responds by secreting large amounts of LH and FSH into the bloodstream (see Figure 27.13). The positive feedback loop by which more estrogen triggers release of more LH and FSH only occurs at this point in the cycle.
It is this large burst of LH (called the LH surge) that leads to ovulation of the dominant follicle. The LH surge induces many changes in the dominant follicle, including stimulating the resumption of meiosis of the primary oocyte to a secondary oocyte. As noted earlier, the polar body that results from unequal cell division simply degrades. The LH surge also triggers proteases (enzymes that cleave proteins) to break down structural proteins in the ovary wall on the surface of the bulging dominant follicle. This degradation of the wall, combined with pressure from the large, fluid-filled antrum, results in the expulsion of the oocyte surrounded by granulosa cells into the peritoneal cavity. This release is ovulation.
In the next section, you will follow the ovulated oocyte as it travels toward the uterus, but there is one more important event that occurs in the ovarian cycle. The surge of LH also stimulates a change in the granulosa and theca cells that remain in the follicle after the oocyte has been ovulated. This change is called luteinization (recall that the full name of LH is luteinizing hormone), and it transforms the collapsed follicle into a new endocrine structure called the corpus luteum, a term meaning “yellowish body” (see Figure 27.12). Instead of estrogen, the luteinized granulosa and theca cells of the corpus luteum begin to produce large amounts of the sex steroid hormone progesterone, a hormone that is critical for the establishment and maintenance of pregnancy. Progesterone triggers negative feedback at the hypothalamus and pituitary, which keeps GnRH, LH, and FSH secretions low, so no new dominant follicles develop at this time.
The post-ovulatory phase of progesterone secretion is known as the luteal phase of the ovarian cycle. If pregnancy does not occur within 10 to 12 days, the corpus luteum will stop secreting progesterone and degrade into the corpus albicans, a nonfunctional “whitish body” that will disintegrate in the ovary over a period of several months. During this time of reduced progesterone secretion, FSH and LH are once again stimulated, and the follicular phase begins again with a new cohort of early tertiary follicles beginning to grow and secrete estrogen.
The Uterine Tubes
The uterine tubes (also called fallopian tubes or oviducts) serve as the conduit of the oocyte from the ovary to the uterus (Figure 27.14). Each of the two uterine tubes is close to, but not directly connected to, the ovary and divided into sections. The isthmus is the narrow medial end of each uterine tube that is connected to the uterus. The wide distal infundibulum flares out with slender, finger-like projections called fimbriae. The middle region of the tube, called the ampulla, is where fertilization often occurs. The uterine tubes also have three layers: an outer serosa, a middle smooth muscle layer, and an inner mucosal layer. In addition to its mucus-secreting cells, the inner mucosa contains ciliated cells that beat in the direction of the uterus, producing a current that will be critical to move the oocyte.
Following ovulation, the secondary oocyte surrounded by a few granulosa cells is released into the peritoneal cavity. The nearby uterine tube, either left or right, receives the oocyte. Unlike sperm, oocytes lack flagella, and therefore cannot move on their own. So how do they travel into the uterine tube and toward the uterus? High concentrations of estrogen that occur around the time of ovulation induce contractions of the smooth muscle along the length of the uterine tube. These contractions occur every 4 to 8 seconds, and the result is a coordinated movement that sweeps the surface of the ovary and the pelvic cavity. Current flowing toward the uterus is generated by coordinated beating of the cilia that line the outside and lumen of the length of the uterine tube. These cilia beat more strongly in response to the high estrogen concentrations that occur around the time of ovulation. As a result of these mechanisms, the oocyte–granulosa cell complex is pulled into the interior of the tube. Once inside, the muscular contractions and beating cilia move the oocyte slowly toward the uterus. When fertilization does occur, sperm typically meet the egg while it is still moving through the ampulla.
INTERACTIVE LINK
Watch this video to observe ovulation and its initiation in response to the release of FSH and LH from the pituitary gland. What specialized structures help guide the oocyte from the ovary into the uterine tube?
If the oocyte is successfully fertilized, the resulting zygote will begin to divide into two cells, then four, and so on, as it makes its way through the uterine tube and into the uterus. There, it will implant and continue to grow. If the egg is not fertilized, it will simply degrade—either in the uterine tube or in the uterus, where it may be shed with the next menstrual period.
Figure 27.14 Ovaries, Uterine Tubes, and Uterus This anterior view shows the relationship of the ovaries, uterine tubes (oviducts), and uterus. Sperm enter through the vagina, and fertilization of an ovulated oocyte usually occurs in the distal uterine tube. From left to right, LM × 400, LM × 20. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)
The open-ended structure of the uterine tubes can have significant health consequences if bacteria or other contagions enter through the vagina and move through the uterus, into the tubes, and then into the pelvic cavity. If this is left unchecked, a bacterial infection (sepsis) could quickly become life-threatening. The spread of an infection in this manner is of special concern when unskilled practitioners perform abortions in non-sterile conditions. Sepsis is also associated with sexually transmitted bacterial infections, especially gonorrhea and chlamydia. These increase a woman’s risk for pelvic inflammatory disease (PID), infection of the uterine tubes or other reproductive organs. Even when resolved, PID can leave scar tissue in the tubes, leading to infertility.
INTERACTIVE LINK
Watch this series of videos to look at the movement of the oocyte through the ovary. The cilia in the uterine tube promote movement of the oocyte. What would likely occur if the cilia were paralyzed at the time of ovulation?
The Uterus and Cervix
The uterus is the muscular organ that nourishes and supports the growing embryo (see Figure 27.14). Its average size is approximately 5 cm wide by 7 cm long (approximately 2 in by 3 in) when a female is not pregnant. It has three sections. The portion of the uterus superior to the opening of the uterine tubes is called the fundus. The middle section of the uterus is called the body of uterus (or corpus). The cervix is the narrow inferior portion of the uterus that projects into the vagina. The cervix produces mucus secretions that become thin and stringy under the influence of high systemic plasma estrogen concentrations, and these secretions can facilitate sperm movement through the reproductive tract.
Several ligaments maintain the position of the uterus within the abdominopelvic cavity. The broad ligament is a fold of peritoneum that serves as a primary support for the uterus, extending laterally from both sides of the uterus and attaching it to the pelvic wall. The round ligament attaches to the uterus near the uterine tubes, and extends to the labia majora. Finally, the uterosacral ligament stabilizes the uterus posteriorly by its connection from the cervix to the pelvic wall.
The wall of the uterus is made up of three layers. The most superficial layer is the serous membrane, or perimetrium, which consists of epithelial tissue that covers the exterior portion of the uterus. The middle layer, or myometrium, is a thick layer of smooth muscle responsible for uterine contractions. Most of the uterus is myometrial tissue, and the muscle fibers run horizontally, vertically, and diagonally, allowing the powerful contractions that occur during labor and the less powerful contractions (or cramps) that help to expel menstrual blood during a woman’s period. Anteriorly directed myometrial contractions also occur near the time of ovulation, and are thought to possibly facilitate the transport of sperm through the female reproductive tract.
The innermost layer of the uterus is called the endometrium. The endometrium contains a connective tissue lining, the lamina propria, which is covered by epithelial tissue that lines the lumen. Structurally, the endometrium consists of two layers: the stratum basalis and the stratum functionalis (the basal and functional layers). The stratum basalis layer is part of the lamina propria and is adjacent to the myometrium; this layer does not shed during menses. In contrast, the thicker stratum functionalis layer contains the glandular portion of the lamina propria and the endothelial tissue that lines the uterine lumen. It is the stratum functionalis that grows and thickens in response to increased levels of estrogen and progesterone. In the luteal phase of the menstrual cycle, special branches off of the uterine artery called spiral arteries supply the thickened stratum functionalis. This inner functional layer provides the proper site of implantation for the fertilized egg, and—should fertilization not occur—it is only the stratum functionalis layer of the endometrium that sheds during menstruation.
Recall that during the follicular phase of the ovarian cycle, the tertiary follicles are growing and secreting estrogen. At the same time, the stratum functionalis of the endometrium is thickening to prepare for a potential implantation. The post-ovulatory increase in progesterone, which characterizes the luteal phase, is key for maintaining a thick stratum functionalis. As long as a functional corpus luteum is present in the ovary, the endometrial lining is prepared for implantation. Indeed, if an embryo implants, signals are sent to the corpus luteum to continue secreting progesterone to maintain the endometrium, and thus maintain the pregnancy. If an embryo does not implant, no signal is sent to the corpus luteum and it degrades, ceasing progesterone production and ending the luteal phase. Without progesterone, the endometrium thins and, under the influence of prostaglandins, the spiral arteries of the endometrium constrict and rupture, preventing oxygenated blood from reaching the endometrial tissue. As a result, endometrial tissue dies and blood, pieces of the endometrial tissue, and white blood cells are shed through the vagina during menstruation, or the menses. The first menses after puberty, called menarche, can occur either before or after the first ovulation.
The Menstrual Cycle
Now that we have discussed the maturation of the cohort of tertiary follicles in the ovary, the build-up and then shedding of the endometrial lining in the uterus, and the function of the uterine tubes and vagina, we can put everything together to talk about the three phases of the menstrual cycle—the series of changes in which the uterine lining is shed, rebuilds, and prepares for implantation.
The timing of the menstrual cycle starts with the first day of menses, referred to as day one of a woman’s period. Cycle length is determined by counting the days between the onset of bleeding in two subsequent cycles. Because the average length of a woman’s menstrual cycle is 28 days, this is the time period used to identify the timing of events in the cycle. However, the length of the menstrual cycle varies among women, and even in the same woman from one cycle to the next, typically from 21 to 32 days.
Just as the hormones produced by the granulosa and theca cells of the ovary “drive” the follicular and luteal phases of the ovarian cycle, they also control the three distinct phases of the menstrual cycle. These are the menses phase, the proliferative phase, and the secretory phase.
Menses Phase
The menses phase of the menstrual cycle is the phase during which the lining is shed; that is, the days that the woman menstruates. Although it averages approximately five days, the menses phase can last from 2 to 7 days, or longer. As shown in Figure 27.15, the menses phase occurs during the early days of the follicular phase of the ovarian cycle, when progesterone, FSH, and LH levels are low. Recall that progesterone concentrations decline as a result of the degradation of the corpus luteum, marking the end of the luteal phase. This decline in progesterone triggers the shedding of the stratum functionalis of the endometrium.
Figure 27.15 Hormone Levels in Ovarian and Menstrual Cycles The correlation of the hormone levels and their effects on the female reproductive system is shown in this timeline of the ovarian and menstrual cycles. The menstrual cycle begins at day one with the start of menses. Ovulation occurs around day 14 of a 28-day cycle, triggered by the LH surge.
Proliferative Phase
Once menstrual flow ceases, the endometrium begins to proliferate again, marking the beginning of the proliferative phase of the menstrual cycle (see Figure 27.15). It occurs when the granulosa and theca cells of the tertiary follicles begin to produce increased amounts of estrogen. These rising estrogen concentrations stimulate the endometrial lining to rebuild.
Recall that the high estrogen concentrations will eventually lead to a decrease in FSH as a result of negative feedback, resulting in atresia of all but one of the developing tertiary follicles. The switch to positive feedback—which occurs with the elevated estrogen production from the dominant follicle—then stimulates the LH surge that will trigger ovulation. In a typical 28-day menstrual cycle, ovulation occurs on day 14. Ovulation marks the end of the proliferative phase as well as the end of the follicular phase.
Secretory Phase
In addition to prompting the LH surge, high estrogen levels increase the uterine tube contractions that facilitate the pick-up and transfer of the ovulated oocyte. High estrogen levels also slightly decrease the acidity of the vagina, making it more hospitable to sperm. In the ovary, the luteinization of the granulosa cells of the collapsed follicle forms the progesterone-producing corpus luteum, marking the beginning of the luteal phase of the ovarian cycle. In the uterus, progesterone from the corpus luteum begins the secretory phase of the menstrual cycle, in which the endometrial lining prepares for implantation (see Figure 27.15). Over the next 10 to 12 days, the endometrial glands secrete a fluid rich in glycogen. If fertilization has occurred, this fluid will nourish the ball of cells now developing from the zygote. At the same time, the spiral arteries develop to provide blood to the thickened stratum functionalis.
If no pregnancy occurs within approximately 10 to 12 days, the corpus luteum will degrade into the corpus albicans. Levels of both estrogen and progesterone will fall, and the endometrium will grow thinner. Prostaglandins will be secreted that cause constriction of the spiral arteries, reducing oxygen supply. The endometrial tissue will die, resulting in menses—or the first day of the next cycle.
DISORDERS OF THE...
Female Reproductive System
Research over many years has confirmed that cervical cancer is most often caused by a sexually transmitted infection with human papillomavirus (HPV). There are over 100 related viruses in the HPV family, and the characteristics of each strain determine the outcome of the infection. In all cases, the virus enters body cells and uses its own genetic material to take over the host cell’s metabolic machinery and produce more virus particles.
HPV infections are common in both men and women. Indeed, a recent study determined that 42.5 percent of females had HPV at the time of testing. These women ranged in age from 14 to 59 years and differed in race, ethnicity, and number of sexual partners. Of note, the prevalence of HPV infection was 53.8 percent among women aged 20 to 24 years, the age group with the highest infection rate.
HPV strains are classified as high or low risk according to their potential to cause cancer. Though most HPV infections do not cause disease, the disruption of normal cellular functions in the low-risk forms of HPV can cause the male or female human host to develop genital warts. Often, the body is able to clear an HPV infection by normal immune responses within 2 years. However, the more serious, high-risk infection by certain types of HPV can result in cancer of the cervix (Figure 27.16). Infection with either of the cancer-causing variants HPV 16 or HPV 18 has been linked to more than 70 percent of all cervical cancer diagnoses. Although even these high-risk HPV strains can be cleared from the body over time, infections persist in some individuals. If this happens, the HPV infection can influence the cells of the cervix to develop precancerous changes.
Risk factors for cervical cancer include having unprotected sex; having multiple sexual partners; a first sexual experience at a younger age, when the cells of the cervix are not fully mature; failure to receive the HPV vaccine; a compromised immune system; and smoking. The risk of developing cervical cancer is doubled with cigarette smoking.
Figure 27.16 Development of Cervical Cancer In most cases, cells infected with the HPV virus heal on their own. In some cases, however, the virus continues to spread and becomes an invasive cancer.
When the high-risk types of HPV enter a cell, two viral proteins are used to neutralize proteins that the host cells use as checkpoints in the cell cycle. The best studied of these proteins is p53. In a normal cell, p53 detects DNA damage in the cell’s genome and either halts the progression of the cell cycle—allowing time for DNA repair to occur—or initiates apoptosis. Both of these processes prevent the accumulation of mutations in a cell’s genome. High-risk HPV can neutralize p53, keeping the cell in a state in which fast growth is possible and impairing apoptosis, allowing mutations to accumulate in the cellular DNA.
The prevalence of cervical cancer in the United States is very low because of regular screening exams called pap smears. Pap smears sample cells of the cervix, allowing the detection of abnormal cells. If pre-cancerous cells are detected, there are several highly effective techniques that are currently in use to remove them before they pose a danger. However, women in developing countries often do not have access to regular pap smears. As a result, these women account for as many as 80 percent of the cases of cervical cancer worldwide.
In 2006, the first vaccine against the high-risk types of HPV was approved. There are now two HPV vaccines available: Gardasil® and Cervarix®. Whereas these vaccines were initially only targeted for women, because HPV is sexually transmitted, both men and women require vaccination for this approach to achieve its maximum efficacy. A recent study suggests that the HPV vaccine has cut the rates of HPV infection by the four targeted strains at least in half. Unfortunately, the high cost of manufacturing the vaccine is currently limiting access to many women worldwide.
The Breasts
Whereas the breasts are located far from the other female reproductive organs, they are considered accessory organs of the female reproductive system. The function of the breasts is to supply milk to an infant in a process called lactation. The external features of the breast include a nipple surrounded by a pigmented areola (Figure 27.17), whose coloration may deepen during pregnancy. The areola is typically circular and can vary in size from 25 to 100 mm in diameter. The areolar region is characterized by small, raised areolar glands that secrete lubricating fluid during lactation to protect the nipple from chafing. When a baby nurses, or draws milk from the breast, the entire areolar region is taken into the mouth.
Breast milk is produced by the mammary glands, which are modified sweat glands. The milk itself exits the breast through the nipple via 15 to 20 lactiferous ducts that open on the surface of the nipple. These lactiferous ducts each extend to a lactiferous sinus that connects to a glandular lobe within the breast itself that contains groups of milk-secreting cells in clusters called alveoli (see Figure 27.17). The clusters can change in size depending on the amount of milk in the alveolar lumen. Once milk is made in the alveoli, stimulated myoepithelial cells that surround the alveoli contract to push the milk to the lactiferous sinuses. From here, the baby can draw milk through the lactiferous ducts by suckling. The lobes themselves are surrounded by fat tissue, which determines the size of the breast; breast size differs between individuals and does not affect the amount of milk produced. Supporting the breasts are multiple bands of connective tissue called suspensory ligaments that connect the breast tissue to the dermis of the overlying skin.
Figure 27.17 Anatomy of the Breast During lactation, milk moves from the alveoli through the lactiferous ducts to the nipple.
During the normal hormonal fluctuations in the menstrual cycle, breast tissue responds to changing levels of estrogen and progesterone, which can lead to swelling and breast tenderness in some individuals, especially during the secretory phase. If pregnancy occurs, the increase in hormones leads to further development of the mammary tissue and enlargement of the breasts.
Hormonal Birth Control
Birth control pills take advantage of the negative feedback system that regulates the ovarian and menstrual cycles to stop ovulation and prevent pregnancy. Typically they work by providing a constant level of both estrogen and progesterone, which negatively feeds back onto the hypothalamus and pituitary, thus preventing the release of FSH and LH. Without FSH, the follicles do not mature, and without the LH surge, ovulation does not occur. Although the estrogen in birth control pills does stimulate some thickening of the endometrial wall, it is reduced compared with a normal cycle and is less likely to support implantation.
Some birth control pills contain 21 active pills containing hormones, and 7 inactive pills (placebos). The decline in hormones during the week that the woman takes the placebo pills triggers menses, although it is typically lighter than a normal menstrual flow because of the reduced endometrial thickening. Newer types of birth control pills have been developed that deliver low-dose estrogens and progesterone for the entire cycle (these are meant to be taken 365 days a year), and menses never occurs. While some women prefer to have the proof of a lack of pregnancy that a monthly period provides, menstruation every 28 days is not required for health reasons, and there are no reported adverse effects of not having a menstrual period in an otherwise healthy individual.
Because birth control pills function by providing constant estrogen and progesterone levels and disrupting negative feedback, skipping even just one or two pills at certain points of the cycle (or even being several hours late taking the pill) can lead to an increase in FSH and LH and result in ovulation. It is important, therefore, that the woman follow the directions on the birth control pill package to successfully prevent pregnancy.
AGING AND THE...
Female Reproductive System
Female fertility (the ability to conceive) peaks when women are in their twenties, and is slowly reduced until a women reaches 35 years of age. After that time, fertility declines more rapidly, until it ends completely at the end of menopause. Menopause is the cessation of the menstrual cycle that occurs as a result of the loss of ovarian follicles and the hormones that they produce. A woman is considered to have completed menopause if she has not menstruated in a full year. After that point, she is considered postmenopausal. The average age for this change is consistent worldwide at between 50 and 52 years of age, but it can normally occur in a woman’s forties, or later in her fifties. Poor health, including smoking, can lead to earlier loss of fertility and earlier menopause.
As a woman reaches the age of menopause, depletion of the number of viable follicles in the ovaries due to atresia affects the hormonal regulation of the menstrual cycle. During the years leading up to menopause, there is a decrease in the levels of the hormone inhibin, which normally participates in a negative feedback loop to the pituitary to control the production of FSH. The menopausal decrease in inhibin leads to an increase in FSH. The presence of FSH stimulates more follicles to grow and secrete estrogen. Because small, secondary follicles also respond to increases in FSH levels, larger numbers of follicles are stimulated to grow; however, most undergo atresia and die. Eventually, this process leads to the depletion of all follicles in the ovaries, and the production of estrogen falls off dramatically. It is primarily the lack of estrogens that leads to the symptoms of menopause.
The earliest changes occur during the menopausal transition, often referred to as peri-menopause, when a women’s cycle becomes irregular but does not stop entirely. Although the levels of estrogen are still nearly the same as before the transition, the level of progesterone produced by the corpus luteum is reduced. This decline in progesterone can lead to abnormal growth, or hyperplasia, of the endometrium. This condition is a concern because it increases the risk of developing endometrial cancer. Two harmless conditions that can develop during the transition are uterine fibroids, which are benign masses of cells, and irregular bleeding. As estrogen levels change, other symptoms that occur are hot flashes and night sweats, trouble sleeping, vaginal dryness, mood swings, difficulty focusing, and thinning of hair on the head along with the growth of more hair on the face. Depending on the individual, these symptoms can be entirely absent, moderate, or severe.
After menopause, lower amounts of estrogens can lead to other changes. Cardiovascular disease becomes as prevalent in women as in men, possibly because estrogens reduce the amount of cholesterol in the blood vessels. When estrogen is lacking, many women find that they suddenly have problems with high cholesterol and the cardiovascular issues that accompany it. Osteoporosis is another problem because bone density decreases rapidly in the first years after menopause. The reduction in bone density leads to a higher incidence of fractures.
Hormone therapy (HT), which employs medication (synthetic estrogens and progestins) to increase estrogen and progestin levels, can alleviate some of the symptoms of menopause. In 2002, the Women’s Health Initiative began a study to observe women for the long-term outcomes of hormone replacement therapy over 8.5 years. However, the study was prematurely terminated after 5.2 years because of evidence of a higher than normal risk of breast cancer in patients taking estrogen-only HT. The potential positive effects on cardiovascular disease were also not realized in the estrogen-only patients. The results of other hormone replacement studies over the last 50 years, including a 2012 study that followed over 1,000 menopausal women for 10 years, have shown cardiovascular benefits from estrogen and no increased risk for cancer. Some researchers believe that the age group tested in the 2002 trial may have been too old to benefit from the therapy, thus skewing the results. In the meantime, intense debate and study of the benefits and risks of replacement therapy is ongoing. Current guidelines approve HT for the reduction of hot flashes or flushes, but this treatment is generally only considered when women first start showing signs of menopausal changes, is used in the lowest dose possible for the shortest time possible (5 years or less), and it is suggested that women on HT have regular pelvic and breast exams.
Development of the Male and Female Reproductive Systems
- Explain how bipotential tissues are directed to develop into male or female sex organs
- Name the rudimentary duct systems in the embryo that are precursors to male or female internal sex organs
- Describe the hormonal changes that bring about puberty, and the secondary sex characteristics of men and women
The development of the reproductive systems begins soon after fertilization of the egg, with primordial gonads beginning to develop approximately one month after conception. Reproductive development continues in utero, but there is little change in the reproductive system between infancy and puberty.
Development of the Sexual Organs in the Embryo and Fetus
Females are considered the “fundamental” sex—that is, without much chemical prompting, all fertilized eggs would develop into females. To become a male, an individual must be exposed to the cascade of factors initiated by a single gene on the male Y chromosome. This is called the SRY (Sex-determining Region of the Y chromosome). Because females do not have a Y chromosome, they do not have the SRY gene. Without a functional SRY gene, an individual will be female.
In both male and female embryos, the same group of cells has the potential to develop into either the male or female gonads; this tissue is considered bipotential. The SRY gene actively recruits other genes that begin to develop the testes, and suppresses genes that are important in female development. As part of this SRY-prompted cascade, germ cells in the bipotential gonads differentiate into spermatogonia. Without SRY, different genes are expressed, oogonia form, and primordial follicles develop in the primitive ovary.
Soon after the formation of the testis, the Leydig cells begin to secrete testosterone. Testosterone can influence tissues that are bipotential to become male reproductive structures. For example, with exposure to testosterone, cells that could become either the glans penis or the glans clitoris form the glans penis. Without testosterone, these same cells differentiate into the clitoris.
Not all tissues in the reproductive tract are bipotential. The internal reproductive structures (for example the uterus, uterine tubes, and part of the vagina in females; and the epididymis, ductus deferens, and seminal vesicles in males) form from one of two rudimentary duct systems in the embryo. For proper reproductive function in the adult, one set of these ducts must develop properly, and the other must degrade. In males, secretions from sustentacular cells trigger a degradation of the female duct, called the Müllerian duct. At the same time, testosterone secretion stimulates growth of the male tract, the Wolffian duct. Without such sustentacular cell secretion, the Müllerian duct will develop; without testosterone, the Wolffian duct will degrade. Thus, the developing offspring will be female. For more information and a figure of differentiation of the gonads, seek additional content on fetal development.
INTERACTIVE LINK
A baby’s gender is determined at conception, and the different genitalia of male and female fetuses develop from the same tissues in the embryo. View this animation to see a comparison of the development of structures of the female and male reproductive systems in a growing fetus. Where are the testes located for most of gestational time?
Further Sexual Development Occurs at Puberty
Puberty is the stage of development at which individuals become sexually mature. Though the outcomes of puberty for boys and girls are very different, the hormonal control of the process is very similar. In addition, though the timing of these events varies between individuals, the sequence of changes that occur is predictable for male and female adolescents. As shown in Figure 27.18, a concerted release of hormones from the hypothalamus (GnRH), the anterior pituitary (LH and FSH), and the gonads (either testosterone or estrogen) is responsible for the maturation of the reproductive systems and the development of secondary sex characteristics, which are physical changes that serve auxiliary roles in reproduction.
The first changes begin around the age of eight or nine when the production of LH becomes detectable. The release of LH occurs primarily at night during sleep and precedes the physical changes of puberty by several years. In pre-pubertal children, the sensitivity of the negative feedback system in the hypothalamus and pituitary is very high. This means that very low concentrations of androgens or estrogens will negatively feed back onto the hypothalamus and pituitary, keeping the production of GnRH, LH, and FSH low.
As an individual approaches puberty, two changes in sensitivity occur. The first is a decrease of sensitivity in the hypothalamus and pituitary to negative feedback, meaning that it takes increasingly larger concentrations of sex steroid hormones to stop the production of LH and FSH. The second change in sensitivity is an increase in sensitivity of the gonads to the FSH and LH signals, meaning the gonads of adults are more responsive to gonadotropins than are the gonads of children. As a result of these two changes, the levels of LH and FSH slowly increase and lead to the enlargement and maturation of the gonads, which in turn leads to secretion of higher levels of sex hormones and the initiation of spermatogenesis and folliculogenesis.
In addition to age, multiple factors can affect the age of onset of puberty, including genetics, environment, and psychological stress. One of the more important influences may be nutrition; historical data demonstrate the effect of better and more consistent nutrition on the age of menarche in girls in the United States, which decreased from an average age of approximately 17 years of age in 1860 to the current age of approximately 12.75 years in 1960, as it remains today. Some studies indicate a link between puberty onset and the amount of stored fat in an individual. This effect is more pronounced in girls, but has been documented in both sexes. Body fat, corresponding with secretion of the hormone leptin by adipose cells, appears to have a strong role in determining menarche. This may reflect to some extent the high metabolic costs of gestation and lactation. In girls who are lean and highly active, such as gymnasts, there is often a delay in the onset of puberty.
Figure 27.18 Hormones of Puberty During puberty, the release of LH and FSH from the anterior pituitary stimulates the gonads to produce sex hormones in both male and female adolescents.
Signs of Puberty
Different sex steroid hormone concentrations between the sexes also contribute to the development and function of secondary sexual characteristics. Examples of secondary sexual characteristics are listed in Table 27.1.
Development of the Secondary Sexual Characteristics
| Male | Female |
|---|---|
| Increased larynx size and deepening of the voice | Deposition of fat, predominantly in breasts and hips |
| Increased muscular development | Breast development |
| Growth of facial, axillary, and pubic hair, and increased growth of body hair | Broadening of the pelvis and growth of axillary and pubic hair |
Table 27.1
As a girl reaches puberty, typically the first change that is visible is the development of the breast tissue. This is followed by the growth of axillary and pubic hair. A growth spurt normally starts at approximately age 9 to 11, and may last two years or more. During this time, a girl’s height can increase 3 inches a year. The next step in puberty is menarche, the start of menstruation.
In boys, the growth of the testes is typically the first physical sign of the beginning of puberty, which is followed by growth and pigmentation of the scrotum and growth of the penis. The next step is the growth of hair, including armpit, pubic, chest, and facial hair. Testosterone stimulates the growth of the larynx and thickening and lengthening of the vocal folds, which causes the voice to drop in pitch. The first fertile ejaculations typically appear at approximately 15 years of age, but this age can vary widely across individual boys. Unlike the early growth spurt observed in females, the male growth spurt occurs toward the end of puberty, at approximately age 11 to 13, and a boy’s height can increase as much as 4 inches a year. In some males, pubertal development can continue through the early 20s.
Key Terms
- alveoli
- (of the breast) milk-secreting cells in the mammary gland
- ampulla
- (of the uterine tube) middle portion of the uterine tube in which fertilization often occurs
- antrum
- fluid-filled chamber that characterizes a mature tertiary (antral) follicle
- areola
- highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling
- Bartholin’s glands
- (also, greater vestibular glands) glands that produce a thick mucus that maintains moisture in the vulva area; also referred to as the greater vestibular glands
- blood–testis barrier
- tight junctions between Sertoli cells that prevent bloodborne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm
- body of uterus
- middle section of the uterus
- broad ligament
- wide ligament that supports the uterus by attaching laterally to both sides of the uterus and pelvic wall
- bulbourethral glands
- (also, Cowper’s glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation
- cervix
- elongate inferior end of the uterus where it connects to the vagina
- clitoris
- (also, glans clitoris) nerve-rich area of the vulva that contributes to sexual sensation during intercourse
- corpus albicans
- nonfunctional structure remaining in the ovarian stroma following structural and functional regression of the corpus luteum
- corpus cavernosum
- either of two columns of erectile tissue in the penis that fill with blood during an erection
- corpus luteum
- transformed follicle after ovulation that secretes progesterone
- corpus spongiosum
- (plural = corpora cavernosa) column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis
- ductus deferens
- (also, vas deferens) duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred as the vas deferens
- ejaculatory duct
- duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra
- endometrium
- inner lining of the uterus, part of which builds up during the secretory phase of the menstrual cycle and then sheds with menses
- epididymis
- (plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation
- fimbriae
- fingerlike projections on the distal uterine tubes
- follicle
- ovarian structure of one oocyte and surrounding granulosa (and later theca) cells
- folliculogenesis
- development of ovarian follicles from primordial to tertiary under the stimulation of gonadotropins
- fundus
- (of the uterus) domed portion of the uterus that is superior to the uterine tubes
- gamete
- haploid reproductive cell that contributes genetic material to form an offspring
- glans penis
- bulbous end of the penis that contains a large number of nerve endings
- gonadotropin-releasing hormone (GnRH)
- hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland
- gonads
- reproductive organs (testes in men and ovaries in women) that produce gametes and reproductive hormones
- granulosa cells
- supportive cells in the ovarian follicle that produce estrogen
- hymen
- membrane that covers part of the opening of the vagina
- infundibulum
- (of the uterine tube) wide, distal portion of the uterine tube terminating in fimbriae
- inguinal canal
- opening in abdominal wall that connects the testes to the abdominal cavity
- isthmus
- narrow, medial portion of the uterine tube that joins the uterus
- labia majora
- hair-covered folds of skin located behind the mons pubis
- labia minora
- thin, pigmented, hairless flaps of skin located medial and deep to the labia majora
- lactiferous ducts
- ducts that connect the mammary glands to the nipple and allow for the transport of milk
- lactiferous sinus
- area of milk collection between alveoli and lactiferous duct
- Leydig cells
- cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell
- mammary glands
- glands inside the breast that secrete milk
- menarche
- first menstruation in a pubertal female
- menses
- shedding of the inner portion of the endometrium out though the vagina; also referred to as menstruation
- menses phase
- phase of the menstrual cycle in which the endometrial lining is shed
- menstrual cycle
- approximately 28-day cycle of changes in the uterus consisting of a menses phase, a proliferative phase, and a secretory phase
- mons pubis
- mound of fatty tissue located at the front of the vulva
- Müllerian duct
- duct system present in the embryo that will eventually form the internal female reproductive structures
- myometrium
- smooth muscle layer of uterus that allows for uterine contractions during labor and expulsion of menstrual blood
- oocyte
- cell that results from the division of the oogonium and undergoes meiosis I at the LH surge and meiosis II at fertilization to become a haploid ovum
- oogenesis
- process by which oogonia divide by mitosis to primary oocytes, which undergo meiosis to produce the secondary oocyte and, upon fertilization, the ovum
- oogonia
- ovarian stem cells that undergo mitosis during female fetal development to form primary oocytes
- ovarian cycle
- approximately 28-day cycle of changes in the ovary consisting of a follicular phase and a luteal phase
- ovaries
- female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone)
- ovulation
- release of a secondary oocyte and associated granulosa cells from an ovary
- ovum
- haploid female gamete resulting from completion of meiosis II at fertilization
- penis
- male organ of copulation
- perimetrium
- outer epithelial layer of uterine wall
- polar body
- smaller cell produced during the process of meiosis in oogenesis
- prepuce
- (also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin
- primary follicles
- ovarian follicles with a primary oocyte and one layer of cuboidal granulosa cells
- primordial follicles
- least developed ovarian follicles that consist of a single oocyte and a single layer of flat (squamous) granulosa cells
- proliferative phase
- phase of the menstrual cycle in which the endometrium proliferates
- prostate gland
- doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation
- puberty
- life stage during which a male or female adolescent becomes anatomically and physiologically capable of reproduction
- rugae
- (of the vagina) folds of skin in the vagina that allow it to stretch during intercourse and childbirth
- scrotum
- external pouch of skin and muscle that houses the testes
- secondary follicles
- ovarian follicles with a primary oocyte and multiple layers of granulosa cells
- secondary sex characteristics
- physical characteristics that are influenced by sex steroid hormones and have supporting roles in reproductive function
- secretory phase
- phase of the menstrual cycle in which the endometrium secretes a nutrient-rich fluid in preparation for implantation of an embryo
- semen
- ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands
- seminal vesicle
- gland that produces seminal fluid, which contributes to semen
- seminiferous tubules
- tube structures within the testes where spermatogenesis occurs
- Sertoli cells
- cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell
- sperm
- (also, spermatozoon) male gamete
- spermatic cord
- bundle of nerves and blood vessels that supplies the testes; contains ductus deferens
- spermatid
- immature sperm cells produced by meiosis II of secondary spermatocytes
- spermatocyte
- cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids
- spermatogenesis
- formation of new sperm, occurs in the seminiferous tubules of the testes
- spermatogonia
- (singular = spermatogonium) diploid precursor cells that become sperm
- spermiogenesis
- transformation of spermatids to spermatozoa during spermatogenesis
- suspensory ligaments
- bands of connective tissue that suspend the breast onto the chest wall by attachment to the overlying dermis
- tertiary follicles
- (also, antral follicles) ovarian follicles with a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum
- testes
- (singular = testis) male gonads
- theca cells
- estrogen-producing cells in a maturing ovarian follicle
- uterine tubes
- (also, fallopian tubes or oviducts) ducts that facilitate transport of an ovulated oocyte to the uterus
- uterus
- muscular hollow organ in which a fertilized egg develops into a fetus
- vagina
- tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby
- vulva
- external female genitalia
- Wolffian duct
- duct system present in the embryo that will eventually form the internal male reproductive structures
Chapter Review
27.1 Anatomy and Physiology of the Male Reproductive System
Gametes are the reproductive cells that combine to form offspring. Organs called gonads produce the gametes, along with the hormones that regulate human reproduction. The male gametes are called sperm. Spermatogenesis, the production of sperm, occurs within the seminiferous tubules that make up most of the testis. The scrotum is the muscular sac that holds the testes outside of the body cavity.
Spermatogenesis begins with mitotic division of spermatogonia (stem cells) to produce primary spermatocytes that undergo the two divisions of meiosis to become secondary spermatocytes, then the haploid spermatids. During spermiogenesis, spermatids are transformed into spermatozoa (formed sperm). Upon release from the seminiferous tubules, sperm are moved to the epididymis where they continue to mature. During ejaculation, sperm exit the epididymis through the ductus deferens, a duct in the spermatic cord that leaves the scrotum. The ampulla of the ductus deferens meets the seminal vesicle, a gland that contributes fructose and proteins, at the ejaculatory duct. The fluid continues through the prostatic urethra, where secretions from the prostate are added to form semen. These secretions help the sperm to travel through the urethra and into the female reproductive tract. Secretions from the bulbourethral glands protect sperm and cleanse and lubricate the penile (spongy) urethra.
The penis is the male organ of copulation. Columns of erectile tissue called the corpora cavernosa and corpus spongiosum fill with blood when sexual arousal activates vasodilatation in the blood vessels of the penis. Testosterone regulates and maintains the sex organs and sex drive, and induces the physical changes of puberty. Interplay between the testes and the endocrine system precisely control the production of testosterone with a negative feedback loop.
27.2 Anatomy and Physiology of the Female Reproductive System
The external female genitalia are collectively called the vulva. The vagina is the pathway into and out of the uterus. The man’s penis is inserted into the vagina to deliver sperm, and the baby exits the uterus through the vagina during childbirth.
The ovaries produce oocytes, the female gametes, in a process called oogenesis. As with spermatogenesis, meiosis produces the haploid gamete (in this case, an ovum); however, it is completed only in an oocyte that has been penetrated by a sperm. In the ovary, an oocyte surrounded by supporting cells is called a follicle. In folliculogenesis, primordial follicles develop into primary, secondary, and tertiary follicles. Early tertiary follicles with their fluid-filled antrum will be stimulated by an increase in FSH, a gonadotropin produced by the anterior pituitary, to grow in the 28-day ovarian cycle. Supporting granulosa and theca cells in the growing follicles produce estrogens, until the level of estrogen in the bloodstream is high enough that it triggers negative feedback at the hypothalamus and pituitary. This results in a reduction of FSH and LH, and most tertiary follicles in the ovary undergo atresia (they die). One follicle, usually the one with the most FSH receptors, survives this period and is now called the dominant follicle. The dominant follicle produces more estrogen, triggering positive feedback and the LH surge that will induce ovulation. Following ovulation, the granulosa cells of the empty follicle luteinize and transform into the progesterone-producing corpus luteum. The ovulated oocyte with its surrounding granulosa cells is picked up by the infundibulum of the uterine tube, and beating cilia help to transport it through the tube toward the uterus. Fertilization occurs within the uterine tube, and the final stage of meiosis is completed.
The uterus has three regions: the fundus, the body, and the cervix. It has three layers: the outer perimetrium, the muscular myometrium, and the inner endometrium. The endometrium responds to estrogen released by the follicles during the menstrual cycle and grows thicker with an increase in blood vessels in preparation for pregnancy. If the egg is not fertilized, no signal is sent to extend the life of the corpus luteum, and it degrades, stopping progesterone production. This decline in progesterone results in the sloughing of the inner portion of the endometrium in a process called menses, or menstruation.
The breasts are accessory sexual organs that are utilized after the birth of a child to produce milk in a process called lactation. Birth control pills provide constant levels of estrogen and progesterone to negatively feed back on the hypothalamus and pituitary, and suppress the release of FSH and LH, which inhibits ovulation and prevents pregnancy.
27.3 Development of the Male and Female Reproductive Systems
The reproductive systems of males and females begin to develop soon after conception. A gene on the male’s Y chromosome called SRY is critical in stimulating a cascade of events that simultaneously stimulate testis development and repress the development of female structures. Testosterone produced by Leydig cells in the embryonic testis stimulates the development of male sexual organs. If testosterone is not present, female sexual organs will develop.
Whereas the gonads and some other reproductive tissues are considered bipotential, the tissue that forms the internal reproductive structures stems from ducts that will develop into only male (Wolffian) or female (Müllerian) structures. To be able to reproduce as an adult, one of these systems must develop properly and the other must degrade.
Further development of the reproductive systems occurs at puberty. The initiation of the changes that occur in puberty is the result of a decrease in sensitivity to negative feedback in the hypothalamus and pituitary gland, and an increase in sensitivity of the gonads to FSH and LH stimulation. These changes lead to increases in either estrogen or testosterone, in female and male adolescents, respectively. The increase in sex steroid hormones leads to maturation of the gonads and other reproductive organs. The initiation of spermatogenesis begins in boys, and girls begin ovulating and menstruating. Increases in sex steroid hormones also lead to the development of secondary sex characteristics such as breast development in girls and facial hair and larynx growth in boys.
Interactive Link Questions
Watch this video to learn about vasectomy. As described in this video, a vasectomy is a procedure in which a small section of the ductus (vas) deferens is removed from the scrotum. This interrupts the path taken by sperm through the ductus deferens. If sperm do not exit through the vas, either because the man has had a vasectomy or has not ejaculated, in what region of the testis do they remain?
2.Watch this video to explore the structures of the male reproductive system and the path of sperm that starts in the testes and ends as the sperm leave the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct?
3.Watch this video to observe ovulation and its initiation in response to the release of FSH and LH from the pituitary gland. What specialized structures help guide the oocyte from the ovary into the uterine tube?
4.Watch this series of videos to look at the movement of the oocyte through the ovary. The cilia in the uterine tube promote movement of the oocyte. What would likely occur if the cilia were paralyzed at the time of ovulation?
5.A baby’s gender is determined at conception, and the different genitalia of male and female fetuses develop from the same tissues in the embryo. View this animation that compares the development of structures of the female and male reproductive systems in a growing fetus. Where are the testes located for most of gestational time?
Review Questions
What are male gametes called?
- ova
- sperm
- testes
- testosterone
Leydig cells ________.
- secrete testosterone
- activate the sperm flagellum
- support spermatogenesis
- secrete seminal fluid
Which hypothalamic hormone contributes to the regulation of the male reproductive system?
- luteinizing hormone
- gonadotropin-releasing hormone
- follicle-stimulating hormone
- androgens
What is the function of the epididymis?
- sperm maturation and storage
- produces the bulk of seminal fluid
- provides nitric oxide needed for erections
- spermatogenesis
Spermatogenesis takes place in the ________.
- prostate gland
- glans penis
- seminiferous tubules
- ejaculatory duct
What are the female gonads called?
- oocytes
- ova
- oviducts
- ovaries
When do the oogonia undergo mitosis?
- before birth
- at puberty
- at the beginning of each menstrual cycle
- during fertilization
From what structure does the corpus luteum originate?
- uterine corpus
- dominant follicle
- fallopian tube
- corpus albicans
Where does fertilization of the egg by the sperm typically occur?
- vagina
- uterus
- uterine tube
- ovary
Why do estrogen levels fall after menopause?
- The ovaries degrade.
- There are no follicles left to produce estrogen.
- The pituitary secretes a menopause-specific hormone.
- The cells of the endometrium degenerate.
The vulva includes the ________.
- lactiferous duct, rugae, and hymen
- lactiferous duct, endometrium, and bulbourethral glands
- mons pubis, endometrium, and hymen
- mons pubis, labia majora, and Bartholin’s glands
What controls whether an embryo will develop testes or ovaries?
- pituitary gland
- hypothalamus
- Y chromosome
- presence or absence of estrogen
Without SRY expression, an embryo will develop ________.
- male reproductive structures
- female reproductive structures
- no reproductive structures
- male reproductive structures 50 percent of the time and female reproductive structures 50 percent of the time
The timing of puberty can be influenced by which of the following?
- genes
- stress
- amount of body fat
- all of the above
Critical Thinking Questions
Briefly explain why mature gametes carry only one set of chromosomes.
21.What special features are evident in sperm cells but not in somatic cells, and how do these specializations function?
22.What do each of the three male accessory glands contribute to the semen?
23.Describe how penile erection occurs.
24.While anabolic steroids (synthetic testosterone) bulk up muscles, they can also affect testosterone production in the testis. Using what you know about negative feedback, describe what would happen to testosterone production in the testis if a male takes large amounts of synthetic testosterone.
25.Follow the path of ejaculated sperm from the vagina to the oocyte. Include all structures of the female reproductive tract that the sperm must swim through to reach the egg.
26.Identify some differences between meiosis in men and women.
27.Explain the hormonal regulation of the phases of the menstrual cycle.
28.Endometriosis is a disorder in which endometrial cells implant and proliferate outside of the uterus—in the uterine tubes, on the ovaries, or even in the pelvic cavity. Offer a theory as to why endometriosis increases a woman’s risk of infertility.
29.Identify the changes in sensitivity that occur in the hypothalamus, pituitary, and gonads as a boy or girl approaches puberty. Explain how these changes lead to the increases of sex steroid hormone secretions that drive many pubertal changes.
30.Explain how the internal female and male reproductive structures develop from two different duct systems.
31.Explain what would occur during fetal development to an XY individual with a mutation causing a nonfunctional SRYgene.
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https://oercommons.org/courseware/lesson/58776/overview
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Development and Inheritance
Introduction
Figure 28.1 Newborn A single fertilized egg develops over the span of nine months into an infant consisting of trillions of cells and capable of surviving outside the womb. (credit: “Seattleye”/flickr.com)
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- List and explain the steps involved in fertilization
- Describe the major events in embryonic development
- Describe the major events in fetal development
- Discuss the adaptations of a woman’s body to pregnancy
- Describe the physiologic adjustments that the newborn must make in the first hours of extrauterine life
- Summarize the physiology of lactation
- Classify and describe the different patterns of inheritance
In approximately nine months, a single cell—a fertilized egg—develops into a fully formed infant consisting of trillions of cells with myriad specialized functions. The dramatic changes of fertilization, embryonic development, and fetal development are followed by remarkable adaptations of the newborn to life outside the womb. An offspring’s normal development depends upon the appropriate synthesis of structural and functional proteins. This, in turn, is governed by the genetic material inherited from the parental egg and sperm, as well as environmental factors.
Fertilization
- Describe the obstacles that sperm must overcome to reach an oocyte
- Explain capacitation and its importance in fertilization
- Summarize the events that occur as a sperm fertilizes an oocyte
Fertilization occurs when a sperm and an oocyte (egg) combine and their nuclei fuse. Because each of these reproductive cells is a haploid cell containing half of the genetic material needed to form a human being, their combination forms a diploid cell. This new single cell, called a zygote, contains all of the genetic material needed to form a human—half from the mother and half from the father.
Transit of Sperm
Fertilization is a numbers game. During ejaculation, hundreds of millions of sperm (spermatozoa) are released into the vagina. Almost immediately, millions of these sperm are overcome by the acidity of the vagina (approximately pH 3.8), and millions more may be blocked from entering the uterus by thick cervical mucus. Of those that do enter, thousands are destroyed by phagocytic uterine leukocytes. Thus, the race into the uterine tubes, which is the most typical site for sperm to encounter the oocyte, is reduced to a few thousand contenders. Their journey—thought to be facilitated by uterine contractions—usually takes from 30 minutes to 2 hours. If the sperm do not encounter an oocyte immediately, they can survive in the uterine tubes for another 3–5 days. Thus, fertilization can still occur if intercourse takes place a few days before ovulation. In comparison, an oocyte can survive independently for only approximately 24 hours following ovulation. Intercourse more than a day after ovulation will therefore usually not result in fertilization.
During the journey, fluids in the female reproductive tract prepare the sperm for fertilization through a process called capacitation, or priming. The fluids improve the motility of the spermatozoa. They also deplete cholesterol molecules embedded in the membrane of the head of the sperm, thinning the membrane in such a way that will help facilitate the release of the lysosomal (digestive) enzymes needed for the sperm to penetrate the oocyte’s exterior once contact is made. Sperm must undergo the process of capacitation in order to have the “capacity” to fertilize an oocyte. If they reach the oocyte before capacitation is complete, they will be unable to penetrate the oocyte’s thick outer layer of cells.
Contact Between Sperm and Oocyte
Upon ovulation, the oocyte released by the ovary is swept into—and along—the uterine tube. Fertilization must occur in the distal uterine tube because an unfertilized oocyte cannot survive the 72-hour journey to the uterus. As you will recall from your study of the oogenesis, this oocyte (specifically a secondary oocyte) is surrounded by two protective layers. The corona radiatais an outer layer of follicular (granulosa) cells that form around a developing oocyte in the ovary and remain with it upon ovulation. The underlying zona pellucida (pellucid = “transparent”) is a transparent, but thick, glycoprotein membrane that surrounds the cell’s plasma membrane.
As it is swept along the distal uterine tube, the oocyte encounters the surviving capacitated sperm, which stream toward it in response to chemical attractants released by the cells of the corona radiata. To reach the oocyte itself, the sperm must penetrate the two protective layers. The sperm first burrow through the cells of the corona radiata. Then, upon contact with the zona pellucida, the sperm bind to receptors in the zona pellucida. This initiates a process called the acrosomal reaction in which the enzyme-filled “cap” of the sperm, called the acrosome, releases its stored digestive enzymes. These enzymes clear a path through the zona pellucida that allows sperm to reach the oocyte. Finally, a single sperm makes contact with sperm-binding receptors on the oocyte’s plasma membrane (Figure 28.2). The plasma membrane of that sperm then fuses with the oocyte’s plasma membrane, and the head and mid-piece of the “winning” sperm enter the oocyte interior.
How do sperm penetrate the corona radiata? Some sperm undergo a spontaneous acrosomal reaction, which is an acrosomal reaction not triggered by contact with the zona pellucida. The digestive enzymes released by this reaction digest the extracellular matrix of the corona radiata. As you can see, the first sperm to reach the oocyte is never the one to fertilize it. Rather, hundreds of sperm cells must undergo the acrosomal reaction, each helping to degrade the corona radiata and zona pellucida until a path is created to allow one sperm to contact and fuse with the plasma membrane of the oocyte. If you consider the loss of millions of sperm between entry into the vagina and degradation of the zona pellucida, you can understand why a low sperm count can cause male infertility.
Figure 28.2 Sperm and the Process of Fertilization Before fertilization, hundreds of capacitated sperm must break through the surrounding corona radiata and zona pellucida so that one can contact and fuse with the oocyte plasma membrane.
When the first sperm fuses with the oocyte, the oocyte deploys two mechanisms to prevent polyspermy, which is penetration by more than one sperm. This is critical because if more than one sperm were to fertilize the oocyte, the resulting zygote would be a triploid organism with three sets of chromosomes. This is incompatible with life.
The first mechanism is the fast block, which involves a near instantaneous change in sodium ion permeability upon binding of the first sperm, depolarizing the oocyte plasma membrane and preventing the fusion of additional sperm cells. The fast block sets in almost immediately and lasts for about a minute, during which time an influx of calcium ions following sperm penetration triggers the second mechanism, the slow block. In this process, referred to as the cortical reaction, cortical granules sitting immediately below the oocyte plasma membrane fuse with the membrane and release zonal inhibiting proteins and mucopolysaccharides into the space between the plasma membrane and the zona pellucida. Zonal inhibiting proteins cause the release of any other attached sperm and destroy the oocyte’s sperm receptors, thus preventing any more sperm from binding. The mucopolysaccharides then coat the nascent zygote in an impenetrable barrier that, together with hardened zona pellucida, is called a fertilization membrane.
The Zygote
Recall that at the point of fertilization, the oocyte has not yet completed meiosis; all secondary oocytes remain arrested in metaphase of meiosis II until fertilization. Only upon fertilization does the oocyte complete meiosis. The unneeded complement of genetic material that results is stored in a second polar body that is eventually ejected. At this moment, the oocyte has become an ovum, the female haploid gamete. The two haploid nuclei derived from the sperm and oocyte and contained within the egg are referred to as pronuclei. They decondense, expand, and replicate their DNA in preparation for mitosis. The pronuclei then migrate toward each other, their nuclear envelopes disintegrate, and the male- and female-derived genetic material intermingles. This step completes the process of fertilization and results in a single-celled diploid zygote with all the genetic instructions it needs to develop into a human.
Most of the time, a woman releases a single egg during an ovulation cycle. However, in approximately 1 percent of ovulation cycles, two eggs are released and both are fertilized. Two zygotes form, implant, and develop, resulting in the birth of dizygotic (or fraternal) twins. Because dizygotic twins develop from two eggs fertilized by two sperm, they are no more identical than siblings born at different times.
Much less commonly, a zygote can divide into two separate offspring during early development. This results in the birth of monozygotic (or identical) twins. Although the zygote can split as early as the two-cell stage, splitting occurs most commonly during the early blastocyst stage, with roughly 70–100 cells present. These two scenarios are distinct from each other, in that the twin embryos that separated at the two-cell stage will have individual placentas, whereas twin embryos that form from separation at the blastocyst stage will share a placenta and a chorionic cavity.
EVERYDAY CONNECTION
In Vitro Fertilization
IVF, which stands for in vitro fertilization, is an assisted reproductive technology. In vitro, which in Latin translates to “in glass,” refers to a procedure that takes place outside of the body. There are many different indications for IVF. For example, a woman may produce normal eggs, but the eggs cannot reach the uterus because the uterine tubes are blocked or otherwise compromised. A man may have a low sperm count, low sperm motility, sperm with an unusually high percentage of morphological abnormalities, or sperm that are incapable of penetrating the zona pellucida of an egg.
A typical IVF procedure begins with egg collection. A normal ovulation cycle produces only one oocyte, but the number can be boosted significantly (to 10–20 oocytes) by administering a short course of gonadotropins. The course begins with follicle-stimulating hormone (FSH) analogs, which support the development of multiple follicles, and ends with a luteinizing hormone (LH) analog that triggers ovulation. Right before the ova would be released from the ovary, they are harvested using ultrasound-guided oocyte retrieval. In this procedure, ultrasound allows a physician to visualize mature follicles. The ova are aspirated (sucked out) using a syringe.
In parallel, sperm are obtained from the male partner or from a sperm bank. The sperm are prepared by washing to remove seminal fluid because seminal fluid contains a peptide, FPP (or, fertilization promoting peptide), that—in high concentrations—prevents capacitation of the sperm. The sperm sample is also concentrated, to increase the sperm count per milliliter.
Next, the eggs and sperm are mixed in a petri dish. The ideal ratio is 75,000 sperm to one egg. If there are severe problems with the sperm—for example, the count is exceedingly low, or the sperm are completely nonmotile, or incapable of binding to or penetrating the zona pellucida—a sperm can be injected into an egg. This is called intracytoplasmic sperm injection (ICSI).
The embryos are then incubated until they either reach the eight-cell stage or the blastocyst stage. In the United States, fertilized eggs are typically cultured to the blastocyst stage because this results in a higher pregnancy rate. Finally, the embryos are transferred to a woman’s uterus using a plastic catheter (tube). Figure 28.3 illustrates the steps involved in IVF.
Figure 28.3 IVF In vitro fertilization involves egg collection from the ovaries, fertilization in a petri dish, and the transfer of embryos into the uterus.
IVF is a relatively new and still evolving technology, and until recently it was necessary to transfer multiple embryos to achieve a good chance of a pregnancy. Today, however, transferred embryos are much more likely to implant successfully, so countries that regulate the IVF industry cap the number of embryos that can be transferred per cycle at two. This reduces the risk of multiple-birth pregnancies.
The rate of success for IVF is correlated with a woman’s age. More than 40 percent of women under 35 succeed in giving birth following IVF, but the rate drops to a little over 10 percent in women over 40.
INTERACTIVE LINK
Go to this site to view resources covering various aspects of fertilization, including movies and animations showing sperm structure and motility, ovulation, and fertilization.
Embryonic Development
- By the end of this section, you will be able to:
- Distinguish the stages of embryonic development that occur before implantation
- Describe the process of implantation
- List and describe four embryonic membranes
- Explain gastrulation
- Describe how the placenta is formed and identify its functions
- Explain how an embryo transforms from a flat disc of cells into a three-dimensional shape resembling a human
- Summarize the process of organogenesis
Throughout this chapter, we will express embryonic and fetal ages in terms of weeks from fertilization, commonly called conception. The period of time required for full development of a fetus in utero is referred to as gestation (gestare = “to carry” or “to bear”). It can be subdivided into distinct gestational periods. The first 2 weeks of prenatal development are referred to as the pre-embryonic stage. A developing human is referred to as an embryo during weeks 3–8, and a fetus from the ninth week of gestation until birth. In this section, we’ll cover the pre-embryonic and embryonic stages of development, which are characterized by cell division, migration, and differentiation. By the end of the embryonic period, all of the organ systems are structured in rudimentary form, although the organs themselves are either nonfunctional or only semi-functional.
Pre-implantation Embryonic Development
Following fertilization, the zygote and its associated membranes, together referred to as the conceptus, continue to be projected toward the uterus by peristalsis and beating cilia. During its journey to the uterus, the zygote undergoes five or six rapid mitotic cell divisions. Although each cleavage results in more cells, it does not increase the total volume of the conceptus (Figure 28.4). Each daughter cell produced by cleavage is called a blastomere (blastos = “germ,” in the sense of a seed or sprout).
Approximately 3 days after fertilization, a 16-cell conceptus reaches the uterus. The cells that had been loosely grouped are now compacted and look more like a solid mass. The name given to this structure is the morula (morula = “little mulberry”). Once inside the uterus, the conceptus floats freely for several more days. It continues to divide, creating a ball of approximately 100 cells, and consuming nutritive endometrial secretions called uterine milk while the uterine lining thickens. The ball of now tightly bound cells starts to secrete fluid and organize themselves around a fluid-filled cavity, the blastocoel. At this developmental stage, the conceptus is referred to as a blastocyst. Within this structure, a group of cells forms into an inner cell mass, which is fated to become the embryo. The cells that form the outer shell are called trophoblasts (trophe = “to feed” or “to nourish”). These cells will develop into the chorionic sac and the fetal portion of the placenta (the organ of nutrient, waste, and gas exchange between mother and the developing offspring).
The inner mass of embryonic cells is totipotent during this stage, meaning that each cell has the potential to differentiate into any cell type in the human body. Totipotency lasts for only a few days before the cells’ fates are set as being the precursors to a specific lineage of cells.
Figure 28.4 Pre-Embryonic Cleavages Pre-embryonic cleavages make use of the abundant cytoplasm of the conceptus as the cells rapidly divide without changing the total volume.
As the blastocyst forms, the trophoblast excretes enzymes that begin to degrade the zona pellucida. In a process called “hatching,” the conceptus breaks free of the zona pellucida in preparation for implantation.
INTERACTIVE LINK
View this time-lapse movie of a conceptus starting at day 3. What is the first structure you see? At what point in the movie does the blastocoel first appear? What event occurs at the end of the movie?
Implantation
At the end of the first week, the blastocyst comes in contact with the uterine wall and adheres to it, embedding itself in the uterine lining via the trophoblast cells. Thus begins the process of implantation, which signals the end of the pre-embryonic stage of development (Figure 28.5). Implantation can be accompanied by minor bleeding. The blastocyst typically implants in the fundus of the uterus or on the posterior wall. However, if the endometrium is not fully developed and ready to receive the blastocyst, the blastocyst will detach and find a better spot. A significant percentage (50–75 percent) of blastocysts fail to implant; when this occurs, the blastocyst is shed with the endometrium during menses. The high rate of implantation failure is one reason why pregnancy typically requires several ovulation cycles to achieve.
Figure 28.5 Pre-Embryonic Development Ovulation, fertilization, pre-embryonic development, and implantation occur at specific locations within the female reproductive system in a time span of approximately 1 week.
When implantation succeeds and the blastocyst adheres to the endometrium, the superficial cells of the trophoblast fuse with each other, forming the syncytiotrophoblast, a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall. In response, the uterine mucosa rebuilds itself and envelops the blastocyst (Figure 28.6). The trophoblast secretes human chorionic gonadotropin (hCG), a hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses. These functions of hCG are necessary for creating an environment suitable for the developing embryo. As a result of this increased production, hCG accumulates in the maternal bloodstream and is excreted in the urine. Implantation is complete by the middle of the second week. Just a few days after implantation, the trophoblast has secreted enough hCG for an at-home urine pregnancy test to give a positive result.
Figure 28.6 Implantation During implantation, the trophoblast cells of the blastocyst adhere to the endometrium and digest endometrial cells until it is attached securely.
Most of the time an embryo implants within the body of the uterus in a location that can support growth and development. However, in one to two percent of cases, the embryo implants either outside the uterus (an ectopic pregnancy) or in a region of uterus that can create complications for the pregnancy. If the embryo implants in the inferior portion of the uterus, the placenta can potentially grow over the opening of the cervix, a condition call placenta previa.
DISORDERS OF THE...
Development of the Embryo
In the vast majority of ectopic pregnancies, the embryo does not complete its journey to the uterus and implants in the uterine tube, referred to as a tubal pregnancy. However, there are also ovarian ectopic pregnancies (in which the egg never left the ovary) and abdominal ectopic pregnancies (in which an egg was “lost” to the abdominal cavity during the transfer from ovary to uterine tube, or in which an embryo from a tubal pregnancy re-implanted in the abdomen). Once in the abdominal cavity, an embryo can implant into any well-vascularized structure—the rectouterine cavity (Douglas’ pouch), the mesentery of the intestines, and the greater omentum are some common sites.
Tubal pregnancies can be caused by scar tissue within the tube following a sexually transmitted bacterial infection. The scar tissue impedes the progress of the embryo into the uterus—in some cases “snagging” the embryo and, in other cases, blocking the tube completely. Approximately one half of tubal pregnancies resolve spontaneously. Implantation in a uterine tube causes bleeding, which appears to stimulate smooth muscle contractions and expulsion of the embryo. In the remaining cases, medical or surgical intervention is necessary. If an ectopic pregnancy is detected early, the embryo’s development can be arrested by the administration of the cytotoxic drug methotrexate, which inhibits the metabolism of folic acid. If diagnosis is late and the uterine tube is already ruptured, surgical repair is essential.
Even if the embryo has successfully found its way to the uterus, it does not always implant in an optimal location (the fundus or the posterior wall of the uterus). Placenta previa can result if an embryo implants close to the internal os of the uterus (the internal opening of the cervix). As the fetus grows, the placenta can partially or completely cover the opening of the cervix (Figure 28.7). Although it occurs in only 0.5 percent of pregnancies, placenta previa is the leading cause of antepartum hemorrhage (profuse vaginal bleeding after week 24 of pregnancy but prior to childbirth).
Figure 28.7 Placenta Previa An embryo that implants too close to the opening of the cervix can lead to placenta previa, a condition in which the placenta partially or completely covers the cervix.
Embryonic Membranes
During the second week of development, with the embryo implanted in the uterus, cells within the blastocyst start to organize into layers. Some grow to form the extra-embryonic membranes needed to support and protect the growing embryo: the amnion, the yolk sac, the allantois, and the chorion.
At the beginning of the second week, the cells of the inner cell mass form into a two-layered disc of embryonic cells, and a space—the amniotic cavity—opens up between it and the trophoblast (Figure 28.8). Cells from the upper layer of the disc (the epiblast) extend around the amniotic cavity, creating a membranous sac that forms into the amnion by the end of the second week. The amnion fills with amniotic fluid and eventually grows to surround the embryo. Early in development, amniotic fluid consists almost entirely of a filtrate of maternal plasma, but as the kidneys of the fetus begin to function at approximately the eighth week, they add urine to the volume of amniotic fluid. Floating within the amniotic fluid, the embryo—and later, the fetus—is protected from trauma and rapid temperature changes. It can move freely within the fluid and can prepare for swallowing and breathing out of the uterus.
Figure 28.8 Development of the Embryonic Disc Formation of the embryonic disc leaves spaces on either side that develop into the amniotic cavity and the yolk sac.
On the ventral side of the embryonic disc, opposite the amnion, cells in the lower layer of the embryonic disk (the hypoblast) extend into the blastocyst cavity and form a yolk sac. The yolk sac supplies some nutrients absorbed from the trophoblast and also provides primitive blood circulation to the developing embryo for the second and third week of development. When the placenta takes over nourishing the embryo at approximately week 4, the yolk sac has been greatly reduced in size and its main function is to serve as the source of blood cells and germ cells (cells that will give rise to gametes). During week 3, a finger-like outpocketing of the yolk sac develops into the allantois, a primitive excretory duct of the embryo that will become part of the urinary bladder. Together, the stalks of the yolk sac and allantois establish the outer structure of the umbilical cord.
The last of the extra-embryonic membranes is the chorion, which is the one membrane that surrounds all others. The development of the chorion will be discussed in more detail shortly, as it relates to the growth and development of the placenta.
Embryogenesis
As the third week of development begins, the two-layered disc of cells becomes a three-layered disc through the process of gastrulation, during which the cells transition from totipotency to multipotency. The embryo, which takes the shape of an oval-shaped disc, forms an indentation called the primitive streak along the dorsal surface of the epiblast. A node at the caudal or “tail” end of the primitive streak emits growth factors that direct cells to multiply and migrate. Cells migrate toward and through the primitive streak and then move laterally to create two new layers of cells. The first layer is the endoderm, a sheet of cells that displaces the hypoblast and lies adjacent to the yolk sac. The second layer of cells fills in as the middle layer, or mesoderm. The cells of the epiblast that remain (not having migrated through the primitive streak) become the ectoderm(Figure 28.9).
Figure 28.9 Germ Layers Formation of the three primary germ layers occurs during the first 2 weeks of development. The embryo at this stage is only a few millimeters in length.
Each of these germ layers will develop into specific structures in the embryo. Whereas the ectoderm and endoderm form tightly connected epithelial sheets, the mesodermal cells are less organized and exist as a loosely connected cell community. The ectoderm gives rise to cell lineages that differentiate to become the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails. Mesodermal cells ultimately become the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys. The endoderm goes on to form the epithelial lining of the gastrointestinal tract, liver, and pancreas, as well as the lungs (Figure 28.10).
Figure 28.10 Fates of Germ Layers in Embryo Following gastrulation of the embryo in the third week, embryonic cells of the ectoderm, mesoderm, and endoderm begin to migrate and differentiate into the cell lineages that will give rise to mature organs and organ systems in the infant.
Development of the Placenta
During the first several weeks of development, the cells of the endometrium—referred to as decidual cells—nourish the nascent embryo. During prenatal weeks 4–12, the developing placenta gradually takes over the role of feeding the embryo, and the decidual cells are no longer needed. The mature placenta is composed of tissues derived from the embryo, as well as maternal tissues of the endometrium. The placenta connects to the conceptus via the umbilical cord, which carries deoxygenated blood and wastes from the fetus through two umbilical arteries; nutrients and oxygen are carried from the mother to the fetus through the single umbilical vein. The umbilical cord is surrounded by the amnion, and the spaces within the cord around the blood vessels are filled with Wharton’s jelly, a mucous connective tissue.
The maternal portion of the placenta develops from the deepest layer of the endometrium, the decidua basalis. To form the embryonic portion of the placenta, the syncytiotrophoblast and the underlying cells of the trophoblast (cytotrophoblast cells) begin to proliferate along with a layer of extraembryonic mesoderm cells. These form the chorionic membrane, which envelops the entire conceptus as the chorion. The chorionic membrane forms finger-like structures called chorionic villi that burrow into the endometrium like tree roots, making up the fetal portion of the placenta. The cytotrophoblast cells perforate the chorionic villi, burrow farther into the endometrium, and remodel maternal blood vessels to augment maternal blood flow surrounding the villi. Meanwhile, fetal mesenchymal cells derived from the mesoderm fill the villi and differentiate into blood vessels, including the three umbilical blood vessels that connect the embryo to the developing placenta (Figure 28.11).
Figure 28.11 Cross-Section of the Placenta In the placenta, maternal and fetal blood components are conducted through the surface of the chorionic villi, but maternal and fetal bloodstreams never mix directly.
The placenta develops throughout the embryonic period and during the first several weeks of the fetal period; placentation is complete by weeks 14–16. As a fully developed organ, the placenta provides nutrition and excretion, respiration, and endocrine function (Table 28.1 and Figure 28.12). It receives blood from the fetus through the umbilical arteries. Capillaries in the chorionic villi filter fetal wastes out of the blood and return clean, oxygenated blood to the fetus through the umbilical vein. Nutrients and oxygen are transferred from maternal blood surrounding the villi through the capillaries and into the fetal bloodstream. Some substances move across the placenta by simple diffusion. Oxygen, carbon dioxide, and any other lipid-soluble substances take this route. Other substances move across by facilitated diffusion. This includes water-soluble glucose. The fetus has a high demand for amino acids and iron, and those substances are moved across the placenta by active transport.
Maternal and fetal blood does not commingle because blood cells cannot move across the placenta. This separation prevents the mother’s cytotoxic T cells from reaching and subsequently destroying the fetus, which bears “non-self” antigens. Further, it ensures the fetal red blood cells do not enter the mother’s circulation and trigger antibody development (if they carry “non-self” antigens)—at least until the final stages of pregnancy or birth. This is the reason that, even in the absence of preventive treatment, an Rh− mother doesn’t develop antibodies that could cause hemolytic disease in her first Rh+ fetus.
Although blood cells are not exchanged, the chorionic villi provide ample surface area for the two-way exchange of substances between maternal and fetal blood. The rate of exchange increases throughout gestation as the villi become thinner and increasingly branched. The placenta is permeable to lipid-soluble fetotoxic substances: alcohol, nicotine, barbiturates, antibiotics, certain pathogens, and many other substances that can be dangerous or fatal to the developing embryo or fetus. For these reasons, pregnant women should avoid fetotoxic substances. Alcohol consumption by pregnant women, for example, can result in a range of abnormalities referred to as fetal alcohol spectrum disorders (FASD). These include organ and facial malformations, as well as cognitive and behavioral disorders.
Functions of the Placenta
| Nutrition and digestion | Respiration | Endocrine function |
|---|---|---|
|
|
|
Table 28.1
Figure 28.12 Placenta This post-expulsion placenta and umbilical cord (white) are viewed from the fetal side.
Organogenesis
Following gastrulation, rudiments of the central nervous system develop from the ectoderm in the process of neurulation(Figure 28.13). Specialized neuroectodermal tissues along the length of the embryo thicken into the neural plate. During the fourth week, tissues on either side of the plate fold upward into a neural fold. The two folds converge to form the neural tube. The tube lies atop a rod-shaped, mesoderm-derived notochord, which eventually becomes the nucleus pulposus of intervertebral discs. Block-like structures called somites form on either side of the tube, eventually differentiating into the axial skeleton, skeletal muscle, and dermis. During the fourth and fifth weeks, the anterior neural tube dilates and subdivides to form vesicles that will become the brain structures.
Folate, one of the B vitamins, is important to the healthy development of the neural tube. A deficiency of maternal folate in the first weeks of pregnancy can result in neural tube defects, including spina bifida—a birth defect in which spinal tissue protrudes through the newborn’s vertebral column, which has failed to completely close. A more severe neural tube defect is anencephaly, a partial or complete absence of brain tissue.
Figure 28.13 Neurulation The embryonic process of neurulation establishes the rudiments of the future central nervous system and skeleton.
The embryo, which begins as a flat sheet of cells, begins to acquire a cylindrical shape through the process of embryonic folding (Figure 28.14). The embryo folds laterally and again at either end, forming a C-shape with distinct head and tail ends. The embryo envelops a portion of the yolk sac, which protrudes with the umbilical cord from what will become the abdomen. The folding essentially creates a tube, called the primitive gut, that is lined by the endoderm. The amniotic sac, which was sitting on top of the flat embryo, envelops the embryo as it folds.
Figure 28.14 Embryonic Folding Embryonic folding converts a flat sheet of cells into a hollow, tube-like structure.
Within the first 8 weeks of gestation, a developing embryo establishes the rudimentary structures of all of its organs and tissues from the ectoderm, mesoderm, and endoderm. This process is called organogenesis.
Like the central nervous system, the heart also begins its development in the embryo as a tube-like structure, connected via capillaries to the chorionic villi. Cells of the primitive tube-shaped heart are capable of electrical conduction and contraction. The heart begins beating in the beginning of the fourth week, although it does not actually pump embryonic blood until a week later, when the oversized liver has begun producing red blood cells. (This is a temporary responsibility of the embryonic liver that the bone marrow will assume during fetal development.) During weeks 4–5, the eye pits form, limb buds become apparent, and the rudiments of the pulmonary system are formed.
During the sixth week, uncontrolled fetal limb movements begin to occur. The gastrointestinal system develops too rapidly for the embryonic abdomen to accommodate it, and the intestines temporarily loop into the umbilical cord. Paddle-shaped hands and feet develop fingers and toes by the process of apoptosis (programmed cell death), which causes the tissues between the fingers to disintegrate. By week 7, the facial structure is more complex and includes nostrils, outer ears, and lenses (Figure 28.15). By the eighth week, the head is nearly as large as the rest of the embryo’s body, and all major brain structures are in place. The external genitalia are apparent, but at this point, male and female embryos are indistinguishable. Bone begins to replace cartilage in the embryonic skeleton through the process of ossification. By the end of the embryonic period, the embryo is approximately 3 cm (1.2 in) from crown to rump and weighs approximately 8 g (0.25 oz).
Figure 28.15 Embryo at 7 Weeks An embryo at the end of 7 weeks of development is only 10 mm in length, but its developing eyes, limb buds, and tail are already visible. (This embryo was derived from an ectopic pregnancy.) (credit: Ed Uthman)
INTERACTIVE LINK
Use this interactive tool to view the process of embryogenesis from fertilization through pregnancy to birth. Can you identify when neurulation occurs in the embryo?
Fetal Development
- Differentiate between the embryonic period and the fetal period
- Briefly describe the process of sexual differentiation
- Describe the fetal circulatory system and explain the role of the shunts
- Trace the development of a fetus from the end of the embryonic period to birth
As you will recall, a developing human is called a fetus from the ninth week of gestation until birth. This 30-week period of development is marked by continued cell growth and differentiation, which fully develop the structures and functions of the immature organ systems formed during the embryonic period. The completion of fetal development results in a newborn who, although still immature in many ways, is capable of survival outside the womb.
Sexual Differentiation
Sexual differentiation does not begin until the fetal period, during weeks 9–12. Embryonic males and females, though genetically distinguishable, are morphologically identical (Figure 28.16). Bipotential gonads, or gonads that can develop into male or female sexual organs, are connected to a central cavity called the cloaca via Müllerian ducts and Wolffian ducts. (The cloaca is an extension of the primitive gut.) Several events lead to sexual differentiation during this period.
During male fetal development, the bipotential gonads become the testes and associated epididymis. The Müllerian ducts degenerate. The Wolffian ducts become the vas deferens, and the cloaca becomes the urethra and rectum.
During female fetal development, the bipotential gonads develop into ovaries. The Wolffian ducts degenerate. The Müllerian ducts become the uterine tubes and uterus, and the cloaca divides and develops into a vagina, a urethra, and a rectum.
Figure 28.16 Sexual Differentiation Differentiation of the male and female reproductive systems does not occur until the fetal period of development.
The Fetal Circulatory System
During prenatal development, the fetal circulatory system is integrated with the placenta via the umbilical cord so that the fetus receives both oxygen and nutrients from the placenta. However, after childbirth, the umbilical cord is severed, and the newborn’s circulatory system must be reconfigured. When the heart first forms in the embryo, it exists as two parallel tubes derived from mesoderm and lined with endothelium, which then fuse together. As the embryo develops into a fetus, the tube-shaped heart folds and further differentiates into the four chambers present in a mature heart. Unlike a mature cardiovascular system, however, the fetal cardiovascular system also includes circulatory shortcuts, or shunts. A shunt is an anatomical (or sometimes surgical) diversion that allows blood flow to bypass immature organs such as the lungs and liver until childbirth.
The placenta provides the fetus with necessary oxygen and nutrients via the umbilical vein. (Remember that veins carry blood toward the heart. In this case, the blood flowing to the fetal heart is oxygenated because it comes from the placenta. The respiratory system is immature and cannot yet oxygenate blood on its own.) From the umbilical vein, the oxygenated blood flows toward the inferior vena cava, all but bypassing the immature liver, via the ductus venosus shunt (Figure 28.17). The liver receives just a trickle of blood, which is all that it needs in its immature, semifunctional state. Blood flows from the inferior vena cava to the right atrium, mixing with fetal venous blood along the way.
Although the fetal liver is semifunctional, the fetal lungs are nonfunctional. The fetal circulation therefore bypasses the lungs by shifting some of the blood through the foramen ovale, a shunt that directly connects the right and left atria and avoids the pulmonary trunk altogether. Most of the rest of the blood is pumped to the right ventricle, and from there, into the pulmonary trunk, which splits into pulmonary arteries. However, a shunt within the pulmonary artery, the ductus arteriosus, diverts a portion of this blood into the aorta. This ensures that only a small volume of oxygenated blood passes through the immature pulmonary circuit, which has only minor metabolic requirements. Blood vessels of uninflated lungs have high resistance to flow, a condition that encourages blood to flow to the aorta, which presents much lower resistance. The oxygenated blood moves through the foramen ovale into the left atrium, where it mixes with the now deoxygenated blood returning from the pulmonary circuit. This blood then moves into the left ventricle, where it is pumped into the aorta. Some of this blood moves through the coronary arteries into the myocardium, and some moves through the carotid arteries to the brain.
The descending aorta carries partially oxygenated and partially deoxygenated blood into the lower regions of the body. It eventually passes into the umbilical arteries through branches of the internal iliac arteries. The deoxygenated blood collects waste as it circulates through the fetal body and returns to the umbilical cord. Thus, the two umbilical arteries carry blood low in oxygen and high in carbon dioxide and fetal wastes. This blood is filtered through the placenta, where wastes diffuse into the maternal circulation. Oxygen and nutrients from the mother diffuse into the placenta and from there into the fetal blood, and the process repeats.
Figure 28.17 Fetal Circulatory System The fetal circulatory system includes three shunts to divert blood from undeveloped and partially functioning organs, as well as blood supply to and from the placenta.
Other Organ Systems
During weeks 9–12 of fetal development, the brain continues to expand, the body elongates, and ossification continues. Fetal movements are frequent during this period, but are jerky and not well-controlled. The bone marrow begins to take over the process of erythrocyte production—a task that the liver performed during the embryonic period. The liver now secretes bile. The fetus circulates amniotic fluid by swallowing it and producing urine. The eyes are well-developed by this stage, but the eyelids are fused shut. The fingers and toes begin to develop nails. By the end of week 12, the fetus measures approximately 9 cm (3.5 in) from crown to rump.
Weeks 13–16 are marked by sensory organ development. The eyes move closer together; blinking motions begin, although the eyes remain sealed shut. The lips exhibit sucking motions. The ears move upward and lie flatter against the head. The scalp begins to grow hair. The excretory system is also developing: the kidneys are well-formed, and meconium, or fetal feces, begins to accumulate in the intestines. Meconium consists of ingested amniotic fluid, cellular debris, mucus, and bile.
During approximately weeks 16–20, as the fetus grows and limb movements become more powerful, the mother may begin to feel quickening, or fetal movements. However, space restrictions limit these movements and typically force the growing fetus into the “fetal position,” with the arms crossed and the legs bent at the knees. Sebaceous glands coat the skin with a waxy, protective substance called vernix caseosa that protects and moisturizes the skin and may provide lubrication during childbirth. A silky hair called lanugo also covers the skin during weeks 17–20, but it is shed as the fetus continues to grow. Extremely premature infants sometimes exhibit residual lanugo.
Developmental weeks 21–30 are characterized by rapid weight gain, which is important for maintaining a stable body temperature after birth. The bone marrow completely takes over erythrocyte synthesis, and the axons of the spinal cord begin to be myelinated, or coated in the electrically insulating glial cell sheaths that are necessary for efficient nervous system functioning. (The process of myelination is not completed until adolescence.) During this period, the fetus grows eyelashes. The eyelids are no longer fused and can be opened and closed. The lungs begin producing surfactant, a substance that reduces surface tension in the lungs and assists proper lung expansion after birth. Inadequate surfactant production in premature newborns may result in respiratory distress syndrome, and as a result, the newborn may require surfactant replacement therapy, supplemental oxygen, or maintenance in a continuous positive airway pressure (CPAP) chamber during their first days or weeks of life. In male fetuses, the testes descend into the scrotum near the end of this period. The fetus at 30 weeks measures 28 cm (11 in) from crown to rump and exhibits the approximate body proportions of a full-term newborn, but still is much leaner.
INTERACTIVE LINK
Visit this site for a summary of the stages of pregnancy, as experienced by the mother, and view the stages of development of the fetus throughout gestation. At what point in fetal development can a regular heartbeat be detected?
The fetus continues to lay down subcutaneous fat from week 31 until birth. The added fat fills out the hypodermis, and the skin transitions from red and wrinkled to soft and pink. Lanugo is shed, and the nails grow to the tips of the fingers and toes. Immediately before birth, the average crown-to-rump length is 35.5–40.5 cm (14–16 in), and the fetus weighs approximately 2.5–4 kg (5.5–8.8 lbs). Once born, the newborn is no longer confined to the fetal position, so subsequent measurements are made from head-to-toe instead of from crown-to-rump. At birth, the average length is approximately 51 cm (20 in).
DISORDERS OF THE...
Developing Fetus
Throughout the second half of gestation, the fetal intestines accumulate a tarry, greenish black meconium. The newborn’s first stools consist almost entirely of meconium; they later transition to seedy yellow stools or slightly formed tan stools as meconium is cleared and replaced with digested breast milk or formula, respectively. Unlike these later stools, meconium is sterile; it is devoid of bacteria because the fetus is in a sterile environment and has not consumed any breast milk or formula. Typically, an infant does not pass meconium until after birth. However, in 5–20 percent of births, the fetus has a bowel movement in utero, which can cause major complications in the newborn.
The passage of meconium in the uterus signals fetal distress, particularly fetal hypoxia (i.e., oxygen deprivation). This may be caused by maternal drug abuse (especially tobacco or cocaine), maternal hypertension, depletion of amniotic fluid, long labor or difficult birth, or a defect in the placenta that prevents it from delivering adequate oxygen to the fetus. Meconium passage is typically a complication of full-term or post-term newborns because it is rarely passed before 34 weeks of gestation, when the gastrointestinal system has matured and is appropriately controlled by nervous system stimuli. Fetal distress can stimulate the vagus nerve to trigger gastrointestinal peristalsis and relaxation of the anal sphincter. Notably, fetal hypoxic stress also induces a gasping reflex, increasing the likelihood that meconium will be inhaled into the fetal lungs.
Although meconium is a sterile substance, it interferes with the antibiotic properties of the amniotic fluid and makes the newborn and mother more vulnerable to bacterial infections at birth and during the perinatal period. Specifically, inflammation of the fetal membranes, inflammation of the uterine lining, or neonatal sepsis (infection in the newborn) may occur. Meconium also irritates delicate fetal skin and can cause a rash.
The first sign that a fetus has passed meconium usually does not come until childbirth, when the amniotic sac ruptures. Normal amniotic fluid is clear and watery, but amniotic fluid in which meconium has been passed is stained greenish or yellowish. Antibiotics given to the mother may reduce the incidence of maternal bacterial infections, but it is critical that meconium is aspirated from the newborn before the first breath. Under these conditions, an obstetrician will extensively aspirate the infant’s airways as soon as the head is delivered, while the rest of the infant’s body is still inside the birth canal.
Aspiration of meconium with the first breath can result in labored breathing, a barrel-shaped chest, or a low Apgar score. An obstetrician can identify meconium aspiration by listening to the lungs with a stethoscope for a coarse rattling sound. Blood gas tests and chest X-rays of the infant can confirm meconium aspiration. Inhaled meconium after birth could obstruct a newborn’s airways leading to alveolar collapse, interfere with surfactant function by stripping it from the lungs, or cause pulmonary inflammation or hypertension. Any of these complications will make the newborn much more vulnerable to pulmonary infection, including pneumonia.
Maternal Changes During Pregnancy, Labor, and Birth
- Explain how estrogen, progesterone, and hCG are involved in maintaining pregnancy
- List the contributors to weight gain during pregnancy
- Describe the major changes to the maternal digestive, circulatory, and integumentary systems during pregnancy
- Summarize the events leading to labor
- Identify and describe each of the three stages of childbirth
A full-term pregnancy lasts approximately 270 days (approximately 38.5 weeks) from conception to birth. Because it is easier to remember the first day of the last menstrual period (LMP) than to estimate the date of conception, obstetricians set the due date as 284 days (approximately 40.5 weeks) from the LMP. This assumes that conception occurred on day 14 of the woman’s cycle, which is usually a good approximation. The 40 weeks of an average pregnancy are usually discussed in terms of three trimesters, each approximately 13 weeks. During the second and third trimesters, the pre-pregnancy uterus—about the size of a fist—grows dramatically to contain the fetus, causing a number of anatomical changes in the mother (Figure 28.18).
Figure 28.18 Size of Uterus throughout Pregnancy The uterus grows throughout pregnancy to accommodate the fetus.
Effects of Hormones
Virtually all of the effects of pregnancy can be attributed in some way to the influence of hormones—particularly estrogens, progesterone, and hCG. During weeks 7–12 from the LMP, the pregnancy hormones are primarily generated by the corpus luteum. Progesterone secreted by the corpus luteum stimulates the production of decidual cells of the endometrium that nourish the blastocyst before placentation. As the placenta develops and the corpus luteum degenerates during weeks 12–17, the placenta gradually takes over as the endocrine organ of pregnancy.
The placenta converts weak androgens secreted by the maternal and fetal adrenal glands to estrogens, which are necessary for pregnancy to progress. Estrogen levels climb throughout the pregnancy, increasing 30-fold by childbirth. Estrogens have the following actions:
- They suppress FSH and LH production, effectively preventing ovulation. (This function is the biological basis of hormonal birth control pills.)
- They induce the growth of fetal tissues and are necessary for the maturation of the fetal lungs and liver.
- They promote fetal viability by regulating progesterone production and triggering fetal synthesis of cortisol, which helps with the maturation of the lungs, liver, and endocrine organs such as the thyroid gland and adrenal gland.
- They stimulate maternal tissue growth, leading to uterine enlargement and mammary duct expansion and branching.
Relaxin, another hormone secreted by the corpus luteum and then by the placenta, helps prepare the mother’s body for childbirth. It increases the elasticity of the symphysis pubis joint and pelvic ligaments, making room for the growing fetus and allowing expansion of the pelvic outlet for childbirth. Relaxin also helps dilate the cervix during labor.
The placenta takes over the synthesis and secretion of progesterone throughout pregnancy as the corpus luteum degenerates. Like estrogen, progesterone suppresses FSH and LH. It also inhibits uterine contractions, protecting the fetus from preterm birth. This hormone decreases in late gestation, allowing uterine contractions to intensify and eventually progress to true labor. The placenta also produces hCG. In addition to promoting survival of the corpus luteum, hCG stimulates the male fetal gonads to secrete testosterone, which is essential for the development of the male reproductive system.
The anterior pituitary enlarges and ramps up its hormone production during pregnancy, raising the levels of thyrotropin, prolactin, and adrenocorticotropic hormone (ACTH). Thyrotropin, in conjunction with placental hormones, increases the production of thyroid hormone, which raises the maternal metabolic rate. This can markedly augment a pregnant woman’s appetite and cause hot flashes. Prolactin stimulates enlargement of the mammary glands in preparation for milk production. ACTH stimulates maternal cortisol secretion, which contributes to fetal protein synthesis. In addition to the pituitary hormones, increased parathyroid levels mobilize calcium from maternal bones for fetal use.
Weight Gain
The second and third trimesters of pregnancy are associated with dramatic changes in maternal anatomy and physiology. The most obvious anatomical sign of pregnancy is the dramatic enlargement of the abdominal region, coupled with maternal weight gain. This weight results from the growing fetus as well as the enlarged uterus, amniotic fluid, and placenta. Additional breast tissue and dramatically increased blood volume also contribute to weight gain (Table 28.2). Surprisingly, fat storage accounts for only approximately 2.3 kg (5 lbs) in a normal pregnancy and serves as a reserve for the increased metabolic demand of breastfeeding.
During the first trimester, the mother does not need to consume additional calories to maintain a healthy pregnancy. However, a weight gain of approximately 0.45 kg (1 lb) per month is common. During the second and third trimesters, the mother’s appetite increases, but it is only necessary for her to consume an additional 300 calories per day to support the growing fetus. Most women gain approximately 0.45 kg (1 lb) per week.
Contributors to Weight Gain During Pregnancy
| Component | Weight (kg) | Weight (lb) |
|---|---|---|
| Fetus | 3.2–3.6 | 7–8 |
| Placenta and fetal membranes | 0.9–1.8 | 2–4 |
| Amniotic fluid | 0.9–1.4 | 2–3 |
| Breast tissue | 0.9–1.4 | 2–3 |
| Blood | 1.4 | 4 |
| Fat | 0.9–4.1 | 3–9 |
| Uterus | 0.9–2.3 | 2–5 |
| Total | 10–16.3 | 22–36 |
Table 28.2
Changes in Organ Systems During Pregnancy
As the woman’s body adapts to pregnancy, characteristic physiologic changes occur. These changes can sometimes prompt symptoms often referred to collectively as the common discomforts of pregnancy.
Digestive and Urinary System Changes
Nausea and vomiting, sometimes triggered by an increased sensitivity to odors, are common during the first few weeks to months of pregnancy. This phenomenon is often referred to as “morning sickness,” although the nausea may persist all day. The source of pregnancy nausea is thought to be the increased circulation of pregnancy-related hormones, specifically circulating estrogen, progesterone, and hCG. Decreased intestinal peristalsis may also contribute to nausea. By about week 12 of pregnancy, nausea typically subsides.
A common gastrointestinal complaint during the later stages of pregnancy is gastric reflux, or heartburn, which results from the upward, constrictive pressure of the growing uterus on the stomach. The same decreased peristalsis that may contribute to nausea in early pregnancy is also thought to be responsible for pregnancy-related constipation as pregnancy progresses.
The downward pressure of the uterus also compresses the urinary bladder, leading to frequent urination. The problem is exacerbated by increased urine production. In addition, the maternal urinary system processes both maternal and fetal wastes, further increasing the total volume of urine.
Circulatory System Changes
Blood volume increases substantially during pregnancy, so that by childbirth, it exceeds its preconception volume by 30 percent, or approximately 1–2 liters. The greater blood volume helps to manage the demands of fetal nourishment and fetal waste removal. In conjunction with increased blood volume, the pulse and blood pressure also rise moderately during pregnancy. As the fetus grows, the uterus compresses underlying pelvic blood vessels, hampering venous return from the legs and pelvic region. As a result, many pregnant women develop varicose veins or hemorrhoids.
Respiratory System Changes
During the second half of pregnancy, the respiratory minute volume (volume of gas inhaled or exhaled by the lungs per minute) increases by 50 percent to compensate for the oxygen demands of the fetus and the increased maternal metabolic rate. The growing uterus exerts upward pressure on the diaphragm, decreasing the volume of each inspiration and potentially causing shortness of breath, or dyspnea. During the last several weeks of pregnancy, the pelvis becomes more elastic, and the fetus descends lower in a process called lightening. This typically ameliorates dyspnea.
The respiratory mucosa swell in response to increased blood flow during pregnancy, leading to nasal congestion and nose bleeds, particularly when the weather is cold and dry. Humidifier use and increased fluid intake are often recommended to counteract congestion.
Integumentary System Changes
The dermis stretches extensively to accommodate the growing uterus, breast tissue, and fat deposits on the thighs and hips. Torn connective tissue beneath the dermis can cause striae (stretch marks) on the abdomen, which appear as red or purple marks during pregnancy that fade to a silvery white color in the months after childbirth.
An increase in melanocyte-stimulating hormone, in conjunction with estrogens, darkens the areolae and creates a line of pigment from the umbilicus to the pubis called the linea nigra (Figure 28.19). Melanin production during pregnancy may also darken or discolor skin on the face to create a chloasma, or “mask of pregnancy.”
Figure 28.19 Linea Nigra The linea nigra, a dark medial line running from the umbilicus to the pubis, forms during pregnancy and persists for a few weeks following childbirth. The linea nigra shown here corresponds to a pregnancy that is 22 weeks along.
Physiology of Labor
Childbirth, or parturition, typically occurs within a week of a woman’s due date, unless the woman is pregnant with more than one fetus, which usually causes her to go into labor early. As a pregnancy progresses into its final weeks, several physiological changes occur in response to hormones that trigger labor.
First, recall that progesterone inhibits uterine contractions throughout the first several months of pregnancy. As the pregnancy enters its seventh month, progesterone levels plateau and then drop. Estrogen levels, however, continue to rise in the maternal circulation (Figure 28.20). The increasing ratio of estrogen to progesterone makes the myometrium (the uterine smooth muscle) more sensitive to stimuli that promote contractions (because progesterone no longer inhibits them). Moreover, in the eighth month of pregnancy, fetal cortisol rises, which boosts estrogen secretion by the placenta and further overpowers the uterine-calming effects of progesterone. Some women may feel the result of the decreasing levels of progesterone in late pregnancy as weak and irregular peristaltic Braxton Hicks contractions, also called false labor. These contractions can often be relieved with rest or hydration.
Figure 28.20 Hormones Initiating Labor A positive feedback loop of hormones works to initiate labor.
A common sign that labor will be short is the so-called “bloody show.” During pregnancy, a plug of mucus accumulates in the cervical canal, blocking the entrance to the uterus. Approximately 1–2 days prior to the onset of true labor, this plug loosens and is expelled, along with a small amount of blood.
Meanwhile, the posterior pituitary has been boosting its secretion of oxytocin, a hormone that stimulates the contractions of labor. At the same time, the myometrium increases its sensitivity to oxytocin by expressing more receptors for this hormone. As labor nears, oxytocin begins to stimulate stronger, more painful uterine contractions, which—in a positive feedback loop—stimulate the secretion of prostaglandins from fetal membranes. Like oxytocin, prostaglandins also enhance uterine contractile strength. The fetal pituitary also secretes oxytocin, which increases prostaglandins even further. Given the importance of oxytocin and prostaglandins to the initiation and maintenance of labor, it is not surprising that, when a pregnancy is not progressing to labor and needs to be induced, a pharmaceutical version of these compounds (called pitocin) is administered by intravenous drip.
Finally, stretching of the myometrium and cervix by a full-term fetus in the vertex (head-down) position is regarded as a stimulant to uterine contractions. The sum of these changes initiates the regular contractions known as true labor, which become more powerful and more frequent with time. The pain of labor is attributed to myometrial hypoxia during uterine contractions.
Stages of Childbirth
The process of childbirth can be divided into three stages: cervical dilation, expulsion of the newborn, and afterbirth (Figure 28.21).
Cervical Dilation
For vaginal birth to occur, the cervix must dilate fully to 10 cm in diameter—wide enough to deliver the newborn’s head. The dilation stage is the longest stage of labor and typically takes 6–12 hours. However, it varies widely and may take minutes, hours, or days, depending in part on whether the mother has given birth before; in each subsequent labor, this stage tends to be shorter.
Figure 28.21 Stages of Childbirth The stages of childbirth include Stage 1, early cervical dilation; Stage 2, full dilation and expulsion of the newborn; and Stage 3, delivery of the placenta and associated fetal membranes. (The position of the newborn’s shoulder is described relative to the mother.)
True labor progresses in a positive feedback loop in which uterine contractions stretch the cervix, causing it to dilate and efface, or become thinner. Cervical stretching induces reflexive uterine contractions that dilate and efface the cervix further. In addition, cervical dilation boosts oxytocin secretion from the pituitary, which in turn triggers more powerful uterine contractions. When labor begins, uterine contractions may occur only every 3–30 minutes and last only 20–40 seconds; however, by the end of this stage, contractions may occur as frequently as every 1.5–2 minutes and last for a full minute.
Each contraction sharply reduces oxygenated blood flow to the fetus. For this reason, it is critical that a period of relaxation occur after each contraction. Fetal distress, measured as a sustained decrease or increase in the fetal heart rate, can result from severe contractions that are too powerful or lengthy for oxygenated blood to be restored to the fetus. Such a situation can be cause for an emergency birth with vacuum, forceps, or surgically by Caesarian section.
The amniotic membranes rupture before the onset of labor in about 12 percent of women; they typically rupture at the end of the dilation stage in response to excessive pressure from the fetal head entering the birth canal.
Expulsion Stage
The expulsion stage begins when the fetal head enters the birth canal and ends with birth of the newborn. It typically takes up to 2 hours, but it can last longer or be completed in minutes, depending in part on the orientation of the fetus. The vertex presentation known as the occiput anterior vertex is the most common presentation and is associated with the greatest ease of vaginal birth. The fetus faces the maternal spinal cord and the smallest part of the head (the posterior aspect called the occiput) exits the birth canal first.
In fewer than 5 percent of births, the infant is oriented in the breech presentation, or buttocks down. In a complete breech, both legs are crossed and oriented downward. In a frank breech presentation, the legs are oriented upward. Before the 1960s, it was common for breech presentations to be delivered vaginally. Today, most breech births are accomplished by Caesarian section.
Vaginal birth is associated with significant stretching of the vaginal canal, the cervix, and the perineum. Until recent decades, it was routine procedure for an obstetrician to numb the perineum and perform an episiotomy, an incision in the posterior vaginal wall and perineum. The perineum is now more commonly allowed to tear on its own during birth. Both an episiotomy and a perineal tear need to be sutured shortly after birth to ensure optimal healing. Although suturing the jagged edges of a perineal tear may be more difficult than suturing an episiotomy, tears heal more quickly, are less painful, and are associated with less damage to the muscles around the vagina and rectum.
Upon birth of the newborn’s head, an obstetrician will aspirate mucus from the mouth and nose before the newborn’s first breath. Once the head is birthed, the rest of the body usually follows quickly. The umbilical cord is then double-clamped, and a cut is made between the clamps. This completes the second stage of childbirth.
Afterbirth
The delivery of the placenta and associated membranes, commonly referred to as the afterbirth, marks the final stage of childbirth. After expulsion of the newborn, the myometrium continues to contract. This movement shears the placenta from the back of the uterine wall. It is then easily delivered through the vagina. Continued uterine contractions then reduce blood loss from the site of the placenta. Delivery of the placenta marks the beginning of the postpartum period—the period of approximately 6 weeks immediately following childbirth during which the mother’s body gradually returns to a non-pregnant state. If the placenta does not birth spontaneously within approximately 30 minutes, it is considered retained, and the obstetrician may attempt manual removal. If this is not successful, surgery may be required.
It is important that the obstetrician examines the expelled placenta and fetal membranes to ensure that they are intact. If fragments of the placenta remain in the uterus, they can cause postpartum hemorrhage. Uterine contractions continue for several hours after birth to return the uterus to its pre-pregnancy size in a process called involution, which also allows the mother’s abdominal organs to return to their pre-pregnancy locations. Breastfeeding facilitates this process.
Although postpartum uterine contractions limit blood loss from the detachment of the placenta, the mother does experience a postpartum vaginal discharge called lochia. This is made up of uterine lining cells, erythrocytes, leukocytes, and other debris. Thick, dark, lochia rubra (red lochia) typically continues for 2–3 days, and is replaced by lochia serosa, a thinner, pinkish form that continues until about the tenth postpartum day. After this period, a scant, creamy, or watery discharge called lochia alba (white lochia) may continue for another 1–2 weeks.
Adjustments of the Infant at Birth and Postnatal Stages
- Discuss the importance of an infant’s first breath
- Explain the closing of the cardiac shunts
- Describe thermoregulation in the newborn
- Summarize the importance of intestinal flora in the newborn
From a fetal perspective, the process of birth is a crisis. In the womb, the fetus was snuggled in a soft, warm, dark, and quiet world. The placenta provided nutrition and oxygen continuously. Suddenly, the contractions of labor and vaginal childbirth forcibly squeeze the fetus through the birth canal, limiting oxygenated blood flow during contractions and shifting the skull bones to accommodate the small space. After birth, the newborn’s system must make drastic adjustments to a world that is colder, brighter, and louder, and where he or she will experience hunger and thirst. The neonatal period (neo- = “new”; -natal = “birth”) spans the first to the thirtieth day of life outside of the uterus.
Respiratory Adjustments
Although the fetus “practices” breathing by inhaling amniotic fluid in utero, there is no air in the uterus and thus no true opportunity to breathe. (There is also no need to breathe because the placenta supplies the fetus with all the oxygenated blood it needs.) During gestation, the partially collapsed lungs are filled with amniotic fluid and exhibit very little metabolic activity. Several factors stimulate newborns to take their first breath at birth. First, labor contractions temporarily constrict umbilical blood vessels, reducing oxygenated blood flow to the fetus and elevating carbon dioxide levels in the blood. High carbon dioxide levels cause acidosis and stimulate the respiratory center in the brain, triggering the newborn to take a breath.
The first breath typically is taken within 10 seconds of birth, after mucus is aspirated from the infant’s mouth and nose. The first breaths inflate the lungs to nearly full capacity and dramatically decrease lung pressure and resistance to blood flow, causing a major circulatory reconfiguration. Pulmonary alveoli open, and alveolar capillaries fill with blood. Amniotic fluid in the lungs drains or is absorbed, and the lungs immediately take over the task of the placenta, exchanging carbon dioxide for oxygen by the process of respiration.
Circulatory Adjustments
The process of clamping and cutting the umbilical cord collapses the umbilical blood vessels. In the absence of medical assistance, this occlusion would occur naturally within 20 minutes of birth because the Wharton’s jelly within the umbilical cord would swell in response to the lower temperature outside of the mother’s body, and the blood vessels would constrict. Natural occlusion has occurred when the umbilical cord is no longer pulsating. For the most part, the collapsed vessels atrophy and become fibrotic remnants, existing in the mature circulatory system as ligaments of the abdominal wall and liver. The ductus venosus degenerates to become the ligamentum venosum beneath the liver. Only the proximal sections of the two umbilical arteries remain functional, taking on the role of supplying blood to the upper part of the bladder (Figure 28.22).
Figure 28.22 Neonatal Circulatory System A newborn’s circulatory system reconfigures immediately after birth. The three fetal shunts have been closed permanently, facilitating blood flow to the liver and lungs.
The newborn’s first breath is vital to initiate the transition from the fetal to the neonatal circulatory pattern. Inflation of the lungs decreases blood pressure throughout the pulmonary system, as well as in the right atrium and ventricle. In response to this pressure change, the flow of blood temporarily reverses direction through the foramen ovale, moving from the left to the right atrium, and blocking the shunt with two flaps of tissue. Within 1 year, the tissue flaps usually fuse over the shunt, turning the foramen ovale into the fossa ovalis. The ductus arteriosus constricts as a result of increased oxygen concentration, and becomes the ligamentum arteriosum. Closing of the ductus arteriosus ensures that all blood pumped to the pulmonary circuit will be oxygenated by the newly functional neonatal lungs.
Thermoregulatory Adjustments
The fetus floats in warm amniotic fluid that is maintained at a temperature of approximately 98.6°F with very little fluctuation. Birth exposes newborns to a cooler environment in which they have to regulate their own body temperature. Newborns have a higher ratio of surface area to volume than adults. This means that their body has less volume throughout which to produce heat, and more surface area from which to lose heat. As a result, newborns produce heat more slowly and lose it more quickly. Newborns also have immature musculature that limits their ability to generate heat by shivering. Moreover, their nervous systems are underdeveloped, so they cannot quickly constrict superficial blood vessels in response to cold. They also have little subcutaneous fat for insulation. All these factors make it harder for newborns to maintain their body temperature.
Newborns, however, do have a special method for generating heat: nonshivering thermogenesis, which involves the breakdown of brown adipose tissue, or brown fat, which is distributed over the back, chest, and shoulders. Brown fat differs from the more familiar white fat in two ways:
- It is highly vascularized. This allows for faster delivery of oxygen, which leads to faster cellular respiration.
- It is packed with a special type of mitochondria that are able to engage in cellular respiration reactions that produce less ATP and more heat than standard cellular respiration reactions.
The breakdown of brown fat occurs automatically upon exposure to cold, so it is an important heat regulator in newborns. During fetal development, the placenta secretes inhibitors that prevent metabolism of brown adipose fat and promote its accumulation in preparation for birth.
Gastrointestinal and Urinary Adjustments
In adults, the gastrointestinal tract harbors bacterial flora—trillions of bacteria that aid in digestion, produce vitamins, and protect from the invasion or replication of pathogens. In stark contrast, the fetal intestine is sterile. The first consumption of breast milk or formula floods the neonatal gastrointestinal tract with beneficial bacteria that begin to establish the bacterial flora.
The fetal kidneys filter blood and produce urine, but the neonatal kidneys are still immature and inefficient at concentrating urine. Therefore, newborns produce very dilute urine, making it particularly important for infants to obtain sufficient fluids from breast milk or formula.
HOMEOSTATIC IMBALANCES
Homeostasis in the Newborn: Apgar Score
In the minutes following birth, a newborn must undergo dramatic systemic changes to be able to survive outside the womb. An obstetrician, midwife, or nurse can estimate how well a newborn is doing by obtaining an Apgar score. The Apgar score was introduced in 1952 by the anesthesiologist Dr. Virginia Apgar as a method to assess the effects on the newborn of anesthesia given to the laboring mother. Healthcare providers now use it to assess the general wellbeing of the newborn, whether or not analgesics or anesthetics were used.
Five criteria—skin color, heart rate, reflex, muscle tone, and respiration—are assessed, and each criterion is assigned a score of 0, 1, or 2. Scores are taken at 1 minute after birth and again at 5 minutes after birth. Each time that scores are taken, the five scores are added together. High scores (out of a possible 10) indicate the baby has made the transition from the womb well, whereas lower scores indicate that the baby may be in distress.
The technique for determining an Apgar score is quick and easy, painless for the newborn, and does not require any instruments except for a stethoscope. A convenient way to remember the five scoring criteria is to apply the mnemonic APGAR, for “appearance” (skin color), “pulse” (heart rate), “grimace” (reflex), “activity” (muscle tone), and “respiration.”
Of the five Apgar criteria, heart rate and respiration are the most critical. Poor scores for either of these measurements may indicate the need for immediate medical attention to resuscitate or stabilize the newborn. In general, any score lower than 7 at the 5-minute mark indicates that medical assistance may be needed. A total score below 5 indicates an emergency situation. Normally, a newborn will get an intermediate score of 1 for some of the Apgar criteria and will progress to a 2 by the 5-minute assessment. Scores of 8 or above are normal.
Lactation
- Describe the structure of the lactating breast
- Summarize the process of lactation
- Explain how the composition of breast milk changes during the first days of lactation and in the course of a single feeding
Lactation is the process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to an infant sucking at the nipple. Breast milk provides ideal nutrition and passive immunity for the infant, encourages mild uterine contractions to return the uterus to its pre-pregnancy size (i.e., involution), and induces a substantial metabolic increase in the mother, consuming the fat reserves stored during pregnancy.
Structure of the Lactating Breast
Mammary glands are modified sweat glands. The non-pregnant and non-lactating female breast is composed primarily of adipose and collagenous tissue, with mammary glands making up a very minor proportion of breast volume. The mammary gland is composed of milk-transporting lactiferous ducts, which expand and branch extensively during pregnancy in response to estrogen, growth hormone, cortisol, and prolactin. Moreover, in response to progesterone, clusters of breast alveoli bud from the ducts and expand outward toward the chest wall. Breast alveoli are balloon-like structures lined with milk-secreting cuboidal cells, or lactocytes, that are surrounded by a net of contractile myoepithelial cells. Milk is secreted from the lactocytes, fills the alveoli, and is squeezed into the ducts. Clusters of alveoli that drain to a common duct are called lobules; the lactating female has 12–20 lobules organized radially around the nipple. Milk drains from lactiferous ducts into lactiferous sinuses that meet at 4 to 18 perforations in the nipple, called nipple pores. The small bumps of the areola (the darkened skin around the nipple) are called Montgomery glands. They secrete oil to cleanse the nipple opening and prevent chapping and cracking of the nipple during breastfeeding.
The Process of Lactation
The pituitary hormone prolactin is instrumental in the establishment and maintenance of breast milk supply. It also is important for the mobilization of maternal micronutrients for breast milk.
Near the fifth week of pregnancy, the level of circulating prolactin begins to increase, eventually rising to approximately 10–20 times the pre-pregnancy concentration. We noted earlier that, during pregnancy, prolactin and other hormones prepare the breasts anatomically for the secretion of milk. The level of prolactin plateaus in late pregnancy, at a level high enough to initiate milk production. However, estrogen, progesterone, and other placental hormones inhibit prolactin-mediated milk synthesis during pregnancy. It is not until the placenta is expelled that this inhibition is lifted and milk production commences.
After childbirth, the baseline prolactin level drops sharply, but it is restored for a 1-hour spike during each feeding to stimulate the production of milk for the next feeding. With each prolactin spike, estrogen and progesterone also increase slightly.
When the infant suckles, sensory nerve fibers in the areola trigger a neuroendocrine reflex that results in milk secretion from lactocytes into the alveoli. The posterior pituitary releases oxytocin, which stimulates myoepithelial cells to squeeze milk from the alveoli so it can drain into the lactiferous ducts, collect in the lactiferous sinuses, and discharge through the nipple pores. It takes less than 1 minute from the time when an infant begins suckling (the latent period) until milk is secreted (the let-down). Figure 28.23 summarizes the positive feedback loop of the let-down reflex.
Figure 28.23 Let-Down Reflex A positive feedback loop ensures continued milk production as long as the infant continues to breastfeed.
The prolactin-mediated synthesis of milk changes with time. Frequent milk removal by breastfeeding (or pumping) will maintain high circulating prolactin levels for several months. However, even with continued breastfeeding, baseline prolactin will decrease over time to its pre-pregnancy level. In addition to prolactin and oxytocin, growth hormone, cortisol, parathyroid hormone, and insulin contribute to lactation, in part by facilitating the transport of maternal amino acids, fatty acids, glucose, and calcium to breast milk.
Changes in the Composition of Breast Milk
In the final weeks of pregnancy, the alveoli swell with colostrum, a thick, yellowish substance that is high in protein but contains less fat and glucose than mature breast milk (Table 28.3). Before childbirth, some women experience leakage of colostrum from the nipples. In contrast, mature breast milk does not leak during pregnancy and is not secreted until several days after childbirth.
Compositions of Human Colostrum, Mature Breast Milk, and Cow’s Milk (g/L)
| Human colostrum | Human breast milk | Cow’s milk* | |
|---|---|---|---|
| Total protein | 23 | 11 | 31 |
| Immunoglobulins | 19 | 0.1 | 1 |
| Fat | 30 | 45 | 38 |
| Lactose | 57 | 71 | 47 |
| Calcium | 0.5 | 0.3 | 1.4 |
| Phosphorus | 0.16 | 0.14 | 0.90 |
| Sodium | 0.50 | 0.15 | 0.41 |
Table 28.3 *Cow’s milk should never be given to an infant. Its composition is not suitable and its proteins are difficult for the infant to digest.
Colostrum is secreted during the first 48–72 hours postpartum. Only a small volume of colostrum is produced—approximately 3 ounces in a 24-hour period—but it is sufficient for the newborn in the first few days of life. Colostrum is rich with immunoglobulins, which confer gastrointestinal, and also likely systemic, immunity as the newborn adjusts to a nonsterile environment.
After about the third postpartum day, the mother secretes transitional milk that represents an intermediate between mature milk and colostrum. This is followed by mature milk from approximately postpartum day 10 (see Table 28.3). As you can see in the accompanying table, cow’s milk is not a substitute for breast milk. It contains less lactose, less fat, and more protein and minerals. Moreover, the proteins in cow’s milk are difficult for an infant’s immature digestive system to metabolize and absorb.
The first few weeks of breastfeeding may involve leakage, soreness, and periods of milk engorgement as the relationship between milk supply and infant demand becomes established. Once this period is complete, the mother will produce approximately 1.5 liters of milk per day for a single infant, and more if she has twins or triplets. As the infant goes through growth spurts, the milk supply constantly adjusts to accommodate changes in demand. A woman can continue to lactate for years, but once breastfeeding is stopped for approximately 1 week, any remaining milk will be reabsorbed; in most cases, no more will be produced, even if suckling or pumping is resumed.
Mature milk changes from the beginning to the end of a feeding. The early milk, called foremilk, is watery, translucent, and rich in lactose and protein. Its purpose is to quench the infant’s thirst. Hindmilk is delivered toward the end of a feeding. It is opaque, creamy, and rich in fat, and serves to satisfy the infant’s appetite.
During the first days of a newborn’s life, it is important for meconium to be cleared from the intestines and for bilirubin to be kept low in the circulation. Recall that bilirubin, a product of erythrocyte breakdown, is processed by the liver and secreted in bile. It enters the gastrointestinal tract and exits the body in the stool. Breast milk has laxative properties that help expel meconium from the intestines and clear bilirubin through the excretion of bile. A high concentration of bilirubin in the blood causes jaundice. Some degree of jaundice is normal in newborns, but a high level of bilirubin—which is neurotoxic—can cause brain damage. Newborns, who do not yet have a fully functional blood–brain barrier, are highly vulnerable to the bilirubin circulating in the blood. Indeed, hyperbilirubinemia, a high level of circulating bilirubin, is the most common condition requiring medical attention in newborns. Newborns with hyperbilirubinemia are treated with phototherapy because UV light helps to break down the bilirubin quickly.
Patterns of inheritance
- Differentiate between genotype and phenotype
- Describe how alleles determine a person’s traits
- Summarize Mendel’s experiments and relate them to human genetics
- Explain the inheritance of autosomal dominant and recessive and sex-linked genetic disorders
We have discussed the events that lead to the development of a newborn. But what makes each newborn unique? The answer lies, of course, in the DNA in the sperm and oocyte that combined to produce that first diploid cell, the human zygote.
From Genotype to Phenotype
Each human body cell has a full complement of DNA stored in 23 pairs of chromosomes. Figure 28.24 shows the pairs in a systematic arrangement called a karyotype. Among these is one pair of chromosomes, called the sex chromosomes, that determines the sex of the individual (XX in females, XY in males). The remaining 22 chromosome pairs are called autosomal chromosomes. Each of these chromosomes carries hundreds or even thousands of genes, each of which codes for the assembly of a particular protein—that is, genes are “expressed” as proteins. An individual’s complete genetic makeup is referred to as his or her genotype. The characteristics that the genes express, whether they are physical, behavioral, or biochemical, are a person’s phenotype.
You inherit one chromosome in each pair—a full complement of 23—from each parent. This occurs when the sperm and oocyte combine at the moment of your conception. Homologous chromosomes—those that make up a complementary pair—have genes for the same characteristics in the same location on the chromosome. Because one copy of a gene, an allele, is inherited from each parent, the alleles in these complementary pairs may vary. Take for example an allele that encodes for dimples. A child may inherit the allele encoding for dimples on the chromosome from the father and the allele that encodes for smooth skin (no dimples) on the chromosome from the mother.
Figure 28.24 Chromosomal Complement of a Male Each pair of chromosomes contains hundreds to thousands of genes. The banding patterns are nearly identical for the two chromosomes within each pair, indicating the same organization of genes. As is visible in this karyotype, the only exception to this is the XY sex chromosome pair in males. (credit: National Human Genome Research Institute)
Although a person can have two identical alleles for a single gene (a homozygous state), it is also possible for a person to have two different alleles (a heterozygous state). The two alleles can interact in several different ways. The expression of an allele can be dominant, for which the activity of this gene will mask the expression of a nondominant, or recessive, allele. Sometimes dominance is complete; at other times, it is incomplete. In some cases, both alleles are expressed at the same time in a form of expression known as codominance.
In the simplest scenario, a single pair of genes will determine a single heritable characteristic. However, it is quite common for multiple genes to interact to confer a feature. For instance, eight or more genes—each with their own alleles—determine eye color in humans. Moreover, although any one person can only have two alleles corresponding to a given gene, more than two alleles commonly exist in a population. This phenomenon is called multiple alleles. For example, there are three different alleles that encode ABO blood type; these are designated IA, IB, and i.
Over 100 years of theoretical and experimental genetics studies, and the more recent sequencing and annotation of the human genome, have helped scientists to develop a better understanding of how an individual’s genotype is expressed as their phenotype. This body of knowledge can help scientists and medical professionals to predict, or at least estimate, some of the features that an offspring will inherit by examining the genotypes or phenotypes of the parents. One important application of this knowledge is to identify an individual’s risk for certain heritable genetic disorders. However, most diseases have a multigenic pattern of inheritance and can also be affected by the environment, so examining the genotypes or phenotypes of a person’s parents will provide only limited information about the risk of inheriting a disease. Only for a handful of single-gene disorders can genetic testing allow clinicians to calculate the probability with which a child born to the two parents tested may inherit a specific disease.
Mendel’s Theory of Inheritance
Our contemporary understanding of genetics rests on the work of a nineteenth-century monk. Working in the mid-1800s, long before anyone knew about genes or chromosomes, Gregor Mendel discovered that garden peas transmit their physical characteristics to subsequent generations in a discrete and predictable fashion. When he mated, or crossed, two pure-breeding pea plants that differed by a certain characteristic, the first-generation offspring all looked like one of the parents. For instance, when he crossed tall and dwarf pure-breeding pea plants, all of the offspring were tall. Mendel called tallness dominantbecause it was expressed in offspring when it was present in a purebred parent. He called dwarfism recessive because it was masked in the offspring if one of the purebred parents possessed the dominant characteristic. Note that tallness and dwarfism are variations on the characteristic of height. Mendel called such a variation a trait. We now know that these traits are the expression of different alleles of the gene encoding height.
Mendel performed thousands of crosses in pea plants with differing traits for a variety of characteristics. And he repeatedly came up with the same results—among the traits he studied, one was always dominant, and the other was always recessive. (Remember, however, that this dominant–recessive relationship between alleles is not always the case; some alleles are codominant, and sometimes dominance is incomplete.)
Using his understanding of dominant and recessive traits, Mendel tested whether a recessive trait could be lost altogether in a pea lineage or whether it would resurface in a later generation. By crossing the second-generation offspring of purebred parents with each other, he showed that the latter was true: recessive traits reappeared in third-generation plants in a ratio of 3:1 (three offspring having the dominant trait and one having the recessive trait). Mendel then proposed that characteristics such as height were determined by heritable “factors” that were transmitted, one from each parent, and inherited in pairs by offspring.
In the language of genetics, Mendel’s theory applied to humans says that if an individual receives two dominant alleles, one from each parent, the individual’s phenotype will express the dominant trait. If an individual receives two recessive alleles, then the recessive trait will be expressed in the phenotype. Individuals who have two identical alleles for a given gene, whether dominant or recessive, are said to be homozygous for that gene (homo- = “same”). Conversely, an individual who has one dominant allele and one recessive allele is said to be heterozygous for that gene (hetero- = “different” or “other”). In this case, the dominant trait will be expressed, and the individual will be phenotypically identical to an individual who possesses two dominant alleles for the trait.
It is common practice in genetics to use capital and lowercase letters to represent dominant and recessive alleles. Using Mendel’s pea plants as an example, if a tall pea plant is homozygous, it will possess two tall alleles (TT). A dwarf pea plant must be homozygous because its dwarfism can only be expressed when two recessive alleles are present (tt). A heterozygous pea plant (Tt) would be tall and phenotypically indistinguishable from a tall homozygous pea plant because of the dominant tall allele. Mendel deduced that a 3:1 ratio of dominant to recessive would be produced by the random segregation of heritable factors (genes) when crossing two heterozygous pea plants. In other words, for any given gene, parents are equally likely to pass down either one of their alleles to their offspring in a haploid gamete, and the result will be expressed in a dominant–recessive pattern if both parents are heterozygous for the trait.
Because of the random segregation of gametes, the laws of chance and probability come into play when predicting the likelihood of a given phenotype. Consider a cross between an individual with two dominant alleles for a trait (AA) and an individual with two recessive alleles for the same trait (aa). All of the parental gametes from the dominant individual would be A, and all of the parental gametes from the recessive individual would be a (Figure 28.25). All of the offspring of that second generation, inheriting one allele from each parent, would have the genotype Aa, and the probability of expressing the phenotype of the dominant allele would be 4 out of 4, or 100 percent.
This seems simple enough, but the inheritance pattern gets interesting when the second-generation Aa individuals are crossed. In this generation, 50 percent of each parent’s gametes are A and the other 50 percent are a. By Mendel’s principle of random segregation, the possible combinations of gametes that the offspring can receive are AA, Aa, aA (which is the same as Aa), and aa. Because segregation and fertilization are random, each offspring has a 25 percent chance of receiving any of these combinations. Therefore, if an Aa × Aa cross were performed 1000 times, approximately 250 (25 percent) of the offspring would be AA; 500 (50 percent) would be Aa (that is, Aa plus aA); and 250 (25 percent) would be aa. The genotypic ratio for this inheritance pattern is 1:2:1. However, we have already established that AA and Aa (and aA) individuals all express the dominant trait (i.e., share the same phenotype), and can therefore be combined into one group. The result is Mendel’s third-generation phenotype ratio of 3:1.
Figure 28.25 Random Segregation In the formation of gametes, it is equally likely that either one of a pair alleles from one parent will be passed on to the offspring. This figure follows the possible combinations of alleles through two generations following a first-generation cross of homozygous dominant and homozygous recessive parents. The recessive phenotype, which is masked in the second generation, has a 1 in 4, or 25 percent, chance of reappearing in the third generation.
Mendel’s observation of pea plants also included many crosses that involved multiple traits, which prompted him to formulate the principle of independent assortment. The law states that the members of one pair of genes (alleles) from a parent will sort independently from other pairs of genes during the formation of gametes. Applied to pea plants, that means that the alleles associated with the different traits of the plant, such as color, height, or seed type, will sort independently of one another. This holds true except when two alleles happen to be located close to one other on the same chromosome. Independent assortment provides for a great degree of diversity in offspring.
Mendelian genetics represent the fundamentals of inheritance, but there are two important qualifiers to consider when applying Mendel’s findings to inheritance studies in humans. First, as we’ve already noted, not all genes are inherited in a dominant–recessive pattern. Although all diploid individuals have two alleles for every gene, allele pairs may interact to create several types of inheritance patterns, including incomplete dominance and codominance.
Secondly, Mendel performed his studies using thousands of pea plants. He was able to identify a 3:1 phenotypic ratio in second-generation offspring because his large sample size overcame the influence of variability resulting from chance. In contrast, no human couple has ever had thousands of children. If we know that a man and woman are both heterozygous for a recessive genetic disorder, we would predict that one in every four of their children would be affected by the disease. In real life, however, the influence of chance could change that ratio significantly. For example, if a man and a woman are both heterozygous for cystic fibrosis, a recessive genetic disorder that is expressed only when the individual has two defective alleles, we would expect one in four of their children to have cystic fibrosis. However, it is entirely possible for them to have seven children, none of whom is affected, or for them to have two children, both of whom are affected. For each individual child, the presence or absence of a single gene disorder depends on which alleles that child inherits from his or her parents.
Autosomal Dominant Inheritance
In the case of cystic fibrosis, the disorder is recessive to the normal phenotype. However, a genetic abnormality may be dominant to the normal phenotype. When the dominant allele is located on one of the 22 pairs of autosomes (non-sex chromosomes), we refer to its inheritance pattern as autosomal dominant. An example of an autosomal dominant disorder is neurofibromatosis type I, a disease that induces tumor formation within the nervous system that leads to skin and skeletal deformities. Consider a couple in which one parent is heterozygous for this disorder (and who therefore has neurofibromatosis), Nn, and one parent is homozygous for the normal gene, nn. The heterozygous parent would have a 50 percent chance of passing the dominant allele for this disorder to his or her offspring, and the homozygous parent would always pass the normal allele. Therefore, four possible offspring genotypes are equally likely to occur: Nn, Nn, nn, and nn. That is, every child of this couple would have a 50 percent chance of inheriting neurofibromatosis. This inheritance pattern is shown in Figure 28.26, in a form called a Punnett square, named after its creator, the British geneticist Reginald Punnett.
Figure 28.26 Autosomal Dominant Inheritance Inheritance pattern of an autosomal dominant disorder, such as neurofibromatosis, is shown in a Punnett square.
Other genetic diseases that are inherited in this pattern are achondroplastic dwarfism, Marfan syndrome, and Huntington’s disease. Because autosomal dominant disorders are expressed by the presence of just one gene, an individual with the disorder will know that he or she has at least one faulty gene. The expression of the disease may manifest later in life, after the childbearing years, which is the case in Huntington’s disease (discussed in more detail later in this section).
Autosomal Recessive Inheritance
When a genetic disorder is inherited in an autosomal recessive pattern, the disorder corresponds to the recessive phenotype. Heterozygous individuals will not display symptoms of this disorder, because their unaffected gene will compensate. Such an individual is called a carrier. Carriers for an autosomal recessive disorder may never know their genotype unless they have a child with the disorder.
An example of an autosomal recessive disorder is cystic fibrosis (CF), which we introduced earlier. CF is characterized by the chronic accumulation of a thick, tenacious mucus in the lungs and digestive tract. Decades ago, children with CF rarely lived to adulthood. With advances in medical technology, the average lifespan in developed countries has increased into middle adulthood. CF is a relatively common disorder that occurs in approximately 1 in 2000 Caucasians. A child born to two CF carriers would have a 25 percent chance of inheriting the disease. This is the same 3:1 dominant:recessive ratio that Mendel observed in his pea plants would apply here. The pattern is shown in Figure 28.27, using a diagram that tracks the likely incidence of an autosomal recessive disorder on the basis of parental genotypes.
On the other hand, a child born to a CF carrier and someone with two unaffected alleles would have a 0 percent probability of inheriting CF, but would have a 50 percent chance of being a carrier. Other examples of autosome recessive genetic illnesses include the blood disorder sickle-cell anemia, the fatal neurological disorder Tay–Sachs disease, and the metabolic disorder phenylketonuria.
Figure 28.27 Autosomal Recessive Inheritance The inheritance pattern of an autosomal recessive disorder with two carrier parents reflects a 3:1 probability of expression among offspring. (credit: U.S. National Library of Medicine)
X-linked Dominant or Recessive Inheritance
An X-linked transmission pattern involves genes located on the X chromosome of the 23rd pair (Figure 28.28). Recall that a male has one X and one Y chromosome. When a father transmits a Y chromosome, the child is male, and when he transmits an X chromosome, the child is female. A mother can transmit only an X chromosome, as both her sex chromosomes are X chromosomes.
When an abnormal allele for a gene that occurs on the X chromosome is dominant over the normal allele, the pattern is described as X-linked dominant. This is the case with vitamin D–resistant rickets: an affected father would pass the disease gene to all of his daughters, but none of his sons, because he donates only the Y chromosome to his sons (see Figure 28.28a). If it is the mother who is affected, all of her children—male or female—would have a 50 percent chance of inheriting the disorder because she can only pass an X chromosome on to her children (see Figure 28.28b). For an affected female, the inheritance pattern would be identical to that of an autosomal dominant inheritance pattern in which one parent is heterozygous and the other is homozygous for the normal gene.
Figure 28.28 X-Linked Patterns of Inheritance A chart of X-linked dominant inheritance patterns differs depending on whether (a) the father or (b) the mother is affected with the disease. (credit: U.S. National Library of Medicine)
X-linked recessive inheritance is much more common because females can be carriers of the disease yet still have a normal phenotype. Diseases transmitted by X-linked recessive inheritance include color blindness, the blood-clotting disorder hemophilia, and some forms of muscular dystrophy. For an example of X-linked recessive inheritance, consider parents in which the mother is an unaffected carrier and the father is normal. None of the daughters would have the disease because they receive a normal gene from their father. However, they have a 50 percent chance of receiving the disease gene from their mother and becoming a carrier. In contrast, 50 percent of the sons would be affected (Figure 28.29).
With X-linked recessive diseases, males either have the disease or are genotypically normal—they cannot be carriers. Females, however, can be genotypically normal, a carrier who is phenotypically normal, or affected with the disease. A daughter can inherit the gene for an X-linked recessive illness when her mother is a carrier or affected, or her father is affected. The daughter will be affected by the disease only if she inherits an X-linked recessive gene from both parents. As you can imagine, X-linked recessive disorders affect many more males than females. For example, color blindness affects at least 1 in 20 males, but only about 1 in 400 females.
Figure 28.29 X-Linked Recessive Inheritance Given two parents in which the father is normal and the mother is a carrier of an X-linked recessive disorder, a son would have a 50 percent probability of being affected with the disorder, whereas daughters would either be carriers or entirely unaffected. (credit: U.S. National Library of Medicine)
Other Inheritance Patterns: Incomplete Dominance, Codominance, and Lethal Alleles
Not all genetic disorders are inherited in a dominant–recessive pattern. In incomplete dominance, the offspring express a heterozygous phenotype that is intermediate between one parent’s homozygous dominant trait and the other parent’s homozygous recessive trait. An example of this can be seen in snapdragons when red-flowered plants and white-flowered plants are crossed to produce pink-flowered plants. In humans, incomplete dominance occurs with one of the genes for hair texture. When one parent passes a curly hair allele (the incompletely dominant allele) and the other parent passes a straight-hair allele, the effect on the offspring will be intermediate, resulting in hair that is wavy.
Codominance is characterized by the equal, distinct, and simultaneous expression of both parents’ different alleles. This pattern differs from the intermediate, blended features seen in incomplete dominance. A classic example of codominance in humans is ABO blood type. People are blood type A if they have an allele for an enzyme that facilitates the production of surface antigen A on their erythrocytes. This allele is designated IA. In the same manner, people are blood type B if they express an enzyme for the production of surface antigen B. People who have alleles for both enzymes (IA and IB) produce both surface antigens A and B. As a result, they are blood type AB. Because the effect of both alleles (or enzymes) is observed, we say that the IA and IB alleles are codominant. There is also a third allele that determines blood type. This allele (i) produces a nonfunctional enzyme. People who have two i alleles do not produce either A or B surface antigens: they have type O blood. If a person has IA and i alleles, the person will have blood type A. Notice that it does not make any difference whether a person has two IA alleles or one IA and one i allele. In both cases, the person is blood type A. Because IA masks i, we say that IA is dominant to i. Table 28.4 summarizes the expression of blood type.
Expression of Blood Types
| Blood type | Genotype | Pattern of inheritance |
|---|---|---|
| A | IAIA or IAi | IA is dominant to i |
| B | IBIB or IBi | IB is dominant to i |
| AB | IAIB | IA is co-dominant to IB |
| O | ii | Two recessive alleles |
Table 28.4
Certain combinations of alleles can be lethal, meaning they prevent the individual from developing in utero, or cause a shortened life span. In recessive lethal inheritance patterns, a child who is born to two heterozygous (carrier) parents and who inherited the faulty allele from both would not survive. An example of this is Tay–Sachs, a fatal disorder of the nervous system. In this disorder, parents with one copy of the allele for the disorder are carriers. If they both transmit their abnormal allele, their offspring will develop the disease and will die in childhood, usually before age 5.
Dominant lethal inheritance patterns are much more rare because neither heterozygotes nor homozygotes survive. Of course, dominant lethal alleles that arise naturally through mutation and cause miscarriages or stillbirths are never transmitted to subsequent generations. However, some dominant lethal alleles, such as the allele for Huntington’s disease, cause a shortened life span but may not be identified until after the person reaches reproductive age and has children. Huntington’s disease causes irreversible nerve cell degeneration and death in 100 percent of affected individuals, but it may not be expressed until the individual reaches middle age. In this way, dominant lethal alleles can be maintained in the human population. Individuals with a family history of Huntington’s disease are typically offered genetic counseling, which can help them decide whether or not they wish to be tested for the faulty gene.
Mutations
A mutation is a change in the sequence of DNA nucleotides that may or may not affect a person’s phenotype. Mutations can arise spontaneously from errors during DNA replication, or they can result from environmental insults such as radiation, certain viruses, or exposure to tobacco smoke or other toxic chemicals. Because genes encode for the assembly of proteins, a mutation in the nucleotide sequence of a gene can change amino acid sequence and, consequently, a protein’s structure and function. Spontaneous mutations occurring during meiosis are thought to account for many spontaneous abortions (miscarriages).
Chromosomal Disorders
Sometimes a genetic disease is not caused by a mutation in a gene, but by the presence of an incorrect number of chromosomes. For example, Down syndrome is caused by having three copies of chromosome 21. This is known as trisomy 21. The most common cause of trisomy 21 is chromosomal nondisjunction during meiosis. The frequency of nondisjunction events appears to increase with age, so the frequency of bearing a child with Down syndrome increases in women over 36. The age of the father matters less because nondisjunction is much less likely to occur in a sperm than in an egg.
Whereas Down syndrome is caused by having three copies of a chromosome, Turner syndrome is caused by having just one copy of the X chromosome. This is known as monosomy. The affected child is always female. Women with Turner syndrome are sterile because their sexual organs do not mature.
CAREER CONNECTION
Genetic Counselor
Given the intricate orchestration of gene expression, cell migration, and cell differentiation during prenatal development, it is amazing that the vast majority of newborns are healthy and free of major birth defects. When a woman over 35 is pregnant or intends to become pregnant, or her partner is over 55, or if there is a family history of a genetic disorder, she and her partner may want to speak to a genetic counselor to discuss the likelihood that their child may be affected by a genetic or chromosomal disorder. A genetic counselor can interpret a couple’s family history and estimate the risks to their future offspring.
For many genetic diseases, a DNA test can determine whether a person is a carrier. For instance, carrier status for Fragile X, an X-linked disorder associated with mental retardation, or for cystic fibrosis can be determined with a simple blood draw to obtain DNA for testing. A genetic counselor can educate a couple about the implications of such a test and help them decide whether to undergo testing. For chromosomal disorders, the available testing options include a blood test, amniocentesis (in which amniotic fluid is tested), and chorionic villus sampling (in which tissue from the placenta is tested). Each of these has advantages and drawbacks. A genetic counselor can also help a couple cope with the news that either one or both partners is a carrier of a genetic illness, or that their unborn child has been diagnosed with a chromosomal disorder or other birth defect.
To become a genetic counselor, one needs to complete a 4-year undergraduate program and then obtain a Master of Science in Genetic Counseling from an accredited university. Board certification is attained after passing examinations by the American Board of Genetic Counseling. Genetic counselors are essential professionals in many branches of medicine, but there is a particular demand for preconception and prenatal genetic counselors.
INTERACTIVE LINK
Visit the National Society of Genetic Counselors website for more information about genetic counselors.
INTERACTIVE LINK
Visit the American Board of Genetic Counselors, Inc., website for more information about genetic counselors.
Key Terms
- acrosomal reaction
- release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilization
- acrosome
- cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte
- afterbirth
- third stage of childbirth in which the placenta and associated fetal membranes are expelled
- allantois
- finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder
- allele
- alternative forms of a gene that occupy a specific locus on a specific gene
- amnion
- transparent membranous sac that encloses the developing fetus and fills with amniotic fluid
- amniotic cavity
- cavity that opens up between the inner cell mass and the trophoblast; develops into amnion
- autosomal chromosome
- in humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY)
- autosomal dominant
- pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
- autosomal recessive
- pattern of recessive inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
- blastocoel
- fluid-filled cavity of the blastocyst
- blastocyst
- term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated fetal membranes and placenta
- blastomere
- daughter cell of a cleavage
- Braxton Hicks contractions
- weak and irregular peristaltic contractions that can occur in the second and third trimesters; they do not indicate that childbirth is imminent
- brown adipose tissue
- highly vascularized fat tissue that is packed with mitochondria; these properties confer the ability to oxidize fatty acids to generate heat
- capacitation
- process that occurs in the female reproductive tract in which sperm are prepared for fertilization; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers
- carrier
- heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to his or her offspring
- chorion
- membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi
- chorionic membrane
- precursor to the chorion; forms from extra-embryonic mesoderm cells
- chorionic villi
- projections of the chorionic membrane that burrow into the endometrium and develop into the placenta
- cleavage
- form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells
- codominance
- pattern of inheritance that corresponds to the equal, distinct, and simultaneous expression of two different alleles
- colostrum
- thick, yellowish substance secreted from a mother’s breasts in the first postpartum days; rich in immunoglobulins
- conceptus
- pre-implantation stage of a fertilized egg and its associated membranes
- corona radiata
- in an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilization can occur
- cortical reaction
- following fertilization, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida creating a fertilization membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy
- dilation
- first stage of childbirth, involving an increase in cervical diameter
- dominant
- describes a trait that is expressed both in homozygous and heterozygous form
- dominant lethal
- inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span
- ductus arteriosus
- shunt in the pulmonary trunk that diverts oxygenated blood back to the aorta
- ductus venosus
- shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava
- ectoderm
- primary germ layer that develops into the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails
- ectopic pregnancy
- implantation of an embryo outside of the uterus
- embryo
- developing human during weeks 3–8
- embryonic folding
- process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder
- endoderm
- primary germ layer that goes on to form the gastrointestinal tract, liver, pancreas, and lungs
- epiblast
- upper layer of cells of the embryonic disc that forms from the inner cell mass; gives rise to all three germ layers
- episiotomy
- incision made in the posterior vaginal wall and perineum that facilitates vaginal birth
- expulsion
- second stage of childbirth, during which the mother bears down with contractions; this stage ends in birth
- fertilization
- unification of genetic material from male and female haploid gametes
- fertilization membrane
- impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy
- fetus
- developing human during the time from the end of the embryonic period (week 9) to birth
- foramen ovale
- shunt that directly connects the right and left atria and helps divert oxygenated blood from the fetal pulmonary circuit
- foremilk
- watery, translucent breast milk that is secreted first during a feeding and is rich in lactose and protein; quenches the infant’s thirst
- gastrulation
- process of cell migration and differentiation into three primary germ layers following cleavage and implantation
- genotype
- complete genetic makeup of an individual
- gestation
- in human development, the period required for embryonic and fetal development in utero; pregnancy
- heterozygous
- having two different alleles for a given gene
- hindmilk
- opaque, creamy breast milk delivered toward the end of a feeding; rich in fat; satisfies the infant’s appetite
- homozygous
- having two identical alleles for a given gene
- human chorionic gonadotropin (hCG)
- hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses and secure an environment suitable for the developing embryo
- hypoblast
- lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac
- implantation
- process by which a blastocyst embeds itself in the uterine endometrium
- incomplete dominance
- pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes
- inner cell mass
- cluster of cells within the blastocyst that is fated to become the embryo
- involution
- postpartum shrinkage of the uterus back to its pre-pregnancy volume
- karyotype
- systematic arrangement of images of chromosomes into homologous pairs
- lactation
- process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to sucking at the nipple
- lanugo
- silk-like hairs that coat the fetus; shed later in fetal development
- let-down reflex
- release of milk from the alveoli triggered by infant suckling
- lightening
- descent of the fetus lower into the pelvis in late pregnancy; also called “dropping”
- lochia
- postpartum vaginal discharge that begins as blood and ends as a whitish discharge; the end of lochia signals that the site of placental attachment has healed
- meconium
- fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile
- mesoderm
- primary germ layer that becomes the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys
- morula
- tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself
- mutation
- change in the nucleotide sequence of DNA
- neural fold
- elevated edge of the neural groove
- neural plate
- thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue
- neural tube
- precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium
- neurulation
- embryonic process that establishes the central nervous system
- nonshivering thermogenesis
- process of breaking down brown adipose tissue to produce heat in the absence of a shivering response
- notochord
- rod-shaped, mesoderm-derived structure that provides support for growing fetus
- organogenesis
- development of the rudimentary structures of all of an embryo’s organs from the germ layers
- parturition
- childbirth
- phenotype
- physical or biochemical manifestation of the genotype; expression of the alleles
- placenta
- organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus
- placenta previa
- low placement of fetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows
- placentation
- formation of the placenta; complete by weeks 14–16 of pregnancy
- polyspermy
- penetration of an oocyte by more than one sperm
- primitive streak
- indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation
- prolactin
- pituitary hormone that establishes and maintains the supply of breast milk; also important for the mobilization of maternal micronutrients for breast milk
- Punnett square
- grid used to display all possible combinations of alleles transmitted by parents to offspring and predict the mathematical probability of offspring inheriting a given genotype
- quickening
- fetal movements that are strong enough to be felt by the mother
- recessive
- describes a trait that is only expressed in homozygous form and is masked in heterozygous form
- recessive lethal
- inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span
- sex chromosomes
- pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes
- shunt
- circulatory shortcut that diverts the flow of blood from one region to another
- somite
- one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo
- syncytiotrophoblast
- superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall
- trait
- variation of an expressed characteristic
- trimester
- division of the duration of a pregnancy into three 3-month terms
- trophoblast
- fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated fetal membranes
- true labor
- regular contractions that immediately precede childbirth; they do not abate with hydration or rest, and they become more frequent and powerful with time
- umbilical cord
- connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the fetus and returns nutrients and oxygen from the mother
- vernix caseosa
- waxy, cheese-like substance that protects the delicate fetal skin until birth
- X-linked
- pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair
- X-linked dominant
- pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd pair
- X-linked recessive
- pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd pair
- yolk sac
- membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure
- zona pellucida
- thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilization can occur
- zygote
- fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines
Chapter Review
28.1 Fertilization
Hundreds of millions of sperm deposited in the vagina travel toward the oocyte, but only a few hundred actually reach it. The number of sperm that reach the oocyte is greatly reduced because of conditions within the female reproductive tract. Many sperm are overcome by the acidity of the vagina, others are blocked by mucus in the cervix, whereas others are attacked by phagocytic leukocytes in the uterus. Those sperm that do survive undergo a change in response to those conditions. They go through the process of capacitation, which improves their motility and alters the membrane surrounding the acrosome, the cap-like structure in the head of a sperm that contains the digestive enzymes needed for it to attach to and penetrate the oocyte.
The oocyte that is released by ovulation is protected by a thick outer layer of granulosa cells known as the corona radiata and by the zona pellucida, a thick glycoprotein membrane that lies just outside the oocyte’s plasma membrane. When capacitated sperm make contact with the oocyte, they release the digestive enzymes in the acrosome (the acrosomal reaction) and are thus able to attach to the oocyte and burrow through to the oocyte’s zona pellucida. One of the sperm will then break through to the oocyte’s plasma membrane and release its haploid nucleus into the oocyte. The oocyte’s membrane structure changes in response (cortical reaction), preventing any further penetration by another sperm and forming a fertilization membrane. Fertilization is complete upon unification of the haploid nuclei of the two gametes, producing a diploid zygote.
28.2 Embryonic Development
As the zygote travels toward the uterus, it undergoes numerous cleavages in which the number of cells doubles (blastomeres). Upon reaching the uterus, the conceptus has become a tightly packed sphere of cells called the morula, which then forms into a blastocyst consisting of an inner cell mass within a fluid-filled cavity surrounded by trophoblasts. The blastocyst implants in the uterine wall, the trophoblasts fuse to form a syncytiotrophoblast, and the conceptus is enveloped by the endometrium. Four embryonic membranes form to support the growing embryo: the amnion, the yolk sac, the allantois, and the chorion. The chorionic villi of the chorion extend into the endometrium to form the fetal portion of the placenta. The placenta supplies the growing embryo with oxygen and nutrients; it also removes carbon dioxide and other metabolic wastes.
Following implantation, embryonic cells undergo gastrulation, in which they differentiate and separate into an embryonic disc and establish three primary germ layers (the endoderm, mesoderm, and ectoderm). Through the process of embryonic folding, the fetus begins to take shape. Neurulation starts the process of the development of structures of the central nervous system and organogenesis establishes the basic plan for all organ systems.
28.3 Fetal Development
The fetal period lasts from the ninth week of development until birth. During this period, male and female gonads differentiate. The fetal circulatory system becomes much more specialized and efficient than its embryonic counterpart. It includes three shunts—the ductus venosus, the foramen ovale, and the ductus arteriosus—that enable it to bypass the semifunctional liver and pulmonary circuit until after childbirth. The brain continues to grow and its structures differentiate. Facial features develop, the body elongates, and the skeleton ossifies. In the womb, the developing fetus moves, blinks, practices sucking, and circulates amniotic fluid. The fetus grows from an embryo measuring approximately 3.3 cm (1.3 in) and weighing 7 g (0.25 oz) to an infant measuring approximately 51 cm (20 in) and weighing an average of approximately 3.4 kg (7.5 lbs). Embryonic organ structures that were primitive and nonfunctional develop to the point that the newborn can survive in the outside world.
28.4 Maternal Changes During Pregnancy, Labor, and Birth
Hormones (especially estrogens, progesterone, and hCG) secreted by the corpus luteum and later by the placenta are responsible for most of the changes experienced during pregnancy. Estrogen maintains the pregnancy, promotes fetal viability, and stimulates tissue growth in the mother and developing fetus. Progesterone prevents new ovarian follicles from developing and suppresses uterine contractility.
Pregnancy weight gain primarily occurs in the breasts and abdominal region. Nausea, heartburn, and frequent urination are common during pregnancy. Maternal blood volume increases by 30 percent during pregnancy and respiratory minute volume increases by 50 percent. The skin may develop stretch marks and melanin production may increase.
Toward the late stages of pregnancy, a drop in progesterone and stretching forces from the fetus lead to increasing uterine irritability and prompt labor. Contractions serve to dilate the cervix and expel the newborn. Delivery of the placenta and associated fetal membranes follows.
28.5 Adjustments of the Infant at Birth and Postnatal Stages
The first breath a newborn takes at birth inflates the lungs and dramatically alters the circulatory system, closing the three shunts that directed oxygenated blood away from the lungs and liver during fetal life. Clamping and cutting the umbilical cord collapses the three umbilical blood vessels. The proximal umbilical arteries remain a part of the circulatory system, whereas the distal umbilical arteries and the umbilical vein become fibrotic. The newborn keeps warm by breaking down brown adipose tissue in the process of nonshivering thermogenesis. The first consumption of breast milk or formula floods the newborn’s sterile gastrointestinal tract with beneficial bacteria that eventually establish themselves as the bacterial flora, which aid in digestion.
28.6 Lactation
The lactating mother supplies all the hydration and nutrients that a growing infant needs for the first 4–6 months of life. During pregnancy, the body prepares for lactation by stimulating the growth and development of branching lactiferous ducts and alveoli lined with milk-secreting lactocytes, and by creating colostrum. These functions are attributable to the actions of several hormones, including prolactin. Following childbirth, suckling triggers oxytocin release, which stimulates myoepithelial cells to squeeze milk from alveoli. Breast milk then drains toward the nipple pores to be consumed by the infant. Colostrum, the milk produced in the first postpartum days, provides immunoglobulins that increase the newborn’s immune defenses. Colostrum, transitional milk, and mature breast milk are ideally suited to each stage of the newborn’s development, and breastfeeding helps the newborn’s digestive system expel meconium and clear bilirubin. Mature milk changes from the beginning to the end of a feeding. Foremilk quenches the infant’s thirst, whereas hindmilk satisfies the infant’s appetite.
28.7 Patterns of Inheritance
There are two aspects to a person’s genetic makeup. Their genotype refers to the genetic makeup of the chromosomes found in all their cells and the alleles that are passed down from their parents. Their phenotype is the expression of that genotype, based on the interaction of the paired alleles, as well as how environmental conditions affect that expression.
Working with pea plants, Mendel discovered that the factors that account for different traits in parents are discretely transmitted to offspring in pairs, one from each parent. He articulated the principles of random segregation and independent assortment to account for the inheritance patterns he observed. Mendel’s factors are genes, with differing variants being referred to as alleles and those alleles being dominant or recessive in expression. Each parent passes one allele for every gene on to offspring, and offspring are equally likely to inherit any combination of allele pairs. When Mendel crossed heterozygous individuals, he repeatedly found a 3:1 dominant–recessive ratio. He correctly postulated that the expression of the recessive trait was masked in heterozygotes but would resurface in their offspring in a predictable manner.
Human genetics focuses on identifying different alleles and understanding how they express themselves. Medical researchers are especially interested in the identification of inheritance patterns for genetic disorders, which provides the means to estimate the risk that a given couple’s offspring will inherit a genetic disease or disorder. Patterns of inheritance in humans include autosomal dominance and recessiveness, X-linked dominance and recessiveness, incomplete dominance, codominance, and lethality. A change in the nucleotide sequence of DNA, which may or may not manifest in a phenotype, is called a mutation.
Interactive Link Questions
View this time-lapse movie of a conceptus starting at day 3. What is the first structure you see? At what point in the movie does the blastocoel first appear? What event occurs at the end of the movie?
2.Visit this site for a summary of the stages of pregnancy, as experienced by the mother, and view the stages of development of the fetus throughout gestation. At what point in fetal development can a regular heartbeat be detected?
Review Questions
Sperm and ova are similar in terms of ________.
- size
- quantity produced per year
- chromosome number
- flagellar motility
Although the male ejaculate contains hundreds of millions of sperm, ________.
- most do not reach the oocyte
- most are destroyed by the alkaline environment of the uterus
- it takes millions to penetrate the outer layers of the oocyte
- most are destroyed by capacitation
As sperm first reach the oocyte, they will contact the ________.
- acrosome
- corona radiata
- sperm-binding receptors
- zona pellucida
Fusion of pronuclei occurs during ________.
- spermatogenesis
- ovulation
- fertilization
- capacitation
Sperm must first complete ________ to enable the fertilization of an oocyte.
- capacitation
- the acrosomal reaction
- the cortical reaction
- the fast block
Cleavage produces daughter cells called ________.
- trophoblasts
- blastocysts
- morulae
- blastomeres
The conceptus, upon reaching the uterus, first ________.
- implants
- divides
- disintegrates
- hatches
The inner cell mass of the blastocyst is destined to become the ________.
- embryo
- trophoblast
- chorionic villi
- placenta
Which primary germ layer gave rise to the cells that eventually became the central nervous system?
- endoderm
- ectoderm
- acrosome
- mesoderm
What would happen if the trophoblast did not secrete hCG upon implantation of the blastocyst?
- The cells would not continue to divide.
- The corpus luteum would continue to produce progesterone and estrogen.
- Menses would flush the blastocyst out of the uterus.
- The uterine mucosa would not envelop the blastocyst.
During what process does the amnion envelop the embryo?
- embryonic folding
- gastrulation
- implantation
- organogenesis
The placenta is formed from ________.
- the embryo’s mesenchymal cells
- the mother’s endometrium only
- the mother’s endometrium and the embryo’s chorionic membrane
- the mother’s endometrium and the embryo’s umbilical cord
The foramen ovale causes the fetal circulatory system to bypass the ________.
- liver
- lungs
- kidneys
- gonads
What happens to the urine excreted by the fetus when the kidneys begin to function?
- The umbilical cord carries it to the placenta for removal.
- The endometrium absorbs it.
- It adds to the amniotic fluid.
- It is turned into meconium.
During weeks 9–12 of fetal development, ________.
- bone marrow begins to assume erythrocyte production
- meconium begins to accumulate in the intestines
- surfactant production begins in the fetal lungs
- the spinal cord begins to be myelinated
Progesterone secreted by the placenta suppresses ________ to prevent maturation of ovarian follicles.
- LH and estrogen
- hCG and FSH
- FSH and LH
- estrogen and hCG
Which of the following is a possible culprit of “morning sickness”?
- increased minute respiration
- decreased intestinal peristalsis
- decreased aldosterone secretion
- increased blood volume
How does the decrease in progesterone at the last weeks of pregnancy help to bring on labor?
- stimulating FSH production
- decreasing the levels of estrogens
- dilating the cervix
- decreasing the inhibition of uterine contractility
Which of these fetal presentations is the easiest for vaginal birth?
- complete breech
- vertex occiput anterior
- frank breech
- vertex occiput posterior
Which of these shunts exists between the right and left atria?
- foramen ovale
- ductus venosus
- ductus arteriosis
- foramen venosus
Why is brown fat important?
- It is the newborn’s primary source of insulation.
- It can be broken down to generate heat for thermoregulation.
- It can be broken down for energy between feedings.
- It can be converted to white fat.
Constriction of umbilical blood vessels during vaginal birth ________.
- causes respiratory alkalosis
- inhibits the respiratory center in the brain
- elevates carbon dioxide levels in the blood
- both a and b
Alveoli are connected to the lactiferous sinuses by ________.
- lactocytes
- lactiferous ducts
- nipple pores
- lobules
How is colostrum most important to a newborn?
- It helps boost the newborn’s immune system.
- It provides much needed fat.
- It satisfies the newborn’s thirst.
- It satisfies the infant’s appetite.
Mature breast milk ________.
- has more sodium than cow’s milk
- has more calcium than cow’s milk
- has more protein than cow’s milk
- has more fat than cow’s milk
Marfan syndrome is inherited in an autosomal dominant pattern. Which of the following is true?
- Female offspring are more likely to be carriers of the disease.
- Male offspring are more likely to inherit the disease.
- Male and female offspring have the same likelihood of inheriting the disease.
- Female offspring are more likely to inherit the disease.
In addition to codominance, the ABO blood group antigens are also an example of ________.
- incomplete dominance
- X-linked recessive inheritance
- multiple alleles
- recessive lethal inheritance
Zoe has cystic fibrosis. Which of the following is the most likely explanation?
- Zoe probably inherited one faulty allele from her father, who is a carrier, and one normal allele from her mother.
- Zoe probably inherited one faulty allele from her mother, who must also have cystic fibrosis, and one normal allele from her father.
- Zoe must have inherited faulty alleles from both parents, both of whom must also have cystic fibrosis.
- Zoe must have inherited faulty alleles from both parents, both of whom are carriers.
Critical Thinking Questions
Darcy and Raul are having difficulty conceiving a child. Darcy ovulates every 28 days, and Raul’s sperm count is normal. If we could observe Raul’s sperm about an hour after ejaculation, however, we’d see that they appear to be moving only sluggishly. When Raul’s sperm eventually encounter Darcy’s oocyte, they appear to be incapable of generating an adequate acrosomal reaction. Which process has probably gone wrong?
32.Sherrise is a sexually active college student. On Saturday night, she has unprotected sex with her boyfriend. On Tuesday morning, she experiences the twinge of mid-cycle pain that she typically feels when she is ovulating. This makes Sherrise extremely anxious that she might soon learn she is pregnant. Is Sherrise’s concern valid? Why or why not?
33.Approximately 3 weeks after her last menstrual period, a sexually active woman experiences a brief episode of abdominopelvic cramping and minor bleeding. What might be the explanation?
34.The Food and Nutrition Board of the Institute of Medicine recommends that all women who might become pregnant consume at least 400 µg/day of folate from supplements or fortified foods. Why?
35.What is the physiological benefit of incorporating shunts into the fetal circulatory system?
36.Why would a premature infant require supplemental oxygen?
37.Devin is 35 weeks pregnant with her first child when she arrives at the birthing unit reporting that she believes she is in labor. She states that she has been experiencing diffuse, mild contractions for the past few hours. Examination reveals, however, that the plug of mucus blocking her cervix is intact and her cervix has not yet begun to dilate. She is advised to return home. Why?
38.Janine is 41 weeks pregnant with her first child when she arrives at the birthing unit reporting that she believes she has been in labor “for days” but that “it’s just not going anywhere.” During the clinical exam, she experiences a few mild contractions, each lasting about 15–20 seconds; however, her cervix is found to be only 2 cm dilated, and the amniotic sac is intact. Janine is admitted to the birthing unit and an IV infusion of pitocin is started. Why?
39.Describe how the newborn’s first breath alters the circulatory pattern.
40.Newborns are at much higher risk for dehydration than adults. Why?
41.Describe the transit of breast milk from lactocytes to nipple pores.
42.A woman who stopped breastfeeding suddenly is experiencing breast engorgement and leakage, just like she did in the first few weeks of breastfeeding. Why?
43.Explain why it was essential that Mendel perform his crosses using a large sample size?
44.How can a female carrier of an X-linked recessive disorder have a daughter who is affected?
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2025-03-18T00:38:18.820419
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https://oercommons.org/courseware/lesson/58766/overview
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The Cardiovascular System: Blood Vessels and Circulation
Introduction
Figure 20.1 Blood Vessels While most blood vessels are located deep from the surface and are not visible, the superficial veins of the upper limb provide an indication of the extent, prominence, and importance of these structures to the body. (credit: Colin Davis)
CHAPTER OBJECTIVES
After studying this chapter, you will be able to:
- Compare and contrast the anatomical structure of arteries, arterioles, capillaries, venules, and veins
- Accurately describe the forces that account for capillary exchange
- List the major factors affecting blood flow, blood pressure, and resistance
- Describe how blood flow, blood pressure, and resistance interrelate
- Discuss how the neural and endocrine mechanisms maintain homeostasis within the blood vessels
- Describe the interaction of the cardiovascular system with other body systems
- Label the major blood vessels of the pulmonary and systemic circulations
- Identify and describe the hepatic portal system
- Describe the development of blood vessels and fetal circulation
- Compare fetal circulation to that of an individual after birth
In this chapter, you will learn about the vascular part of the cardiovascular system, that is, the vessels that transport blood throughout the body and provide the physical site where gases, nutrients, and other substances are exchanged with body cells. When vessel functioning is reduced, blood-borne substances do not circulate effectively throughout the body. As a result, tissue injury occurs, metabolism is impaired, and the functions of every bodily system are threatened.
Structure and Function of Blood Vessels
- Compare and contrast the three tunics that make up the walls of most blood vessels
Distinguish between elastic arteries, muscular arteries, and arterioles on the basis of structure, location, and function
- Describe the basic structure of a capillary bed, from the supplying metarteriole to the venule into which it drains
- Explain the structure and function of venous valves in the large veins of the extremities
Blood is carried through the body via blood vessels. An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. Eventually, the smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged, and then combine with other vessels that exit capillaries to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart.
Arteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit (Figure 20.2). Systemic arteries provide blood rich in oxygen to the body’s tissues. The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange. Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation. Although arteries and veins differ structurally and functionally, they share certain features.
Figure 20.2 Cardiovascular Circulation The pulmonary circuit moves blood from the right side of the heart to the lungs and back to the heart. The systemic circuit moves blood from the left side of the heart to the head and body and returns it to the right side of the heart to repeat the cycle. The arrows indicate the direction of blood flow, and the colors show the relative levels of oxygen concentration.
Shared Structures
Different types of blood vessels vary slightly in their structures, but they share the same general features. Arteries and arterioles have thicker walls than veins and venules because they are closer to the heart and receive blood that is surging at a far greater pressure (Figure 20.3). Each type of vessel has a lumen—a hollow passageway through which blood flows. Arteries have smaller lumens than veins, a characteristic that helps to maintain the pressure of blood moving through the system. Together, their thicker walls and smaller diameters give arterial lumens a more rounded appearance in cross section than the lumens of veins.
Figure 20.3 Structure of Blood Vessels (a) Arteries and (b) veins share the same general features, but the walls of arteries are much thicker because of the higher pressure of the blood that flows through them. (c) A micrograph shows the relative differences in thickness. LM × 160. (Micrograph provided by the Regents of the University of Michigan Medical School © 2012)
By the time blood has passed through capillaries and entered venules, the pressure initially exerted upon it by heart contractions has diminished. In other words, in comparison to arteries, venules and veins withstand a much lower pressure from the blood that flows through them. Their walls are considerably thinner and their lumens are correspondingly larger in diameter, allowing more blood to flow with less vessel resistance. In addition, many veins of the body, particularly those of the limbs, contain valves that assist the unidirectional flow of blood toward the heart. This is critical because blood flow becomes sluggish in the extremities, as a result of the lower pressure and the effects of gravity.
The walls of arteries and veins are largely composed of living cells and their products (including collagenous and elastic fibers); the cells require nourishment and produce waste. Since blood passes through the larger vessels relatively quickly, there is limited opportunity for blood in the lumen of the vessel to provide nourishment to or remove waste from the vessel’s cells. Further, the walls of the larger vessels are too thick for nutrients to diffuse through to all of the cells. Larger arteries and veins contain small blood vessels within their walls known as the vasa vasorum—literally “vessels of the vessel”—to provide them with this critical exchange. Since the pressure within arteries is relatively high, the vasa vasorum must function in the outer layers of the vessel (see Figure 20.3) or the pressure exerted by the blood passing through the vessel would collapse it, preventing any exchange from occurring. The lower pressure within veins allows the vasa vasorum to be located closer to the lumen. The restriction of the vasa vasorum to the outer layers of arteries is thought to be one reason that arterial diseases are more common than venous diseases, since its location makes it more difficult to nourish the cells of the arteries and remove waste products. There are also minute nerves within the walls of both types of vessels that control the contraction and dilation of smooth muscle. These minute nerves are known as the nervi vasorum.
Both arteries and veins have the same three distinct tissue layers, called tunics (from the Latin term tunica), for the garments first worn by ancient Romans; the term tunic is also used for some modern garments. From the most interior layer to the outer, these tunics are the tunica intima, the tunica media, and the tunica externa (see Figure 20.3). Table 20.1 compares and contrasts the tunics of the arteries and veins.
Comparison of Tunics in Arteries and Veins
| Arteries | Veins | |
|---|---|---|
| General appearance | Thick walls with small lumens Generally appear rounded | Thin walls with large lumens Generally appear flattened |
| Tunica intima | Endothelium usually appears wavy due to constriction of smooth muscle Internal elastic membrane present in larger vessels | Endothelium appears smooth Internal elastic membrane absent |
| Tunica media | Normally the thickest layer in arteries Smooth muscle cells and elastic fibers predominate (the proportions of these vary with distance from the heart) External elastic membrane present in larger vessels | Normally thinner than the tunica externa Smooth muscle cells and collagenous fibers predominate Nervi vasorum and vasa vasorum present External elastic membrane absent |
| Tunica externa | Normally thinner than the tunica media in all but the largest arteries Collagenous and elastic fibers Nervi vasorum and vasa vasorum present | Normally the thickest layer in veins Collagenous and smooth fibers predominate Some smooth muscle fibers Nervi vasorum and vasa vasorum present |
Table 20.1
Tunica Intima
The tunica intima (also called the tunica interna) is composed of epithelial and connective tissue layers. Lining the tunica intima is the specialized simple squamous epithelium called the endothelium, which is continuous throughout the entire vascular system, including the lining of the chambers of the heart. Damage to this endothelial lining and exposure of blood to the collagenous fibers beneath is one of the primary causes of clot formation. Until recently, the endothelium was viewed simply as the boundary between the blood in the lumen and the walls of the vessels. Recent studies, however, have shown that it is physiologically critical to such activities as helping to regulate capillary exchange and altering blood flow. The endothelium releases local chemicals called endothelins that can constrict the smooth muscle within the walls of the vessel to increase blood pressure. Uncompensated overproduction of endothelins may contribute to hypertension (high blood pressure) and cardiovascular disease.
Next to the endothelium is the basement membrane, or basal lamina, that effectively binds the endothelium to the connective tissue. The basement membrane provides strength while maintaining flexibility, and it is permeable, allowing materials to pass through it. The thin outer layer of the tunica intima contains a small amount of areolar connective tissue that consists primarily of elastic fibers to provide the vessel with additional flexibility; it also contains some collagenous fibers to provide additional strength.
In larger arteries, there is also a thick, distinct layer of elastic fibers known as the internal elastic membrane (also called the internal elastic lamina) at the boundary with the tunica media. Like the other components of the tunica intima, the internal elastic membrane provides structure while allowing the vessel to stretch. It is permeated with small openings that allow exchange of materials between the tunics. The internal elastic membrane is not apparent in veins. In addition, many veins, particularly in the lower limbs, contain valves formed by sections of thickened endothelium that are reinforced with connective tissue, extending into the lumen.
Under the microscope, the lumen and the entire tunica intima of a vein will appear smooth, whereas those of an artery will normally appear wavy because of the partial constriction of the smooth muscle in the tunica media, the next layer of blood vessel walls.
Tunica Media
The tunica media is the substantial middle layer of the vessel wall (see Figure 20.3). It is generally the thickest layer in arteries, and it is much thicker in arteries than it is in veins. The tunica media consists of layers of smooth muscle supported by connective tissue that is primarily made up of elastic fibers, most of which are arranged in circular sheets. Toward the outer portion of the tunic, there are also layers of longitudinal muscle. Contraction and relaxation of the circular muscles decrease and increase the diameter of the vessel lumen, respectively. Specifically in arteries, vasoconstriction decreases blood flow as the smooth muscle in the walls of the tunica media contracts, making the lumen narrower and increasing blood pressure. Similarly, vasodilation increases blood flow as the smooth muscle relaxes, allowing the lumen to widen and blood pressure to drop. Both vasoconstriction and vasodilation are regulated in part by small vascular nerves, known as nervi vasorum, or “nerves of the vessel,” that run within the walls of blood vessels. These are generally all sympathetic fibers, although some trigger vasodilation and others induce vasoconstriction, depending upon the nature of the neurotransmitter and receptors located on the target cell. Parasympathetic stimulation does trigger vasodilation as well as erection during sexual arousal in the external genitalia of both sexes. Nervous control over vessels tends to be more generalized than the specific targeting of individual blood vessels. Local controls, discussed later, account for this phenomenon. (Seek additional content for more information on these dynamic aspects of the autonomic nervous system.) Hormones and local chemicals also control blood vessels. Together, these neural and chemical mechanisms reduce or increase blood flow in response to changing body conditions, from exercise to hydration. Regulation of both blood flow and blood pressure is discussed in detail later in this chapter.
The smooth muscle layers of the tunica media are supported by a framework of collagenous fibers that also binds the tunica media to the inner and outer tunics. Along with the collagenous fibers are large numbers of elastic fibers that appear as wavy lines in prepared slides. Separating the tunica media from the outer tunica externa in larger arteries is the external elastic membrane (also called the external elastic lamina), which also appears wavy in slides. This structure is not usually seen in smaller arteries, nor is it seen in veins.
Tunica Externa
The outer tunic, the tunica externa (also called the tunica adventitia), is a substantial sheath of connective tissue composed primarily of collagenous fibers. Some bands of elastic fibers are found here as well. The tunica externa in veins also contains groups of smooth muscle fibers. This is normally the thickest tunic in veins and may be thicker than the tunica media in some larger arteries. The outer layers of the tunica externa are not distinct but rather blend with the surrounding connective tissue outside the vessel, helping to hold the vessel in relative position. If you are able to palpate some of the superficial veins on your upper limbs and try to move them, you will find that the tunica externa prevents this. If the tunica externa did not hold the vessel in place, any movement would likely result in disruption of blood flow.
Arteries
An artery is a blood vessel that conducts blood away from the heart. All arteries have relatively thick walls that can withstand the high pressure of blood ejected from the heart. However, those close to the heart have the thickest walls, containing a high percentage of elastic fibers in all three of their tunics. This type of artery is known as an elastic artery (Figure 20.4). Vessels larger than 10 mm in diameter are typically elastic. Their abundant elastic fibers allow them to expand, as blood pumped from the ventricles passes through them, and then to recoil after the surge has passed. If artery walls were rigid and unable to expand and recoil, their resistance to blood flow would greatly increase and blood pressure would rise to even higher levels, which would in turn require the heart to pump harder to increase the volume of blood expelled by each pump (the stroke volume) and maintain adequate pressure and flow. Artery walls would have to become even thicker in response to this increased pressure. The elastic recoil of the vascular wall helps to maintain the pressure gradient that drives the blood through the arterial system. An elastic artery is also known as a conducting artery, because the large diameter of the lumen enables it to accept a large volume of blood from the heart and conduct it to smaller branches.
Figure 20.4 Types of Arteries and Arterioles Comparison of the walls of an elastic artery, a muscular artery, and an arteriole is shown. In terms of scale, the diameter of an arteriole is measured in micrometers compared to millimeters for elastic and muscular arteries.
Farther from the heart, where the surge of blood has dampened, the percentage of elastic fibers in an artery’s tunica intima decreases and the amount of smooth muscle in its tunica media increases. The artery at this point is described as a muscular artery. The diameter of muscular arteries typically ranges from 0.1 mm to 10 mm. Their thick tunica media allows muscular arteries to play a leading role in vasoconstriction. In contrast, their decreased quantity of elastic fibers limits their ability to expand. Fortunately, because the blood pressure has eased by the time it reaches these more distant vessels, elasticity has become less important.
Notice that although the distinctions between elastic and muscular arteries are important, there is no “line of demarcation” where an elastic artery suddenly becomes muscular. Rather, there is a gradual transition as the vascular tree repeatedly branches. In turn, muscular arteries branch to distribute blood to the vast network of arterioles. For this reason, a muscular artery is also known as a distributing artery.
Arterioles
An arteriole is a very small artery that leads to a capillary. Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. The critical endothelial lining of the tunica intima is intact. The tunica media is restricted to one or two smooth muscle cell layers in thickness. The tunica externa remains but is very thin (see Figure 20.4).
With a lumen averaging 30 micrometers or less in diameter, arterioles are critical in slowing down—or resisting—blood flow and, thus, causing a substantial drop in blood pressure. Because of this, you may see them referred to as resistance vessels. The muscle fibers in arterioles are normally slightly contracted, causing arterioles to maintain a consistent muscle tone—in this case referred to as vascular tone—in a similar manner to the muscular tone of skeletal muscle. In reality, all blood vessels exhibit vascular tone due to the partial contraction of smooth muscle. The importance of the arterioles is that they will be the primary site of both resistance and regulation of blood pressure. The precise diameter of the lumen of an arteriole at any given moment is determined by neural and chemical controls, and vasoconstriction and vasodilation in the arterioles are the primary mechanisms for distribution of blood flow.
Capillaries
A capillary is a microscopic channel that supplies blood to the tissues themselves, a process called perfusion. Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). The diameter of a capillary lumen ranges from 5–10 micrometers; the smallest are just barely wide enough for an erythrocyte to squeeze through. Flow through capillaries is often described as microcirculation.
The wall of a capillary consists of the endothelial layer surrounded by a basement membrane with occasional smooth muscle fibers. There is some variation in wall structure: In a large capillary, several endothelial cells bordering each other may line the lumen; in a small capillary, there may be only a single cell layer that wraps around to contact itself.
For capillaries to function, their walls must be leaky, allowing substances to pass through. There are three major types of capillaries, which differ according to their degree of “leakiness:” continuous, fenestrated, and sinusoid capillaries (Figure 20.5).
Continuous Capillaries
The most common type of capillary, the continuous capillary, is found in almost all vascularized tissues. Continuous capillaries are characterized by a complete endothelial lining with tight junctions between endothelial cells. Although a tight junction is usually impermeable and only allows for the passage of water and ions, they are often incomplete in capillaries, leaving intercellular clefts that allow for exchange of water and other very small molecules between the blood plasma and the interstitial fluid. Substances that can pass between cells include metabolic products, such as glucose, water, and small hydrophobic molecules like gases and hormones, as well as various leukocytes. Continuous capillaries not associated with the brain are rich in transport vesicles, contributing to either endocytosis or exocytosis. Those in the brain are part of the blood-brain barrier. Here, there are tight junctions and no intercellular clefts, plus a thick basement membrane and astrocyte extensions called end feet; these structures combine to prevent the movement of nearly all substances.
Figure 20.5 Types of Capillaries The three major types of capillaries: continuous, fenestrated, and sinusoid.
Fenestrated Capillaries
A fenestrated capillary is one that has pores (or fenestrations) in addition to tight junctions in the endothelial lining. These make the capillary permeable to larger molecules. The number of fenestrations and their degree of permeability vary, however, according to their location. Fenestrated capillaries are common in the small intestine, which is the primary site of nutrient absorption, as well as in the kidneys, which filter the blood. They are also found in the choroid plexus of the brain and many endocrine structures, including the hypothalamus, pituitary, pineal, and thyroid glands.
Sinusoid Capillaries
A sinusoid capillary (or sinusoid) is the least common type of capillary. Sinusoid capillaries are flattened, and they have extensive intercellular gaps and incomplete basement membranes, in addition to intercellular clefts and fenestrations. This gives them an appearance not unlike Swiss cheese. These very large openings allow for the passage of the largest molecules, including plasma proteins and even cells. Blood flow through sinusoids is very slow, allowing more time for exchange of gases, nutrients, and wastes. Sinusoids are found in the liver and spleen, bone marrow, lymph nodes (where they carry lymph, not blood), and many endocrine glands including the pituitary and adrenal glands. Without these specialized capillaries, these organs would not be able to provide their myriad of functions. For example, when bone marrow forms new blood cells, the cells must enter the blood supply and can only do so through the large openings of a sinusoid capillary; they cannot pass through the small openings of continuous or fenestrated capillaries. The liver also requires extensive specialized sinusoid capillaries in order to process the materials brought to it by the hepatic portal vein from both the digestive tract and spleen, and to release plasma proteins into circulation.
Metarterioles and Capillary Beds
A metarteriole is a type of vessel that has structural characteristics of both an arteriole and a capillary. Slightly larger than the typical capillary, the smooth muscle of the tunica media of the metarteriole is not continuous but forms rings of smooth muscle (sphincters) prior to the entrance to the capillaries. Each metarteriole arises from a terminal arteriole and branches to supply blood to a capillary bed that may consist of 10–100 capillaries.
The precapillary sphincters, circular smooth muscle cells that surround the capillary at its origin with the metarteriole, tightly regulate the flow of blood from a metarteriole to the capillaries it supplies. Their function is critical: If all of the capillary beds in the body were to open simultaneously, they would collectively hold every drop of blood in the body and there would be none in the arteries, arterioles, venules, veins, or the heart itself. Normally, the precapillary sphincters are closed. When the surrounding tissues need oxygen and have excess waste products, the precapillary sphincters open, allowing blood to flow through and exchange to occur before closing once more (Figure 20.6). If all of the precapillary sphincters in a capillary bed are closed, blood will flow from the metarteriole directly into a thoroughfare channel and then into the venous circulation, bypassing the capillary bed entirely. This creates what is known as a vascular shunt. In addition, an arteriovenous anastomosis may bypass the capillary bed and lead directly to the venous system.
Although you might expect blood flow through a capillary bed to be smooth, in reality, it moves with an irregular, pulsating flow. This pattern is called vasomotion and is regulated by chemical signals that are triggered in response to changes in internal conditions, such as oxygen, carbon dioxide, hydrogen ion, and lactic acid levels. For example, during strenuous exercise when oxygen levels decrease and carbon dioxide, hydrogen ion, and lactic acid levels all increase, the capillary beds in skeletal muscle are open, as they would be in the digestive system when nutrients are present in the digestive tract. During sleep or rest periods, vessels in both areas are largely closed; they open only occasionally to allow oxygen and nutrient supplies to travel to the tissues to maintain basic life processes.
Figure 20.6 Capillary Bed In a capillary bed, arterioles give rise to metarterioles. Precapillary sphincters located at the junction of a metarteriole with a capillary regulate blood flow. A thoroughfare channel connects the metarteriole to a venule. An arteriovenous anastomosis, which directly connects the arteriole with the venule, is shown at the bottom.
Venules
A venule is an extremely small vein, generally 8–100 micrometers in diameter. Postcapillary venules join multiple capillaries exiting from a capillary bed. Multiple venules join to form veins. The walls of venules consist of endothelium, a thin middle layer with a few muscle cells and elastic fibers, plus an outer layer of connective tissue fibers that constitute a very thin tunica externa (Figure 20.7). Venules as well as capillaries are the primary sites of emigration or diapedesis, in which the white blood cells adhere to the endothelial lining of the vessels and then squeeze through adjacent cells to enter the tissue fluid.
Veins
A vein is a blood vessel that conducts blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens (see Figure 20.7). Because they are low-pressure vessels, larger veins are commonly equipped with valves that promote the unidirectional flow of blood toward the heart and prevent backflow toward the capillaries caused by the inherent low blood pressure in veins as well as the pull of gravity. Table 20.2 compares the features of arteries and veins.
Figure 20.7 Comparison of Veins and Venules Many veins have valves to prevent back flow of blood, whereas venules do not. In terms of scale, the diameter of a venule is measured in micrometers compared to millimeters for veins.
Comparison of Arteries and Veins
| Arteries | Veins | |
|---|---|---|
| Direction of blood flow | Conducts blood away from the heart | Conducts blood toward the heart |
| General appearance | Rounded | Irregular, often collapsed |
| Pressure | High | Low |
| Wall thickness | Thick | Thin |
| Relative oxygen concentration | Higher in systemic arteries Lower in pulmonary arteries | Lower in systemic veins Higher in pulmonary veins |
| Valves | Not present | Present most commonly in limbs and in veins inferior to the heart |
Table 20.2
DISORDERS OF THE...
Cardiovascular System: Edema and Varicose Veins
Despite the presence of valves and the contributions of other anatomical and physiological adaptations we will cover shortly, over the course of a day, some blood will inevitably pool, especially in the lower limbs, due to the pull of gravity. Any blood that accumulates in a vein will increase the pressure within it, which can then be reflected back into the smaller veins, venules, and eventually even the capillaries. Increased pressure will promote the flow of fluids out of the capillaries and into the interstitial fluid. The presence of excess tissue fluid around the cells leads to a condition called edema.
Most people experience a daily accumulation of tissue fluid, especially if they spend much of their work life on their feet (like most health professionals). However, clinical edema goes beyond normal swelling and requires medical treatment. Edema has many potential causes, including hypertension and heart failure, severe protein deficiency, renal failure, and many others. In order to treat edema, which is a sign rather than a discrete disorder, the underlying cause must be diagnosed and alleviated.
Figure 20.8 Varicose Veins Varicose veins are commonly found in the lower limbs. (credit: Thomas Kriese)
Edema may be accompanied by varicose veins, especially in the superficial veins of the legs (Figure 20.8). This disorder arises when defective valves allow blood to accumulate within the veins, causing them to distend, twist, and become visible on the surface of the integument. Varicose veins may occur in both sexes, but are more common in women and are often related to pregnancy. More than simple cosmetic blemishes, varicose veins are often painful and sometimes itchy or throbbing. Without treatment, they tend to grow worse over time. The use of support hose, as well as elevating the feet and legs whenever possible, may be helpful in alleviating this condition. Laser surgery and interventional radiologic procedures can reduce the size and severity of varicose veins. Severe cases may require conventional surgery to remove the damaged vessels. As there are typically redundant circulation patterns, that is, anastomoses, for the smaller and more superficial veins, removal does not typically impair the circulation. There is evidence that patients with varicose veins suffer a greater risk of developing a thrombus or clot.
Veins as Blood Reservoirs
In addition to their primary function of returning blood to the heart, veins may be considered blood reservoirs, since systemic veins contain approximately 64 percent of the blood volume at any given time (Figure 20.9). Their ability to hold this much blood is due to their high capacitance, that is, their capacity to distend (expand) readily to store a high volume of blood, even at a low pressure. The large lumens and relatively thin walls of veins make them far more distensible than arteries; thus, they are said to be capacitance vessels.
Figure 20.9 Distribution of Blood Flow
When blood flow needs to be redistributed to other portions of the body, the vasomotor center located in the medulla oblongata sends sympathetic stimulation to the smooth muscles in the walls of the veins, causing constriction—or in this case, venoconstriction. Less dramatic than the vasoconstriction seen in smaller arteries and arterioles, venoconstriction may be likened to a “stiffening” of the vessel wall. This increases pressure on the blood within the veins, speeding its return to the heart. As you will note in Figure 20.9, approximately 21 percent of the venous blood is located in venous networks within the liver, bone marrow, and integument. This volume of blood is referred to as venous reserve. Through venoconstriction, this “reserve” volume of blood can get back to the heart more quickly for redistribution to other parts of the circulation.
CAREER CONNECTION
Vascular Surgeons and Technicians
Vascular surgery is a specialty in which the physician deals primarily with diseases of the vascular portion of the cardiovascular system. This includes repair and replacement of diseased or damaged vessels, removal of plaque from vessels, minimally invasive procedures including the insertion of venous catheters, and traditional surgery. Following completion of medical school, the physician generally completes a 5-year surgical residency followed by an additional 1 to 2 years of vascular specialty training. In the United States, most vascular surgeons are members of the Society of Vascular Surgery.
Vascular technicians are specialists in imaging technologies that provide information on the health of the vascular system. They may also assist physicians in treating disorders involving the arteries and veins. This profession often overlaps with cardiovascular technology, which would also include treatments involving the heart. Although recognized by the American Medical Association, there are currently no licensing requirements for vascular technicians, and licensing is voluntary. Vascular technicians typically have an Associate’s degree or certificate, involving 18 months to 2 years of training. The United States Bureau of Labor projects this profession to grow by 29 percent from 2010 to 2020.
INTERACTIVE LINK
Visit this site to learn more about vascular surgery.
INTERACTIVE LINK
Visit this site to learn more about vascular technicians.
Blood Flow, Blood Pressure, and Resistance
- Distinguish between systolic pressure, diastolic pressure, pulse pressure, and mean arterial pressure
- Describe the clinical measurement of pulse and blood pressure
- Identify and discuss five variables affecting arterial blood flow and blood pressure
- Discuss several factors affecting blood flow in the venous system
Blood flow refers to the movement of blood through a vessel, tissue, or organ, and is usually expressed in terms of volume of blood per unit of time. It is initiated by the contraction of the ventricles of the heart. Ventricular contraction ejects blood into the major arteries, resulting in flow from regions of higher pressure to regions of lower pressure, as blood encounters smaller arteries and arterioles, then capillaries, then the venules and veins of the venous system. This section discusses a number of critical variables that contribute to blood flow throughout the body. It also discusses the factors that impede or slow blood flow, a phenomenon known as resistance.
As noted earlier, hydrostatic pressure is the force exerted by a fluid due to gravitational pull, usually against the wall of the container in which it is located. One form of hydrostatic pressure is blood pressure, the force exerted by blood upon the walls of the blood vessels or the chambers of the heart. Blood pressure may be measured in capillaries and veins, as well as the vessels of the pulmonary circulation; however, the term blood pressure without any specific descriptors typically refers to systemic arterial blood pressure—that is, the pressure of blood flowing in the arteries of the systemic circulation. In clinical practice, this pressure is measured in mm Hg and is usually obtained using the brachial artery of the arm.
Components of Arterial Blood Pressure
Arterial blood pressure in the larger vessels consists of several distinct components (Figure 20.10): systolic and diastolic pressures, pulse pressure, and mean arterial pressure.
Systolic and Diastolic Pressures
When systemic arterial blood pressure is measured, it is recorded as a ratio of two numbers (e.g., 120/80 is a normal adult blood pressure), expressed as systolic pressure over diastolic pressure. The systolic pressure is the higher value (typically around 120 mm Hg) and reflects the arterial pressure resulting from the ejection of blood during ventricular contraction, or systole. The diastolic pressure is the lower value (usually about 80 mm Hg) and represents the arterial pressure of blood during ventricular relaxation, or diastole.
Figure 20.10 Systemic Blood Pressure The graph shows the components of blood pressure throughout the blood vessels, including systolic, diastolic, mean arterial, and pulse pressures.
Pulse Pressure
As shown in Figure 20.10, the difference between the systolic pressure and the diastolic pressure is the pulse pressure. For example, an individual with a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg would have a pulse pressure of 40 mmHg.
Generally, a pulse pressure should be at least 25 percent of the systolic pressure. A pulse pressure below this level is described as low or narrow. This may occur, for example, in patients with a low stroke volume, which may be seen in congestive heart failure, stenosis of the aortic valve, or significant blood loss following trauma. In contrast, a high or wide pulse pressure is common in healthy people following strenuous exercise, when their resting pulse pressure of 30–40 mm Hg may increase temporarily to 100 mm Hg as stroke volume increases. A persistently high pulse pressure at or above 100 mm Hg may indicate excessive resistance in the arteries and can be caused by a variety of disorders. Chronic high resting pulse pressures can degrade the heart, brain, and kidneys, and warrant medical treatment.
Mean Arterial Pressure
Mean arterial pressure (MAP) represents the “average” pressure of blood in the arteries, that is, the average force driving blood into vessels that serve the tissues. Mean is a statistical concept and is calculated by taking the sum of the values divided by the number of values. Although complicated to measure directly and complicated to calculate, MAP can be approximated by adding the diastolic pressure to one-third of the pulse pressure or systolic pressure minus the diastolic pressure:
MAP = diastolic BP + (systolic-diastolic BP)3MAP = diastolic BP + (systolic-diastolic BP)3
In Figure 20.10, this value is approximately 80 + (120 − 80) / 3, or 93.33. Normally, the MAP falls within the range of 70–110 mm Hg. If the value falls below 60 mm Hg for an extended time, blood pressure will not be high enough to ensure circulation to and through the tissues, which results in ischemia, or insufficient blood flow. A condition called hypoxia, inadequate oxygenation of tissues, commonly accompanies ischemia. The term hypoxemia refers to low levels of oxygen in systemic arterial blood. Neurons are especially sensitive to hypoxia and may die or be damaged if blood flow and oxygen supplies are not quickly restored.
Pulse
After blood is ejected from the heart, elastic fibers in the arteries help maintain a high-pressure gradient as they expand to accommodate the blood, then recoil. This expansion and recoiling effect, known as the pulse, can be palpated manually or measured electronically. Although the effect diminishes over distance from the heart, elements of the systolic and diastolic components of the pulse are still evident down to the level of the arterioles.
Because pulse indicates heart rate, it is measured clinically to provide clues to a patient’s state of health. It is recorded as beats per minute. Both the rate and the strength of the pulse are important clinically. A high or irregular pulse rate can be caused by physical activity or other temporary factors, but it may also indicate a heart condition. The pulse strength indicates the strength of ventricular contraction and cardiac output. If the pulse is strong, then systolic pressure is high. If it is weak, systolic pressure has fallen, and medical intervention may be warranted.
Pulse can be palpated manually by placing the tips of the fingers across an artery that runs close to the body surface and pressing lightly. While this procedure is normally performed using the radial artery in the wrist or the common carotid artery in the neck, any superficial artery that can be palpated may be used (Figure 20.11). Common sites to find a pulse include temporal and facial arteries in the head, brachial arteries in the upper arm, femoral arteries in the thigh, popliteal arteries behind the knees, posterior tibial arteries near the medial tarsal regions, and dorsalis pedis arteries in the feet. A variety of commercial electronic devices are also available to measure pulse.
Figure 20.11 Pulse Sites The pulse is most readily measured at the radial artery, but can be measured at any of the pulse points shown.
Measurement of Blood Pressure
Blood pressure is one of the critical parameters measured on virtually every patient in every healthcare setting. The technique used today was developed more than 100 years ago by a pioneering Russian physician, Dr. Nikolai Korotkoff. Turbulent blood flow through the vessels can be heard as a soft ticking while measuring blood pressure; these sounds are known as Korotkoff sounds. The technique of measuring blood pressure requires the use of a sphygmomanometer (a blood pressure cuff attached to a measuring device) and a stethoscope. The technique is as follows:
- The clinician wraps an inflatable cuff tightly around the patient’s arm at about the level of the heart.
- The clinician squeezes a rubber pump to inject air into the cuff, raising pressure around the artery and temporarily cutting off blood flow into the patient’s arm.
- The clinician places the stethoscope on the patient’s antecubital region and, while gradually allowing air within the cuff to escape, listens for the Korotkoff sounds.
Although there are five recognized Korotkoff sounds, only two are normally recorded. Initially, no sounds are heard since there is no blood flow through the vessels, but as air pressure drops, the cuff relaxes, and blood flow returns to the arm. As shown in Figure 20.12, the first sound heard through the stethoscope—the first Korotkoff sound—indicates systolic pressure. As more air is released from the cuff, blood is able to flow freely through the brachial artery and all sounds disappear. The point at which the last sound is heard is recorded as the patient’s diastolic pressure.
Figure 20.12 Blood Pressure Measurement When pressure in a sphygmomanometer cuff is released, a clinician can hear the Korotkoff sounds. In this graph, a blood pressure tracing is aligned to a measurement of systolic and diastolic pressures.
The majority of hospitals and clinics have automated equipment for measuring blood pressure that work on the same principles. An even more recent innovation is a small instrument that wraps around a patient’s wrist. The patient then holds the wrist over the heart while the device measures blood flow and records pressure.
Variables Affecting Blood Flow and Blood Pressure
Five variables influence blood flow and blood pressure:
- Cardiac output
- Compliance
- Volume of the blood
- Viscosity of the blood
- Blood vessel length and diameter
Recall that blood moves from higher pressure to lower pressure. It is pumped from the heart into the arteries at high pressure. If you increase pressure in the arteries (afterload), and cardiac function does not compensate, blood flow will actually decrease. In the venous system, the opposite relationship is true. Increased pressure in the veins does not decrease flow as it does in arteries, but actually increases flow. Since pressure in the veins is normally relatively low, for blood to flow back into the heart, the pressure in the atria during atrial diastole must be even lower. It normally approaches zero, except when the atria contract (see Figure 20.10).
Cardiac Output
Cardiac output is the measurement of blood flow from the heart through the ventricles, and is usually measured in liters per minute. Any factor that causes cardiac output to increase, by elevating heart rate or stroke volume or both, will elevate blood pressure and promote blood flow. These factors include sympathetic stimulation, the catecholamines epinephrine and norepinephrine, thyroid hormones, and increased calcium ion levels. Conversely, any factor that decreases cardiac output, by decreasing heart rate or stroke volume or both, will decrease arterial pressure and blood flow. These factors include parasympathetic stimulation, elevated or decreased potassium ion levels, decreased calcium levels, anoxia, and acidosis.
Compliance
Compliance is the ability of any compartment to expand to accommodate increased content. A metal pipe, for example, is not compliant, whereas a balloon is. The greater the compliance of an artery, the more effectively it is able to expand to accommodate surges in blood flow without increased resistance or blood pressure. Veins are more compliant than arteries and can expand to hold more blood. When vascular disease causes stiffening of arteries, compliance is reduced and resistance to blood flow is increased. The result is more turbulence, higher pressure within the vessel, and reduced blood flow. This increases the work of the heart.
A Mathematical Approach to Factors Affecting Blood Flow
Jean Louis Marie Poiseuille was a French physician and physiologist who devised a mathematical equation describing blood flow and its relationship to known parameters. The same equation also applies to engineering studies of the flow of fluids. Although understanding the math behind the relationships among the factors affecting blood flow is not necessary to understand blood flow, it can help solidify an understanding of their relationships. Please note that even if the equation looks intimidating, breaking it down into its components and following the relationships will make these relationships clearer, even if you are weak in math. Focus on the three critical variables: radius (r), vessel length (λ), and viscosity (η).
Poiseuille’s equation:
Blood flow = π ΔP r48ηλBlood flow = π ΔP r48ηλ- π is the Greek letter pi, used to represent the mathematical constant that is the ratio of a circle’s circumference to its diameter. It may commonly be represented as 3.14, although the actual number extends to infinity.
- ΔP represents the difference in pressure.
- r4 is the radius (one-half of the diameter) of the vessel to the fourth power.
- η is the Greek letter eta and represents the viscosity of the blood.
- λ is the Greek letter lambda and represents the length of a blood vessel.
One of several things this equation allows us to do is calculate the resistance in the vascular system. Normally this value is extremely difficult to measure, but it can be calculated from this known relationship:
Blood flow = ΔPResistanceBlood flow = ΔPResistanceIf we rearrange this slightly,
Resistance = ΔPBlood flowResistance = ΔPBlood flowThen by substituting Pouseille’s equation for blood flow:
Resistance =8ηλπr4Resistance =8ηλπr4By examining this equation, you can see that there are only three variables: viscosity, vessel length, and radius, since 8 and π are both constants. The important thing to remember is this: Two of these variables, viscosity and vessel length, will change slowly in the body. Only one of these factors, the radius, can be changed rapidly by vasoconstriction and vasodilation, thus dramatically impacting resistance and flow. Further, small changes in the radius will greatly affect flow, since it is raised to the fourth power in the equation.
We have briefly considered how cardiac output and blood volume impact blood flow and pressure; the next step is to see how the other variables (contraction, vessel length, and viscosity) articulate with Pouseille’s equation and what they can teach us about the impact on blood flow.
Blood Volume
The relationship between blood volume, blood pressure, and blood flow is intuitively obvious. Water may merely trickle along a creek bed in a dry season, but rush quickly and under great pressure after a heavy rain. Similarly, as blood volume decreases, pressure and flow decrease. As blood volume increases, pressure and flow increase.
Under normal circumstances, blood volume varies little. Low blood volume, called hypovolemia, may be caused by bleeding, dehydration, vomiting, severe burns, or some medications used to treat hypertension. It is important to recognize that other regulatory mechanisms in the body are so effective at maintaining blood pressure that an individual may be asymptomatic until 10–20 percent of the blood volume has been lost. Treatment typically includes intravenous fluid replacement.
Hypervolemia, excessive fluid volume, may be caused by retention of water and sodium, as seen in patients with heart failure, liver cirrhosis, some forms of kidney disease, hyperaldosteronism, and some glucocorticoid steroid treatments. Restoring homeostasis in these patients depends upon reversing the condition that triggered the hypervolemia.
Blood Viscosity
Viscosity is the thickness of fluids that affects their ability to flow. Clean water, for example, is less viscous than mud. The viscosity of blood is directly proportional to resistance and inversely proportional to flow; therefore, any condition that causes viscosity to increase will also increase resistance and decrease flow. For example, imagine sipping milk, then a milkshake, through the same size straw. You experience more resistance and therefore less flow from the milkshake. Conversely, any condition that causes viscosity to decrease (such as when the milkshake melts) will decrease resistance and increase flow.
Normally the viscosity of blood does not change over short periods of time. The two primary determinants of blood viscosity are the formed elements and plasma proteins. Since the vast majority of formed elements are erythrocytes, any condition affecting erythropoiesis, such as polycythemia or anemia, can alter viscosity. Since most plasma proteins are produced by the liver, any condition affecting liver function can also change the viscosity slightly and therefore alter blood flow. Liver abnormalities such as hepatitis, cirrhosis, alcohol damage, and drug toxicities result in decreased levels of plasma proteins, which decrease blood viscosity. While leukocytes and platelets are normally a small component of the formed elements, there are some rare conditions in which severe overproduction can impact viscosity as well.
Vessel Length and Diameter
The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood. Likewise, if the vessel is shortened, the resistance will decrease and flow will increase.
The length of our blood vessels increases throughout childhood as we grow, of course, but is unchanging in adults under normal physiological circumstances. Further, the distribution of vessels is not the same in all tissues. Adipose tissue does not have an extensive vascular supply. One pound of adipose tissue contains approximately 200 miles of vessels, whereas skeletal muscle contains more than twice that. Overall, vessels decrease in length only during loss of mass or amputation. An individual weighing 150 pounds has approximately 60,000 miles of vessels in the body. Gaining about 10 pounds adds from 2000 to 4000 miles of vessels, depending upon the nature of the gained tissue. One of the great benefits of weight reduction is the reduced stress to the heart, which does not have to overcome the resistance of as many miles of vessels.
In contrast to length, the diameter of blood vessels changes throughout the body, according to the type of vessel, as we discussed earlier. The diameter of any given vessel may also change frequently throughout the day in response to neural and chemical signals that trigger vasodilation and vasoconstriction. The vascular tone of the vessel is the contractile state of the smooth muscle and the primary determinant of diameter, and thus of resistance and flow. The effect of vessel diameter on resistance is inverse: Given the same volume of blood, an increased diameter means there is less blood contacting the vessel wall, thus lower friction and lower resistance, subsequently increasing flow. A decreased diameter means more of the blood contacts the vessel wall, and resistance increases, subsequently decreasing flow.
The influence of lumen diameter on resistance is dramatic: A slight increase or decrease in diameter causes a huge decrease or increase in resistance. This is because resistance is inversely proportional to the radius of the blood vessel (one-half of the vessel’s diameter) raised to the fourth power (R = 1/r4). This means, for example, that if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times. And if an artery or arteriole dilates to twice its initial radius, then resistance in the vessel will decrease to 1/16 of its original value and flow will increase 16 times.
The Roles of Vessel Diameter and Total Area in Blood Flow and Blood Pressure
Recall that we classified arterioles as resistance vessels, because given their small lumen, they dramatically slow the flow of blood from arteries. In fact, arterioles are the site of greatest resistance in the entire vascular network. This may seem surprising, given that capillaries have a smaller size. How can this phenomenon be explained?
Figure 20.13 compares vessel diameter, total cross-sectional area, average blood pressure, and blood velocity through the systemic vessels. Notice in parts (a) and (b) that the total cross-sectional area of the body’s capillary beds is far greater than any other type of vessel. Although the diameter of an individual capillary is significantly smaller than the diameter of an arteriole, there are vastly more capillaries in the body than there are other types of blood vessels. Part (c) shows that blood pressure drops unevenly as blood travels from arteries to arterioles, capillaries, venules, and veins, and encounters greater resistance. However, the site of the most precipitous drop, and the site of greatest resistance, is the arterioles. This explains why vasodilation and vasoconstriction of arterioles play more significant roles in regulating blood pressure than do the vasodilation and vasoconstriction of other vessels.
Part (d) shows that the velocity (speed) of blood flow decreases dramatically as the blood moves from arteries to arterioles to capillaries. This slow flow rate allows more time for exchange processes to occur. As blood flows through the veins, the rate of velocity increases, as blood is returned to the heart.
Figure 20.13 Relationships among Vessels in the Systemic Circuit The relationships among blood vessels that can be compared include (a) vessel diameter, (b) total cross-sectional area, (c) average blood pressure, and (d) velocity of blood flow.
DISORDERS OF THE...
Cardiovascular System: Arteriosclerosis
Compliance allows an artery to expand when blood is pumped through it from the heart, and then to recoil after the surge has passed. This helps promote blood flow. In arteriosclerosis, compliance is reduced, and pressure and resistance within the vessel increase. This is a leading cause of hypertension and coronary heart disease, as it causes the heart to work harder to generate a pressure great enough to overcome the resistance.
Arteriosclerosis begins with injury to the endothelium of an artery, which may be caused by irritation from high blood glucose, infection, tobacco use, excessive blood lipids, and other factors. Artery walls that are constantly stressed by blood flowing at high pressure are also more likely to be injured—which means that hypertension can promote arteriosclerosis, as well as result from it.
Recall that tissue injury causes inflammation. As inflammation spreads into the artery wall, it weakens and scars it, leaving it stiff (sclerotic). As a result, compliance is reduced. Moreover, circulating triglycerides and cholesterol can seep between the damaged lining cells and become trapped within the artery wall, where they are frequently joined by leukocytes, calcium, and cellular debris. Eventually, this buildup, called plaque, can narrow arteries enough to impair blood flow. The term for this condition, atherosclerosis (athero- = “porridge”) describes the mealy deposits (Figure 20.14).
Figure 20.14 Atherosclerosis (a) Atherosclerosis can result from plaques formed by the buildup of fatty, calcified deposits in an artery. (b) Plaques can also take other forms, as shown in this micrograph of a coronary artery that has a buildup of connective tissue within the artery wall. LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Sometimes a plaque can rupture, causing microscopic tears in the artery wall that allow blood to leak into the tissue on the other side. When this happens, platelets rush to the site to clot the blood. This clot can further obstruct the artery and—if it occurs in a coronary or cerebral artery—cause a sudden heart attack or stroke. Alternatively, plaque can break off and travel through the bloodstream as an embolus until it blocks a more distant, smaller artery.
Even without total blockage, vessel narrowing leads to ischemia—reduced blood flow—to the tissue region “downstream” of the narrowed vessel. Ischemia in turn leads to hypoxia—decreased supply of oxygen to the tissues. Hypoxia involving cardiac muscle or brain tissue can lead to cell death and severe impairment of brain or heart function.
A major risk factor for both arteriosclerosis and atherosclerosis is advanced age, as the conditions tend to progress over time. Arteriosclerosis is normally defined as the more generalized loss of compliance, “hardening of the arteries,” whereas atherosclerosis is a more specific term for the build-up of plaque in the walls of the vessel and is a specific type of arteriosclerosis. There is also a distinct genetic component, and pre-existing hypertension and/or diabetes also greatly increase the risk. However, obesity, poor nutrition, lack of physical activity, and tobacco use all are major risk factors.
Treatment includes lifestyle changes, such as weight loss, smoking cessation, regular exercise, and adoption of a diet low in sodium and saturated fats. Medications to reduce cholesterol and blood pressure may be prescribed. For blocked coronary arteries, surgery is warranted. In angioplasty, a catheter is inserted into the vessel at the point of narrowing, and a second catheter with a balloon-like tip is inflated to widen the opening. To prevent subsequent collapse of the vessel, a small mesh tube called a stent is often inserted. In an endarterectomy, plaque is surgically removed from the walls of a vessel. This operation is typically performed on the carotid arteries of the neck, which are a prime source of oxygenated blood for the brain. In a coronary bypass procedure, a non-vital superficial vessel from another part of the body (often the great saphenous vein) or a synthetic vessel is inserted to create a path around the blocked area of a coronary artery.
Venous System
The pumping action of the heart propels the blood into the arteries, from an area of higher pressure toward an area of lower pressure. If blood is to flow from the veins back into the heart, the pressure in the veins must be greater than the pressure in the atria of the heart. Two factors help maintain this pressure gradient between the veins and the heart. First, the pressure in the atria during diastole is very low, often approaching zero when the atria are relaxed (atrial diastole). Second, two physiologic “pumps” increase pressure in the venous system. The use of the term “pump” implies a physical device that speeds flow. These physiological pumps are less obvious.
Skeletal Muscle Pump
In many body regions, the pressure within the veins can be increased by the contraction of the surrounding skeletal muscle. This mechanism, known as the skeletal muscle pump (Figure 20.15), helps the lower-pressure veins counteract the force of gravity, increasing pressure to move blood back to the heart. As leg muscles contract, for example during walking or running, they exert pressure on nearby veins with their numerous one-way valves. This increased pressure causes blood to flow upward, opening valves superior to the contracting muscles so blood flows through. Simultaneously, valves inferior to the contracting muscles close; thus, blood should not seep back downward toward the feet. Military recruits are trained to flex their legs slightly while standing at attention for prolonged periods. Failure to do so may allow blood to pool in the lower limbs rather than returning to the heart. Consequently, the brain will not receive enough oxygenated blood, and the individual may lose consciousness.
Figure 20.15 Skeletal Muscle Pump The contraction of skeletal muscles surrounding a vein compresses the blood and increases the pressure in that area. This action forces blood closer to the heart where venous pressure is lower. Note the importance of the one-way valves to assure that blood flows only in the proper direction.
Respiratory Pump
The respiratory pump aids blood flow through the veins of the thorax and abdomen. During inhalation, the volume of the thorax increases, largely through the contraction of the diaphragm, which moves downward and compresses the abdominal cavity. The elevation of the chest caused by the contraction of the external intercostal muscles also contributes to the increased volume of the thorax. The volume increase causes air pressure within the thorax to decrease, allowing us to inhale. Additionally, as air pressure within the thorax drops, blood pressure in the thoracic veins also decreases, falling below the pressure in the abdominal veins. This causes blood to flow along its pressure gradient from veins outside the thorax, where pressure is higher, into the thoracic region, where pressure is now lower. This in turn promotes the return of blood from the thoracic veins to the atria. During exhalation, when air pressure increases within the thoracic cavity, pressure in the thoracic veins increases, speeding blood flow into the heart while valves in the veins prevent blood from flowing backward from the thoracic and abdominal veins.
Pressure Relationships in the Venous System
Although vessel diameter increases from the smaller venules to the larger veins and eventually to the venae cavae (singular = vena cava), the total cross-sectional area actually decreases (see Figure 20.15a and b). The individual veins are larger in diameter than the venules, but their total number is much lower, so their total cross-sectional area is also lower.
Also notice that, as blood moves from venules to veins, the average blood pressure drops (see Figure 20.15c), but the blood velocity actually increases (see Figure 20.15). This pressure gradient drives blood back toward the heart. Again, the presence of one-way valves and the skeletal muscle and respiratory pumps contribute to this increased flow. Since approximately 64 percent of the total blood volume resides in systemic veins, any action that increases the flow of blood through the veins will increase venous return to the heart. Maintaining vascular tone within the veins prevents the veins from merely distending, dampening the flow of blood, and as you will see, vasoconstriction actually enhances the flow.
The Role of Venoconstriction in Resistance, Blood Pressure, and Flow
As previously discussed, vasoconstriction of an artery or arteriole decreases the radius, increasing resistance and pressure, but decreasing flow. Venoconstriction, on the other hand, has a very different outcome. The walls of veins are thin but irregular; thus, when the smooth muscle in those walls constricts, the lumen becomes more rounded. The more rounded the lumen, the less surface area the blood encounters, and the less resistance the vessel offers. Vasoconstriction increases pressure within a vein as it does in an artery, but in veins, the increased pressure increases flow. Recall that the pressure in the atria, into which the venous blood will flow, is very low, approaching zero for at least part of the relaxation phase of the cardiac cycle. Thus, venoconstriction increases the return of blood to the heart. Another way of stating this is that venoconstriction increases the preload or stretch of the cardiac muscle and increases contraction.
Capillary Exchange
- Identify the primary mechanisms of capillary exchange
- Distinguish between capillary hydrostatic pressure and blood colloid osmotic pressure, explaining the contribution of each to net filtration pressure
- Compare filtration and reabsorption
- Explain the fate of fluid that is not reabsorbed from the tissues into the vascular capillaries
The primary purpose of the cardiovascular system is to circulate gases, nutrients, wastes, and other substances to and from the cells of the body. Small molecules, such as gases, lipids, and lipid-soluble molecules, can diffuse directly through the membranes of the endothelial cells of the capillary wall. Glucose, amino acids, and ions—including sodium, potassium, calcium, and chloride—use transporters to move through specific channels in the membrane by facilitated diffusion. Glucose, ions, and larger molecules may also leave the blood through intercellular clefts. Larger molecules can pass through the pores of fenestrated capillaries, and even large plasma proteins can pass through the great gaps in the sinusoids. Some large proteins in blood plasma can move into and out of the endothelial cells packaged within vesicles by endocytosis and exocytosis. Water moves by osmosis.
Bulk Flow
The mass movement of fluids into and out of capillary beds requires a transport mechanism far more efficient than mere diffusion. This movement, often referred to as bulk flow, involves two pressure-driven mechanisms: Volumes of fluid move from an area of higher pressure in a capillary bed to an area of lower pressure in the tissues via filtration. In contrast, the movement of fluid from an area of higher pressure in the tissues into an area of lower pressure in the capillaries is reabsorption. Two types of pressure interact to drive each of these movements: hydrostatic pressure and osmotic pressure.
Hydrostatic Pressure
The primary force driving fluid transport between the capillaries and tissues is hydrostatic pressure, which can be defined as the pressure of any fluid enclosed in a space. Blood hydrostatic pressure is the force exerted by the blood confined within blood vessels or heart chambers. Even more specifically, the pressure exerted by blood against the wall of a capillary is called capillary hydrostatic pressure (CHP), and is the same as capillary blood pressure. CHP is the force that drives fluid out of capillaries and into the tissues.
As fluid exits a capillary and moves into tissues, the hydrostatic pressure in the interstitial fluid correspondingly rises. This opposing hydrostatic pressure is called the interstitial fluid hydrostatic pressure (IFHP). Generally, the CHP originating from the arterial pathways is considerably higher than the IFHP, because lymphatic vessels are continually absorbing excess fluid from the tissues. Thus, fluid generally moves out of the capillary and into the interstitial fluid. This process is called filtration.
Osmotic Pressure
The net pressure that drives reabsorption—the movement of fluid from the interstitial fluid back into the capillaries—is called osmotic pressure (sometimes referred to as oncotic pressure). Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in. Osmotic pressure is determined by osmotic concentration gradients, that is, the difference in the solute-to-water concentrations in the blood and tissue fluid. A region higher in solute concentration (and lower in water concentration) draws water across a semipermeable membrane from a region higher in water concentration (and lower in solute concentration).
As we discuss osmotic pressure in blood and tissue fluid, it is important to recognize that the formed elements of blood do not contribute to osmotic concentration gradients. Rather, it is the plasma proteins that play the key role. Solutes also move across the capillary wall according to their concentration gradient, but overall, the concentrations should be similar and not have a significant impact on osmosis. Because of their large size and chemical structure, plasma proteins are not truly solutes, that is, they do not dissolve but are dispersed or suspended in their fluid medium, forming a colloid rather than a solution.
The pressure created by the concentration of colloidal proteins in the blood is called the blood colloidal osmotic pressure (BCOP). Its effect on capillary exchange accounts for the reabsorption of water. The plasma proteins suspended in blood cannot move across the semipermeable capillary cell membrane, and so they remain in the plasma. As a result, blood has a higher colloidal concentration and lower water concentration than tissue fluid. It therefore attracts water. We can also say that the BCOP is higher than the interstitial fluid colloidal osmotic pressure (IFCOP), which is always very low because interstitial fluid contains few proteins. Thus, water is drawn from the tissue fluid back into the capillary, carrying dissolved molecules with it. This difference in colloidal osmotic pressure accounts for reabsorption.
Interaction of Hydrostatic and Osmotic Pressures
The normal unit used to express pressures within the cardiovascular system is millimeters of mercury (mm Hg). When blood leaving an arteriole first enters a capillary bed, the CHP is quite high—about 35 mm Hg. Gradually, this initial CHP declines as the blood moves through the capillary so that by the time the blood has reached the venous end, the CHP has dropped to approximately 18 mm Hg. In comparison, the plasma proteins remain suspended in the blood, so the BCOP remains fairly constant at about 25 mm Hg throughout the length of the capillary and considerably below the osmotic pressure in the interstitial fluid.
The net filtration pressure (NFP) represents the interaction of the hydrostatic and osmotic pressures, driving fluid out of the capillary. It is equal to the difference between the CHP and the BCOP. Since filtration is, by definition, the movement of fluid out of the capillary, when reabsorption is occurring, the NFP is a negative number.
NFP changes at different points in a capillary bed (Figure 20.16). Close to the arterial end of the capillary, it is approximately 10 mm Hg, because the CHP of 35 mm Hg minus the BCOP of 25 mm Hg equals 10 mm Hg. Recall that the hydrostatic and osmotic pressures of the interstitial fluid are essentially negligible. Thus, the NFP of 10 mm Hg drives a net movement of fluid out of the capillary at the arterial end. At approximately the middle of the capillary, the CHP is about the same as the BCOP of 25 mm Hg, so the NFP drops to zero. At this point, there is no net change of volume: Fluid moves out of the capillary at the same rate as it moves into the capillary. Near the venous end of the capillary, the CHP has dwindled to about 18 mm Hg due to loss of fluid. Because the BCOP remains steady at 25 mm Hg, water is drawn into the capillary, that is, reabsorption occurs. Another way of expressing this is to say that at the venous end of the capillary, there is an NFP of −7 mm Hg.
Figure 20.16 Capillary Exchange Net filtration occurs near the arterial end of the capillary since capillary hydrostatic pressure (CHP) is greater than blood colloidal osmotic pressure (BCOP). There is no net movement of fluid near the midpoint since CHP = BCOP. Net reabsorption occurs near the venous end since BCOP is greater than CHP.
The Role of Lymphatic Capillaries
Since overall CHP is higher than BCOP, it is inevitable that more net fluid will exit the capillary through filtration at the arterial end than enters through reabsorption at the venous end. Considering all capillaries over the course of a day, this can be quite a substantial amount of fluid: Approximately 24 liters per day are filtered, whereas 20.4 liters are reabsorbed. This excess fluid is picked up by capillaries of the lymphatic system. These extremely thin-walled vessels have copious numbers of valves that ensure unidirectional flow through ever-larger lymphatic vessels that eventually drain into the subclavian veins in the neck. An important function of the lymphatic system is to return the fluid (lymph) to the blood. Lymph may be thought of as recycled blood plasma. (Seek additional content for more detail on the lymphatic system.)
INTERACTIVE LINK
Watch this video to explore capillaries and how they function in the body. Capillaries are never more than 100 micrometers away. What is the main component of interstitial fluid?
Homeostatic Regulation of the Vascular System
- Discuss the mechanisms involved in the neural regulation of vascular homeostasis
- Describe the contribution of a variety of hormones to the renal regulation of blood pressure
- Identify the effects of exercise on vascular homeostasis
- Discuss how hypertension, hemorrhage, and circulatory shock affect vascular health
In order to maintain homeostasis in the cardiovascular system and provide adequate blood to the tissues, blood flow must be redirected continually to the tissues as they become more active. In a very real sense, the cardiovascular system engages in resource allocation, because there is not enough blood flow to distribute blood equally to all tissues simultaneously. For example, when an individual is exercising, more blood will be directed to skeletal muscles, the heart, and the lungs. Following a meal, more blood is directed to the digestive system. Only the brain receives a more or less constant supply of blood whether you are active, resting, thinking, or engaged in any other activity.
Table 20.3 provides the distribution of systemic blood at rest and during exercise. Although most of the data appears logical, the values for the distribution of blood to the integument may seem surprising. During exercise, the body distributes more blood to the body surface where it can dissipate the excess heat generated by increased activity into the environment.
Systemic Blood Flow During Rest, Mild Exercise, and Maximal Exercise in a Healthy Young Individual
| Organ | Resting (mL/min) | Mild exercise (mL/min) | Maximal exercise (mL/min) |
|---|---|---|---|
| Skeletal muscle | 1200 | 4500 | 12,500 |
| Heart | 250 | 350 | 750 |
| Brain | 750 | 750 | 750 |
| Integument | 500 | 1500 | 1900 |
| Kidney | 1100 | 900 | 600 |
| Gastrointestinal | 1400 | 1100 | 600 |
| Others (i.e., liver, spleen) | 600 | 400 | 400 |
| Total | 5800 | 9500 | 17,500 |
Table 20.3
Three homeostatic mechanisms ensure adequate blood flow, blood pressure, distribution, and ultimately perfusion: neural, endocrine, and autoregulatory mechanisms. They are summarized in Figure 20.17.
Figure 20.17 Summary of Factors Maintaining Vascular Homeostasis Adequate blood flow, blood pressure, distribution, and perfusion involve autoregulatory, neural, and endocrine mechanisms.
Neural Regulation
The nervous system plays a critical role in the regulation of vascular homeostasis. The primary regulatory sites include the cardiovascular centers in the brain that control both cardiac and vascular functions. In addition, more generalized neural responses from the limbic system and the autonomic nervous system are factors.
The Cardiovascular Centers in the Brain
Neurological regulation of blood pressure and flow depends on the cardiovascular centers located in the medulla oblongata. This cluster of neurons responds to changes in blood pressure as well as blood concentrations of oxygen, carbon dioxide, and hydrogen ions. The cardiovascular center contains three distinct paired components:
- The cardioaccelerator centers stimulate cardiac function by regulating heart rate and stroke volume via sympathetic stimulation from the cardiac accelerator nerve.
- The cardioinhibitor centers slow cardiac function by decreasing heart rate and stroke volume via parasympathetic stimulation from the vagus nerve.
- The vasomotor centers control vessel tone or contraction of the smooth muscle in the tunica media. Changes in diameter affect peripheral resistance, pressure, and flow, which affect cardiac output. The majority of these neurons act via the release of the neurotransmitter norepinephrine from sympathetic neurons.
Although each center functions independently, they are not anatomically distinct.
There is also a small population of neurons that control vasodilation in the vessels of the brain and skeletal muscles by relaxing the smooth muscle fibers in the vessel tunics. Many of these are cholinergic neurons, that is, they release acetylcholine, which in turn stimulates the vessels’ endothelial cells to release nitric oxide (NO), which causes vasodilation. Others release norepinephrine that binds to β2 receptors. A few neurons release NO directly as a neurotransmitter.
Recall that mild stimulation of the skeletal muscles maintains muscle tone. A similar phenomenon occurs with vascular tone in vessels. As noted earlier, arterioles are normally partially constricted: With maximal stimulation, their radius may be reduced to one-half of the resting state. Full dilation of most arterioles requires that this sympathetic stimulation be suppressed. When it is, an arteriole can expand by as much as 150 percent. Such a significant increase can dramatically affect resistance, pressure, and flow.
Baroreceptor Reflexes
Baroreceptors are specialized stretch receptors located within thin areas of blood vessels and heart chambers that respond to the degree of stretch caused by the presence of blood. They send impulses to the cardiovascular center to regulate blood pressure. Vascular baroreceptors are found primarily in sinuses (small cavities) within the aorta and carotid arteries: The aortic sinuses are found in the walls of the ascending aorta just superior to the aortic valve, whereas the carotid sinuses are in the base of the internal carotid arteries. There are also low-pressure baroreceptors located in the walls of the venae cavae and right atrium.
When blood pressure increases, the baroreceptors are stretched more tightly and initiate action potentials at a higher rate. At lower blood pressures, the degree of stretch is lower and the rate of firing is slower. When the cardiovascular center in the medulla oblongata receives this input, it triggers a reflex that maintains homeostasis (Figure 20.18):
- When blood pressure rises too high, the baroreceptors fire at a higher rate and trigger parasympathetic stimulation of the heart. As a result, cardiac output falls. Sympathetic stimulation of the peripheral arterioles will also decrease, resulting in vasodilation. Combined, these activities cause blood pressure to fall.
- When blood pressure drops too low, the rate of baroreceptor firing decreases. This will trigger an increase in sympathetic stimulation of the heart, causing cardiac output to increase. It will also trigger sympathetic stimulation of the peripheral vessels, resulting in vasoconstriction. Combined, these activities cause blood pressure to rise.
Figure 20.18 Baroreceptor Reflexes for Maintaining Vascular Homeostasis Increased blood pressure results in increased rates of baroreceptor firing, whereas decreased blood pressure results in slower rates of fire, both initiating the homeostatic mechanism to restore blood pressure.
The baroreceptors in the venae cavae and right atrium monitor blood pressure as the blood returns to the heart from the systemic circulation. Normally, blood flow into the aorta is the same as blood flow back into the right atrium. If blood is returning to the right atrium more rapidly than it is being ejected from the left ventricle, the atrial receptors will stimulate the cardiovascular centers to increase sympathetic firing and increase cardiac output until homeostasis is achieved. The opposite is also true. This mechanism is referred to as the atrial reflex.
Chemoreceptor Reflexes
In addition to the baroreceptors are chemoreceptors that monitor levels of oxygen, carbon dioxide, and hydrogen ions (pH), and thereby contribute to vascular homeostasis. Chemoreceptors monitoring the blood are located in close proximity to the baroreceptors in the aortic and carotid sinuses. They signal the cardiovascular center as well as the respiratory centers in the medulla oblongata.
Since tissues consume oxygen and produce carbon dioxide and acids as waste products, when the body is more active, oxygen levels fall and carbon dioxide levels rise as cells undergo cellular respiration to meet the energy needs of activities. This causes more hydrogen ions to be produced, causing the blood pH to drop. When the body is resting, oxygen levels are higher, carbon dioxide levels are lower, more hydrogen is bound, and pH rises. (Seek additional content for more detail about pH.)
The chemoreceptors respond to increasing carbon dioxide and hydrogen ion levels (falling pH) by stimulating the cardioaccelerator and vasomotor centers, increasing cardiac output and constricting peripheral vessels. The cardioinhibitor centers are suppressed. With falling carbon dioxide and hydrogen ion levels (increasing pH), the cardioinhibitor centers are stimulated, and the cardioaccelerator and vasomotor centers are suppressed, decreasing cardiac output and causing peripheral vasodilation. In order to maintain adequate supplies of oxygen to the cells and remove waste products such as carbon dioxide, it is essential that the respiratory system respond to changing metabolic demands. In turn, the cardiovascular system will transport these gases to the lungs for exchange, again in accordance with metabolic demands. This interrelationship of cardiovascular and respiratory control cannot be overemphasized.
Other neural mechanisms can also have a significant impact on cardiovascular function. These include the limbic system that links physiological responses to psychological stimuli, as well as generalized sympathetic and parasympathetic stimulation.
Endocrine Regulation
Endocrine control over the cardiovascular system involves the catecholamines, epinephrine and norepinephrine, as well as several hormones that interact with the kidneys in the regulation of blood volume.
Epinephrine and Norepinephrine
The catecholamines epinephrine and norepinephrine are released by the adrenal medulla, and enhance and extend the body’s sympathetic or “fight-or-flight” response (see Figure 20.17). They increase heart rate and force of contraction, while temporarily constricting blood vessels to organs not essential for flight-or-fight responses and redirecting blood flow to the liver, muscles, and heart.
Antidiuretic Hormone
Antidiuretic hormone (ADH), also known as vasopressin, is secreted by the cells in the hypothalamus and transported via the hypothalamic-hypophyseal tracts to the posterior pituitary where it is stored until released upon nervous stimulation. The primary trigger prompting the hypothalamus to release ADH is increasing osmolarity of tissue fluid, usually in response to significant loss of blood volume. ADH signals its target cells in the kidneys to reabsorb more water, thus preventing the loss of additional fluid in the urine. This will increase overall fluid levels and help restore blood volume and pressure. In addition, ADH constricts peripheral vessels.
Renin-Angiotensin-Aldosterone Mechanism
The renin-angiotensin-aldosterone mechanism has a major effect upon the cardiovascular system (Figure 20.19). Renin is an enzyme, although because of its importance in the renin-angiotensin-aldosterone pathway, some sources identify it as a hormone. Specialized cells in the kidneys found in the juxtaglomerular apparatus respond to decreased blood flow by secreting renin into the blood. Renin converts the plasma protein angiotensinogen, which is produced by the liver, into its active form—angiotensin I. Angiotensin I circulates in the blood and is then converted into angiotensin II in the lungs. This reaction is catalyzed by the enzyme angiotensin-converting enzyme (ACE).
Angiotensin II is a powerful vasoconstrictor, greatly increasing blood pressure. It also stimulates the release of ADH and aldosterone, a hormone produced by the adrenal cortex. Aldosterone increases the reabsorption of sodium into the blood by the kidneys. Since water follows sodium, this increases the reabsorption of water. This in turn increases blood volume, raising blood pressure. Angiotensin II also stimulates the thirst center in the hypothalamus, so an individual will likely consume more fluids, again increasing blood volume and pressure.
Figure 20.19 Hormones Involved in Renal Control of Blood Pressure In the renin-angiotensin-aldosterone mechanism, increasing angiotensin II will stimulate the production of antidiuretic hormone and aldosterone. In addition to renin, the kidneys produce erythropoietin, which stimulates the production of red blood cells, further increasing blood volume.
Erythropoietin
Erythropoietin (EPO) is released by the kidneys when blood flow and/or oxygen levels decrease. EPO stimulates the production of erythrocytes within the bone marrow. Erythrocytes are the major formed element of the blood and may contribute 40 percent or more to blood volume, a significant factor of viscosity, resistance, pressure, and flow. In addition, EPO is a vasoconstrictor. Overproduction of EPO or excessive intake of synthetic EPO, often to enhance athletic performance, will increase viscosity, resistance, and pressure, and decrease flow in addition to its contribution as a vasoconstrictor.
Atrial Natriuretic Hormone
Secreted by cells in the atria of the heart, atrial natriuretic hormone (ANH) (also known as atrial natriuretic peptide) is secreted when blood volume is high enough to cause extreme stretching of the cardiac cells. Cells in the ventricle produce a hormone with similar effects, called B-type natriuretic hormone. Natriuretic hormones are antagonists to angiotensin II. They promote loss of sodium and water from the kidneys, and suppress renin, aldosterone, and ADH production and release. All of these actions promote loss of fluid from the body, so blood volume and blood pressure drop.
Autoregulation of Perfusion
As the name would suggest, autoregulation mechanisms require neither specialized nervous stimulation nor endocrine control. Rather, these are local, self-regulatory mechanisms that allow each region of tissue to adjust its blood flow—and thus its perfusion. These local mechanisms include chemical signals and myogenic controls.
Chemical Signals Involved in Autoregulation
Chemical signals work at the level of the precapillary sphincters to trigger either constriction or relaxation. As you know, opening a precapillary sphincter allows blood to flow into that particular capillary, whereas constricting a precapillary sphincter temporarily shuts off blood flow to that region. The factors involved in regulating the precapillary sphincters include the following:
- Opening of the sphincter is triggered in response to decreased oxygen concentrations; increased carbon dioxide concentrations; increasing levels of lactic acid or other byproducts of cellular metabolism; increasing concentrations of potassium ions or hydrogen ions (falling pH); inflammatory chemicals such as histamines; and increased body temperature. These conditions in turn stimulate the release of NO, a powerful vasodilator, from endothelial cells (see Figure 20.17).
- Contraction of the precapillary sphincter is triggered by the opposite levels of the regulators, which prompt the release of endothelins, powerful vasoconstricting peptides secreted by endothelial cells. Platelet secretions and certain prostaglandins may also trigger constriction.
Again, these factors alter tissue perfusion via their effects on the precapillary sphincter mechanism, which regulates blood flow to capillaries. Since the amount of blood is limited, not all capillaries can fill at once, so blood flow is allocated based upon the needs and metabolic state of the tissues as reflected in these parameters. Bear in mind, however, that dilation and constriction of the arterioles feeding the capillary beds is the primary control mechanism.
The Myogenic Response
The myogenic response is a reaction to the stretching of the smooth muscle in the walls of arterioles as changes in blood flow occur through the vessel. This may be viewed as a largely protective function against dramatic fluctuations in blood pressure and blood flow to maintain homeostasis. If perfusion of an organ is too low (ischemia), the tissue will experience low levels of oxygen (hypoxia). In contrast, excessive perfusion could damage the organ’s smaller and more fragile vessels. The myogenic response is a localized process that serves to stabilize blood flow in the capillary network that follows that arteriole.
When blood flow is low, the vessel’s smooth muscle will be only minimally stretched. In response, it relaxes, allowing the vessel to dilate and thereby increase the movement of blood into the tissue. When blood flow is too high, the smooth muscle will contract in response to the increased stretch, prompting vasoconstriction that reduces blood flow.
Figure 20.20 summarizes the effects of nervous, endocrine, and local controls on arterioles.
Figure 20.20 Summary of Mechanisms Regulating Arteriole Smooth Muscle and Veins
Effect of Exercise on Vascular Homeostasis
The heart is a muscle and, like any muscle, it responds dramatically to exercise. For a healthy young adult, cardiac output (heart rate × stroke volume) increases in the nonathlete from approximately 5.0 liters (5.25 quarts) per minute to a maximum of about 20 liters (21 quarts) per minute. Accompanying this will be an increase in blood pressure from about 120/80 to 185/75. However, well-trained aerobic athletes can increase these values substantially. For these individuals, cardiac output soars from approximately 5.3 liters (5.57 quarts) per minute resting to more than 30 liters (31.5 quarts) per minute during maximal exercise. Along with this increase in cardiac output, blood pressure increases from 120/80 at rest to 200/90 at maximum values.
In addition to improved cardiac function, exercise increases the size and mass of the heart. The average weight of the heart for the nonathlete is about 300 g, whereas in an athlete it will increase to 500 g. This increase in size generally makes the heart stronger and more efficient at pumping blood, increasing both stroke volume and cardiac output.
Tissue perfusion also increases as the body transitions from a resting state to light exercise and eventually to heavy exercise (see Figure 20.20). These changes result in selective vasodilation in the skeletal muscles, heart, lungs, liver, and integument. Simultaneously, vasoconstriction occurs in the vessels leading to the kidneys and most of the digestive and reproductive organs. The flow of blood to the brain remains largely unchanged whether at rest or exercising, since the vessels in the brain largely do not respond to regulatory stimuli, in most cases, because they lack the appropriate receptors.
As vasodilation occurs in selected vessels, resistance drops and more blood rushes into the organs they supply. This blood eventually returns to the venous system. Venous return is further enhanced by both the skeletal muscle and respiratory pumps. As blood returns to the heart more quickly, preload rises and the Frank-Starling principle tells us that contraction of the cardiac muscle in the atria and ventricles will be more forceful. Eventually, even the best-trained athletes will fatigue and must undergo a period of rest following exercise. Cardiac output and distribution of blood then return to normal.
Regular exercise promotes cardiovascular health in a variety of ways. Because an athlete’s heart is larger than a nonathlete’s, stroke volume increases, so the athletic heart can deliver the same amount of blood as the nonathletic heart but with a lower heart rate. This increased efficiency allows the athlete to exercise for longer periods of time before muscles fatigue and places less stress on the heart. Exercise also lowers overall cholesterol levels by removing from the circulation a complex form of cholesterol, triglycerides, and proteins known as low-density lipoproteins (LDLs), which are widely associated with increased risk of cardiovascular disease. Although there is no way to remove deposits of plaque from the walls of arteries other than specialized surgery, exercise does promote the health of vessels by decreasing the rate of plaque formation and reducing blood pressure, so the heart does not have to generate as much force to overcome resistance.
Generally as little as 30 minutes of noncontinuous exercise over the course of each day has beneficial effects and has been shown to lower the rate of heart attack by nearly 50 percent. While it is always advisable to follow a healthy diet, stop smoking, and lose weight, studies have clearly shown that fit, overweight people may actually be healthier overall than sedentary slender people. Thus, the benefits of moderate exercise are undeniable.
Clinical Considerations in Vascular Homeostasis
Any disorder that affects blood volume, vascular tone, or any other aspect of vascular functioning is likely to affect vascular homeostasis as well. That includes hypertension, hemorrhage, and shock.
Hypertension and Hypotension
Chronically elevated blood pressure is known clinically as hypertension. It is defined as chronic and persistent blood pressure measurements of 140/90 mm Hg or above. Pressures between 120/80 and 140/90 mm Hg are defined as prehypertension. About 68 million Americans currently suffer from hypertension. Unfortunately, hypertension is typically a silent disorder; therefore, hypertensive patients may fail to recognize the seriousness of their condition and fail to follow their treatment plan. The result is often a heart attack or stroke. Hypertension may also lead to an aneurism (ballooning of a blood vessel caused by a weakening of the wall), peripheral arterial disease (obstruction of vessels in peripheral regions of the body), chronic kidney disease, or heart failure.
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Hemorrhage
Minor blood loss is managed by hemostasis and repair. Hemorrhage is a loss of blood that cannot be controlled by hemostatic mechanisms. Initially, the body responds to hemorrhage by initiating mechanisms aimed at increasing blood pressure and maintaining blood flow. Ultimately, however, blood volume will need to be restored, either through physiological processes or through medical intervention.
In response to blood loss, stimuli from the baroreceptors trigger the cardiovascular centers to stimulate sympathetic responses to increase cardiac output and vasoconstriction. This typically prompts the heart rate to increase to about 180–200 contractions per minute, restoring cardiac output to normal levels. Vasoconstriction of the arterioles increases vascular resistance, whereas constriction of the veins increases venous return to the heart. Both of these steps will help increase blood pressure. Sympathetic stimulation also triggers the release of epinephrine and norepinephrine, which enhance both cardiac output and vasoconstriction. If blood loss were less than 20 percent of total blood volume, these responses together would usually return blood pressure to normal and redirect the remaining blood to the tissues.
Additional endocrine involvement is necessary, however, to restore the lost blood volume. The angiotensin-renin-aldosterone mechanism stimulates the thirst center in the hypothalamus, which increases fluid consumption to help restore the lost blood. More importantly, it increases renal reabsorption of sodium and water, reducing water loss in urine output. The kidneys also increase the production of EPO, stimulating the formation of erythrocytes that not only deliver oxygen to the tissues but also increase overall blood volume. Figure 20.21 summarizes the responses to loss of blood volume.
Figure 20.21 Homeostatic Responses to Loss of Blood Volume
Circulatory Shock
The loss of too much blood may lead to circulatory shock, a life-threatening condition in which the circulatory system is unable to maintain blood flow to adequately supply sufficient oxygen and other nutrients to the tissues to maintain cellular metabolism. It should not be confused with emotional or psychological shock. Typically, the patient in circulatory shock will demonstrate an increased heart rate but decreased blood pressure, but there are cases in which blood pressure will remain normal. Urine output will fall dramatically, and the patient may appear confused or lose consciousness. Urine output less than 1 mL/kg body weight/hour is cause for concern. Unfortunately, shock is an example of a positive-feedback loop that, if uncorrected, may lead to the death of the patient.
There are several recognized forms of shock:
- Hypovolemic shock in adults is typically caused by hemorrhage, although in children it may be caused by fluid losses related to severe vomiting or diarrhea. Other causes for hypovolemic shock include extensive burns, exposure to some toxins, and excessive urine loss related to diabetes insipidus or ketoacidosis. Typically, patients present with a rapid, almost tachycardic heart rate; a weak pulse often described as “thread;” cool, clammy skin, particularly in the extremities, due to restricted peripheral blood flow; rapid, shallow breathing; hypothermia; thirst; and dry mouth. Treatments generally involve providing intravenous fluids to restore the patient to normal function and various drugs such as dopamine, epinephrine, and norepinephrine to raise blood pressure.
- Cardiogenic shock results from the inability of the heart to maintain cardiac output. Most often, it results from a myocardial infarction (heart attack), but it may also be caused by arrhythmias, valve disorders, cardiomyopathies, cardiac failure, or simply insufficient flow of blood through the cardiac vessels. Treatment involves repairing the damage to the heart or its vessels to resolve the underlying cause, rather than treating cardiogenic shock directly.
- Vascular shock occurs when arterioles lose their normal muscular tone and dilate dramatically. It may arise from a variety of causes, and treatments almost always involve fluid replacement and medications, called inotropic or pressor agents, which restore tone to the muscles of the vessels. In addition, eliminating or at least alleviating the underlying cause of the condition is required. This might include antibiotics and antihistamines, or select steroids, which may aid in the repair of nerve damage. A common cause is sepsis (or septicemia), also called “blood poisoning,” which is a widespread bacterial infection that results in an organismal-level inflammatory response known as septic shock. Neurogenic shock is a form of vascular shock that occurs with cranial or spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region. Anaphylactic shock is a severe allergic response that causes the widespread release of histamines, triggering vasodilation throughout the body.
- Obstructive shock, as the name would suggest, occurs when a significant portion of the vascular system is blocked. It is not always recognized as a distinct condition and may be grouped with cardiogenic shock, including pulmonary embolism and cardiac tamponade. Treatments depend upon the underlying cause and, in addition to administering fluids intravenously, often include the administration of anticoagulants, removal of fluid from the pericardial cavity, or air from the thoracic cavity, and surgery as required. The most common cause is a pulmonary embolism, a clot that lodges in the pulmonary vessels and interrupts blood flow. Other causes include stenosis of the aortic valve; cardiac tamponade, in which excess fluid in the pericardial cavity interferes with the ability of the heart to fully relax and fill with blood (resulting in decreased preload); and a pneumothorax, in which an excessive amount of air is present in the thoracic cavity, outside of the lungs, which interferes with venous return, pulmonary function, and delivery of oxygen to the tissues.
Circulatory Pathways
- Identify the vessels through which blood travels within the pulmonary circuit, beginning from the right ventricle of the heart and ending at the left atrium
- Create a flow chart showing the major systemic arteries through which blood travels from the aorta and its major branches, to the most significant arteries feeding into the right and left upper and lower limbs
- Create a flow chart showing the major systemic veins through which blood travels from the feet to the right atrium of the heart
Virtually every cell, tissue, organ, and system in the body is impacted by the circulatory system. This includes the generalized and more specialized functions of transport of materials, capillary exchange, maintaining health by transporting white blood cells and various immunoglobulins (antibodies), hemostasis, regulation of body temperature, and helping to maintain acid-base balance. In addition to these shared functions, many systems enjoy a unique relationship with the circulatory system. Figure 20.22 summarizes these relationships.
Figure 20.22 Interaction of the Circulatory System with Other Body Systems
As you learn about the vessels of the systemic and pulmonary circuits, notice that many arteries and veins share the same names, parallel one another throughout the body, and are very similar on the right and left sides of the body. These pairs of vessels will be traced through only one side of the body. Where differences occur in branching patterns or when vessels are singular, this will be indicated. For example, you will find a pair of femoral arteries and a pair of femoral veins, with one vessel on each side of the body. In contrast, some vessels closer to the midline of the body, such as the aorta, are unique. Moreover, some superficial veins, such as the great saphenous vein in the femoral region, have no arterial counterpart. Another phenomenon that can make the study of vessels challenging is that names of vessels can change with location. Like a street that changes name as it passes through an intersection, an artery or vein can change names as it passes an anatomical landmark. For example, the left subclavian artery becomes the axillary artery as it passes through the body wall and into the axillary region, and then becomes the brachial artery as it flows from the axillary region into the upper arm (or brachium). You will also find examples of anastomoses where two blood vessels that previously branched reconnect. Anastomoses are especially common in veins, where they help maintain blood flow even when one vessel is blocked or narrowed, although there are some important ones in the arteries supplying the brain.
As you read about circular pathways, notice that there is an occasional, very large artery referred to as a trunk, a term indicating that the vessel gives rise to several smaller arteries. For example, the celiac trunk gives rise to the left gastric, common hepatic, and splenic arteries.
As you study this section, imagine you are on a “Voyage of Discovery” similar to Lewis and Clark’s expedition in 1804–1806, which followed rivers and streams through unfamiliar territory, seeking a water route from the Atlantic to the Pacific Ocean. You might envision being inside a miniature boat, exploring the various branches of the circulatory system. This simple approach has proven effective for many students in mastering these major circulatory patterns. Another approach that works well for many students is to create simple line drawings similar to the ones provided, labeling each of the major vessels. It is beyond the scope of this text to name every vessel in the body. However, we will attempt to discuss the major pathways for blood and acquaint you with the major named arteries and veins in the body. Also, please keep in mind that individual variations in circulation patterns are not uncommon.
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Pulmonary Circulation
Recall that blood returning from the systemic circuit enters the right atrium (Figure 20.23) via the superior and inferior venae cavae and the coronary sinus, which drains the blood supply of the heart muscle. These vessels will be described more fully later in this section. This blood is relatively low in oxygen and relatively high in carbon dioxide, since much of the oxygen has been extracted for use by the tissues and the waste gas carbon dioxide was picked up to be transported to the lungs for elimination. From the right atrium, blood moves into the right ventricle, which pumps it to the lungs for gas exchange. This system of vessels is referred to as the pulmonary circuit.
The single vessel exiting the right ventricle is the pulmonary trunk. At the base of the pulmonary trunk is the pulmonary semilunar valve, which prevents backflow of blood into the right ventricle during ventricular diastole. As the pulmonary trunk reaches the superior surface of the heart, it curves posteriorly and rapidly bifurcates (divides) into two branches, a left and a right pulmonary artery. To prevent confusion between these vessels, it is important to refer to the vessel exiting the heart as the pulmonary trunk, rather than also calling it a pulmonary artery. The pulmonary arteries in turn branch many times within the lung, forming a series of smaller arteries and arterioles that eventually lead to the pulmonary capillaries. The pulmonary capillaries surround lung structures known as alveoli that are the sites of oxygen and carbon dioxide exchange.
Once gas exchange is completed, oxygenated blood flows from the pulmonary capillaries into a series of pulmonary venules that eventually lead to a series of larger pulmonary veins. Four pulmonary veins, two on the left and two on the right, return blood to the left atrium. At this point, the pulmonary circuit is complete. Table 20.4 defines the major arteries and veins of the pulmonary circuit discussed in the text.
Figure 20.23 Pulmonary Circuit Blood exiting from the right ventricle flows into the pulmonary trunk, which bifurcates into the two pulmonary arteries. These vessels branch to supply blood to the pulmonary capillaries, where gas exchange occurs within the lung alveoli. Blood returns via the pulmonary veins to the left atrium.
Pulmonary Arteries and Veins
| Vessel | Description |
|---|---|
| Pulmonary trunk | Single large vessel exiting the right ventricle that divides to form the right and left pulmonary arteries |
| Pulmonary arteries | Left and right vessels that form from the pulmonary trunk and lead to smaller arterioles and eventually to the pulmonary capillaries |
| Pulmonary veins | Two sets of paired vessels—one pair on each side—that are formed from the small venules, leading away from the pulmonary capillaries to flow into the left atrium |
Table 20.4
Overview of Systemic Arteries
Blood relatively high in oxygen concentration is returned from the pulmonary circuit to the left atrium via the four pulmonary veins. From the left atrium, blood moves into the left ventricle, which pumps blood into the aorta. The aorta and its branches—the systemic arteries—send blood to virtually every organ of the body (Figure 20.24).
Figure 20.24 Systemic Arteries The major systemic arteries shown here deliver oxygenated blood throughout the body.
The Aorta
The aorta is the largest artery in the body (Figure 20.25). It arises from the left ventricle and eventually descends to the abdominal region, where it bifurcates at the level of the fourth lumbar vertebra into the two common iliac arteries. The aorta consists of the ascending aorta, the aortic arch, and the descending aorta, which passes through the diaphragm and a landmark that divides into the superior thoracic and inferior abdominal components. Arteries originating from the aorta ultimately distribute blood to virtually all tissues of the body. At the base of the aorta is the aortic semilunar valve that prevents backflow of blood into the left ventricle while the heart is relaxing. After exiting the heart, the ascending aorta moves in a superior direction for approximately 5 cm and ends at the sternal angle. Following this ascent, it reverses direction, forming a graceful arc to the left, called the aortic arch. The aortic arch descends toward the inferior portions of the body and ends at the level of the intervertebral disk between the fourth and fifth thoracic vertebrae. Beyond this point, the descending aorta continues close to the bodies of the vertebrae and passes through an opening in the diaphragm known as the aortic hiatus. Superior to the diaphragm, the aorta is called the thoracic aorta, and inferior to the diaphragm, it is called the abdominal aorta. The abdominal aorta terminates when it bifurcates into the two common iliac arteries at the level of the fourth lumbar vertebra. See Figure 20.25 for an illustration of the ascending aorta, the aortic arch, and the initial segment of the descending aorta plus major branches; Table 20.5 summarizes the structures of the aorta.
Figure 20.25 Aorta The aorta has distinct regions, including the ascending aorta, aortic arch, and the descending aorta, which includes the thoracic and abdominal regions.
Components of the Aorta
| Vessel | Description |
|---|---|
| Aorta | Largest artery in the body, originating from the left ventricle and descending to the abdominal region, where it bifurcates into the common iliac arteries at the level of the fourth lumbar vertebra; arteries originating from the aorta distribute blood to virtually all tissues of the body |
| Ascending aorta | Initial portion of the aorta, rising superiorly from the left ventricle for a distance of approximately 5 cm |
| Aortic arch | Graceful arc to the left that connects the ascending aorta to the descending aorta; ends at the intervertebral disk between the fourth and fifth thoracic vertebrae |
| Descending aorta | Portion of the aorta that continues inferiorly past the end of the aortic arch; subdivided into the thoracic aorta and the abdominal aorta |
| Thoracic aorta | Portion of the descending aorta superior to the aortic hiatus |
| Abdominal aorta | Portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries |
Table 20.5
Coronary Circulation
The first vessels that branch from the ascending aorta are the paired coronary arteries (see Figure 20.25), which arise from two of the three sinuses in the ascending aorta just superior to the aortic semilunar valve. These sinuses contain the aortic baroreceptors and chemoreceptors critical to maintain cardiac function. The left coronary artery arises from the left posterior aortic sinus. The right coronary artery arises from the anterior aortic sinus. Normally, the right posterior aortic sinus does not give rise to a vessel.
The coronary arteries encircle the heart, forming a ring-like structure that divides into the next level of branches that supplies blood to the heart tissues. (Seek additional content for more detail on cardiac circulation.)
Aortic Arch Branches
There are three major branches of the aortic arch: the brachiocephalic artery, the left common carotid artery, and the left subclavian (literally “under the clavicle”) artery. As you would expect based upon proximity to the heart, each of these vessels is classified as an elastic artery.
The brachiocephalic artery is located only on the right side of the body; there is no corresponding artery on the left. The brachiocephalic artery branches into the right subclavian artery and the right common carotid artery. The left subclavian and left common carotid arteries arise independently from the aortic arch but otherwise follow a similar pattern and distribution to the corresponding arteries on the right side (see Figure 20.23).
Each subclavian artery supplies blood to the arms, chest, shoulders, back, and central nervous system. It then gives rise to three major branches: the internal thoracic artery, the vertebral artery, and the thyrocervical artery. The internal thoracic artery, or mammary artery, supplies blood to the thymus, the pericardium of the heart, and the anterior chest wall. The vertebral arterypasses through the vertebral foramen in the cervical vertebrae and then through the foramen magnum into the cranial cavity to supply blood to the brain and spinal cord. The paired vertebral arteries join together to form the large basilar artery at the base of the medulla oblongata. This is an example of an anastomosis. The subclavian artery also gives rise to the thyrocervical artery that provides blood to the thyroid, the cervical region of the neck, and the upper back and shoulder.
The common carotid artery divides into internal and external carotid arteries. The right common carotid artery arises from the brachiocephalic artery and the left common carotid artery arises directly from the aortic arch. The external carotid artery supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx. These branches include the lingual, facial, occipital, maxillary, and superficial temporal arteries. The internal carotid artery initially forms an expansion known as the carotid sinus, containing the carotid baroreceptors and chemoreceptors. Like their counterparts in the aortic sinuses, the information provided by these receptors is critical to maintaining cardiovascular homeostasis (see Figure 20.23).
The internal carotid arteries along with the vertebral arteries are the two primary suppliers of blood to the human brain. Given the central role and vital importance of the brain to life, it is critical that blood supply to this organ remains uninterrupted. Recall that blood flow to the brain is remarkably constant, with approximately 20 percent of blood flow directed to this organ at any given time. When blood flow is interrupted, even for just a few seconds, a transient ischemic attack (TIA), or mini-stroke, may occur, resulting in loss of consciousness or temporary loss of neurological function. In some cases, the damage may be permanent. Loss of blood flow for longer periods, typically between 3 and 4 minutes, will likely produce irreversible brain damage or a stroke, also called a cerebrovascular accident (CVA). The locations of the arteries in the brain not only provide blood flow to the brain tissue but also prevent interruption in the flow of blood. Both the carotid and vertebral arteries branch once they enter the cranial cavity, and some of these branches form a structure known as the arterial circle (or circle of Willis), an anastomosis that is remarkably like a traffic circle that sends off branches (in this case, arterial branches to the brain). As a rule, branches to the anterior portion of the cerebrum are normally fed by the internal carotid arteries; the remainder of the brain receives blood flow from branches associated with the vertebral arteries.
The internal carotid artery continues through the carotid canal of the temporal bone and enters the base of the brain through the carotid foramen where it gives rise to several branches (Figure 20.26 and Figure 20.27). One of these branches is the anterior cerebral artery that supplies blood to the frontal lobe of the cerebrum. Another branch, the middle cerebral artery, supplies blood to the temporal and parietal lobes, which are the most common sites of CVAs. The ophthalmic artery, the third major branch, provides blood to the eyes.
The right and left anterior cerebral arteries join together to form an anastomosis called the anterior communicating artery. The initial segments of the anterior cerebral arteries and the anterior communicating artery form the anterior portion of the arterial circle. The posterior portion of the arterial circle is formed by a left and a right posterior communicating artery that branches from the posterior cerebral artery, which arises from the basilar artery. It provides blood to the posterior portion of the cerebrum and brain stem. The basilar artery is an anastomosis that begins at the junction of the two vertebral arteries and sends branches to the cerebellum and brain stem. It flows into the posterior cerebral arteries. Table 20.6 summarizes the aortic arch branches, including the major branches supplying the brain.
Figure 20.26 Arteries Supplying the Head and Neck The common carotid artery gives rise to the external and internal carotid arteries. The external carotid artery remains superficial and gives rise to many arteries of the head. The internal carotid artery first forms the carotid sinus and then reaches the brain via the carotid canal and carotid foramen, emerging into the cranium via the foramen lacerum. The vertebral artery branches from the subclavian artery and passes through the transverse foramen in the cervical vertebrae, entering the base of the skull at the vertebral foramen. The subclavian artery continues toward the arm as the axillary artery.
Figure 20.27 Arteries Serving the Brain This inferior view shows the network of arteries serving the brain. The structure is referred to as the arterial circle or circle of Willis.
Aortic Arch Branches and Brain Circulation
| Vessel | Description |
|---|---|
| Brachiocephalic artery | Single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of the thoracic region |
| Subclavian artery | The right subclavian artery arises from the brachiocephalic artery while the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system |
| Internal thoracic artery | Also called the mammary artery; arises from the subclavian artery; supplies blood to the thymus, pericardium of the heart, and anterior chest wall |
| Vertebral artery | Arises from the subclavian artery and passes through the vertebral foramen through the foramen magnum to the brain; joins with the internal carotid artery to form the arterial circle; supplies blood to the brain and spinal cord |
| Thyrocervical artery | Arises from the subclavian artery; supplies blood to the thyroid, the cervical region, the upper back, and shoulder |
| Common carotid artery | The right common carotid artery arises from the brachiocephalic artery and the left common carotid artery arises from the aortic arch; each gives rise to the external and internal carotid arteries; supplies the respective sides of the head and neck |
| External carotid artery | Arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx |
| Internal carotid artery | Arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with the branches of the vertebral artery, forming the arterial circle; supplies blood to the brain |
| Arterial circle or circle of Willis | An anastomosis located at the base of the brain that ensures continual blood supply; formed from the branches of the internal carotid and vertebral arteries; supplies blood to the brain |
| Anterior cerebral artery | Arises from the internal carotid artery; supplies blood to the frontal lobe of the cerebrum |
| Middle cerebral artery | Another branch of the internal carotid artery; supplies blood to the temporal and parietal lobes of the cerebrum |
| Ophthalmic artery | Branch of the internal carotid artery; supplies blood to the eyes |
| Anterior communicating artery | An anastomosis of the right and left internal carotid arteries; supplies blood to the brain |
| Posterior communicating artery | Branches of the posterior cerebral artery that form part of the posterior portion of the arterial circle; supplies blood to the brain |
| Posterior cerebral artery | Branch of the basilar artery that forms a portion of the posterior segment of the arterial circle of Willis; supplies blood to the posterior portion of the cerebrum and brain stem |
| Basilar artery | Formed from the fusion of the two vertebral arteries; sends branches to the cerebellum, brain stem, and the posterior cerebral arteries; the main blood supply to the brain stem |
Table 20.6
Thoracic Aorta and Major Branches
The thoracic aorta begins at the level of vertebra T5 and continues through to the diaphragm at the level of T12, initially traveling within the mediastinum to the left of the vertebral column. As it passes through the thoracic region, the thoracic aorta gives rise to several branches, which are collectively referred to as visceral branches and parietal branches (Figure 20.28). Those branches that supply blood primarily to visceral organs are known as the visceral branches and include the bronchial arteries, pericardial arteries, esophageal arteries, and the mediastinal arteries, each named after the tissues it supplies. Each bronchial artery (typically two on the left and one on the right) supplies systemic blood to the lungs and visceral pleura, in addition to the blood pumped to the lungs for oxygenation via the pulmonary circuit. The bronchial arteries follow the same path as the respiratory branches, beginning with the bronchi and ending with the bronchioles. There is considerable, but not total, intermingling of the systemic and pulmonary blood at anastomoses in the smaller branches of the lungs. This may sound incongruous—that is, the mixing of systemic arterial blood high in oxygen with the pulmonary arterial blood lower in oxygen—but the systemic vessels also deliver nutrients to the lung tissue just as they do elsewhere in the body. The mixed blood drains into typical pulmonary veins, whereas the bronchial artery branches remain separate and drain into bronchial veins described later. Each pericardial artery supplies blood to the pericardium, the esophageal artery provides blood to the esophagus, and the mediastinal artery provides blood to the mediastinum. The remaining thoracic aorta branches are collectively referred to as parietal branches or somatic branches, and include the intercostal and superior phrenic arteries. Each intercostal artery provides blood to the muscles of the thoracic cavity and vertebral column. The superior phrenic artery provides blood to the superior surface of the diaphragm. Table 20.7 lists the arteries of the thoracic region.
Figure 20.28 Arteries of the Thoracic and Abdominal Regions The thoracic aorta gives rise to the arteries of the visceral and parietal branches.
Arteries of the Thoracic Region
| Vessel | Description |
|---|---|
| Visceral branches | A group of arterial branches of the thoracic aorta; supplies blood to the viscera (i.e., organs) of the thorax |
| Bronchial artery | Systemic branch from the aorta that provides oxygenated blood to the lungs; this blood supply is in addition to the pulmonary circuit that brings blood for oxygenation |
| Pericardial artery | Branch of the thoracic aorta; supplies blood to the pericardium |
| Esophageal artery | Branch of the thoracic aorta; supplies blood to the esophagus |
| Mediastinal artery | Branch of the thoracic aorta; supplies blood to the mediastinum |
| Parietal branches | Also called somatic branches, a group of arterial branches of the thoracic aorta; include those that supply blood to the thoracic wall, vertebral column, and the superior surface of the diaphragm |
| Intercostal artery | Branch of the thoracic aorta; supplies blood to the muscles of the thoracic cavity and vertebral column |
| Superior phrenic artery | Branch of the thoracic aorta; supplies blood to the superior surface of the diaphragm |
Table 20.7
Abdominal Aorta and Major Branches
After crossing through the diaphragm at the aortic hiatus, the thoracic aorta is called the abdominal aorta (see Figure 20.28). This vessel remains to the left of the vertebral column and is embedded in adipose tissue behind the peritoneal cavity. It formally ends at approximately the level of vertebra L4, where it bifurcates to form the common iliac arteries. Before this division, the abdominal aorta gives rise to several important branches. A single celiac trunk (artery) emerges and divides into the left gastric artery to supply blood to the stomach and esophagus, the splenic artery to supply blood to the spleen, and the common hepatic artery, which in turn gives rise to the hepatic artery proper to supply blood to the liver, the right gastric artery to supply blood to the stomach, the cystic artery to supply blood to the gall bladder, and several branches, one to supply blood to the duodenum and another to supply blood to the pancreas. Two additional single vessels arise from the abdominal aorta. These are the superior and inferior mesenteric arteries. The superior mesenteric artery arises approximately 2.5 cm after the celiac trunk and branches into several major vessels that supply blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine. The inferior mesenteric artery supplies blood to the distal segment of the large intestine, including the rectum. It arises approximately 5 cm superior to the common iliac arteries.
In addition to these single branches, the abdominal aorta gives rise to several significant paired arteries along the way. These include the inferior phrenic arteries, the adrenal arteries, the renal arteries, the gonadal arteries, and the lumbar arteries. Each inferior phrenic artery is a counterpart of a superior phrenic artery and supplies blood to the inferior surface of the diaphragm. The adrenal artery supplies blood to the adrenal (suprarenal) glands and arises near the superior mesenteric artery. Each renal arterybranches approximately 2.5 cm inferior to the superior mesenteric arteries and supplies a kidney. The right renal artery is longer than the left since the aorta lies to the left of the vertebral column and the vessel must travel a greater distance to reach its target. Renal arteries branch repeatedly to supply blood to the kidneys. Each gonadal artery supplies blood to the gonads, or reproductive organs, and is also described as either an ovarian artery or a testicular artery (internal spermatic), depending upon the sex of the individual. An ovarian artery supplies blood to an ovary, uterine (Fallopian) tube, and the uterus, and is located within the suspensory ligament of the uterus. It is considerably shorter than a testicular artery, which ultimately travels outside the body cavity to the testes, forming one component of the spermatic cord. The gonadal arteries arise inferior to the renal arteries and are generally retroperitoneal. The ovarian artery continues to the uterus where it forms an anastomosis with the uterine artery that supplies blood to the uterus. Both the uterine arteries and vaginal arteries, which distribute blood to the vagina, are branches of the internal iliac artery. The four paired lumbar arteries are the counterparts of the intercostal arteries and supply blood to the lumbar region, the abdominal wall, and the spinal cord. In some instances, a fifth pair of lumbar arteries emerges from the median sacral artery.
The aorta divides at approximately the level of vertebra L4 into a left and a right common iliac artery but continues as a small vessel, the median sacral artery, into the sacrum. The common iliac arteries provide blood to the pelvic region and ultimately to the lower limbs. They split into external and internal iliac arteries approximately at the level of the lumbar-sacral articulation. Each internal iliac artery sends branches to the urinary bladder, the walls of the pelvis, the external genitalia, and the medial portion of the femoral region. In females, they also provide blood to the uterus and vagina. The much larger external iliac artery supplies blood to each of the lower limbs. Figure 20.29 shows the distribution of the major branches of the aorta into the thoracic and abdominal regions. Figure 20.30 shows the distribution of the major branches of the common iliac arteries. Table 20.8 summarizes the major branches of the abdominal aorta.
Figure 20.29 Major Branches of the Aorta The flow chart summarizes the distribution of the major branches of the aorta into the thoracic and abdominal regions.
Figure 20.30 Major Branches of the Iliac Arteries The flow chart summarizes the distribution of the major branches of the common iliac arteries into the pelvis and lower limbs. The left side follows a similar pattern to the right.
Vessels of the Abdominal Aorta
| Vessel | Description |
|---|---|
| Celiac trunk | Also called the celiac artery; a major branch of the abdominal aorta; gives rise to the left gastric artery, the splenic artery, and the common hepatic artery that forms the hepatic artery to the liver, the right gastric artery to the stomach, and the cystic artery to the gall bladder |
| Left gastric artery | Branch of the celiac trunk; supplies blood to the stomach |
| Splenic artery | Branch of the celiac trunk; supplies blood to the spleen |
| Common hepatic artery | Branch of the celiac trunk that forms the hepatic artery, the right gastric artery, and the cystic artery |
| Hepatic artery proper | Branch of the common hepatic artery; supplies systemic blood to the liver |
| Right gastric artery | Branch of the common hepatic artery; supplies blood to the stomach |
| Cystic artery | Branch of the common hepatic artery; supplies blood to the gall bladder |
| Superior mesenteric artery | Branch of the abdominal aorta; supplies blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine |
| Inferior mesenteric artery | Branch of the abdominal aorta; supplies blood to the distal segment of the large intestine and rectum |
| Inferior phrenic arteries | Branches of the abdominal aorta; supply blood to the inferior surface of the diaphragm |
| Adrenal artery | Branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands |
| Renal artery | Branch of the abdominal aorta; supplies each kidney |
| Gonadal artery | Branch of the abdominal aorta; supplies blood to the gonads or reproductive organs; also described as ovarian arteries or testicular arteries, depending upon the sex of the individual |
| Ovarian artery | Branch of the abdominal aorta; supplies blood to ovary, uterine (Fallopian) tube, and uterus |
| Testicular artery | Branch of the abdominal aorta; ultimately travels outside the body cavity to the testes and forms one component of the spermatic cord |
| Lumbar arteries | Branches of the abdominal aorta; supply blood to the lumbar region, the abdominal wall, and spinal cord |
| Common iliac artery | Branch of the aorta that leads to the internal and external iliac arteries |
| Median sacral artery | Continuation of the aorta into the sacrum |
| Internal iliac artery | Branch from the common iliac arteries; supplies blood to the urinary bladder, walls of the pelvis, external genitalia, and the medial portion of the femoral region; in females, also provides blood to the uterus and vagina |
| External iliac artery | Branch of the common iliac artery that leaves the body cavity and becomes a femoral artery; supplies blood to the lower limbs |
Table 20.8
Arteries Serving the Upper Limbs
As the subclavian artery exits the thorax into the axillary region, it is renamed the axillary artery. Although it does branch and supply blood to the region near the head of the humerus (via the humeral circumflex arteries), the majority of the vessel continues into the upper arm, or brachium, and becomes the brachial artery (Figure 20.31). The brachial artery supplies blood to much of the brachial region and divides at the elbow into several smaller branches, including the deep brachial arteries, which provide blood to the posterior surface of the arm, and the ulnar collateral arteries, which supply blood to the region of the elbow. As the brachial artery approaches the coronoid fossa, it bifurcates into the radial and ulnar arteries, which continue into the forearm, or antebrachium. The radial artery and ulnar artery parallel their namesake bones, giving off smaller branches until they reach the wrist, or carpal region. At this level, they fuse to form the superficial and deep palmar arches that supply blood to the hand, as well as the digital arteries that supply blood to the digits. Figure 20.32 shows the distribution of systemic arteries from the heart into the upper limb. Table 20.9 summarizes the arteries serving the upper limbs.
Figure 20.31 Major Arteries Serving the Thorax and Upper Limb The arteries that supply blood to the arms and hands are extensions of the subclavian arteries.
Figure 20.32 Major Arteries of the Upper Limb The flow chart summarizes the distribution of the major arteries from the heart into the upper limb.
Arteries Serving the Upper Limbs
| Vessel | Description |
|---|---|
| Axillary artery | Continuation of the subclavian artery as it penetrates the body wall and enters the axillary region; supplies blood to the region near the head of the humerus (humeral circumflex arteries); the majority of the vessel continues into the brachium and becomes the brachial artery |
| Brachial artery | Continuation of the axillary artery in the brachium; supplies blood to much of the brachial region; gives off several smaller branches that provide blood to the posterior surface of the arm in the region of the elbow; bifurcates into the radial and ulnar arteries at the coronoid fossa |
| Radial artery | Formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region |
| Ulnar artery | Formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the carpal region where it fuses with the radial artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region |
| Palmar arches (superficial and deep) | Formed from anastomosis of the radial and ulnar arteries; supply blood to the hand and digital arteries |
| Digital arteries | Formed from the superficial and deep palmar arches; supply blood to the digits |
Table 20.9
Arteries Serving the Lower Limbs
The external iliac artery exits the body cavity and enters the femoral region of the lower leg (Figure 20.33). As it passes through the body wall, it is renamed the femoral artery. It gives off several smaller branches as well as the lateral deep femoral artery that in turn gives rise to a lateral circumflex artery. These arteries supply blood to the deep muscles of the thigh as well as ventral and lateral regions of the integument. The femoral artery also gives rise to the genicular artery, which provides blood to the region of the knee. As the femoral artery passes posterior to the knee near the popliteal fossa, it is called the popliteal artery. The popliteal artery branches into the anterior and posterior tibial arteries.
The anterior tibial artery is located between the tibia and fibula, and supplies blood to the muscles and integument of the anterior tibial region. Upon reaching the tarsal region, it becomes the dorsalis pedis artery, which branches repeatedly and provides blood to the tarsal and dorsal regions of the foot. The posterior tibial artery provides blood to the muscles and integument on the posterior surface of the tibial region. The fibular or peroneal artery branches from the posterior tibial artery. It bifurcates and becomes the medial plantar artery and lateral plantar artery, providing blood to the plantar surfaces. There is an anastomosis with the dorsalis pedis artery, and the medial and lateral plantar arteries form two arches called the dorsal arch (also called the arcuate arch) and the plantar arch, which provide blood to the remainder of the foot and toes. Figure 20.34 shows the distribution of the major systemic arteries in the lower limb. Table 20.10 summarizes the major systemic arteries discussed in the text.
Figure 20.33 Major Arteries Serving the Lower Limb Major arteries serving the lower limb are shown in anterior and posterior views.
Figure 20.34 Systemic Arteries of the Lower Limb The flow chart summarizes the distribution of the systemic arteries from the external iliac artery into the lower limb.
Arteries Serving the Lower Limbs
| Vessel | Description |
|---|---|
| Femoral artery | Continuation of the external iliac artery after it passes through the body cavity; divides into several smaller branches, the lateral deep femoral artery, and the genicular artery; becomes the popliteal artery as it passes posterior to the knee |
| Deep femoral artery | Branch of the femoral artery; gives rise to the lateral circumflex arteries |
| Lateral circumflex artery | Branch of the deep femoral artery; supplies blood to the deep muscles of the thigh and the ventral and lateral regions of the integument |
| Genicular artery | Branch of the femoral artery; supplies blood to the region of the knee |
| Popliteal artery | Continuation of the femoral artery posterior to the knee; branches into the anterior and posterior tibial arteries |
| Anterior tibial artery | Branches from the popliteal artery; supplies blood to the anterior tibial region; becomes the dorsalis pedis artery |
| Dorsalis pedis artery | Forms from the anterior tibial artery; branches repeatedly to supply blood to the tarsal and dorsal regions of the foot |
| Posterior tibial artery | Branches from the popliteal artery and gives rise to the fibular or peroneal artery; supplies blood to the posterior tibial region |
| Medial plantar artery | Arises from the bifurcation of the posterior tibial arteries; supplies blood to the medial plantar surfaces of the foot |
| Lateral plantar artery | Arises from the bifurcation of the posterior tibial arteries; supplies blood to the lateral plantar surfaces of the foot |
| Dorsal or arcuate arch | Formed from the anastomosis of the dorsalis pedis artery and the medial and plantar arteries; branches supply the distal portions of the foot and digits |
| Plantar arch | Formed from the anastomosis of the dorsalis pedis artery and the medial and plantar arteries; branches supply the distal portions of the foot and digits |
Table 20.10
Overview of Systemic Veins
Systemic veins return blood to the right atrium. Since the blood has already passed through the systemic capillaries, it will be relatively low in oxygen concentration. In many cases, there will be veins draining organs and regions of the body with the same name as the arteries that supplied these regions and the two often parallel one another. This is often described as a “complementary” pattern. However, there is a great deal more variability in the venous circulation than normally occurs in the arteries. For the sake of brevity and clarity, this text will discuss only the most commonly encountered patterns. However, keep this variation in mind when you move from the classroom to clinical practice.
In both the neck and limb regions, there are often both superficial and deeper levels of veins. The deeper veins generally correspond to the complementary arteries. The superficial veins do not normally have direct arterial counterparts, but in addition to returning blood, they also make contributions to the maintenance of body temperature. When the ambient temperature is warm, more blood is diverted to the superficial veins where heat can be more easily dissipated to the environment. In colder weather, there is more constriction of the superficial veins and blood is diverted deeper where the body can retain more of the heat.
The “Voyage of Discovery” analogy and stick drawings mentioned earlier remain valid techniques for the study of systemic veins, but veins present a more difficult challenge because there are numerous anastomoses and multiple branches. It is like following a river with many tributaries and channels, several of which interconnect. Tracing blood flow through arteries follows the current in the direction of blood flow, so that we move from the heart through the large arteries and into the smaller arteries to the capillaries. From the capillaries, we move into the smallest veins and follow the direction of blood flow into larger veins and back to the heart. Figure 20.35 outlines the path of the major systemic veins.
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Figure 20.35 Major Systemic Veins of the Body The major systemic veins of the body are shown here in an anterior view.
The right atrium receives all of the systemic venous return. Most of the blood flows into either the superior vena cava or inferior vena cava. If you draw an imaginary line at the level of the diaphragm, systemic venous circulation from above that line will generally flow into the superior vena cava; this includes blood from the head, neck, chest, shoulders, and upper limbs. The exception to this is that most venous blood flow from the coronary veins flows directly into the coronary sinus and from there directly into the right atrium. Beneath the diaphragm, systemic venous flow enters the inferior vena cava, that is, blood from the abdominal and pelvic regions and the lower limbs.
The Superior Vena Cava
The superior vena cava drains most of the body superior to the diaphragm (Figure 20.36). On both the left and right sides, the subclavian vein forms when the axillary vein passes through the body wall from the axillary region. It fuses with the external and internal jugular veins from the head and neck to form the brachiocephalic vein. Each vertebral vein also flows into the brachiocephalic vein close to this fusion. These veins arise from the base of the brain and the cervical region of the spinal cord, and flow largely through the intervertebral foramina in the cervical vertebrae. They are the counterparts of the vertebral arteries. Each internal thoracic vein, also known as an internal mammary vein, drains the anterior surface of the chest wall and flows into the brachiocephalic vein.
The remainder of the blood supply from the thorax drains into the azygos vein. Each intercostal vein drains muscles of the thoracic wall, each esophageal vein delivers blood from the inferior portions of the esophagus, each bronchial vein drains the systemic circulation from the lungs, and several smaller veins drain the mediastinal region. Bronchial veins carry approximately 13 percent of the blood that flows into the bronchial arteries; the remainder intermingles with the pulmonary circulation and returns to the heart via the pulmonary veins. These veins flow into the azygos vein, and with the smaller hemiazygos vein (hemi- = “half”) on the left of the vertebral column, drain blood from the thoracic region. The hemiazygos vein does not drain directly into the superior vena cava but enters the brachiocephalic vein via the superior intercostal vein.
The azygos vein passes through the diaphragm from the thoracic cavity on the right side of the vertebral column and begins in the lumbar region of the thoracic cavity. It flows into the superior vena cava at approximately the level of T2, making a significant contribution to the flow of blood. It combines with the two large left and right brachiocephalic veins to form the superior vena cava.
Table 20.11 summarizes the veins of the thoracic region that flow into the superior vena cava.
Figure 20.36 Veins of the Thoracic and Abdominal Regions Veins of the thoracic and abdominal regions drain blood from the area above the diaphragm, returning it to the right atrium via the superior vena cava.
Veins of the Thoracic Region
| Vessel | Description |
|---|---|
| Superior vena cava | Large systemic vein; drains blood from most areas superior to the diaphragm; empties into the right atrium |
| Subclavian vein | Located deep in the thoracic cavity; formed by the axillary vein as it enters the thoracic cavity from the axillary region; drains the axillary and smaller local veins near the scapular region and leads to the brachiocephalic vein |
| Brachiocephalic veins | Pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins flow into it; drain the upper thoracic region and lead to the superior vena cava |
| Vertebral vein | Arises from the base of the brain and the cervical region of the spinal cord; passes through the intervertebral foramina in the cervical vertebrae; drains smaller veins from the cranium, spinal cord, and vertebrae, and leads to the brachiocephalic vein; counterpart of the vertebral artery |
| Internal thoracic veins | Also called internal mammary veins; drain the anterior surface of the chest wall and lead to the brachiocephalic vein |
| Intercostal vein | Drains the muscles of the thoracic wall and leads to the azygos vein |
| Esophageal vein | Drains the inferior portions of the esophagus and leads to the azygos vein |
| Bronchial vein | Drains the systemic circulation from the lungs and leads to the azygos vein |
| Azygos vein | Originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, esophageal veins, bronchial veins, and other veins draining the mediastinal region, and leads to the superior vena cava |
| Hemiazygos vein | Smaller vein complementary to the azygos vein; drains the esophageal veins from the esophagus and the left intercostal veins, and leads to the brachiocephalic vein via the superior intercostal vein |
Table 20.11
Veins of the Head and Neck
Blood from the brain and the superficial facial vein flow into each internal jugular vein (Figure 20.37). Blood from the more superficial portions of the head, scalp, and cranial regions, including the temporal vein and maxillary vein, flow into each external jugular vein. Although the external and internal jugular veins are separate vessels, there are anastomoses between them close to the thoracic region. Blood from the external jugular vein empties into the subclavian vein. Table 20.12 summarizes the major veins of the head and neck.
Major Veins of the Head and Neck
| Vessel | Description |
|---|---|
| Internal jugular vein | Parallel to the common carotid artery, which is more or less its counterpart, and passes through the jugular foramen and canal; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein |
| Temporal vein | Drains blood from the temporal region and flows into the external jugular vein |
| Maxillary vein | Drains blood from the maxillary region and flows into the external jugular vein |
| External jugular vein | Drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein |
Table 20.12
Venous Drainage of the Brain
Circulation to the brain is both critical and complex (see Figure 20.37). Many smaller veins of the brain stem and the superficial veins of the cerebrum lead to larger vessels referred to as intracranial sinuses. These include the superior and inferior sagittal sinuses, straight sinus, cavernous sinuses, left and right sinuses, the petrosal sinuses, and the occipital sinuses. Ultimately, sinuses will lead back to either the inferior jugular vein or vertebral vein.
Most of the veins on the superior surface of the cerebrum flow into the largest of the sinuses, the superior sagittal sinus. It is located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri and, at first glance in images or models, can be mistaken for the subarachnoid space. Most reabsorption of cerebrospinal fluid occurs via the chorionic villi (arachnoid granulations) into the superior sagittal sinus. Blood from most of the smaller vessels originating from the inferior cerebral veins flows into the great cerebral vein and into the straight sinus. Other cerebral veins and those from the eye socket flow into the cavernous sinus, which flows into the petrosal sinus and then into the internal jugular vein. The occipital sinus, sagittal sinus, and straight sinuses all flow into the left and right transverse sinuses near the lambdoid suture. The transverse sinuses in turn flow into the sigmoid sinuses that pass through the jugular foramen and into the internal jugular vein. The internal jugular vein flows parallel to the common carotid artery and is more or less its counterpart. It empties into the brachiocephalic vein. The veins draining the cervical vertebrae and the posterior surface of the skull, including some blood from the occipital sinus, flow into the vertebral veins. These parallel the vertebral arteries and travel through the transverse foramina of the cervical vertebrae. The vertebral veins also flow into the brachiocephalic veins. Table 20.13 summarizes the major veins of the brain.
Figure 20.37 Veins of the Head and Neck This left lateral view shows the veins of the head and neck, including the intercranial sinuses.
Major Veins of the Brain
| Vessel | Description |
|---|---|
| Superior sagittal sinus | Enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein |
| Great cerebral vein | Receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus |
| Straight sinus | Enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and leads to the left or right transverse sinus |
| Cavernous sinus | Enlarged vein that receives blood from most of the other cerebral veins and the eye socket, and leads to the petrosal sinus |
| Petrosal sinus | Enlarged vein that receives blood from the cavernous sinus and leads into the internal jugular veins |
| Occipital sinus | Enlarged vein that drains the occipital region near the falx cerebelli and leads to the left and right transverse sinuses, and also the vertebral veins |
| Transverse sinuses | Pair of enlarged veins near the lambdoid suture that drains the occipital, sagittal, and straight sinuses, and leads to the sigmoid sinuses |
| Sigmoid sinuses | Enlarged vein that receives blood from the transverse sinuses and leads through the jugular foramen to the internal jugular vein |
Table 20.13
Veins Draining the Upper Limbs
The digital veins in the fingers come together in the hand to form the palmar venous arches (Figure 20.38). From here, the veins come together to form the radial vein, the ulnar vein, and the median antebrachial vein. The radial vein and the ulnar vein parallel the bones of the forearm and join together at the antebrachium to form the brachial vein, a deep vein that flows into the axillary vein in the brachium.
The median antebrachial vein parallels the ulnar vein, is more medial in location, and joins the basilic vein in the forearm. As the basilic vein reaches the antecubital region, it gives off a branch called the median cubital vein that crosses at an angle to join the cephalic vein. The median cubital vein is the most common site for drawing venous blood in humans. The basilic vein continues through the arm medially and superficially to the axillary vein.
The cephalic vein begins in the antebrachium and drains blood from the superficial surface of the arm into the axillary vein. It is extremely superficial and easily seen along the surface of the biceps brachii muscle in individuals with good muscle tone and in those without excessive subcutaneous adipose tissue in the arms.
The subscapular vein drains blood from the subscapular region and joins the cephalic vein to form the axillary vein. As it passes through the body wall and enters the thorax, the axillary vein becomes the subclavian vein.
Many of the larger veins of the thoracic and abdominal region and upper limb are further represented in the flow chart in Figure 20.39. Table 20.14 summarizes the veins of the upper limbs.
Figure 20.38 Veins of the Upper Limb This anterior view shows the veins that drain the upper limb.
Figure 20.39 Veins Flowing into the Superior Vena Cava The flow chart summarizes the distribution of the veins flowing into the superior vena cava.
Veins of the Upper Limbs
| Vessel | Description |
|---|---|
| Digital veins | Drain the digits and lead to the palmar arches of the hand and dorsal venous arch of the foot |
| Palmar venous arches | Drain the hand and digits, and lead to the radial vein, ulnar veins, and the median antebrachial vein |
| Radial vein | Vein that parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein |
| Ulnar vein | Vein that parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein |
| Brachial vein | Deeper vein of the arm that forms from the radial and ulnar veins in the lower arm; leads to the axillary vein |
| Median antebrachial vein | Vein that parallels the ulnar vein but is more medial in location; intertwines with the palmar venous arches; leads to the basilic vein |
| Basilic vein | Superficial vein of the arm that arises from the median antebrachial vein, intersects with the median cubital vein, parallels the ulnar vein, and continues into the upper arm; along with the brachial vein, it leads to the axillary vein |
| Median cubital vein | Superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a v; a frequent site from which to draw blood |
| Cephalic vein | Superficial vessel in the upper arm; leads to the axillary vein |
| Subscapular vein | Drains blood from the subscapular region and leads to the axillary vein |
| Axillary vein | The major vein in the axillary region; drains the upper limb and becomes the subclavian vein |
Table 20.14
The Inferior Vena Cava
Other than the small amount of blood drained by the azygos and hemiazygos veins, most of the blood inferior to the diaphragm drains into the inferior vena cava before it is returned to the heart (see Figure 20.36). Lying just beneath the parietal peritoneum in the abdominal cavity, the inferior vena cava parallels the abdominal aorta, where it can receive blood from abdominal veins. The lumbar portions of the abdominal wall and spinal cord are drained by a series of lumbar veins, usually four on each side. The ascending lumbar veins drain into either the azygos vein on the right or the hemiazygos vein on the left, and return to the superior vena cava. The remaining lumbar veins drain directly into the inferior vena cava.
Blood supply from the kidneys flows into each renal vein, normally the largest veins entering the inferior vena cava. A number of other, smaller veins empty into the left renal vein. Each adrenal vein drains the adrenal or suprarenal glands located immediately superior to the kidneys. The right adrenal vein enters the inferior vena cava directly, whereas the left adrenal vein enters the left renal vein.
From the male reproductive organs, each testicular vein flows from the scrotum, forming a portion of the spermatic cord. Each ovarian vein drains an ovary in females. Each of these veins is generically called a gonadal vein. The right gonadal vein empties directly into the inferior vena cava, and the left gonadal vein empties into the left renal vein.
Each side of the diaphragm drains into a phrenic vein; the right phrenic vein empties directly into the inferior vena cava, whereas the left phrenic vein empties into the left renal vein. Blood supply from the liver drains into each hepatic vein and directly into the inferior vena cava. Since the inferior vena cava lies primarily to the right of the vertebral column and aorta, the left renal vein is longer, as are the left phrenic, adrenal, and gonadal veins. The longer length of the left renal vein makes the left kidney the primary target of surgeons removing this organ for donation. Figure 20.40 provides a flow chart of the veins flowing into the inferior vena cava. Table 20.15 summarizes the major veins of the abdominal region.
Figure 20.40 Venous Flow into Inferior Vena Cava The flow chart summarizes veins that deliver blood to the inferior vena cava.
Major Veins of the Abdominal Region
| Vessel | Description |
|---|---|
| Inferior vena cava | Large systemic vein that drains blood from areas largely inferior to the diaphragm; empties into the right atrium |
| Lumbar veins | Series of veins that drain the lumbar portion of the abdominal wall and spinal cord; the ascending lumbar veins drain into the azygos vein on the right or the hemiazygos vein on the left; the remaining lumbar veins drain directly into the inferior vena cava |
| Renal vein | Largest vein entering the inferior vena cava; drains the kidneys and flows into the inferior vena cava |
| Adrenal vein | Drains the adrenal or suprarenal; the right adrenal vein enters the inferior vena cava directly and the left adrenal vein enters the left renal vein |
| Testicular vein | Drains the testes and forms part of the spermatic cord; the right testicular vein empties directly into the inferior vena cava and the left testicular vein empties into the left renal vein |
| Ovarian vein | Drains the ovary; the right ovarian vein empties directly into the inferior vena cava and the left ovarian vein empties into the left renal vein |
| Gonadal vein | Generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual |
| Phrenic vein | Drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein empties into the left renal vein |
| Hepatic vein | Drains systemic blood from the liver and flows into the inferior vena cava |
Table 20.15
Veins Draining the Lower Limbs
The superior surface of the foot drains into the digital veins, and the inferior surface drains into the plantar veins, which flow into a complex series of anastomoses in the feet and ankles, including the dorsal venous arch and the plantar venous arch (Figure 20.41). From the dorsal venous arch, blood supply drains into the anterior and posterior tibial veins. The anterior tibial vein drains the area near the tibialis anterior muscle and combines with the posterior tibial vein and the fibular vein to form the popliteal vein. The posterior tibial vein drains the posterior surface of the tibia and joins the popliteal vein. The fibular vein drains the muscles and integument in proximity to the fibula and also joins the popliteal vein. The small saphenous vein located on the lateral surface of the leg drains blood from the superficial regions of the lower leg and foot, and flows into to the popliteal vein. As the popliteal vein passes behind the knee in the popliteal region, it becomes the femoral vein. It is palpable in patients without excessive adipose tissue.
Close to the body wall, the great saphenous vein, the deep femoral vein, and the femoral circumflex vein drain into the femoral vein. The great saphenous vein is a prominent surface vessel located on the medial surface of the leg and thigh that collects blood from the superficial portions of these areas. The deep femoral vein, as the name suggests, drains blood from the deeper portions of the thigh. The femoral circumflex vein forms a loop around the femur just inferior to the trochanters and drains blood from the areas in proximity to the head and neck of the femur.
As the femoral vein penetrates the body wall from the femoral portion of the upper limb, it becomes the external iliac vein, a large vein that drains blood from the leg to the common iliac vein. The pelvic organs and integument drain into the internal iliac vein, which forms from several smaller veins in the region, including the umbilical veins that run on either side of the bladder. The external and internal iliac veins combine near the inferior portion of the sacroiliac joint to form the common iliac vein. In addition to blood supply from the external and internal iliac veins, the middle sacral vein drains the sacral region into the common iliac vein. Similar to the common iliac arteries, the common iliac veins come together at the level of L5 to form the inferior vena cava.
Figure 20.42 is a flow chart of veins flowing into the lower limb. Table 20.16 summarizes the major veins of the lower limbs.
Figure 20.41 Major Veins Serving the Lower Limbs Anterior and posterior views show the major veins that drain the lower limb into the inferior vena cava.
Figure 20.42 Major Veins of the Lower Limb The flow chart summarizes venous flow from the lower limb.
Veins of the Lower Limbs
| Vessel | Description |
|---|---|
| Plantar veins | Drain the foot and flow into the plantar venous arch |
| Dorsal venous arch | Drains blood from digital veins and vessels on the superior surface of the foot |
| Plantar venous arch | Formed from the plantar veins; flows into the anterior and posterior tibial veins through anastomoses |
| Anterior tibial vein | Formed from the dorsal venous arch; drains the area near the tibialis anterior muscle and flows into the popliteal vein |
| Posterior tibial vein | Formed from the dorsal venous arch; drains the area near the posterior surface of the tibia and flows into the popliteal vein |
| Fibular vein | Drains the muscles and integument near the fibula and flows into the popliteal vein |
| Small saphenous vein | Located on the lateral surface of the leg; drains blood from the superficial regions of the lower leg and foot, and flows into the popliteal vein |
| Popliteal vein | Drains the region behind the knee and forms from the fusion of the fibular, anterior, and posterior tibial veins; flows into the femoral vein |
| Great saphenous vein | Prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and flows into the femoral vein |
| Deep femoral vein | Drains blood from the deeper portions of the thigh and flows into the femoral vein |
| Femoral circumflex vein | Forms a loop around the femur just inferior to the trochanters; drains blood from the areas around the head and neck of the femur; flows into the femoral vein |
| Femoral vein | Drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall |
| External iliac vein | Formed when the femoral vein passes into the body cavity; drains the legs and flows into the common iliac vein |
| Internal iliac vein | Drains the pelvic organs and integument; formed from several smaller veins in the region; flows into the common iliac vein |
| Middle sacral vein | Drains the sacral region and flows into the left common iliac vein |
| Common iliac vein | Flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; formed from the union of the external and internal iliac veins near the inferior portion of the sacroiliac joint |
Table 20.16
Hepatic Portal System
The liver is a complex biochemical processing plant. It packages nutrients absorbed by the digestive system; produces plasma proteins, clotting factors, and bile; and disposes of worn-out cell components and waste products. Instead of entering the circulation directly, absorbed nutrients and certain wastes (for example, materials produced by the spleen) travel to the liver for processing. They do so via the hepatic portal system (Figure 20.43). Portal systems begin and end in capillaries. In this case, the initial capillaries from the stomach, small intestine, large intestine, and spleen lead to the hepatic portal vein and end in specialized capillaries within the liver, the hepatic sinusoids. You saw the only other portal system with the hypothalamic-hypophyseal portal vessel in the endocrine chapter.
The hepatic portal system consists of the hepatic portal vein and the veins that drain into it. The hepatic portal vein itself is relatively short, beginning at the level of L2 with the confluence of the superior mesenteric and splenic veins. It also receives branches from the inferior mesenteric vein, plus the splenic veins and all their tributaries. The superior mesenteric vein receives blood from the small intestine, two-thirds of the large intestine, and the stomach. The inferior mesenteric vein drains the distal third of the large intestine, including the descending colon, the sigmoid colon, and the rectum. The splenic vein is formed from branches from the spleen, pancreas, and portions of the stomach, and the inferior mesenteric vein. After its formation, the hepatic portal vein also receives branches from the gastric veins of the stomach and cystic veins from the gall bladder. The hepatic portal vein delivers materials from these digestive and circulatory organs directly to the liver for processing.
Because of the hepatic portal system, the liver receives its blood supply from two different sources: from normal systemic circulation via the hepatic artery and from the hepatic portal vein. The liver processes the blood from the portal system to remove certain wastes and excess nutrients, which are stored for later use. This processed blood, as well as the systemic blood that came from the hepatic artery, exits the liver via the right, left, and middle hepatic veins, and flows into the inferior vena cava. Overall systemic blood composition remains relatively stable, since the liver is able to metabolize the absorbed digestive components.
Figure 20.43 Hepatic Portal System The liver receives blood from the normal systemic circulation via the hepatic artery. It also receives and processes blood from other organs, delivered via the veins of the hepatic portal system. All blood exits the liver via the hepatic vein, which delivers the blood to the inferior vena cava. (Different colors are used to help distinguish among the different vessels in the system.)
Development of Blood Vessels and Fetal Circulation
- Describe the development of blood vessels
- Describe the fetal circulation
In a developing embryo,the heart has developed enough by day 21 post-fertilization to begin beating. Circulation patterns are clearly established by the fourth week of embryonic life. It is critical to the survival of the developing human that the circulatory system forms early to supply the growing tissue with nutrients and gases, and to remove waste products. Blood cells and vessel production in structures outside the embryo proper called the yolk sac, chorion, and connecting stalk begin about 15 to 16 days following fertilization. Development of these circulatory elements within the embryo itself begins approximately 2 days later. You will learn more about the formation and function of these early structures when you study the chapter on development. During those first few weeks, blood vessels begin to form from the embryonic mesoderm. The precursor cells are known as hemangioblasts. These in turn differentiate into angioblasts, which give rise to the blood vessels and pluripotent stem cells, which differentiate into the formed elements of blood. (Seek additional content for more detail on fetal development and circulation.) Together, these cells form masses known as blood islands scattered throughout the embryonic disc. Spaces appear on the blood islands that develop into vessel lumens. The endothelial lining of the vessels arise from the angioblasts within these islands. Surrounding mesenchymal cells give rise to the smooth muscle and connective tissue layers of the vessels. While the vessels are developing, the pluripotent stem cells begin to form the blood.
Vascular tubes also develop on the blood islands, and they eventually connect to one another as well as to the developing, tubular heart. Thus, the developmental pattern, rather than beginning from the formation of one central vessel and spreading outward, occurs in many regions simultaneously with vessels later joining together. This angiogenesis—the creation of new blood vessels from existing ones—continues as needed throughout life as we grow and develop.
Blood vessel development often follows the same pattern as nerve development and travels to the same target tissues and organs. This occurs because the many factors directing growth of nerves also stimulate blood vessels to follow a similar pattern. Whether a given vessel develops into an artery or a vein is dependent upon local concentrations of signaling proteins.
As the embryo grows within the mother’s uterus, its requirements for nutrients and gas exchange also grow. The placenta—a circulatory organ unique to pregnancy—develops jointly from the embryo and uterine wall structures to fill this need. Emerging from the placenta is the umbilical vein, which carries oxygen-rich blood from the mother to the fetal inferior vena cava via the ductus venosus to the heart that pumps it into fetal circulation. Two umbilical arteries carry oxygen-depleted fetal blood, including wastes and carbon dioxide, to the placenta. Remnants of the umbilical arteries remain in the adult. (Seek additional content for more information on the role of the placenta in fetal circulation.)
There are three major shunts—alternate paths for blood flow—found in the circulatory system of the fetus. Two of these shunts divert blood from the pulmonary to the systemic circuit, whereas the third connects the umbilical vein to the inferior vena cava. The first two shunts are critical during fetal life, when the lungs are compressed, filled with amniotic fluid, and nonfunctional, and gas exchange is provided by the placenta. These shunts close shortly after birth, however, when the newborn begins to breathe. The third shunt persists a bit longer but becomes nonfunctional once the umbilical cord is severed. The three shunts are as follows (Figure 20.44):
- The foramen ovale is an opening in the interatrial septum that allows blood to flow from the right atrium to the left atrium. A valve associated with this opening prevents backflow of blood during the fetal period. As the newborn begins to breathe and blood pressure in the atria increases, this shunt closes. The fossa ovalis remains in the interatrial septum after birth, marking the location of the former foramen ovale.
- The ductus arteriosus is a short, muscular vessel that connects the pulmonary trunk to the aorta. Most of the blood pumped from the right ventricle into the pulmonary trunk is thereby diverted into the aorta. Only enough blood reaches the fetal lungs to maintain the developing lung tissue. When the newborn takes the first breath, pressure within the lungs drops dramatically, and both the lungs and the pulmonary vessels expand. As the amount of oxygen increases, the smooth muscles in the wall of the ductus arteriosus constrict, sealing off the passage. Eventually, the muscular and endothelial components of the ductus arteriosus degenerate, leaving only the connective tissue component of the ligamentum arteriosum.
- The ductus venosus is a temporary blood vessel that branches from the umbilical vein, allowing much of the freshly oxygenated blood from the placenta—the organ of gas exchange between the mother and fetus—to bypass the fetal liver and go directly to the fetal heart. The ductus venosus closes slowly during the first weeks of infancy and degenerates to become the ligamentum venosum.
Figure 20.44 Fetal Shunts The foramen ovale in the interatrial septum allows blood to flow from the right atrium to the left atrium. The ductus arteriosus is a temporary vessel, connecting the aorta to the pulmonary trunk. The ductus venosus links the umbilical vein to the inferior vena cava largely through the liver.
Key Terms
- abdominal aorta
- portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries
- adrenal artery
- branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands
- adrenal vein
- drains the adrenal or suprarenal glands that are immediately superior to the kidneys; the right adrenal vein enters the inferior vena cava directly and the left adrenal vein enters the left renal vein
- anaphylactic shock
- type of shock that follows a severe allergic reaction and results from massive vasodilation
- angioblasts
- stem cells that give rise to blood vessels
- angiogenesis
- development of new blood vessels from existing vessels
- anterior cerebral artery
- arises from the internal carotid artery; supplies the frontal lobe of the cerebrum
- anterior communicating artery
- anastomosis of the right and left internal carotid arteries; supplies blood to the brain
- anterior tibial artery
- branches from the popliteal artery; supplies blood to the anterior tibial region; becomes the dorsalis pedis artery
- anterior tibial vein
- forms from the dorsal venous arch; drains the area near the tibialis anterior muscle and leads to the popliteal vein
- aorta
- largest artery in the body, originating from the left ventricle and descending to the abdominal region where it bifurcates into the common iliac arteries at the level of the fourth lumbar vertebra; arteries originating from the aorta distribute blood to virtually all tissues of the body
- aortic arch
- arc that connects the ascending aorta to the descending aorta; ends at the intervertebral disk between the fourth and fifth thoracic vertebrae
- aortic hiatus
- opening in the diaphragm that allows passage of the thoracic aorta into the abdominal region where it becomes the abdominal aorta
- aortic sinuses
- small pockets in the ascending aorta near the aortic valve that are the locations of the baroreceptors (stretch receptors) and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis
- arterial circle
- (also, circle of Willis) anastomosis located at the base of the brain that ensures continual blood supply; formed from branches of the internal carotid and vertebral arteries; supplies blood to the brain
- arteriole
- (also, resistance vessel) very small artery that leads to a capillary
- arteriovenous anastomosis
- short vessel connecting an arteriole directly to a venule and bypassing the capillary beds
- artery
- blood vessel that conducts blood away from the heart; may be a conducting or distributing vessel
- ascending aorta
- initial portion of the aorta, rising from the left ventricle for a distance of approximately 5 cm
- atrial reflex
- mechanism for maintaining vascular homeostasis involving atrial baroreceptors: if blood is returning to the right atrium more rapidly than it is being ejected from the left ventricle, the atrial receptors will stimulate the cardiovascular centers to increase sympathetic firing and increase cardiac output until the situation is reversed; the opposite is also true
- axillary artery
- continuation of the subclavian artery as it penetrates the body wall and enters the axillary region; supplies blood to the region near the head of the humerus (humeral circumflex arteries); the majority of the vessel continues into the brachium and becomes the brachial artery
- axillary vein
- major vein in the axillary region; drains the upper limb and becomes the subclavian vein
- azygos vein
- originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, esophageal veins, bronchial veins, and other veins draining the mediastinal region; leads to the superior vena cava
- basilar artery
- formed from the fusion of the two vertebral arteries; sends branches to the cerebellum, brain stem, and the posterior cerebral arteries; the main blood supply to the brain stem
- basilic vein
- superficial vein of the arm that arises from the palmar venous arches, intersects with the median cubital vein, parallels the ulnar vein, and continues into the upper arm; along with the brachial vein, it leads to the axillary vein
- blood colloidal osmotic pressure (BCOP)
- pressure exerted by colloids suspended in blood within a vessel; a primary determinant is the presence of plasma proteins
- blood flow
- movement of blood through a vessel, tissue, or organ that is usually expressed in terms of volume per unit of time
- blood hydrostatic pressure
- force blood exerts against the walls of a blood vessel or heart chamber
- blood islands
- masses of developing blood vessels and formed elements from mesodermal cells scattered throughout the embryonic disc
- blood pressure
- force exerted by the blood against the wall of a vessel or heart chamber; can be described with the more generic term hydrostatic pressure
- brachial artery
- continuation of the axillary artery in the brachium; supplies blood to much of the brachial region; gives off several smaller branches that provide blood to the posterior surface of the arm in the region of the elbow; bifurcates into the radial and ulnar arteries at the coronoid fossa
- brachial vein
- deeper vein of the arm that forms from the radial and ulnar veins in the lower arm; leads to the axillary vein
- brachiocephalic artery
- single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of the thoracic region
- brachiocephalic vein
- one of a pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins lead to it; drains the upper thoracic region and flows into the superior vena cava
- bronchial artery
- systemic branch from the aorta that provides oxygenated blood to the lungs in addition to the pulmonary circuit
- bronchial vein
- drains the systemic circulation from the lungs and leads to the azygos vein
- capacitance
- ability of a vein to distend and store blood
- capacitance vessels
- veins
- capillary
- smallest of blood vessels where physical exchange occurs between the blood and tissue cells surrounded by interstitial fluid
- capillary bed
- network of 10–100 capillaries connecting arterioles to venules
- capillary hydrostatic pressure (CHP)
- force blood exerts against a capillary
- cardiogenic shock
- type of shock that results from the inability of the heart to maintain cardiac output
- carotid sinuses
- small pockets near the base of the internal carotid arteries that are the locations of the baroreceptors and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis
- cavernous sinus
- enlarged vein that receives blood from most of the other cerebral veins and the eye socket, and leads to the petrosal sinus
- celiac trunk
- (also, celiac artery) major branch of the abdominal aorta; gives rise to the left gastric artery, the splenic artery, and the common hepatic artery that forms the hepatic artery to the liver, the right gastric artery to the stomach, and the cystic artery to the gall bladder
- cephalic vein
- superficial vessel in the upper arm; leads to the axillary vein
- cerebrovascular accident (CVA)
- blockage of blood flow to the brain; also called a stroke
- circle of Willis
- (also, arterial circle) anastomosis located at the base of the brain that ensures continual blood supply; formed from branches of the internal carotid and vertebral arteries; supplies blood to the brain
- circulatory shock
- also simply called shock; a life-threatening medical condition in which the circulatory system is unable to supply enough blood flow to provide adequate oxygen and other nutrients to the tissues to maintain cellular metabolism
- common carotid artery
- right common carotid artery arises from the brachiocephalic artery, and the left common carotid arises from the aortic arch; gives rise to the external and internal carotid arteries; supplies the respective sides of the head and neck
- common hepatic artery
- branch of the celiac trunk that forms the hepatic artery, the right gastric artery, and the cystic artery
- common iliac artery
- branch of the aorta that leads to the internal and external iliac arteries
- common iliac vein
- one of a pair of veins that flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; divides into external and internal iliac veins near the inferior portion of the sacroiliac joint
- compliance
- degree to which a blood vessel can stretch as opposed to being rigid
- continuous capillary
- most common type of capillary, found in virtually all tissues except epithelia and cartilage; contains very small gaps in the endothelial lining that permit exchange
- cystic artery
- branch of the common hepatic artery; supplies blood to the gall bladder
- deep femoral artery
- branch of the femoral artery; gives rise to the lateral circumflex arteries
- deep femoral vein
- drains blood from the deeper portions of the thigh and leads to the femoral vein
- descending aorta
- portion of the aorta that continues downward past the end of the aortic arch; subdivided into the thoracic aorta and the abdominal aorta
- diastolic pressure
- lower number recorded when measuring arterial blood pressure; represents the minimal value corresponding to the pressure that remains during ventricular relaxation
- digital arteries
- formed from the superficial and deep palmar arches; supply blood to the digits
- digital veins
- drain the digits and feed into the palmar arches of the hand and dorsal venous arch of the foot
- dorsal arch
- (also, arcuate arch) formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply the distal portions of the foot and digits
- dorsal venous arch
- drains blood from digital veins and vessels on the superior surface of the foot
- dorsalis pedis artery
- forms from the anterior tibial artery; branches repeatedly to supply blood to the tarsal and dorsal regions of the foot
- ductus arteriosus
- shunt in the fetal pulmonary trunk that diverts oxygenated blood back to the aorta
- ductus venosus
- shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava
- elastic artery
- (also, conducting artery) artery with abundant elastic fibers located closer to the heart, which maintains the pressure gradient and conducts blood to smaller branches
- esophageal artery
- branch of the thoracic aorta; supplies blood to the esophagus
- esophageal vein
- drains the inferior portions of the esophagus and leads to the azygos vein
- external carotid artery
- arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx
- external elastic membrane
- membrane composed of elastic fibers that separates the tunica media from the tunica externa; seen in larger arteries
- external iliac artery
- branch of the common iliac artery that leaves the body cavity and becomes a femoral artery; supplies blood to the lower limbs
- external iliac vein
- formed when the femoral vein passes into the body cavity; drains the legs and leads to the common iliac vein
- external jugular vein
- one of a pair of major veins located in the superficial neck region that drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein
- femoral artery
- continuation of the external iliac artery after it passes through the body cavity; divides into several smaller branches, the lateral deep femoral artery, and the genicular artery; becomes the popliteal artery as it passes posterior to the knee
- femoral circumflex vein
- forms a loop around the femur just inferior to the trochanters; drains blood from the areas around the head and neck of the femur; leads to the femoral vein
- femoral vein
- drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall
- fenestrated capillary
- type of capillary with pores or fenestrations in the endothelium that allow for rapid passage of certain small materials
- fibular vein
- drains the muscles and integument near the fibula and leads to the popliteal vein
- filtration
- in the cardiovascular system, the movement of material from a capillary into the interstitial fluid, moving from an area of higher pressure to lower pressure
- foramen ovale
- shunt that directly connects the right and left atria and helps to divert oxygenated blood from the fetal pulmonary circuit
- genicular artery
- branch of the femoral artery; supplies blood to the region of the knee
- gonadal artery
- branch of the abdominal aorta; supplies blood to the gonads or reproductive organs; also described as ovarian arteries or testicular arteries, depending upon the sex of the individual
- gonadal vein
- generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual
- great cerebral vein
- receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus
- great saphenous vein
- prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and leads to the femoral vein
- hemangioblasts
- embryonic stem cells that appear in the mesoderm and give rise to both angioblasts and pluripotent stem cells
- hemiazygos vein
- smaller vein complementary to the azygos vein; drains the esophageal veins from the esophagus and the left intercostal veins, and leads to the brachiocephalic vein via the superior intercostal vein
- hepatic artery proper
- branch of the common hepatic artery; supplies systemic blood to the liver
- hepatic portal system
- specialized circulatory pathway that carries blood from digestive organs to the liver for processing before being sent to the systemic circulation
- hepatic vein
- drains systemic blood from the liver and flows into the inferior vena cava
- hypertension
- chronic and persistent blood pressure measurements of 140/90 mm Hg or above
- hypervolemia
- abnormally high levels of fluid and blood within the body
- hypovolemia
- abnormally low levels of fluid and blood within the body
- hypovolemic shock
- type of circulatory shock caused by excessive loss of blood volume due to hemorrhage or possibly dehydration
- hypoxia
- lack of oxygen supply to the tissues
- inferior mesenteric artery
- branch of the abdominal aorta; supplies blood to the distal segment of the large intestine and rectum
- inferior phrenic artery
- branch of the abdominal aorta; supplies blood to the inferior surface of the diaphragm
- inferior vena cava
- large systemic vein that drains blood from areas largely inferior to the diaphragm; empties into the right atrium
- intercostal artery
- branch of the thoracic aorta; supplies blood to the muscles of the thoracic cavity and vertebral column
- intercostal vein
- drains the muscles of the thoracic wall and leads to the azygos vein
- internal carotid artery
- arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with branches of the vertebral artery forming the arterial circle; supplies blood to the brain
- internal elastic membrane
- membrane composed of elastic fibers that separates the tunica intima from the tunica media; seen in larger arteries
- internal iliac artery
- branch from the common iliac arteries; supplies blood to the urinary bladder, walls of the pelvis, external genitalia, and the medial portion of the femoral region; in females, also provide blood to the uterus and vagina
- internal iliac vein
- drains the pelvic organs and integument; formed from several smaller veins in the region; leads to the common iliac vein
- internal jugular vein
- one of a pair of major veins located in the neck region that passes through the jugular foramen and canal, flows parallel to the common carotid artery that is more or less its counterpart; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein
- internal thoracic artery
- (also, mammary artery) arises from the subclavian artery; supplies blood to the thymus, pericardium of the heart, and the anterior chest wall
- internal thoracic vein
- (also, internal mammary vein) drains the anterior surface of the chest wall and leads to the brachiocephalic vein
- interstitial fluid colloidal osmotic pressure (IFCOP)
- pressure exerted by the colloids within the interstitial fluid
- interstitial fluid hydrostatic pressure (IFHP)
- force exerted by the fluid in the tissue spaces
- ischemia
- insufficient blood flow to the tissues
- Korotkoff sounds
- noises created by turbulent blood flow through the vessels
- lateral circumflex artery
- branch of the deep femoral artery; supplies blood to the deep muscles of the thigh and the ventral and lateral regions of the integument
- lateral plantar artery
- arises from the bifurcation of the posterior tibial arteries; supplies blood to the lateral plantar surfaces of the foot
- left gastric artery
- branch of the celiac trunk; supplies blood to the stomach
- lumbar arteries
- branches of the abdominal aorta; supply blood to the lumbar region, the abdominal wall, and spinal cord
- lumbar veins
- drain the lumbar portion of the abdominal wall and spinal cord; the superior lumbar veins drain into the azygos vein on the right or the hemiazygos vein on the left; blood from these vessels is returned to the superior vena cava rather than the inferior vena cava
- lumen
- interior of a tubular structure such as a blood vessel or a portion of the alimentary canal through which blood, chyme, or other substances travel
- maxillary vein
- drains blood from the maxillary region and leads to the external jugular vein
- mean arterial pressure (MAP)
- average driving force of blood to the tissues; approximated by taking diastolic pressure and adding 1/3 of pulse pressure
- medial plantar artery
- arises from the bifurcation of the posterior tibial arteries; supplies blood to the medial plantar surfaces of the foot
- median antebrachial vein
- vein that parallels the ulnar vein but is more medial in location; intertwines with the palmar venous arches
- median cubital vein
- superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a v; a frequent site for a blood draw
- median sacral artery
- continuation of the aorta into the sacrum
- mediastinal artery
- branch of the thoracic aorta; supplies blood to the mediastinum
- metarteriole
- short vessel arising from a terminal arteriole that branches to supply a capillary bed
- microcirculation
- blood flow through the capillaries
- middle cerebral artery
- another branch of the internal carotid artery; supplies blood to the temporal and parietal lobes of the cerebrum
- middle sacral vein
- drains the sacral region and leads to the left common iliac vein
- muscular artery
- (also, distributing artery) artery with abundant smooth muscle in the tunica media that branches to distribute blood to the arteriole network
- myogenic response
- constriction or dilation in the walls of arterioles in response to pressures related to blood flow; reduces high blood flow or increases low blood flow to help maintain consistent flow to the capillary network
- nervi vasorum
- small nerve fibers found in arteries and veins that trigger contraction of the smooth muscle in their walls
- net filtration pressure (NFP)
- force driving fluid out of the capillary and into the tissue spaces; equal to the difference of the capillary hydrostatic pressure and the blood colloidal osmotic pressure
- neurogenic shock
- type of shock that occurs with cranial or high spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region
- obstructive shock
- type of shock that occurs when a significant portion of the vascular system is blocked
- occipital sinus
- enlarged vein that drains the occipital region near the falx cerebelli and flows into the left and right transverse sinuses, and also into the vertebral veins
- ophthalmic artery
- branch of the internal carotid artery; supplies blood to the eyes
- ovarian artery
- branch of the abdominal aorta; supplies blood to the ovary, uterine (Fallopian) tube, and uterus
- ovarian vein
- drains the ovary; the right ovarian vein leads to the inferior vena cava and the left ovarian vein leads to the left renal vein
- palmar arches
- superficial and deep arches formed from anastomoses of the radial and ulnar arteries; supply blood to the hand and digital arteries
- palmar venous arches
- drain the hand and digits, and feed into the radial and ulnar veins
- parietal branches
- (also, somatic branches) group of arterial branches of the thoracic aorta; includes those that supply blood to the thoracic cavity, vertebral column, and the superior surface of the diaphragm
- perfusion
- distribution of blood into the capillaries so the tissues can be supplied
- pericardial artery
- branch of the thoracic aorta; supplies blood to the pericardium
- petrosal sinus
- enlarged vein that receives blood from the cavernous sinus and flows into the internal jugular vein
- phrenic vein
- drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein leads to the left renal vein
- plantar arch
- formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply the distal portions of the foot and digits
- plantar veins
- drain the foot and lead to the plantar venous arch
- plantar venous arch
- formed from the plantar veins; leads to the anterior and posterior tibial veins through anastomoses
- popliteal artery
- continuation of the femoral artery posterior to the knee; branches into the anterior and posterior tibial arteries
- popliteal vein
- continuation of the femoral vein behind the knee; drains the region behind the knee and forms from the fusion of the fibular and anterior and posterior tibial veins
- posterior cerebral artery
- branch of the basilar artery that forms a portion of the posterior segment of the arterial circle; supplies blood to the posterior portion of the cerebrum and brain stem
- posterior communicating artery
- branch of the posterior cerebral artery that forms part of the posterior portion of the arterial circle; supplies blood to the brain
- posterior tibial artery
- branch from the popliteal artery that gives rise to the fibular or peroneal artery; supplies blood to the posterior tibial region
- posterior tibial vein
- forms from the dorsal venous arch; drains the area near the posterior surface of the tibia and leads to the popliteal vein
- precapillary sphincters
- circular rings of smooth muscle that surround the entrance to a capillary and regulate blood flow into that capillary
- pulmonary artery
- one of two branches, left and right, that divides off from the pulmonary trunk and leads to smaller arterioles and eventually to the pulmonary capillaries
- pulmonary circuit
- system of blood vessels that provide gas exchange via a network of arteries, veins, and capillaries that run from the heart, through the body, and back to the lungs
- pulmonary trunk
- single large vessel exiting the right ventricle that divides to form the right and left pulmonary arteries
- pulmonary veins
- two sets of paired vessels, one pair on each side, that are formed from the small venules leading away from the pulmonary capillaries that flow into the left atrium
- pulse
- alternating expansion and recoil of an artery as blood moves through the vessel; an indicator of heart rate
- pulse pressure
- difference between the systolic and diastolic pressures
- radial artery
- formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region
- radial vein
- parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein
- reabsorption
- in the cardiovascular system, the movement of material from the interstitial fluid into the capillaries
- renal artery
- branch of the abdominal aorta; supplies each kidney
- renal vein
- largest vein entering the inferior vena cava; drains the kidneys and leads to the inferior vena cava
- resistance
- any condition or parameter that slows or counteracts the flow of blood
- respiratory pump
- increase in the volume of the thorax during inhalation that decreases air pressure, enabling venous blood to flow into the thoracic region, then exhalation increases pressure, moving blood into the atria
- right gastric artery
- branch of the common hepatic artery; supplies blood to the stomach
- sepsis
- (also, septicemia) organismal-level inflammatory response to a massive infection
- septic shock
- (also, blood poisoning) type of shock that follows a massive infection resulting in organism-wide inflammation
- sigmoid sinuses
- enlarged veins that receive blood from the transverse sinuses; flow through the jugular foramen and into the internal jugular vein
- sinusoid capillary
- rarest type of capillary, which has extremely large intercellular gaps in the basement membrane in addition to clefts and fenestrations; found in areas such as the bone marrow and liver where passage of large molecules occurs
- skeletal muscle pump
- effect on increasing blood pressure within veins by compression of the vessel caused by the contraction of nearby skeletal muscle
- small saphenous vein
- located on the lateral surface of the leg; drains blood from the superficial regions of the lower leg and foot, and leads to the popliteal vein
- sphygmomanometer
- blood pressure cuff attached to a device that measures blood pressure
- splenic artery
- branch of the celiac trunk; supplies blood to the spleen
- straight sinus
- enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and flows into the left or right transverse sinus
- subclavian artery
- right subclavian arises from the brachiocephalic artery, whereas the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system
- subclavian vein
- located deep in the thoracic cavity; becomes the axillary vein as it enters the axillary region; drains the axillary and smaller local veins near the scapular region; leads to the brachiocephalic vein
- subscapular vein
- drains blood from the subscapular region and leads to the axillary vein
- superior mesenteric artery
- branch of the abdominal aorta; supplies blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine
- superior phrenic artery
- branch of the thoracic aorta; supplies blood to the superior surface of the diaphragm
- superior sagittal sinus
- enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein
- superior vena cava
- large systemic vein; drains blood from most areas superior to the diaphragm; empties into the right atrium
- systolic pressure
- larger number recorded when measuring arterial blood pressure; represents the maximum value following ventricular contraction
- temporal vein
- drains blood from the temporal region and leads to the external jugular vein
- testicular artery
- branch of the abdominal aorta; will ultimately travel outside the body cavity to the testes and form one component of the spermatic cord
- testicular vein
- drains the testes and forms part of the spermatic cord; the right testicular vein empties directly into the inferior vena cava and the left testicular vein empties into the left renal vein
- thoracic aorta
- portion of the descending aorta superior to the aortic hiatus
- thoroughfare channel
- continuation of the metarteriole that enables blood to bypass a capillary bed and flow directly into a venule, creating a vascular shunt
- thyrocervical artery
- arises from the subclavian artery; supplies blood to the thyroid, the cervical region, the upper back, and shoulder
- transient ischemic attack (TIA)
- temporary loss of neurological function caused by a brief interruption in blood flow; also known as a mini-stroke
- transverse sinuses
- pair of enlarged veins near the lambdoid suture that drain the occipital, sagittal, and straight sinuses, and leads to the sigmoid sinuses
- trunk
- large vessel that gives rise to smaller vessels
- tunica externa
- (also, tunica adventitia) outermost layer or tunic of a vessel (except capillaries)
- tunica intima
- (also, tunica interna) innermost lining or tunic of a vessel
- tunica media
- middle layer or tunic of a vessel (except capillaries)
- ulnar artery
- formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the carpal region where it fuses with the radial artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region
- ulnar vein
- parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein
- umbilical arteries
- pair of vessels that runs within the umbilical cord and carries fetal blood low in oxygen and high in waste to the placenta for exchange with maternal blood
- umbilical vein
- single vessel that originates in the placenta and runs within the umbilical cord, carrying oxygen- and nutrient-rich blood to the fetal heart
- vasa vasorum
- small blood vessels located within the walls or tunics of larger vessels that supply nourishment to and remove wastes from the cells of the vessels
- vascular shock
- type of shock that occurs when arterioles lose their normal muscular tone and dilate dramatically
- vascular shunt
- continuation of the metarteriole and thoroughfare channel that allows blood to bypass the capillary beds to flow directly from the arterial to the venous circulation
- vascular tone
- contractile state of smooth muscle in a blood vessel
- vascular tubes
- rudimentary blood vessels in a developing fetus
- vasoconstriction
- constriction of the smooth muscle of a blood vessel, resulting in a decreased vascular diameter
- vasodilation
- relaxation of the smooth muscle in the wall of a blood vessel, resulting in an increased vascular diameter
- vasomotion
- irregular, pulsating flow of blood through capillaries and related structures
- vein
- blood vessel that conducts blood toward the heart
- venous reserve
- volume of blood contained within systemic veins in the integument, bone marrow, and liver that can be returned to the heart for circulation, if needed
- venule
- small vessel leading from the capillaries to veins
- vertebral artery
- arises from the subclavian artery and passes through the vertebral foramen through the foramen magnum to the brain; joins with the internal carotid artery to form the arterial circle; supplies blood to the brain and spinal cord
- vertebral vein
- arises from the base of the brain and the cervical region of the spinal cord; passes through the intervertebral foramina in the cervical vertebrae; drains smaller veins from the cranium, spinal cord, and vertebrae, and leads to the brachiocephalic vein; counterpart of the vertebral artery
- visceral branches
- branches of the descending aorta that supply blood to the viscera
Chapter Review
20.1 Structure and Function of Blood Vessels
Blood pumped by the heart flows through a series of vessels known as arteries, arterioles, capillaries, venules, and veins before returning to the heart. Arteries transport blood away from the heart and branch into smaller vessels, forming arterioles. Arterioles distribute blood to capillary beds, the sites of exchange with the body tissues. Capillaries lead back to small vessels known as venules that flow into the larger veins and eventually back to the heart.
The arterial system is a relatively high-pressure system, so arteries have thick walls that appear round in cross section. The venous system is a lower-pressure system, containing veins that have larger lumens and thinner walls. They often appear flattened. Arteries, arterioles, venules, and veins are composed of three tunics known as the tunica intima, tunica media, and tunica externa. Capillaries have only a tunica intima layer. The tunica intima is a thin layer composed of a simple squamous epithelium known as endothelium and a small amount of connective tissue. The tunica media is a thicker area composed of variable amounts of smooth muscle and connective tissue. It is the thickest layer in all but the largest arteries. The tunica externa is primarily a layer of connective tissue, although in veins, it also contains some smooth muscle. Blood flow through vessels can be dramatically influenced by vasoconstriction and vasodilation in their walls.
20.2 Blood Flow, Blood Pressure, and Resistance
Blood flow is the movement of blood through a vessel, tissue, or organ. The slowing or blocking of blood flow is called resistance. Blood pressure is the force that blood exerts upon the walls of the blood vessels or chambers of the heart. The components of blood pressure include systolic pressure, which results from ventricular contraction, and diastolic pressure, which results from ventricular relaxation. Pulse pressure is the difference between systolic and diastolic measures, and mean arterial pressure is the “average” pressure of blood in the arterial system, driving blood into the tissues. Pulse, the expansion and recoiling of an artery, reflects the heartbeat. The variables affecting blood flow and blood pressure in the systemic circulation are cardiac output, compliance, blood volume, blood viscosity, and the length and diameter of the blood vessels. In the arterial system, vasodilation and vasoconstriction of the arterioles is a significant factor in systemic blood pressure: Slight vasodilation greatly decreases resistance and increases flow, whereas slight vasoconstriction greatly increases resistance and decreases flow. In the arterial system, as resistance increases, blood pressure increases and flow decreases. In the venous system, constriction increases blood pressure as it does in arteries; the increasing pressure helps to return blood to the heart. In addition, constriction causes the vessel lumen to become more rounded, decreasing resistance and increasing blood flow. Venoconstriction, while less important than arterial vasoconstriction, works with the skeletal muscle pump, the respiratory pump, and their valves to promote venous return to the heart.
20.3 Capillary Exchange
Small molecules can cross into and out of capillaries via simple or facilitated diffusion. Some large molecules can cross in vesicles or through clefts, fenestrations, or gaps between cells in capillary walls. However, the bulk flow of capillary and tissue fluid occurs via filtration and reabsorption. Filtration, the movement of fluid out of the capillaries, is driven by the CHP. Reabsorption, the influx of tissue fluid into the capillaries, is driven by the BCOP. Filtration predominates in the arterial end of the capillary; in the middle section, the opposing pressures are virtually identical so there is no net exchange, whereas reabsorption predominates at the venule end of the capillary. The hydrostatic and colloid osmotic pressures in the interstitial fluid are negligible in healthy circumstances.
20.4 Homeostatic Regulation of the Vascular System
Neural, endocrine, and autoregulatory mechanisms affect blood flow, blood pressure, and eventually perfusion of blood to body tissues. Neural mechanisms include the cardiovascular centers in the medulla oblongata, baroreceptors in the aorta and carotid arteries and right atrium, and associated chemoreceptors that monitor blood levels of oxygen, carbon dioxide, and hydrogen ions. Endocrine controls include epinephrine and norepinephrine, as well as ADH, the renin-angiotensin-aldosterone mechanism, ANH, and EPO. Autoregulation is the local control of vasodilation and constriction by chemical signals and the myogenic response. Exercise greatly improves cardiovascular function and reduces the risk of cardiovascular diseases, including hypertension, a leading cause of heart attacks and strokes. Significant hemorrhage can lead to a form of circulatory shock known as hypovolemic shock. Sepsis, obstruction, and widespread inflammation can also cause circulatory shock.
20.5 Circulatory Pathways
The right ventricle pumps oxygen-depleted blood into the pulmonary trunk and right and left pulmonary arteries, which carry it to the right and left lungs for gas exchange. Oxygen-rich blood is transported by pulmonary veins to the left atrium. The left ventricle pumps this blood into the aorta. The main regions of the aorta are the ascending aorta, aortic arch, and descending aorta, which is further divided into the thoracic and abdominal aorta. The coronary arteries branch from the ascending aorta. After oxygenating tissues in the capillaries, systemic blood is returned to the right atrium from the venous system via the superior vena cava, which drains most of the veins superior to the diaphragm, the inferior vena cava, which drains most of the veins inferior to the diaphragm, and the coronary veins via the coronary sinus. The hepatic portal system carries blood to the liver for processing before it enters circulation. Review the figures provided in this section for circulation of blood through the blood vessels.
20.6 Development of Blood Vessels and Fetal Circulation
Blood vessels begin to form from the embryonic mesoderm. The precursor hemangioblasts differentiate into angioblasts, which give rise to the blood vessels and pluripotent stem cells that differentiate into the formed elements of the blood. Together, these cells form blood islands scattered throughout the embryo. Extensions known as vascular tubes eventually connect the vascular network. As the embryo grows within the mother’s womb, the placenta develops to supply blood rich in oxygen and nutrients via the umbilical vein and to remove wastes in oxygen-depleted blood via the umbilical arteries. Three major shunts found in the fetus are the foramen ovale and ductus arteriosus, which divert blood from the pulmonary to the systemic circuit, and the ductus venosus, which carries freshly oxygenated blood high in nutrients to the fetal heart.
Interactive Link Questions
Watch this video to explore capillaries and how they function in the body. Capillaries are never more than 100 micrometers away. What is the main component of interstitial fluid?
2.Listen to this CDC podcast to learn about hypertension, often described as a “silent killer.” What steps can you take to reduce your risk of a heart attack or stroke?
Review Questions
The endothelium is found in the ________.
- tunica intima
- tunica media
- tunica externa
- lumen
Nervi vasorum control ________.
- vasoconstriction
- vasodilation
- capillary permeability
- both vasoconstriction and vasodilation
Closer to the heart, arteries would be expected to have a higher percentage of ________.
- endothelium
- smooth muscle fibers
- elastic fibers
- collagenous fibers
Which of the following best describes veins?
- thick walled, small lumens, low pressure, lack valves
- thin walled, large lumens, low pressure, have valves
- thin walled, small lumens, high pressure, have valves
- thick walled, large lumens, high pressure, lack valves
An especially leaky type of capillary found in the liver and certain other tissues is called a ________.
- capillary bed
- fenestrated capillary
- sinusoid capillary
- metarteriole
In a blood pressure measurement of 110/70, the number 70 is the ________.
- systolic pressure
- diastolic pressure
- pulse pressure
- mean arterial pressure
A healthy elastic artery ________.
- is compliant
- reduces blood flow
- is a resistance artery
- has a thin wall and irregular lumen
Which of the following statements is true?
- The longer the vessel, the lower the resistance and the greater the flow.
- As blood volume decreases, blood pressure and blood flow also decrease.
- Increased viscosity increases blood flow.
- All of the above are true.
Slight vasodilation in an arteriole prompts a ________.
- slight increase in resistance
- huge increase in resistance
- slight decrease in resistance
- huge decrease in resistance
Venoconstriction increases which of the following?
- blood pressure within the vein
- blood flow within the vein
- return of blood to the heart
- all of the above
Hydrostatic pressure is ________.
- greater than colloid osmotic pressure at the venous end of the capillary bed
- the pressure exerted by fluid in an enclosed space
- about zero at the midpoint of a capillary bed
- all of the above
Net filtration pressure is calculated by ________.
- adding the capillary hydrostatic pressure to the interstitial fluid hydrostatic pressure
- subtracting the fluid drained by the lymphatic vessels from the total fluid in the interstitial fluid
- adding the blood colloid osmotic pressure to the capillary hydrostatic pressure
- subtracting the blood colloid osmotic pressure from the capillary hydrostatic pressure
Which of the following statements is true?
- In one day, more fluid exits the capillary through filtration than enters through reabsorption.
- In one day, approximately 35 mm of blood are filtered and 7 mm are reabsorbed.
- In one day, the capillaries of the lymphatic system absorb about 20.4 liters of fluid.
- None of the above are true.
Clusters of neurons in the medulla oblongata that regulate blood pressure are known collectively as ________.
- baroreceptors
- angioreceptors
- the cardiomotor mechanism
- the cardiovascular center
In the renin-angiotensin-aldosterone mechanism, ________.
- decreased blood pressure prompts the release of renin from the liver
- aldosterone prompts increased urine output
- aldosterone prompts the kidneys to reabsorb sodium
- all of the above
In the myogenic response, ________.
- muscle contraction promotes venous return to the heart
- ventricular contraction strength is decreased
- vascular smooth muscle responds to stretch
- endothelins dilate muscular arteries
A form of circulatory shock common in young children with severe diarrhea or vomiting is ________.
- hypovolemic shock
- anaphylactic shock
- obstructive shock
- hemorrhagic shock
The coronary arteries branch off of the ________.
- aortic valve
- ascending aorta
- aortic arch
- thoracic aorta
Which of the following statements is true?
- The left and right common carotid arteries both branch off of the brachiocephalic trunk.
- The brachial artery is the distal branch of the axillary artery.
- The radial and ulnar arteries join to form the palmar arch.
- All of the above are true.
Arteries serving the stomach, pancreas, and liver all branch from the ________.
- superior mesenteric artery
- inferior mesenteric artery
- celiac trunk
- splenic artery
The right and left brachiocephalic veins ________.
- drain blood from the right and left internal jugular veins
- drain blood from the right and left subclavian veins
- drain into the superior vena cava
- all of the above are true
The hepatic portal system delivers blood from the digestive organs to the ________.
- liver
- hypothalamus
- spleen
- left atrium
Blood islands are ________.
- clusters of blood-filtering cells in the placenta
- masses of pluripotent stem cells scattered throughout the fetal bone marrow
- vascular tubes that give rise to the embryonic tubular heart
- masses of developing blood vessels and formed elements scattered throughout the embryonic disc
Which of the following statements is true?
- Two umbilical veins carry oxygen-depleted blood from the fetal circulation to the placenta.
- One umbilical vein carries oxygen-rich blood from the placenta to the fetal heart.
- Two umbilical arteries carry oxygen-depleted blood to the fetal lungs.
- None of the above are true.
The ductus venosus is a shunt that allows ________.
- fetal blood to flow from the right atrium to the left atrium
- fetal blood to flow from the right ventricle to the left ventricle
- most freshly oxygenated blood to flow into the fetal heart
- most oxygen-depleted fetal blood to flow directly into the fetal pulmonary trunk
Critical Thinking Questions
Arterioles are often referred to as resistance vessels. Why?
29.Cocaine use causes vasoconstriction. Is this likely to increase or decrease blood pressure, and why?
30.A blood vessel with a few smooth muscle fibers and connective tissue, and only a very thin tunica externa conducts blood toward the heart. What type of vessel is this?
31.You measure a patient’s blood pressure at 130/85. Calculate the patient’s pulse pressure and mean arterial pressure. Determine whether each pressure is low, normal, or high.
32.An obese patient comes to the clinic complaining of swollen feet and ankles, fatigue, shortness of breath, and often feeling “spaced out.” She is a cashier in a grocery store, a job that requires her to stand all day. Outside of work, she engages in no physical activity. She confesses that, because of her weight, she finds even walking uncomfortable. Explain how the skeletal muscle pump might play a role in this patient’s signs and symptoms.
33.A patient arrives at the emergency department with dangerously low blood pressure. The patient’s blood colloid osmotic pressure is normal. How would you expect this situation to affect the patient’s net filtration pressure?
34.True or false? The plasma proteins suspended in blood cross the capillary cell membrane and enter the tissue fluid via facilitated diffusion. Explain your thinking.
35.A patient arrives in the emergency department with a blood pressure of 70/45 confused and complaining of thirst. Why?
36.Nitric oxide is broken down very quickly after its release. Why?
37.Identify the ventricle of the heart that pumps oxygen-depleted blood and the arteries of the body that carry oxygen-depleted blood.
38.What organs do the gonadal veins drain?
39.What arteries play the leading roles in supplying blood to the brain?
40.All tissues, including malignant tumors, need a blood supply. Explain why drugs called angiogenesis inhibitors would be used in cancer treatment.
41.Explain the location and importance of the ductus arteriosus in fetal circulation.
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oercommons
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2025-03-18T00:38:19.033148
|
10/14/2019
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https://oercommons.org/courseware/lesson/72073/overview
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Chapter 2 Reading Guide
Overview
This reading guide is intended to be used with the Open Stax Anatomy and Physiology textbook.
Open Stax Anatomy and Physiology Chapter 2 Reading Guide
Human Anatomy and Physiology
Chapter 2: The Chemical Foundation of Life
2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks
____________________ is any substance that occupies space and has mass.
______________ are specific types of matter with unique chemical and physical properties.
_______ naturally occurring elements with 118 recognized elements, some man made.
Four elements are common to all living organisms
_________________ (C)
_________________ (O)
_________________ (N)
_________________ (H)
The structure of the atom
___________ are the smallest part of an element that retains the properties of that element.
Atoms are made up of two regions
__________ – the center of the atom which holds the positively charged __________ and non-charged (neutral) __________. Protons and neutrons contribute to the total mass of the atom
____________________– is the outermost region where the negatively charged __________ are found, very little mass, 1/1800 of a proton.
Atomic Number and Mass
Atoms of a given element have a characteristic number of protons and electrons.
___________– the number of protons in the nucleus of an atom.
Each element has its own unique atomic number.
Each element has a variable number of neutrons which results in ___________. Atoms of the same element can vary in their number of neutrons.
______________________– the sum of the protons and neutrons in the nucleus of an atom.
______________________– the calculated mean of the mass numbers of the naturally occurring isotopes for a given element.
Isotopes
___________ are the different forms of an element that have the same number of protons but vary in the number of neutrons.
______________________ are isotopes that emit energy and particles in the process of radioactive decay to seek a more stable configuration.
The Behavior of Electrons
Atoms interact with other atoms to form ___________ by chemical bonding
In the electron cloud electrons occupy discrete areas of space called ___________.
Electrons also form discrete energy levels from the nucleus called ___________.
The shell closes to the nucleus can only hold a maximum number of___electrons
Once the first shell is full, the second shell can hold up to a maximum of_____electrons.
Once the second shell is filled the third shell will hold a maximum of 18 electrons.
______________________is the outermost shell of an atom. The number of electrons in this shell determines an atoms reactivity, the tendency by which it will form bonds with other atoms.
2.2 Chemical Bonds
A ___________ is an electrostatic attraction between atoms that holds them in the same general vicinity.
Two or more atoms with a stable chemical bond together form a ___________.
If the atoms are the same element, molecular hydrogen, or molecular oxygen, H2 or O2
If two or more atoms bonded are different elements, that is called a compound, H2O, CH4, NaCl; water, methane and table salt are compounds.
Types of Chemical Bonding
Ionic bonding
When an atom loses or gains one or more electrons it becomes an ion.
A ___________ is a positively charged ion, H+, Ca2+, or Al3+ it donates one or more electrons to another atom
An ___________ is a negatively charged ion O2-, Clꟷ, it accepts one or more electrons from an electron donor.
This results in an ionic compound held together by ionic bonding, Na+ Cl ꟷ
Covalent bonding:
Result from the sharing of one or more pairs of electrons between atoms
Sharing of electrons result in stable chemical bonds that are stronger than ionic bonds
Types of covalent bonds:
______________________– result from the equal sharing of electrons between atoms in a molecule.
E.g. H2, O2, and CO2
Polar Covalent Bonding:
Occur due to the unequal sharing of electrons in a molecule
Results in a molecule that will have regions of opposite charge
Best example is a molecule of water.
Hydrogen bonding
An interaction between a weakly positive hydrogen atom and a more electronegative atom (oxygen or nitrogen) in a different molecule.
______________________ form between water molecules (H2O) or molecules of ammonia (NH3).
Hydrogen bonds link the base pairs in a molecule of DNA.
Hydrogen bonds are responsible for secondary structure in protein molecules.
2.3 Chemical Reactions
The role of energy in chemical reactions
Energy is required for any chemical reaction to take place.
There are different types of energy.
______________________– energy available to do work, make things happen.
______________________– the energy stored in the chemical bonds of a molecule.
______________________– energy of motion, energy doing work, making things happen.
Chemical reactions that overall release energy is called ______________________
Chemical reactions that store energy in chemical bonds are called ______________________.
Types of Chemical Reactions
______________________– joins different substances together to produce a new substance. A + B →AB
______________________– breaks down a larger substance into two or more smaller substances. AB → A + B
______________________– a chemical reaction in which synthesis and decomposition occur simultaneously. AB + CD → AC + BD
Factors that influence the rate of chemical reactions
Properties of the reactants
Different elements are more reactive than others.
Atoms of the reactants have easy access to one another
Size of the reactants, smaller molecules will react faster than larger ones due to the number of chemical bonds involved.
Temperature
Temperature has a direct effect on reaction rates, the higher the temperature the faster the reaction occurs.
Concentration
The more particles in a specific area means the faster the reaction will occur.
Pressure
By decreasing the area increase the amount of force (pressure) pushing on the reactants, thus speeding up the reaction accordingly
Enzymes and other catalysts
___________– is any substance that can speed up a chemical reaction without being changed by the reaction.
___________ – biological catalysts composed of either protein or RNA molecules.
___________ – the amount of kinetic energy needed to start a chemical reaction.
Enzymes facilitate the chemical reactions of metabolism. Enzymes lower the activation energy requirement for a reaction to occur.
2.4 Inorganic Compounds Essential to Human Functioning
Inorganic vs Organic Compounds
______________________– any substance that does not contain carbon and hydrogen together.
E.g. HCl, H2O, CO2, NaCl, NaOH
______________________– any substance that contains carbon and hydrogen together and synthesized into covalent bonds.
The role of water in the functioning of the human body.
Water is essential to the functioning of the human body; it plays several important roles. Approximately, 70% of the adult human is made up of water.
Lubrication and Cooling
Heat sink – water cools the body and dissipates heat without a change in temperature.
Water is a component of liquid mixtures
All cells are kept moist by a water-based mixture called a ___________.
A solution is a mixture of___________dissolved into a ___________.
Water is the universal solvent of biological systems
The role of water in biological based chemical reactions
In biological systems water is either created or consumed by the reaction.
______________________reactions – create water by forming covalent bonds between different atoms. One reactant gives up a hydrogen atom (H) and the other a hydroxyl group (OH).
______________________– consumer water molecules by adding a hydrogen atom to one reactant and the hydroxyl group to the other reactant when breaking a covalent bond.
Salts
Salts are the products that form as a result of ionic bonding. When salts are dissolved in water, they dissociate into ions other than H+ and OHꟷ
Dissolved salts in solution are ___________, they can transmit electrical impulses
This is important for nerve cell conduction and muscle contractions.
Acids and Bases
Acids and bases dissociate into ions dissolved in solution. They are electrolytes and they change the properties of the solution they are dissolved into.
___________ – any substance that releases hydrogen ions into a solution.
A ______________________ is any acid that dissociates completely into ions in a solution.
E.g. include hydrochloric acid (HCl) and sulfuric acid (H2SO4)
A ______________________does not dissociate completely into a solution.
E.g. include acetic acid (vinegar) and citric acid.
___________ – any substance that releases hydroxide ions (OHꟷ) into solution or accepts H+ dissolved in solution.
A ______________________will dissociate completely into ions in solution
E.g. are sodium hydroxide (NaOH) or potassium hydroxide (KOH).
A ______________________does not dissociate complete into solution.
The concept of pH
The pH scale measures the relative acidity or alkalinity of a solution
pH = negative base 10 logarithm of the hydrogen ion concentration of a solution.
pH = ꟷ log10 [H+]
A solution with a pH of 4 is 10 times more acidic than a solution with a pH of 5
A solution with a pH of 10 is ten times more alkaline than a solution with a pH of 9.
Buffers
A buffer is a mixture of a weak acid and its conjugate base.
Buffers are important in living systems in minimizing pH changes by tying up any excess hydrogen or hydroxide ions in solution.
Buffers maintain acid-base balance or homeostasis.
2.5 Organic Compounds Essential to Human Functioning
The Chemistry of Carbon
Carbon atoms have a valence of four
They will share electrons with up to four different atoms forming stable covalent bonds, thus can form large structures with a carbon backbone.
Functional groups
Small grouping of atoms linked by covalent bonds, that similarly covalently bond with a carbon backbone.
Function together in chemical reactions as a single unit.
The functional groups most important to human physiology.
___________ (ꟷOH) are polar groups involved in dehydration and hydrolysis reactions
___________ (ꟷ ) components of fatty acids and amino acids
___________ (ꟷNH3) a component of amino acids
___________ (ꟷCH3) associated with fatty acids and amino acids
___________ (ꟷPO4) associated with phospholipids and nucleotides
Biological macromolecules
A structure with a carbon backbone that is made up of smaller repeating units called ___________. Biological macromolecules may also be called ___________.
Carbohydrates
A molecule with the basic chemical formula C(H2O)n which literally means watered carbon.
______________________ are the monomers of carbohydrates; they are also called simple sugars. Simple sugars are a source of energy for cells and tissues.
E.g. include glucose (C6H12O6) and fructose and galactose.
______________________ consist of two simple sugar molecules joined in a dehydration synthesis reaction.
E.g. include lactose (glucose + galactose), sucrose (fructose + glucose).
______________________ are the polymers of carbohydrates. They consist of hundreds and thousands of sugars joined. The storage form of carbohydrates and a structural component of plant cell walls.
E.g. include the starches amylose, amylopectin, glycogen, and cellulose.
Lipids
Are a source of energy for cells, they are hydrocarbon molecules with few oxygen atoms attached.
Types of Lipids
______________________ a common dietary lipid otherwise known as fat.
Formed from the synthesis of one ___________ molecule and three fatty acid molecules joined by dehydration synthesis reactions.
Fatty acids are long chains of hydrocarbons with a methyl group at one end and a carboxyl group at the opposite end
___________ Fatty acids have no carbon-carbon double bonds in the hydrocarbon tail.
___________ fatty acids will have one or more carbon-carbon double bonds in the hydrocarbon tail.
___________ – consist of a hydrophilic, phosphate head joined to two hydrophobic fatty acids. They create the phospholipid bilayer structure of all cell membranes.
___________ consist of four fused carbon rings. Cholesterol is the base steroid of animal systems, they maintain the integrity of cell membranes, provide the foundation for steroid hormones, and compose bile salts.
___________ – are derived from unsaturated fatty acids that serve as a signaling mechanism, they regulate blood pressure and inflammation and sensitivity to pain.
Proteins
Proteins make up the structure of hair, keratin of skin, collagen of bones, the meninges covering the brain and spinal cord. They also function as enzymes inside cells.
Proteins are a polymer made up of monomers called ______________________.
All amino acids have the same basic structure
An amino group attached to a central carbon atom called the alpha carbon.
A hydrogen atom attached to the alpha carbon
A carboxyl group attached to another side of the alpha carbon
An R group attached to the fourth side; the R group is unique to each amino acid. There are 20 different amino acids that make up the proteins of the human body.
Amino acids link together by peptide bonds, a covalent bond between the amino group of one amino acid and the carboxyl group of the adjacent amino acid by dehydration synthesis reactions.
The basic amino acid structure. Each amino acid has its own unique side chain or R group.
Amino acids join by covalent bonds called peptide bonds. Each peptide bond results in the formation of a water molecule
Shape of proteins
A protein’s shape is crucial to its function. If the protein does not have the correct shape it does not function.
The shape of the protein is initially determined by the sequence of amino acids in a polypeptide chain, this is called ______________________.
______________________is the polypeptide chain twisting to another shape called an ___________ helix or ______________________sheet.
The secondary structure further folds into a 3-D shape called ______________________. Disulfide bridges covalent link different cysteine residues in a single polypeptide chain. Hydrogen bonds and other interactions help maintain a proteins 3D shape.
When proteins are exposed to high heat or drastic changes in pH, they will lose their shape, which is called ______________________.
Nucleotides – are the building blocks of DNA and RNA and certain other molecules such as ATP, NADH, NADPH.
Each nucleotide is made up of three subunits
Pentose sugar
Nitrogen containing base
Phosphate group
______________________ are made up of nucleotides. The two nucleic acids DNA and RNA only differ in the type of pentose sugar associated with their nucleotides.
Nucleotides are organized into two groups
Purines (adenine and guanine)
Composed of a double ring structure with several nitrogen atoms covalently bonded together.
Pyrimidines (cytosine, thymine, and uracil)
Nitrogen containing bases with a single ring structure.
Chapter 2: The Chemical Foundation of Life
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oercommons
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2025-03-18T00:38:19.086932
|
Bryon Spicci
|
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"url": "https://oercommons.org/courseware/lesson/72073/overview",
"title": "Chapter 2 Reading Guide",
"author": "Lecture Notes"
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https://oercommons.org/courseware/lesson/73498/overview
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Fig 1.12 Regions of the Human Body (no labels, no lines)
Overview
Testable image from section 1.6 of OpenStax Anatomy and Physiology. Stripped-away the boxes and lines.
1.6 Anatomical Terminology - Body Regions
Here is an edited version of the testable image provided in the OpenStax Anatomy and Physiology textbook. I removed all the boxes and lines.
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oercommons
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2025-03-18T00:38:19.106038
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Chris Baker
|
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/73498/overview",
"title": "Fig 1.12 Regions of the Human Body (no labels, no lines)",
"author": "Assessment"
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https://oercommons.org/courseware/lesson/65748/overview
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Introduction to OER Search
OER Student Advocacy Toolkit 2020 - docx version
OER Student Advocacy Toolkit 2020 - pdf version
Sample Student Survey
Style Guide
OER Student Advocate Toolkit
Overview
This toolkit was created by OER student leaders in the CCC and CSU systems. The toolkit's purpose is to motivate students to get involved in OER advocacy and the Open Education movement, as well as make it known that students can make a difference in their education. Education costs can be cut to a fraction of the price with OER, which would allow for more students to be able to access knowledge and higher education. While this toolkit contains some examples and suggestions specific to California institutions, it can still be helpful for all college students.
Thanks to the Michelson 20MM Foundation's financial support students were paid for their work and contributions in creating this document, as well as presenting at conferences.
OER Student Advocate Toolkit publication
This toolkit was created by OER Student Advocate Leaders in the California Community College (CCC) System and the California State University (CSU) System. The toolkit's purpose is to motivate students to get involved in OER advocacy and the Open Education movement, as well as make it known that students can make a difference in their education. Education costs can be cut to a fraction of the price with OER, which would allow for more students to be able to access knowledge and higher education. While this toolkit contains some examples and suggestions specific to California institutions, it can still be helpful for all college students.
There are two versions: docx for easy editing and pdf.
Thank you to the Michelson 20MM Foundation for generous support for this project.
Appendix/Supplemental Materials Files
These files are referenced in the OER Student Advocate Toolkit:
- Introduction to OER Search
- Inkscape PowerPoint
- Student Survey
- Style Guide Packet
The files are uploaded in this section and also currently available via the following URLs:
- https://drive.google.com/file/d/15Nrm_ndX_9vUwEKsUv0qdkEqn5291wN2/view
- https://drive.google.com/drive/folders/1dwuOAFbN5COByeMm3Y4DGLEaGO83u9Dl
- https://drive.google.com/drive/folders/1E9SrcQOW1OtUeO13Lvc1ehHkQC8hsNS1
- https://drive.google.com/drive/folders/1U-MKN5dvGI6fLQEkm224H4UvvrvvJ-lI
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oercommons
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2025-03-18T00:38:19.132629
|
Full Course
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{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/65748/overview",
"title": "OER Student Advocate Toolkit",
"author": "Public Relations"
}
|
https://oercommons.org/courseware/lesson/92786/overview
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Open Textbooks for Rural AZ Publishing Template
Overview
Open Textbooks for Rural Arizona participants are invited to remix this template to share their courses, textbooks, and other OER material on our Hub.
How To Remix This Template
Open Textbooks for Rural Arizona participants are invited to remix this template to share their courses, textbooks, and other OER material on our Hub. Please follow the steps below:
- Login and click the remix button on this resource to create your own version.
- Change the title to describe your specific material.
- Insert a description of the material(s) you are sharing and your recommendation of how other faculty can adapt and use in their class.
- Insert a public link to access the material. Please be sure the setting are for public access so others can view and/or download the material. For example, if sharing through Canvas, be sure the material is shared through the Canvas Commons.
- Attach the file in the native format of the software program that you used. For example:
- If you are creating ancillary materials using Google slides or MS Word then you would upload the .odp file or a MS Word .docx file.
- If you are creating a Canvas or Moodle course, you would upload the common cartidge file.
- Please note, the more course files formats you can provide, the easier it will be for all users to access it.
- Delete this section and instructions in other sections before publishing.
- When ready to publish, click next to update the overview, license, and description of your resoucrse, and then click publish.
Material Description
Add your material description here including the course name and number, and learning outcomes.
Add a public link to the material here. Please be sure the setting are for public access so others can view and/or download the material. For example, if sharing through Canvas, be sure the material is shared through the Canvas Commons.
Attached your syllabus (if applicable) here by clicking the Attach Section paperclick image below, then choose the correct file form from your computer, name your syllabus, and save.
Material Attachement
Attach the resource here by clicking the Attach Section paperclick image below, then choose the correct file form from your computer, name your material(s), and save.
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oercommons
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2025-03-18T00:38:19.169843
|
Lecture Notes
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/92786/overview",
"title": "Open Textbooks for Rural AZ Publishing Template",
"author": "Lecture"
}
|
https://oercommons.org/courseware/lesson/113511/overview
|
Chapter 7 Lecture Guide to Accompany Open Stax Anatomy and Physiology
Overview
This lecture outline accompanies the chapter 7 PowerPoint for Open Stax Anatomy and Physiology 2E.
Chapter
7.1: Divisions of the Skeletal system
- The ____________ consists of the 206 bones of the adult body.
- The skeletal system is the skeleton, cartilage, and ligaments that support and shape the body.
- Functions of the skeletal system
- Provide a rigid internal structure that can support the body's weight against the force of gravity.
- Provide a structure upon which muscles can act to produce body movements
- Protection of internal organs
- Primary sites for storage of minerals
- Stores fat, houses the blood-producing tissues of the body
- The two major divisions of the skeleton:
- ___________
- Forms the vertical, central axis of the body
- Includes the bones of the head, neck, chest, and back
- Protects the brain, spinal cord, heart, and lungs.
- Serves as the attachment site for muscles that move the head, neck, and back.
- Includes the ______, the __________ column, (__________ (24 bones), _________ and ___________) and the ____________ cage (12 pairs of ribs and sternum).
- Other structures included are the ___________ bone, and ear ____________.
- __________________________________
- Bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton
7.2 The Skull
- ___________ – protects the brain and supports the face
- _________ bones
- Underly facial structures
- Form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws
- _________ case (cranial vault)
- Surrounds and protects the brain and houses the middle and inner ear structures.
- The skull consists of 22 individual bones
- Twenty-one is immobile and united into a single unit.
- The 22nd bone is the ________________ (lower jaw), which is the only movable bone of the skull.
Anterior View of Skull
- _________ – bony socket that houses the eyeball, and muscles of the eye and upper eyelid.
- _________________ margin – Upper margin of the anterior orbit.
- __________________ foramen – located at the midpoint of the supraorbital margin, provides passage for a sensory nerve to the skin of the forehead.
- __________________ foramen – located below the orbit, the point of emergence for the sensory nerve that supplies the anterior face below the orbit.
- ________ cavity – located inside the nasal area of the skull.
- ________ septum – divides the nasal cavity into halves, formed by the:
- _______________ plate of the ethmoid bone (superior portion)
- ________ bone – forms the inferior portion of the nasal septum.
- ________ nasal ________ - large bony plate projecting from each lateral wall of the nasal cavity (independent bone of the skull)
- ________ nasal concha – located above inferior nasal concha, part of ethmoid bone.
- ________ nasal concha – smaller and out of sight above the middle concha, just lateral to the perpendicular plate in the upper nasal cavity
Lateral View of Skull
- _______________ arch – an arch of bone on the side of the skull from the cheek to above the ear canal.
- Formed by two processes
- Temporal process of the zygomatic bone – a short anterior component that forms the cheekbone
- Zygomatic process of the temporal bone – extends forward from the temporal bone to join the temporal process
Bones of the Brain Case
- Cranial cavity – interior cavity occupied by the brain.
- Calvaria – skullcap,
- The floor of the braincase is referred to as the base of the skull.
- It is subdivided into three large spaces.
- Anterior cranial fossa
- Middle cranial fossa
- Posterior cranial fossa
- The braincase consists of eight bones.
- ________– upper lateral side of the skull, paired bones with right and left sides.
- ________ forms the lower lateral side of the skull
- Landmarks of the temporal bone
- ________ acoustic meatus – ear canal
- ________ acoustic meatus – connects the middle and inner ear cavities.
- ______________ fossa – mandible joins the jaw
- ________ tubercle – located anterior to the mandibular fossa, contributes to the temporomandibular joint with mandibular fossa
- ________ process - attachment site for muscles and a ligament that supports the hyoid bone.
- ________________ foramen – small opening between the styloid and mastoid processes.
- ________ process – considerable prominence which serves as a site for muscle attachment.
- ________ ridge – located in the floor of the cranial cavity, houses the structures of the middle and inner ears
- ________ canal provides passage through the base of the skull for the carotid artery.
- ________ bone forms the forehead
- ________ – slight depression between the eyebrows.
- Forms the supraorbital margin of the orbit
- ________ bone – the single bone that forms the posterior skull and posterior base of the cranial cavity
- External occipital protuberance – serves as an attachment site for a ligament.
- Superior nuchal line – the most superior point of attachment of neck muscles
- Foramen magnum – a large opening that allows the spinal cord passage as it exits the skull.
- Occipital condyles – form joints with the first cervical vertebra and support the skull on top of the vertebral column.
- ________ bone serves as the keystone of the skull and forms much of the base of the central skull.
- Lesser wings – mark the boundary between the anterior and posterior fossa.
- Sella turcica (Turk's saddle)
- Hypophyseal (pituitary) fossa houses the pituitary gland.
- Greater wings
- Medial and lateral pterygoid plates
- Right and left medial pterygoid plates to form the posterior, lateral walls of the nasal cavity.
- The lateral pterygoid plates serve as muscle attachment sites
- ________ bone – single midline bone, forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, and the medial wall of the orbit.
- Crista Galli – bony projection serves as the anterior attachment point for the dura mater.
- Cribriform plate – contains olfactory foramina; small nerve branches from the olfactory areas pass through these on the way to the brain.
- Ethmoid air spaces part of the paranasal sinus system
Sutures of the Skull
- ________ – immovable joint between adjacent skull bones.
- The coronal suture runs from left to right across the skull within the coronal section plane, joining the frontal and paired parietal bones.
- The sagittal suture extends posteriorly from the coronal suture, running along the midline at the top of the skull, unites the paired parietal bones
- Lambdoid suture joins the occipital bone to the right and left parietal and temporal bones.
- Squamous suture on the lateral skull unites the squamous portion of the temporal bone with the parietal bone.
- Pterion: a small H-shaped suture that unites the frontal, parietal, temporal, and greater wing of the sphenoid bone.
Facial Bones of the Skull
- ________ bone – (maxilla (plural = maxillae)) forms the upper jaw, most of the hard palate, the medial floor of the orbit, and the lateral base of the nose.
- Alveolar process of the maxilla
- The curved inferior margin that forms the upper jaw and contains the upper teeth.
- Infraorbital foramen – located on the anterior maxilla just below the orbit, the point of exit for a sensory nerve
- Palatine process – located on the inferior skull join at the midline to form the hard anterior palate.
- Hard palate – a bony plate that forms the roof of the mouth and floor of the nasal cavity.
- ________ bone – includes the lateral walls of the nasal cavity and medial wall of each orbit.
- _______________ bone is also known as the cheekbone, forms much of the lateral wall of the orbit and lateral–inferior margins of the anterior orbital opening. The short temporal process projects posteriorly to include the anterior portion of the zygomatic arch
- ________ bone – one of two small bones that form the bridge of the nose
- ________ bone forms the anterior, medial wall of each orbit.
- Nasolacrimal canal – tears of eye drain at the medial corner of the eye into this canal
- ___________ nasal concha – a curved bony plate that projects into the nasal cavity space from the lower lateral wall. The largest of the nasal concha.
- ________ – an unpaired bone forms the posterior-inferior part of the nasal septum.
- ________forms the lower jaw and the only movable bone of the skull
- The ramus of the mandible is the posterior, vertical orientation of the lower jawbone.
- The angle of the mandible – where the body and ramus come together
- Coronoid process – the anterior projection provides attachment for biting muscles
- The condylar process is the posterior projection of the mandible, which is topped by the oval-shaped condyle.
- Alveolar process – the upper border of the mandibular body serves to anchor the lower teeth
- Mental protuberance – the chin
- Mental foramen – exit site for a sensory nerve
The Orbit
- The bony socket that houses the eyeball and contains the muscles to move the eyeball or open the upper eyelid.
- The walls of the orbit are formed from seven bones
- The frontal bone forms the roof
- Zygomatic bone forms the lateral wall and lateral floor.
- Maxilla forms the medial floor
- Palatine helps form the medial floor
- Ethmoid and lacrimal bones make up the medial wall.
- Sphenoid bone forms the posterior orbit
- The ________ canal allows the passage of the optic nerve from the retina to the brain.
- The ________ orbital fissure provides passage for the ophthalmic artery, sensory nerves, and motor nerves for eye movements.
The Nasal Septum and Nasal Concha
- Composed of bone and cartilage
- Formed by the perpendicular plate of the ethmoid and vomer bones
- ________ cartilage fills in the gap between the ethmoid and vomer bones and separates the left and right nostrils.
- ________ conchae (superior, middle, and inferior)
- Bony plates curve downward, swirl incoming air, warm and moisturize incoming air
Cranial Fossae
- Divide the floor of the cranial cavity into three spaces
- ________ cranial fossa – most anterior and the shallowest
- Overlies the orbits and contains the frontal lobes of the brain
- ________ cranial fossa – deeper and posterior to the anterior fossa
- Extends from the lesser wings to the petrous ridges.
- Has the following openings:
- ________ canal provides a passageway for the optic nerve.
- Superior orbital ________ allows passage of nerves
- Foramen ________ – exit point for sensory nerve
- Foramen ________ – passage for sensory nerve
- Foramen ________ – passageway for a vital artery
- ________ canal – a passage for the internal carotid artery
- Foramen lacerum
- Posterior Cranial Fossa
- The deepest portion of the cranial cavity.
- Contains the foramen ________
- Hypoglossal ________ – passageway for cranial nerve XII
- ________ foramen – passageway for several cranial nerves and veins that return blood from the brain.
- Paranasal Sinuses
- Hollow air-filled spaces located within certain bones of the skull
- Communicate with the nasal cavity and are lined with nasal mucosa
- Reduce bone mass, lighten the skull, and add resonance to the voice.
- ________ sinus is located above the eyebrows within the frontal bone.
- ________ sinus – the most prominent sinus, which is paired and located within the left and right maxillary bones
- ________ sinus – single midline sinus located within the sphenoid bone
- ________ air cells – multiple small spaces separated by fragile bony walls. It is located on both sides of the ethmoid bone.
Hyoid bone
- An independent bone that does not articulate with any other bone.
- Located in the upper neck near the level of the inferior mandible
- Serves as the base for the tongue and is attached to the larynx and pharynx.
7.3 The Vertebral Column
Also known as the spinal column or spine
It consists of a sequence of vertebrae, each separated by an intervertebral disc.
It supports the head, neck, and body and allows their movements.
It protects the spinal cord, which passes down the back through openings in the vertebrae.
Regions of the Vertebral Column
- 24 vertebrae, plus sacrum and coccyx
- Five regions
- Neck – 7 cervical vertebrae designated C1 – C7
- Upper back – 12 thoracic vertebrae designated T1 – T12
- Lower back – 5 lumbar vertebrae designated L1 – L5
- Sacrum – the fusion of five sacral vertebrae
- Coccyx – tailbone results from the fusion of three to four coccygeal vertebrae.
Curvatures of the Vertebral Column
- Four curvatures along its length increase the column's strength, flexibility, and ability to absorb shock.
- Primary and Secondary curvatures
- Primary curves are retained from the fetal curvature
- ________ curve involves the thoracic vertebrae
- __________________l curve forms by the sacrum and coccyx
- Secondary curves develop after birth, opposite to the original fetal curvature.
- ________ curve (neck region) develops as the infant begins to hold its head upright when sitting.
- ________ curve (lower back) develops as the child begins to stand and walk. Generally deeper in females
- Disorders in spinal curvatures
- ________ (hunchback) excessive posterior curvature of the thoracic region.
- ________ (swayback), an excessive anterior curvature, happens in pregnant women before childbirth or in obesity.
- ________ – an abnormal lateral curvature accompanied by twisting of the vertebral column.
General Structure of a Vertebra
- ________ – anterior portion that supports the body weight. Increase in size and thickness going down the vertebral column
- _______________ discs separate the bodies of individual vertebrae.
- ________l arch - forms the posterior portion of each vertebra.
- Left and right ________
- Each pedicel forms one of the lateral sides of the vertebral arch
- Left and right ________
- Each lamina forms part of the posterior roof of the vertebral arch.
- ________ foramen – a large opening that contains the spinal cord
- Vertebral foramina align to form the vertebral (spinal) canal
- _______________ foramen – openings through which a spinal nerve exits from the vertebral column.
- __________ process – projects laterally and arises from between the pedicel and lamina
- ________ process – projects posteriorly at the midline of the back
- Superior articular ________ faces upward joins with the i________ articular process of the next higher vertebra
Regional Modifications of Vertebrae
- Cervical vertebrae
- Small body, carry the least amount of weight
- ____________ foramen – found in the transverse processes of cervical vertebrae, carry the vertebral artery up into the brain
- Flatter superior and inferior articular processes
- C1 vertebrae (atlas) do not have a body or spinous process
- Ring-shaped, consisting of an anterior and posterior arch.
- C2 vertebra (axis) is the axis of left-right rotation and contains the dens (odontoid process)
- Thoracic vertebrae
- Larger bodies than cervical vertebrae
- The spinous process is more prolonged and points downward
- Have several additional articulation sites.
- ________ – point of rib attachment
- ________ facets located on the lateral sides of each body of a thoracic vertebra
- Lumbar vertebrae
- Carry the most weight and have extensive and thick vertebral bodies.
- Large, articular processes, superior faces backward and inferior faces forward
Sacrum and Coccyx
- Sacrum
- Triangular-shaped bone, thick and wide, formed by the fusion of five sacral vertebrae
- Features
- Median sacral ________ – a bumpy ridge that is the remnant of fused spinous processes found on the posterior surface on the midline.
- ________ sacral crest – fused transverse processes
- ________ promontory – the anterior lip of the superior base of the sacrum
- Sacral ________l – a bony tunnel passing through the sacrum
- Sacral ________s – inferior tip of the sacrum
- Sacral __________a – series of paired openings (posterior and anterior) allow for the passage of the sacral spinal nerves
- Superior ___________ process articulates with the inferior articular process of the L5 vertebrae
- Coccyx
- The tailbone is derived from the fusion of the four tiny coccygeal vertebrae
- Articulates with the inferior tip of the sacrum
Intervertebral Discs and Ligaments of the Vertebral Column
- Intervertebral Disc
- A fibrocartilaginous pad that fills the gap between adjacent vertebral bodies.
- Anchored to the bodies of its adjacent vertebrae
- Provide padding between vertebrae
- Thinner in the cervical region and thickest in the lumbar region
- Two parts
- ________ fibrosis - is the tough fibrous outer layer
- ________ pulposus - softer, more gel-like material with high water content.
Ligaments of the Vertebral Column
- ________ longitudinal ligament – runs down the anterior side of the vertebral column, resists excess backward bending of the vertebral column
- ___________________ ligament – located on the posterior side of the vertebral column. It interconnects the spinous processes of the thoracic and lumbar vertebrae
- ________ ligament – attached to the cervical spinous processes and extends upward and posteriorly to the midline base of the skull
- __________ longitudinal ligament – attached to the posterior sides of the vertebral bodies
- Ligamentum ________ – Short, paired ligaments that interconnect the lamina regions of adjacent vertebrae.
7.4 The Thoracic Cage
The thoracic cage consists of 12 pairs of ribs with their costal cartilages and the sternum.
It protects the heart and lungs
- Sternum
- Elongated flat bone that anchors the anterior thoracic cage
- Three parts
- ____________ – more comprehensive, superior portion
- __________ (suprasternal) notch – shallow U-shaped border
- __________ notch – a shallow depression located at either side of the superior-lateral margins of the manubrium
- ________ angle joins the manubrium to the body
- ________ – elongated central portion
- __________ process – the inferior tip of the sternum
Parts of a Typical Rib
- ________ - the posterior end of a typical rib
- Articulates with the costal facet of a thoracic vertebrae
- ________ – lateral to the head
- ________ – articulates with the facet located on the transverse process of the vertebrae.
- ________ – the remainder of the rib
- ________ – lateral to the tubercle, the point at which the rib has the most significant degree of curvature, forming the most posterior extent of the thoracic cage
- ________ groove – a shallow passageway for blood vessels and nerves
Rib Classifications
- ________ cartilage – ending of each rib made of hyaline cartilage, attach ribs directly or indirectly to the sternum.
- ________ ribs – are ribs 1 – 7 (vertebrosternal ribs). Attach directly to the sternum by costal cartilage.
- ________ ribs – are ribs 8 – 12 (vertebrochondral ribs). Costal cartilage from these ribs does not attach directly to the sternum.
- For ribs 8 -10, the costal cartilages are attached to the cartilage of the next higher rib.
- __________ ribs – false ribs 10 – 12. These short ribs do not attach to the sternum at all.
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oercommons
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2025-03-18T00:38:19.312235
|
02/27/2024
|
{
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"url": "https://oercommons.org/courseware/lesson/113511/overview",
"title": "Chapter 7 Lecture Guide to Accompany Open Stax Anatomy and Physiology",
"author": "Bryon Spicci"
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|
https://oercommons.org/courseware/lesson/112222/overview
|
https://www.satscorecalculator.us/digital-sat-score-calculator.html
SAT Score Calculator And Digital SAT Score Calculator
Overview
The Best New SAT Score Calculator For Students Who Want To Calculate SAT Score And Digital SAT Score. Accurate SAT Score results will Be Show To You. Also, We Have The Best New Digital SAT Score Calculator For Students. Each test is scored on a scale of 200 to 800; However, in some tests, it was not possible to achieve 200 points. For example, if someone gets every question wrong on a Level 2 math test, he or she could receive 310 points depending on the curve of that test. The exception was the ELPT, which was scored on a scale of 901 to 999. In addition, the foreign language tests, which included both reading and listening, gave average scores for both, between 20 and 80.
SAT Score Calculator
if You Are a Student Then You Are in the right place to calculate Your SAT Score and Digital Score. Here In This SAT Score Calculator, You Can Find The Features And Options to Calculate Your SAT Score And Digital SAT Score. As College Board Announces SAT Score Paper Exam Will Convert To Digital SAT Score In 2024. Here In This Digital SAT Score Calculator, You Can Check Your Digital SAT Score With Digital SAT Percentile.
Before the new SAT Reasoning Test (which included a writing portion) was first released in March 2005, some colleges required applicants to take three SAT subject tests, including a writing test and two other tests of the applicant's choice. on SA. However, when writing became a standard part of the SAT Reasoning Test, most colleges recommended that applicants submit scores from one of the two SAT Subject Tests. Technical schools may recommend or require Level 2 in Chemistry Physics and Mathematics. None of the schools required three-subject exams, and Georgetown was the only school that "strongly recommended" three-subject exams.
Caltech, which previously required subject tests, will no longer require or consider them starting in 2020.
Schools also disagreed on whether students should take the ACT instead of the SAT: Some schools considered the ACT as an alternative to the SAT and some SAT subjects, while others accepted the ACT but required subject tests. as an alternative to the SAT. ACT Score Calculator Good. Information about the school's special testing requirements can usually be found on the school's official website.
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oercommons
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2025-03-18T00:38:19.332837
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02/04/2024
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{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/112222/overview",
"title": "SAT Score Calculator And Digital SAT Score Calculator",
"author": "Warma Kajoki"
}
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https://oercommons.org/courseware/lesson/119788/overview
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Project Kickoff and Rubric
Project Partner Evaluation Form
Half-Semester Student Projects Focused on Complex Problems
Overview
This resource is a step-by-step guide to mentoring students through a half-semester project focused on a complex social or environmental issue. Based on the project portion of my course, Designing the Future World, students are assisted to select a topic important to them and develop a proposed intervention which they present at an open house at the end of the semester.
Overview
This resource is a step-by-step guide to mentoring students through a half-semester project focused on a complex social or environmental issue. Based on the project portion of my course, Designing the Future World, students are assisted to select a topic important to them and develop a proposed intervention which they present at an open house at the end of the semester.
Discipline
This project can be used in many discipline-based courses. It is perhaps best suited for problem- and project-based learning and interdisciplinary approaches. I'm a social scientist and have used it for interdisciplinary courses focused on complex social and environmental problems.
Learning Objectives
Identify complex problems ("wicked problems") with social and environmental significance, and describe how these problems might be remediated by purposeful human design activity.
Use “Design Thinking” and critical thinking skills to select a complex problem of social and/or environmental significance and plan a design approach to the selected problem.
Following one of the design processes we have studied, design and execute a “concept prototype” for a device or policy that addresses the complex problem you have selected.
Reflect on what you have read, discussed, and done in the course, and how it may contribute to shaping your future behavior, career path, and/or ethical commitments.
Class size range
This half semester mentored project is attention intensive for the instructor (but also really fun and interesting). I have had a maximum of 24 students per class (and students work in pairs, so 12 projects). Unless the instructor has good teaching assistants I would say that is a maximum because of the amount of coaching and feedback necessary.
Time needed
I begin this process at the half-semester mark, and from then on, about half of all class meeting time each week is devoted to the project. Students are reporting weekly either to the whole class or in brief meetings with the instructor to get feedback and shape their project.
Materials Needed
- Display boards for the final meeting of the semester, during which students display their project, including a poster-style explanation of the problem they are addressing and their proposed intervention.
- Each two-student team is also required to create a "concept prototype" to illustrate the intervention they propose. Since each artifact will be unique to the students creating it and their intentions, there is no set list of materials. I taught in a room with access to lots of craft materials, but this is not strictly necessary. Students can obtain their own materials; I started offering $20 to each team with a demonstrated need to purchase supplies, which can be useful in a setting with low income students.
- One way to add meaning to the challenge of making an artifact, which is a required part of the assignment, would be to require student to use scrap and recycled materials wherever possible, teaching an additional lesson in sustainability.
Lesson Instructions
This week-by-week breakdown assumes a 13 or 14 week semester. You can either start earlier if your semester is shorter, or compress the weeks.
Week 1. Introduction to the project. Describe the half-semester project. Give students a handout with the assignment and the rubric you will use to evaluate the project. Give students 2 minutes to think about what important social, economic, environmental, etc issue they would be interested in working on--either one we have studied or something else they care about. Tell them they will have time to make a final decision in the coming week or even two, so no absolute commitment is needed today. Find partners. I had students work in pairs. This worked well. It meant the work was not the product of one mind alone (which improved it) and reduced the danger of slacking off by a team member. To assist with forming teams I ran a quick "Speed Dating" exercise (although I avoided calling it that). All the students stood up and found someone in the room to talk to (preferably someone they didn't know already). They had one minute to tell their partner what they were interested in as a project topic, then one minute to listen to their partner's ideas. Then they found another partner. I repeated this 3 or 4 times. If there was an odd number of students in the class I partnered with one student, or sometimes I allowed one group of 3. Some students will want to work with their friends, roommates, etc and I do allow this, but I also encourage them to be openminded and find people who share their interests. Form teams. Next I hand out the assignment for the coming week, which asks students to report on who is on their team, and how they have made plans to stay in touch. It also asks them to list four topics that are of greatest interest to them, why they are interested, and some very preliminary thoughts about what they might do to address each topic. I also hand out a copy of the form I will ask them to fill out at the end of the course, evaluating their partner, so that they will have a sense of what I expect and that I will want to know how the partnership went. After all of this, I leave the last 15 minutes or so of the class for them to talk among themselves and try to form partnerships. If they have successfully found a partner, they report this to me before leaving. Anyone who has not found a partner by the end of class (including anyone who is absent) is assigned a partner by me.
Week 2. Meeting with each team. The project portion of this class session is devoted to individual meetings with each team. Teams sign up for 5 minute sessions of feedback from me. When not meeting with me, students work with their partners to further develop and research their ideas. When meeting with a team, I look at the homework (their thoughts and plans for the project) and give them feedback. I ask if they have a favorite topic. Some topics and approaches fit far better with this project than others; for example highly technical projects (eg. improved storage of nuclear waste) are not a good fit. Usually I will have to urge the pair to narrow down and become much more specific (instead of "ending homelessness," finding a particular need of the local homeless population and trying to address it). Occasionally the team has fixated on a particular solution already and I urge them to broaden their thinking, especially if the idea seems infeasible or inappropriate. Most of the time, though, it's narrowing the focus that is needed,
Week 3. Two minute slide shows. The assignment for today, for each team, is to present a two minute slide show about their project to the class. I stress that they are presenting work-in-progress and that they are not bound by what they present, but that it's a chance to show where they are in the process and get feedback from their fellow students and from me. Each team is tasked with addressing the following questions in their slide show:
What is the “wicked problem” or need you have selected to address?
Why is this problem important?
What relevant information have your gathered so far? (Be sure to include sources/references in small type on your slide.) What additional information do you hope to collect?
What sort of project artifact are you currently planning to create? Describe and/or show an illustration.
What sorts of information do you plan to include on your project display board?
Last week, teams met with me privately; this week they go public by presenting to their fellow students. Students seem to enjoy knowing what others are working on and following their evolution; occasionally two teams are working on similar things and I can help guide them to different aspects of the same topic so that they are not working on precisely the same problem.
If there is time left over, I do a fun Playfulness exercise (the reading assignment for this week, from the Bernstein and Bernstein book Sparks of Genius, is on playfulness in creativity and design). I invite students to get out Lego, modeling clay, craft materials, etc from the cupboards and work on answering the question: "What if your project were a map, a son, a dance, a pantomime (Charades), a toy, a poem, a quiz show, or a pun? What would it look/sound like?"
Week 4. Project work session. This class is dedicated to students working with their partner on their project, plus brief 5 minute consultations with me, as in Week 2. The project deliverables are 1) a display board/poster explaining the problem they selected and the intervention they are proposing, 2) an artifact that is either a concept prototype of a device, or some other interactive representation (a quiz that visitors can take, for example), and 3) an "elevator pitch" that they can recite at the end-of-semester open house to tell visitors succinctly what their project is about. At this class they get blank display boards and start mocking up what their boards will look like and what text they will use. I give them handouts about the design process and about what makes for a good display board (large type, color, some images). Once again teams sign up on the whiteboard for a 5 minute meeting with me, but most of their time is spent working together on aspects of their project.
Week 5. Project work session. The homework for today is to bring a printed draft of the text and images the teams plan to use on their display boards, and evidence of significant progress on their artifact. Not all students have access to color printing, so some of this class is devoted to giving them the opportunity, with the printer in the classroom, to print the final version of their display board text (which they can then glue to the display board). I spend my time reading their drafts and circulating as they work, to answer questions and give feedback. This is the final in-class work opportunity before student present a substantially finished project to their fellow students next week.
Week 6. In class project presentation. Each team in turn presents their project to their fellow students. Due today was a script for an "elevator pitch," a 60-second monologue about the problem and their team's approach to improving the situation they have been researching. Unlike the assignments in previous weeks, which both team members have collaborated on and submitted jointly, each person writes their own elevator pitch in their own voice, emphasizing the things they find most important. I don't require students to memorize or recite their pitch verbatim--I just want them to have thought through what they most want to say in the brief time they have. When presenting today, each student speaks for 60 to 90 seconds. I tell them not to worry about overlap between what they say and what their partner says. The purpose of this exercise is to prepare them for next week's open house, when they and their partner might speak separately to visitors. This also gives them a "preliminary deadline" for project completion, so that they don't leave everything until the last minute. After all teams have presented, students can use any time left to put finishing touches on their project. Ideally, by the end of class all projects will be complete and ready for next week's open house.
Week 7. Open House. The class open house is a public event, which I publicize with posters and announcements in the university newsletter. I tell students to invite their friends and family (and a few actually do). When a student entrepreneurship program was created on campus, I started inviting the three staff people from the program. They were among the best visitors, because they really took time giving feedback for each project, and they also encouraged the teams to continue their work past the end of the course, using the resources of the entrepreneurship program. The open house was almost universally loved by the students--even those who really didn't want to participate discovered how much they had accomplished when they saw the interest their project attracted from visitors.
Designing the Future World was my favorite course to teach, and the project was my favorite part of the course. Generally, students loved being able to pursue what they were interested in and being able to shape the project in the way they wanted, with guidance from me to make sure they didn't go off the rails. Each year a few students would volunteer that this was their favorite course, either this semester or during their whole college career. I am willing to bet that they remembered the course and the project longer than they remembered most other academic things from college, in part because they were thinking with things and making something original to them.
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oercommons
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2025-03-18T00:38:19.365486
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Module
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"url": "https://oercommons.org/courseware/lesson/119788/overview",
"title": "Half-Semester Student Projects Focused on Complex Problems",
"author": "Lesson Plan"
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https://oercommons.org/courseware/lesson/76794/overview
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Master Your Mind
Overview
Video on improving mental health by using this acronym.
Video on improving mental health by using this acronym
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oercommons
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2025-03-18T00:38:19.382971
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01/29/2021
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/76794/overview",
"title": "Master Your Mind",
"author": "Rhonelee Soria"
}
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https://oercommons.org/courseware/lesson/67463/overview
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Challenges and Rewards of a culturally-informed approach
Cultural Competence Continuum
Cultural Competency: A Systematic Review of Healthcare Provider and Educational Interventions
Empathy
Impact of Culture and Ethnicity on Sexual and Sexual Function
Learning Disabilities and Ethnicity
Respect for Diversity
Self-assessment Checklist
Understanding Culture and Diversity
Want a More Just World?
Why Cultural Diversity Matters
Workshop to Explore Cultural
Overview
In this workshop participants will be able to discuss cultural sensitivity and learn to embrace diversity. Cultural blindness — being “fair” by treating everyone the same is often hard to view as problematic. Discussion in this workshop will focus on inspiring students to understand different cultures and beliefs as well as the importance of culturally sensitivity to these different beliefs. This workshop will encourage participants to; explore their own biases, consider different points of view and will utilize cultural lenses to develop cultural sensitivity.
Introduction to Cultural Sensitivity
Discuss: What's the Difference? Cultural Competence, Awareness, and Sensitivity
Administer the survey before the students engage in the workshop and upon completion of the workshop. Click here to take the Survey
What is Cultural Sensitivity?
Let's Discuss Cultural Sensitivity?
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oercommons
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2025-03-18T00:38:19.411953
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Diagram/Illustration
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"url": "https://oercommons.org/courseware/lesson/67463/overview",
"title": "Workshop to Explore Cultural",
"author": "Assessment"
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https://oercommons.org/courseware/lesson/78114/overview
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Cash Out Game
Counting Coins Song for Kids
Counting Money Game
Oklahoma Academic Standards - 2nd Grade Math
Money Math
Overview
A second-grade lesson plan focused on helping students learn how to count change.
Prior to Learning
Overview: A 2nd-grade lesson plan designed to help students learn how to count change up to $1.00.
Oklahoma Academic Standards: 2.N.4.1 Determine the value of a collection(s) of coins up to one dollar using the cent symbol. 2.N.4.2 Use a combination of coins to represent a given amount of money up to one dollar.
Objective: Students will be able to count change up to $1.00 in order to buy a prize.
Focus question: How does learning how to count change help me in the real world?
Vocabulary:
Change: currency in the form of coins
Penny: a coin worth 1 cent
Nickel: a coin worth 5 cents
Dime: a coin worth 10 cents
Quarter: a coin worth 25 cents
Materials: Computers, whiteboard, a bag of change (2 quarters, 5 dimes, 5 nickels, and 5 pennies, $1.30 total) for each student, candy (taffy, bubble gum, suckers, and mini chocolates), and a SMARTBoard or projector.
Accommodations: for ELLs, we will review the equivalent change for their native language's culture. For special needs, students may buddy up and help each other with counting.
Lesson and Activity
Instructional Procedures:
1. Introduction: the teacher will start with a discussion about counting change. Students will be informed of the objectives and asked the focus question: How does learning how to count change help me in the real world?
2. First, we will go over what each of the coins looks like. Students will take all of their coins out of their bags and sort them into piles based on looks. 1) Silver versus bronze/copper, 2) bigger versus smaller, and 3) all 4 different types.
3. Next, we will go over how much each of these is worth. 1) quarters are worth 25 cents (demonstrate the cent symbol on the board) and are the biggest out of the four, 2) dimes are worth 10 cents and are the smallest, 3) nickels are worth 5 cents and are the second biggest, and 4) pennies are worth 1 cent and are the second smallest.
4. Then, we will watch the video "Counting Coins Song for Kids | Learning About Money Song For Kids" on YouTube.
5. Finally, we will discuss how to add up coins to make bigger coins, as talked about in the video. A penny is worth 1 cent; a nickel is worth 5 cents, or 5 pennies; a dime is worth 10 cents, or 10 pennies, or 2 nickels; a quarter is worth 25 cents, or 25 pennies, or 5 nickels, or 2 dimes and 1 nickel. Important note: "penny" and "cent" are not interchangeable terms, pennies are worth 1 cent and therefore you can use 5 pennies to equal 1 nickel.
Activity/Formative Assessment:
1. Students will practice giving out change through this interactive game: https://mrnussbaum.com/cash-out-online-game
Instructions: Visit the website. Select "PLAY." Difficulty settings should be Easy, display hints No, and show change amount Yes. Select "BEGIN GAME." Once the game loads, click on the correct coins to make change for the animals. Continue until the timer runs out.
2. Students will practice buying things by playing this game: https://www.abcya.com/games/counting_money
Instructions: Visit the website. Once it loads, click the big play button on the screen. Select Level 1 and then select Beginner. Click "OK" to continue after you listen to the directions. Then, drag and drop the correct coins into the yellow box. Once you finish your answer, click "CHECK" to check your answer. Keep going until you collect all 10 fish.
3. As a prize for their hard work, students will get to keep the change given to them at the beginning of the lesson. After playing both games, students will then transfer this into real life. With the coins that they were given, they will have the option to buy different candy from the "store," which will be at my desk. Students will come up one-by-one with their change and buy candy, making sure they don't go over the amount of money they were given. If they have the exact change, they will need to give it to me as so. If they don't have exact change, they will need to tell me how much money I should give back to them as change. If they don't use all of their money, they will be allowed to keep it.
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oercommons
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2025-03-18T00:38:19.437277
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Lesson
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"url": "https://oercommons.org/courseware/lesson/78114/overview",
"title": "Money Math",
"author": "Activity/Lab"
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https://oercommons.org/courseware/lesson/91558/overview
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Healthcare Data Exchange: Authorization and Authentication
Overview
This course provides a comprehensive review of health data security and privacy standards, frameworks, and protocols. This course uses Meld to provide learners with hands-on activities using data querying and the SMART-on-FHIR Launch framework. Upon successful completion of this course, learners will be able to: understand the legal frameworks guiding security and privacy requirements in healthcare; describe how data exchange works using APIs; understand authentication and authorization protocols and frameworks; describe how UDAP and its specifications play a role in the future of health data exchange; query Meld for synthetic patient data using Hoppscotch.io; register and launch a SMART-on-FHIR application.
Overview of Course
This course provides a comprehensive review of health data security and privacy standards, frameworks, and protocols. This course uses Meld to provide learners with hands-on activities using data querying and the SMART-on-FHIR Launch framework. Upon successful completion of this course, learners will be able to: understand the legal frameworks guiding security and privacy requirements in healthcare; describe how data exchange works using APIs; understand authentication and authorization protocols and frameworks; describe how UDAP and its specifications play a role in the future of health data exchange; query Meld for synthetic patient data using Hoppscotch.io; register and launch a SMART-on-FHIR application.
Subject: Health, Medicine and Nursing, Information Science
Level: Community College / Lower Division, College / Upper Division, Graduate / Professional
Material Type: Activity/Lab, Diagram/Illustration, Full Course, Lesson Plan, Reading, Student Guide
Author: Interoperability Institute
Date Added:
License: Creative Commons Attribution Non-Commercial No Derivatives
Language: English
Media Format: Graphics/Photos, Text/HTML
Healthcare Data Exchange History
Learning Objectives:
After completing this lesson, you will be able to:
Understand the legal framework that guides patient privacy and security
Describe Transport Layer Security
Security and Privacy
HIPAA Right of Access
In 1996, the Health Insurance Portability and Accountability (HIPAA) Act was established to protect patients' medical records. HIPAA distinctly identifies rules for maintaining privacy and security of the patients' protected health information (PHI) record. The Privacy and Security rules outline very clear expectations for how to ensure the patient record is kept confidential and secure.
HIPAA’s Privacy Rule puts the patient in the driver’s seat of their records by allowing them to control the access and use of his or her personal information. Covered entities, such as health plans or providers, must provide patients, their representatives and approved third parties with access to their protected health information through designated record sets. A designated health record set will include medical records, coverage, claims, adjudication, or case management records maintained by or for the covered entity or health plan.
Patients and/or their legal representatives can submit via writing or electronic format a copy of their PHI from any covered entities. If submitting a request for a third party to access their record, patients will sign a waiver for each individual entity they would like to be able to view their health data. This portion of HIPAA also requires that covered entities must provide patients with three different methods of obtaining their health data to avoid delays in patient access—physically going into the provider’s office, technological route (such as emails or mobile apps), or physically mailing to the patient’s address.
Covered entities are required to verify that the request has come from the patient, but the method and type of verification process is left to the discretion of the covered entity as long as the selected verification process does not inhibit or delay the patients access to the PHI.
As technology has progressed, the use of application programming interfaces (APIs) has become increasingly common in the healthcare landscape. These APIs must abide by the rules laid out by HIPAA, meaning that they must provide individuals with an electronic request that can approve or deny the electronic transmission of PHI. These regulations have led to appropriate privacy protections and data security safeguard being implemented within the APIs and other healthcare applications.
The following are key areas for privacy consideration when implementing APIs in healthcare:
- Provide patients electronic access (e.g., an electronic form within a patient portal) to request transmission of PHI in accordance with the HIPAA Privacy rule.
- Enable technology that will allow individuals to choose what specific types of health information (e.g., medication lists, allergies) they want to share if they are requesting the records be provided to a third party.
- Provide clear and easily accessible options to revoke third party access permissions.
Security Considerations
Security Considerations
The Security Rule addresses the protection of patient PHI from unauthorized internal or external access including administrative, technical, and physical safeguards. The utilization of APIs for data sharing is becoming more prevalent with the adoption of the HL7 FHIR standard. When implementing APIs in healthcare, there are multiple key areas for security consideration.
Encryption-Use - TLS with strong cipher suites to help protect the health information in transit via the API from the EHR to the third-party. TLS will be discussed further below.
Input Validation of API Calls - Assure that arbitrary code cannot be executed as well as assuring that the input meets that size/shape/type required.
Access Controls
Identity Proofing- The process of attributing an online identifier with a person, standards like 800-63A cover these requirements in detail.
Credentialing- Also develop technical and administrative policies that explain how to issue credentials to individuals that will grant them access to their health information.
Verification of Access controls Auth and Auth
Strongly consider implementing risk-based authentication controls, which is a method of applying varying levels of stringency to the authentication process, that flow from the organization’s security risk assessment. The controls, and are commensurate with the type of data, level of sensitivity of the information, and user type.
Create systems with technical authorization controls that are flexible enough to support individual privacy preferences that are can limit API use, access, or disclosure based on what is necessary to satisfy a particular purpose or carrying out a function.
Service Provider Security- Evaluate any service provider’s infrastructure, security practices, and technical capabilities for hosting implementations of APIs and apps that store, handle, and access health information. This assures that the service provider will appropriately safeguard the health information in a way that is consistent with the organization’s security policy.
Data Integrity-Put in place data integrity protection controls that can detect when unauthorized alterations are made to health information made accessible through the API.
Patient Access Security-Ensure that EHR patient portals that interact with the API are secure and protected against known vulnerabilities that attackers could exploit.
TLS
Transport Layer Security (TLS) is a secure transport and session protocol that provides confidentiality to web traffic using cryptography. TLS is used to create secure a communications channel for client-server applications by encrypting online traffic in flight and like confidential data communicated between a user’s web browser and a webserver.
Communication/Data Exchange
Learning Objectives:
After completing this lesson, you will be able to:
Describe RESTful API architecture
Understand how APIs and applications communicate
Understand the basics of GraphQL and how it is used by FHIR
What is an API?
What is an API?
An API is an application programming interface where the interface is a shared endpoint for computer systems to exchange information. Web APIs allow communication between applications and systems over the internet to access and share data.
APIs are typically implemented according to a set of standards, such as REST or GraphQL which are described in the following sections.
HTTP Protocol
HyperText Transport Protocol (HTTP) is the foundation of data exchange on the web. Clients and servers communicate by exchanging messages. HTTP is a client-server protocol. The client such as a web application sends a message, which is called a request, and receives an answer from the server, which is called a response.
HTTP requests and responses are structured in a similar manner. This structure includes:
A start-line that describes the request method to be implemented or its success/failure status.
An optional set of headers specifying the request or describing the body of the message.
An optional body containing data associated with the request
What is REST?
What is REST?
The term ‘REST’ stands for “representational state transfer”, a software architectural style created to guide the design and development of web architecture. REST is an API pattern that has become widely popularized over the last decade. The REST pattern standardized the way that APIs are planned, configured, built, and managed. A RESTful architecture style promotes interoperability between systems on the Internet by standardizing the method of communication. There are several key components of RESTful APIs including resources, endpoints, request methods, and response status codes.
Resources
A resource is defined as any complex data type. For example, a patient record is a type of resource.
Endpoints
When an API is interacting with another system, the point of communication is an endpoint. An endpoint is a URI that enables an API to access another server. The endpoint is the point at which the API connects with the application server. When a request is made, the API endpoint provides a response.
Request Methods
Client applications can interact with a server using HTTP request methods. These methods include:
GET – used to read or request a resource from the server
POST – used to create a new resource in the server
PUT – used to update existing resources in the server or create a resource if the resource does not already exist in the server. In more technical terms, if the request URI refers to an existing resource, the request will modify the version residing in the origin server. If the request URI does not point to an existing resource, the origin server can create the resource with that URI.
[Insert example of a PUT request here]
DELETE – used to remove a resource from the server
Response Status Codes
A response status code indicates the result of a client request. Common HTTP response status codes include:
- 200 OK
- 201 CREATED
- 204 NO CONTENT
- 400 BAD REQUEST
- 401 UNAUTHORIZED CLIENT REQUEST
- 403 FORBIDDEN
- 404 NOT FOUND
- 500 COULD NOT PROCESS REQUEST (Umbrella for errors)
CRUD Operations
CRUD
CRUD stands for CREATE, READ, UPDATE, and DELETE. The CREATE command creates new records through INSERT statements, similar to a POST command. The READ command reads data based on input parameters. The UPDATE command modifies records without overwriting them. The DELETE command deletes records where specified.
REST is an API architecture while CRUD is a cycle for maintaining records. CRUD can be mapped to HTTP protocols, as can resources in RESTful architecture.
GRAPHQL
GRAPHQL
What is GraphQL?
GraphQL is a query language for APIs that allows for contractual interaction between a client and server.
GraphQL vs. REST
REST APIs typically require loading data from multiple URLs, also known as endpoints. In contrast, GraphQL APIs enables client applications to retrieve all necessary data in a single request. GraphQL APIs are organized by type and field rather than endpoints, allowing clients to specify the type of data they wish to receive from the server. GraphQL queries access the properties of singular resources and simultaneously follow references between resources. A benefit of using GraphQL is its ability to return predictable results, along with its clear and standard versioning guidelines.
Using GraphQL with FHIR
Currently, GraphQL is not a formal standard and the language is still under development. However, the GraphQL interface can used as simplified interface in front of a standards-compatible RESTful API.
A GraphQL query must start by selecting a resource type and a search criteria:
[base URI]/[Type]/[id]/$graphql
Authentication and Identity
Learning Objectives:
After completing this lesson, you will be able to:
Describe Authentication and Identity
Understand the protocol of basic authentication
Identify different forms of authentication
Understand how OpenID Connect utilizes authentication
Understand how Security Assertion Markup Language (SAML) utilizes authentication
What is Authentication?
What is Authentication?
Understanding the meaning of identity is vital to understanding what authentication is and how it works. Identity is a single body or bodes of information which can provide a unique value to identify a person, organization, or entity. Authentication is the process of verifying the identity of a user.
There are various forms of authentication that can be used depending on the circumstance of the situation. The simplest form of authentication is known as basic authentication. This is a method for an HTTP user agent, such as a web user, to provide a username and password when making a request to a server.
Basic authentication will generally follow the steps outlined below.
Steps on the Server Side
After receiving an unauthenticated request, the server will want the user who submitted the request to authenticate themselves. To do this, the server will send an HTTP 401 Unauthorized Status line response and a www-authenticate header field to the user.
- www-authenticate: basic realm = “User Visible Realm”
Steps on the Client Side
When a user would like to authenticate themselves to the server, it may use the authorization header field. This field would be constructed as follows:
- The username and password are combined with a single colon
- The resulting string is encoded by an octet sequence
- The resulting string is encoded by using a variant of Base64 (+/- with padding)
- The authorization method and a space is then added to the beginning of the encoding string
Types of Authentication
Types of Authentication
There are many different types of authentication. There are several factors that are considered when selecting the appropriate authentication type, such as security needs, how the user will access the server, how many users the server will have, and what may be required by law—depending on the content within the server. Here are a couple of authentication methods that can be chosen based on the above factors.
Password-Based Authentication
The most common form of authentication. The user will input a unique ID or username which will identify which user is trying to access the server. Then the user will input a key or password which confirms the identity of the user.
Certificate-Based Authentication
Digital certificates are used to identify the user trying to access the server. The digital certificate contains the digital identity of the user, including the public key and the digital signature of the certificate authority. Digital Certificates prove the ownership of a public key, therefore indicating the user can have access to the server.
Computer Recognition Authentication
Computer recognition verifies the user’s identity by confirming that they are using a particular device. This form of authentication utilizes a software plug-in on the user’s computer the first time that they log in, it will leave a cryptographic device marker which will be for authentication in the future.
Biometric Authentication
Unique biological characteristics of individual users are verified using this process. Common forms of biometric authentication methods include facial recognition, fingerprint scanners, speaker recognition, and eye scanners.
Token-Based Authentication
Users enter their credentials once and receive a unique encrypted string of characters, known as a token. Users can then use the received token to access protected systems instead of needing to reenter their credentials.
Multi-Factor Authentication
This method of authentication requires two or more independent ways to identify users. Examples include all of the authentication methods above, as well as, user phone numbers, captcha tests, or applications specifically created for multi-factor authentication.
There are a number of ways for a system to identify users. In addition to the methods discussed above, the three most common ways for a system to identify a user include:
A password or a PIN
A smartphone application (ex: Duo security)
A fingerprint or facial recognition
Security Assertion Markup Language (SAML)
Security Assertion Markup Language (SAML)
SAML is an open standard that enables Single Sign-On (SSO). This provides users with the ability to seamlessly access multiple applications, websites, or servers while only using one set of login credentials. As an XML-based standard, SAML is quite flexible. Single implementations can support SSO connections with many different federation partners utilizing SAML.
SAML holds the main position for federated identity deployments and has been deployed in thousands of large enterprises, government entities, and service providers.
SAML will generally follow the steps below (assuming an IP named Identity+ and a service provider Imaginary Company):
- A user tries to log in to Imaginary Company through their web browser
- Imaginary Company responds by generating a SAML request
- The web browser server redirects the user to the SSO URL—Identity+
- Identity+ parses the SAML request and authenticates the user—this can be done using several authentication methods, the service provider would decide which one. Once the user is authenticated, Identity+ generates the SAML response.
- Identity+ returns the encoded SAML response to the web browser.
- The web browser sends the SAML response to the Imaginary Company to verify.
- If Imaginary Company successfully verifies the response, the user will then be logged into Imaginary Company.
Authorization
Learning Objectives:
In this section you will learn about:
- The purpose of Authorization.
- The process that occurs during Authorization.
- How Authorization is implemented through OAuth 2.0.
- OAuth 2.0 roles and flows.
What is Authorization?
What is Authorization?
Authorization is a process that determines what a user can and cannot access after they have completed the authentication process successfully. It verifies whether access is allowed through an established set of policies and rules where at times, an Access Token is transmitted to the client if the authorization is approved. Not all authorization requires an Access Token. If an individual is not authorized for a specific resource, even if they have proven their identity, they can still be denied access.
This process is generally governed by OAuth 2.0 in web applications, which will be discussed in the implementation section that follows.
Example
An employee is looking receive authorization for a specific file that contains protected information and data. Once they have successfully completed authentication, they then begin the authorization process by providing their credentials to the file owner through a server that is typically separate from the resource server. The resource owner decides on whether that employee has the appropriate credentials and need for that file and grants them an Access Token that allows them to access the file on a different server under a new unique set of credentials in which the only protected file they will have access to is that one specifically. The employee is then allowed to utilize that file, and that file only.
Implementation
OAuth 2.0
OAuth 2.0 is a protocol that allows a user to grant an external or third-party website or application access to a client of that user’s protected resources, without necessarily revealing their long-term credentials or even their identity in some instances. This process introduces an authorization layer that separates the role of the client from that of the resource owner.
Within the process, the client begins by requesting access to resources that are in control of the resource owner and is hosted by the resource’s server. The client is then issued a unique set of credentials different than those of the resource owner to access the resource.
Instead of using the resource owner’s credentials to access protected resources, the client will obtain an access token, which is typically a string denoting a specific scope (permissions represented by the access token), lifetime (how long the client will have access), and other attributes that are tied to the granted access.
An OAuth 2.0 flow contains the following four roles within the process:
- Resource Owner: Entity that has the power to grant the access to a protected resource.
- Client: Application requesting access to a protected resource on behalf of the Resource Owner.
- Resource Server: Server that is hosting the protected resources and the API that the client wants permission to access.
- Authorization Server: Server that authenticates the Resource Owner and then transmits access to tokens after getting proper authorization. In this case, AuthO.
OAuth 2.0 also defines four flows to receive an Access Token. These flows are defined as grant types and deciding which one is suited for an individual’s case depends mostly on the application type that is being used. The grant types are:
- Authorization Code Flow: used by Web Apps executing on a server, also used by mobile apps using the Proof Key for Code Exchange technique.
- Implicit Flow with Form Post: used by JavaScript-centric apps executing on the user’s browser.
- Resource Owner Password Flow: used by highly trusted apps.
- Client Credentials Flow: used for machine-to-machine communication.
The Future of Healthcare Data Exchange
Learning Objectives:
- The status of healthcare data exchange (maybe rename technical barriers?)
- Overview of UDAP
- Why UDAP is important for future growth in data exchange
- Where UDAP is currently being used
- The specifications within it (summary)
- JWT-Based Client Authentication
- Trusted Dynamic Client Registration
- JWT-Based Authorization Assertion
- Certifications & Endorsements
- Tiered OAuth
6. Levels of security found
7. Compare/Contrast SMART-on-FHIR
What is the status in healthcare data exchange?
Currently, HL7 FHIR has some technical barriers that make it difficult for FHIR to scale. FAST (FHIR at Scale TaskForce) has determined that there are six main issues that need to be addressed.
1. Directory Services
- Inability to find FHIR endpoints and its associated capabilities/characteristics
- No directory or some form of maintenance for endpoint information or validation
- Need the ability to restrict discoverability of specific endpoints
2. Identity
- Unique identifies are not meaningful outside the organization they come from
- ‘Cross-walks’ (small orgs that exchange patient and provider rosters to make a common key) are not scalable
- Need a minimum amount of data
- Response, including error messages, needs to consider privacy
- Overlaps, duplicate records, and incorrect matches could require legislation beyond that of technical recommendations
- Enable identity cross-walks
3. Security
- Inability to ensure that the requestor has been properly authenticated and has the authorization to view and use the data
- It is not clear how to scale and administer Open Authorization
4. Testing, Conformance, & Certification
- Requirements formatted for ease of what should be tested and certified
- Lack of minimum baseline of FHIR conformance
- Require validation through automated tooling
- Use test driven development
- There is currently no governing body to grant
5. Versioning
- Need to be able to support multiple versions of FHIR
- Importance of a capability statement to determine functions
6. Scaling
- Various interoperability models
- Inconsistent response time and predictability
- Difficulties in linking patients and their records
- Performance issues as FHIR becomes adopted
What is UDAP?
Unified Data Access Profiles (UDAP) are building blocks to improve the scalability of the FHIR ecosystem guided by the ONC’s FHIR at Scale Taskforce’s Security Tiger Team (FAST: Scalable Registration, Authentication, and Authorization for FHIR Ecosystem Participants Luis Maas, MD, Ph.D. May 28, 2021). By extending the OAuth 2.0 and SMART App Launch frameworks, UDAP supports secure and scalable workflows for applications that implement the authorization code or client credentials flow.
Client Authentication
JWT-Based Client Authentication
Implemented as an extension to the OAuth 2.0 framework, a client application constructs, and signs a JSON Web Token (JWT). This token is used by the client application as an Authentication Token, which is included in its request for an access token as a client assertion to authenticate itself to the Authorization Server’s token endpoint.
The client app first directs the end-user to the Authorization Server’s authorization endpoint to obtain an authorization code. The client app then creates an Authentication Token, which is included in the app’s request to the server’s token endpoint. This gives the client control of a private key and provides the digital certificate needed to validate the signature. The Authentication Token is a signed JWT and includes the following key-value pairs:
Iss: contains URI of the Client Token Service
Sub: the client ID issued by the authentication server to the client application
Aud: token endpoint URI of the authorization server
Exp: token expiration time expressed as seconds
Iat: issued at time expressed as seconds
Iti: token identifier used to identify token replay (occurs when a hacker listens to a secure network communication, intercepts it, and fraudulently delays or resends it to misdirect the receiver into doing what the hacker wants)
The client app uses this token to authenticate itself in its request for an access token from the Authorization Server. The server validates the digital signature on the Authentication Token and returns a token response if the request is approved.
Dynamic Client Registration
Dynamic Client Registration
UDAP extends OAuth2 and OpenID Connect and lesser utilized aspects of related RFCs to leverage trusted digital certificate authorities to build a trust community. This eliminates the need for every FHIR endpoint to manually register every client application by enabling the automated reuse of OpenID credentials or digital certificates in JWT (JSON Web Token) based authentication. Authorization servers requested by client applications confirm UDAP support through metadata and direct the client to register on the server.
Dynamic Client Registration identifies and dynamically registers trusted client applications that have been pre-screened by certificate authorities. Using Trusted Dynamic Client Registration, the client directs the user to the server’s authorization endpoint to obtain an authorization code. The client then creates a signed JWT. The JWT provides the metadata required for registration, establishes client app control of a private key, and provides the digital certificate needed to validate the signature and establish trust.
The client app requests registration by submitting this token to the Authorization Server’s authorization endpoint, which validates the request. If the request is approved, the Authorization Server returns a response including the Client ID issued by the server for the client app to use.
Open Authorization
Tiered OAuth for User Authentication
UDAP Tiered OAuth for User Authentication provides another way to authorize users. This method leverages Identity Providers (IdP) and existing credentials to determine authorization decisions for resource holders. In this system, when a client application requests authorization or authentication from a resource holder, the resource holder requests user authentication from a trusted upstream IdP and uses the authentication request information and IdP’s information to deny or accept the client application. This reduces information leakage as client apps or third-party apps are not solely responsible for authentication.
TLS Client Authentication
TLS Client Authentication
This client authentication protocol can be used with any OAuth 2.0 grant mechanism where a client app authenticates the Authorization Server’s token endpoint by transmitting a certificate during the TLS handshake to obtain an access token. This includes authorization code flow, client credentials flow, or other extension grant flows utilizing the token endpoint by client apps. Before granting an access token, the Authorization Server validates the digital signature on the client certificate during the handshake and evaluates the trust chain for this certificate.
UDAP & SMART-on-FHIR
Currently, FHIR standards require that client applications and payers support the standalone launch sequence of the SMART App Launch framework for user authorization and client authentication. UDAP Dynamic Client Registration allows client applications and servers to automate the negotiation of trust and technical requirements without manual intervention.
UDAP can be used to extend OAuth 2.0 and the SMART App Launch Framework for consumer-facing applications. Client application operators must register each application with the Authorization Servers identified by the FHIR servers that they will exchange data with. The Authorization Servers should support dynamic registration (specified in the UDAP Dynamic Client Registration Protocol).
Authorization Process:
Client applications must follow the OAuth 2.0 authorization code grant flow, as extended by the SMART App Launch Framework, to obtain access tokens to access FHIR resources. Client applications will request an authorization code per the SMART App Launch Framework, but are not required to include a launch scope or launch context requirement scope. Additionally, client applications and servers may choose to support UDAP Tiered OAuth for User Authentication to allow cross-organizational and/or third party user authentication.
In the next section, a technical activity demonstrates how to register and launch a SMART application using some of the authentication and authorization frameworks discussed in this lesson.
Glossary
Access Token – Contains the security credentials for a login session and identifies the user, user groups, user privileges, and sometimes a specific application
API – Application Programming Interface
Authentication - A mechanism to verify the identity of a user
Authorization - A mechanism to determine the level of access of a user to system resources
Covered Entities – A health care provider, a health plan
CRUD – Create, Read, Update, Delete
Encryption – The process of encoding information
FHIR – Fast Healthcare Interoperability Resources
HIPAA – Health Insurance Portability and Accountability Act
HL7 (Health Level 7) – International standards for the transfer of clinical and administrative healthcare data between software applications
HTTP – Hyper Text Transfer Protocol
Identity Proofing – The process of verifying that the identity of a person
OAuth – Open Authorization
ONC – Office of the National Coordinator for Health
PHI – Protected Health Information
REST – Representational State Transfer
SAML – Security Assertion Markup Language
SSO – Single Sign-On
TLS – Transport Layer Security
UDAP – Unified Data Access Profiles
XML – Extensible Markup Language
Sources
Healthcare Data Exchange History:
https://www.healthit.gov/sites/default/files/privacy-security-api.pdf
https://www.hl7.org/fhir/security.html
https://www.techsoup.org/support/articles-and-how-tos/introduction-to-transport-layer-security
Communication/Data Exchange:
https://www.healthcareitnews.com/news/what-you-need-know-about-healthcare-apis-and-interoperability
https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview
https://developer.mozilla.org/en-US/docs/Web/HTTP/Messages
https://stevenpcurtis.medium.com/rest-vs-crud-ca5522bf3fc3
https://stevenpcurtis.medium.com/endpoint-vs-api-ee96a91e88ca
http://hl7.org/fhir/r4/graphql.html
https://asymmetrik.com/getting-started-with-fhir-and-graphql/
Authentication and Identity:
What is: Multifactor Authentication (microsoft.com)
https://auth0.com/blog/how-saml-authentication-works/
https://www.pingidentity.com/en/resources/client-library/articles/saml.html
Authorization:
https://auth0.com/docs/authorization/protocols/protocol-oauth2
https://developer.okta.com/blog/2019/10/21/illustrated-guide-to-oauth-and-oidc
The Future of Healthcare Data Exchange:
http://hl7.org/fhir/us/carin-bb/STU1/Authorization_Authentication_and_Registration.html
https://docs.google.com/document/d/1HgOlUWMEsZHBChuP4DACRka4ap2S8UwSTkAz4oY6bCo/edit
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oercommons
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2025-03-18T00:38:19.508532
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Full Course
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https://oercommons.org/courseware/lesson/124149/overview
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Bonding, Resonance, and Ozone Lesson Plan - Day 1
Bonding & Resonance - Day 1 Slideshow
Day 1 - Build a Molecule Phet Worksheet
Day 1 Guided Notes - Resonance, Bonding, & Lewis Structures
Day 2 - Benzene Modeling Template
Day 2 Guided Notes - Resonance, Reactivity, and Isomers
Day 2 - Resonance vs Isomers Game Slidedeck
O-Chem Lesson Plans For Teens
Resonance, Reactivity, and Isomers Slideshow - Day 2
Bonding & Resonance with Benzene & Ozone Lesson Plans
Overview
Welcome
Our goal is to design high school chemistry lesson plans that integrate fundamental organic chemisty concepts. These lessons aim to bridge the gap between introductory chemistry and organic chemistry, giving students a head start in understanding molecular structures, reactions, and more, in a way that is engaging and accessible. By connecting these core ideas with hands-on experiments, real-world applucations, and interactive learning tools, students will be better equipped to understand the relevance of organic chemistry in everyday life and future scientific studies.
For additional organic chemistry lesson plans, view the following:
Overview
Welcome
Our goal is to design high school chemistry lesson plans that integrate fundamental organic chemisty concepts. These lessons aim to bridge the gap between introductory chemistry and organic chemistry, giving students a head start in understanding molecular structures, reactions, and more, in a way that is engaging and accessible. By connecting these core ideas with hands-on experiments, real-world applucations, and interactive learning tools, students will be better equipped to understand the relevance of organic chemistry in everyday life and future scientific studies.
For additional organic chemistry lesson plans, view the following:
Feedback
We value your feedback and would like to know how to make our lesson plans more engaging, accessible, and clear. Please take the following survey for this set of lesson plans, Bonding & Resonance, by using the following link:
Day 1 - Bonding, Resonance, and Ozone
Day 1 - Bonding, Resonance, and Ozone
Brief Description:
Students will explore bonding within organic and inorganic compounds to discover bonding patterns. Students will then identify and explain how bonding patterns impact the stability and prominence of a molecule through resonance.
Specific Learning Outcomes for This Lesson:
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Standard (from Utah SEEd Standards):
Standard CHEM.2.1
Analyze data to predict the type of bonding most likely to occur between two elements using the patterns of reactivity on the periodic table. Emphasize the types and strengths of attractions between charged particles in ionic, covalent, and metallic bonds. Examples could include the attraction between electrons on one atom and the nucleus of another atom in a covalent bond or between ions in an ionic compound. (PS1.A, PS2.B)
Standard CHEM.2.2
Plan and carry out an investigation to compare the properties of substances at the bulk scale and relate them to molecular structures. Emphasize using models to explain or describe the strength of electrical forces between particles. Examples of models could include Lewis dot structures or ball and stick models. Examples of particles could include ions, atoms, molecules, or networked materials (such as graphite). Examples of properties could include melting point and boiling point, vapor pressure, solubility, or surface tension. (PS1.A)
Standard CHEM.2.3
Engage in argument supported by evidence that the functions of natural and designed macromolecules are related to their chemical structures. Emphasize the roles of attractive forces between and within molecules. Examples could include non-covalent interactions between base pairs in DNA allowing it to be unzipped for replication, the network of atoms in a diamond conferring hardness, or the nonpolar nature of polyester (PET) making it quick-drying. (PS1.A)
Day 2 - Bonding, Resonance, and Benzene
Day 2 - Bonding, Resonance, and Benzene
Brief Lesson Description: Students will explore bonding within organic and inorganic compounds to discover bonding patterns. Students will then identify and explain how bonding patterns impact the stability and prominence of a molecule through resonance. | |
Standard (from Utah SEEd Standards): Standard CHEM.2.1 Analyze data to predict the type of bonding most likely to occur between two elements using the patterns of reactivity on the periodic table. Emphasize the types and strengths of attractions between charged particles in ionic, covalent, and metallic bonds. Examples could include the attraction between electrons on one atom and the nucleus of another atom in a covalent bond or between ions in an ionic compound. (PS1.A, PS2.B) Standard CHEM.2.2 Plan and carry out an investigation to compare the properties of substances at the bulk scale and relate them to molecular structures. Emphasize using models to explain or describe the strength of electrical forces between particles. Examples of models could include Lewis dot structures or ball and stick models. Examples of particles could include ions, atoms, molecules, or networked materials (such as graphite). Examples of properties could include melting point and boiling point, vapor pressure, solubility, or surface tension. (PS1.A) Standard CHEM.2.3 Engage in argument supported by evidence that the functions of natural and designed macromolecules are related to their chemical structures. Emphasize the roles of attractive forces between and within molecules. Examples could include non-covalent interactions between base pairs in DNA allowing it to be unzipped for replication, the network of atoms in a diamond conferring hardness, or the nonpolar nature of polyester (PET) making it quick-drying. (PS1.A) | |
Specific Learning Outcomes for This Lesson:
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oercommons
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2025-03-18T00:38:19.543681
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Lesson
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"author": "Interactive"
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https://oercommons.org/courseware/lesson/71834/overview
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Abnormal Psychology by Rosenberg and Kosslyn
Abnormal Psychology by Rosenberg and Kosslyn (2011)
An Introduction to Brain and Behavior by Kolby, Wishaw, & Tesky
Chapter 2 of Abnormal Psychology by Rosenberg & Kosslyn
History of Mental Illness
History of Psychology
http://www.brainm.com/software/pubs/books/Abnormal_Psychology-NeuroPsychoSocial.pdf
Understanding Schizophrenia - Linking Neurobiology to Clinical Symptoms
What Are Psychological Disorders?
Abnormal Psychology
Overview
This text is being developed for Abnormal Psychology lower division undergraduate courses. It is published now to allow students access to the course materials as it develops.
Chapter 1: Intruduction to Abnormal Psychology
This text is being developed for undergraduate studies of abnormal psychology. It is not expected to be complete until the end of fall 2022.
Many clinical words and initials like OCD, narcissist, bipolar, schizophrenia, and sociopath have been freely and at times carelessly used for years (Harbeck, 2016). In this chapter, we will explore the difference between what is abnormal (McLeod, 2018) and mental disorders per the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM–5; American Psychiatric Association, 2013), and the field of abnormal psychology (Rosenberg & Kosslyn, 2014). We will examine questions like:
- What is a mental disorder?
- What determines what is a mental disorder?
- Is it our thoughts?
- Is it our actions?
- Is it what people think of us?
- Is it society in general?
- Is it our genetics?
- Is it our parents?
- Is it our friends, our teacher, or a therapist?
Chapter 2: Historical Development of Mental Illness: From Prehistoric to the 18th Century
In prehistoric times (prior to recorded history), historian and archeologist believed that mystical forces attributed to behavioral and psychological abnormalities (Halgin & Whitbourne, 2007; Rosenberg & Kosslyn, 2014; Sue, Sue, Sue & Sue, 2016). Over half a million years ago societies like in ancient Egypt and Mesopotamia believed that evil spirits possessed a person due as punishment for some wrongdoing, revenge by a sorcerer or ancestral spirits. Healers attempted to used exorcism and trephining (puncturing a hole in the skull) to allow the evil spirits to exit the body.
In 7th century B.C. China, it was believed that mental disorders were caused by an imbalance of the Qi (Chi), which is still used in traditional Chinese medicine (TCM; Hui-Chu et al, 2012; Rosenberg & Kosslyn, 2014). The Qi refers to all substances physical and non-physical such as water and energy (Atkins, 2018). In TCM there needs to be a balance between the yin (energy) and the yang (physical). According to this belief, mental and physical ailments arise from an imbalance of the yin and yang. Restoration of the imbalance using acupuncture, herbal medicine along with meditation is used (Rosenberg & Kosslyn, 2014; Atkins, 2018).
In ancient Greece, Hippocrates (460 – 370 B.C.) known as the father of modern medicine and developer of the Hippocratic Oath, also developed a theory that body and mental ailments were derived from an imbalance of four humors: black bile (the element of earth found in the spleen), yellow bile (the element of fire found in the gallbladder), phlegm (the element of water found in the brain, and blood (the element of air found in the heart; Halgin & Whitbourne, 2007; Rosenberg & Kosslyn, 2014; U.S. National Library of Medicine, 2011). An excess of the black bile lead to depression. Anger and impulsiveness were due to a surplus of yellow bile. Blood humor served above all the humors, as it circulated through the body delivering the other three humors. Mania was brought about from having too much blood and yellow bile. Draining one of blood was a practice when one was believed to have too much of blood humor. Hippocrates also believed that women suffered hysteria due to their wondering uterus seeking conception and its remedy was matrimony and/or sexual engagement. Other notable contributors to the study of mental illness were Plato (428–347 B.C.) and Aristotle (384–322 B.C.; “Introduction to Psychology: 1.2 The Evolution of Psychology: History, Approaches, and Questions,” 2015). Plato, a pupil of Socrates (known for being imprisoned and executed for disrespecting the gods and poisoning the minds of youth), who brought us most of what we know about Socrates (470 – 399 B.C.) in his dialogues (Hare, 2010; McGoodwin, 2019; Plato, nd/2011) aired in the side of nature, where behaviors and mental attributes were innate (“Introduction to Psychology: 1.2 The Evolution of Psychology: History, Approaches, and Questions,” 2015; Lewkowicz, 2012; Sue, Sue, Sue & Sue, 2016). Plato also argued in favor of women being equal to men and allowed them in his Academy. (Thorne, 2005, p. 33). Aristotle, a student of Plato argued on the side of nurture, where every child is born with a tabula rasa. The movement from mystical forces to more natural explanations for mental illness continued in ancient Greece for a millennium and brought to Rome by the Greek physician Galen (129-216 A.D.; Rosenberg & Kosslyn, 2014; Sue, Sue, Sue & Sue, 2016, Whitourne, 2020). Galen contributed greatly to the field of physiology developing the understanding of the nervous system through his animal studies.
During the middle ages (500-1400 A.D.), a reemergence of supernatural forces afflicting a person was the explanation for mental illnesses (Rosenberg & Kosslyn, 2014; Sue, Sue, Sue & Sue, 2016, Whitourne, 2020). With the fall of the Roman Empire and conversion of Greek and Roman mythologies to Christianity (Constantine [272 –337] became the first emperor of Rome to convert to Christianity), European treatment of the mentally ill was once again through payer, exorcism, confinement, and at times torture and death. The dogmas of Socrates, Hippocrates, Plato, Aristotle and Galen were for the time in the protections of monks and scholars, while little literature in science was completed during the Saxon, Viking, and other wars and plagues and famine covered Europe (Brinson, 2016; Sue, Sue, Sue & Sue, 2016).
The shift once again from supernatural forces being responsible for mental illness to physical matter can be traced to Cartesian Dualism during the Renaissance (1400-1600; Rosenberg & Kosslyn, 2014; Pinel & Barnes, 2017). French philosopher René Descartes (1596-1650) proposed that the mind and the body are separate and distinct where man can physically study the body, while the mind, an intangible thing, cannot physically be studied. Furthermore, physical ailments are found within the body, while mental ailments are in the mind. This is known as Cartesian Dualism and found favor with the religious atmosphere at the time; it can be found in practice today. Like Descartes, British philosopher John Locke (1632 –1704) believed that mental ailments were found in the mind through irrational thoughts and can be healed through rationalization (Baker & Sperry, 2020; “Introduction to Psychology: 1.2 The Evolution of Psychology: History, Approaches, and Questions,” 2015; Rosenberg & Kosslyn, 2014). Locke is also credited for the evolution of empirical evidence. The Renaissance also saw the development of institutions for the mentally insane (Rosenberg & Kosslyn, 2014; Sue, Sue, Sue & Sue, 2016; Farreras, 2020). The first asylum was built in Valencia, Spain in 1409. Although, these asylums were built to treat the mentally insane, some became houses of maltreatment of the mentally ill. The most infamous of these asylums in this time was the Hospital of St. Mary of Bethlehem in London, which shifted from a regular hospital to an institution for the insane in 1547. Patients at St. Mary’s were put in cages and displayed to paying patrons in an effort to discourage lifestyles that lead mental illness.
The immoral treatment of the mentally ill had become evident by the 18th Century, and a humanitarian movement to restructure the treatment of patients in asylums began (Rosenberg & Kosslyn, 2014; Sue, Sue, Sue & Sue, 2016; Farreras, 2020). Most notable in this period was French physician Philippe Pinel (1745–1826). Dr. Pinel ordered the removal of chains, transfer to lit rooms, and proper diet of patients at La Bicêtre, a French hospital for men, and later at the Salpêtrière, a hospital for women in Paris. Together with a former patient, Jean-Baptise Pussin, Dr. Pinel created the principals for moral treatment of the mentally insane. The movement crossed oceans and most notable person in the United States that moved for reform of mental institutions was a New England schoolteacher by the name of Dorothea Dix (1802-1887), she taught Sunday school to female inmates after she retired and found that mentally ill inmates suffered poor housing and treatment conditions. She worked tirelessly for the next 40 years to reform such conditions and helped change legislation and raised millions of dollars to help build 30 mental hospitals in the United States and Canada.
Chapter 3: Neuropsychosocial Approach to Mental Disorders
Over the ages many approaches to understanding mental disorders have been developed that helped us gain further insight to their etiology (Rosenberg & Kosslyn, 2011, p. xxi). The neuropsychosocial model combines some of these approaches by examining genetics and biology (development of our bodies), psychological factors (personal experiences and perceptions in behavior, cognition, and emotion), and social influences in the etiology of mental disorders. This chapter provides a brief overview of the neuropsychsocial approach.
Since Mendel’s experimentation with the pea plant and Darwin’s publication of On the Origins of Species, we have looked to our ancestors, parents, and genes to explain our biology and behavior (Darwin, 1859; Kolby, Wishaw, & Tesky, 2016; Rosenberg & Kosslyn, 2011. pp. 32-69; Twesigye, 2010). Although we may have the blueprints for our physical and behavioral development in our deoxyribonucleic acid (DNA), biological and behavioral developments are influenced by an interaction with our environment. In looking into the etiology of mental disorders, we first examine DNA. Behavioral genetics, a field that explores the behaviors influenced by genes and the interaction of the environment, attempts to identify genes that are attributed to our behavior. We will find that some genes have been linked to disorders such as mood disorders, schizophrenia spectrum disorders, and autism spectrum disorders. Most interesting is our current understanding of epigenetics and generational epigenetics. Epigenetics is the expression of our genes influenced by the environment. Generational epigenetics involve genes that have been turned on or off in parents that can be turned on or off by the same stimuli in their offspring.
While our genes are the blueprints to our physical and behavioral development, it is how they are expressed in our development during gestation and postnatal development through life that influences our biology (Kolby, Wishaw, & Tesky, 2016; Rosenberg & Kosslyn, 2011, p. 42; Twesigye, 2010). During prenatal development, teratogens like nicotine, alcohol, hormone mimicking chemicals and parental stress are biological influences, which alter our nervous and endocrine systems. These biological influences have been linked to many mental disorders like attention deficit disorder type I and II (ADHD-type I; ADHD type II), mood disorders, and anxiety disorders. These biological influences can also alter our nervous and endocrine systems during our lifespan.
The etiology of mental disorders can also point to psychological factors (Kolby, Wishaw, & Tesky, 2016; Rosenberg & Kosslyn, 2011, p. 48; Twesigye, 2010). These factors are individual experiences using perspectives like psychodynamics, behaviorism, cognitive and humanism. In psychodynamic theories, attachment theories have been linked to mental disorders like reactive attachment disorder, depression, and antisocial personality disorder. Disorders like phobias, eating disorders, and ADHDs have been linked to classical and operant conditioning. The cognitive perspective has been used to explain the development of cognitive distortions in disorders like mood disorders, anxiety disorders, and personality disorders. In the humanistic perspective, models like Abraham Maslow’s hierarchy of needs is used to look at etiology of mental disorders like anxiety and depression, where these disorders are a result of needs not being met.
Social factors like oppression, discrimination, and job loss, is also taken into account when examining the neuropsychosocial approach (Kolby, Wishaw, & Tesky, 2016; Rosenberg & Kosslyn, 2011, p. 60; Twesigye, 2010). Social factors can also be family dynamics like divorce, having an alcoholic partner or relative in the home, or enmeshed family. Social factors can also be outside the home like government, economic recession or depression, and war.
In using the neuropsychosocial approach, it is widely understood by abnormal psychologist that each three factors influence each other ((Kolby, Wishaw, & Tesky, 2016; Rosenberg & Kosslyn, 2011, pp. 32-69; Twesigye, 2010). This interinfluence is commonly known as the neuropsychosocial feedback loop. If an individual is influenced by oppression, their neurotransmitters and hormones affect their psychological mental state, or if an individual has thoughts that the world is going to end, these thoughts can prevent them from finding work, which eventually affects their nutritional intake. Taking the neuropsychosocial model into account in understanding the etiology and treatment of mental disorders provides researchers and clinicians tools in applied psychology.
Chapter 4: Assessments and Diagnoses
Please read Chapter 3 of Abnormal Psychology by Rosenberg and Kosslyn (2011)
Chapter 5: Mood Disorders
Please read Chapter 6 of Abnormal Psychology by Rosenberg and Kosslyn (2011).
Chapter 6: Anxiety Disorders
Please read Chapter 7 of Abnormal Psychology by Rosenberg and Kosslyn (2011).
Chapter 7: Dissociative and Somatic Disorders
Please read Chapter 8 of Abnormal Psychology by Rosenberg and Kosslyn (2011).
Chapter 8: Schizophrenia Spectrum and Other Psychotic Disorders
Please read Chapter 12 of Abnormal Psychology by Rosenberg and Kosslyn (2011).
Chapter 9: Personality Disorders
Please read Chapter 13 of Abnormal Psychology by Rosenberg and Kosslyn (2011).
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oercommons
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2025-03-18T00:38:19.595174
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Ramon Herrera
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https://oercommons.org/courseware/lesson/121744/overview
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Explaining Vectors in Visuals
Overview
This is a brief introduction to visual vectors in media for visual designers - or anyone who is curious about creating direction in media.
What are visual vectors?
Visual vectors are directional cues in visual design that tell the viewer how to look at your design - it tells them what to look at, where to look, and when they should be looking. They can be created with lines, shapes, words, movement or positioning. They help to create a flow within you work that helps viewers get information in a proper order and ensure key elements receive proper attention. If text is included visual vectors also help to enhance readability.
Below is a video that showcases strong use of visual vectors. Watch and notice how movement, shapes and lines help guide your eyes along the video. It feels very natural which is the result of great design. This is a great video to introduce more about vectors and the different types that exist.
Graphic Vectors
Graphic vectors are considered to be the weakest type of visual vector. They are elements that use lines, shapes and object placement to subtly suggest direction in a composition. It is important to remember that graphic vectors are static and suggest direction with careful placement. This works better in graphic design than in motion design but it is not overall a strong choice. Some examples of graphic vectors could be a horizon in a picture of a beach, a movie scene shot from the end of a hallway showing someone at the other end, or a diagonal line across a poster. Below is a visual example.
Index Vectors
Index vectors blatanlty suggest directions with things like gaze, gestures or subject alignments. As this is a more upfront method for guiding the eye of the viewer, it can be akin to pointing at what you want someone else to look at. These help create narrative clarity and are used more commonly in films. This type of vector is strong in both graphic and motion design. A well known example of this would be a character's gaze or eyeline in a close up or mid body shot or an arrow in a scene/ a character that is pointing at a specific direction.
Below is a visual example.
Motion Vectors
Motion vectors are the strongest type of vector. We're no longer suggesting a direction, we are showing it. When an element is moving across the frame this is a motion vector. This is because our eyes will naturally follow the object as it is moving, there is no question of what to look at or think where it's going as we will be actively following along. Movement can be actual, implied or graphic depending on the type of media it is. The strongest use of a motion vector is when an object moves along the x and y axis parallel to the lens it is shot from.
Below is a visual example/
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oercommons
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2025-03-18T00:38:19.612034
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Student Guide
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{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/121744/overview",
"title": "Explaining Vectors in Visuals",
"author": "Graphic Design"
}
|
https://oercommons.org/courseware/lesson/125321/overview
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https://youtu.be/URUJD5NEXC8?si=087x15SQo6PYwHAQ
Animal Cell
Overview
Animal cells are eukaryotic cells with several essential organelles. The nucleus controls cellular activities and contains DNA. Mitochondria generate energy, while the endoplasmic reticulum (rough and smooth) aids in protein and lipid synthesis. The Golgi apparatus modifies and packages proteins. Lysosomes break down waste, and ribosomes synthesize proteins. The cytoskeleton maintains the cell's shape and aids in movement, while centrioles are involved in cell division. The plasma membrane regulates the exchange of materials, and the cytoplasm houses the organelles. Together, these organelles ensure proper cell function and survival.
Introduction
Animal cells are the basic structural and functional units of life in animals. They are eukaryotic cells, meaning they have a well-defined nucleus and membrane-bound organelles. Unlike plant cells, animal cells do not have a cell wall or chloroplasts but contain specialized structures such as lysosomes and centrioles.
These cells perform essential functions such as growth, reproduction, energy production, and waste removal. Key organelles like the nucleus (which controls cell activities), mitochondria (the powerhouse of the cell), endoplasmic reticulum (for protein and lipid synthesis), and Golgi apparatus (for packaging and transporting materials) work together to maintain cellular processes.
Understanding animal cells helps us explore biological functions, disease mechanisms, and advancements in medical science, including genetics and biotechnology.
Organelles of Animal Cell
Organelles of Animal Cells
Nucleus
- The control center of the cell, containing the cell's genetic material (DNA).
- Responsible for regulating growth, metabolism, protein synthesis, and cell division.
- Surrounded by a double membrane known as the nuclear envelope.
Mitochondria
- Known as the powerhouse of the cell, they produce energy in the form of ATP through cellular respiration.
- They have their own DNA and can replicate independently.
Endoplasmic Reticulum (ER)
- A network of membranes involved in the synthesis, folding, modification, and transport of proteins and lipids.
- Rough ER (with ribosomes) helps in protein synthesis.
- Smooth ER (without ribosomes) is involved in lipid synthesis and detoxification processes.
Golgi Apparatus
- Functions in modifying, sorting, and packaging proteins and lipids for delivery to different parts of the cell or for secretion outside the cell.
- Composed of a series of flattened sacs called cisternae.
Lysosomes
- Contain enzymes that break down waste materials and cellular debris.
- They are involved in digestion and the recycling of cellular components.
Ribosomes
- Tiny structures either floating freely in the cytoplasm or attached to the rough ER.
- They are the site of protein synthesis, translating genetic information from mRNA into proteins.
Cytoskeleton
- A network of protein filaments (microfilaments, intermediate filaments, and microtubules) that maintain the shape of the cell, enable movement, and anchor organelles.
- Involved in cell division and transport within the cell.
Centrioles
- Found in animal cells and play a crucial role in cell division.
- Help in the formation of the spindle fibers during mitosis.
Plasma Membrane
- The outer boundary of the cell, composed of a lipid bilayer with embedded proteins.
- Regulates the movement of substances in and out of the cell, maintaining homeostasis.
Cytoplasm
- The jelly-like substance between the plasma membrane and the nucleus, in which organelles are suspended.
- It allows for the movement of molecules and plays a role in cellular processes.
Each of these organelles works in harmony to keep the animal cell functioning properly and allows the organism to survive and thrive.
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oercommons
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2025-03-18T00:38:19.634943
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02/18/2025
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/125321/overview",
"title": "Animal Cell",
"author": "Sikha R"
}
|
https://oercommons.org/courseware/lesson/123175/overview
|
Application and Reflection - Module One
Overview
This resource is part of the OERizona Advanced Course. This section is the application and reflection section for Module One.
Completing Module 1 - Google Form
Thank you for your thoughtful collaboration and thorough evaluations as part of the OERizona Advanced Course Module One.
To support your reflection and application of this Module, please complete the Module One Application and Reflection Google Form. Please note: it will ask you for the URLs to the three OER that you evaluated. You should be able to find those resources under your "My Items".
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oercommons
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2025-03-18T00:38:19.647681
|
12/18/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/123175/overview",
"title": "OERizona Advanced OER Skills, Evaluating OER, Application and Reflection - Module One",
"author": null
}
|
https://oercommons.org/courseware/lesson/86864/overview
|
Education Standards
2. Who Am I - My Feelings Make a Song
3. Who Am I - Master Image Slides
SEL 3 Signature Practices Playbook | CASEL
SEL-Music Lesson: Who Am I - My Feelings Make a Song
Overview
This unit by Northshore School District, Washington, contains four progressive lesson activities created for primary grades which connect Washington Social Emotional Learning (SEL) Standards 1, 4 and 5 with Washington Music Standards 1, 2 and 8 using the creating/responding processes to generate original songs and express personal feelings.
Unit Overview
Sample song and material templates were created by the author, Kelly Foster Griffin - Northshore School District, for this unit and may be reused, downloaded, shared, and adapted. The lesson format, with its Welcoming Inclusion, Engaging Strategies and Optimistic Closure, is based on the components of the SEL 3 Signature Practices Playbook 2019.
Table of Contents
- Activity One: Sharing Feelings Playing “Emotion Charades”
Students will play a game identifying an emotion from non-verbal cues: body language, eye contact and facial expressions. SEL Standard/Indicators: Self-Awareness/SEL.K-2.1A.1 With adult assistance, I can recognize, identify, and name my emotions, feelings, and thoughts. SEL.K-2.1A.3 With adult assistance, I can verbally express my emotions or feelings. - Activity Two: Creating a Call & Response Song Using Feelings
Students will work in small groups and contribute a personal feeling to use in the lyrics of a new song. SEL Standard/Indicators: Self-Awareness/SEL.K-2.1A.1-3 With guidance, I can verbally express my emotions or feelings. Social Management/SEL.K-2.5A.1-2 With guidance, I can work collaboratively as a member of a team. WA Music Standard/Indicators: Creating (Imagine)/MU: Cr:1 Generate and conceptualize artistic ideas and work. - Activity Three: Interpreting Personal Meaning to Instrumental Music
Students will listen and dance to varied examples of instrumental music and answer the question, “What is it saying?” SEL Standard/Indicators: Self-Awareness/SEL.K-2.1A.2 Recognize how different emotions, feelings, and thoughts feel in my body. Social Awareness/SEL.K-2.4A.2 Recognize that people can have different feelings when faced with the same situations. Social Management/SEL.K-2.5A.1 Demonstrate attentive listening skills. SEL.K-2.5A.2 Demonstrate the ability to wait, take turns, and share with others. WA Music Standard/Indicators: Responding (Interpret)/MU: Re:8.1.1 With limited guidance, identify expressive qualities that reflect the creators’ expressive intent. - Activity Four: Expressing Personal Feelings Through Percussion Instruments
Using a Call & Response song form, students will substitute body percussion or percussion instruments in place of words to express their feelings. WA SEL Standard/Indicators: Self-Awareness/SEL.K-2.1A.2 Recognize how different emotions, feelings, and thoughts feel in my body. SEL.K-2.2A.2 Identify strategies to help me be in control of myself and ask for additional assistance as needed. WA Music Standard/Indicators: MU: Cr:2.1.1a With limited guidance, demonstrate and discuss personal reasons for selecting musical ideas that represent expressive intent.
Attribution and License
Attribution
This lesson was developed by Kelly Foster Griffin, NBCT - Music Specialist Moorlands Elementary, Northshore School District
SEL 3 Signature Practices Playbook copyright Collaborative for Academic, Social, and Emotional Learning (CASEL) and developed by the 2016-2017 Oakland Unified School District SEL Team based on the 2013 work of CASEL Consultant Ann McKay Bryson. | License Agreement
Social Emotional Learning: Standards, Benchmarks, and Indicators developed for the Washington Office of Superintendent of Public Instruction by the SEL Workgroup is licensed under a Creative Commons Attribution 4.0 International License.
Washington Arts K–12 Learning Standards by the Washington Office of Superintendent of Public Instruction are licensed under a Creative Commons Attribution Non-Commercial 4.0 International License.
Cover Image by Gerd Altmann from Pixabay
License
Except where otherwise noted, this lesson by Northshore School District is licensed under a Creative Commons Attribution License. All logos and trademarks are the property of their respective owners.
Activity One: Sharing Feelings Playing “Emotion Charades”
WA SEL Standard: Self-Awareness
- SEL.K-2.1A.1 With adult assistance, I can recognize, identify, and name my emotions, feelings, and thoughts.
- SEL.K-2.1A.3 With adult assistance, I can verbally express my emotions or feelings.
Age Range: Primary
Duration: 20 minutes
Materials:
- Emotion Cards
- Whiteboard or projector to display ideas
Vocabulary:
- Charade
- Emotions
- Facial Expressions
- Body Language
Playing a Game (Welcoming Inclusion Activity)
Today we are going to learn a new game called Charades. Charades is a type of guessing game where you have to act out a word without talking. You are going to be guessing an emotion. Emotions are inside feelings that come from a mood, an event, or an interaction with others.
When and Why: Games reinforce positive connections, lift up the energy in the room and provide a safe space to explore feelings through play-acting.
- SEL Focus: Participants will recognize, identify, and name emotions, feelings, and thoughts, in self and in others by observing how it feels/looks in the body and verbally expressing these emotions or feelings.
- Modifications and Variations: The activity can be limited to emotions that students identified in class or to additional emotions named on the emotion cards.
What emotions or feelings have you experienced?
Students brainstorm emotions they have felt in partners or trios.
Create a class list of these emotions and try to demonstrate their meaning using facial expressions only – no sounds or words.
How do we play Emotion Charades?
The player chooses an emotion card from the list above (or alternatively, an emotion beyond the brainstormed list.)
The player must act out the emotion without making any sound or touching others.
The player can use eye contact, facial expressions - moving the muscles in the face to express the emotion; and body language – hand gestures, posture, and movement to demonstrate the emotion.
To make sure everyone has a chance to “read” the emotion, the player must walk past the whole group once using body language, and facial expressions before the guessing can start.
Teammates can put a thumbs up when they are ready to guess the emotion.
The player can make a circular hand gesture when they hear a guess on the right track and touch their nose when the word is guessed.
Playing the game
The teacher chooses an emotion from the list (or from the emotion cards) and demonstrates how to play the game. Students call out their guesses until the correct emotion is named.
Repeat the game with students taking the lead role.
Option: Choose a small group of students to act out the emotion instead of one player.
Printable Emotion Cards
Debrief
List the emotions that were used in the game and identify them as positive, negative, or neutral emotions using smiley, sad or neutral faces. Emphasize that we all have these emotions in common and feel them from time to time.
Create a simple Echo Song by improvising a melody using the emotions as lyrics and having students repeat it. (Students not ready to share may tell another person their emotion or “pass.”) Here is a sample melody:
Optimistic Closure
When and Why? Optimistic Closure activities allow time to reflect, bring all voices back into the room and provide essential feedback to the teacher about the collective experience.
Ask one or more of the following questions:
- What was something that challenged your brain?
- What were the clues that helped you recognize and identify the emotions of others?
- What emotions did you feel while playing the game?
Activity Two: Creating a Call & Response Song Using Feelings
WA SEL Standard: Self-Awareness, Social Management
- SEL.K-2.1A.1-3 With guidance, I can contribute a personal feeling to use in a song
- SEL.K-2.5A.1-2 With guidance, I can work collaboratively as a member of a team.
WA Music Standard:
- MU: Cr:1 Generate and conceptualize artistic ideas and work. (Imagine)
Age Range: Primary
Duration: 30 minutes
Materials:
- Whiteboard/projector
- Song template
- Paper
- Pencil
- Crayons
Vocabulary:
- Lyrics
- Lyricist
- Call & Response Song
- Melody
- Collaborator
Engaging Strategies: Co-Creating and Group Singing
When and Why: This activity allows for individuals to contribute their own ideas in a small group project. It fosters creativity, listening skills and collaboration with others.
SEL Focus: This activity builds self and social awareness by identifying emotions and perspectives expressed by others. It also promotes social management by demonstrating attentive listening skills, the ability to wait, take turns and share with others.
- Music Focus: Participants will contribute lyrics for a new song about feelings within a Call & Response musical form.
- Modifications and variations: Pair up students who may need additional support instead of having individuals respond alone. Sing and play several “Call & Response” songs suitable for children such as “Shoo Turkey” or “John the Rabbit” to deepen understanding of the song form and share the cultural, historical & stylistic context of each song.
Begin with a Review
Play several rounds of “Emotion Charades” or optionally,
Have the teacher display an emotion card to the class without looking and have the students move about the room by acting out the emotion using facial expressions and body language only – no speaking or touching. The teacher guesses the emotion on the card. Repeat with a student in the teacher’s role.
“Let’s create a song about our feelings.”
In this next activity, we are going to choose three emotions from the Charades game, and later, a personal feeling to create lyrics for a new song. Lyrics are the words in a song. A person who writes lyrics to songs is called a lyricist.
Introduce the Song Template
The teacher shows a visual of the song template below and performs the song for the students by filling in the blanks with emotions used in the prior activity.
When students are ready, they can sing the response independently while the teacher sings the call.
- sample melody
Introduce “Call & Response” form
Are you singing the same words as me – like an “echo” - or are you singing something different? (Different.)
This is a type of song form called Call & Response. Call & Response songs have a leader give the call and the group sing the response. The group response uses a different melody – or song tune. It is like a musical conversation.
- Ask for student volunteers to take the lead “call” role with the rest of the class singing the response. Students are encouraged to make up their own call melody with the response staying the same each time.
Small Group Work
Students are grouped in threes. (If there is an uneven number, a group of two will work with one child using the teacher’s example or contributing two emotions).
Individuals choose their emotion and the small group comes to an agreement on the order they wish to present their emotions.
- Allow time for some experimentation and rehearsal.
- Teacher checks in with groups and provides guidance as needed.
Whole Group Sharing
Students come back together and sit near teammates in a circle formation to allow equal access in the conversation as all students can see each other, with no one sitting in front or behind.
Going around the circle, students take turns singing (or speaking) their emotion on the “call” while the group sings the responses.
- To support the start of the singing, the teacher can provide a hand “conducting” gesture and a preparation breath.
- Ideally, keep the verses flowing from one to the next without comment so the music can have a stronger emotional impact.
- Option: If an individual or group needs more support in the lead “call” role, choose additional students to assist or have the whole class sing both parts.
Debrief
Congratulations on becoming a collaborator! A collaborator is a person who helps a team with creating a new song. By working together, you became collaborators on a new verse for our song.
- Celebrate personal risk-taking and acknowledge individuals being emotionally vulnerable.
- Option: If time allows, provide teams a paper, pencils, and crayons to capture their unique verse. Have teammates illustrate the emotion they chose and display the verses around the room.
Optimistic Closure
Ask one or more of the following questions:
What is something you had in common with another classmate?
- What is something several people had in common?
- What is something you appreciated in your small group?
Activity 3: Interpreting Personal Meaning to Instrumental Music
WA SEL Standard: Self-Awareness, Social Awareness, Social Management
- SEL.K-2.1A.2 Recognize how different emotions, feelings, and thoughts feel in my body.
- SEL.K-2.4A.2 Recognize that people can have different feelings when faced with the same situations.
- SEL.K-2.5A.1 Demonstrate attentive listening skills.
- SEL.K-2.5A.2 Demonstrate the ability to wait, take turns, and share with others
WA Music Standard:
- MU: Re8.1.1 With limited guidance, identify expressive qualities that reflect creators’/performers’ expressive intent.
Age Range: Primary
Duration: 20 minutes
Materials:
- 2-4 instrumental music examples to play
- Response template
Vocabulary:
- Communication
- Perspective
- Point of View
What Is It Saying? (Engaging Strategies)
There is a famous saying, from Hans Christian Anderson “Where words fail, music speaks” Today we are going to explore the idea of music as a form of communication. Communication occurs when you or someone else shares ideas, thoughts, or feelings. It can happen through words, signs, behaviors and even sounds. In this activity, I will play music to which you will be listening and dancing. As you listen to the music, what is it saying?
When and Why: This activity taps into the therapeutic qualities of music play to encourage positive changes in mood and overall well-being. It provides opportunities to exchange ideas and listen to the perspective of others. Dancing/moving to music brings energy into the room.
- SEL Focus: This activity builds self-awareness by reflecting on music, identifying the feelings it evokes and assigning personal meaning. It practices relationship skills and social engagement, as partners share their ideas and actively listen to different perspectives.
- Music Focus: Participants will describe what is felt and heard (perceived/experienced) when responding to music.
- Modifications and variations: Instead of dancing or moving to music, students may draw or write about what the music is trying to convey. Partners of 2-3 may be preselected instead of chosen spontaneously depending on the comfortability level.
- Preparation: Before the activity, choose several instrumental musical selections to play for students that elicit a variety of different moods (e.g., Ellington w/Coltrane, In a Sentimental Mood; Mussorgsky’s Pictures of an Exhibition, Mvt IV: The Old Castle; Chiquinha Gonzaga’s Atraente; Beethoven’s 5th Symphony Mvt 1).
Play the Game
When the music stops, find a partner, and take turns sharing about what you think the music is saying.
You may hear ideas that are similar or different from your own. In this game, there will be no right or wrong answers, only different perspectives. A perspective is a way of thinking about something – also called point of view. If your partner has a different perspective or point of view, ask them to tell you more and listen carefully to understand. It may open up your mind to an idea you had not considered.
- When the music restarts, thank your partner for sharing their idea and we’ll play again.
- Resume the game with the same music a few more times to allow opportunities to share with new partners and listen to other perspectives on the same music.
- Repeat the activity with a new, contrasting musical example.
Debrief
Provide background information to students about the musical selections: (Composer, title, historic context, insights from program notes, etc.)
If desired, have students write or draw a picture about what they think the music is saying.
Sample Response Form:
Optimistic Closure
Bring the whole group back to a circle or seated position and ask several questions:
What was the music saying to you?
- How did your dancing relate to the music?
- How was it to share and listen to one another?
- What made your heart feel good?
Activity Four: Expressing Personal Feelings Through Instruments
WA SEL Standard: Self-Awareness
SEL.K-2.1A.2 Recognize how different emotions, feelings, and thoughts feel in my body.
SEL.K-2.2A.2 Identify strategies to help me be in control of myself and ask for additional assistance as needed.
WA Music Standard:
- MU: Cr:2.1.1 a. With limited guidance, demonstrate and discuss personal reasons for selecting musical ideas that represent expressive intent.
Age Range: Primary
Duration: 30 minutes
Materials:
- a variety of percussion instruments (woods, metals, shakers, drums)
- backing track
Vocabulary:
- body percussion
- rhythm
- backing track
Four-Beat Echo Patterns (Engaging Strategies)
- When and Why: This activity helps individuals nonverbally express their internal feelings through a creative process. It incorporates movement, a backing track, and instruments to invigorate the learning process.
SEL Focus: Participants practice the SEL skills of self-awareness by identifying or choosing an emotion to express through body percussion patterns and rhythm instruments. It also promotes self-management (impulse control) by being able to start and stop the playing of instruments, thus allowing others to share.
- Music Focus: Participants will create/improvise 4-beat rhythm patterns using body percussion (e.g., stomp, pat, clap, snap), and non-pitched percussion instruments.
Modifications and Variations:
- This activity can easily be adapted for grades K – 5.
- Primary students will find success by limiting improvisations to body percussion patterns first before handing out non-pitched percussion instruments. Modify snaps to finger pinches for youngest learners.
- “Found” instruments such as: wood sticks, stones, pebble-filled cans, and plastic buckets can be substituted for store-bought instruments.
- It is okay for individuals to listen and observe first before joining the activity or play with a partner.
- For intermediate students or deeper explorations into improvisation and musical forms try:
- Lengthening the improvisations to 8-beats and taking turns with a partner creating “Question-Answer” phrases
- Setting up barred Orff instruments in E minor pentatonic: E GAB D (no F or C bars) to aid melodic improvisation
- Extending individual improvisations to 24 beats (3 phrases) to support a continual flow of a musical idea. Have the group sing or play together the final response on phrase 4 - “All these feelings are mine” as a cue for the next player to be ready to start
Preparation Suggestions:
- Put together non-pitched instrument kits to speed up the process of passing out instruments.
- Make sure students have had previous lessons on instrument care; opportunities to pick them up, play them and set them down.
Review the Song, “All These Feelings”
Begin the activity in circle formation and review the Call & Response song, “All These Feelings” from Activity 2 using three pictures from the emotion cards.
Have students close their eyes and give a thumbs up when they are ready to share a feeling. Using the emotions offered by students, repeat “All These Feelings” as many times as needed to complete the circle.
- As done previously, encourage students to lead their own “call” by singing (or speaking) their emotion with the group taking the responses.
Introduce Body Percussion
We have learned new ways to discover feelings through body language, eye contact, listening to music and creating song lyrics. Today, we are going to share feelings through body percussion and instruments. Body percussion is when you use your body as an instrument to create different sounds such as when you stomp your feet, pat your legs, clap your hands, and snap your fingers. I will be making rhythm using body percussion. Rhythm is the way the words go in music.
Be My Echo. The teacher performs four-beat echo patterns and students repeat them back.
- Let’s add a backing track to our body percussion. Backing tracks are used to help musicians add extra parts to their music without having to increase the size of the band.
- Play the sample backing track (or other music in 4/4 time) and continue as before.
- Try hiding the words in your head. The teacher continues leading 4-beat body percussion patterns without saying the lyrics. Students follow the teacher's example.
- Ask for student volunteers to lead the class with body percussion patterns over the backing track.
Add Percussion Instruments
We are going to work in a small group and explore our feelings through instruments. You will take turns leading and echoing. You can lead with body percussion or switch to a percussion instrument depending on what you prefer. Think about matching the instrument and rhythms to the feeling you have chosen for this activity.
The teacher reviews the names of the instruments, how to play and care for them.
- Have students sit in groups of 3’s or 4’s.
- Briefly discuss and have a student group demonstrate how to work together successfully, (e.g., take turns, respectfully ask to use an instrument, play them with care, etc.)
- Hand out the instrument kits.
- Practice a common signal to bring students back to silence (e.g., “4-3-2-1, ready rest.”)
- Allow time for some experimentation and play the backing track as background music.
- Teacher checks in with groups and provides guidance as needed.
- After ample exploration time has occurred, bring the class back to focus with the attention signal.
Debrief
- Provide small groups the opportunity to share 30-60 seconds of their work. It is okay to “pass” if they are uncomfortable with sharing or not ready to share at this time.
- Applaud and cheer for each performance.
Optimistic Closure
- Have individuals reflect on their artist choices:
Why did I choose my instrument?
How did the instrument and rhythms I chose represent emotion?
Extension Activity
In a future lesson, have individuals revise their team verses and create their own verse by replacing their “feeling words” with similes of animals, things in nature or colors to represent the emotion behind the lyrics. For example:
Sample Template:
I feel like turtle (Yes, yes)
Hiding in a shell (Fine, fine)
I feel like a turtle (yes, yes)
And all these feelings are mine!
Or:
I feel like river (Yes, yes)
Wandering blue (Fine, fine)
I feel like a river (yes, yes)
And all these feelings are mine!
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oercommons
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2025-03-18T00:38:19.772253
|
Lesson
|
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/86864/overview",
"title": "SEL-Music Lesson: Who Am I - My Feelings Make a Song",
"author": "Social Science"
}
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https://oercommons.org/courseware/lesson/123173/overview
|
Demonstration of OER Evaluation Tools
Overview
This resource is part of the OERizona Advanced Course. This section explores the tools of OER evaluation that support discoverability and iteration of OER. In this section, the user can see a sample demonstration on how to use the evaluation tools that are built into OER Commons.
OER Evaluation Goals
In this section, we will demonstrate how to use the built-in Evaluation tools on the OER Commons platform. As a reminder, evaluation is a key aspect of iteration and continued improvement. Open Educational Resources (OER) are designed to be discoverable, dynamic resources, which are iterated, thus benefitting both the creator and the user.
- OER authors have chosen to license their work with open licenses so their resources can be found and used by others. Many OER creators also are actively interested in feedback and collaboration.
- OER users can contribute to the OER community by leaving supportive and evaluative feedback so that other users can see different viewpoints. This also supports authors as they iterate their work.
OER Evaluation can incorporate many different quality indicators. In this section, we will demonstrate the use of two rubrics.
- A nonprofit education organization called Achieve has created a rubric for evaluting OER with special focus on criteria that are unique to OER.
- OERizona also has a quality review rubric. Using these tools can help provide similar frames of reference across Arizona as users seek to compare reiews and compare resources.
Using the OER Evaluation Tools
OER Commons is designed to allow three different types of evaluation tools.
- Star rating - this tool is on the main information page about each resource and allows registered users to leave ratings using sras up to 5 stars total. This allows users to provide a quick set of feedback for an overall, quantitative rating.
- Comments - OER Commons has a comment section for each resrouce. Registered users can leave individual, open-ended comments on each resource. Some networks and collaborative communities may choose to use specific sentence stems to represent cohesive, systematic review systems. Any qualitative feedback left in the OER Achieve Rubric will also populate as comments.
- Achieve OER Rubric - OER Commons was designed to have an embedded evaluation tool to allow users to qualitiatively and quantitatively evaluate resources. This allows users to see feedback that are aligned with quality indicators as. The Rubric has number scores for each indicator as well as space for qualitative feedback. The qualitattive feedback populates as comments and the quantative scores are averaged and can be used to sort search results.
The OERizona rubric has multiple indicators of quality. These can be populated into the OER Commons review features by using the comment feature, as seen in the demonstration below.
Demonstration of OER Evaluation Tools
Joanna to film video of evaluating this resource.
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oercommons
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2025-03-18T00:38:19.789323
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12/18/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/123173/overview",
"title": "OERizona Advanced OER Skills, Evaluating OER, Demonstration of OER Evaluation Tools",
"author": null
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https://oercommons.org/courseware/lesson/86881/overview
|
Education Standards
2. Who Are We Together- Communicating Emotions (editable)
Emotion Cards - Print and Cut
Synectics_ Emotions and Locations
Who Are We Together - Synectics
SEL-Music Unit: Who Are We Together? Communicating Emotions
Overview
This unit, developed by Northshore School District in Washington, contains four days of lessons where students engage with music from a variety of cultures and analyze how emotions are communicated through different styles of music. Students will make connections between showing emotions with their words, their bodies and with instruments and will perform instruments as an ensemble to communicate different emotions.
Overview
his lesson was developed by Elise Harris- Northshore School District. The lesson format, with its Welcoming Inclusion, Engaging Strategies and Optimistic Closure are based on the components of the SEL 3 Signature Practices Playbook 2019
This unit contains activities that connect SEL Standard 2, 6 and Music Standards 7, 8,9. The nine activities can be spread out over multiple lessons or grouped together in the three suggested lessons below.
Table of Contents
Lesson One: We Can Identify Our Own Emotions and Respect the Emotions of Others
Activity 1: (Welcoming/Inclusion Activity) Synectics Locations and Emotions
- Activity 2: (Engaging Strategies) Emotions in Music, Audio World Tour
- Activity 3: (Optimistic Closing) Mix and Mingle
Lesson Two: We Can Understand Each Other’s Emotions
- Activity 1: (Welcoming/Inclusion Activity) Emotions Look Like/Sound Like Maître d’ Game
- Activity 2: (Engaging Strategies) Emotions expressed through instruments, Turn and Talk
- Activity 3: (Optimistic Closing) What emotion do you hear? game
Lesson 3 – We Can Express Emotions as an Ensemble
- Activity 1: Activity 1: (Welcoming/Inclusion Activity) Deedle, Deedle Dumpling Greeting Frenzy
- Activity 2: Engaging Strategies) Hey Diddle Diddle variations
- Activity 3: Optimistic Closing) One Minute Accolade
Attribution and License
Attribution
This lesson was developed by Elise Harris - Northshore School District.
SEL 3 Signature Practices Playbook copyright Collaborative for Academic, Social, and Emotional Learning (CASEL) and developed by the 2016-2017 Oakland Unified School District SEL Team based on the 2013 work of CASEL Consultant Ann McKay Bryson. | License Agreement
Social Emotional Learning: Standards, Benchmarks, and Indicators developed for the Washington Office of Superintendent of Public Instruction by the SEL Workgroup is licensed under a Creative Commons Attribution 4.0 International License.
Washington Arts K–12 Learning Standards by the Washington Office of Superintendent of Public Instruction are licensed under a Creative Commons Attribution Non-Commercial 4.0 International License.
Image by Gustavo Rezende from Pixabay
License
Except where otherwise noted, this lesson by Northshore School District is licensed under a Creative Commons Attribution License. All logos and trademarks are the property of their respective owners.
Lesson One: We Can Identify Our Own Emotions and Respect the Emotions of Others
WA SEL Standard: Social Engagement
- SEL.K-2.6B.1: With adult assistance, I can engage in activities with peers from different cultures in a way that shows I respect them.
- SEL.K-2.6B.2: With adult assistance, I can identify how members of a diverse community rely on each other.
WA Music Standard:
- Anchor 7.2: Perceive and analyze artistic work.
MU: Re7.2.1 With limited guidance, demonstrate and identify how specific music concepts (such as beat or pitch) are used in various styles of music for a purpose. - Anchor 8: Interpret intent and meaning in artistic work.
MU: Re8.1.1 With limited guidance, demonstrate and identify expressive qualities (such as dynamics and tempo) that reflect creators'/performers' expressive intent.
Age Range: Grades K-2
Duration: 30 minutes
Activity One: (Welcoming/Inclusion Activity) Synectics: Locations and Emotions
We can feel different emotions in different places
- Time: 4-7 minutes
- When and why: Open the lesson with this activity to build emotional vocabulary and encourage different viewpoints. Use this activity to prepare students for Lesson 1, Activity 2. (Adapted from SEL Playbook, p. 17.)
- SEL Focus: This activity provides opportunities for Social Awareness, Perspective-taking, and Respect for others.
“Synectics” is a problem-solving technique that seeks to promote creative thinking, typically among small groups of people of diverse experience and expertise.
Definition from Oxford Languages
Steps
- Open the Synectics: Locations and Emotions slides.
- Show the first slide with the title and image of a location.
- Explain that the task is to complete the sentence stem: “The__(location)__ is_(emotion)____ because…” For example, “The playground is happy because there are lots of fun things to do.” “The playground is sad because it is empty.”
- Participants generate as many comparisons as they are able between the given emotion and any of displayed images in 1-2 minutes. They may turn and talk with a partner or small group to share their ideas.
- Ask for several volunteers to share their “location and emotion sentence.” Encourage volunteers that are able to share a new emotion or description to demonstrate how we all have different perspectives.
Debrief: After brainstorming is complete, ask students if they noticed any ideas that were different from what they first thought of. Did hearing someone else’s perspective give you any new ideas?
Modifications and variations: Add new location images that will have meaning to your students, like pictures from around your school building or town. Students may also bring in their own images. Allow students to use a sentence stem that shows the opposite: “__(location)___ is not ___(emotion)____ because…”
Activity Two: (Engaging Strategies) Emotions in Music, Audio World Tour
Music can make us feel different emotions
Time: 20 minutes
- When and why: This is an adaptation of “Gallery Walk,” (SEL Playbook, p. 27). Rather than walking around the room like at an art gallery, this activity allows students to brainstorm the emotions they can hear in music and make predictions about the occasions at which each piece of music might be heard.
- SEL Focus: During this activity, students show Self-Awareness (Identifying emotions) by connecting emotions with musical elements that can communicate these emotions. They will show Social Awareness (Appreciating diversity and Respect for others) by experiencing music from different cultures that may not fit their predictions for how musical elements and emotions are related.
Steps
- Start by brainstorming a list of emotions that can be felt through music. Write on a whiteboard or chart paper with space next to each word. Try to group similar words together (i.e., anger, mad)
- Using another color marker, go back to each group of emotions and ask what clues students might hear in the music to know what emotion the music is communicating. This list can include many expressive elements such as tempo, dynamics, and pitch as well as specific instruments.
- Listen to 4 musical examples from different cultures but don’t tell students yet what occasion this music is used for. You can use any song you like or choose from the suggestions below. Share recordings of performances for different occasions: wedding, festival, holiday, patriotic, funeral, lullaby, war, etc.
- A note on choosing recordings: It is ok if you don’t know all of the elements of a country’s unique musical style. It is more important to represent a variety of cultures, especially those that represent your students. Be open with students that you are learning as well and that you are excited when they can be the experts in a new style of music.
- Consider sharing only the audio if you are using a video example so that students aren’t influenced by the images and have to use the musical clues to determine the emotions.
- After each song, analyze the musical clues (tempo, dynamics, pitch, instruments, etc.) and make a prediction of what type of occasion this music might be used for. Encourage students to give evidence with their reason. (For younger grades, encourage complete sentences. You can provide sentence starters such as “This music sounds like it would be at a ______________ because _______________.”
- After students make their prediction on a piece, reveal the occasion it would be used at. Ask if it matched their prediction? If not, can they make some guesses why it might be different?
Recording suggestions
- Native Wedding Dance by Melvin John, Moosachie Hills Canada YouTube Link
- Olympic Hymn, Official Olympic Anthem YouTube Link
- Dungdungwen kanto, Wedding Song/Lullaby from The Phillipines YouTube Link Translation Link
- Siman Tov U'mazal Tov, Wedding/Celebration song from Israel YouTube Link Translation Link
- La nòvia, Wedding Song from Occitania (Southern France) YouTube Link Translation Link
- Senzenina (Senzeni), Funeral and Protest Song from South Africa YouTube Link Translation Link
- Aijā žūžū lāča bērni, Lullaby from Latvia YouTube Link Translation Link
- Arrurú, Lullaby from Mexico YouTube Link Translation Link
- Er is een jarig hoera hoera, Birthday song from Belgium YouTube Link Translation Link
- La mulţi ani cu sănătate! Birthday song from Romania YouTube Link Translation Link
- 恭喜恭喜 (Gong Xi Gong Xi) Chinese New Year Song YouTube Link Translation Link
Debrief: Ask one or more of these questions:
- What is something you appreciated about doing this activity?
- What was challenging about it?
Modifications and variations:
Play four examples of music from one country, but for different occasions.
- Play four examples of music for the same occasion, but from four different countries.
Activity Three: (Optimistic Closing) Mix and Mingle
We can understand emotions from each other’s experiences
Time: 3-5 minutes
- When and why: Close the lesson with this activity to build community by encouraging participants to interact with each other and sets the expectation that everyone’s emotions and experiences are valued. (Adapted from SEL Playbook, p. 16.)
- SEL Focus: This activity builds Relationship Skills (Accurate Self-Perception and Social Engagement), as participants share their ideas and actively listen to divergent perspectives.
Steps
- On a whiteboard or piece of paper, ask participants to write down a response to a prompt related to the previous activities from the lesson. Examples: “What is a place that makes you feel happy?” “Where do you go to feel calm?” “What sound surprises you?”
- When you announce, “Mix and Mingle!” and turn on music, students move around the room.
- When the music stops, students find a partner near them. Help with pairing if needed.
- Partners share their responses, listen actively to each other, and ask a follow-up question. Example: “What about your room makes you happy?” “Why does the park make you feel calm?” “When do you usually hear the sound that surprises you?” (You may want to coach the class on follow-up questions with a few student leaders before starting the activity.)
- Start the music again and repeat with as many partners as time allows.
Debrief
- What were some of the things you appreciated about doing this activity?
- What was challenging about it?
- What SEL skills did you use?
Modifications and Variations
Use this activity at the beginning of class to prepare students for the content that will be
Lesson Two: We Can Understand Each Other’s Emotions
WA SEL Standard: Social Awareness, Social Engagement
- SEL.K-2.4A Demonstrates awareness of other people’s emotions, perspectives, cultures, languages, histories, identities, and abilities.
- SEL.K-2.4A.1 Identify emotions and perspectives expressed by others.
- SEL.K-2.6B.3 With adult assistance, I can positively and respectfully interact in peer and group activities and interactions.
WA Music Standard:
- Anchor 9: Apply criteria to evaluate artistic work.
MU: Re9.1.1 With limited guidance, apply personal and expressive preferences in the evaluation of music for specific purposes
Age Range: Grades K-2
Duration: 25-35 minutes
Activity 1: (Welcoming/Inclusion Activity) Emotions look like/sound like, Maître d’ game
We can show different emotions with our faces, our bodies, and our voices.
Time: 4-7 minutes
- When and why: Open the lesson with this activity to build emotional vocabulary and encourage different viewpoints. Use this activity to prepare students for Lesson 1, Activity 2. (Adapted from SEL Playbook, p. 17.)
- SEL Focus: This activity provides opportunities for Social Awareness, Perspective-taking, and Respect for others.
Steps:
- Using a list of emotions, ask students to select 5 emotions they would like to focus on to perform today.
- Write the selected emotions on the board or chart paper to create an emotion menu. Only fill in the left column for now.
- Play the game “Maître d’” (p. 30 in SEL Playbook)
- Share that the vocabulary word maître d’ is a word in French that means “master of the house.” They are the person at a restaurant who is the head waiter and often takes reservations and leads you to your table.
- Students mingle while the music is playing.
- When the music stops the maître d’ calls out a table and number, for example: “Table for three!”
- Students quickly make their table of three. Students without a table walk up to the maître d’ and form a small group or are joined with the closest table.
- The maître d’ calls out an emotion from the menu. Students show the emotion with their body and make any sounds that match the emotion.
- Continue the game by calling out different size tables and different emotions off of the menu.
- After several rounds of the game, invite students back to their spots. Ask for suggestions of what each emotion looked like and sounded like and write the ideas on the menu.
Debrief:
- Ask students which emotion was the funniest at their table.
- Which emotion was the hardest to show?
Modifications and variations:
- Try the game maître d’ with pantomime. Explain that this is a silent restaurant so when an emotion is called out, students show the emotion with their body but can’t make a sound.
Activity 2: (Engaging Strategies) Emotions expressed through instruments, Turn and Talk
We can describe emotions using words and sounds
- Time: 15-20 minutes
- When and why: This activity can be used for instrument exploration and to provide all students a low-risk opportunity to perform alone.
- SEL Focus: During this activity, students show Self-Awareness (Identifying emotions) by connecting emotions with musical elements (dynamics, tempo, pitch) that can communicate these emotions.
Steps:
- Prior to the lesson, have a variety of instruments set out in a circle, rows or any formation that works for rotating between instruments. Create any combination with the instruments you have or allow students to help you select instruments they want in the ensemble.
Instrument suggestions include:
- Large drums: tubanos, djembes
- Hand drums with mallets
- Small percussion: wood blocks, maracas, egg shakers, guiros, rhythm sticks, etc.
- Barred instruments C Pentatonic Scale (remove all Fs and Bs): Xylophones, metallophones, bells
- Making connections: Ask the class to “Think about the emotions from the maître d’ game. We will be trying to communicate these same emotions on our instruments but won’t have our words or body language to communicate, only the sounds of the instruments. Take one minute to yourself and think if you had a drum or other percussion instrument, how you would play your instrument to make it sound like each emotion.”
- After a few moments of think-time, invite students to turn and talk with their partner to describe how they would play each emotion. They can also act out with their hands how they would play the instrument differently for each emotion.
- Go through the Emotion Menu and add student ideas of how they would play an instrument for each emotion in the “Sounds like “column.
- Invite students to move to the instruments already arranged in the room or hand out instruments in the manner that works best in your class.
- Go around the circle and ask each student to say any emotion and then demonstrate the sound. The class then copies that sound for 4 beats. They can choose from the menu, choose a new idea, or use an idea that has already been said. Example, “Angry sounds like this…” “Silly sounds like this…” Remind students that the sound of instruments may not change much with each emotion, but the physical motion of how they play it can also communicate the emotion.
Debrief
- How did you decide to play the instrument?
- What emotions were difficult to communicate on an instrument?
- Which emotions have a similar sound?
- What differences did you hear?
Modifications and variations
- This instrument activity can be a noisy one! If students struggle to stop playing after the 4-beat echo, try using a visual cue like bringing your hands together as a timer. Another option is having smaller groups echo.
- If you have a wide assortment of instruments, day one use only unpitched instruments. Day 2 use barred instruments.
Activity 3: (Optimistic Closing) “What emotion do you hear?” game
We can interpret each other’s emotions
- Time: 4-7 minutes
- When and why: Close the lesson with this activity to further apply the skills in lesson 2.2, giving students the opportunity to perform for the class and demonstrate their ability to play a variety of emotions on an instrument.
- SEL Focus: This activity helps students demonstrate Self-Awareness (Identifying emotions and Self-confidence)
Materials
- two drums for the performers
- whiteboards and markers or paper and pencils for all students
- emotions written on note cards or print and cut the emotion cards
Steps
- Prepare students for the game by asking a student to suggest an emotion and another student to tell you how to demonstrate it on the drum. With each emotion you demonstrate, point out a difference in how you played to communicate the emotion.
- Invite two volunteers to perform a secret emotion at the front of the room.
- Give each a drum and have them face the class.
- With your back to the class and facing the performers, hold up a secret emotion card.
- The two performers play what they think the emotion would sound like for approximately 8 -16 beats while students draw an emoji showing their guess.
- The performers each choose one person to take their place until every student has had a turn to perform.
Debrief
- Did you prefer performing or guessing?
- How does your energy feel after this activity?
Modifications and variations
- Rather than two drums, try one drum and one pitch instrument.
- Rather than two instruments, have one student use an instrument and one student pantomime the emotion.
- If there isn’t time for all students to perform, use it over several lessons until everyone has had a turn.
Lesson Three: We Can Express Emotions as an Ensemble
WA SEL Standard: Social Engagement
- SEL.K-2.6B.3 With adult assistance, I can positively and respectfully interact in peer and group activities and interactions.
WA Music Standard:
- Anchor 9: Apply criteria to evaluate artistic work.
MU: Re9.1.1 With limited guidance, apply personal and expressive preferences in the evaluation of music for specific purposes
Age Range: Grade K-2
Duration: 30-40 minutes
Activity 1: (Welcoming/Inclusion Activity) Deedle, Deedle Dumpling Greeting Frenzy
We can collaborate with a partner on ideas to perform
Time: 5-7 minutes
- When and why: “Greeting Frenzy” lifts up the energy in the room and reinforces positive connections. (adapted from SEL Playbook, p. 12)
- SEL Focus: This activity helps students demonstrate Self-Awareness (Identifying emotions and Self-confidence)
Steps:
- Practice a short poem together.
- Practice again while keeping the steady beat (patting, clapping, etc.)
- Explain: “You will have 15 seconds to find a partner, say hello by name and decide together what motion you will do to keep the beat.”
- Use an agreed-upon attention signal to quiet the room and say the poem together. This could be something like four beats played on a drum, clapping a rhythm echo pattern, or counting “1,2, ready, go.”
- As the pairs all perform the poem with their motion, notice several students to highlight. “I noticed how student A and B kept the beat by tapping their toes. I noticed how student C and D were able to keep the beat while doing a chicken dance.” Encourage both the simple and silly movements.
- Repeat at least 4 times so that everyone gets a chance to be greeted by name by a variety of classmates.
Debrief:
- Ask students “How is your energy?”
- Do you notice a lift in the room? Why do you think that is?
Modifications and variations:
- Rather than wandering to find a partner, set up two concentric circles. Students go through the activity with the partner they are facing then the outer circle takes one step to the right to find their next partner. This will speed up the activity and ensure that everyone has a different partner each time.
Activity 2: (Engaging Strategies) Hey Diddle Diddle Variations
We can perform emotions as an ensemble
- Time: 20-25 minutes
- When and why: This activity can be used in any instrument exploration activity to help students experiment with emotions in music and elements of musical expression.
- SEL Focus: This activity builds Self-Awareness (Identifying emotions and Self-confidence), Responsible Decision-Making (Evaluating and reflecting) and Relationship Skills (Communication and teamwork) as participants identify emotions, demonstrate how to play them on an instrument and work together as a class to perform together.
Prior to the lesson, have a variety of instruments set out in a circle, rows or any formation that works for rotating between instruments. Create any combination with the instruments you have or allow students to help you select instruments they want in the ensemble.
Instrument suggestions include:
- Large drums: tubanos, djembes
- Hand drums with mallets
- Small percussion: wood blocks, maracas, egg shakers, guiros, rhythm sticks, etc.
- Barred instruments C Pentatonic Scale (remove all Fs and Bs): Xylophones, metallophones, bells
Performance note. If using barred instruments, guide students through different ways of performing: one note at a time, two notes together, notes that are close together, notes that are far apart, etc.
Steps:
- Practice a familiar poem or song that can represent different emotions.
Suggestion:
- After speaking the poem together several times, encourage students to think of what emotions could be felt by the characters in this poem. For example, “What character might be feeling scared?” “What character might be feeling silly?” “What character might be feeling joyful?” “What feeling do you think the dish and the spoon might have?”
- Practice the poem again as students clap the rhythm. (Match the syllables of each word.)
- Explain that we are now going to work as an ENSEMBLE, a group that performs together, to communicate each emotion with our instruments instead of our words.
- Move to the instruments in the circle or allow each student to bring an instrument back to their spot.
- Review with students some of the ways they communicated emotions on instruments during Lesson 2, Activity 2 and 3. Ask a student to name an emotion and show on their instrument how they would play (happy, sad, scared, silly, etc.) The class copies the example of the leader. Do this process for a few emotions. Consider asking if there is another way we could show each emotion. Example, “I notice how student A played MAD on their instrument by playing really loud. Does someone have an idea of another way we can play mad?”
- Ask a volunteer to choose a character and emotion. (Example: Silly like the dog. Scared like the cow.) The class all performs the rhythm of the poem on their instrument conveying the emotion that was suggested.
- After performing, have the whole class rotate instruments and ask a new volunteer to choose a character and an emotion. Repeat this process as many times as you like.
Debrief
- Is there an instrument that didn’t seem like it fits a certain mood?
- Is there an instrument that you wish we had that would have made our music sound more happy, sad, scared, etc.
Modifications and variations:
- If you have a wide assortment of instruments, day one use only unpitched instruments and day two use barred instruments.
- If the triple meter of “Hey Diddle Diddle” is a challenge for younger students, consider a poem in duple meter such as “Two, Four, Six, Eight.”
Activity 3: (Optimistic Closing) One-Minute Accolade
Celebrate our performance!
Time: 4-5 minutes
- When and why: Quick, meaningful, and informative! Use this activity immediately following a performance activity, such as “Hey Diddle Diddle Variations.” Musicians grow from reflecting on their own performance as well as the performance of others. (Adapted from SEL Playbook, p. 41.)
- SEL Focus: This activity focuses on Self-Awareness (Accurate Self Perception) as participants reflect on their learning and performing; Self-Management (Impulse Control) as they choose how to contribute and share airtime; and Social Awareness (Respect for Others) as they absorb the reflections that are shared.
Steps
- Inform the class that you will be setting a timer for one minute (or longer if time permits.) During that time, the group will see how many people they can hear from.
- Invite students to think silently for one minute about just ONE of the reflection questions provided. Reflection suggestions: Something you appreciated today. Something that went well today. Something you improved as the class time went on. Something you noticed a classmate working hard on. Something that you are grateful for. Tell them to raise their hand or give a thumbs up when they have their idea ready.
- Choose one topic to start with, for example “Something you appreciated today.” Select one person to start when the timer starts. After they share, students can chime in with their own idea. They do not have to wait to be called on, but they do need to pay attention to when the speaker is done and be mindful not to interrupt. Encourage students to mind their airtime so that many students can share.
- When the timer goes off, allow the student speaking to finish, and end the activity.
- Move to the next reflection question and choose a different student to share. Repeat the same process with the other reflection questions.
- It is ok if not everyone has a turn. This activity can be used frequently, and students will become more comfortable with the flow of sharing and listening.
Debrief
- As students transition to the next activity, encourage them to think about one thing that was shared that stood out to them.
- Encourage the students that shared to think how they can help other voices be heard next time.
Modifications and variations
- You can change the reflection prompts and the time limits in any way that suits your group.
- If you are noticing a few voices dominating the conversation, utilize those students as the timekeepers and facilitators. Empower them to invite other students into the conversation with questions like “student A, I am curious what you thought.”
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oercommons
|
2025-03-18T00:38:19.911460
|
Lesson Plan
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/86881/overview",
"title": "SEL-Music Unit: Who Are We Together? Communicating Emotions",
"author": "Lesson"
}
|
https://oercommons.org/courseware/lesson/108016/overview
|
Education Standards
Circle Format Self-assessment Community & Cognition - Advanced Mid
Circle Format Self-assessment Culture _ Connection - Advanced Mid
WL Self Assessment Circles - Advanced Mid
Overview
Research shows that engaging students in self-assessment positively impacts language learning, motivation, and learner autonomy. To help World Language Educators accomplish this, the Nebraska Department of Education invited experienced world language teachers across the state to create student-friendly assessments in the form of can-do statements in the summer of 2023. This document is a student-friendly self-assessment activity for Advanced Low world language learners created based on the 2019 Nebraska World Language Standards. The language use described in all can-do statements is meant for the target language, except for the second for standard 3.1 and the first for standard 4.2. It is recommended that world language teachers engage students with this document three times in an academic year: pre-course, mid-course, and post-course. Engaging students with this self-assessment activity will help students see growth over time and hopefully attribute growth to effective learning practices. Please feel free to contact chrystal.liu@nebraska.gov for any questions or concerns.
Description
Research shows that engaging students in self-assessment positively impacts language learning, motivation, and learner autonomy. To help World Language Educators accomplish this, the Nebraska Department of Education invited experienced world language teachers across the state to create student-friendly assessments in the form of can-do statements in the summer of 2023.
This document is a student-friendly self-assessment activity for Advanced High level world language learners created based on the 2019 Nebraska World Language Standards. The language use described in all can-do statements is meant for the target language, except for the second for standard 3.1 and the first for standard 4.2.
It is recommended that word language teachers engage students with this document three times in an academic year: pre-course, mid-course, and post-course. Engaging students with this self-assessment activity will help students see growth over time and hopefully attribute growth to effective learning practices. Please feel free to contact chrystal.liu@nebraska.gov for any questions or concerns.
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oercommons
|
2025-03-18T00:38:19.944656
|
Dorann Avey
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/108016/overview",
"title": "WL Self Assessment Circles - Advanced Mid",
"author": "Chrystal Liu"
}
|
https://oercommons.org/courseware/lesson/116200/overview
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Washington State Characteristics of a High-Quality Outdoor School
Overview
The Washington State Characteristics of a High-Quality Outdoor School is a tool to review, assess and develop an action plan for improvement to support quality overnight outdoor educational experinces for all Washington students.
Washington State Characteristics of a High-Quality Outdoor School
The Washington State Legislature created the Outdoor Learning Grants Program to develop and support outdoor educational experiences for students in all geographic regions and include high levels of accessibility for students with disabilities.
All students in Washington deserve well-rounded and meaningful outdoor education experiences. To assist schools and sites in creating programs that enrich and challenge children, the state Legislature requires a set of guidelines for high-quality outdoor schools in our state. The rubrics and growth tools presented here are genuinely meant to foster program growth and promote positive outdoor learning through overnight outdoor educational experiences.
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oercommons
|
2025-03-18T00:38:19.961824
|
Roberta McFarland
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/116200/overview",
"title": "Washington State Characteristics of a High-Quality Outdoor School",
"author": "Assessment"
}
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https://oercommons.org/courseware/lesson/122564/overview
|
Goals for OER Advanced Course Module 3 - Creating OER
Overview
This resource describes the goals and outcomes of Module 3 of the OERizona Advanced Course. The following resources within the Module and Course are designed to support OERizona faculty as they create their OER.
Goals and Outcomes
OERizona Advanced Course Overarching Goal:
Support Arizona faculty in creating OER to increase the number of Arizona-specific OER.
Outcomes of Module Three:
Review open licensing to support selecting a license for your work
Review the OERizona collection to identify potential gap areas
Create OER by using the tools embedded in OER Commons
Connect with local faculty who are creating OER
Reflect on the experience of creating OER
Notes for exploring this course:
- The course uses a drop down menu to navigate beween the sections. The drop-down menu is displayed at the top of every lesson's content page.
- You can also navigate using the OERizona Advanced OER Skills Course Homepage.
- A certificate of completion of the course that includes contact hours is available upon completion of all coursework. This is determined through the use of Google Forms. For questions, please contact info@oerizona.org.
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oercommons
|
2025-03-18T00:38:19.976221
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12/04/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/122564/overview",
"title": "OERizona Advanced OER Skills, Author a Starter OER, Goals for OER Advanced Course Module 3 - Creating OER",
"author": null
}
|
https://oercommons.org/courseware/lesson/54410/overview
|
Mini-lecture: Types of chemical reactions
Types of Chemical Reactions
Overview
This module gives an overview of the main types of chemical reactions in first-semester general chemistry:
1- Combination
2- Decomposition
3- Single Displacement
4- Double Displacement
5- Combustion
Classifying Types of Reactions
Before we can predict the product/s in chemical reactions, we first learn 5 basic types:
1- Combination
2- Decomposition
3- Single Displacement
4- Double Displacement (aka Exchange)
5- Combustion
|
oercommons
|
2025-03-18T00:38:19.994690
|
05/16/2019
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/54410/overview",
"title": "Types of Chemical Reactions",
"author": "Amy Petros"
}
|
https://oercommons.org/courseware/lesson/125403/overview
|
One Octave Scale Worksheet
Overview
Worksheet for orchestra students to notate one octave scale, arpeggio, key signature, and draw a fingerboard map.
One Octave Scale Worksheet for Orchestra
Orchestra students should know how to notate scales, including key signature and arpeggios. This worksheet includes notating the scale with key signature, the arpeggio, and a fingerboard map of the scale to ensure student comprehension. Worksheet is attached.
|
oercommons
|
2025-03-18T00:38:20.011425
|
Zoe Harbison
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/125403/overview",
"title": "One Octave Scale Worksheet",
"author": "Assessment"
}
|
https://oercommons.org/courseware/lesson/108452/overview
|
Play as Learning
Overview
This is a template for an inquiry project in a senior level early childhood course.
Audience Interaction
Play Based Learning: Introduction
Learning through play should include updated research about playful experiences, explain the role of both the child and the adult, and state the desired outcome of the play. 1
Play is a spectrum that can vary from being child-directed, adult-guided, or adult directed. 1
Holistic skills developed by play include socio-emotional learning, creative thinking, global competence, innovation, and physical development. 1
Neuroscientists have found that play stimulates the production of a protein that is responsible for growth of neurons and synapses. In this way, play is directly responsible for some growth in the brain. 1
Playful experiences lead to deeper learning
Learning through Play-Student Experiences
- Learning through play can build creative, social, cognitive, engagement skills etc. (1). To include play in class, schools have to think about how the students are going to accept playful learning. It has been confirmed that play is relevant and useful in primary schools (1).
Let’s first see what play is and how to use it in schools.
https://youtu.be/t9xyrAsCe0M?si=h-wP1ekWtngHtTHY
- It’s important to know your students, know how they interact with one another, and know how they learn best. Because this affects how they experience play as learning. Each student is different, so each student will have a different reaction to play. So being able to adapt and have options for every student is a big part of play as learning. A good way to help students experiment with different types of play is to put them into groups and let them rotate throughout the room.
Types of Play Based Learning
Problem-based learning
Involves working through and reflecting on problems in small self directed groups with guidance from teachers as facilitators
"CI 149 Tues 4PM Problem Based Learning" is licensed under CC BY 4.0
Guided discovery learning
Occurs when the learner is not provided with the target information and must find it independently
"Guided Discovery Lesson Plan" is licensed under CC BY 4.0
Inquiry-based learning
Student centered approach to teaching and learning where a unit of work is organized around relevant, authentic, open ended questions
“Inquiry in Social Studies-A Lesson from Grade 1" is licensed under CC BY 4.0
Play, Learning, and the Brain
Play is essential for brain development. Brains develop rapidly by age 2; our brains are 80% of adult weight, and by age 5, they are 90% of adult size. Play stimulates cognitive functions such as creativity, critical thinking, and problem-solving. Play encourages children to explore the world around them. Furthermore, play boosts social and emotional development by allowing children to communicate, cooperate, and empathize, crucial skills for real-life situations. For these reasons, merging play into the school curriculum makes learning pleasurable and nurtures well-rounded individuals with healthy and adaptable brains. Play is crucial for the development of motor skills, fine motor skills, and gross motor skills. For example, kicking legs as an infant, clapping hands as a toddler, and running around obstacles as a child.
A lack of play in school can damage children’s development and well-being. It is a crucial part of a child’s learning process. Removing play from schools puts children at risk of hindering their academic performance. It removes their opportunity to become well-rounded individuals. Play is not a luxury. It is a necessity for healthy child development.
Parts of the Brain
- Cerebrum
- The largest part of the brain.
- Controls the organs that control our senses, such as touch, hearing, vision, and temperature.
- Initiates and coordinates movement
- Cerebellum
- Coordinates and regulates muscular activity
- Brainstem
- Sends information to the body to regulate heart rate, breathing, balance, etc.
- Frontal Lobes
- Associated with planning, memory, impulse control, and reasoning.
This is a fantastic activity for students to build language skills through collaboration with students. Through imaginative play, children have the opportunity to role-play real-life experiences. This dramatic play allows children to be store owners, bakers, customers, or cashiers. They are taking orders, checking out customers, making decisions, etc. Children boost fine motor skills through imaginative play by handling money and preparing food. They also have the opportunity to make decisions. It allows them to express their emotions and boost their creativity.
For more information about this imaginative play, visit: https://oercommons.org/authoring/47526-dramatic-play-grocery-store-bakery/view
Final Conclusion
The learners that are relevant to learning through play and that were studied, were learners aged 6-12. Experiences from learning through play are designed to make purposeful use of resources to incorporate child-led, teacher-led, and teacher guided opportunities. Learning through play builds social, cognitive, creative engagement skills etc.(1)
It creates a positive learning environment by reducing stress and promoting inclusivity. Children should be given ample opportunities to engage in numerous forms of play for their holistic development. Play should be recognized as a significant part of early childhood education and should be integrated into the curriculum.
References:
"Brain Pictures" is licensed under CC BY-NC-SA 4.0
"Connected learning " by Nic Askew is in the Public Domain
"Dramatic Play-Grocery Store/Bakery" by MSDE Admin, Cheri Helmstetter, Amy Toms, Kristen Johnson, Bob Wagner is licensed under CC BY-NC-SA 4.0
Learning Through Play at School-A Framework for Policy and Practice" by Parker, Thomson, Berry is licensed under CC BY 4.0
"Loaf of Bread" is licensed under CC BY 4.0
"Stages of Development" by Lisa Rosen-Aydlett is licensed under CC BY 4.0
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oercommons
|
2025-03-18T00:38:20.036268
|
Gillian Adams
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/108452/overview",
"title": "Play as Learning",
"author": "Kara Rees"
}
|
https://oercommons.org/courseware/lesson/100255/overview
|
Activity One: Sharing Feelings Playing “Emotion Charades”
Emotions Chart
Social and Emotional Learning (SEL)
Overview
This is a template for an inquiry project in a senior level early childhood course.
Introduction
The purpose of this inquiry project aims to give insight into the importance of acknowledging and encouraging the expression, identification, and regulation of students' emotions or feelings through conversation in the classroom. While learning in the classroom is taking place, opportunities, even small ones, will be made present for activities involving emotional and social learning.
The following are some of those activities:
1. Emotional Charades
2. Emotions Chart
3. The Skittles Feeling Game
Social and Emotional Learning (SEL) is defined by CASEL, or the Collaborative for Academic, Social, and Emotional Learning, as "an integral part of education and human development. ... It is the process through which all young people and adults acquire and apply the knowledge, skills, and attitudes to develop healthy identities, manage emotions and achieve personal and collective goals, feel and show empathy for others, establish and maintain supportive relationships, and make responsible and caring decisions.
SEL also advances educational equity and excellence through authentic school-family-community partnerships to establish learning environments and experiences that feature trusting and collaborative relationships, rigorous and meaningful curriculum and instruction, and ongoing evaluation." (CASEL, Fundamentals of SEL, 2022)
The framework for Social and Emotional Learning focuses on five broad categories that encompass the integration of all five aspects into every area and subject of academic learning. These categories include Identity and Agency, Emotional Regulation, Cognitive Regulation, Social Skills, and Public Spirit. (Frey et al., All learning is social and emotional, Chapter 1, pg. 15, 2019)
Resources:
AbbyThePup. (2021, January 25). Emotions. Self-published image, Retrieved February 17, 2023, from https://commons.wikimedia.org/wiki/File:Emotions_(Abby_the_Pup).jpg
CASEL. (2022, March 11). Fundamentals of SEL. CASEL. Retrieved February 17, 2023, from https://casel.org/fundamentals-of-sel/
Frey, N., Fisher, D., & Smith, D. (2019). In All learning is social and emotional: Helping students develop essential skills for the classroom and beyond (Chapter 1, p. 15). Textbook, ASCD.
Activity 1
The name of this activity is Emotional Charades. It is an activity that promotes emotional development.
In this game, we are going to build on students' skills in expressing and identifying emotions. The class will need to be split up into two teams. Before you begin, you need to make sure the students know how to play.
The teacher must first explain what 'Charades' means.
Charades - a game that involves acting without talking.
Before the activity starts, the teacher can run a ‘practice’ or 'test' round where educators show or demonstrate to the students what is expected of them.
Activity:
In this activity, the teacher will point at an emotion on the emotions chart provided above after selecting a student from one of the teams to stand in front of the class. The selected student will walk around the class and act out the emotion without talking or touching anyone. If their team thinks they know the emotion, they can put up a thumbs up and take a guess. The two teams will continue to take turns in choosing students to express their feelings until everyone has participated to their abilities. By the end of the game, the teacher will have the points tallied and know who won.
Extension: This game or activity can be played multiple times as the year progresses and as students' social-emotional development and social competence increases. Over time, as students demonstrate understanding and developmental progress, additional cards can be included that depict new vocabulary associated with new emotions.
A few examples could include adding the words jealous, thrilled, startled, distaste, intrigued, and
Why is this important?:
This allows students to practice expressing different forms of emotion, which can promote students' positive development of self-awareness, self-esteem, self-concept.
Charades allow the other students to work on identifying the emotion of other peers in the classroom.
This activity shows the students that a classroom is a safe place for expressing their own emotions.
Activity 2
The name for this activity is the Emotions Chart. This is an activity that focuses on and fosters emotional identification.
The following video goes over ten different emotions.
10 things your Emotions are trying to tell you video:
The video also talks about the feelings and actions associated with different emotions. This is a great video to get your students thinking about emotions and can help them identify their own, as well as those of others. The video aids students to communicate their feelings effectively and clearly, in order to be the best they can be. The video talks about core memories and how they are attached to emotions. It helps students understand why they or others around them may act the way they do. It’s crucial for students to understand their own personal emotional awareness to interpret their needs and wants, all to help them thrive socially as well as academically.
By granting your students the opportunity to fill out an emotions chart daily not only helps you as an educator to understand your students' feelings but also helps the students themselves gain an understanding of how they’re feeling. The following chart aids students in understanding, identifying, and communicating how their emotions.
"Emotions Chart" by Morgan Luebke is licensed under CC BY-SA 4.0
The chart also gives students insight into how their other classmates are feeling and helps them understand why others act the way they do that particular day. The emotional chart can be used daily and even at home as well. The chart assists in developing emotional awareness in children.
Activity 3
The final activity is The Skittles Feeling game. This is an activity focusing on emotional and social sharing.
This activity would be good for students in the 2nd-5th grade areas as instruction wouldn’t need to be reminded and clarified much for the most part.
After lunchtime would be an opportune time to play this game. Stopping or pausing instruction to allow 15 minutes for this activity.
Each table will have a copy of the skittles feeling game chart instructions.
Each student will receive a small cup with approximately 8-10 skittles in it, for 10 minutes, students will go around in a circle at their table pulling skittles and sharing one thing that correlates to each skittle color pulled out from their individual cup.
While everyone is discussing at their tables, students will be allowed to eat the skittles that were in their cups previously.
At the end of the activity, we will have a class discussion of how they felt the activity went and if they think they benefited from the activity.
Resources
Stocks, W. (2017, July 7). The emotions candy game. Hope 4 Hurting Kids. Retrieved from https://hope4hurtingkids.com/emotions/understanding-emotions/emotions-candy-game/
Benefits of Social-Emotional Learning and How It Applies to the Teacher
These activities provided beforehand showcase examples of how Social-Emotional Learning (SEL) can or could be used within or accompanying content areas of the curriculum to promote and foster the development of students' social competence and emotional intelligence.
Fun Fact: A meta-analysis that viewed over 213 studies involving more than 270,000 students discovered that SEL interventions and implementation of the five core competencies that make up the framework of Social-Emotional Learning in schools increased students' academic learning by 11 percentile points compared to those who didn't participate. (CASEL, What Does The Research Say, Benefits of SEL, 2022)
However, as mentioned in the introduction, there will be small and surprising moments unrelated to critical instruction where teachers can discover opportunities to aid students in developing their emotional awareness, identifying those feelings, and providing ways of being able to regulate emotions for student success in everyday functioning and academic learning.
Examples of Small Interactions and Strategies to Promote Social-Emotional Learning in The Classroom:
- Model persistence during challenging tasks, explaining that unsuccessful attempts to do
something are not failures but simply steps toward learning what will work. - Play games with rules periodically to help children learn to focus their attention and
regulate their impulses to achieve a goal. - Reinforce children’s good choices and link their actions to positive outcomes.
- Establish developmentally and culturally appropriate expectations for children’s
behavior, especially expectations for self-control and self-regulation. - Acknowledge and express appreciation for children’s empathic responses.
- Provide specific feedback to children about their efforts, reinforcing their choices that
support learning and linking their actions to outcomes. - Coach and guide children’s behavior by using positive, respectful phrasing and tone to
prompt problem-solving and to give brief instructions and reminders.
These and more examples can be found in the OER textbook, Introduction to Curriculum for Early Childhood Education, by Jennifer Paris, Kristin Beeve, and Clint Springer in chapter 7 on pg. 149 and 150.
With the information we have learned and discovered so far about Social-Emotional Learning (SEL), we must always keep in mind that as educators working with young developing children, students will need repetition, coaching, alternatives, and reminders for memory formation and understanding to occur.
This applies to classroom teachers because it demonstrates and showcases the power and abilities, we hold that can influence students' decision-making, problem-solving skills, conflict resolution, memory formation, feelings toward academic learning and school, perception of themselves, and social relationships with peers and others. The activities we choose, the environment we cultivate, physically and relationship-related, how we model behavior, and how we interact with students can come together to create a classroom that fosters the development of Social-Emotional Learning (SEL).
Image Created by Giulia Forsythe.
Eighty percent of educators from across 15 countries believe positive emotions are critical for academic success, and emotional well-being is crucial for developing foundational literacies and communication skills. (CASEL, What Does The Research Say, Benefits of SEL, 2022)
Resources:
CASEL. (2022, May 26). What Does The Research Say? CASEL. Retrieved February 17, 2023, from http://casel.org/fundamentals-of-sel/what-does-the-research-say/
Forsythe, Giulia. (2022, June 13). Social Emotional Learning Diagram. Retrieved February 17, 2023, https://commons.wikimedia.org/wiki/File:Social_Emotional_Learning_Diagram.jpeg
Johnson, A., Paris, J., Beeve, K., Springer, C., & Johnson, A. (2019). Introduction to curriculum for early childhood education (1.1 ed., Chapter 7, pp. 149–150)., OER College of the Canyons. Retrieved February 17, 2023, https://drive.google.com/file/d/1CG-nXzs4xzTMBl32HbYcdtbRhiW1Z1YD/view
Conclusion
Social and Emotional Learning (SEL) takes root in the heart of the classroom by providing the foundation for how the classroom environment can flourish, even if it is sometimes subtle and not always noticed. Social and Emotional Learning (SEL) being implemented and used to its fullest potential within the classroom gives opportunities for educators and students to strengthen, repair, or create relationships not just in school but outside of it as well.
By allowing students to openly express and converse their emotions in the classrooms, the school community will become more of an open space and allow for great teamwork and relationships between students and the teacher.
“I've learned that people will forget what you said, people will forget what you did, but people will never forget how you made them feel.”
- Maya Angelou
Resources:
Smith, Mathew. John. (March 9, 2019). Maya Angelou. Baltimore M.D. Hopkins Hospital, Retrieved February 17, 2023, https://commons.wikimedia.org/wiki/File:Maya_Angelou_(47327455761).jpg
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oercommons
|
2025-03-18T00:38:20.071277
|
Morgan Luebke
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/100255/overview",
"title": "Social and Emotional Learning (SEL)",
"author": "Aleks Nira"
}
|
https://oercommons.org/courseware/lesson/60869/overview
|
Parenting Styles
Overview
A review of different parenting styles with an emphasis on authoritative parenting.
Parenting Styles: Why Authoritative Parenting is the Best
Author: Carson Manning
Editor: Heather Whittaker
Being a parent is one of the most challenging and rewarding responsibilities a person can take on. The method individuals use to handle such a responsibility is up to them but it is important to remember that different approaches result in different outcomes. Davies, Cummings, and Winter (2004) suggest that parenting style has a significant effect on a child's behavior. These different methods of parenting can be classified into four parenting styles. According to Dr. Maryann Rosenthal, coauthor of Be a Parent, Not a Pushover (2006), “…the two main components that make up parenting styles are responsiveness and demandingness.” Varying degrees of responsiveness and demandingness make up the parenting styles of authoritarian, authoritative, permissive, and disengaged.
Authoritarian Style can be described as unresponsive and demanding. Parents who use this style insist their children live by a rigid set of rules. Authoritarian parents value rules and obedience above all else and they make that known to their children. According to Davies et al. (2004), authoritarian parents limit their child’s independence by making them follow strict rules that are enforced with harsh punishments. This limited independence results in clearly stated rules that are followed but the purpose of the rules is not fully communicated or understood by the child (Baumrind, 1991). That is because children of authoritarian parents learn to question what their authority figures expect of them, but not the authority of such a figure.
Authoritarian parents, like all others, have positive and negative aspects. One positive aspect is that children are more likely to accept rules. One argument against this style is that just because children accept the rules, that does not mean they will follow them. This parenting style will teach children rules but may not communicate the justification for them. Children and adolescents learn to view rules as arbitrary and understand that they are established with no justification. Another problem is that it may result in children who are more anxious and have fewer social skills. Children of authoritarian parents experiment less in their social environments and prioritize responding to the perceived authority figure. These children may feel anxious as a result of always second-guessing their decisions and actions in fear of breaking the rules or not meeting expectations (Steinberg, 1994).
Authoritative parenting can be described as a form of control that uses understanding and communication to achieve desired outcomes. Authoritative parents value instilling obedience in their children through communication. According to Sartaj and Aslam (2010), these parents are assertive without being intrusive or restrictive. Authoritative parents encourage obedience by setting clear rules and may even predetermine punishments and/or reinforcements for behaviors. Authoritative parents want their children to listen to them and they are willing to listen to their children in return (Cheryl, 2005). That creates a give and take relationship between parents and their children which is one reason why authoritative parenting is associated with better outcomes than all the others and is considered the optimal form of parenting (Baumrind, 1991).
Another advantage of authoritative style is it allows children to develop social skills by fostering the development of their own voice. Children of authoritative parents express themselves and act in such a way that they feel justified. This allows them to develop a robust sense of self and independence. Children of authoritative parents become more independent with time but their actions are monitored. They tend to make better choices as a result of their monitored independence because autonomy was fostered from a young age by their parents. These advantages give us insight into why children of authoritative parents are usually better off in adulthood.
Permissive parents demand less of children and focus less on child obedience. This parenting style lets children be more expressive but comes at the cost of children developing behavioral issues. These behavioral issues may go unresolved because permissive parents are less likely to intervene. These behavioral issues are most likely the result of children not having some sort of standard to follow. These children are allowed to be more independent but lack guidance in developing their independence.
This parenting style comes with some advantages. One of the advantages is that children can be creative and learn to be independent. Children of permissive parents learn to make more decisions but they may lack knowledge on what decision is most reasonable. This is one of the drawbacks of this permissiveness. Children have no guide to follow when they are making decisions and they may have to depend on trial and error. Parents who use this style are less involved and that can result in children having poor relationships with their parents.
Disengaged parenting can be described as dissociated. Parents see themselves as fully separated from their children, and therefore, show minimal involvement in their life. This parenting style may meet the child’s basic needs but gives very little in the way of care and guidance.
It is clear that not all parenting styles are equal. Parents should aim to be responsive and moderately demanding. These two characteristics make up the authoritative parenting style. Parents can be responsive by valuing communication with their children. Listen to your child's thoughts and opinions before making any decision and then explain the reasoning behind your decision. Be demanding about the rules that are fully communicated, but avoid being overly rigid. Rigidity in setting rules may instill the fear of making mistakes in the child. As a result, children learn to fear to make mistakes and often question their every move. There is no perfect guide to being a parent but we can facilitate better outcomes for children through educating about optimal parenting approaches.
References
Baumrind, D. (1991). Parenting styles and adolescent development. In R. Lerner, A. C. Peterson, & J. Brooks-Gunn (Eds.). The Encyclopedia on Adolescence (pp. 746-758). NY: Garland.
Davies, P. T., Cummings, E. M., & Winter, M. A. (2004) Pathways between profiles of family functioning, child security in the interparental subsystem, and child psychological problems. Development and Psychopathology, 16, 525–550.
Rosenthal, M., & Fetherling, D. (2006). Be a parent, not a pushover: a guide to raising happy, emotionally healthy teens. Nashville: Nelson Books.
Steinberg, L. (1994). Authoritative parenting and adolescent adjustment across varied ecological niches. Journal of Responsible Adolescence, 1, 19-36.
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oercommons
|
2025-03-18T00:38:20.092656
|
12/17/2019
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/60869/overview",
"title": "Parenting Styles",
"author": "Heather Whittaker"
}
|
https://oercommons.org/courseware/lesson/54350/overview
|
CLT explained
Climate Change Data
Fuel Efficiency Lab Data
TI 83/84 Emulator
Unit Exam Rubric
Topics
Fall Schedule
Statistics
Overview
A general statistics course, which includes understanding data, measures of central tendency, measures of variation, binomial distributions, normal distributions, correlation and regression, probability and sampling distributions, Central Limit Theorem, confidence intervals, estimates of population parameters and hypothesis testing. Interpretation and data analysis are emphasized.
PREREQUISITES: A grade of C or better in MAT 100 (Intermediate Algebra) or MAT 120 (Math Modeling for Liberal Arts) and placement above or successful completion of ENG 060 (Preparations for College Reading III). A student needs a thorough knowledge of Algebra, good reading skills and familiarity with the graphing calculator before entering this course.
Syllabus
MAT177-80 Semester
PROFESSOR: your name here
Office: ______________
Telephone: ###-###-####
E-mail: I do not open emails if I do not recognize the sender
IMPORTANT: In the subject line, write Stats, Your Name and Topic
(Ex: Statistics, Jim Bird, Ch.1 question)
Office Hours: by appointment or on Google+ hangouts
COURSE
DESCRIPTION: A general statistics course, which includes understanding data, measures of central tendency, measures of variation, binomial distributions, normal distributions, correlation and regression, probability and sampling distributions, Central Limit Theorem, confidence intervals, estimates of population parameters and hypothesis testing. Interpretation and data analysis are emphasized.
PREREQUISITES: A grade of C or better in MAT 100 (Intermediate Algebra) or MAT 120 (Math Modeling for Liberal Arts) and placement above or successful completion of ENG 060 (Preparations for College Reading III). A student needs a thorough knowledge of Algebra, good reading skills and familiarity with the graphing calculator before entering this course.
TEXT BUNDLE ISBN: 0321643933 from the Bedford bookstore (781-276-4211) includes:
- Elementary Statistics by Mario F. Triola, ELEVENTH edition, Pearson, Addison-Wesley, 2010 (White cover with windmills in a field)
- MyMathLab Student Access Code (More on MyMathLab below)
- Graphing Calculator Manual for TI-83/84 Plus, And TI-89 by Patricia Humphrey (we require a TI-83 or 84 Plus, NOT a TI-89)
The bundle sells for slightly more than a new text alone. If you buy a used text, you can buy a MyMathLab access code online separately with a credit card but it may end up costing more. The text and MyMathLab access code are required. The Access code allows you to read the text online as an e-book and is necessary for homework and quizzes.
CALCULATOR: A TI-83 or TI-84 Plus is required. It is used in all math courses starting with Intermediate Algebra. Calculator activities are an integral part of the course.
Students are solely responsible for using any other calculator, including the TI-89.
A TI-connectivity kit (cable and software) connects the calculator to your computer so you can copy the calculator screen onto a word document. You will need it for the projects. It comes with some of the calculators. If not, you can buy it separately from a store or visit http://www.education.ti.com/store. If you prefer not to buy it, you can use the ones in the Math labs (AR 214 in Bedford or Room 406B in Lowell City bldg.)
INTENSIVE VALUES: This course satisfies the Writing and the Computer Intensive Values.
ATTENDANCE: Attendance and active participation during the whole class period improves students’ chance of success. Students who nap, socialize or for any reason do not participate in class work will be marked absent. Habitual tardiness is discouraged. If the instructor is delayed, wait 15 minutes before leaving, to avoid being marked absent.
Students can access the course websites from home in order to do homework and keep track of syllabus adjustments especially test dates.
Students who miss more than a week of classes should call or email the instructor.
Winter Weather: A delayed opening means the College opens at 10AM. Look for school closings on Blackboard, TV, Radio or Call (781) 280-3200 or (978) 656-3200. Consider your safety and make your own decision about driving based on the road conditions in your area. Students are not penalized for absence due to inclement weather.
TEACHING PROCEDURE: In addition to class meetings, this course uses Course Compass with MyMathLab. Students use MyMathLab to do online assignments and they use the graphing calculator extensively, thus minimizing computations and maximizing focus on assumptions and interpretations of results. The instructor leads class discussions, lectures, demonstrates the use of the calculator, posts course materials and announcements, and evaluates students’ work. Students stay informed by attending class and by reading online announcements. Students’ efforts determine how well they learn. Students use their organizational skills to stay involved and meet all the deadlines. A pro-active attitude is necessary to stay organized, meet assignment deadlines and adjust to syllabus changes (if any) in a timely way.
CLASS ATMOSPHERE/ BEHAVIOR: An interactive, relaxed, and courteous atmosphere helps students achieve their full potential. Students are expected to focus on the subject matter and be mindful of the instructor and other students. Misconduct and disruptive behavior are not acceptable. Social conversations, swearing, moving around or going in and out of class or any other disruptions are not tolerated. A student who continues to disrupt the learning process will be referred to the Dean and may be expelled from class. See the Student Handbook for policies and procedures set by the college.
Cell phones have to be silenced and put away. No text messaging. Cell phones are not to be used as calculators. In case of emergency (ex. sick child), notify the instructor and put cell phone on vibrate mode.
CRITICAL THINKING: Students evaluate relevant facts, state questions, list assumptions, and determine appropriate statistical methods to analyze information. They collect and/or study data from different perspectives and in different contexts. They solve problems from a variety of disciplines such as education, business, economics, health and social science. Many text exercises are based on real data. Students justify their conclusions and list sources of bias.
Grading: Your grade for the course will be computed based upon the following weighting system.
| Weekly Classwork & Attendance | 15% |
| Lecture Notes | 15% |
| Homework | 20% |
| 5 Unit Tests | 30% |
| Final Project | 15% |
| Group Evaluation | 5% |
Plagiarism is a very serious offense. Any plagiarized work (copied, without quoting the source, in part or fully, (from another student, the internet, a magazine, a book, or any other source) will result in a grade of ZERO.
SUPPORT:
- Math Tutoring Centers: Free tutoring. Ask for the Statistics tutors’ hours. Not all tutors can help with Statistics. Bedford: AR214 781-280-3707. Lowell: 406B on the 4th floor of the City building 978-656-3368.
- CourseCompass/MyMathLab: www.coursecompass.com
- Click on ebook, Tools for success and Multimedia library.
- CourseCompass Technical Support:
(1) 1-800-677-6337 (Monday-Friday 8AM-8PM and Sunday 5PM- 12AM)
(2) Click on Help and send email using the Product Support e-mail form
- Online Tutoring Sun through Thurs 5PM-12AM. 1-800-877-3016 or Visit the Tutor Center's registration page to sign up for tutoring. When asked for a registration, provide your access code.
- Middlesex computer support: 978-656-3301 for help with questions related to College computer issues (NOT for CourseCompass or MyMathLab)
- Writing Labs: For help with project writing, AR 211 in Bedford and 406B in Lowell. Also, use the spell check function on your computer.
- study group Form a study group to help each other. Helping each other does not mean copying from each other. Cheating has severe consequences.
Course Objectives
The extensive use of the graphing calculator reduces the drudgery of computations and allows us to concentrate on analysis, assumptions, and methodology. Real data collected by students as well as data obtained by searching the web or looking at library sources are the basis of some projects. The projects increase in difficulty and sophistication as the semester progresses.
Producing Data
- Identify population and sample
- List different sampling methods and evaluate them.
- Explain under-coverage and non-response
- Recognize the effect of the wording of questions on the responses.
- Differentiate between an observational study and an experiment.
- Recognize bias due to confounding of explanatory variables with lurking variables
- Identify the factors (explanatory variables), treatments, response variables, and experimental units or subjects in an experiment.
- Explain placebo effect and double-blind experiments
Describing data
- Identify variables
- Describe data graphically and numerically
- Find outliers
- Discuss the effect of extreme values on the mean, the median, and the standard deviation.
- Make a decision about which measure of central tendency to use and support that decision.
- Define a density curve and give the area under it.
- Define a normal curve
- Find the area under a normal curve corresponding to a given interval on the horizontal axis and vice versa
Sampling Distributions and Probability
- Identify parameters and statistics
- Define sampling distribution
- Describe the bias and variability of a statistic in terms of the mean and spread of its sampling distribution.
- State the connection between variability and sample size.
- Define probability and list the probability rules
- Recognize when a problem involves a sample proportion or a sample mean
- Find the mean and standard deviation of the sampling distribution of or
- List the requirements needed for the normal to approximate the sampling distribution of.
- State the Central limit theorem and explain its significance
- Use the normal distribution to calculate probabilities that concern or
- State the law of large numbers
Confidence Intervals and Significance Tests
- State in non-technical language what is meant by statements of confidence such as “95% confident”.
- Find a confidence interval for a population mean for known or unknown σ and explain what it means
- Find a confidence interval for a population proportion and explain what it means.
- Recognize when you can safely use a confidence interval formula and when the sample design or a small sample from a skewed population makes it inaccurate.
- Explain the interconnection between sample size, level of confidence and margin of error
- Find the sample size required to obtain a confidence interval of specified margin of error when the confidence level is given.
- Explain the connection between confidence level, significance level, and critical values.
- State the null and alternative hypotheses in a testing situation when the parameter in question is a population mean or a population proportion p
- Explain in non-technical language the meaning of the P-value.
- Find the z statistic and the P-value
- Assess statistical significance at standard levels either by comparing P to
- Explain the connection between significance testing and the importance of an effect.
- List the assumptions behind hypothesis testing for a proportion and for a mean
- Recognize from the design of a study whether one-sample, matched pairs, or two-sample procedures are needed.
- Use the t procedure to obtain confidence intervals and to perform significance tests after checking for normality and for outliers.
- Use the z procedure to give a confidence interval for a population proportion p and to carry out significance tests.
Examining Relationships
- Identify the explanatory and the response variables
- Draw a scatter plot for two quantitative variables
- Compute the correlation coefficient r for quantitative variables
- Find the least-squares regression line and graph it
- Use r2 to describe how much of the variation in one variable can be accounted for by a straight-line relationship with another variable.
- Recognize outliers and potentially influential observations
- Calculate the residuals and plot them. Recognize unusual patterns.
- Find possible lurking variables and explain how they might affect the conclusion
- Explain the difference between correlation and cause-and-effect
Chapter Lectures YouTube Playlist
Homework Problems YouTube Playlist
This is the YouTube Playlist URL for the homework problem videos I am creating
https://www.youtube.com/playlist?list=PLlSSosOI1uj4IRzzOFFSnbYMzlnyqIqKi
Chapter 1
1.3 - https://www.youtube.com/watch?v=3TPXLZ_DTTY&list=PLlSSosOI1uj4IRzzOFFSnbYMzlnyqIqKi&index=2&t=63s
1.15 - https://www.youtube.com/watch?v=l1a6cnwCGfc&list=PLlSSosOI1uj4IRzzOFFSnbYMzlnyqIqKi&index=3&t=0s
Chapter 2
2.1 - https://www.youtube.com/watch?v=T-okn19YWNE&list=PLlSSosOI1uj4IRzzOFFSnbYMzlnyqIqKi&index=4&t=0s
Chapter 4
2.11 - https://www.youtube.com/watch?v=asCUv6RKWpc&list=PLlSSosOI1uj4IRzzOFFSnbYMzlnyqIqKi&index=5&t=0s
2.16 - https://www.youtube.com/watch?v=-H1n8Hsp6Nc&list=PLlSSosOI1uj4IRzzOFFSnbYMzlnyqIqKi&index=5
Final Project
Statistics 177
Final Project
You will choose two different numerical variables from the data set, randomly select 60 countries, and analyze this information using the methods of descriptive and inferential statistics.
Section 1 –Analyze each of the two variables separately.
(40 POINTS)
Your project should include the following:
- An introduction explaining what two variables you want to explore using statistical methods. State the individuals and the two variables.
- A complete table of data.
- Frequency tables and histograms for the two distributions. A separate frequency table and histogram for each variable.
Discuss the choice of classes. How did you come up with it? How could choosing different classes change your histogram?
- Detailed descriptions of both histograms in words:
What is the shape of this distribution? What is the center? How much variation is in the data?
Are there any outliers?
- A stemplot for each variable.
- Detailed interpretation for each stemplot in words: range, mode(s), symmetry or skewness, outliers.
- Median, mean, and mode for each variable. For each of the two variables compare its mean, median and mode and comment on their differences and similarities. Give the standard deviation for each variable and explain its meaning.
- Use the range rule of thumb to estimate the standard deviation of each variable and compare this approximation with the values found in number 7.
- The five-number summary and a boxplot for each distribution. Give a detailed interpretation of each five-number summary in words.
Section 2 –Determine if there is correlation between your two variables.
(40 POINTS)
Using your data, you will explore possible connections between your two variables by completing the following.
- Make a scatterplot of all your data: one dot for each individual (60 dots). Label both axes clearly. Comment on your choice of the explanatory and response variables: which of the two variables you made explanatory and why.
- Regression line: its equation and graph together with the scatterplot.
- Correlation coefficient and its complete interpretation in words: sign, strength, what it means in terms of your specific variables.
- Coefficient of determination: its value, what it means in terms of your specific variables.
- Predictions made with the help of the regression line. Choose two different values of x and find what values of y you can predict for them; then choose two different values of y and find what values of x you can predict for them. Comment on reliability of these predictions in your particular case: use the value of correlation to estimate how reliable they are.
- Conclusion and Interpretation. Summarize your findings. Discuss possible outliers and influential points. Discuss possible errors involving lurking variables.
Section 3 –Determine if there is a difference between Global Income Groups.
(20 POINTS)
Using your data, you will determine if there is a difference between one of the variables you chose based upon the Income Groups the countries chosen belongs.
- State both the null and alternative hypotheses.
- State your choice of significance level and why you chose this level?
- Explain why or why not the null hypothesis was rejected. Use a p-value and F-value in your explanation.
- Write statements that explain what rejecting or not rejecting the null hypothesis means.
- What are your overall conclusions?
|
oercommons
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2025-03-18T00:38:20.137674
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05/15/2019
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/54350/overview",
"title": "Statistics",
"author": "Jordana Shaw"
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https://oercommons.org/courseware/lesson/74303/overview
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Project Management for a Changing Climate
Overview
Adapting to a changing climate will involve governments, businesses, societies and other organizations with diverse perspectives, mandates and capacities. Project managers, through their effective direction of complex projects, occupy a critical role and must ensure that their projects consider the implications of a changing climate. This course will help you recognize climate change factors that could affect successful outcomes for your project and formulate strategies you can use to address them. You can expect to leave this course better prepared to add a climate change lens to your project planning.
Welcome to Project Management for a Changing Climate
Welcome to Project Management for a Changing Climate
Course Instructor: Susan Todd, CPA CA, MRM
"Project Management for a Changing Climate" by Sue Todd, Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Welcome to this 4-week course, PROJECT MANAGEMENT FOR A CHANGING CLIMATE. My name is Susan Todd and I'll be facilitating the course.
Adapting to a changing climate will involve governments, businesses, societies and other organizations with diverse perspectives, mandates and capacities. Project managers, through their effective direction of complex projects, occupy a critical role and must ensure that their projects consider the implications of a changing climate. This course will help you recognize climate change factors that could affect successful outcomes for your project and formulate strategies you can use to address them. You can expect to leave this course better prepared to add a climate change lens to your project planning.
For this course, the definition of “project” is broad and the content is suitable for a diverse range of professionals who enjoy multidisciplinary learning environments.
The course is structured in four modules, that cover:
- Perspective: perspectives that are key to developing a climate change lens for project management;
- Planning: planning for climate change throughout the project life;
- Engaging: engaging team members, and those affected by climate change; and
- Applying: applying a climate change lens to a real project.
Each week you will have readings and/or videos for information and perspective, and activities where you will engage with peers to reflect upon and integrate core concepts. We will also use a case study about a project manager in a fictional transit agency that will challenge you to practise your learning as we go. In the final module, you will apply your learning to a real project you’re involved in.
Most of the learning activities you can do when the time is right for you. However, I recommend that you complete the activities for each module in the order specified so that you're prepared to engage with peers in a synchronous session on Friday afternoon each week. I will post the highlights from each week in a course Announcement as a summary of our learning.
The course requires a foundational understanding of climate change impacts and risks. This can be provided by Dr. Stewart Cohen's course. If you haven't taken this course, I strongly recommend reviewing the two key reports that are highlighted as Foundational Reading in Module 1.
This page provides a quick reference for the whole course. The sequence of activities for each module can also be found in the Overview of each module.
<sample course schedule>
Module | Date | Course Activities |
Course Introduction and Module 1 - Perspective | November 2 to November 8 | Welcome and Introduction to the course. Module 1 Activities
|
Module 2 - Engaging | November 9 to November 15 | Module 2 Activities |
Module 3 - Planning | November 16 to November 22 | Module 3 Activities |
Module 4 - Applying | November 23 to November 29 | Module 4 Activities |
Introduction to Adaptation Learning Network
Welcome to the Adaptation Learning Network (ALN). This course is one of eleven courses developed for professionals working in BC. These courses are designed for people who are addressing climate adaptation risks and impacts in their communities and jobs.
WHY DOES THIS MATTER?
Climate change adaptation requires expertise from many perspectives. The ALN is committed to connecting people, professional interests, and regions to advance skills, knowledge and solutions.
JOIN THE NETWORK
To join the network, sign up for our monthly newsletter here, and follow us on social media (Twitter, LinkedIn) to get adaptation news and hear about our latest course offerings and events.
LEARN MORE
To learn more about the Adaptation Learning Network read this 5-minute introduction
Join the Adaptation Learning Network
Module 1 - Perspective
"Project Management for a Changing Climate – Module 1 - Perspective" by Sue Todd, Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Welcome to Module 1, Perspective. In this Module you'll have an opportunity to consider your perspective on climate change as a project manager, recognize valuable perspectives that others bring, and consider when and how an interdisciplinary approach can enhance project management for a changing climate.
Module 1 Learning Goals
This Module will help you:
- learn who is in the group, including the skills, backgrounds, knowledge and experience they can share that is relevant to climate change adaptation
- reflect on your motivation for considering climate change in your projects
- understand what’s different about managing projects in a changing climate
Module 1 Readings and Resources
Foundational Readings
These provide background on climate change impacts and risks. They should be considered essential for those who have not taken the course Introduction to Climate Change with Dr. Stewart Cohen and recommended for others. Focus on Executive Summaries.
- Canada's Changing Climate Report
- Canadian Council of Academies - Canada's Top Climate Change Risks
- Strategic Climate Risk Assessment for BC, Government of BC (2019)
Required readings for Module 1 activities - also included in Course Content
Perspective from UK professional: Climate change and project management: Re-thinking the relationship, Peter W.G. Morris (2017), https://www.apm.org.uk/blog/climate-change-and-project-management-re-thinking-the-relationship/
Perspective from US PM association leader: Thoughts on Climate Change and Project Management, Joel Carboni (2017) https://epress.lib.uts.edu.au/journals/index.php/PMRP/article/view/5462/5854
Perspective from European Financing Institutions: Integrating Climate Change Information and Adaptation in Project Development, Emerging Experience from Practitioners https://www.ebrd.com/what-we-do/get/integrating-climate-change-adaptation-in-project-development.pdf
Perspective: The Resilience of Indigenous Peoples to Environmental Change James D. Ford, Nia King, Eranga K. Galappaththi, Tristan Pearce, Graham McDowell, and Sherilee L. Harper, https://www.cell.com/one-earth/pdfExtended/S2590-3322(20)30250-5
Required for all modules:
Other resources with additional perspectives:
Low Carbon Resilience: Best Practices For Professionals, Final Report (2018) Adaptation to Climate Change Team, SFU Faculty of Environment https://act-adapt.org/wp-content/uploads/2018/12/lcr_best_practices_final.pdf (especially pages 8-16)
Adaptive Management in Climate Change Adaptation, Fact sheet undated, Ontario Centre for Climate Impacts and Adaptation Resources. http://climateontario.ca/doc/factsheets/AdaptiveManagement-final.pdf
Uncertainty, Climate Change, and Adaptive Management, Conservation Ecology, Vol. 1, No. 2 (1997) Garry Peterson, Giulio Alessandro De Leo, Jessica J. Hellmann, Marco A. Janssen, Ann Kinzig, Jay R. Malcolm, Karen L. O'Brien, Shealagh E. Pope, Dale S. Rothman, Elena Shevliakova and Robert R.T. Tinch, https://www.jstor.org/stable/26271660
Adaptive Management and Climate Change Adaptation: Two Mutually Beneficial Areas of Practice (2019) David Marmorek, Marc Nelitz, Jimena Eyzaguirre, Carol Murray, Clint Alexander, Paper No. JAWRA‐18‐0047‐P of the Journal of the American Water Resources Association (JAWRA), https://essa.com/wp-content/uploads/2019/07/Marmorek_et_al._in-press.-AM-and-CCA-two-mutually-beneficial-areas-of-practice-.pdf
Latour’s Axioms, a collection of extracts from Bruno Latour (1996) Aramis or the Love of Technology, Harvard University Press assembled by course developers.
Module 1 Course Content
Module 1 Overview
Let's get started.
In Module 1 you'll have an opportunity to consider your perspective on climate change as a project manager, recognize valuable perspectives that others bring, and consider when and how an interdisciplinary approach can enhance project management for a changing climate.
This module consists of the following activities:
1.1 Reading and viewing a variety of perspectives on climate change
1.2 Exploring what climate change means for you as a project manager (Discussion Forum)
1.3 Participating in live Collaborate discussion
1.4 Preparing for future modules by familiarizing yourself with the Smoky River Transit case study
At the end of the week I will summarize the main points that we have discussed online and in our Collaborate session and post these as a course Announcement.
Click here to move to the next page or use the Forward and Back arrows to navigate through the content for in each module.
1.1 Perspectives on project management and climate change
Watch the following videos and read at least two of the following perspectives on project management and climate change.
After viewing the videos and reading the articles/report, reflect on their messages and what they mean for project managers in Canada. How well do you think climate change is being addressed by project managers in Canada?
Video: An Engineering Perspective: Harshan Radhakrishnan, Manager, Climate Change and Sustainability Initiatives Engineers and Geoscientists BC
Video: A Low Carbon Resilience Perspective: Deborah Harford, Executive Director, ACT, Simon Fraser University
Perspective from UK professional: Climate change and project management: Re-thinking the relationship, Peter W.G. Morris (2017), https://www.apm.org.uk/blog/climate-change-and-project-management-re-thinking-the-relationship/
Perspective from US project management association leader: Thoughts on Climate Change and Project Management, Joel Carboni (2017) https://epress.lib.uts.edu.au/journals/index.php/PMRP/article/view/5462/5854
Perspective from European financing institution: Integrating Climate Change Information and Adaptation in Project Development, Emerging Experience from Practitioners https://www.ebrd.com/what-we-do/get/integrating-climate-change-adaptation-in-project-development.pdf
Perspective: The Resilience of Indigenous Peoples to Environmental Change James D. Ford, Nia King, Eranga K. Galappaththi, Tristan Pearce, Graham McDowell, and Sherilee L. Harper, https://www.cell.com/one-earth/pdfExtended/S2590-3322(20)30250-5
1.2 Climate Change: What does it mean for you as a project manager? (Discussion forum)
Take a moment to reflect on how climate change will affect your work and projects and post your thoughts to the discussion forum titled "Climate Change: What does it mean for me?"
Try to keep your post brief (100 words). Read and respond to one or two of your colleague's posts.
Be prepared to join the synchronous session to review the Discussion Forum results and discuss the biggest challenges and opportunities for project managers in a changing climate.
1.3 Synchronous (Collaborate) discussion
In this session we will discuss the highlights and key learnings from the previous activities. We will use Collaborate.
Join the Collaborate session prepared to discuss:
- How well do you think climate change is being addressed by project managers in Canada?
- What does climate change mean for you as a project manager?
We will have one hour for our discussion. To make the best use of our time together and ensure we can hear from everyone, let's agree to follow these norms:
- Put your mic on mute unless you're speaking
- If bandwidth is an issue, use the same guidance for video
- Use the raise a hand feature to indicate you have something to say
- Indicate if your comment continues the current discussion point or introduces a new idea and be prepared to hold onto it if someone else has something to add to the current thread
- Use the chat feature for short comments or to post a relevant link
1.4 Introducing Smoky River Transit
In Modules 2 and 3 we will be using the Smoky River Transit case study. You can prepare by:
- Reading the Case Study – Smoky River Transit
- Watching the video interview 1 with Robert Siddall, former CFO of Metrolinx, where we discuss:
- How is climate change going to change project management for large infrastructure projects?
- What skills sets or perspectives are needed?
Module 2 - Engaging
"Project Management for a Changing Climate-Module 2-Engaging" by Sue Todd, Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Welcome to Module 2, Engaging. In this Module, you'll have an opportunity to consider the people affected by climate change and your project's response to it. This includes people internal to your organization and others, such as neighbouring communities or Indigenous people.
Module 2 Learning Goals
This Module will help you:
- Understand the risks climate change poses to people internal or external to your organization
- Engage people and communities who could be affected by climate change and your project's response to it
Readings and Resources
Resources and additional reading:
Required readings for Module 2 activities, also included in Course Content
Climate Risks- Engaging People Vulnerable to Climate Impacts, Summary Report, Evergreen (2020) https://www.evergreen.ca/downloads/pdfs/Evergreen_Climate_Risks_Key_Findings_2020_FINAL.pdf
ACCC Resource Manual: Reflection on Adaptation Planning Processes and Experiences, (2013), Street, R. and S. Opitz-Stapleton, DflD-China: Beijing, http://www.asiapacificadapt.net/content/adapting-climate-change-china-phase-i-resource-manual
Health and climate change toolkit for project managers, World Health Organization (no date) https://www.who.int/globalchange/resources/toolkit/en/
Required for all modules:
Other readings and resources:
Public participation, engagement, and climate change adaptation: A review of the research literature (2019), Stephan Hügel | Anna R. Davies https://onlinelibrary.wiley.com/doi/full/10.1002/wcc.645 (especially section 4.1 on The “wicked problem of participation and engagement”)
Working on a warmer planet: The effect of heat stress on productivity and decent work (2019) Tord Kjellstrom, Nicolas Maître, Catherine Saget, Matthias Otto and Tahmina Karimova, International Labour Organization https://www.ilo.org/global/publications/books/WCMS_711919/lang--en/index.htm
Old ways for new challenges: Indigenous Adaptation to Climate Change, https://coastadapt.com.au/sites/default/files/case_studies/CS08_Indigenous_adaptation.pdf
Victorian Government DSE (Department of Sustainability and Environment). 2005. Effective Engagement: Building Relationships with Community and Other Stakeholders. Book 3 The Engagement Toolkit. https://sustainingcommunity.files.wordpress.com/2018/05/effective-engagement-book-3.pdf
RESIN: Supporting decision-making for resilient Cities, Supporting Tools and Methods.http://wiki.resin.itti.com.pl/supporting-tools/#Stakeholder%20identification%20and%20management%20tools
Smith, T., A. Leitch, and D. Thomsen. 2016: Community Engagement. CoastAdapt Information Manual 9, National Climate Change Adaptation Research Facility, Gold Coast, https://coastadapt.com.au/sites/default/files/information-manual/IM09_community_engagement.pdf
Module 2 Overview
Module 2 builds on our understanding of diverse perspectives and equips us for the work of engaging stakeholders and others who are important to our project. We will see that engagement is useful at all stages of a project for two reasons:
- It ensures that our project will consider and address the needs and views of people who could be affected by our project
- It provides vital information that can help ensure the success of our project.
Activities for this module will include:
2.1 Reading and viewing guidance on engagement
2.2 Sharing engagement experience (Discussion Forum)
2.3 Preparing to discuss Smoky River case study
2.4 Participating in live Collaborate discussion
2.1 Guidance on engagement
The readings and video resources for this week will help us in two areas:
- understanding who can be affected by climate change, including vulnerable populations. This prepares us to think broadly about whom your project will serve or whom it will impact in unexpected ways.
- enhancing our ability to engage effectively
Please watch the video with Erica Crawford, read the articles and explore the WHO toolkit. Then reflect and share your experience in this Module's discussion forum.
Watch: video clip with Erica Crawford, Adaptation Planner, Shift Collaborative
Read:
Climate Risks- Engaging People Vulnerable to Climate Impacts, Summary Report, Evergreen (2020) https://www.evergreen.ca/downloads/pdfs/Evergreen_Climate_Risks_Key_Findings_2020_FINAL.pdfACCC
Resource Manual: Reflection on Adaptation Planning Processes and Experiences, (2013), Street, R. and S. Opitz-Stapleton, DflD-China: Beijing, http://www.asiapacificadapt.net/content/adapting-climate-change-china-phase-i-resource-manual
Explore:
Health and climate change toolkit for project managers, World Health Organization (no date) https://www.who.int/globalchange/resources/toolkit/en/
Now, take some time to reflect and then share your story of what has worked well and what hasn’t to identify and respond to climate change implications for your projects.
Post your story to the Discussion Forum titled "Project Management Engagement – Engagement Stories".
2.2 Engagement stories (Discussion Forum)
Once you have done the readings and seen the video, take some time to reflect and then share your engagement story related to climate change. This can be from the perspective of a participant, a facilitator or a project manager. Include what has worked well and what hasn’t to identify and respond to climate change implications for your projects. If you haven't played a role in engagement around climate change, consider posting a story about a situation that would have benefited from engagement.
Post your story to the Discussion Forum titled "Engagement Stories".
2.3 Smoky River Transit Case
If you haven't already, familiarize yourself with the Smoky River case study materials in Module 1.
Read the Smoky River Transit Case and watch Robert Siddall video 1
Then watch video interview 2 with Robert Siddall.
In preparation for the synchronous session, consider the following questions:
Which transit stakeholders tend to be most affected by climate change and how should organizations engage with them to ensure projects consider the impacts on them?
In regards to the Smoky River Transit Case:
- What climate change risks should Hazel include in her project plan for the short term, longer term?
- What data would help Hazel manage uncertainty about future climate change and where/how could she get it?
- Who should Hazel involve/engage to ensure that her project plan adequately addresses climate change risks for both the project and the people affected by it?
2.4 Week 2 Synchronous Collaborate session
In this session we will discuss some of the questions in the Smoky River case study relevant to engaging stakeholders.
Join the synchronous (Collaborate) session prepared to discuss:
- Which transit stakeholders tend to be most affected by climate change and how should organizations engage with them to ensure projects consider the impacts on them?
In regards to the Smoky River Transit Case questions:
- What climate change risks should Hazel include in her project plan for the short term, longer term?
- Who should Hazel involve/engage to ensure that her project plan adequately addresses climate change risks for both the project and the people affected by it?
We will have one hour for our discussion.
Module 2 Discussion Forums
In this module I invite you to share your engagement story related to climate change. This can be from the perspective of a participant, a facilitator or a project manager. Include what has worked well and what hasn’t to identify and respond to climate change implications for your projects. If you haven't played a role in engagement around climate change, consider posting a story about a situation that would have benefited from engagement
Module 3 - Planning
"Project Management for a Changing Climate – Module 3 - Planning" by Sue Todd, Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Welcome to Module 3, Planning. In this Module you'll have an opportunity to integrate climate change implications with standard project management planning considerations. You’ll also start applying them in a case study situation.
Module 3 Learning Goals
This Module will help you:
- Develop awareness of how climate change affects project management in all stages
- Focus on what you can do in the planning stage to address climate change
- Find tools, frameworks or approaches to help you add a climate change lens to your planning
Readings and Resources
Required for Module 3.1 activities - also included in Course Content
The Four Phases of Project Management, Harvard Business Review staff (2016).
Guidelines for Project Managers: Making vulnerable investments climate resilient, Report for the European Commission (2012), Acclimatise and COWI, https://web.law.columbia.edu/sites/default/files/microsites/climate-change/ec_guidelines_for_project_managers.pdf
Climate Compass - A climate risk management framework for Commonwealth agencies (2018), CSIRO, Australia, https://www.environment.gov.au/climate-change/adaptation/publications/climate-compass-climate-risk-management-framework
Summary of ISO 14090 Principles - Summary assembled by course developer from ISO 14090:2019 Adaptation to climate change — Principles, requirements and guidelines https://www.iso.org/standard/68507.html
Required for Module 3.2 Activities
ReTooling for climate change site to familiarize yourself with some available tools https://www.retooling.ca/retooling_essentials.html
European Climate Adaptation Platform Climate-ADAPT https://climate-adapt.eea.europa.eu/knowledge/tools/uncertainty-guidance/topic3
Required for all modules:
Other readings and resources that may be helpful for Module 3.3 tools swap meet:
Climate Lens - General Guidance, Infrastructure Canada, https://www.infrastructure.gc.ca/pub/other-autre/cl-occ-eng.html#1.1
Strategic Assessment of Climate Change, Environment and Climate Change Canada, July 2020 https://www.strategicassessmentclimatechange.ca/
Climate Data Canada portal, https://climatedata.ca/
Data portal, Pacific Climate Impacts Consortium (PCIC), University of Victoria https://pacificclimate.org/data
Plan2Adapt, a PCIC tool https://pacificclimate.org/analysis-tools/plan2adapt
PIEVC Engineering Protocol, Public Infrastructure Engineering Vulnerability Committee https://pievc.ca/
Study of the Impacts of Climate Change on Precipitation and Stormwater Management, Metro Vancouver http://www.metrovancouver.org/services/liquid-waste/LiquidWastePublications/Climatechangeimpactsprecipitationstormwater2050-2100%E2%80%93Technical-brief-2018.pdf
Adapting to Climate Change Canada’s First National Engineering Vulnerability Assessment of Public Infrastructure (2008), Canadian Council of Professional Engineers, https://pievc.ca/sites/default/files/adapting_to_climate_change_report_final.pdf
ISO 14090:2019 Adaptation to climate change — Principles, requirements and guidelines https://www.iso.org/standard/68507.html
Core principles for successfully implementing and upscaling Nature-based Solutions (2019) E. Cohen-Shacham, et al, Environmental Science and Policy 98, accessible from https://www.iucn.org/theme/ecosystem-management/our-work/iucn-global-standard-nature-based-solutions
Galore Creek Mining Case Study http://www.climateontario.ca/doc/reports/fbc_mining_case_study_galore_creek.pdf
Metrolinx Climate Adaptation Strategy (2018) Download PDF from http://www.metrolinx.com/en/aboutus/sustainability/default.aspx
Module 3 Course Content
Module 3: Overview
In Module 3, we explore familiar territory for project managers, project planning, through the lens of climate change. As we have heard in Module 1 interviews, there is an abundance of resources on climate change. We will gain familiarity with these tools and exchange lessons learned in applying them.
Activities for this module will include:
3.1 Adding climate change considerations to a standard project management approach (Google doc)
3.2 Gaining familiarity with climate change tools
3.3 Participating in virtual swap meet of climate change tools (Padlet)
3.4 Preparing to discuss Smoky River case study planning issues
3.5 Participating in live Collaborate discussion
3.1 Climate change considerations in planning (readings and Google doc)
The project management approaches and frameworks you use now continue to be relevant in a time of climate change, but we may need to approach them with a new perspective and understanding of climate risks and key stakeholders.
In this section we will take a traditional project management framework and consider how climate change considerations can inform it. We will build this collaboratively through a Google doc. See below.
Let's start by reading or scanning the following:
The Four Phases of Project Management, Harvard Business Review staff (2016) https://hbr.org/2016/11/the-four-phases-of-project-management
Guidelines for Project Managers: Making vulnerable investments climate resilient, Report for the European Commission (2012), Acclimatise and COWI, https://web.law.columbia.edu/sites/default/files/microsites/climate-change/ec_guidelines_for_project_managers.pdf
Climate Compass - A climate risk management framework for Commonwealth agencies (2018), CSIRO, Australia, https://www.environment.gov.au/climate-change/adaptation/publications/climate-compass-climate-risk-management-framework
Summary of ISO 14090 Principles https://csonline.royalroads.ca/moodle/pluginfile.php/90933/mod_page/content/13/Summary%20of%20ISO%2014090%20Principles.docx
Once you have absorbed enough of these documents contribute to the Module 3 Google Doc to show where and how climate change considerations might show up in the HBR approach.
Contribute to a Module 3 Google Doc to show where and how climate change considerations might show up in the HBR approach.
<Note to instructor: Create a google doc with the following:>
Project Management Stage | How could you consider climate change at this stage? |
Planning |
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Determine the real problem to solve |
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Identify stakeholders |
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Define project objectives |
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Determine scope, resource and major tasks |
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Prepare for trade-offs |
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Build Up |
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Assemble your team |
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Plan assignments |
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Create the schedule |
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Hold kickoff meeting |
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Develop budget |
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Implementation |
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Monitor and control process and budget |
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Report progress |
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Hold weekly meetings |
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Manage problems |
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Closeout |
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Evaluate project performance |
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Close out project |
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Debrief with team |
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3.2 Climate change tools for project management in the planning stage
To effectively integrate climate change into your project planning you may need the following kinds of "tools" (term used loosely):
- Climate change information and education - general or specific science-based knowledge about how climate change works and what kinds of impacts we can expect
- Data services - services that help us understand how the climate may change in the locations that matter to our project
- Risk assessment - tools to help you understand climate change hazards specific to your project, recognize vulnerabilities, evaluate risks, and develop options to address the risks
- Community planning - tools for preparing and implementing local climate change strategies
- Sector or location specific guidance - guides, manuals, case studies and other tools
Below are two great places to start to get a sense of the tools available. Please explore:
ReTooling for climate change site to familiarize yourself with some available tools https://www.retooling.ca/retooling_essentials.html
European Climate Adaptation Platform Climate-ADAPT https://climate-adapt.eea.europa.eu/knowledge/tools/uncertainty-guidance/topic3
The readings and resources section for this module is organized around the above categories (some tools span categories and other categorization is possible).
Once you're familiar with some tools, our next activity will be to share our experiences or tips about tools, through a virtual "swap meet". In a swap meet, you show up with stuff you have used and want to share, and you can pick up some new stuff.
Use the Padlet in word or video to tell us about one tool you're bringing to the swap meet. How did you use it and why do you love it? You can also ask others if they have a used tool that might help you.
3.3 Virtual Swap Meet (Padlet)
Welcome to our climate change tools swap meet!
In a swap meet, you show up with stuff you have used and want to share, and you can pick up some new stuff.
Use the Padlet through words or video to tell us about one tool you're bringing to the swap meet. How did you use it and why do you love it? You can also ask others if they have a used tool that might help you.
3.4 Smoky River Transit Case Study
In our synchronous session this week, we will discuss some planning questions in our case study. To prepare, please review the case and watch the video.
Review: Smoky River Transit Case
Watch video interview 3 with Robert Siddall – Question: What are the most useful things project managers can do at the planning stage of a new transit project, to consider climate change?
Reflect on questions 2 & 4 in the Case Study
Join the synchronous session to discuss possible responses.
3.5 Week 3 Synchronous (Collaborate) session
In this session we will continue our discussion of the Smoky River case study, with a focus on a key planning issue - data needs.
Join the session prepared to discuss:
- What data would help Hazel manage uncertainty about future climate change and where/how could she get it?
We will have one hour for our discussion.
Module 4 - Applying
"Project Management for a Changing Climate – Module 4- Applying" by Sue Todd, Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Welcome to Module 4 the final module in this course. In this module you will pull together all your learning from the course so far to apply them to a real project you are managing, with feedback from peers.
Module 4 Learning Goals
This Module will help you:
- Address practical issues in project management related to climate change
- Identify and address potential issues in communicating about and getting buy-in to your project's climate change response
- Gain practice in applying a climate change lens to your own project. You will also identify potential issues in communicating about and getting buy-in to your project's climate change response.
Module 4 Readings and Resources
Required reading for Module 4 activities - also included in Course Content
Article on change management and the ADKAR model, https://www.prosci.com/resources/articles/the-what-why-and-how-of-change-management
Being an Effective Change Agent: A Guide (2016) Stephanie Bertels, Jess Schulschenk, Andrea Ferry, Vanvessa Otto-Mentz, Esther Speck https://embeddingproject.org/resources/being-an-effective-change-agent
Guidance on how to build a business case for climate change adaptation: Lessons from coastal Australia (2018), Coast Adapt, Department of the Environment and Energy, Australia
https://coastadapt.com.au/how-develop-business-case (includes business plan template)
Required for all modules:
Module 4 Overview
In Module 4 we will look at change management and business case approaches that can help you gain support for addressing climate change in your project planning. We will apply these insights to Smoky River Transit in a final Discussion Forum and to your own project in a Google doc. For our final Collaborate session, Robert Siddall will join us live to take your questions.
Activities in this module include:
4.1 Video and readings about making the case for a new lens on project management
4.2 Smoky River Transit (Discussion Forum)
4.3 Application to your own project (Google doc)
4.4 Synchronous session with guest Robert Siddall
4.5 Course wrap and celebration (Padlet)
4.1 Making the case for a new lens on project management
Project managers who see the benefit of including climate change considerations in their planning, may encounter obstacles in the form of colleagues, bosses, stakeholders and others who do not see the need for it. These groups or individuals may be reluctant because they are concerned about delays or extra costs or they may not believe the benefits will outweigh the costs.
Introducing climate change perspectives to an established way of working may require a change management approach.
It may also require new business case tools that integrate climate change thinking.
Watch video interview 4 with Robert Siddall – Question: What is the most useful thing project managers can do to ensure organizational support for a climate change lens on project management?
Read:
Article on change management and the ADKAR model, https://www.prosci.com/resources/articles/the-what-why-and-how-of-change-management
Being an Effective Change Agent: A Guide (2016) Stephanie Bertels, Jess Schulschenk, Andrea Ferry, Vanvessa Otto-Mentz, Esther Speck https://embeddingproject.org/resources/being-an-effective-change-agent
You can also explore this guide from Australia:
Guidance on how to build a business case for climate change adaptation: Lessons from coastal Australia (2018), Coast Adapt, Department of the Environment and Energy, Australia
https://coastadapt.com.au/how-develop-business-case (includes business plan template)
Once you've absorbed enough of these resources, move on to apply them to the Smoky River Transit case study.
4.2 Smoky River Transit (Discussion Forum)
Refresh your memory of the Smoky River Transit Case
Reflect on what Hazel might need to do to build organizational support for a climate change lens on the new transit line project
Contribute your ideas to the Robert Siddall Discussion Forum.
4.3 Application to your own project
You've learned some approaches and tried them out on Smoky River Transit. Now it's time to apply them to your own project and get helpful suggestions from your peers.
Contribute to this Google Doc.
<note to instructor: create a google doc with the following>:
Module 4 – Google Doc: Putting a climate change lens on your project.
Project name or nickname | Description max 20 words | Biggest climate change risks (max 3) | Vulnerable stakeholders (max 3) | Biggest anticipated challenge | One thing you can do to address climate change | Peer Suggestions |
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You will complete the first six columns for one project. One row per project.
In the final column, peers may suggest ideas to overcome your biggest challenge and additional things you can do to address climate change for this project.
4.5 Course Wrap and Celebration (Padlet)
Congratulations to the first cohort of Project Management for a Changing Climate! You've completed all Modules of this course.
You've learned some new perspectives, gained insight to stakeholder engagement, adapted project management approaches, discovered climate change tools, and found ways to build support for your climate change lens. You've applied your learning to a case study and then to a real project.
This is a good time to look back and reflect on what you've learned and think about what you want to do next.
Our final Padlet provides an opportunity to share your learning highlight, to signal your next move and to support your new friends in their journey.
Module 4 Discussion Forums
Watch the video interview with Robert Siddall – Question: What is the most useful thing project managers can do to ensure organizational support for a climate change lens on project management?
Reflect on what Hazel might need to do to build organizational support for a climate change lens on the new transit line project
Contents of the forum are not included in compile. To see the content, please visit the course.
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oercommons
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2025-03-18T00:38:20.493616
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Environmental Studies
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/74303/overview",
"title": "Project Management for a Changing Climate",
"author": "Environmental Science"
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https://oercommons.org/courseware/lesson/69323/overview
|
Climate Change Adaptation Fundamentals
Overview
This course has been designed to help professionals working across multiple disciplines bring a climate change adaptation lens to their current and future projects.
Introduction and Welcome
Climate Change Adaptation Fundamentals
| "Climate Change Adaptation Fundamentals – Introduction and Welcome" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Introduction and Welcome
Welcome to this 4-week course, Climate Change Adaptation Fundamentals. My name is Dr. Stewart Cohen and I'll be facilitating the course using videos, discussion forums, and other learning activities each week/module.
This course has been designed to help professionals working across multiple disciplines bring a climate change adaptation lens to their current and future projects. It’s structured in four modules, that cover:
- what the current climate change situation is, including the latest science and scenarios;
- why climate change matters to professionals and planners, in terms of risk and impact;
- what we can do about it, through examples and methods of adaptation, and;
- how to bring adaptation tools, data and processes into your work, with a practice project.
At the end of the course, participants will understand basic climate change science and scenarios, and be able to identify the data and tools required to plan an adaptation project.
Each module includes one or more video-lectures and discussion forums that are designed to prompt reflection and integration of core concepts. The final module involves learners in a capstone activity designed to support the application of the learning to a real-world, learner-relevant case example. Each module also contains resources (e.g., relevant reports, video links).
Although you are not required to engage in the learning activities at any specific time, it is recommended that you complete the activities for each module within that week in order to maximize learning and provide opportunities for meaningful discussion with the instructor and your fellow learners.
Throughout this course we will also be listening to portions of the CBC Podcast 2050: Degrees of Change. This podcast features Johanna Wagstaffe, a Vancouver based meteorologist. It provides a portrait of BC in the year 2050 based on current climate change science projections. The podcast blends evidence-informed perspectives on climate change and climate adaptation with a fictional account of a young girl, Ariadne, as she navigates a climate changed world. Though we provide links to specific clips of interest, you may find it worthwhile to listen to the entire, 7-part series, which you can access here.
We will start here by listening to this excerpt of the CBC Podcast 2050: Degrees of Change News Montage. Stop listening at 1:44 and return to this screen.
The course is guided by myself, Dr. Stewart Cohen, and story strategist Denise Withers. In the following video, we introduce ourselves and provide an overview of the course.
http://admin.video.ubc.ca/tiny/lr1wj Video attribution: "Climate Change Adaptation Fundamentals - Module 1 introduction to module 1" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY. |
Doctor Climate Change Blog
https://doctorclimatechange.com/
Readings & Resources
This page is a compilation of all of the course readings and resources used in all Modules.
Glossary of Key Terms from 2014 IPCC 5th Assessment Report, Working Group II
The Canadian Institute for Climate Choices
Executive Summary of Canada's Changing Climate Report (2019)
Full report (includes link to individual chapters)
Pacific Climate Impacts Consortium (PCIC) is our regional climate service centre. PCIC conducts quantitative studies on the impacts of climate change and climate variability in the Pacific and Yukon region, providing regional climate information for planning.
The BC Government's Resources for Preparing and Adapting to Climate Change is a great resource for existing tools, climate change health facts, the recent BC Climate Risk Assessment, which we discuss in Module 3.
You may also want to dive into Canada's interactive Climate Atlas, where you can explore how various aspects of climate change are playing out in different regions of Canada and explore maps, graphs and climatedata for provinces, local regions and cities across the country.
The Canadian Centre for Climate Services is another resource for climate resources, climate change concepts and trends, climate data, and has a climate-service support desk if you have further questions.
Abbott and Chapman – sections on the 2017 wildfire
Canada’s Changing Climate Report – Executive Summary
Canada’s Changing Climate Report – Chapter 8
IPCC 5th Assessment, Working Group II, Summary for Policymakers (SPM)
Council of Canadian Academies, Canada’s Top Climate Change Risks – method and summary of results
BC Government, Preliminary Strategic Climate Risk Assessment for British Columbia – method and summary of results
Cohen, S. J. (2010). From observer to extension agent – using research experiences to enable proactive responses to climate change. Climate change, 100(1), 131-135.
Sendai Framework for Disaster Risk Reduction A global, non-binding agreement followed by 187 countries that focuses on best practices for disaster risk reduction and resilience building.
Climate preparedness and adaptation strategy
BC Climate Risk Assessment (scheduled to be released in late 2020)
Tools (these are technical resources, so just focus on the overall framing and application)
Adaptation examples in British Columbia
Qualicum Beach Waterfront Plan
Vancouver Climate Change Adaptation Strategy
Adaptation / Mitigation links
IPCC 5th Assessment Report, Working Group II, Chapter 2 (focus on Section 2.5.1 – Assessing synergies and trade-offs with mitigation, including Figure 2-4)
| "Climate Change Adaptation Fundamentals – Introduction and Welcome" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Module 1- What's the Problem?
Climate Change Adaptation Fundamentals
Module 1 – What’s the Problem? Course Content
"Climate Change Adaptation Fundamentals - Module 1" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
Module 1 Learning Goals
This Module will help you:
- Understand the evidence for our knowledge of historic climate trends for Canada
- Explore scenario-based projections of future climate change for Canada
- Become aware of the range of climate services available in Canada
- Consider examples of how climate change affects water resources, snow and ice cover, and oceans along Canada’s coastlines
Readings and Resources
Canada’s Changing Climate Report
Read the Executive Summary, and refer to the full report in case you would like to go into greater depth on particular topics.
Executive Summary of Canada's Changing Climate Report (2019)
Full report (includes link to individual chapters)
Pacific Climate Impacts Consortium (PCIC) is our regional climate service centre. PCIC conducts quantitative studies on the impacts of climate change and climate variability in the Pacific and Yukon region, providing regional climate information for planning.
The BC Government's Resources for Preparing and Adapting to Climate Change is a great resource for existing tools, climate change health facts, the recent BC Climate Risk Assessment, which we discuss in Module 2.
You may also want to dive into Canada's interactive Climate Atlas, where you can explore how various aspects of climate change are playing out in different regions of Canada and explore maps, graphs and climate data for provinces, local regions and cities across the country.
The Canadian Centre for Climate Services is another resource for climate resources, climate change concepts and trends, climate data, and has a climate-service support desk if you have further questions.
Module 1 Overview
Let's get started. Module 1 consists of 3 sub-modules that cover the following topics:
- Core concepts of climate science
- Global context
- Greenhouse effect, global trend on GHG concentrations, global temperature trend
- Difference between weather, natural climate variability, climate change
- Weather, natural climate variability, & climate change each represent different time scales, from immediate short-term days and weeks, to years, to multiple decades
- BC trends and scenarios
- Using climate change information in applications
- Sources of climate and climate change information
- Importance of tracking changes in water, snow and ice
Module 1.1: Climate trends
Module 1.1 begins with a video-lecture on climate trends where Denise and I explore some of the fundamental concepts of climate science and an overview of how climate change is impacting Canada.
http://admin.video.ubc.ca/tiny/xmtm5
Video attribution: "Climate Change Adaptation Fundamentals - Module 1 video 1.1" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
By the end of this module, you will be able to identify and understand the core climate science concepts, including the differences between adaptation and mitigation and how they overlap, the difference between weather and climate, and some of the current trends in what we are seeing, globally and regionally.
From the CBC podcast, here is an audio clip which features Trevor Murdock, a climate scientist with the Pacific Climate Impacts Consortium in Victoria, BC. In this clip, Trevor describes how climate change is affecting BC. The clips starts at 05:00 Stop listening at 9:55 and return to this screen.
Module 1.2: Climate change scenarios
This next video lecture focuses on climate modelling and change scenarios. As with Module 1.1, view the video lecture below.
http://admin.video.ubc.ca/tiny/i2gy0 Video attribution: "Climate Change Adaptation Fundamentals - Module 1 video 1.2" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY. |
Now Listen to the following excerpt from the CBC podcast 2050: Degrees of Change. Johanna Wagstaffe, Prof. Simon Donner, UBC, and Trevor Murdock, PCIC, on greenhouse gasses affecting the climate: (14:53) Stop listening at 17:10 and return to this screen.
Module 1.3: Climate change information for applications
This module provides an overview of climate services available in Canada, and examples of applications of climate change scenario information. Highlights from the 2019 federal government publication, Canada’s Changing Climate Report, are also presented.
Start by watching the video lecture:
http://admin.video.ubc.ca/tiny/ui9my Video attribution: "Climate Change Adaptation Fundamentals - Module 1 video 1.3" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY. |
After watching the video, listen to the following excerpts from the CBC podcast 2050: Degrees of Change.
- Johanna Wagstaffe and Prof. Stéphane Dery, UNBC, on precipitation and streamflow in the Fraser River Basin: (05:50) Stop listening at 8:14 and return to this page.
- Johanna Wagstaffe and Prof. Brian Menounous, UNBC, on glaciers: (19:02) Stop listening at 22:49 and return to this page.
Module 1 Summary: Take Home Messages
This last video of Module 1 provides a high level summary of the key take home messages from this module.
http://admin.video.ubc.ca/tiny/ui9my Video attribution: "Climate Change Adaptation Fundamentals - Module 1 video module 1 summary" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY. |
Before moving on to Module 2, we invite you to consider the implications of human-caused climate change to you in both your professional and personal lives. How would a rapidly warming climate affect your vision of your future, or the work that you currently do? How might it affect the future of your community?
If you are interested in more information on the basics of climate change and related tools and resources, we recommend exploring the following links:
Pacific Climate Impacts Consortium (PCIC) is our regional climate service centre. PCIC conducts quantitative studies on the impacts of climate change and climate variability in the Pacific and Yukon region, providing regional climate information for planning.
The BC Government's Resources for Preparing and Adapting to Climate Change is a great resource for existing tools, climate change health facts, the recent BC Climate Risk Assessment, which we discuss in Module 3.
You may also want to dive into Canada's interactive Climate Atlas, where you can explore how various aspects of climate change are playing out in different regions of Canada and explore maps, graphs and climate data for provinces, local regions and cities across the country.
And finally, the Canadian Centre for Climate Services is another resource for climate resources, climate change concepts and trends, climate data, and has a climate-service support desk if you have further questions.
| "Climate Change Adaptation Fundamentals - Module 1" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details. |
Module 2 - What's at stake?
Climate Change Adaptation Fundamentals
"Climate Change Adaptation Fundamentals - Module 2" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
Module 2 - What's at stake?
Welcome to Module 2. The focus of this module is on the projected risks of future climate change scenarios, including examples of how they have been determined. You will have the opportunity to listen to additional clips from CBC’s 2050: Degrees of Change podcasts, and to hear from Dr. Johanna Wolf, Senior Policy Analyst with the BC Climate Action Secretariat. Dr. Wolf led the Preliminary Strategic Climate Risk Assessment for British Columbia.
Module 2 Learning Goals
This Module will help you:
- Understand the outcomes of the review of the 2017 wildfire season in British Columbia
- Consider examples of expert judgement of climate change risk for Canada, and for British Columbia, including ratings of likelihood, consequence, and adaptation potential
- Explore aspects of the climate change information supply chain
Readings and Resources
Read sections from the following:
Abbott and Chapman – sections on the 2017 wildfire
Canada’s Changing Climate Report – Executive Summary
Canada’s Changing Climate Report – Chapter 8
IPCC 5th Assessment, Working Group II, Summary for Policymakers (SPM)
Council of Canadian Academies, Canada’s Top Climate Change Risks – method and summary of results
BC Government, Preliminary Strategic Climate Risk Assessment for British Columbia – method and summary of results
Cohen, From observer to extension agent – using research experiences to enable proactive responses to climate change <paywalled journal>
Module 2 Overview
Let's get started. Module 2 consists of 5 sub-modules that cover the following topics:
- The 2017 wildfire season in British Columbia; impacts and response
- Framing of risk in the context of climate change
- The role of expert judgement in assessing climate change risk
- Climate change risk assessment for Canada, including ratings of adaptation potential
- Climate change risk assessment for British Columbia
- The climate change information supply chain, and the role of practitioners within it
Module 2.0: Wildfires
With Module 2 we move from understanding the basic concepts of climate science, to exploring what climate change means to us in terms of risks and impacts - what is at stake. Let's begin with this video lecture: http://admin.video.ubc.ca/tiny/irxa3
Video attribution: "Climate Change Adaptation Fundamentals - Module 2 wildfires" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
The climate risks and impacts we face change from geographic region to region, and climate adaptation requires understanding these regional impacts and shaping adaptation measures to those specific impacts and contexts. One of the climate risks we face in BC is an increase in the length of the wildfire season and the severity and frequency of wildfire events. In this clip from the CBC podcast 2050: Degrees of Change, forest fire ecologist Robert Gray discusses the impacts of climate change on BC's forests
- 0300 Stop listening at 7:09 and return to this screen.
Module 2.1: Understanding risk and impact
Wildfire risks are only one of the risks we face in a climate changed future. In this next video lecture, we explore why it is important for professionals thinking about adaptation to understand how climate change is resulting in changing climate statistics, and the influence of those changes on the assessment of future climate risks and their impacts.
http://admin.video.ubc.ca/tiny/0ohlf
Video attribution: "Climate Change Adaptation Fundamentals - Module 2.1 risk framing" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
To do this, we return to the global environment to explore the trends in weather and climate catastrophes and the projected changes in climate extremes based on low and high emission scenarios. We will explore climate change scenarios for BC, and some of the findings from the recent climate risk assessment for our province.
With climate change comes the need to focus attention not only on understanding and planning for individual risks, such as wildfires, but also on compound risks -- where two or more events can co-occur and interact. In this way, climate change is influencing not only the nature of the risks we face, but also how practitioners will need to adapt their planning and decision making to account for compound and complex scenarios involving multiple environmental and social factors and uncertainty:
Module 2.2: Canada's top climate change risks
Building on the base of Module 2.1, we now explore in greater depth some of Canada's top projected climate change risks and what this means for potential climate adaptation.
Let’s start by listening to the following video lecture:
http://admin.video.ubc.ca/tiny/mqt40
Video attribution: "Climate Change Adaptation Fundamentals - Module 2.2 Canada climate" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
(Those interested in learning more about these risks, can click on this link to the full Canadian Council of Academies Canada's Top Climate Change Risk report.)
Looking forward to Module 2.3, where we will be looking at climate change risks in BC, listen to this brief interview with Dr. Johanna Wolf from the BC Climate Adaptation Secretariat, as she describes to CBC Kamloops Daybreak host, Shelley Joyce, some of the key findings of the recently published BC Strategic Climate Risk Assessment.
Module 2.3: BC's top climate change risks
http://admin.video.ubc.ca/tiny/rvp3x
Video attribution: "Climate Change Adaptation Fundamentals - Module 2.3 BC climate" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
Building from Dr. Wolf's overview of the Strategic Climate Risk Assessment for British Columbia, we take a deeper dive into that report and its implications for the province:
The risk profile this report provides is important but it is still very conceptual. What do these risks mean on the ground? To explore and humanize these risks we return to the CBC podcast 2050: Degrees of Change.
In this clip we hear from Emily McNair, part of the Climate Action Initiative working with farmers in BC to plan for climate changes, and Lydia Real, whose farm sits on Westham Island in the Fraser River Delta. Her farm is threatened by sea level rise the increasing risk of what is known as a salt wedge, or the influx of salt water into the fresh water she uses for irrigation:
● 5:11Stop listening at 7:45 and return to this screen.
Module 2.4: Climate change information supply chain
So the risks we face in the changing climate are diverse, complex and characterized by uncertainty. In the face of this complexity, knowledge translation and knowledge sharing between climate scientists - the producers of climate information - and professionals such as yourselves - the consumers of climate information - is critical.
In Module 1, we explored some examples of the kinds of information being shared by two of Canada's key climate knowledge producers - the Pacific Climate Impacts Consortium or PCIC for short, and the Quebec-based Ouranos. Here in Module 2.4, we shall consider the "supply chain" of climate change information, and the role of practitioners within it:
http://admin.video.ubc.ca/tiny/7muas
Video attribution: "Climate Change Adaptation Fundamentals - Module 2.4 information supply chain " by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
"Climate Change Adaptation Fundamentals - Module 2" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
Module 3 - What can we do?
Climate Change Adaptation Fundamentals
"Climate Change Adaptation Fundamentals - Module 3" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
Module 3 - What can we do?
Welcome to Module 3. Here, we consider how planned adaptation to future climate change differs from adapting on the basis of past experience. Several adaptation cases from various communities in British Columbia are described. We will also consider the climate change information supply chain, and the role of practitioners within it.
Module 3 Learning Goals
This Module will help you:
- Understand global-scale climate change risks, and why they matter
- Explore some tools that can enable practitioners to assess and plan for flood and wildfire risks
- Consider examples of proactive adaptation being planned or implemented in British Columbia
- Understand potential synergies and trade-offs between climate change adaptation and mitigation of greenhouse gas emissions
Readings and Resources
Sendai Framework for Disaster Risk Reduction A global, non-binding agreement followed by 187 countries that focuses on best practices for disaster risk reduction and resilience building.
Climate preparedness and adaptation strategy
BC Climate Risk Assessment (scheduled to be released in late 2020)
Tools (these are technical resources, so just focus on the overall framing and application)
Adaptation examples in British Columbia
Qualicum Beach Waterfront Plan
Vancouver Climate Change Adaptation Strategy
Adaptation / Mitigation links
IPCC 5th Assessment Report, Working Group II, Chapter 2 (focus on Section 2.5.1 – Assessing synergies and trade-offs with mitigation, including Figure 2-4)
Module 3 Course Content
Module 3: Overview
In the previous modules we have explored some of the ways in which climate change is affecting us regionally, including identifying and discussing some of the climate risks we face here in BC. In this module, we now move on to explore what we can do about those risks.
Topics covered include:
- Links between Disaster Risk Reduction and climate change adaptation
- examples of tools for assessing climate change risk to support adaptation planning
- examples of ongoing adaptation activities in British Columbia
- links between adaptation and mitigation of greenhouse gas emissions
Module 3.1: What can we do?
Having explored the profile of risks we face here in BC and in Canada, it is now time to focus on what we can do about those risks. Reducing the risks of catastrophic climate related events and disasters is a priority not only for those focusing on climate adaptation, but also for professionals working in emergency management. In fact, there are many overlaps between disaster risk reduction (DRR) and climate change adaptation (CCA). Both focus on reducing risks and associated vulnerabilities, and increasing resilience. Just as our emissions reduction goals are being shaped by climate science and the Paris Agreement, our disaster risk reduction goals in Canada are being guided by the Sendai Framework for Disaster Risk Reduction - a global, non-binding agreement signed by 187 countries that focuses on best practices for disaster risk reduction (DRR) and resilience building.
In this first video, we hear from Dr. Matt Godsoe, Director with Public Safety Canada, the federal agency responsible for emergency and disaster management. Dr. Godsoe shares his research on the current and future state of disaster risk reduction in Canada and what the current trends suggest about the future human, economic and environmental costs of disasters and and our capacity for resilience:
http://admin.video.ubc.ca/tiny/lv1sq
Video attribution: "Climate Change Adaptation Fundamentals - Module 3.1 adaptation" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
The provincial government is currently revising the Emergency Management Act, to better reflect the DRR goals of the Sendai Framework's and support a more fulsome integration and consideration of indigenous knowledge and rights, and climate change.
At the same time, the province is also crafting a new climate preparedness and adaptation strategy to better reflect the climate risks identified in the BC Climate Risk Assessment discussed in Module 2. These separate but related initiatives highlight the need for coordinated planning and cross sector collaboration. In the following video lecture we will explore some of the challenges and opportunities for such planning, including some examples currently underway in British Columbia.
Now let's return to the CBC podcast 2050: Degrees of Change to get a sense of the range of adaptation already underway in BC. We begin with a clip featuring Doug Smith, the City of Vancouver's Director of Sustainability talking about the Olympic Village neighbourhood in Vancouver, and the implications of sea level rise for that neighbourhood and the city more generally:
5:15 Stop listening at 5:57 and return to this screen.
The next clip features John Vanderden, a Vancouver based engineer discussing dyke adaptations along the Fraser River as another approach to adapting to sea level rise:
20:30 Stop listening at 23:57 and return to this screen.
The final podcast clip features forest-fire ecologist Robert Gray discussing the ways we will need to adapt to support forests being resilient to forest fires and drought in the future:
8:14 Stop listening at 10:47 and return to this screen.
Module 3.2: Adaptation examples from BC
With those adaptation examples from Module 3.1in mind, we now take a deeper dive into adaptation:
http://admin.video.ubc.ca/tiny/bajah
Video attribution: "Climate Change Adaptation Fundamentals - Module 3.2 adaptation BC" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
Module 3.3: Adaptation - mitigation linkages and summary
In this final video lecture of Module 3, we bring everything together, discussing the linkages between climate change adaptation and climate change mitigation, exploring the synergies (co-benefits) and trade-offs that these two sides of climate action present.
http://admin.video.ubc.ca/tiny/fbtkh
Video attribution: "Climate Change Adaptation Fundamentals - Module 3.3 adaptation mitigation linkage summary" by Stewart Cohen, Climate Change Fundamentals, Adaptation Learning Network is licensed under CC BY 4.0. The images used in the slides in the video are not CC BY.
Activity: Regional Context
Think about your own regional context and pick one example of climate change adaptation that will be necessary in the future that you can work on in the next module.
"Climate Change Adaptation Fundamentals - Module 3" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
Module 4: Knowledge and skills to practice
Climate Change Adaptation Fundamentals
"Climate Change Adaptation Fundamentals - Module 4" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
Module 4: Knowledge and skills to practice
Welcome to Module 4 the final module in this course. The overarching goal of this course is to support your capacity to incorporate adaptation into the work you do. So, we now shift from learning about climate change, climate risk, and climate adaption, to a reflective activity designed to help each of you synthesize what you’ve learned and explore ways to put your new knowledge and skills into practice.
The Module 4 activity focuses on crafting a future adaptation story that is relevant to you and your profession and professional goals.
Module 4 Learning Goals
In Module 4, you’re going to use your own work background, and, reflecting on the previous Modules, create a story about how you might design a climate change adaptation activity that could be carried out from within your field of practice.
This experience is something that you can take with you upon completion of this course.
Module 4 Activity
As a way to pull together all the threads of the previous module, we invite you to use your time during this final week of the course to create a future story* about how you might design a climate change adaptation project in your region / domain. Your story could be anything from a one-page outline, to a flow chart, to a short slide deck. The idea is to take some time to think about a challenge you're currently facing or might face in your work, and explore the steps you could take to apply a climate change adaptation lens to that work.
When preparing your story, it might be helpful to ensure it describes:
- The specific challenge or opportunity you’d like to tackle.
- The key steps you know you’d need to take to succeed.
- Expected obstacles you don’t yet know how to overcome.
- Stakeholders, collaborators, regulators and other people you’d need to work with.
- Required resources to get the job done.
- The ideal outcome, along with measures of success.
When describing how you'll approach solving the problem, it may be helpful to consider some of the core concepts we’ve covered in the course, such as:
- Risk assessment.
- Compound risks.
- Impact.
- Access to data.
- Information supply chains.
- Expert judgement.
- Historic vs future perspectives.
- Mitigation-adaptation interactions.
Again, your story can take any form you choose: text, audio, photos, video or even a webpage. Please don't worry about the packaging of your story; I'm most interested in seeing what you propose to do, how you might do it, and what might get in your way. I encourage you to explore something that is relevant to you - a project that’s on your desk now, or something that may come up in the near future, so that this exercise has real value for you.
*Note that every story describes the experience of a hero as s/he solves a problem. While most stories are about things that have already happened, future stories simply describe proposed / desired approaches to solving problems in the future. In many ways, future stories are strategies.
Activity Schedule
Here's a schedule of suggested steps to help you complete the activity. Note that all are optional; however, we encourage you to participate in all the steps to maximize the learning benefit.
Monday
Sketch out your proposed project, including known and unknown activities and obstacles.
Wednesday
Prepare your story, referencing the two bulleted lists on the Module 4 Activity section to guide your content. Don’t be afraid to identify gaps in available skills, resources, data, knowledge that will need to be filled. This is a learning exercise - it’s okay if you don’t have all the answers!
Thursday
Submit and share your story.
"Climate Change Adaptation Fundamentals - Module 4" by Stewart Cohen, Climate Change Fundamentals , Adaptation Learning Network is licensed under CC BY 4.0 except where indicated. For external links to resources, review the rights and permission details.
|
oercommons
|
2025-03-18T00:38:20.841012
|
Physical Science
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/69323/overview",
"title": "Climate Change Adaptation Fundamentals",
"author": "Environmental Studies"
}
|
https://oercommons.org/courseware/lesson/113895/overview
|
Scientific computing with open-source software
Overview
This is the textbook of a graduate course given in 2024 at the University of Twente on "Scientific computing with
open-source software".
General
There are many great open-source software packages. These packages can be utilised by PhD students (and staff) for modelling, simulation, image processing, data analysis, etc. Open-source means their source code is available and fully modifiable. This makes them ideally suited for academic research as they can be adapted to solve new problems that are beyond the current state-of-the-art. However, since these tools often lack easy-to-use, point-and-click graphical user interfaces, knowledge of software development can aid in their use, and is essential for making modification and improvements.
This course will teach you the basics required to utilise open-source codes for various mechanical engineering applications. In the first week, we teach you the basics programming (in Python and C++), and show you how to write structured and reusable code. We then introduce tools for managing and maintaining software (git, cmake, etc), and discuss how code can be shared and developed together. In the second week, we discuss common methods used in scientific computing. We discuss use of the programming language, code structure, and how to build upon an existing code base. Finally, we show examples and explain how they can be used for your own research.
Lecturers
Thomas Weinhart (University of Twente)
Anthony Thornton (University of Twente)
Igor Ostanin (University of Twente)
Gertjan van Zwieten (Evalf Computing)
Benjamin Uekermann (University of Stuttgart)
Edwin van der Weide (University of Twente)
Andrew Hazel (University of Manchester)
Prerequisites
Participation in the course is facilitated by basic familiarity with programming and numerical methods. However, the course can be taken without any previous knowledge.
|
oercommons
|
2025-03-18T00:38:20.861600
|
Thomas Weinhart
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/113895/overview",
"title": "Scientific computing with open-source software",
"author": "Textbook"
}
|
https://oercommons.org/courseware/lesson/92431/overview
|
National Library of Medicine
PubMed Central
Social Anxiety Disorder
Overview
Mental health information surrounding social anxiety disorder.
Defining Social Anxiety Disorder & Its Prevelance
Social anxiety disorder (SAD) involves the fear or anxiety of social occures for which an individual may or may not be facing judgement from others in public. Being in these social situations consistently fear or anxiety in the person, and they feel they will be judged negatively. Because of this, these individuals often avoid social situations that may enhance their internal anxiety, which causes imparment in their social abilities or impedes their functionality in society. Research has shown between 5-10% of the world's population suffers from social anxiety disorder, with between 8.4-15% of the world will experience social anxiety at some point in their lifetime, showing that this disorder is not limited to a select few.
Stereotypes of Social Anxiety Disorder
1."Scared of Public Speaking"
False: Various social settings can trigger symptoms of social anxiety, and while public speaking is the most common setting, it is not the only. Other social anxiety triggers include attending social gatherings such as parties, dining in a restaurant, and even in more severe cases, answering the telephone. Social anxiety symptoms can happen anywhere and anytime.
2. "You're just shy"
False: Shyness and social anxiety do share common traits, they are not the same. Shyness is deemed as a personality trait that does not require therapy nor treatment. However, social anxiety disorder is a diagnosis that requires treatment to prevent any worsening. There is also a difference in symptom severity, such as people with social anxiety disorder have much worse symptoms. In addition, social anxiety disruptes their daily functioning in the world, while shyness does not.
3. "Trauma causes Social Anxiety"
False: While some people with social anxiety may have had a traumatic event that triggered their disorder, this is not always the case for every case. Sometimes, social anxiety disorder can be triggered by trivial things, or nothing at all. This is something that can be discussed with a professional therapist and can look through your history. However, it is not prevelant enough for this to be a general consensus.
Self-Coping with Social Anxiety Disorder
When feeling uncomfortable in social situations, there are some technique that can help lessen your anxiety:
1. Trying to Relax
Studies have shown taking slow, calming, breaths can calm your fight or flight response in these situations, especially since our bodies naturally begin breathing faster when anxious. By taking slow breaths through your nose, you may not eliminate anxiety, but it will make the social situations a bit more bearable.
2. Reshaping Thoughts
Often with social anxiety, those with the disorder suffering from negative thoughts about not only themselves, but about the social situation. Some thoughts such as "Everyone will stare at me" or "No one will like me" are examples of what this can sound like. However, with reshaping your thoughts, a person will realize that these thoughts are hypothesis of what they think they think will happen, and not based on facts. By training yourself not to heighten the situation, clarity will come to your thoughts, and anxiety might lessen.
Intervention & Treatment
While self-coping mechanism are temporarily helpful, medical and professional help is the best form a treatment in the long-term for social anxiety.
1. Medication
Medication has been used frequently by medical professionals to reduce social anxiety symptoms. Although there are multiple medications, the advice of medical professions are helpful in decided what is best for a patient. In addition, it is not adviced that medication be the only form of treatment. Multiple studies have found that the best form a treatment is a combination of medication and therapy.
2. Cognitive-Behavioral Therapy
CBT has been proven to help multiple disorders, general anxiety, and specified forms of anxiety such as social anxiety disorder. With a professional, strategies address the physical reaction, thoughts, and behaviors included in social situations. The physical reaction, according to researchers, with CBT will allow the body to calm itself and reduce the physical symptoms of SAD. In addition, a professional can help with reshaping your thoughts, by providing strategies to avoid such negative thoughts. Finally, by reshaping the behavior, will help with stopping the avoidance of social situations. CBT is a great mechanism that will address all forms of social anxiety disorder, to make life a bit more liveable.
|
oercommons
|
2025-03-18T00:38:20.885327
|
Reading
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/92431/overview",
"title": "Social Anxiety Disorder",
"author": "Social Work"
}
|
https://oercommons.org/courseware/lesson/92504/overview
|
CS Badge
CS Training Syllabus
Rubric for Discussion Board
Rubric for Discussion Board
Rubric for Discussion Board
Rubric for Lesson Plan
Integrating Computer Science
Overview
In this training, participants will be learning how to integrate computer science into their own classrooms. This scaffolded training will guide participants to eventually solve real-world problems and design their own lessons of integration.
Getting Started
This course is geared toward K-12 educators needing to learn how to incorporate CS into their classes. The modules offer a scaffolded approach that builds participants' ability in developing CS integration lessons. Explore Sections 2 and 3 before beginning learning modules. You will be able to evaluate the training at the end of the course. Any specific positives or negatives will help me improve the course for everyone!
My name is [insert name] and I will be your instructor for this course! Please contact me with any questions at my email: [insert email].
Class Information
You will find the syllabus attached below, please review it before starting the learning modules.
There are four learning modules:
- The Importance of Computer Science
- Computer Science Standards
- Examples of Integration
- Create Your Own Lesson
The assignment due dates are as follows:
Getting to Know Each Other and Module 1 - due at the end of Day 1
Module 2 - due at the end of Day 2
Module 3 - due at the end of Day 3
Module 4 - due at the end of Day 7
You will be required to complete a discussion board post and responses for Modules 1-3. You will be required to complete a lesson plan for Module 4.
Getting to Know Each Other
It is important to be familiar with each other since we are going to be having community discussions for each module. Module 4 will require a partner assignment as well.
To get to know each other a little better, make a post to the discussion board with information about yourself. Use the following prompts if you would like.
- Subject(s) you teach
- Years of experience
- Hobbies
- Anything you hoping to learn
The Importance of Computer Science
Essential Question: Why is Computer Science (CS) important for students to learn?
Step One: Explore the following websites:
Step Two: Develop a working definition for CS in your own words.
Step Three: Make a list of characteristics of CS. Use the given websites to help you, or find your own resources.
Step Four: Answer the question: Do you think CS is important to teach in school? Why or why not? Use a reference to support your answer.
Step Five: Post your responses from steps two through four to the discussion board.
Step Six: Read your classmates' responses and use their definitions and characteristics for CS to adjust your own.
Step Seven: Edit your original post and write "EDIT:" followed by your edited definition for CS.
Computer Science Standards
Essential Question: What are the reoccurring standards that students see each year?
Step One: Locate your local Computer Science (CS) standards.
Step Two: Find any reoccurring standards.
Step Three: Post on the discussion board by completing one of the following prompts:
List any reoccurring CS standard in your own words. Reflect on the various standards and explain why you think they are reoccurring.
OR
Reflect on past lessons. Are there any reoccurring standards that fit well with your current subject? Are there any standards that you already incorporate in some way? How?
Step Four: Respond to a classmate using the following prompts:
- Note any differing standards
- Should any concepts be added?
- Do you have any other ideas for how they could integrate those reoccurring standards or ways they can improve their idea?
Examples of Integration
Essential Questions: How can CS be incorporated best in a given subject? Which OERs would fit best with your curriculum?
Step One: Watch the following video: CS integration in ELA
Step Two: Explore the websites and Open Educational Resources (OERs) based on your chosen subject:
ELA
- Code.org ELA Game CS and Poetry
- Character Study Coding
- Punctuation Practice Robotics
- 3 Ways to Integrate
- 5 Ways to Integrate
Math
- Fractions Robotics Lesson
- Coordinate Plan Robotics Lesson
- Data Visualization
- 3 Ways to Integrate
- 5 Ways to Integrate
- CS Integration in Math
Science
- Robotics Integration Physical Science
- Mars Rover Robotics Lesson
- Inherited Traits Robotics Lesson
- Ecosystems Coding
- Life Cycles Coding
- 3 Ways to Integrate
- 5 Ways to Integrate
Social Studies
PE
Gifted
Step Three: Describe an example, from the resources provided or your own, of a lesson that would be useful in your classroom. Are there any other ways you can expand the lesson to cover more CS standards or make them more applicable for your class and grade level?
Step Four: Locate and describe a website, program, or video that would be useful for integrating CS into the subject you teach.
Step Five: Combine steps 3-4 into a discussion post using paragraph, poster, or infographic form.
Step Six: Respond to two classmates about their ideas and the resources they provided.
Create Your Own Lesson
Essential Question: How would an effective computer science integration lesson plan look for a singular subject?
Step One: Post the following information about yourself on the discussion board:
- The subject(s) you teach
- The grade level you teach
- The technology you have available in your classroom or school (ex: Ipads, 1:1 laptops, robots, computer lab)
Step Two: Find your partner(s) from the list provided by the instructor.
Step Three: Create a lesson for your partner using any preferable template. This lesson should integrate CS in their classroom using the available technology and resources. The lesson should involve their current subject and CS.
Step Four: Share the lesson by replying to your partner on the discussion board.
Step Five: Explore the discussion board for any lessons that you may find useful.
*Be sure to add any prep work needed for the lesson to be successful.
Course Evaluation
Please offer any specific feedback you have by going to the following link:
Don't forget to download your badge for completing this training!
|
oercommons
|
2025-03-18T00:38:20.924281
|
Mathematics
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/92504/overview",
"title": "Integrating Computer Science",
"author": "Life Science"
}
|
https://oercommons.org/courseware/lesson/74099/overview
|
HS+ English and Life Science (2020)
Overview
This theme-based English course integrates reading, writing, listening, speaking, and critical thinking skills around assignments and activities focusing on life science. This competency-based class allows students to work at their own pace, exit at a level appropriate to demonstrated skills and knowledge, and earn high school credits in English, Lab Science, Science and/or electives.
About this course
This theme-based English course integrates reading, writing, listening, speaking, and critical thinking skills around assignments and activities focusing on life science.
Topics include:
- Life Science And Ways Of Knowing
- The Smallest Units Of Matter And How They Connect
- Cells, The Building Blocks Of Living Matter
- Genetic Makeup: The Code For Living Matter And Replication
- Communities Of Life And Their Interdependence
This competency-based class allows students to work at their own pace, exit at a level appropriate to demonstrated skills and knowledge, and earn high school credits in English, Lab Science, Science and/or electives.
Culturally Responsive Approach
This course was intentionally developed to align with the Washington State Board for Community and Technical College’s vision, mission, values and strategic plan. The Culturally Responsive Scorecard, developed by NYU Steinhardt, was a guiding document in the development of this course. Sincere efforts were made to develop a culturally responsive curriculum that is inclusive of all students, with particular emphasis on highlighting the histories, experiences, and strengths of historically underserved populations. Faculty planning to teach this course should review modules thoroughly prior to presenting material to students. The HS+ Instructor Resource Guide provides resources and strategies that may be a useful starting place for faculty to address gaps in knowledge and confidence.
Course Outcomes
- Identify, define, and describe terms and concepts related to Ways of Knowing, Chemistry of Life, Cells, Genes, and Ecology.
- Identify tools to use in academic reading and reflecting on readings
- Know types and methods for data collection
- Explain differences and similarities between experimental testing and observational research.
- Conduct and record research.
- Identify the methods of scientific presentation
- Describe the economics of environmental exploitation.
- Identify Indigenous and Western Methodologies of scientific research
- Use a rubric for self and peer evaluation
- Demonstrate research and organizational skills
- Understand the value of science communicators.
College and Career Readiness Standards
Throughout the course students demonstrate the following:
Reading
- Reading anchor standard 4: Interpret words and phrases as they are used in a text, including determining technical, connotative, and figurative meanings, and analyze how specific word choices shape meaning or tone.
- Reading anchor standard 5: Analyze the structure of texts, including how specific sentences, paragraphs, and larger portions of the text (e.g., a section, chapter, scene, or stanza) relate to each other and the whole.
- Reading anchor standard 10: Read and comprehend complex literary and informational texts independently and proficiently.
Writing
- Writing anchor standard 5: Develop and strengthen writing as needed by planning, revising, editing, rewriting, or trying a new approach.
- Writing anchor standard 6: Use technology, including the Internet, to produce and publish writing and to interact and collaborate with others.
- Writing anchor standard 7: Conduct short as well as more sustained research projects based on focused questions, demonstrating understanding of the subject under investigation.
- Speaking and Listening
- Speaking and Listening anchor standard 5: Make strategic use of digital media and visual displays of data to express information and enhance understanding of presentations.
|
oercommons
|
2025-03-18T00:38:20.940538
|
SBCTC Admin
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/74099/overview",
"title": "HS+ English and Life Science (2020)",
"author": "Full Course"
}
|
https://oercommons.org/courseware/lesson/118326/overview
|
Videos on Parabolas
Overview
Explore Parabolas in this free video unit as a part of Project MathTalk. It is comprised of 10 lessons with 5-7 short videos in each lesson. Featuring the reasoning of Grade 10 students, the unit explores how to make sense of the geometric definition of a parabola. The videos provide a foundation for the Common Core State Standard: “Derive the equation of a parabola given a focus and directrix.” Showing these videos are great for classrooms that want to make connections between Geometry and Algebra.
|
oercommons
|
2025-03-18T00:38:20.953528
|
07/24/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/118326/overview",
"title": "Videos on Parabolas",
"author": "Joanne Lobato"
}
|
https://oercommons.org/courseware/lesson/79244/overview
|
Readings
Overview
In this chapter we will explore two skills most of us think we’ve already mastered, or at least can do well enough to get by: reading and notetaking. The goal is to make sure you’ve honed these skills well enough to lead you to success in college.
Introduction
“The mark of a successful college student is the mastery of knowing not only what to study but also how to study it.” – Patricia I. Mulcahy-Ernt & David C. Caverly
Figure 7.1. Each of us reads and records information in our own way.
(Credits: CollegeDegrees360 / Flickr / CC BY-SA 2.0)
Student Survey
Think about how you read – your habits or techniques, how academic, informational, and leisure reading differ, and what has and hasn’t worked well in the past. With that in mind, consider the questions below. They will help you determine how this chapter’s content relates to how you tackle academic reading.
On a scale of 1 (I need significant improvement) to 4 (I’m doing great), reflect on how you’re doing right now on these statements:
- I am reading on a college level.
- I take good notes that help me study for exams.
- I understand how to manage all the reading I need to do for college.
- I recognize the need for different notetaking strategies for different college subjects.
As we are introduced to new concepts and practices, it can be enlightening to reflect on how our understanding changes over time. We’ll revisit these questions at the end of the chapter to see if your perspective changes as we move forward.
Learning Objectives
In this chapter we will explore two skills most of us think we’ve already mastered, or at least can do well enough to get by: reading and notetaking. The goal is to make sure you’ve honed these skills well enough to lead you to success in college. By the end of this chapter, you should be able to do the following:
- Discuss the way reading in college differs from your prior reading experiences.
- Identify how to adapt to the shift from surface reading to in-depth academic reading.
- Demonstrate the usefulness of strong notetaking for your college courses.
Being a savvy information consumer is increasingly important because of the amount of information we encounter. Not only do we need to critically evaluate that information, but also with a lens that separates fact from opinion, builds upon prior knowledge, and identifies credible sources. Reading and other literacies help us make sense of the world - from simple reminders to pick up milk to complex treatises on global concerns, we read to comprehend, and in so doing, our brains expand and we are better equipped to participate in scholarly conversations.
In college, as we deliberately work to become stronger readers and better note takers, we are working toward ensuring success in our courses and increasing our chances to be successful in the future. Seems like a win-win, doesn’t it? But why? Well, reading improves our vocabulary, critical thinking, ability to make connections between dissimilar parts, and verbal fluency (Cunningham and Stanovich).
Research continues to support the premise that one of the most significant learning skills necessary for success in any field is reading. If reading “isn’t your thing” or it’s an area you’ve always struggled in, make that your challenge. Take advantage of the study aids you have available, including human, electronic, and physical resources, to increase your fluency and performance. Your academic journey, personal information seeking, and professional endeavors will all benefit. I challenge you to find a way to make it your new “thing”.
Attributions
Content on this page is a derivative of “Reading and Notetaking: Introduction” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
References
Cunningham, A.E. & Stanovich, K.E. (Spring/Summer 1998). What Reading Does for the Mind. American Educator, 22(1/2), 5.
Mulcahy-Ernt, P.I. & Caverly, D.C. (2009). Strategic Study-Reading in Handbook of College Reading and Study Strategy Research, 177.
Types of Reading
If you don’t particularly enjoy reading, don’t despair. People read for a variety of reasons – leisure, information, academic, professional, etc. You may just have to step back and reflect on your reading habits, likes, dislikes, and struggles to find ways to overcome your personal obstacles. Consider adjusting your schedule to allow for more reading time, especially in college. Perhaps change how, when, or where you read, explore using an immersive reader app, or combine text with audio books. Every class will expect you to read more than you probably have in the past. Be prepared.
We read small items for immediate information, such as notes, billboards, text messages, or directional signs. Online there’s a plethora of quick (and not-so-quick) information about fixing a faucet, sewing a button, or tying a knot. Each encounter is designed to meet a specific goal. They may not be stunning works of art, but they don’t need to be. When we consider why we read or watch more complex items, we can usually categorize it into two categories: 1) reading to introduce new content and 2) reading to understand familiar content with greater depth.
Reading to Introduce New Content
Imagine your roommate is majoring in a topic you are completely unfamiliar with. You want your semester together to go well but know little about one another. Talking about each other's classes might help. So, you decide to do a little Googling. You don’t need to go in-depth into their area of study – you just need to scratch the surface.
Chances are, you have done this sort of exploratory reading before. You may have read reviews of a new restaurant or looked at what people said about a movie or video game before deciding to spend the money. This reading helped you decide. In academic settings, much of what you read in your courses may be relatively new content to you. Or your prior knowledge was fairly general and your coursework leads you to dig deeper through reading. You may find you need to schedule more time for reading and digesting the information.
Consider This… Imagining that you were given a chapter to read in your American history class about the Gettysburg Address, write down what you already know about this historic document. How might thinking through this prior knowledge help you better understand the text? |
Reading to Better Understand Familiar Content
Reading about unfamiliar content is one thing, but what if you already know something about the topic? Do you still need to keep reading about it? Probably.
With familiar content, you can do some initial skimming of the text to determine what you already know, and mark what may be new information or a different perspective. You may not have to give your full attention to what you already know, but you will probably spend more time on the new nuggets of information so you can mesh it with what you already know. Is this writer claiming a radical new definition for the topic or an entirely opposite way to consider the subject matter? Are they connecting it to other topics or disciplines in ways you may have not considered?
Figure 7.2. A bookstore or library can be a great place to explore. Aside from resources listed on your course syllabi, you may find something that interests you or helps with your course work.
When we encounter material in a discipline-specific context and have some familiarity with the topic, we sometimes allow ourselves to become overconfident in our knowledge. Reading an article or two or watching a documentary on a subject does not make someone an expert or scholar on the topic. A scholar thoroughly studies a subject, usually for years, and works to understand all the possible perspectives, potential misunderstandings, and personal biases about the topic. Our goal is for you to one day be an expert or scholar in your field.
Attributions
Content on this page is a derivative of “Reading and Notetaking: The Nature and Types of Reading” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
Time for Reading
Reading textbooks, scholarly articles, or other in-depth material for class can seem daunting, so a strategic approach is certainly recommended. How much time should you allot to the task? What reading strategy should you use?
Early in the semester, pull out your class syllabi and determine the reading requirements and expectations for each class. You will also need to understand your instructors’ expectations about students’ depth of reading. Do you need to read for detail, skim texts to become familiar with the topic, or a mixture of these approaches? Will you need to read prior to the lecture, after lecture, or both? Knowing this will help you decide how to schedule your time, how to tackle the reading assignments, and how to structure your notes.
Still not convinced this how you really want to spend your time while in college? It will pay off in the end. Are you apprehensive because you struggle with reading? Remember that reading is just one way of getting information and with today’s technology you can supplement text with audio, video, immersive reader, and translator apps. Find the tools that work for you.
So, how do you carve out the time? A couple approaches include determining your usual reading pace, scheduling active reading sessions, and practicing recursive reading.
Determining Your Reading Pace. Select a section of text in a textbook or novel. Beginning at the top of a page, mark your starting point and time yourself reading that material for 5 minutes. Note how many pages you read. Multiply the number of pages by 12. This will determine your hourly average reading pace. Of course, your pace can be influenced by many factors – dense material, internal and external distractions, lack of interest or dull content, etc. - but it gives you a good estimate.
For illustration purposes, if you were able to read 3 pages in 5 minutes, you should be able to read about 36 similarly formatted pages in one hour. Knowing this, you can determine how much time you need to finish an assigned text (chapter, book, article, etc.). If the novel you’re reading for English class is 350 pages, take the total page count (350) and divide by your hourly reading rate (36 pages per hour). It should take 9 to 10 hours to finish. Now you can schedule time to read for about 45 minutes a day for two weeks and you’ll be done with the novel.
Reader | Pages Read in 5 Minutes | Pages per Hour | Approximate Hours to Read 350 Pages |
Angel | 2 | 24 | 14 hrs, 35 mins |
You | 3 | 36 | 9 hrs, 43 mins |
River | 4 | 48 | 7 hrs, 20 mins |
Jordan | 5 | 60 | 5 hrs, 50 mins |
Scheduling Time for Active Reading. When you set your reading pace, you were reading straight through – not stopping to re-read, look up definitions, or take notes. These are components of active reading, which takes about twice as long as reading through text without stopping. Learning to actively read is an important practice as you work to grasp new or complex concepts. Therefore, we need to schedule time for this type of reading, as well.
Consider the reading expectations for each class – depth of reading, complexity of content, number or type of items, etc. Calculate your reading pace for each classes’ reading requirements. The amount of time calculated for active reading may look unachievable – that is why scheduling is so important. Once you spread the task out over time, it is much more achievable.
Example Reading Times for Novel and Active Reading | |||||
Reader | Pages Read in 5 Minutes | Pages per Hour | Approximate Hours to Read 350 Pages | Actively Read Pages per Hour | Approximate Hours to Actively Read 350 Pages |
Angel | 2 | 24 | 14 hrs, 35 mins | 12 | 29 hrs, 10 mins |
You | 3 | 36 | 9 hrs, 43 mins | 18 | 19 hrs, 24 mins |
River | 4 | 48 | 7 hrs, 20 mins | 24 | 14 hrs, 35 mins |
Jordan | 5 | 60 | 5 hrs, 50 mins | 30 | 11 hrs, 40 mins |
Attributions
Content on this page is a derivative of “Reading and Notetaking: Effective Reading Strategies” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
Tackling the Text
If you Google ideas or talk to tutors, they may mention the acronym for their favorite active reading strategy - SQ3R, P2R, ISR, and PARR are just a few. Don’t let that intimidate you; the strategies all boil down to one overarching concept – methods for reading to learn and remember. Let’s get started.
Preview. Start by previewing or prereading the textbook, chapter, or article you’ve been assigned. You’ll want to take note of how long the text is, the headings or sections and overall organization, any images or graphics and their subtext, and the comprehension or review questions at the end, if there are any. Next, look for an introduction at the beginning of the text and a summary or conclusion at the end. These will provide the most condensed version of the text’s content and key points. Each of these prereading components will help prime your mind for the next steps.
Actively Read. Now comes the bulk of the work - actively reading the text by breaking it into chunks, section by section or paragraph by paragraph, and taking notes as you go. Writing your notes in a question-and-answer format may help structure them for easier re-reading later. For instance, rephrase section headings as question statements. What is the author is trying to tell you? Then write your notes as answers to those questions. Apply the tip you learned in grade school: pay attention to the bolded items; they are bold for a reason. If you run across terminology you don’t know, look it up and write the definition using words that make sense to you. Revisit the images and graphics. Make note of their surroundings and how the author uses them to illustrate a point.
If you run across something that really doesn’t make sense, no matter how many times you reread it, mark the page with a post-it-note so you can follow up on it later. But don’t forget about it. Ask a classmate or tutor, do some additional research, or ask your professor.
Did you notice we didn’t mention highlighting? We’re all guilty of highlighting for the sake of highlighting. Do you really remember what you highlight? Probably not. Do you highlight because it keeps you focused on the text? Instead, consider using your finger, the end of your pen, or a reading guide to track the text as you read. If highlighting really is your go-to-technique, as soon as you highlight something go to your notes and write down what you felt was important.
Now that you’ve make it through the text, go back and reread the summary or conclusion. It should make more sense now and will help draw connections between your prior and new knowledge.
Take a break. Research shows that spreading learning out over time helps your brain form stronger connections to the material, enabling better recall and application of the new knowledge later and for longer. This is one reason instructors recommend against cramming for tests. That said, now is a good time to walk away from the text for a day or two, shifting gears to read for a different class or work on other assignments.
Revisit and review. After a couple days, return to your notes and the text. Review your notes, comparing them to your lecture notes and any other new knowledge you’ve gained since reading the text. If needed, add to your notes to help provide clarity. The final step is to write a summary, using your own words, that combines your notes from the text and your notes from lecture, answering questions you had asked of the author when you initially started the reading.
Well before your or my time, Aristotle said, “exercise in repeatedly recalling a thing strengthens the memory.” That’s really our goal in learning, right? To make the learned material stick for the long term. Some of your courses will need you to continually build on your prior learning throughout the semester – and potentially throughout your college career. Set time in your schedule for regular, incremental review of your notes. Over time you should be able to read just the headings in your notes and know the associated details, retrieving them from memory.
"How to Read a Textbook – Study Tips – Improve Reading Skills", by Kimberly Hatch Harrison, Socratica, located at https://youtu.be/l0vfLGHoREU
Attributions
Content on this page is a derivative of “Reading and Notetaking: Effective Reading Strategies” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
Reading in College
Different disciplines or subjects in college may have different expectations, but you can depend on all subjects asking you to read to some degree. You can succeed in meeting college reading requirements by learning to read actively, researching the topic and author, and recognizing how your own preconceived notions or biases affect your reading. As we’ve mentioned in a previous section, reading for college isn’t the same as reading for pleasure or personal interest.
Your instructor may ask you to read articles, chapters, books, primary or secondary sources, technical information, and more. They may want you to have a general background on a topic before you dive into a discussion in class, to enrich discussions you’ve already had in small or large groups, or in preparation for an assignment. Part of the challenge is to review each course’s syllabus and pay attention to your instructors’ expectations to appropriately plan your reading time.
Consider This… Can you think of a time when you’ve struggled reading college content for a class? Which of the strategies we’ve covered might have helped you with the reading and, subsequently, understanding and retention of the content? Why do you think those strategies would work? |
Reading Primary and Secondary Sources. Primary sources are original documents such as letters, speeches, photographs, legal documents, and a variety of other texts and artifacts. When scholars look at these to understand a historical event or scientific challenge and then write about their findings, the scholar’s article is considered a secondary source.
Primary sources may contain dated material that we now believe to be inaccurate. It may contain the personal beliefs and biases the original writer didn’t intent to openly publish, and it may even present fanciful or creative ideas that do not support current knowledge. Think of your own personal account of an event you witnessed. Your perspective will influence which details you include, including first impressions, unintentional biases, and misperceptions. Even a when a photographer is capturing an event, what is and isn’t included in the frame, their vantage point and image composition, tells a story about the photographer’s perspective, bias, or intent.
Likewise, secondary sources are inevitably another person’s interpretation of the primary source. Readers should remain aware of potential biases the secondary source writer inserts in the writing that may influence the reader. Most scholars work hard to avoid bias in their writing; you as a reader are trusting the writer to present a balanced perspective but must read critically. When possible, read the primary source in conjunction with the secondary source. Seek alternate secondary sources, compare their perspectives, and try to draw your own conclusions.
Reading Scholarly Articles. Many scholars of a subject, including your instructors, publish their research in academic or trade journals. Academic, or scholarly, articles report on recent discoveries or original research, theoretical discussions, or the critical review of other published works or other scholars’ research. Often they are peer-reviewed, or referred, by other subject scholars before they are published to ensure the content is supported by research, logical arguments, and solid writing. As a rising scholar, you will conduct your own research in many of your classes and your instructors will likely recommend using academic journal articles as part of your research.
Trade journals are like academic journals except that they are written by and for professionals and practitioners in the field and cover industry or trade news, research, trends, legal updates, and other topics of interest to practitioners. Some trade journal articles are peer-reviewed prior to publishing and most can carry as much trustworthiness as a scholarly, peer-reviewed article. Example industries that rely heavily on trade journals are education, nursing, criminal justice and public safety, specific business sectors, construction sciences, and hospitality.
Reading Graphics. Authors include graphics in their text for a variety of reasons. In a mathematics textbook, many of the graphics are formulas, illustrations, and sample problems. In the sciences, graphics may be diagrams, processes, charts, or data from experiments. In social sciences, charts may be combined with images, maps, and other graphics to illustrate a concept. Often the graphic has a caption and is referenced in the surrounding paragraphs.
In each instance, inclusion of the visual element was intentional. Resist the urge to skim past these – it may be one of the key items that stands out in your memory later. As you review the image, question why the author included it in the text. What message does it reinforce or clarify? What stands out in the graphic?
We’ll use the map of the Napoleon’s Battle of the Waterloo Campaign to illustrate the thought process you could follow when “reading” the visuals in your text. Ask yourself these questions:
- What is the main point of this map/graphic/image/etc.?
- Who is the intended audience?
- Is it tied to a person (who), event or thing (what), period (when), or location (where)?
- What does the legend (explanation of symbols) include – or not include?
- What other information do I need to make sense of this graphic?
Figure 7.3. Graphics, charts, graphs, and other visual items often convey important information and may appear on exams or other situations where you’ll need to demonstrate knowledge. (Credit: Wikipedia Commons / Attribution CC0 – Public Domain)
Reflection Question... Can you think of times you have struggled reading for a class? What technique did you use? Is there something from what you’ve read so far in this chapter that might have helped you understand the content? Why do you think those strategies would work? |
Attributions
Content on this page is a derivative of “Reading and Notetaking: Effective Reading Strategies” and “Reading and Notetaking: Taking Notes” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
Notetaking
Notes help you organize ideas and make meaning of information from readings, class lectures, and other information sources. Taking notes helps you stay focused on the topic and task (lecture, reading, etc.). Strong notes will build on your prior knowledge, help you discuss trends or patterns in the information, direct you toward areas where you may need to research further, and is a vital component in active reading, which we mentioned in a previous section.
Think of your notes as potential study guides. In the Tackling the Text section we talked about revisiting your notes regularly – this remains true for long term, sustained retention of all new information. Even if you have a photographic memory, notes are not a one-and-done deal – we need to reread, revise, rest, and revisit regularly.
Research on this topic concludes that without active engagement after taking notes, most students forget 60–75% of the material within two days. This is called the Ebbinghaus Forgetting Curve, named after 19th-century German psychologist Hermann Ebbinghaus, and with practice you can avoid the Curve by reinforcing what you learned with regular review intervals starting shortly after you’ve taken notes (Fuchs, 1997).
Consider This… Do you currently have a preferred way to take notes? When did you start using it? Has it been effective? What other strategy might work for you? |
Preparing to Take Notes
Why do we take notes? What are your priorities? Special techniques or habits? Are you looking for new, more effective ways to take notes? The notetaking process is personal and unique to you – just like one person’s method of organizing is different than another’s. The trick is figuring out what works best for you.
The best notes are ones you take in a methodical manner that makes frequent revision and review easy as you progress through a topic or class. Remember in grade school when the supply list included 3-ring binders and dividers? It was the teachers’ way of teaching us to be organized. For some students it worked - but not for all. Perhaps over the years you’ve discovered graph-paper composition books or a notetaking app works better for you. Maybe you’re still trying to figure it out. That’s okay – just keep trying.
Figure 7.4. The best notes are the ones you take in an organized manner. Frequent review and further annotation are important to build a deep and useful understanding of the material. (Credit: English106 / Flickr / Attribution 2.0 Generic (CC-BY 2.0))
There is relatively new research on whether handwritten or typed notes are more effective for retention of material. Mueller and Oppenheimer (2014) agree that handwriting notes and using a computer for notetaking have pros and cons, and most researchers agree that the format is less important than what students do with the notes.
Attributions
Content on this page is a derivative of “Reading and Notetaking: Taking Notes” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
References
Fuchs, A. H. (1997). Ebbinghaus’s contributions to psychology after 1885. American Journal of Psychology, 110(4), 621–634.
Mueller, P. A., & Oppenheimer, D. M. (2014). The Pen Is Mightier Than the Keyboard: Advantages of Longhand Over Laptop Note Taking. Psychological Science, 25(6), 1159–1168.
Notetaking Systems
Whichever notetaking system you choose – computer-based, pen & paper, sketched, note cards, text annotations, and so on - the best one is the one that you will use consistently and accomplishes its goal. The art of notetaking is not automatic for anyone; it takes practice. Unless your instructor expects a specific notetaking style in their class, you are free to use techniques from of different systems to match your style.
Just keep yourself – and your notes – organized. At the very least, start notes with an identifier, including the date, course name, topic, and any other information you think will help you when you revisit the notes later. Consider leaving some blank space in your notes so you can add new ideas, questions, or clarifications to the original notes as your knowledge on the topic expands through additional readings, lectures, and explorations.
You may have a notetaking style you have used for all your classes. When you were in high school, this one-size-fits-all approach may have worked. Now that you’re in college, reading and studying more advanced topics, your old method may still work but you should have some different strategies in place if you find that your previous method isn’t working. Sometimes different subjects need different notetaking strategies.
Cornell Method. One of the most recognizable notetaking systems is the Cornell Method, a method devised by Cornell University education professor Dr. Walter Pauk in the 1940s. In this system, you take a sheet of notebook paper and draw lines to divide the paper into four sections: a two inch horizontal section at the top of the page, two inch section at the bottom of the page, and a vertical line in the center section two inches from the left edge, leaving the biggest area to the right of the vertical line. In the top section include information that provides context for the notes – topic, class, date, the overarching question the notes will answer, etc.
Figure 7.5. The Cornell Method provides a structured, organized approach that can be customized.
Use the largest section (middle-right of the page) to record the main points of the lecture or reading, preferably in your own words. Abbreviate or use symbols if they make sense to you and use bullet points or phrases instead of complete sentences. After the note-taking session, set the notes aside for a few hours. Then pull out your notes and re-read what you wrote, fill in any details you missed or need to clarify. Then in the narrow section in the center of the page, write key ideas from the adjacent column. In the left column add one- or two-word key ideas or clues that will help you recall the information later.
Once you are satisfied with the middle sections, summarize this page of notes in two or three sentences in the section at the bottom of the sheet. Before you move onto something else, cover the large notes column, and quiz yourself over the key ideas. Repeat this step often to reinforce your ability to make the connections between lectures, readings, and assignments.
Watch this video from the Learning Strategies Center at Cornell for ideas on how to adapt Cornell Notes to different classes or note-taking purposes.
"How to Use Cornell Notes", by Learning Strategies Center at Cornell University,
located at https://youtu.be/nX-xshA_0m8
Outlining. You can take notes in a formal outline if you prefer, using traditional outline numbering (Roman numerals, indented capital letters, and Arabic numerals) or a multi-level bulleted list. In both, each indent indicates the transition from a higher-level topic to the related concepts and then to the supporting information. Some people only need keywords to spark their memory, but others will need phrases or complete sentences, especially if the material is complex. The main benefit of an outline is how organized it is - but can be tricky if the lecture or presentation is moving quickly or covering many diverse topics - though it may work well when actively reading.
The following outline excerpt illustrates the basic idea:
- Dogs (main topic–usually general)
- German Shepherd (concept related to main topic)
- Protection (supporting info about the concept)
- Assertive
- Loyal
- Weimaraner (concept related to main topic)
- Family-friendly (supporting info about the concept)
- Active
- Healthy
- German Shepherd (concept related to main topic)
- Cats (main topic)
- Siamese
Chart or Table. Having difficulty comparing or contrasting main ideas? A chart might help. Divide your paper into columns with headings that include topics or categories you’ll need to remember. Then write notes in the appropriate columns as that information comes to light in the presentation or the reading. This instantly provides an organized set of notes to review later.
Example of a Chart to Organize Ideas and Categories | ||||
Structure | Types | Functions in Body | Additional Notes | |
Carbohydrates | ||||
Lipids | ||||
Proteins | ||||
Nucleic Acid |
Concept Mapping and Visual Notetaking. A visual notetaking method is called mapping, mind mapping, or concept mapping, although each of these names can have slightly different uses. Many variations can be found online, but the basic principles are that you are making connections between main ideas through a graphic representation. Some can get elaborate with colors and shapes, but simple is certainly okay – remember, match your style and personal preference. No matter how much artistic flair is in the map, the general concept is for main ideas to be front-and-center with supporting concepts branching out.
Figure 7.6. Mind mapping can be an effective, personal approach to organizing information. (Credits: Safety Professionals Chennai, Elementofblank, & http://mindmapping.bg / Wikimedia Commons / CC BY-SA).
Feeling exceptionally artistic? Consider drawing representations of concepts instead of using only text or adding color for emphasis. According to educator Sherrill Knezel in her article “The Power of Visual Notetaking,” this strategy is effective because “when students use images and text in notetaking, it gives them two different ways to pull up the information, doubling their chances of recall.” Not artistic? Don’t worry; the images don’t need to be perfect, just lodged in your memory.
"Drawing in Class", by Rachel Smith at TEDxUFM,
located at https://youtu.be/3tJPeumHNLY
Not sure which method to use? Play with different types of notetaking techniques and find the method – or methods – you like best. Once you find what works for you, stick with it. You will become more efficient the more you use it, and your notetaking, review, and recall will become, if not easier, certainly more organized, and memorable.
Attributions
Content on this page is a derivative of “Reading and Notetaking: Taking Notes” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
References
Knezel, S. (2016, December 28). The Power of Visual Notetaking. Education Week. https://www.edweek.org/education/opinion-the-power-of-visual-notetaking/2016/12
Annotating Your Notes
Annotating notes - adding additional details, new insights, or clarifications - after the initial notetaking session will up your study skills game by reinforcing the material in your mind and strengthening your memory. Annotations can refer to anything you do with a text to enhance it for your particular use. The annotations can include highlighting vocabulary terms, writing in definitions for unfamiliar terms, adding questions in the margin, underlining or circling key concepts, drawing images to catch your attention, or otherwise marking a text for future reference.
Highlighting is one form of annotation. However, the only reason to highlight is to draw attention to small bits so you can easily pick out that ever-so-important information later. A common mistake we have all made is not knowing when to stop and ending up with a page full of yellow (or whatever color(s) you prefer). If what you need to recall from the passage is a particularly fitting definition of a vocabulary term or concept, highlighting the entire paragraph is less effective than highlighting just the actual term. Your mantra for highlighting text should be less is more. Always read the text first, then go back and highlight what you feel needs special emphasis.
Another way to annotate is to underline significant words or passages. Sure, it is not quite as much fun as colorful cousin highlighting, underlining provides precision to your emphasis. Need extra emphasis? Underline twice or draw a box around the information or use different colors. I personally like to draw stars and arrows to draw my eye to text or images I need to remember, research further, or revisit again later.
Realistically, you may end up doing each of these annotation styles in the same text at different times. Repeated review is critical to learning, so plan to come back to the same text multiple times, adding annotations each time as your understanding evolves. With experience in reading discipline-specific texts, writing papers, or taking tests, you will know better what to include in your annotations.
Figure 7.7. Annotations may include highlighting important concepts, defining terms, writing questions, underlining or circling key terms, or otherwise marking a text for future reference.
What you have to remember while you are annotating, especially if you are going to annotate multiple types, is to not overdo whatever method(s) you use. Be neat about it - its organization needs to make sense when you revisit the material later.
Attributions
Content on this page is a derivative of “Reading and Notetaking: Taking Notes” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
Developing Your Strategy
Marlon was totally organized and ready to take notes in a designated course notebook at the beginning of every philosophy class session. He always dated his page and wrote in the discussion topic. He had various colored highlighters ready to code the different purposes he had defined: vocabulary in pink, confusing concepts in green, and yellow for sections that would need additional explanations. He also used his own shorthand and a variety of symbols for questions (question mark), probable test items (eyes), additional reading suggestions (star), and questions he would ask his instructor before the next class. Doing everything so precisely, Marlon’s methods seemed like a perfect example of how to take notes for success. Inevitably though, by the end of the hour-and-a-half class, Marlon was frantically switching between writing tools unable to maintain the same pace as the instructor. What went wrong?
He had a solid plan and was clearly organized and had a plan. But what he was trying to accomplish might have been more successful over time during his reread, review, and revise (or annotate) study sessions. Marlon was suffering from trying to do too much all at once. It’s an honest mistake, but it added to his stress level.
Notetaking in class is just the beginning. Your instructor likely gave you an assignment to read or complete before class so you are prepared for the material that will be presented during class. In class you may be occupied by more than passively sitting-and-getting. It is reasonable to anticipate group discussions, working with classmates, or performing some other activity that would take you away from note taking. Does that mean you should ignore taking notes for that day? Most likely not. You may need to summarize the activities from class, make note of points that stand out in your memory, or any questions that come to mind after the activities.
Return to Your Notes. Later go back to your notes and add in missing parts. It is best to do this within the first 24-hours after class, if not on the same day. Just as you may generate questions as you read new material, you may leave class with new questions. Write those down in your notes for that class and make it a point to ask the instructor, read more on the topic, do a little research, or combination of all of these.
Just as we calculated the amount of time you will need to read the various texts assigned in your classes then setting a schedule, it is just as important to intentionally schedule time to revisit your notes - notes from lectures as well as readings. Write it in your planner, set a reminder on your phone, include it in your plan for the day or week - whatever works best for you.
Your notes should enhance how you understand the lessons, readings, lab sessions, and assignments, helping you prepare for not only the next test but for a growing understanding of the subject. The cycle of reading, notetaking in class, reviewing and enhancing your notes, and preparing for tests is part of a continuum you will ideally carry into your professional life.
Try not to take short cuts; recognize each step in the cycle as a building block. Learning doesn’t end, which shouldn’t fill you with dread; it should help you recognize that all this work you’re doing in the classroom and during your study and review sessions is ongoing and cumulative. Practicing effective strategies now will help you be a stronger professional.
Attributions
Content on this page is a derivative of “Reading and Notetaking: Taking Notes” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
Chapter Summary
Reading and notetaking are major components of successful studying and learning. In college the expectation is that you will likely consume considerable amounts of information in each subject through readings, research, lectures, conversation, and more. You may encounter reading situations, such as journal articles and long or technical textbook chapters, that are more difficult to understand than texts you have read previously. As you progress through your college courses, use reading strategies to help you complete the reading assignments and retain the information. Likewise, you will need to take notes that are complete and comprehensive, yet organized, to help you study and recall the information. Learn to be deliberate in your reading and notetaking.
Remember the questions we asked at the beginning of this chapter? It is time to revisit them. As you answer them, consider what we’ve discussed in this chapter and reflect on your progress as a reader and notetaker. As a reminder, answer on a scale of 1 (weak) to 4 (strong).
- I am reading on a college level.
- I take good notes that help me study for exams.
- I understand how to manage all the reading I need to do for college.
- I recognize the need for different notetaking strategies for different college subjects.
Compare your scores to those you recorded at the beginning of the chapter. What has changed? Are there strategies or practices you have been trying as you’ve read through this text or one that you plan on trying this semester? Develop a plan and put it into action.
Attributions
Content on this page is a derivative of “Reading and Notetaking: Summary” and “Reading and Notetaking: Rethinking” by Amy Baldwin, published by OpenStax, and is licensed CC BY 4.0. Access for free at https://openstax.org/books/college-success/pages/1-introduction.
|
oercommons
|
2025-03-18T00:38:21.069584
|
Heather F. Adair
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/79244/overview",
"title": "Foundations for College Success, Reading Strategies, Readings",
"author": "Forrest Lane"
}
|
https://oercommons.org/courseware/lesson/15203/overview
|
Introduction
Federalism figures prominently in the U.S. political system. Specifically, the federal design spelled out in the Constitution divides powers between two levels of government—the states and the federal government—and creates a mechanism for them to check and balance one another. As an institutional design, federalism both safeguards state interests and creates a strong union led by a capable central government.
American federalism also seeks to balance the forces of decentralization and centralization. We see decentralization when we cross state lines and encounter different taxation levels, welfare eligibility requirements, and voting regulations, to name just a few. Centralization is apparent in the fact that the federal government is the only entity permitted to print money, to challenge the legality of state laws, or to employ money grants and mandates to shape state actions. Colorful billboards with simple messages may greet us at state borders (Figure), but behind them lies a complex and evolving federal design that has structured relationships between states and the federal government since the late 1700s.
What specific powers and responsibilities are granted to the federal and state governments? How does our process of government keep these separate governing entities in balance? To answer these questions and more, this chapter traces the origins, evolution, and functioning of the American system of federalism, as well as its advantages and disadvantages for citizens.
|
oercommons
|
2025-03-18T00:38:21.086724
|
07/10/2017
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/15203/overview",
"title": "American Government, Students and the System, American Federalism, Introduction",
"author": null
}
|
https://oercommons.org/courseware/lesson/79897/overview
|
OpenStax Anatomy & Physiology Quizlet Overview OpenStax Anatomy & Physiology Quizlet list https://docs.google.com/document/d/1LUTRcOW4ZRyCpvH_qNSkN9HD73cX6qK2yeEq6DhB62s/edit?usp=sharing
|
oercommons
|
2025-03-18T00:38:21.111656
|
05/05/2021
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/79897/overview",
"title": "OpenStax Anatomy & Physiology Quizlet",
"author": "Rob Adams"
}
|
https://oercommons.org/courseware/lesson/99827/overview
|
Books
Final Paper-Media Content Analysis
Final Paper-Rubric
Final Paper-Three Benchmarks
History of Popular Music Slideshow
Intro to Mass Media - Combined OER
Magazines
Media Issues (Representation, Laws, Regs, Politics, and Democracy)
Movies
Movies
Movies Slideshow
New Media
Newspapers and Journalism
Overview and Introduction
Popular Music
Radio
Video Games
Introduction to Mass Media Hybrid Text
Overview
This hybrid text seeks to introduce students to mass media and communications by combining two existing OER resources -- "Understanding Media and Culture: An Introduction to Mass Communication" a 750-page book from 2016 from the University of Minnesota Libraries and Mark Poepsel's 100-page book "Media, Society, Culture, and You" from 2017 -- into a single 400-page textbook (50 of which are bibliographic references), to form a comprehensive yet accessible introductory level text that teachers and students alike can augment and update with contemporary examples.
Full Text and Overview
By combining the pertinent sections of each text and rearranging the order to embed some of the module-related "issues" into each section (rather than keeping many of the "media issues" a separate section as some texts do), this hybrid text encourages each professor (and by extension their students) to add relevant contemporary examples. Furthermore, the hybrid text front-loads some of these issues, that then play out over the ensuing discussions of each medium.
It also includes a section of issues that are pertinent to all media, such as cultural representation, laws, regulations, politics, and democracy.
The text (and accompanying Final Paper idea, adapted from Jennifer Bauer and Gordon Curry's) was combined with the following SLOs in mind:
- Identify themes and messages across multiple mass media.
- Analyze a mass media piece based on its formal characteristics.
- Explain some of the objectives of different theories and major players in the media.
- Apply critical theories to analyze media arts in critical observation, writing, and discussion.
- Make aesthetic judgments using your own standards and politics.
This hybrid text seeks to introduce students to mass media and communications by combining two existing OER resources -- "Understanding Media and Culture: An Introduction to Mass Communication" a 750-page book from 2016 from the University of Minnesota Libraries and Mark Poepsel's 100-page book "Media, Society, Culture, and You" from 2017 -- into a single 400-page textbook (50 of which are bibliographic references), to form a comprehensive yet accessible introductory level text that teachers and students alike can augment and update with contemporary examples.
Setting the Stage: What is Mass Media and why does it matter?
Provides an overview of Mass Media, common culture, and main methodologies as a way to contextualize the rest of the text's deeper coverage of individual media types.
Internet and New Media
By starting with the media that is most prevalent in students' lives, and due to its ubiquity is often taken for granted, the student is thrust into a tangible consideration of the ways in which "the medium is (indeed) the message."
Newspapers and Journalism
Due to the prevalence of obtaining news via social media and/or various news aggregators that either deliver stories out of context or narrow one's exposure due to algorithms, and the increased drive for media literacy in light of these "new media" delivery methods, introducing students to journalism and newspapers as the next module has proven beneficial.
Books
Other suggested resources include:
TED overview of Books: (4mins) -- www.youtube.com/watch?v=_YqYtdPUis4
E-Books vs Physical Books:
Why Physical Books Still Outsell e-Books (CNBC-6mins) www.youtube.com/watch?v=5Em-U9onvGI
(Cull the stats and opinion from this video; update the stats for 2022, for slides)
Why Borders Failed and Barnes & Noble Survived (NPR - 3mins)
https://www.npr.org/2011/07/19/138514209/why-borders-failed-while-barnes-and-noble-survived
Why Indy Bookstores? (NPR-3mins)
Graphic Novels:
History of: https://www.youtube.com/watch?v=0xw3N2GIUZc (6minutes)
Stan Lee on Banned Books Week: https://www.youtube.com/watch?v=oCu9hs73kb0 (2 minutes)
Magazines
From general interest to niche, and from print (and mailed) to online versions, the expansion, contraction, and possble rebirth of magazines echoes the trajectory of its print counterparts (books and newspapers).
Popular & Recorded Music
The accompanying slideshow is a representation of what you can ask students to create based on the readings to synthesize the material, or something you can create to preface or review the readings with them.
Radio
Controlling the airwaves meant much more than ruling the charts...
Movies
The slideshow is another example of what students can create to synthesize and share the material, or what the instructor can use to preface or review the material.
Television
TV is everywhere and "on the go" now showing convergence not only within a medium, but how technology is blurring the boundary between television and movies, just as it has shifted our understabnding of what "radio" is. Also, the lack of "real time" and "same space" has shifted the idea of communal experience... by this module students should be personally reinforcing the ideas of how media and our use of it has not only shifted global and poltical considerations, but also personal and interpersonal considerations.
Digital Gaming
Creating and living in a digital world. By placing this module here, it is chronological, but it also rounds out the trajectory of the course for our mosty highly interactive media (new media and digital gaming). A case could be made for including Digital Gaming as the third module, but by including it here, it brings in the idea of narrative of movies and tv, as well as the shift in communcal spaces.
Advertising and PR
And in the penultimate module, Advertising and PR, we also round out the trajectory of ubiquitous persences, and since it is the most tangibly associated with societal issues and concerns, it makes a good lead-in to the remaining "Issues" covered in the final module.
Media Issues
Along the way, the previous modules have shown you medium-specific or medium-related issues that pertain to various media; in addition, issues of representation, laws, regulations, politics, and democracy persist across all media. A case could be made for this to come earlier in the semester, and this textbook seeks to integrates some of the other issues more distinctly along the way, while also highlighting some of the over-arching ones here.
Along the way, the previous modules have shown you medium-specific or medium-related issues that pertain to various media. In addition, as you will see in this module, issues of representation, laws, regulations, politics, and democracy persist across all media.
Media Coverage Assignment
I have used this as an earlier in the semester assignment as well, after newspapers and journalism, but it could also go after television, or before digital gaming depending on the flow and/or length of your semester.
This assignment challenges you to use your critical thinking skills to analyze and evaluate media coverage of a recent event or issue. You will examine several different media sources and evaluate the media coverage as a whole.
|
oercommons
|
2025-03-18T00:38:21.163846
|
Adam Webster
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/99827/overview",
"title": "Introduction to Mass Media Hybrid Text",
"author": "Textbook"
}
|
https://oercommons.org/courseware/lesson/124484/overview
|
Ka Lima Hema
Overview
An ukulele etude to be played with only the left hand. It is based on a Samai and uses maqamat.
Left hand etude for ukulele (low G)
To be played with only the left hand.
An ukulele etude to be played with only the left hand. It is based on a Samai and uses maqamat.
To be played with only the left hand.
|
oercommons
|
2025-03-18T00:38:21.179856
|
02/08/2025
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/124484/overview",
"title": "Ka Lima Hema",
"author": "Eric Schroeder"
}
|
https://oercommons.org/courseware/lesson/69411/overview
|
Education Standards
syllabus
MICRO CONTROLLER 8051 for Diploma Students
Overview
In this Course we learn about history, terminology, block diagram, working and applications of 8051.
A microcontroller is an electronic device belonging to the microcomputer family. These are fabricated using the VLSI technology on a single chip. There are microcontrollers available in the present market with different word length starting from 4 bit, 8 bit, 64 bit to 128 bit.
MICRO CONTROLLER Subject Introduction
OBJECTIVES:
- On completion of the following units of syllabus contents, the students must be able to
- Explain Architecture of 8051 Microcontroller.
- Explain the functions of various registers.
- Understand interrupt structure of 8051.
- Understand serial data communication concepts.
- Understand the programming techniques.
- Explain various addressing modes.
- Write simple programs using 8051.
- Understand the block diagram and control word formats for peripheral devices.
- Understand how to interface with RS232C.
- Understand how to interface with 8255.
- Understand various application of 8051 Microcontroller
TOPICS AND ALLOCATION:
Unit | Topic | Time (Hrs.) |
I | Architecture & Instruction set of 8051 | 19 |
II | Programming Examples | 13 |
III | I/O and Timer | 15 |
IV | Interrupt and Serial Communication | 16 |
V | Interfacing Techniques | 19 |
| Revision – Test | 8 |
| TOTAL | 90 |
Introduction to Micro Processor & Micro controller
History of Microprocessor
Evolution of Microprocessors
We can categorize the microprocessor according to the generations or according to the size of the microprocessor:
First Generation (4 - bit Microprocessors)
The first generation microprocessors were introduced in the year 1971-1972 by Intel Corporation. It was named Intel 4004 since it was a 4-bit processor.
It was a processor on a single chip. It could perform simple arithmetic and logical operations such as addition, subtraction, Boolean OR and Boolean AND.
I had a control unit capable of performing control functions like fetching an instruction from storage memory, decoding it, and then generating control pulses to execute it.
Second Generation (8 - bit Microprocessor)
The second generation microprocessors were introduced in 1973 again by Intel. It was a first 8 - bit microprocessor which could perform arithmetic and logic operations on 8-bit words. It was Intel 8008, and another improved version was Intel 8088.
Third Generation (16 - bit Microprocessor)
The third generation microprocessors, introduced in 1978 were represented by Intel's 8086, Zilog Z800 and 80286, which were 16 - bit processors with a performance like minicomputers.
Fourth Generation (32 - bit Microprocessors)
Several different companies introduced the 32-bit microprocessors, but the most popular one is the Intel 80386.
Fifth Generation (64 - bit Microprocessors)
From 1995 to now we are in the fifth generation. After 80856, Intel came out with a new processor namely Pentium processor followed by Pentium Pro CPU, which allows multiple CPUs in a single system to achieve multiprocessing.
ARCHITECTURE & INSTRUCTION SET OF 8051
ARCHITECTUREOF 8051
Comparison of Microprocessor and Microcontroller - Block diagram of Microcontroller –Functions of each block - Pin details of 8051 – ALU –ROM– RAM – Memory Organization of 8051 - Special function registers –Program Counter – PSW register – Stack - I/O Ports – Timer – Interrupt – Serial Port – Oscillator and Clock - Clock Cycle – State - Machine Cycle –Instruction cycle – Reset – Power on Reset – Overview of 8051 family
The pin diagram of 8051 microcontroller looks as follows −
Pins 1 to 8 − These pins are known as Port 1. This port doesn’t serve any other functions. It is internally pulled up, bi-directional I/O port.
Pin 9 − It is a RESET pin, which is used to reset the microcontroller to its initial values.
Pins 10 to 17 − These pins are known as Port 3. This port serves some functions like interrupts, timer input, control signals, serial communication signals RxD and TxD, etc.
Pins 18 & 19 − These pins are used for interfacing an external crystal to get the system clock.
Pin 20 − This pin provides the power supply to the circuit.
Pins 21 to 28 − These pins are known as Port 2. It serves as I/O port. Higher order address bus signals are also multiplexed using this port.
Pin 29 − This is PSEN pin which stands for Program Store Enable. It is used to read a signal from the external program memory.
Pin 30 − This is EA pin which stands for External Access input. It is used to enable/disable the external memory interfacing.
Pin 31 − This is ALE pin which stands for Address Latch Enable. It is used to demultiplex the address-data signal of port.
Pins 32 to 39 − These pins are known as Port 0. It serves as I/O port. Lower order address and data bus signals are multiplexed using this port.
Pin 40 − This pin is used to provide power supply to the circuit.
The 8051 microcontroller is an 8-bit microcontroller. Let us see the major components of 8051 microcontroller and their functions.
An 8051 microcontroller has the following 12 major components:
1. ALU (Arithmetic and Logic Unit)
2. PC (Program Counter)
3. Registers
4. Timers and counters
5. Internal RAM and ROM
6. Four general purpose parallel input/output ports
7. Interrupt control logic with five sources of interrupt
8. Serial date communication
9. PSW (Program Status Word)
10. Data Pointer (DPTR)
11. Stack Pointer (SP)
12. Data and Address bus.
1. ALU
All arithmetic and logical functions are carried out by the ALU.
Addition, subtraction with carry, and multiplication come under arithmetic operations.
Logical AND, OR and exclusive OR (XOR) come under logical operations.
2. Program Counter (PC)
A program counter is a 16-bit register and it has no internal address. The basic function of program counter is to fetch from memory the address of the next instruction to be executed. The PC holds the address of the next instruction residing in memory and when a command is encountered, it produces that instruction. This way the PC increments automatically, holding the address of the next instruction.
3. Registers
Registers are usually known as data storage devices. 8051 microcontroller has 2 registers, namely Register A and Register B. Register A serves as an accumulator while Register B functions as a general purpose register. These registers are used to store the output of mathematical and logical instructions.
The operations of addition, subtraction, multiplication and division are carried out by Register A. Register B is usually unused and comes into picture only when multiplication and division functions are carried out by Register A. Register A also involved in data transfers between the microcontroller and external memory.
8051 microcontroller also has 7 Special Function Registers (SFRs). They are:
1. Serial Port Data Buffer (SBUF)
2. Timer/Counter Control (TCON)
3. Timer/Counter Mode Control (TMOD)
4. Serial Port Control (SCON)
5. Power Control (PCON)
6. Interrupt Priority (IP)
7. Interrupt Enable Control (IE)
4. Timers and Counters
Synchronization among internal operations can be achieved with the help of clock circuits which are responsible for generating clock pulses. During each clock pulse a particular operation will be carried out, thereby, assuring synchronization among operations. For the formation of an oscillator, we are provided with two pins XTAL1 and XTAL2 which are used for connecting a resonant network in 8051 microcontroller device. In addition to this, circuit also consists of four more pins. They are,
Internal operations can be synchronized using clock circuits which produce clock pulses. With each clock pulse, a particular function will be accomplished and hence synchronization is achieved. There are two pins XTAL1 and XTAL2 which form an oscillator circuit which connect to a resonant network in the microcontroller. The circuit also has 4 additional pins -
1. EA: External enable
2. ALE: Address latch enable
3. PSEN: Program store enable and
4. RST: Reset.
Quartz crystal is used to generate periodic clock pulses.
5. Internal RAM and ROM
ROM
A code of 4K memory is incorporated as on-chip ROM in 8051. The 8051 ROM is a non-volatile memory meaning that its contents cannot be altered and hence has a similar range of data and program memory, i.e, they can address program memory as well as a 64K separate block of data memory.
RAM
The 8051 microcontroller is composed of 128 bytes of internal RAM. This is a volatile memory since its contents will be lost if power is switched off. These 128 bytes of internal RAM are divided into 32 working registers which in turn constitute 4 register banks (Bank 0-Bank 3) with each bank consisting of 8 registers (R0 - R7). There are 128 addressable bits in the internal RAM.
6. Four General Purpose Parallel Input/Output Ports
The 8051 microcontroller has four 8-bit input/output ports. These are:
PORT P0: When there is no external memory present, this port acts as a general purpose input/output port. In the presence of external memory, it functions as a multiplexed address and data bus. It performs a dual role.
PORT P1: This port is used for various interfacing activities. This 8-bit port is a normal I/O port i.e. it does not perform dual functions.
PORT P2: Similar to PORT P0, this port can be used as a general purpose port when there is no external memory but when external memory is present it works in conjunction with PORT PO as an address bus. This is an 8-bit port and performs dual functions.
PORT P3: PORT P3 behaves as a dedicated I/O port
7. Interrupt Control
An event which is used to suspend or halt the normal program execution for a temporary period of time in order to serve the request of another program or hardware device is called an interrupt. An interrupt can either be an internal or external event which suspends the microcontroller for a while and thereby obstructs the sequential flow of a program.
There are two ways of giving interrupts to a microcontroller – one is by sending software instructions and the other is by sending hardware signals. The interrupt mechanism keeps the normal program execution in a "put on hold" mode and executes a subroutine program and after the subroutine is executed, it gets back to its normal program execution. This subroutine program is also called an interrupt handler. A subroutine is executed when a certain event occurs.
In 8051, 5 sources of interrupts are provided. They are:
a) 2 external interrupt sources connected through INT0 and INT1
b) 3 external interrupt sources- serial port interrupt, Timer Flag 0 and Timer Flag 1.
The pins connected are as follows:
1. ALE (Address Latch Enable) - Latches the address signals on Port P0
2. EA (External Address) - Holds the 4K bytes of program memory
3. PSEN (Program Store Enable) - Reads external program memory
4. RST (Reset) - Reset the ports and internal registers upon start up
8. Serial Data Communication
A method of establishing communication among computers is by transmitting and receiving data bits is a serial connection network. In 8051, the SBUF (Serial Port Data Buffer) register holds the data; the SCON (Serial Control) register manages the data communication and the PCON (Power Control) register manages the data transfer rates. Further, two pins - RXD and TXD, establish the serial network.
The SBUF register has 2 parts – one for storing the data to be transmitted and another for receiving data from outer sources. The first function is done using TXD pin and the second function is done using RXD pin.
There are 4 programmable modes in serial data communication. They are:
1. Serial Data mode 0 (shift register mode)
2. Serial Data mode 1 (standard UART)
3. Serial Data mode 2 (multiprocessor mode)
4. Serial Data mode 3
9. PSW (Program Status Word)
Program Status Word or PSW is a hardware register which is a memory location which holds a program's information and also monitors the status of the program this is currently being executed. PSW also has a pointer which points towards the address of the next instruction to be executed. PSW register has 3 fields namely are instruction address field, condition code field and error status field. We can say that PSW is an internal register that keeps track of the computer at every instant.
Generally, the instruction of the result of a program is stored in a single bit register called a 'flag'. The are7 flags in the PSW of 8051. Among these 7 flags, 4 are math flags and 3 are general purpose or user flags.
The 4 Math flags are:
• Carry (c)
• Auxiliary carry (AC)
• Overflow (OV)
• Parity (P)
The 3 General purpose flags or User flags are:
• FO
• GFO
• GF 1
10. Data Pointer (DPTR)
The data pointer or DPTR is a 16-bit register. It is made up of two 8-bit registers called DPH and DPL. Separate addresses are assigned to each of DPH and DPL. These 8-bit registers are used for the storing the memory addresses that can be used to access internal and external data/code.
11. Stack Pointer (SP)
The stack pointer (SP) in 8051 is an 8-bit register. The main purpose of SP is to access the stack. As it has 8-bits it can take values in the range 00 H to FF H. Stack is a special area of data in memory. The SP acts as a pointer for an address that points to the top of the stack.
12. Data and Address Bus
A bus is group of wires using which data transfer takes place from one location to another within a system. Buses reduce the number of paths or cables needed to set up connection between components.
There are mainly two kinds of buses - Data Bus and Address Bus
Data Bus: The purpose of data bus is to transfer data. It acts as an electronic channel using which data travels. Wider the width of the bus, greater will be the transmission of data.
Address Bus: The purpose of address bus is to transfer information but not data. The information tells from where within the components, the data should be sent to or received from. The capacity or memory of the address bus depends on the number of wires that transmit a single address bit.
Overview of 8051 family
Common and Basic Features of 8051 CPU based Microcontroller
8051 Microcontroller is equipped with lots of advanced features with following features:-
- On Chip ROM 4 KB bytes Program Read Only Memory.
- Total 128 bytes of Random Access Memory on Chip.
- Four 8051 Memory Register Banks
- User defined 128 software flags
- Bidirectional 8 bit data bus to fetch data
- Unidirectional 16 bit bus to communicate
- General Purpose Registers 32 each with 8 bit
- Total 16 bit Timers for timing operations.
- Internal and External two interrupts
- Four Ports with 8 bit data transfer
- 16 Bit program data pointer and counter
- It also has few special features like UARTs, Operational Amp
- Analog to digital converter ADC, DAC.
INSTRUCTION SET OF 8051
Instruction set of 8051 – Classification of 8051 Instructions - Data transfer instructions – Arithmetic Instructions – Logical instructions –Branching instructions – Bit Manipulation Instructions
- Writing a Program for any Microcontroller consists of giving commands to the Microcontroller in a particular order in which they must be executed in order to perform a specific task. The commands to the Microcontroller are known as a Microcontroller’s Instruction Set.
- Just as our sentences are made of words, a Microcontroller’s (for that matter, any computer) program is made of Instructions. Instructions written in a program tell the Microcontroller which operation to carry out.
- An Instruction Set is unique to a family of computers. This tutorial introduces the 8051 Microcontroller Instruction Set also called as the MCS-51 Instruction Set.
- As the 8051 family of Microcontrollers are 8-bit processors, the 8051 Microcontroller Instruction Set is optimized for 8-bit control applications. As a typical 8-bit processor, the 8051 Microcontroller instructions have 8-bit Opcodes. As a result, the 8051 Microcontroller instruction set can have up to 28 = 256 Instructions
Argument | Description |
addr11 | An 11-bit address destination. This argument is used by ACALL and AJMP instructions. The target of the CALL or JMP must lie within the same 2K page as the first byte of the following instruction. |
addr16 | A 16-bit address destination. This argument is used by LCALL and LJMP instructions. |
bit | A direct addressed bit in internal data RAM or SFR memory. |
direct | An internal data RAM location (0-127) or SFR (128-255). |
immediate | A constant included in the instruction encoding. |
offset | A signed (two's complement) 8-bit offset (-128 to 127) relative to the first byte of the following instruction. |
@Ri | An internal data RAM location (0-255) addressed indirectly through R0 or R1. |
Rn | Register R0-R7. |
Alphabetical List of Instructions
|
|
DATA TRANSFER | ARITHMETIC | LOGICAL | BOOLEAN | PROGRAM BRANCHING |
MOV | ADD | ANL | CLR | LJMP |
MOVC | ADDC | ORL | SETB | AJMP |
MOVX | SUBB | XRL | MOV | SJMP |
PUSH | INC | CLR | JC | JZ |
POP | DEC | CPL | JNC | JNZ |
XCH | MUL | RL | JB | CJNE |
XCHD | DIV | RLC | JNB | DJNZ |
| DA A | RR | JBC | NOP |
|
| RRC | ANL | LCALL |
|
| SWAP | ORL | ACALL |
|
|
| CPL | RET |
|
|
|
| RETI |
|
|
|
| JMP |
ta moving / handling Instructions:
Mnemonics | Operational description | Addressing mode | No. of bytes occupied | No. of cycles used |
Mov a,#num | Copy the immediate data num in to acc | immediate | 2 | 1 |
Mov Rx,a | Copy the data from acc to Rx | register | 1 | 1 |
Mov a,Rx | Copy the data from Rx to acc | register | 1 | 1 |
Mov Rx,#num | Copy the immediate data num in to Rx | immediate | 2 | 1 |
Mov a,add | Copy the data from direct address add to acc | direct | 2 | 1 |
Mov add,a | Copy the data from acc to direct address add | direct | 2 | 1 |
Mov add,#num | Copy the immediate data num in to direct address | direct | 3 | 2 |
Mov add1,add2 | Copy the data from add2 to add1 | direct | 3 | 2 |
Mov Rx,add | Copy the data from direct address add to Rx | direct | 2 | 2 |
Mov add,Rx | Copy the data from Rx to direct address add | direct | 2 | 2 |
Mov @Rp,a | Copy the data in acc to address in Rp | Indirect | 1 | 1 |
Mov a,@Rp | Copy the data that is at address in Rp to acc | Indirect | 1 | 1 |
Mov add,@Rp | Copy the data that is at address in Rp to add | Indirect | 2 | 2 |
Mov @Rp,add | Copy the data in add to address in Rp | Indirect | 2 | 2 |
Mov @Rp,#num | Copy the immediate byte num to the address in Rp | Indirect | 2 | 1 |
Movx a,@Rp | Copy the content of external add in Rp to acc | Indirect | 1 | 2 |
Movx a,@DPTR | Copy the content of external add in DPTR to acc | Indirect | 1 | 2 |
Movx @Rp,a | Copy the content of acc to the external add in Rp | Indirect | 1 | 2 |
Movx @DPTR,a | Copy the content of acc to the external add in DPTR | Indirect | 1 | 2 |
Movc a,@a+DPTR | The address is formed by adding acc and DPTR and its content is copied to acc | indirect | 1 | 2 |
Movc a, @a+PC | The address is formed by adding acc and PC and its content is copied to acc | indirect | 1 | 2 |
Push add | Increment SP and copy the data from source add to internal RAM address contained in SP | Direct | 2 | 2 |
Pop add | copy the data from internal RAM address contained in SP to destination add and decrement SP | direct | 2 | 2 |
Xch a, Rx | Exchange the data between acc and Rx | Register | 1 | 1 |
Xch a, add | Exchange the data between acc and given add | Direct | 2 | 1 |
Xch a,@Rp | Exchange the data between acc and address in Rp | Indirect | 1 | 1 |
Xchd a, @Rp | Exchange only lower nibble of acc and address in Rp | indirect | 1 | 1 |
Logical Instructions: –
Mnemonics | Operational description | Addressing mode | No. of bytes occupied | No. of cycles used |
Anl a, #num | AND each bit of acc with same bit of immediate num, stores result in acc | Immediate | 2 | 1 |
Anl a, add | AND each bit of acc with same bit of content in add, stores result in acc | Direct | 2 | 1 |
Anl a, Rx | AND each bit of acc with same bit of content of Rx, stores result in acc | Register | 1 | 1 |
Anl a, @Rp | AND each bit of acc with same bit of content of add given by Rp, stores result in acc | Indirect | 1 | 1 |
Anl add, a | AND each bit of acc with same bit of direct add num, stores result in add | Direct | 2 | 1 |
Anl add, #num | AND each bit of direct add with same bit of immediate num, stores result in add | direct | 3 | 2 |
orl a, #num | OR each bit of acc with same bit of immediate num, stores result in acc | Immediate | 2 | 1 |
orl a, add | OR each bit of acc with same bit of content in add, stores result in acc | Direct | 2 | 1 |
orl a, Rx | OR each bit of acc with same bit of content of Rx, stores result in acc | Register | 1 | 1 |
orl a, @Rp | OR each bit of acc with same bit of content of add given by Rp, stores result in acc | Indirect | 1 | 1 |
orl add, a | OR each bit of acc with same bit of direct add num, stores result in add | Direct | 2 | 1 |
orl add, #num | OR each bit of direct add with same bit of immediate num, stores result in add | direct | 3 | 2 |
Xrl a, #num | XOR each bit of acc with same bit of immediate num, stores result in acc | Immediate | 2 | 1 |
Xrl a, add | XOR each bit of acc with same bit of content in add, stores result in acc | Direct | 2 | 1 |
Xrl a, Rx | XOR each bit of acc with same bit of content of Rx, stores result in acc | Register | 1 | 1 |
Xrl a, @Rp | XOR each bit of acc with same bit of content of add given by Rp, stores result in acc | Indirect | 1 | 1 |
Xrl add, a | XOR each bit of acc with same bit of direct add num, stores result in add | Direct | 2 | 1 |
Xrl add, #num | XOR each bit of direct add with same bit of immediate num, stores result in add | direct | 3 | 2 |
Clr a | Clear each bit of acc | Direct | 1 | 1 |
Cpl a | Complement each bit of acc | direct | 1 | 1 |
Anl c, b | AND carry with given bit b, stores result in carry | — | 2 | 2 |
Anl c, /b | AND carry with complement of given bit b, stores result in carry | — | 2 | 2 |
Orl c, b | OR carry with given bit b, stores result in carry | — | 2 | 2 |
Orl c, /b | OR carry with complement of given bit b, stores result in carry | — | 2 | 2 |
Cpl c | Complement carry flag | — | 1 | 1 |
Cpl b | Complement bit b | — | 2 | 1 |
Clr c | Clear carry flag | — | 1 | 1 |
Clr b | Clear given bit b | — | 2 | 1 |
Mov c, b | Copy bit b to carry | — | 2 | 1 |
Mov b, c | Copy carry to bit b | — | 2 | 2 |
Setb c | Set carry flag | — | 1 | 1 |
Setb b | Set bit b | — | 2 | 1 |
Rl a | Rotate acc one bit left | — | 1 | 1 |
Rr a | Rotate acc one bit right | — | 1 | 1 |
Rlc a | Rotate acc one bit left with carry | — | 1 | 1 |
Rrc a | Rotate acc one bit right with carry | — | 1 | 1 |
Swap a | Exchange upper and lower nibble of acc | — | 1 | 1 |
Arithmetic Instructions: –
Mnemonics | Operational description | Addressing mode | No. of bytes occupied | No. of cycles used |
Inc a | Add 1 to acc | Register | 1 | 1 |
Inc Rr | Add 1 to register Rr | Register | 1 | 1 |
Inc add | Add 1 to the content of add | Direct | 2 | 1 |
Inc @rp | Add 1 to the content of the address in Rp | indirect | 1 | 1 |
Inc DPTR | Add 1 to DPTR | Register | 1 | 2 |
dec a | Subtract 1 from acc | Register | 1 | 1 |
dec Rr | Subtract 1 from Rr | Register | 1 | 1 |
dec add | Subtract 1 from content of add | Direct | 2 | 1 |
dec @rp | Subtract 1 from the content of address | indirect | 1 | 1 |
Add a, #num | Add the immediate num with acc and stores result in acc | immediate | 2 | 1 |
Add a, Rx | Add the data in Rx with acc and stores result in acc | Register | 1 | 1 |
Add a, add | Add the data in add with acc and stores result in acc | Direct | 2 | 1 |
Add a, @Rp | Add the data at the address in Rp with acc and stores result in acc
| Indirect | 1 | 1 |
Addc a,#num | Add the immediate num with acc and carry, stores result in acc | immediate | 2 | 1 |
Addc a, Rx | Add the data in Rx with acc and carry, stores result in acc | Register | 1 | 1 |
Addc a, add | Add the data in add with acc and carry, stores result in acc | Direct | 2 | 1 |
Addc a, @Rp | Add the data at the address in Rp with acc and carry, stores result in acc | Indirect | 1 | 1 |
Subb a, #num | Subtract immediate num and carry from acc; stores the result in acc | immediate | 2 | 1 |
Subb a, add | Subtract the content of add and carry from acc; stores the result in acc | Register | 1 | 1 |
Subb a, Rx | Subtract the data in Rx and carry from acc; stores the result in acc | Direct | 2 | 1 |
Subb a, @Rp | Subtract the data at the address in Rp and carry from acc; stores the result in acc | Indirect | 1 | 1 |
Mul ab | Multiply acc and register B. store the lower byte of result in acc and higher byte in B | — | 1 | 4 |
div ab | divide acc by register B. store quotient in acc and remainder in B | — | 1 | 4 |
Da a | After addition of two packed BCD numbers, adjust the sum to decimal format | — | 1 | 1 |
Branching Instructions: –
Mnemonic | Operational description | No of bytes occupied | No. of cycles used |
Jc label | Jump to label if carry is set to 1 | 2 | 2 |
Jnc label | Jump to label if carry is cleared to 0 | 2 | 2 |
Jb b,label | Jump to label if given bit is set to 1 | 3 | 2 |
Jnb b,label | Jump to label if given bit is cleared to 0 | 3 | 2 |
Jbc b,label | Jump to label if given bit is set. Clear the bit | 3 | 2 |
Cjne a, add, label | Compare the content of accumulator with the content of given address and if not equal jump to label | 3 | 2 |
Cjne a, #num, label | Compare the content of accumulator with immediate number and if not equal jump to label | 3 | 2 |
Cjne Rx, #num, label | Compare the content of Rx with the immediate number and if not equal jump to label | 3 | 2 |
Cjne @Rp, #num, label | Compare the content of location in Rp with immediate number and if not equal jump to label | 3 | 2 |
Djnz Rx, label | Decrement the content of Rx and jump to the label if it is not zero | 2 | 2 |
Djnz add, label | Decrement the content of address and jump to the label if it is not zero | 3 | 2 |
Jz label | Jump to the label if content of accumulator is 0 | 2 | 2 |
Jnz label | Jump to the label if content of accumulator is not 0 | 2 | 2 |
Jmp @a+dptr | Jump to the address created by adding the contents on accumulator and dptr | 1 | 2 |
Ajmp sadd | Take a jump to absolute short range address sadd | 2 | 2 |
Ljmp ladd | Take a jump to absolute long range address sadd | 3 | 2 |
Sjmp radd | Take a jump to relative address radd | 2 | 2 |
nop | Short form of no operation means do nothing and go to next instruction | 1 | 1 |
Acall sadd | Pushes the content of Acc on stack and load it will absolute short range address sadd | 2 | 2 |
Lcall ladd | Pushes the content of Acc on stack and load it will absolute long range address sadd | 3 | 2 |
Ret | returns from subroutine by restoring the Acc from stack using pop operation | 1 | 2 |
reti | Returns from interrupt subroutine by restoring Acc from stack using pop operation | 1 | 2 |
Bit-oriented Instructions
Similar to logic instructions, bit-oriented instructions perform logic operations. The difference is that these are performed upon single bits.
Here some simple assembly language programs for 8051 microcontroller are given to understand the operation of different instructions and to understand the logic behind particular program. First the statement of the program that describes what should be done is given. Then the solution is given which describes the logic how it will be done and last the code is given with necessary comments.
Statement 1: – exchange the content of FFh and FF00h
Solution: – here one is internal memory location and other is memory external location. so first the content of ext memory location FF00h is loaded in acc. then the content of int memory location FFh is saved first and then content of acc is transferred to FFh. now saved content of FFh is loaded in acc and then it is transferred to FF00h.
Mov dptr, #0FF00h ; take the address in dptr
Movx a, @dptr ; get the content of 0050h in a
Mov r0, 0FFh ; save the content of 50h in r0
Mov 0FFh, a ; move a to 50h
Mov a, r0 ; get content of 50h in a
Movx @dptr, a ; move it to 0050h
Duplication and Subtraction
Statement 2: – store the higher nibble of r7 in to both nibbles of r6
Solution: –first we shall get the upper nibble of r7 in r6. Then we swap nibbles of r7 and make OR operation with r6 so the upper and lower nibbles are duplicated
Mov a, r7 ; get the content in acc
Anl a, #0F0h ; mask lower bit
Mov r6, a ; send it to r6
Swap a ; xchange upper and lower nibbles of acc
Orl a, r6 ; OR operation
Mov r6, a ; finally load content in r6
Statement 3: – treat r6-r7 and r4-r5 as two 16 bit registers. Perform subtraction between them. Store the result in 20h (lower byte) and 21h (higher byte).
Solution: – first we shall clear the carry. Then subtract the lower bytes afterward then subtract higher bytes.
Clr c ; clear carry
Mov a, r4 ; get first lower byte
Subb a, r6 ; subtract it with other
Mov 20h, a ; store the result
Mov a, r5 ; get the first higher byte
Subb a, r7 ; subtract from other
Mov 21h, a ; store the higher byte
Division & Data Transfer
Statement 4: – divide the content of r0 by r1. Store the result in r2 (answer) and r3 (reminder). Then restore the original content of r0.
Solution:-after getting answer to restore original content we have to multiply answer with divider and then add reminder in that.
Mov a, r0 ; get the content of r0 and r1
Mov b, r1 ; in register A and B
Div ab ; divide A by B
Mov r2, a ; store result in r2
Mov r3, b ; and reminder in r3
Mov b, r1 ; again get content of r1 in B
Mul ab ; multiply it by answer
Add a, r3 ; add reminder in new answer
Mov r0, a ; finally restore the content of r0
Statement 5: – transfer the block of data from 20h to 30h to external location 1020h to 1030h.
Solution: – here we have to transfer 10 data bytes from internal to external RAM. So first, we need one counter. Then we need two pointers one for source second for destination.
Mov r7, #0Ah ; initialize counter by 10d
Mov r0, #20h ; get initial source location
Mov dptr, #1020h ; get initial destination location
Nxt: Mov a, @r0 ; get first content in acc
Movx @dptr, a ; move it to external location
Inc r0 ; increment source location
Inc dptr ; increase destination location
Djnz r7, nxt ; decrease r7. if zero then over otherwise move next
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oercommons
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2025-03-18T00:38:21.603091
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Reading
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/69411/overview",
"title": "MICRO CONTROLLER 8051 for Diploma Students",
"author": "Lesson"
}
|
https://oercommons.org/courseware/lesson/79689/overview
|
OpenStax Biology
Principles of Biology I
Overview
This is a Community College course syllabus used for our BIO 103, Principles of Biology I course. The OpenStax Biology textbook was used with this course along with virtual labs through Merlot.
BIO 103
I. COURSE DESCRIPTION:
This is an introductory course for science majors. It covers physical, chemical, and biological principles common to all organisms. These principles are explained through a study of cell structure and function, cellular reproduction, basic biochemistry, cell energetics, cellular respiration, the process of photosynthesis, and Mendelian and molecular genetics. CREDIT HOURS: 4 PREREQUISITE: None
II. REQUIRED MATERIALS:
In this course, we will use the following resources this semester:
https://virtuallabs.merlot.org/index.html (Links to an external site.)
https://openstax.org/details/books/biology-2e
- I.D./Library card for Trenholm State Library and Resource Centers to use as a resource for homework and other course assignments
- Access to Canvas (Canvas runs on Windows, Mac, Linux, iOS, Android, or any other device with a modern web browser.)
- Access to your Trenholm student email (Please note: I will not open or reply to emails sent from your personal email). With this in mind, please only message me using Canvas or your Trenholm student email.
III. COURSE OBJECTIVES:
By the end of the course, students will be able to:
- explain the fundamental processes of life;
- apply the scientific method in theory and laboratory;
- explain the diversity and taxonomic hierarchy of life;
- differentiate the basic characteristics of viruses, eukaryotes, and prokaryotes;
- summarize photosynthesis and cellular respiration, with an emphasis on the transformation of energy and matter;
- apply the basic principles of genetics to predict inheritance patterns;
- identify the basic principles of biochemistry including the structure and functions of macromolecules;
- describe cell structures and their functions;
- differentiate the types and stages of cellular reproduction; and
- explain the processes of molecular genetics.
IV. COURSE OUTLINE OF TOPICS:
Content Outline
- Evolution, the Themes of Biology, and Scientific Inquiry
- Basic Chemistry
- Properties of Water
- Macromolecules
- Cell Function and Structure
- Prokaryotes vs. Eukaryotes
- Membrane Transport
- The Cell Cycle
- Meiosis
- Energy & Metabolism
- Cellular Respiration
- Photosynthesis
- Genetics
- Molecular Genetics
Labs
- Chemistry of Life
- Microscopy
- Prokaryotic and Eukaryotic cells
- Cellular Transport
- Cellular Respiration
- Photosynthesis
- Mitosis
- Meiosis
- Pedigree
V. EVALUATION AND ASSESSMENT:
Chapter Tests -25%
Labs/Quizzes/Assignments/Discussions-20%
Midterm Project-20%
Comprehensive Final Exam-35%
Grades will be based upon A=90-100%, B=80-89%, C=70-79%, D=60-69%, and F=below 60%
Assignment Deadlines
Assignment deadlines are always on Sunday night at 11:59 pm. It is your responsibility to leave enough time to deal with possible technical or personal issues that may arise. I will always post/open assignments 7 days prior to when they are due and I will close assignments 7 days after the due date. With this in mind, please plan accordingly and sign-in/check Canvas at least twice a week.
Extra Credit
I may occasionally grant extra credit opportunities to the entire class. I do not offer/give extra on an individual basis.
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oercommons
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2025-03-18T00:38:21.648220
|
Amy Smith
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/79689/overview",
"title": "Principles of Biology I",
"author": "Syllabus"
}
|
https://oercommons.org/courseware/lesson/84244/overview
|
Business 300 Syllabus
Business 300: Introduction to Business
Overview
Introduction to Business is a survey business course providing a multidisciplinary exami-nation of how culture, society, human behavior and economic systems interact with le-gal, international, political, and financial institutions to affect business policy and practic-es within the U.S. and the global marketplace. Students will evaluate how these influences impact the primary areas of business in-cluding: organizational structure and design; leadership, human resource management, and organized labor practices; marketing; organizational communication; technology; entrepreneurship; legal, accounting, and financial practices; the stock and securities markets; and therefore, affect a business’ ability to achieve its organizational goals.
Business 300 Syllabus and Sample Assignment
Introduction to Business is a survey business course providing a multidisciplinary exami-nation of how culture, society, human behavior and economic systems interact with le-gal, international, political, and financial institutions to affect business policy and practic-es within the U.S. and the global marketplace. Students will evaluate how these influences impact the primary areas of business in-cluding: organizational structure and design; leadership, human resource management, and organized labor practices; marketing; organizational communication; technology; entrepreneurship; legal, accounting, and financial practices; the stock and securities markets; and therefore, affect a business’ ability to achieve its organizational goals.
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oercommons
|
2025-03-18T00:38:21.666622
|
Open for Antiracism Program (OFAR)
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/84244/overview",
"title": "Business 300: Introduction to Business",
"author": "Syllabus"
}
|
https://oercommons.org/courseware/lesson/79690/overview
|
5-Letter Lock
Breakout Answers
Congratulations Page
Cover Page
Directional Lock
6th Grade Ancient Greece Breakout
Overview
This is a breakout lesson created for a 6th grade unit on Ancient Greece.
Teacher Items
- Make one copy of each page on cardstock for every group/box.
- Laminate the cover page to the front of a large manila envelope.
- Laminate the cardstock pages. Cut and put one copy of each lock page in the laminated envelopes.
- If you want to give students a hint, make a hint card to place in each envelope.
- Put one copy of the congratulation page inside each lock box.
- Prepare your locks for each group in advance.
- Divide students into groups.
- Review expectations.
- Determine the amount of time allowed to solve the puzzles and display on the board. http://www.viewpure.com/PUVRWT77OHk?start=0&end=0
- Pass out the boxes and envelopes.
- Have fun!
Breakout Materials
These are the materials needed to create the breakout game.
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oercommons
|
2025-03-18T00:38:21.689640
|
Game
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/79690/overview",
"title": "6th Grade Ancient Greece Breakout",
"author": "Assessment"
}
|
https://oercommons.org/courseware/lesson/126943/overview
|
Sign in to see your Hubs
Sign in to see your Groups
Create a standalone learning module, lesson, assignment, assessment or activity
Submit OER from the web for review by our librarians
Please log in to save materials. Log in
Test for captions
or
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oercommons
|
2025-03-18T00:38:21.710087
|
02/27/2025
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/126943/overview",
"title": "Testing for Captions",
"author": "Joanna Schimizzi"
}
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https://oercommons.org/courseware/lesson/59988/overview
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Project Management
Overview
Description
This module is an introduction to Project Management and its essentials. By the end of this module, you will have a solid knowledge about managing a project and how to turn a plan into a success like a pro.
What is a Project?
A project is a temporary endeavour designed to produce a unique product, service or result with a defined beginning and end undertaken to meet unique goals and objectives, typically to bring about beneficial change or added value. The end is reached when the project's objectives have been achieved or when the project is terminated because its objectives will not or cannot be met, or when the need for the project no longer exists. A project may also be terminated if the client (customer, sponsor, or champion) wishes to terminate the project.
Every project creates a unique product, service, or result. The outcome of the project may be tangible or intangible.
A project can create:
- A product that can be either a component of another item, an enhancement of an item, or an end item in itself;
- A service or a capability to perform a service (e.g., a business function that supports production or distribution);
- An improvement in the existing product or service lines (e.g., A Six Sigma project undertaken to reduce defects);
- A result, such as an outcome or document (e.g, a research project that develops knowledge that can be used to determine whether a trend exists or a new process will benefit society).
Examples of projects include, by are not limited to:
- Developing a new product, service, or a result;
- Effecting a change in the structure, processes, staffing, or style of an organization;
- Developing or acquiring a new or modified information system (hardware or software)
- Conducting a research effort whose outcome will be aptly recorded;
- Constructing a building, industrial plant, or infrastructure; or
- Implementing, improving, or enhancing existing business processes and procedures.
A project is a temporary endeavour designed to produce a unique product, service or result with a defined beginning and end undertaken to meet unique goals and objectives, typically to bring about beneficial change or added value. The end is reached when the project's objectives have been achieved or when the project is terminated because its objectives will not or cannot be met, or when the need for the project no longer exists. A project may also be terminated if the client (customer, sponsor, or champion) wishes to terminate the project.
Every project creates a unique product, service, or result. The outcome of the project may be tangible or intangible.
A project can create:
- A product that can be either a component of another item, an enhancement of an item, or an end item in itself;
- A service or a capability to perform a service (e.g., a business function that supports production or distribution);
- An improvement in the existing product or service lines (e.g., A Six Sigma project undertaken to reduce defects);
- A result, such as an outcome or document (e.g, a research project that develops knowledge that can be used to determine whether a trend exists or a new process will benefit society).
Examples of projects include, by are not limited to:
- Developing a new product, service, or a result;
- Effecting a change in the structure, processes, staffing, or style of an organization;
- Developing or acquiring a new or modified information system (hardware or software)
- Conducting a research effort whose outcome will be aptly recorded;
- Constructing a building, industrial plant, or infrastructure; or
- Implementing, improving, or enhancing existing business processes and procedures.
What is Project Management?
Project management is the application of knowledge, skills, tools, and techniques to project activities to meet the project requirements.
Project management is the practice of 1) initiating, 2) planning, 3) executing, 4) controlling, and 5) closing the work of a team to achieve specific goals and meet specific success criteria at the specified time. We will talk more about the 5 practices in section 3 of this module.
The primary challenge of project management is to achieve all of the project goals within the given constraints. This information is usually described in project documentation, created at the beginning of the development process.
The object of project management is to produce a complete project which complies with the client's objectives. In many cases, the objective of project management is also to shape or reform the client's brief to feasibly address the client's objectives. Once the client's objectives are clearly established they should influence all decisions made by other people involved in the project – for example, project managers, designers, contractors and sub-contractors.
Managing a project typically includes, but is not limited to:
- Scope,
- Quality,
- Schedule,
- Budget
- Resources, and
- Risks
Project management is the application of knowledge, skills, tools, and techniques to project activities to meet the project requirements.
Project management is the practice of 1) initiating, 2) planning, 3) executing, 4) controlling, and 5) closing the work of a team to achieve specific goals and meet specific success criteria at the specified time. We will talk more about the 5 practices in section 3 of this module.
The primary challenge of project management is to achieve all of the project goals within the given constraints. This information is usually described in project documentation, created at the beginning of the development process.
The object of project management is to produce a complete project which complies with the client's objectives. In many cases, the objective of project management is also to shape or reform the client's brief to feasibly address the client's objectives. Once the client's objectives are clearly established they should influence all decisions made by other people involved in the project – for example, project managers, designers, contractors and sub-contractors.
Managing a project typically includes, but is not limited to:
- Scope,
- Quality,
- Schedule,
- Budget
- Resources, and
- Risks
Project Management Lifecycle
A process is a set of interrelated actions and activities performed to create a pre-specified product, service, or result. Each process is characterized by its inputs, the tools and techniques that can be applied, and the resulting outputs. The project manager needs to consider organizational process assets and enterprise environmental factors. These should be taken into account for every process, even if they are not explicitly listed as inputs in the process specification. Organizational process assets provide guidelines and criteria for tailoring the organization's processes to the specific needs of the project.
In order for a project to be successful, the project team should:
- Select appropriate processes required to meet the project objectives
- Use a defined approach that can be adapted to meet requirements
- Establish and maintain appropriate communication and engagement with stakeholders
- Comply with requirements to meet stakeholder needs and expectations
- Balance the competing constraints of scope, schedule, budget, quality, resources, and risk to produce the specified product, service or result.
The project processes are performed by the project team with stakeholder interaction and generally fall into one of two major categories:
- Project management processes. These processes ensure the effective flow of the project throughout its life cycle. These processes encompass the tools and techniques involved in applying the skills and capabilities described in the knowledge areas.
- Product-oriented processes. These processes specify and create projects product. Product-oriented processes are typically defined by the project life cycle and vary by application area as well as the phase of the product life cycle. The scope of the project cannot be defined without some basic understanding of how to create the specified product.
When a project is poorly navigated and falls short of budget and timeline goals, it can cost you more than just money' it can cause irreparable damage to reputation, confidence, and client trust. The answer isn't just dedicated project managers, but instilling your entire team at every level with project management abilities.
Initiate
● Identify a project's stakeholders.
● Establish clear and measurable project outcomes.
● Create a well-defined project scope statement
Plan
● Identify, assess, and manage project risks.
● Create a realistic and well-defined project schedule.
Execute
● Hold team members accountable for project plans.
● Conduct consistent team-accountability sessions.
Monitor & Control
● Create a clear communication plan around the project that includes regular project status reports and project changes.
Close
● Reward and recognize the contributions of project team members.
● Formally close projects by documenting lessons learned
Below is a video explaining the 5 cycles of project management
A process is a set of interrelated actions and activities performed to create a pre-specified product, service, or result. Each process is characterized by its inputs, the tools and techniques that can be applied, and the resulting outputs. The project manager needs to consider organizational process assets and enterprise environmental factors. These should be taken into account for every process, even if they are not explicitly listed as inputs in the process specification. Organizational process assets provide guidelines and criteria for tailoring the organization's processes to the specific needs of the project.
In order for a project to be successful, the project team should:
- Select appropriate processes required to meet the project objectives
- Use a defined approach that can be adapted to meet requirements
- Establish and maintain appropriate communication and engagement with stakeholders
- Comply with requirements to meet stakeholder needs and expectations
- Balance the competing constraints of scope, schedule, budget, quality, resources, and risk to produce the specified product, service or result.
The project processes are performed by the project team with stakeholder interaction and generally fall into one of two major categories:
- Project management processes. These processes ensure the effective flow of the project throughout its life cycle. These processes encompass the tools and techniques involved in applying the skills and capabilities described in the knowledge areas.
- Product-oriented processes. These processes specify and create projects product. Product-oriented processes are typically defined by the project life cycle and vary by application area as well as the phase of the product life cycle. The scope of the project cannot be defined without some basic understanding of how to create the specified product.
When a project is poorly navigated and falls short of budget and timeline goals, it can cost you more than just money' it can cause irreparable damage to reputation, confidence, and client trust. The answer isn't just dedicated project managers, but instilling your entire team at every level with project management abilities.
Initiate
● Identify a project's stakeholders.
● Establish clear and measurable project outcomes.
● Create a well-defined project scope statement
Plan
● Identify, assess, and manage project risks.
● Create a realistic and well-defined project schedule.
Execute
● Hold team members accountable for project plans.
● Conduct consistent team-accountability sessions.
Monitor & Control
● Create a clear communication plan around the project that includes regular project status reports and project changes.
Close
● Reward and recognize the contributions of project team members.
● Formally close projects by documenting lessons learned
Below is a video explaining the 5 cycles of project management
Project Management Checklist
Project checklists are useful and considered crucial in identifying the needed resources in a project. It also serves as a maintenance tool when you are bombarded with too many tasks that are looming on their deadlines. When you have an organized list of things to do and priorities to take into account, your workflow will be much easier and frantically running back and forth on what task to tackle first is not an option.
It’s a given that once you create a checklist, you have a clear vision of what you’re supposed to do. For project checklists, it’s more than identifying the tasks, but the objectives of the project as well. You don’t limit your project checklist on your designated tasks, but rather you have to extend that reach to your team and the progress of the project.
A very informative and common list on how to create a project management checklist is provided below;
Understand Your Role
Having a clear understanding of your role is an important pillar of a successful project. Even if it isn’t documented on paper, it will help you ensure that all stakeholders are considered and that you’re aware of your responsibilities in case issues arise.
Identify the Stakeholders
A project is successful when it has met the expectations of all stakeholders. A stakeholder can be anybody directly or indirectly impacted by the project. It is not always easy to determine the project’s stakeholders, particularly those affected indirectly. A stakeholder could be:
- The client
- The project manager
- The project teams
- Consultants
Write a Project Plan
Now you’ve gathered enough information to start planning the project. Use whatever project planning tool that works for you, be it Trello, Scoro, or even a simple spreadsheet.
Some tools are more comprehensive than others, but a rock-solid project plan can be achieved in any solution as long as it helps you to formalize your thoughts and keep consistency
Set Goals
The first step in creating any project plan is setting achievable goals. Meet with the stakeholders and discuss the possible outcomes. Turn the output into a comprehensive list and prioritize the needs. A good technique for doing this is reviewing them against the SMART principle.
The acronym SMART has several slightly different variations, which you can modify depending on your project:
S – specific, significant
M – measurable, motivational
A – agreed upon, attainable, action-oriented
R – realistic, relevant, rewarding, results-oriented
T – time-bound, tangible, trackable
Create a Vision
From the smaller goals, create a wider vision statement. Without a strong, shared vision, it’s hard to gather the momentum needed to get the project off the ground.
The vision statement should explain what the project is hoping to achieve in a few details:
- Where does the project fit with the overall business strategy?
- What will be the project’s outcome?
- How will the project benefit the stakeholders?
Develop the Budget
A project budget is a detailed, time-based estimate of all the costs for your project. You typically develop a budget in phases – from an initial estimate to a detailed version to the final approved project budget.
When starting a project, it is difficult to know how much it will eventually cost – and with so much uncertainty in projects, it can be one of the project manager’s greatest challenges.
Your project budget will be made up of different direct and indirect costs, with a small amount assigned for contingency reserve.
Once you have an idea of how long a project is going to take and how much resources you need, you can calculate the approximate total for the direct and indirect costs.
Determine the Direct Costs
These costs are directly attributed to the project and charged on an item-by-item basis.
- Labour (people) costs
- Consultant fees
- Raw material costs
- Software licences
- Travel costs
Determine the Indirect Costs
These costs signify resources that benefit more than one project, and only a proportion of their total cost is charged to the project.
- Telephone charges
- Office space rent
- Office equipment costs
- General administration costs
- Company insurance costs
Add the Contingency Reserve
Don’t forget to reserve a buffer for your project to cover risks – the contingency reserve. Usually, it’s a percentage of the total project cost and time.
Create a Resource Allocation Plan
An organization’s resources include people, equipment, materials, knowledge, and time.
Find out what resources are available for the project, now and in the future. A resource allocation plan is an important tool in the effective management of scarce resources.
Describe the type of resources needed and the timing of that need. As the project schedule changes, the resource plan must be flexible enough to adjust as these alterations occur.
A Resource Plan will help you to:
- Identify the number of resources required per project activity
- Plan the timeline for using or consuming these resources
- Create a detailed resource utilization schedule
Establish the Deliverables
Using the previously defined goals, create a list of things the project needs to deliver to meet those goals. Simply put – tasks and subtasks. Specify when and how to deliver each item.
Add notes to tasks that might seem confusing or need an explanation. It never hurts to add detail!
Create a Timeline
Create a list of tasks that need to be carried out for each identified deliverable. For each task, determine the following:
- The amount of effort (hours, days, etc.) required for completing the task
- The responsible person who will carry out the task
Once you have established the amount of time needed for each task, you can work out the effort required for each deliverable, and delivery date.
At this point in the planning, you can use project planning software such as Scoro, Wrike, MS Project or any of your choosing, to create your project schedule. Alternatively, use one of the many free templates available.
(Re-)Assess the Deadline
A common problem discovered at this point is that you have an imposed delivery deadline from the client, that, based on your estimates, is unrealistic.
If you discover that you can’t deliver the project in time, you must contact the client immediately.
The options you have:
- Renegotiate the deadline (project delay)
- Employ additional resources (increased cost)
- Reduce the scope of the project (fewer deliverables)
Use the previously created project schedule to justify pursuing one of these options.
Create a Communications Plan
A project must begin with clear communication of the project goals and the effort required to meet them.
Create a document showing:
- Who should be informed about the project?
- How often and when should they be informed
- How will they receive the information?
The most common reporting tool is the weekly or monthly status report, describing how the project is performing, milestones achieved, and the work you’ve planned for the next period.
Create a Risk Management Plan
Although often overlooked, risk management is an important part of project management. It is important to identify as many risks to your project as possible and be prepared if something bad happens.
Here are some examples of common project risks:
- Unclear roles and responsibilities
- Poor communication resulting in misunderstandings, quality problems and rework
- Stakeholders adding or changing requirements after the project has started
- Lack of resource commitment
- Misunderstanding stakeholder needs
- No stakeholder input obtained
- Too optimistic time and cost estimates
Remember: Ignoring risks doesn’t make them go away
Manage the Documentation
To keep the project transparent and everyone on the same page, keep your project plan attached to other project-related documents such as the proposal, time logs, work reports, meeting notes, or anything else that might come in handy.
Format
Having followed this checklist, you should now have an excellent and actionable project plan. Now it’s time to match the content with appearance.
- Include the project information such as the client & project name
- Add your company’s (and the client’s) logo
- Use your company’s branded fonts and colour scheme
Track the Progress
Congratulations, you made it! Don’t forget to update your plan as the project makes progress, and continually measure progress against the plan.
Project managers often use a project KPI dashboard that provides a quick overview of the project’s performance and updates. Having a real-time overview of the KPIs helps to make informed decisions and achieve long-term goals.
Project checklists are useful and considered crucial in identifying the needed resources in a project. It also serves as a maintenance tool when you are bombarded with too many tasks that are looming on their deadlines. When you have an organized list of things to do and priorities to take into account, your workflow will be much easier and frantically running back and forth on what task to tackle first is not an option.
It’s a given that once you create a checklist, you have a clear vision of what you’re supposed to do. For project checklists, it’s more than identifying the tasks, but the objectives of the project as well. You don’t limit your project checklist on your designated tasks, but rather you have to extend that reach to your team and the progress of the project.
A very informative and common list on how to create a project management checklist is provided below;
Understand Your Role
Having a clear understanding of your role is an important pillar of a successful project. Even if it isn’t documented on paper, it will help you ensure that all stakeholders are considered and that you’re aware of your responsibilities in case issues arise.
Identify the Stakeholders
A project is successful when it has met the expectations of all stakeholders. A stakeholder can be anybody directly or indirectly impacted by the project. It is not always easy to determine the project’s stakeholders, particularly those affected indirectly. A stakeholder could be:
- The client
- The project manager
- The project teams
- Consultants
Write a Project Plan
Now you’ve gathered enough information to start planning the project. Use whatever project planning tool that works for you, be it Trello, Scoro, or even a simple spreadsheet.
Some tools are more comprehensive than others, but a rock-solid project plan can be achieved in any solution as long as it helps you to formalize your thoughts and keep consistency
Set Goals
The first step in creating any project plan is setting achievable goals. Meet with the stakeholders and discuss the possible outcomes. Turn the output into a comprehensive list and prioritize the needs. A good technique for doing this is reviewing them against the SMART principle.
The acronym SMART has several slightly different variations, which you can modify depending on your project:
S – specific, significant
M – measurable, motivational
A – agreed upon, attainable, action-oriented
R – realistic, relevant, rewarding, results-oriented
T – time-bound, tangible, trackable
Create a Vision
From the smaller goals, create a wider vision statement. Without a strong, shared vision, it’s hard to gather the momentum needed to get the project off the ground.
The vision statement should explain what the project is hoping to achieve in a few details:
- Where does the project fit with the overall business strategy?
- What will be the project’s outcome?
- How will the project benefit the stakeholders?
Develop the Budget
A project budget is a detailed, time-based estimate of all the costs for your project. You typically develop a budget in phases – from an initial estimate to a detailed version to the final approved project budget.
When starting a project, it is difficult to know how much it will eventually cost – and with so much uncertainty in projects, it can be one of the project manager’s greatest challenges.
Your project budget will be made up of different direct and indirect costs, with a small amount assigned for contingency reserve.
Once you have an idea of how long a project is going to take and how much resources you need, you can calculate the approximate total for the direct and indirect costs.
Determine the Direct Costs
These costs are directly attributed to the project and charged on an item-by-item basis.
- Labour (people) costs
- Consultant fees
- Raw material costs
- Software licences
- Travel costs
Determine the Indirect Costs
These costs signify resources that benefit more than one project, and only a proportion of their total cost is charged to the project.
- Telephone charges
- Office space rent
- Office equipment costs
- General administration costs
- Company insurance costs
Add the Contingency Reserve
Don’t forget to reserve a buffer for your project to cover risks – the contingency reserve. Usually, it’s a percentage of the total project cost and time.
Create a Resource Allocation Plan
An organization’s resources include people, equipment, materials, knowledge, and time.
Find out what resources are available for the project, now and in the future. A resource allocation plan is an important tool in the effective management of scarce resources.
Describe the type of resources needed and the timing of that need. As the project schedule changes, the resource plan must be flexible enough to adjust as these alterations occur.
A Resource Plan will help you to:
- Identify the number of resources required per project activity
- Plan the timeline for using or consuming these resources
- Create a detailed resource utilization schedule
Establish the Deliverables
Using the previously defined goals, create a list of things the project needs to deliver to meet those goals. Simply put – tasks and subtasks. Specify when and how to deliver each item.
Add notes to tasks that might seem confusing or need an explanation. It never hurts to add detail!
Create a Timeline
Create a list of tasks that need to be carried out for each identified deliverable. For each task, determine the following:
- The amount of effort (hours, days, etc.) required for completing the task
- The responsible person who will carry out the task
Once you have established the amount of time needed for each task, you can work out the effort required for each deliverable, and delivery date.
At this point in the planning, you can use project planning software such as Scoro, Wrike, MS Project or any of your choosing, to create your project schedule. Alternatively, use one of the many free templates available.
(Re-)Assess the Deadline
A common problem discovered at this point is that you have an imposed delivery deadline from the client, that, based on your estimates, is unrealistic.
If you discover that you can’t deliver the project in time, you must contact the client immediately.
The options you have:
- Renegotiate the deadline (project delay)
- Employ additional resources (increased cost)
- Reduce the scope of the project (fewer deliverables)
Use the previously created project schedule to justify pursuing one of these options.
Create a Communications Plan
A project must begin with clear communication of the project goals and the effort required to meet them.
Create a document showing:
- Who should be informed about the project?
- How often and when should they be informed
- How will they receive the information?
The most common reporting tool is the weekly or monthly status report, describing how the project is performing, milestones achieved, and the work you’ve planned for the next period.
Create a Risk Management Plan
Although often overlooked, risk management is an important part of project management. It is important to identify as many risks to your project as possible and be prepared if something bad happens.
Here are some examples of common project risks:
- Unclear roles and responsibilities
- Poor communication resulting in misunderstandings, quality problems and rework
- Stakeholders adding or changing requirements after the project has started
- Lack of resource commitment
- Misunderstanding stakeholder needs
- No stakeholder input obtained
- Too optimistic time and cost estimates
Remember: Ignoring risks doesn’t make them go away
Manage the Documentation
To keep the project transparent and everyone on the same page, keep your project plan attached to other project-related documents such as the proposal, time logs, work reports, meeting notes, or anything else that might come in handy.
Format
Having followed this checklist, you should now have an excellent and actionable project plan. Now it’s time to match the content with appearance.
- Include the project information such as the client & project name
- Add your company’s (and the client’s) logo
- Use your company’s branded fonts and colour scheme
Track the Progress
Congratulations, you made it! Don’t forget to update your plan as the project makes progress, and continually measure progress against the plan.
Project managers often use a project KPI dashboard that provides a quick overview of the project’s performance and updates. Having a real-time overview of the KPIs helps to make informed decisions and achieve long-term goals.
References
References
Covey.F. Project Management. Retrieved from https://www.franklincovey.com/Solutions/Productivity/project-management.html
Project.(May 2013). Project Management Checklist. Retrieved from https://project-management.com/project-management-checklist/
Project. (December 2017). Why is it important to have a project checklist?. Retrieved from https://www.project-management.pm/project-checklist/
Scoro.(August 2019).The Ultimate Project Management Checklist. Retrieved from https://www.scoro.com/blog/project-management-checklist
2013 Project Management Institute. A Guide to the Project Management Body of Knowledge (PMBOK Guide). Fifth Edition
References
Covey.F. Project Management. Retrieved from https://www.franklincovey.com/Solutions/Productivity/project-management.html
Project.(May 2013). Project Management Checklist. Retrieved from https://project-management.com/project-management-checklist/
Project. (December 2017). Why is it important to have a project checklist?. Retrieved from https://www.project-management.pm/project-checklist/
Scoro.(August 2019).The Ultimate Project Management Checklist. Retrieved from https://www.scoro.com/blog/project-management-checklist
2013 Project Management Institute. A Guide to the Project Management Body of Knowledge (PMBOK Guide). Fifth Edition
|
oercommons
|
2025-03-18T00:38:21.876302
|
11/22/2019
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/59988/overview",
"title": "Project Management",
"author": "Oula Almadhoun"
}
|
https://oercommons.org/courseware/lesson/82479/overview
|
Diversity and Inclusion in Global Enterprises Questions
Leadership Questions
Principles of Management
Overview
OER BUS 210 Principles of Management
OER BUS 210 Principles of Management
|
oercommons
|
2025-03-18T00:38:21.895575
|
06/16/2021
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/82479/overview",
"title": "Principles of Management",
"author": "Ashli Ree"
}
|
https://oercommons.org/courseware/lesson/101633/overview
|
Pavlov conditioning meme
Walowitz memory meme
Yoda memory meme
Juarez REMIX attempt
Overview
Just trying this out, not really ready to load ACTUAL materials yet. But, here is a funny meme.
Meme opportunity
This is a current extra credit opportunity in several of my classes and I modify it based upon the class to help them see what it is that they are supposed to do. The example that I am placing here is for an introduction to psychology course in the Memory section.
MY OER Goals and Purpose
My OER Goals & Purpose: That I can remix within this platform and it isn't as challenging as originally thought.
My Audience: Right now, this is just for this requirement. But, I am planning on trying a remix of a Developmental Psychology textbook for all of our Developmental Psychology students who take this class to meet psy degree requirements and nursing requirements.
My Team: No one.
Existing Resources: I have a ton or resources in my Moodle classroom and the OER books that I use now.
New Resources: I don't know that I will need ANY new resources! I keep pretty up-to-date!
Supports Needed: Time, time, and more time.
Our Timeline: I am supposed to have my first project finished by the end of this semester. Unfortunately, that one went belly up because I don't see the point in submitting for adoption a book that I won't use because the book I already use is already in the OER commons.
MEME EC Assignment
Social media is a strange and wondrous place, where memes take on lives of their own, and circulate all over the virtual world. A meme is a powerful virtual sound bite – the image and the words stick in our minds. This presents us [psychological scientists] with a unique challenge AND an opportunity. We can give useful information away, as memes.
STEP 1 (UP TO 3 points): The goal of this assignment is for you to communicate some of the concepts you’ve learned in this section (memory) in a quick, effective way by turning them into memes. I want for you to be able to communicate a scientific idea in a quick, accessible way. To do this, I recommend that you first choose a concept from section (memory) that was interesting to you, then think about the sound-bite you’d like to communicate within that concept. Then, think about the best way to make it into a visual. You are encouraged to be funny in your memes, but comedic brilliance is not a requirement. Here are some examples:
Rules:
- Your memes should be submitted as image files (e.g., .jpg, .png) to this forum discussion.
- Any images (pictures) you use must be of you (this way you cannot pull it off of the internet), and you cannot simply mimic one that you found on the internet (NO cheating).
- Along with the image file, please write a very brief (1-3 sentences) explanation of your meme – just state in plain English what the idea is that you are trying to communicate (you can type this part directly into the discussion forum box).
Each meme will be graded based on how well you (a) follow the instructions here, (b) create something that is easy to understand, and (c) communicate correct information. If you do all of these things, you will get full credit.
STEP 2 (UP TO 2 points): In order to get full credit, you must not only post your reply, but also respond/reply to at least ONE other student. Your response/reply must be substantive in nature. You may not simply say, "Yeah, I like what you said." It must be thoughtful, thorough, and further a conversation. Please follow the TQQE method. This means to share your Thoughts on his/her post, find one Quote that you agree/disagree with and discuss, list at least one lingering Question you have about the content or the person's response, and provide any/all Epiphanies that you had either responding to the prompt or from reading this person's response.
HAVE A BLAST with this!
Reflection
Seeing as we adopted 100% OER in PSY in 2018, there have been many benefits to our students and faculty. Students save a ton of money. Faculty don't have to wait for financial aid disbursement dates in order to see students actually engaging with textbook content. The benefits are significant. Yes, it requires that we get creative for ancillary materials, but that is ok.
|
oercommons
|
2025-03-18T00:38:21.921262
|
03/07/2023
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/101633/overview",
"title": "Juarez REMIX attempt",
"author": "Kristin Juarez"
}
|
https://oercommons.org/courseware/lesson/96058/overview
|
Social Justice Mathematics Project 4: Gerrymandering
Overview
This project will explore the idea of election fairness through the concept of Gerrymandering. Gerrymandering is a means of unfairly drawing district boundaries that favor one party over another.There are legal concepts and mathematical concepts that can be considered in determining the fairness of district boundaries.
Objective:
Students will:
- Explore shapes that create fair voting districts.
- Calculate compactness as a measure for voting fairness.
- Discuss the implications of using compactness to measure voting fairness.
Social Justice Mathematics Project 4 "Gerrymandering": Exploring the Information Introduction
This project will explore the idea of election fairness through the concept of Gerrymandering. Gerrymandering is a means of unfairly drawing district boundaries that favor one party over another.There are legal concepts and mathematical concepts that can be considered in determining the fairness of district boundaries.
Objective:
Students will:
- Explore shapes that create fair voting districts.
- Calculate compactness as a measure for voting fairness.
- Discuss the implications of using compactness to measure voting fairness.
Social Justice Mathematics Project 4 "Gerrymandering": Exploring Politics and Math
Under the terms of the Constitution, state legislatures are entitled to drawing congressional districts, and take the sole role of doing so in most states. Some states have opted to have independent commissions draw their districts, while others have advisory commissions, though the final decision is still made by the legislature.In states with only one representative (Alaska, Delaware, Montana, North Dakota, South Dakota, Vermont, Wyoming), it’s easy: the whole state is the one and only district (called an “at-large” district). In the other states, there are many legal restrictions. The easiest to describe are as follows:
• Districts must be (roughly) the same size in population within each state. (A violation of this is called malapportionment.)
• Districts must be contiguous: A person must be able to walk between any two points within the district while remaining in the district.
• Districts must be compact though there is no satisfactory definition of this.
• Districts must respect communities of interest such as neighborhoods, minority communities, etc.
• Districts must not be drawn with racial concerns as the “predominant factor”.
Gerrymandering is the act of purposefully drawing district lines to favor one political group/party over others. • It is named for Massachusetts Governor Elbridge Gerry, who in 1812 approved a map for state senate districts which contained one oddly shaped district, believed to be drawn to favor his Democratic-Republican Party. • Its shape was likened to a monster and a salamander by commentators, resulting in the portmanteau “Gerry-mander”.
But are strange shapes necessarily bad? Consider Illinois’s Fourth Congressional District, which is frequently lambasted for its peculiar “earmuffs” shape. This odd shape doesn’t necessarily demonstrate bad intentions. In this case, the district was “gerrymandered” so as to connect two majority Hispanic parts of Chicago, thereby providing a common voice to this demographic. So it’s not unprecedented to sacrifice shape in favor of a more substantive ideal.
Social Justice Mathematics Project 4 "Gerrymandering": Exploring the Information
Introduction:
Compactness in the redistricting setting is a way to describe shapes that might make for more fair districts for vorting purposes. The basic idea is that the shapes of electoral districts should not be too stretched out nor should the boundaries look like undulating or jagged. There are two measures that we will use to determine whether a certain district (consisting of the area of a shape that is formed by a closed loop boudnary) represents a fair "shape". For the first measure, Polsby-Popper givces a quantification of the jaggedness of a planar shapes boundaries. Basically, if it is too jagged, it is not fair. For the second measure, Reock quantifies the dispersion or oblongness of a shape. Thsi measure essentially claims that a circle is the most fair shape.
Both measures are based on something called the isoperimetric inequality which states that:
\(L^2\ge4\pi(A)\)
Where A is the area enclosed by a planar curve of length L. The only shape for which equality exists between the left and right side is the circle. In that case L= Circumference = C. So since,
\(C=2 \pi r\)
and
\(A = \pi r^2\)
we can see that:
\(L^2 = C^2 = (2 \pi r)^2= 4 \pi^2 r^2 = 4 \pi \cdot \pi r^2 = 4\pi \cdot A\)
Finally, note that the Polsby-Popper measure is the ratio:
\((4 \pi A) \over L^2\)
Answer the following question/s:
1. Suppose each dot is a voter. Notice that the red voters win the majority in the first two districts and the blue voters win the majority in the last three districts. The Polsby-Popper Measure for the first districting option is done for you. Compute the Polsby Popper Measure for the last two districting shapes and determine which of the political parties (blue or red) wins each district.
Districting Option #1
Each district has a length of 10 and a width of 1. Therefore L=Perimeter=22 units. The area of each column/district is 10. Therefore the Polsby-Popper measure is:
\({4 \pi A \over L^2} = {4 \pi 10 \over 22^2} = {40 \pi \over 484} = {125.7 \over 484} = 0.26 \)
Your turn:
Districting Option #2.
Districting Option #3.
Social Justice Mathematics Project 4 "Gerrymandering": Looking at the Concepts More Deeply
These concepts are relevant because since 1967, states which are apportioned more than one representative have been required to be divided into districts (i.e., physical regions which partition the state), each of which must hold its own election for a representative using the plurality method. We will consider more unusual shapes within the rectangular whole.
1. First, compute the Polsby-Popper Measure for each of the following districts, and determine who wins each district (Stars vs. Blanks).
2. Here is a set of questions which starts with the same set-up as the first examples, but it is up to you to create districts with the following criteria:
- Draw 5 districts of 10 people in which the districting results in 3 blue and 2 red districts?
- Draw 5 districts of 10 people in which the districting results in 5 blue districts?
- Draw 5 districts of 10 people in which the districting results in 2 blue and 3 red districts?
3. Finally, consider the following "state" in which there are 36 people, 20 which are blue and 16 of which are "red".
- Can you draw 4 districts of 9 people which result in 4 "blue" districts?
- Can you draw 4 districts of 9 people which result in 1 blue, and 3 red districts?
|
oercommons
|
2025-03-18T00:38:21.941880
|
Political Science
|
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"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/96058/overview",
"title": "Social Justice Mathematics Project 4: Gerrymandering",
"author": "Measurement and Data"
}
|
https://oercommons.org/courseware/lesson/119331/overview
|
What is a Resume?
What is included in a resume and cover letter.
Creating A Resume and Cover Letter
Overview
Create and print (hard copy or digital) documents to aid in obtaining employment such as online resumes, applications, and cover letters.
Students will understand the importance of writing an effective resume and cover letter.
Instructions
Objectives:
Create and print (hard copy or digital) documents to aid in obtaining employment such as online resumes, applications, and cover letters.
Resumes and cover letters are essential tools for applying to jobs, internships, or even college programs. Follow the instructions below to create a professional resume and cover letter that showcase your skills, experiences, and strengths.
1. Read the PowerPoint provided on what is included in a resume and cover letter.
2. Watch the video: What is a Resume?
3. Read Units 1 and 2 about Resume Writing from Saylor Academy.
4. Create a resume and a cover letter using the app of your choice. Be sure to include the key components covered in the reading material.
|
oercommons
|
2025-03-18T00:38:21.961441
|
Homework/Assignment
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/119331/overview",
"title": "Creating A Resume and Cover Letter",
"author": "Full Course"
}
|
https://oercommons.org/courseware/lesson/123535/overview
|
Introduction to Chemistry Labs: Aqueous reactions
Overview
Laboratory Manual of Introduction to Chemistry
Equeous Reactions
Aqueous Reactions
Please watch the video of this experiment
Many chemical reactions occur in an aqueous solution. A solution is a homogeneous mixture of a solute dissolved in a solvent. Solutions may involve gases (such as air), liquids (e.g., blood), or even solids (steel). We will usually deal with aqueous solutions in which water is the solvent.
Solutions allow chemical and biological reactions to happen quickly by providing the medium that brings reactants to close together so they can rearrange and reform. Solutions are also the means by which substances can be transported from one place to another. Liquid solutions are particularly important in geological, environmental, biological, and chemical systems; the universal solvent for these solutions is water. The extent to which these processes occur is determined by the relative strengths of the solute-solute, solute-water, and water-water interactions.
Chemical reactions in aqueous solution may be divided into four major types: precipitation, acid-base, oxidation-reduction, and complexation. This lab will focus on precipitation reactions, in which an insoluble compound is produced from the aqueous reactant solutions.
In Part I, two representative substances (Kl and Pb(N03)2 will be used to investigate the solution properties, the principle of solubility, and the reaction properties of aqueous solutions.
In Part II, a variety of precipitation reactions will be performed by combining aqueous solutions of ionic compounds in pairs, and the reactions that occur will be analyzed and described.
Part I: Why Use Solutions for Reactions?
- Use a spatula to place a small number of Kl crystals on a clean, dry laptop.
Use a (different) spatula to place a few crystals of Pb(N03)2 about 1 cm away from the Kl crystals.
- Push the crystals of Kl and Pb(N03)2 together and gently stir to mix. Record your observations.
- How well do solid Kl and Pb(N03)2 react in the absence of water? Explain
- Add a few drops of H20 to the KI/Pb(N03)2. Gently stir to mix. Record your observations.
- How well do solid Kl and Pb(N03)2 react in the presence of water? Explain
- A pipette makes a pool of water about 5 cm in diameter on the laptop.
Carefully place a few Pb(N03)2 crystals near, but not in, one side of the pool.
Place a few crystals of Kl near, but not in, the other
side of the pool.
- Gently push the Pb(N03)2 crystals into their edge of the pool, and then push the Kl crystals into the other edge. Record your observations.
- Briefly but completely explain the chemistry of what was observed.
- Would it matter if the Kl had been added to the water first and the Pb(N03)2 seconds?
- Based on your results from this investigation, briefly explain why it is important to use solutions to carry out chemical reactions of this type.
Part II: A Bunch o' Chemical Reactions in Aqueous Solutions
- Start with the laptop surface's upper left box in the Reaction Grid. Place 1 drop of Pb(N03)2 solution in the middle of the box, then carefully add one drop of Kl solution.
Describe the appearance of each of the initial solutions before mixing. Then, observe and record any visible changes (such as a color change, formation of a precipitate, the evolution of a gas, etc.) that you observe.
Note: The Grid background is both white and black. Color changes are more easily seen on a white background. The precipitate formation can be seen better on the black background. Please complete the following table:
Observation Table:
Please write your observation of the reaction of every two reagents in the cross square.
Column1Column2Column3Column4Column5Column6Column7Column8
| |||||||
KI | NaCl | Na2SO4 | Na3PO4 | NaC2H3O | Na2CO3 | NaOH | |
Pb(NO3)2 | |||||||
AgNO3 | |||||||
CaCl2 | |||||||
CuCl2 | |||||||
FeNO3 | |||||||
- Repeat this procedure in the top row of the following box, but this time, combine one drop of NaCl with one drop of Pb(N03)2.
- Continue this binary-mixing process in all the other boxes, using the appropriate aqueous solutions indicated on the Reaction Grid. Record your initial and final.
Important Note: Avoid cross-contamination between the pipettes and the solutions on the laptop since this will severely affect your results.
- If you doubt the results of any (possible) reaction, repeat it. If appropriate, add more drops of either substance, stir again, Feel free to explore to your heart's content!
- When done, clean the laptop surface and dispose of the mixtures. Wash your hands with.
Extra Points assignment:
Please watch this video about the Net ionic equation and spectator Ions
Analysis
For each of the following combinations:
|
c) Indicate whether a precipitation reaction has occurred (or not).
d)Identify all spectator ions and state the name of the solid.
1) Reaction of solution of lead(II) nitrate with solution of potassium iodide
2) Reaction of solution of sodium chloride with solution of silver nitrate
3) Reaction of solution of Calcium chloride with solution of sodium sulfate
4) Reaction of solution of silver nitrate with solution of sodium phosphate
5) Reaction of calcium chloride with the solution of sodium phosphate
6) Reaction of solution of sodium acetate with the solution of lead nitrate
7) Reaction of solution of sodium chloride with solution of copper(II) chloride
8) Reaction of solution of Iron(IIi) nitrate with solution of sodium chloride
Your summary of the procedure:
Observations made during the Lab:
List all chemical equations used in the lab:
List all calculations used in the lab:
Answers to any questions posed in the lab:
The results/conclusion of the lab:
Discussion (This section should be very brief and should include conclusions, and the student discusses what can be done in future experiments to prevent any errors and improve results.):
Thanks to Mark Blaser, Shasta College, for the original experimental procedure.
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oercommons
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2025-03-18T00:38:21.992071
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01/05/2025
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https://oercommons.org/courseware/lesson/114774/overview
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Dari: An Introductory Course (Teacher’s Edition)
Overview
This textbook serves as a foundational component in a series of proficiency-based Dari materials designed for adult learners. The Teacher's Edition provides a thorough framework for teaching Dari's speaking, writing, listening, and reading aspects, complete with exercise instructions and solutions. Targeting ACTFL's Novice High/Intermediate Low or ILR levels 0+/1, it emphasizes critical thinking and incorporates pedagogical strategies like Bloom's Taxonomy for intellectual growth. Interactive activities included in the PDF and EPUB formats, available on the LMI website (languagementors.org), make learning Dari dynamic and engaging.
Dari: An Introductory Course (Teacher’s Edition)
This textbook serves as a foundational component in a series of proficiency-based Dari materials designed for adult learners. The Teacher's Edition provides a thorough framework for teaching Dari's speaking, writing, listening, and reading aspects, complete with exercise instructions and solutions. Targeting ACTFL's Novice High/Intermediate Low or ILR levels 0+/1, it emphasizes critical thinking and incorporates pedagogical strategies like Bloom's Taxonomy for intellectual growth. Interactive activities included in the PDF and EPUB formats, available on the LMI website (languagementors.org), make learning Dari dynamic and engaging.
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oercommons
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2025-03-18T00:38:22.010451
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Textbook
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"title": "Dari: An Introductory Course (Teacher’s Edition)",
"author": "World Cultures"
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https://oercommons.org/courseware/lesson/15323/overview
|
Introduction
The summer sun shines brightly on a deserted stretch of beach. Suddenly, a tiny grey head emerges from the sand, then another and another. Soon the beach is teeming with loggerhead sea turtle hatchlings (Figure). Although only minutes old, the hatchlings know exactly what to do. Their flippers are not very efficient for moving across the hot sand, yet they continue onward, instinctively. Some are quickly snapped up by gulls circling overhead and others become lunch for hungry ghost crabs that dart out of their holes. Despite these dangers, the hatchlings are driven to leave the safety of their nest and find the ocean.
Not far down this same beach, Ben and his son, Julian, paddle out into the ocean on surfboards. A wave approaches. Julian crouches on his board, then jumps up and rides the wave for a few seconds before losing his balance. He emerges from the water in time to watch his father ride the face of the wave.
Unlike baby sea turtles, which know how to find the ocean and swim with no help from their parents, we are not born knowing how to swim (or surf). Yet we humans pride ourselves on our ability to learn. In fact, over thousands of years and across cultures, we have created institutions devoted entirely to learning. But have you ever asked yourself how exactly it is that we learn? What processes are at work as we come to know what we know? This chapter focuses on the primary ways in which learning occurs.
References
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Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. Journal of Abnormal and Social Psychology, 63, 575–582.
Cangi, K., & Daly, M. (2013). The effects of token economies on the occurrence of appropriate and inappropriate behaviors by children with autism in a social skills setting. West Chester University: Journal of Undergraduate Research. Retrieved from http://www.wcupa.edu/UndergraduateResearch/journal/documents/cangi_S2012.pdf
Carlson, L., Holscher, C., Shipley, T., & Conroy Dalton, R. (2010). Getting lost in buildings. Current Directions in Psychological Science, 19(5), 284–289.
Cialdini, R. B. (2008). Influence: Science and practice (5th ed.). Boston, MA: Pearson Education.
Chance, P. (2009). Learning and behavior (6th ed.). Belmont, CA: Wadsworth, Cengage Learning.
DeAngelis, T. (2010). ‘Little Albert’ regains his identity. Monitor on Psychology, 41(1), 10.
Franzen, H. (2001, May 24). Gambling, like food and drugs, produces feelings of reward in the brain. Scientific American [online]. Retrieved from http://www.scientificamerican.com/article.cfm?id=gamblinglike-food-and-dru
Fryer, R. G., Jr. (2010, April). Financial incentives and student achievement: Evidence from randomized trials. National Bureau of Economic Research [NBER] Working Paper, No. 15898. Retrieved from http://www.nber.org/papers/w15898
Garcia, J., & Koelling, R. A. (1966). Relation of cue to consequence in avoidance learning. Psychonomic Science, 4, 123–124.
Garcia, J., & Rusiniak, K. W. (1980). What the nose learns from the mouth. In D. Müller-Schwarze & R. M. Silverstein (Eds.), Chemical signals: Vertebrates and aquatic invertebrates (pp. 141–156). New York, NY: Plenum Press.
Gershoff, E. T. (2002). Corporal punishment by parents and associated child behaviors and experiences: A meta-analytic and theoretical review. Psychological Bulletin, 128(4), 539–579. doi:10.1037//0033-2909.128.4.539
Gershoff, E.T., Grogan-Kaylor, A., Lansford, J. E., Chang, L., Zelli, A., Deater-Deckard, K., & Dodge, K. A. (2010). Parent discipline practices in an international sample: Associations with child behaviors and moderation by perceived normativeness. Child Development, 81(2), 487–502.
Hickock, G. (2010). The role of mirror neurons in speech and language processing. Brain and Language, 112, 1–2.
Holmes, S. (1993). Food avoidance in patients undergoing cancer chemotherapy. Support Care Cancer, 1(6), 326–330.
Hunt, M. (2007). The story of psychology. New York, NY: Doubleday.
Huston, A. C., Donnerstein, E., Fairchild, H., Feshbach, N. D., Katz, P. A., Murray, J. P., . . . Zuckerman, D. (1992). Big world, small screen: The role of television in American society. Lincoln, NE: University of Nebraska Press.
Hutton, J. L., Baracos, V. E., & Wismer, W. V. (2007). Chemosensory dysfunction is a primary factor in the evolution of declining nutritional status and quality of life with patients with advanced cancer. Journal of Pain Symptom Management, 33(2), 156–165.
Illinois Institute for Addiction Recovery. (n.d.). WTVP on gambling. Retrieved from http://www.addictionrecov.org/InTheNews/Gambling/
Jacobsen, P. B., Bovbjerg, D. H., Schwartz, M. D., Andrykowski, M. A., Futterman, A. D., Gilewski, T., . . . Redd, W. H. (1993). Formation of food aversions in cancer patients receiving repeated infusions of chemotherapy. Behaviour Research and Therapy, 31(8), 739–748.
Kirsch, SJ (2010). Media and youth: A developmental perspective. Malden MA: Wiley Blackwell.
Lefrançois, G. R. (2012). Theories of human learning: What the professors said (6th ed.). Belmont, CA: Wadsworth, Cengage Learning.
Miller, L. E., Grabell, A., Thomas, A., Bermann, E., & Graham-Bermann, S. A. (2012). The associations between community violence, television violence, intimate partner violence, parent-child aggression, and aggression in sibling relationships of a sample of preschoolers. Psychology of Violence, 2(2), 165–78. doi:10.1037/a0027254
Murrell, A., Christoff, K. & Henning, K. (2007) Characteristics of domestic violence offenders: associations with childhood exposure to violence. Journal of Family Violence, 22(7), 523-532.
Pavlov, I. P. (1927). Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex (G. V. Anrep, Ed. & Trans.). London, UK: Oxford University Press.
Rizzolatti, G., Fadiga, L., Fogassi, L., & Gallese, V. (2002). From mirror neurons to imitation: Facts and speculations. In A. N. Meltzoff & W. Prinz (Eds.), The imitative mind: Development, evolution, and brain bases (pp. 247–66). Cambridge, United Kingdom: Cambridge University Press.
Rizzolatti, G., Fogassi, L., & Gallese, V. (2006, November). Mirrors in the mind. Scientific American [online], pp. 54–61.
Roy, A., Adinoff, B., Roehrich, L., Lamparski, D., Custer, R., Lorenz, V., . . . Linnoila, M. (1988). Pathological gambling: A psychobiological study. Archives of General Psychiatry, 45(4), 369–373. doi:10.1001/archpsyc.1988.01800280085011
Skinner, B. F. (1938). The behavior of organisms: An experimental analysis. New York, NY: Appleton-Century-Crofts.
Skinner, B. F. (1953). Science and human behavior. New York, NY: Macmillan.
Skinner, B. F. (1961). Cumulative record: A selection of papers. New York, NY: Appleton-Century-Crofts.
Skinner’s utopia: Panacea, or path to hell? (1971, September 20). Time [online]. Retrieved from http://www.wou.edu/~girodm/611/Skinner%27s_utopia.pdf
Skolin, I., Wahlin, Y. B., Broman, D. A., Hursti, U-K. K., Larsson, M. V., & Hernell, O. (2006). Altered food intake and taste perception in children with cancer after start of chemotherapy: Perspectives of children, parents and nurses. Supportive Care in Cancer, 14, 369–78.
Thorndike, E. L. (1911). Animal intelligence: An experimental study of the associative processes in animals. Psychological Monographs, 8.
Tolman, E. C., & Honzik, C. H. (1930). Degrees of hunger, reward, and non-reward, and maze performance in rats. University of California Publications in Psychology, 4, 241–256.
Tolman, E. C., Ritchie, B. F., & Kalish, D. (1946). Studies in spatial learning: II. Place learning versus response learning. Journal of Experimental Psychology, 36, 221–229. doi:10.1037/h0060262
Watson, J. B. & Rayner, R. (1920). Conditioned emotional reactions. Journal of Experimental Psychology, 3, 1–14.
Watson, J. B. (1919). Psychology from the standpoint of a behaviorist. Philadelphia, PA: J. B. Lippincott.
Yamamoto, S., Humle, T., & Tanaka, M. (2013). Basis for cumulative cultural evolution in chimpanzees: Social learning of a more efficient tool-use technique. PLoS ONE, 8(1): e55768. doi:10.1371/journal.pone.0055768
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https://oercommons.org/courseware/lesson/15324/overview
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What Is Learning?
Overview
By the end of this section, you will be able to:
- Explain how learned behaviors are different from instincts and reflexes
- Define learning
- Recognize and define three basic forms of learning—classical conditioning, operant conditioning, and observational learning
Birds build nests and migrate as winter approaches. Infants suckle at their mother’s breast. Dogs shake water off wet fur. Salmon swim upstream to spawn, and spiders spin intricate webs. What do these seemingly unrelated behaviors have in common? They all are unlearned behaviors. Both instincts and reflexes are innate behaviors that organisms are born with. Reflexes are a motor or neural reaction to a specific stimulus in the environment. They tend to be simpler than instincts, involve the activity of specific body parts and systems (e.g., the knee-jerk reflex and the contraction of the pupil in bright light), and involve more primitive centers of the central nervous system (e.g., the spinal cord and the medulla). In contrast, instincts are innate behaviors that are triggered by a broader range of events, such as aging and the change of seasons. They are more complex patterns of behavior, involve movement of the organism as a whole (e.g., sexual activity and migration), and involve higher brain centers.
Both reflexes and instincts help an organism adapt to its environment and do not have to be learned. For example, every healthy human baby has a sucking reflex, present at birth. Babies are born knowing how to suck on a nipple, whether artificial (from a bottle) or human. Nobody teaches the baby to suck, just as no one teaches a sea turtle hatchling to move toward the ocean. Learning, like reflexes and instincts, allows an organism to adapt to its environment. But unlike instincts and reflexes, learned behaviors involve change and experience: learning is a relatively permanent change in behavior or knowledge that results from experience. In contrast to the innate behaviors discussed above, learning involves acquiring knowledge and skills through experience. Looking back at our surfing scenario, Julian will have to spend much more time training with his surfboard before he learns how to ride the waves like his father.
Learning to surf, as well as any complex learning process (e.g., learning about the discipline of psychology), involves a complex interaction of conscious and unconscious processes. Learning has traditionally been studied in terms of its simplest components—the associations our minds automatically make between events. Our minds have a natural tendency to connect events that occur closely together or in sequence. Associative learning occurs when an organism makes connections between stimuli or events that occur together in the environment. You will see that associative learning is central to all three basic learning processes discussed in this chapter; classical conditioning tends to involve unconscious processes, operant conditioning tends to involve conscious processes, and observational learning adds social and cognitive layers to all the basic associative processes, both conscious and unconscious. These learning processes will be discussed in detail later in the chapter, but it is helpful to have a brief overview of each as you begin to explore how learning is understood from a psychological perspective.
In classical conditioning, also known as Pavlovian conditioning, organisms learn to associate events—or stimuli—that repeatedly happen together. We experience this process throughout our daily lives. For example, you might see a flash of lightning in the sky during a storm and then hear a loud boom of thunder. The sound of the thunder naturally makes you jump (loud noises have that effect by reflex). Because lightning reliably predicts the impending boom of thunder, you may associate the two and jump when you see lightning. Psychological researchers study this associative process by focusing on what can be seen and measured—behaviors. Researchers ask if one stimulus triggers a reflex, can we train a different stimulus to trigger that same reflex? In operant conditioning, organisms learn, again, to associate events—a behavior and its consequence (reinforcement or punishment). A pleasant consequence encourages more of that behavior in the future, whereas a punishment deters the behavior. Imagine you are teaching your dog, Hodor, to sit. You tell Hodor to sit, and give him a treat when he does. After repeated experiences, Hodor begins to associate the act of sitting with receiving a treat. He learns that the consequence of sitting is that he gets a doggie biscuit (Figure). Conversely, if the dog is punished when exhibiting a behavior, it becomes conditioned to avoid that behavior (e.g., receiving a small shock when crossing the boundary of an invisible electric fence).
Observational learning extends the effective range of both classical and operant conditioning. In contrast to classical and operant conditioning, in which learning occurs only through direct experience, observational learning is the process of watching others and then imitating what they do. A lot of learning among humans and other animals comes from observational learning. To get an idea of the extra effective range that observational learning brings, consider Ben and his son Julian from the introduction. How might observation help Julian learn to surf, as opposed to learning by trial and error alone? By watching his father, he can imitate the moves that bring success and avoid the moves that lead to failure. Can you think of something you have learned how to do after watching someone else?
All of the approaches covered in this chapter are part of a particular tradition in psychology, called behaviorism, which we discuss in the next section. However, these approaches do not represent the entire study of learning. Separate traditions of learning have taken shape within different fields of psychology, such as memory and cognition, so you will find that other chapters will round out your understanding of the topic. Over time these traditions tend to converge. For example, in this chapter you will see how cognition has come to play a larger role in behaviorism, whose more extreme adherents once insisted that behaviors are triggered by the environment with no intervening thought.
Summary
Instincts and reflexes are innate behaviors—they occur naturally and do not involve learning. In contrast, learning is a change in behavior or knowledge that results from experience. There are three main types of learning: classical conditioning, operant conditioning, and observational learning. Both classical and operant conditioning are forms of associative learning where associations are made between events that occur together. Observational learning is just as it sounds: learning by observing others.
Review Questions
Which of the following is an example of a reflex that occurs at some point in the development of a human being?
- child riding a bike
- teen socializing
- infant sucking on a nipple
- toddler walking
Hint:
C
Learning is best defined as a relatively permanent change in behavior that ________.
- is innate
- occurs as a result of experience
- is found only in humans
- occurs by observing others
Hint:
B
Two forms of associative learning are ________ and ________.
- classical conditioning; operant conditioning
- classical conditioning; Pavlovian conditioning
- operant conditioning; observational learning
- operant conditioning; learning conditioning
Hint:
A
In ________ the stimulus or experience occurs before the behavior and then gets paired with the behavior.
- associative learning
- observational learning
- operant conditioning
- classical conditioning
Hint:
D
Critical Thinking Questions
Compare and contrast classical and operant conditioning. How are they alike? How do they differ?
Hint:
Both classical and operant conditioning involve learning by association. In classical conditioning, responses are involuntary and automatic; however, responses are voluntary and learned in operant conditioning. In classical conditioning, the event that drives the behavior (the stimulus) comes before the behavior; in operant conditioning, the event that drives the behavior (the consequence) comes after the behavior. Also, whereas classical conditioning involves an organism forming an association between an involuntary (reflexive) response and a stimulus, operant conditioning involves an organism forming an association between a voluntary behavior and a consequence.
What is the difference between a reflex and a learned behavior?
Hint:
A reflex is a behavior that humans are born knowing how to do, such as sucking or blushing; these behaviors happen automatically in response to stimuli in the environment. Learned behaviors are things that humans are not born knowing how to do, such as swimming and surfing. Learned behaviors are not automatic; they occur as a result of practice or repeated experience in a situation.
Personal Application Questions
What is your personal definition of learning? How do your ideas about learning compare with the definition of learning presented in this text?
What kinds of things have you learned through the process of classical conditioning? Operant conditioning? Observational learning? How did you learn them?
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https://oercommons.org/courseware/lesson/15325/overview
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Classical Conditioning
Overview
By the end of this section, you will be able to:
- Explain how classical conditioning occurs
- Summarize the processes of acquisition, extinction, spontaneous recovery, generalization, and discrimination
Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you have heard of Pavlov and his famous dogs.
Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his experiments in classical conditioning (Figure). As we discussed briefly in the previous section, classical conditioning is a process by which we learn to associate stimuli and, consequently, to anticipate events.
Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist, not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). In his studies with dogs, Pavlov surgically implanted tubes inside dogs’ cheeks to collect saliva. He then measured the amount of saliva produced in response to various foods. Over time, Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food, at the sight of an empty food bowl, and even at the sound of the laboratory assistants' footsteps. Salivating to food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of an empty bowl or the sound of footsteps.
These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs' “psychic secretions” (Pavlov, 1927). To explore this phenomenon in an objective manner, Pavlov designed a series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a bell, a light, and a touch on the leg. Through his experiments, Pavlov realized that an organism has two types of responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned (learned) responses.
In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder in this situation was an unconditioned stimulus (UCS): a stimulus that elicits a reflexive response in an organism. The dogs’ salivation was an unconditioned response (UCR): a natural (unlearned) reaction to a given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:
In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus. Pavlov would sound a tone (like ringing a bell) and then give the dogs the meat powder (Figure). The tone was the neutral stimulus (NS), which is a stimulus that does not naturally elicit a response. Prior to conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for the dogs. Quite simply this pairing means:
When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned stimulus (CS), which is a stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the sound of the assistants’ footsteps. The behavior caused by the conditioned stimulus is called the conditioned response (CR). In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they began to salivate (CR) in anticipation of food.
Now that you have learned about the process of classical conditioning, do you think you can condition Pavlov’s dog? Visit this website to play the game.
View this video to learn more about Pavlov and his dogs.
REAL WORLD APPLICATION OF CLASSICAL CONDITIONING
How does classical conditioning work in the real world? Let’s say you have a cat named Tiger, who is quite spoiled. You keep her food in a separate cabinet, and you also have a special electric can opener that you use only to open cans of cat food. For every meal, Tiger hears the distinctive sound of the electric can opener (“zzhzhz”) and then gets her food. Tiger quickly learns that when she hears “zzhzhz” she is about to get fed. What do you think Tiger does when she hears the electric can opener? She will likely get excited and run to where you are preparing her food. This is an example of classical conditioning. In this case, what are the UCS, CS, UCR, and CR?
What if the cabinet holding Tiger’s food becomes squeaky? In that case, Tiger hears “squeak” (the cabinet), “zzhzhz” (the electric can opener), and then she gets her food. Tiger will learn to get excited when she hears the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus (“zzhzhz”) is called higher-order conditioning, or second-order conditioning. This means you are using the conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet (Figure). It is hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet (“squeak”), use the can opener (“zzhzhz”), and then feed Tiger, Tiger will likely never get excited when hearing the bell alone.
Classical Conditioning at Stingray City
Kate and her husband Scott recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary stingrays have become accustomed to interacting with humans. About 40 years ago, fishermen began to clean fish and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays would swim in to eat (unconditioned response) what the fishermen threw into the water; this continued for years. By the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs. When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know that they will get to eat (conditioned response).
As soon as Kate and Scott reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped into the water with bags of squid, the stingrays’ favorite treat. The swarm of stingrays bumped and rubbed up against their legs like hungry cats (Figure). Kate and Scott were able to feed, pet, and even kiss (for luck) these amazing creatures. Then all the squid was gone, and so were the stingrays.
Classical conditioning also applies to humans, even babies. For example, Sara buys formula in blue canisters for her six-month-old daughter, Angelina. Whenever Sara takes out a formula container, Angelina gets excited, tries to reach toward the food, and most likely salivates. Why does Angelina get excited when she sees the formula canister? What are the UCS, CS, UCR, and CR here?
So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set boundaries. In this example, the edge of the yard elicits fear and anxiety in the dog. Fear and anxiety are the conditioned response.
For a humorous look at conditioning, watch this video clip from the television show The Office, where Jim conditions Dwight to expect a breath mint every time Jim’s computer makes a specific sound.
GENERAL PROCESSES IN CLASSICAL CONDITIONING
Now that you know how classical conditioning works and have seen several examples, let’s take a look at some of the general processes involved. In classical conditioning, the initial period of learning is known as acquisition, when an organism learns to connect a neutral stimulus and an unconditioned stimulus. During acquisition, the neutral stimulus begins to elicit the conditioned response, and eventually the neutral stimulus becomes a conditioned stimulus capable of eliciting the conditioned response by itself. Timing is important for conditioning to occur. Typically, there should only be a brief interval between presentation of the conditioned stimulus and the unconditioned stimulus. Depending on what is being conditioned, sometimes this interval is as little as five seconds (Chance, 2009). However, with other types of conditioning, the interval can be up to several hours.
Taste aversion is a type of conditioning in which an interval of several hours may pass between the conditioned stimulus (something ingested) and the unconditioned stimulus (nausea or illness). Here’s how it works. Between classes, you and a friend grab a quick lunch from a food cart on campus. You share a dish of chicken curry and head off to your next class. A few hours later, you feel nauseous and become ill. Although your friend is fine and you determine that you have intestinal flu (the food is not the culprit), you’ve developed a taste aversion; the next time you are at a restaurant and someone orders curry, you immediately feel ill. While the chicken dish is not what made you sick, you are experiencing taste aversion: you’ve been conditioned to be averse to a food after a single, negative experience.
How does this occur—conditioning based on a single instance and involving an extended time lapse between the event and the negative stimulus? Research into taste aversion suggests that this response may be an evolutionary adaptation designed to help organisms quickly learn to avoid harmful foods (Garcia & Rusiniak, 1980; Garcia & Koelling, 1966). Not only may this contribute to species survival via natural selection, but it may also help us develop strategies for challenges such as helping cancer patients through the nausea induced by certain treatments (Holmes, 1993; Jacobsen et al., 1993; Hutton, Baracos, & Wismer, 2007; Skolin et al., 2006).
Once we have established the connection between the unconditioned stimulus and the conditioned stimulus, how do we break that connection and get the dog, cat, or child to stop responding? In Tiger’s case, imagine what would happen if you stopped using the electric can opener for her food and began to use it only for human food. Now, Tiger would hear the can opener, but she would not get food. In classical conditioning terms, you would be giving the conditioned stimulus, but not the unconditioned stimulus. Pavlov explored this scenario in his experiments with dogs: sounding the tone without giving the dogs the meat powder. Soon the dogs stopped responding to the tone. Extinction is the decrease in the conditioned response when the unconditioned stimulus is no longer presented with the conditioned stimulus. When presented with the conditioned stimulus alone, the dog, cat, or other organism would show a weaker and weaker response, and finally no response. In classical conditioning terms, there is a gradual weakening and disappearance of the conditioned response.
What happens when learning is not used for a while—when what was learned lies dormant? As we just discussed, Pavlov found that when he repeatedly presented the bell (conditioned stimulus) without the meat powder (unconditioned stimulus), extinction occurred; the dogs stopped salivating to the bell. However, after a couple of hours of resting from this extinction training, the dogs again began to salivate when Pavlov rang the bell. What do you think would happen with Tiger’s behavior if your electric can opener broke, and you did not use it for several months? When you finally got it fixed and started using it to open Tiger’s food again, Tiger would remember the association between the can opener and her food—she would get excited and run to the kitchen when she heard the sound. The behavior of Pavlov’s dogs and Tiger illustrates a concept Pavlov called spontaneous recovery: the return of a previously extinguished conditioned response following a rest period (Figure).
Of course, these processes also apply in humans. For example, let’s say that every day when you walk to campus, an ice cream truck passes your route. Day after day, you hear the truck’s music (neutral stimulus), so you finally stop and purchase a chocolate ice cream bar. You take a bite (unconditioned stimulus) and then your mouth waters (unconditioned response). This initial period of learning is known as acquisition, when you begin to connect the neutral stimulus (the sound of the truck) and the unconditioned stimulus (the taste of the chocolate ice cream in your mouth). During acquisition, the conditioned response gets stronger and stronger through repeated pairings of the conditioned stimulus and unconditioned stimulus. Several days (and ice cream bars) later, you notice that your mouth begins to water (conditioned response) as soon as you hear the truck’s musical jingle—even before you bite into the ice cream bar. Then one day you head down the street. You hear the truck’s music (conditioned stimulus), and your mouth waters (conditioned response). However, when you get to the truck, you discover that they are all out of ice cream. You leave disappointed. The next few days you pass by the truck and hear the music, but don’t stop to get an ice cream bar because you’re running late for class. You begin to salivate less and less when you hear the music, until by the end of the week, your mouth no longer waters when you hear the tune. This illustrates extinction. The conditioned response weakens when only the conditioned stimulus (the sound of the truck) is presented, without being followed by the unconditioned stimulus (chocolate ice cream in the mouth). Then the weekend comes. You don’t have to go to class, so you don’t pass the truck. Monday morning arrives and you take your usual route to campus. You round the corner and hear the truck again. What do you think happens? Your mouth begins to water again. Why? After a break from conditioning, the conditioned response reappears, which indicates spontaneous recovery.
Acquisition and extinction involve the strengthening and weakening, respectively, of a learned association. Two other learning processes—stimulus discrimination and stimulus generalization—are involved in distinguishing which stimuli will trigger the learned association. Animals (including humans) need to distinguish between stimuli—for example, between sounds that predict a threatening event and sounds that do not—so that they can respond appropriately (such as running away if the sound is threatening). When an organism learns to respond differently to various stimuli that are similar, it is called stimulus discrimination. In classical conditioning terms, the organism demonstrates the conditioned response only to the conditioned stimulus. Pavlov’s dogs discriminated between the basic tone that sounded before they were fed and other tones (e.g., the doorbell), because the other sounds did not predict the arrival of food. Similarly, Tiger, the cat, discriminated between the sound of the can opener and the sound of the electric mixer. When the electric mixer is going, Tiger is not about to be fed, so she does not come running to the kitchen looking for food.
On the other hand, when an organism demonstrates the conditioned response to stimuli that are similar to the condition stimulus, it is called stimulus generalization, the opposite of stimulus discrimination. The more similar a stimulus is to the condition stimulus, the more likely the organism is to give the conditioned response. For instance, if the electric mixer sounds very similar to the electric can opener, Tiger may come running after hearing its sound. But if you do not feed her following the electric mixer sound, and you continue to feed her consistently after the electric can opener sound, she will quickly learn to discriminate between the two sounds (provided they are sufficiently dissimilar that she can tell them apart).
Sometimes, classical conditioning can lead to habituation. Habituation occurs when we learn not to respond to a stimulus that is presented repeatedly without change. As the stimulus occurs over and over, we learn not to focus our attention on it. For example, imagine that your neighbor or roommate constantly has the television blaring. This background noise is distracting and makes it difficult for you to focus when you’re studying. However, over time, you become accustomed to the stimulus of the television noise, and eventually you hardly notice it any longer.
BEHAVIORISM
John B. Watson, shown in Figure, is considered the founder of behaviorism. Behaviorism is a school of thought that arose during the first part of the 20th century, which incorporates elements of Pavlov’s classical conditioning (Hunt, 2007). In stark contrast with Freud, who considered the reasons for behavior to be hidden in the unconscious, Watson championed the idea that all behavior can be studied as a simple stimulus-response reaction, without regard for internal processes. Watson argued that in order for psychology to become a legitimate science, it must shift its concern away from internal mental processes because mental processes cannot be seen or measured. Instead, he asserted that psychology must focus on outward observable behavior that can be measured.
Watson’s ideas were influenced by Pavlov’s work. According to Watson, human behavior, just like animal behavior, is primarily the result of conditioned responses. Whereas Pavlov’s work with dogs involved the conditioning of reflexes, Watson believed the same principles could be extended to the conditioning of human emotions (Watson, 1919). Thus began Watson’s work with his graduate student Rosalie Rayner and a baby called Little Albert. Through their experiments with Little Albert, Watson and Rayner (1920) demonstrated how fears can be conditioned.
In 1920, Watson was the chair of the psychology department at Johns Hopkins University. Through his position at the university he came to meet Little Albert’s mother, Arvilla Merritte, who worked at a campus hospital (DeAngelis, 2010). Watson offered her a dollar to allow her son to be the subject of his experiments in classical conditioning. Through these experiments, Little Albert was exposed to and conditioned to fear certain things. Initially he was presented with various neutral stimuli, including a rabbit, a dog, a monkey, masks, cotton wool, and a white rat. He was not afraid of any of these things. Then Watson, with the help of Rayner, conditioned Little Albert to associate these stimuli with an emotion—fear. For example, Watson handed Little Albert the white rat, and Little Albert enjoyed playing with it. Then Watson made a loud sound, by striking a hammer against a metal bar hanging behind Little Albert’s head, each time Little Albert touched the rat. Little Albert was frightened by the sound—demonstrating a reflexive fear of sudden loud noises—and began to cry. Watson repeatedly paired the loud sound with the white rat. Soon Little Albert became frightened by the white rat alone. In this case, what are the UCS, CS, UCR, and CR? Days later, Little Albert demonstrated stimulus generalization—he became afraid of other furry things: a rabbit, a furry coat, and even a Santa Claus mask (Figure). Watson had succeeded in conditioning a fear response in Little Albert, thus demonstrating that emotions could become conditioned responses. It had been Watson’s intention to produce a phobia—a persistent, excessive fear of a specific object or situation— through conditioning alone, thus countering Freud’s view that phobias are caused by deep, hidden conflicts in the mind. However, there is no evidence that Little Albert experienced phobias in later years. Little Albert’s mother moved away, ending the experiment, and Little Albert himself died a few years later of unrelated causes. While Watson’s research provided new insight into conditioning, it would be considered unethical by today’s standards.
View scenes from John Watson’s experiment in which Little Albert was conditioned to respond in fear to furry objects.
As you watch the video, look closely at Little Albert’s reactions and the manner in which Watson and Rayner present the stimuli before and after conditioning. Based on what you see, would you come to the same conclusions as the researchers?
Advertising and Associative Learning
Advertising executives are pros at applying the principles of associative learning. Think about the car commercials you have seen on television. Many of them feature an attractive model. By associating the model with the car being advertised, you come to see the car as being desirable (Cialdini, 2008). You may be asking yourself, does this advertising technique actually work? According to Cialdini (2008), men who viewed a car commercial that included an attractive model later rated the car as being faster, more appealing, and better designed than did men who viewed an advertisement for the same car minus the model.
Have you ever noticed how quickly advertisers cancel contracts with a famous athlete following a scandal? As far as the advertiser is concerned, that athlete is no longer associated with positive feelings; therefore, the athlete cannot be used as an unconditioned stimulus to condition the public to associate positive feelings (the unconditioned response) with their product (the conditioned stimulus).
Now that you are aware of how associative learning works, see if you can find examples of these types of advertisements on television, in magazines, or on the Internet.
Summary
Pavlov’s pioneering work with dogs contributed greatly to what we know about learning. His experiments explored the type of associative learning we now call classical conditioning. In classical conditioning, organisms learn to associate events that repeatedly happen together, and researchers study how a reflexive response to a stimulus can be mapped to a different stimulus—by training an association between the two stimuli. Pavlov’s experiments show how stimulus-response bonds are formed. Watson, the founder of behaviorism, was greatly influenced by Pavlov’s work. He tested humans by conditioning fear in an infant known as Little Albert. His findings suggest that classical conditioning can explain how some fears develop.
Review Questions
A stimulus that does not initially elicit a response in an organism is a(n) ________.
- unconditioned stimulus
- neutral stimulus
- conditioned stimulus
- unconditioned response
Hint:
B
In Watson and Rayner’s experiments, Little Albert was conditioned to fear a white rat, and then he began to be afraid of other furry white objects. This demonstrates ________.
- higher order conditioning
- acquisition
- stimulus discrimination
- stimulus generalization
Hint:
D
Extinction occurs when ________.
- the conditioned stimulus is presented repeatedly without being paired with an unconditioned stimulus
- the unconditioned stimulus is presented repeatedly without being paired with a conditioned stimulus
- the neutral stimulus is presented repeatedly without being paired with an unconditioned stimulus
- the neutral stimulus is presented repeatedly without being paired with a conditioned stimulus
Hint:
A
In Pavlov’s work with dogs, the psychic secretions were ________.
- unconditioned responses
- conditioned responses
- unconditioned stimuli
- conditioned stimuli
Hint:
B
Critical Thinking Questions
If the sound of your toaster popping up toast causes your mouth to water, what are the UCS, CS, and CR?
Hint:
The food being toasted is the UCS; the sound of the toaster popping up is the CS; salivating to the sound of the toaster is the CR.
Explain how the processes of stimulus generalization and stimulus discrimination are considered opposites.
Hint:
In stimulus generalization, an organism responds to new stimuli that are similar to the original conditioned stimulus. For example, a dog barks when the doorbell rings. He then barks when the oven timer dings because it sounds very similar to the doorbell. On the other hand, stimulus discrimination occurs when an organism learns a response to a specific stimulus, but does not respond the same way to new stimuli that are similar. In this case, the dog would bark when he hears the doorbell, but he would not bark when he hears the oven timer ding because they sound different; the dog is able to distinguish between the two sounds.
How does a neutral stimulus become a conditioned stimulus?
Hint:
This occurs through the process of acquisition. A human or an animal learns to connect a neutral stimulus and an unconditioned stimulus. During the acquisition phase, the neutral stimulus begins to elicit the conditioned response. The neutral stimulus is becoming the conditioned stimulus. At the end of the acquisition phase, learning has occurred and the neutral stimulus becomes a conditioned stimulus capable of eliciting the conditioned response by itself.
Personal Application Question
Can you think of an example in your life of how classical conditioning has produced a positive emotional response, such as happiness or excitement? How about a negative emotional response, such as fear, anxiety, or anger?
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https://oercommons.org/courseware/lesson/15326/overview
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Operant Conditioning
Overview
By the end of this section, you will be able to:
- Define operant conditioning
- Explain the difference between reinforcement and punishment
- Distinguish between reinforcement schedules
The previous section of this chapter focused on the type of associative learning known as classical conditioning. Remember that in classical conditioning, something in the environment triggers a reflex automatically, and researchers train the organism to react to a different stimulus. Now we turn to the second type of associative learning, operant conditioning. In operant conditioning, organisms learn to associate a behavior and its consequence (Table). A pleasant consequence makes that behavior more likely to be repeated in the future. For example, Spirit, a dolphin at the National Aquarium in Baltimore, does a flip in the air when her trainer blows a whistle. The consequence is that she gets a fish.
| Classical Conditioning | Operant Conditioning | |
|---|---|---|
| Conditioning approach | An unconditioned stimulus (such as food) is paired with a neutral stimulus (such as a bell). The neutral stimulus eventually becomes the conditioned stimulus, which brings about the conditioned response (salivation). | The target behavior is followed by reinforcement or punishment to either strengthen or weaken it, so that the learner is more likely to exhibit the desired behavior in the future. |
| Stimulus timing | The stimulus occurs immediately before the response. | The stimulus (either reinforcement or punishment) occurs soon after the response. |
Psychologist B. F. Skinner saw that classical conditioning is limited to existing behaviors that are reflexively elicited, and it doesn’t account for new behaviors such as riding a bike. He proposed a theory about how such behaviors come about. Skinner believed that behavior is motivated by the consequences we receive for the behavior: the reinforcements and punishments. His idea that learning is the result of consequences is based on the law of effect, which was first proposed by psychologist Edward Thorndike. According to the law of effect, behaviors that are followed by consequences that are satisfying to the organism are more likely to be repeated, and behaviors that are followed by unpleasant consequences are less likely to be repeated (Thorndike, 1911). Essentially, if an organism does something that brings about a desired result, the organism is more likely to do it again. If an organism does something that does not bring about a desired result, the organism is less likely to do it again. An example of the law of effect is in employment. One of the reasons (and often the main reason) we show up for work is because we get paid to do so. If we stop getting paid, we will likely stop showing up—even if we love our job.
Working with Thorndike’s law of effect as his foundation, Skinner began conducting scientific experiments on animals (mainly rats and pigeons) to determine how organisms learn through operant conditioning (Skinner, 1938). He placed these animals inside an operant conditioning chamber, which has come to be known as a “Skinner box” (Figure). A Skinner box contains a lever (for rats) or disk (for pigeons) that the animal can press or peck for a food reward via the dispenser. Speakers and lights can be associated with certain behaviors. A recorder counts the number of responses made by the animal.
Watch this brief video clip to learn more about operant conditioning: Skinner is interviewed, and operant conditioning of pigeons is demonstrated.
In discussing operant conditioning, we use several everyday words—positive, negative, reinforcement, and punishment—in a specialized manner. In operant conditioning, positive and negative do not mean good and bad. Instead, positive means you are adding something, and negative means you are taking something away. Reinforcement means you are increasing a behavior, and punishment means you are decreasing a behavior. Reinforcement can be positive or negative, and punishment can also be positive or negative. All reinforcers (positive or negative) increase the likelihood of a behavioral response. All punishers (positive or negative) decrease the likelihood of a behavioral response. Now let’s combine these four terms: positive reinforcement, negative reinforcement, positive punishment, and negative punishment (Table).
| Reinforcement | Punishment | |
|---|---|---|
| Positive | Something is added to increase the likelihood of a behavior. | Something is added to decrease the likelihood of a behavior. |
| Negative | Something is removed to increase the likelihood of a behavior. | Something is removed to decrease the likelihood of a behavior. |
REINFORCEMENT
The most effective way to teach a person or animal a new behavior is with positive reinforcement. In positive reinforcement, a desirable stimulus is added to increase a behavior.
For example, you tell your five-year-old son, Jerome, that if he cleans his room, he will get a toy. Jerome quickly cleans his room because he wants a new art set. Let’s pause for a moment. Some people might say, “Why should I reward my child for doing what is expected?” But in fact we are constantly and consistently rewarded in our lives. Our paychecks are rewards, as are high grades and acceptance into our preferred school. Being praised for doing a good job and for passing a driver’s test is also a reward. Positive reinforcement as a learning tool is extremely effective. It has been found that one of the most effective ways to increase achievement in school districts with below-average reading scores was to pay the children to read. Specifically, second-grade students in Dallas were paid $2 each time they read a book and passed a short quiz about the book. The result was a significant increase in reading comprehension (Fryer, 2010). What do you think about this program? If Skinner were alive today, he would probably think this was a great idea. He was a strong proponent of using operant conditioning principles to influence students’ behavior at school. In fact, in addition to the Skinner box, he also invented what he called a teaching machine that was designed to reward small steps in learning (Skinner, 1961)—an early forerunner of computer-assisted learning. His teaching machine tested students’ knowledge as they worked through various school subjects. If students answered questions correctly, they received immediate positive reinforcement and could continue; if they answered incorrectly, they did not receive any reinforcement. The idea was that students would spend additional time studying the material to increase their chance of being reinforced the next time (Skinner, 1961).
In negative reinforcement, an undesirable stimulus is removed to increase a behavior. For example, car manufacturers use the principles of negative reinforcement in their seatbelt systems, which go “beep, beep, beep” until you fasten your seatbelt. The annoying sound stops when you exhibit the desired behavior, increasing the likelihood that you will buckle up in the future. Negative reinforcement is also used frequently in horse training. Riders apply pressure—by pulling the reins or squeezing their legs—and then remove the pressure when the horse performs the desired behavior, such as turning or speeding up. The pressure is the negative stimulus that the horse wants to remove.
PUNISHMENT
Many people confuse negative reinforcement with punishment in operant conditioning, but they are two very different mechanisms. Remember that reinforcement, even when it is negative, always increases a behavior. In contrast, punishment always decreases a behavior. In positive punishment, you add an undesirable stimulus to decrease a behavior. An example of positive punishment is scolding a student to get the student to stop texting in class. In this case, a stimulus (the reprimand) is added in order to decrease the behavior (texting in class). In negative punishment, you remove an aversive stimulus to decrease behavior. For example, when a child misbehaves, a parent can take away a favorite toy. In this case, a stimulus (the toy) is removed in order to decrease the behavior.
Punishment, especially when it is immediate, is one way to decrease undesirable behavior. For example, imagine your four-year-old son, Brandon, hit his younger brother. You have Brandon write 100 times “I will not hit my brother" (positive punishment). Chances are he won’t repeat this behavior. While strategies like this are common today, in the past children were often subject to physical punishment, such as spanking. It’s important to be aware of some of the drawbacks in using physical punishment on children. First, punishment may teach fear. Brandon may become fearful of the street, but he also may become fearful of the person who delivered the punishment—you, his parent. Similarly, children who are punished by teachers may come to fear the teacher and try to avoid school (Gershoff et al., 2010). Consequently, most schools in the United States have banned corporal punishment. Second, punishment may cause children to become more aggressive and prone to antisocial behavior and delinquency (Gershoff, 2002). They see their parents resort to spanking when they become angry and frustrated, so, in turn, they may act out this same behavior when they become angry and frustrated. For example, because you spank Brenda when you are angry with her for her misbehavior, she might start hitting her friends when they won’t share their toys.
While positive punishment can be effective in some cases, Skinner suggested that the use of punishment should be weighed against the possible negative effects. Today’s psychologists and parenting experts favor reinforcement over punishment—they recommend that you catch your child doing something good and reward her for it.
Shaping
In his operant conditioning experiments, Skinner often used an approach called shaping. Instead of rewarding only the target behavior, in shaping, we reward successive approximations of a target behavior. Why is shaping needed? Remember that in order for reinforcement to work, the organism must first display the behavior. Shaping is needed because it is extremely unlikely that an organism will display anything but the simplest of behaviors spontaneously. In shaping, behaviors are broken down into many small, achievable steps. The specific steps used in the process are the following:
- Reinforce any response that resembles the desired behavior.
- Then reinforce the response that more closely resembles the desired behavior. You will no longer reinforce the previously reinforced response.
- Next, begin to reinforce the response that even more closely resembles the desired behavior.
- Continue to reinforce closer and closer approximations of the desired behavior.
- Finally, only reinforce the desired behavior.
Shaping is often used in teaching a complex behavior or chain of behaviors. Skinner used shaping to teach pigeons not only such relatively simple behaviors as pecking a disk in a Skinner box, but also many unusual and entertaining behaviors, such as turning in circles, walking in figure eights, and even playing ping pong; the technique is commonly used by animal trainers today. An important part of shaping is stimulus discrimination. Recall Pavlov’s dogs—he trained them to respond to the tone of a bell, and not to similar tones or sounds. This discrimination is also important in operant conditioning and in shaping behavior.
Here is a brief video of Skinner’s pigeons playing ping pong.
It’s easy to see how shaping is effective in teaching behaviors to animals, but how does shaping work with humans? Let’s consider parents whose goal is to have their child learn to clean his room. They use shaping to help him master steps toward the goal. Instead of performing the entire task, they set up these steps and reinforce each step. First, he cleans up one toy. Second, he cleans up five toys. Third, he chooses whether to pick up ten toys or put his books and clothes away. Fourth, he cleans up everything except two toys. Finally, he cleans his entire room.
PRIMARY AND SECONDARY REINFORCERS
Rewards such as stickers, praise, money, toys, and more can be used to reinforce learning. Let’s go back to Skinner’s rats again. How did the rats learn to press the lever in the Skinner box? They were rewarded with food each time they pressed the lever. For animals, food would be an obvious reinforcer.
What would be a good reinforce for humans? For your daughter Sydney, it was the promise of a toy if she cleaned her room. How about Joaquin, the soccer player? If you gave Joaquin a piece of candy every time he made a goal, you would be using a primary reinforcer. Primary reinforcers are reinforcers that have innate reinforcing qualities. These kinds of reinforcers are not learned. Water, food, sleep, shelter, sex, and touch, among others, are primary reinforcers. Pleasure is also a primary reinforcer. Organisms do not lose their drive for these things. For most people, jumping in a cool lake on a very hot day would be reinforcing and the cool lake would be innately reinforcing—the water would cool the person off (a physical need), as well as provide pleasure.
A secondary reinforcer has no inherent value and only has reinforcing qualities when linked with a primary reinforcer. Praise, linked to affection, is one example of a secondary reinforcer, as when you called out “Great shot!” every time Joaquin made a goal. Another example, money, is only worth something when you can use it to buy other things—either things that satisfy basic needs (food, water, shelter—all primary reinforcers) or other secondary reinforcers. If you were on a remote island in the middle of the Pacific Ocean and you had stacks of money, the money would not be useful if you could not spend it. What about the stickers on the behavior chart? They also are secondary reinforcers.
Sometimes, instead of stickers on a sticker chart, a token is used. Tokens, which are also secondary reinforcers, can then be traded in for rewards and prizes. Entire behavior management systems, known as token economies, are built around the use of these kinds of token reinforcers. Token economies have been found to be very effective at modifying behavior in a variety of settings such as schools, prisons, and mental hospitals. For example, a study by Cangi and Daly (2013) found that use of a token economy increased appropriate social behaviors and reduced inappropriate behaviors in a group of autistic school children. Autistic children tend to exhibit disruptive behaviors such as pinching and hitting. When the children in the study exhibited appropriate behavior (not hitting or pinching), they received a “quiet hands” token. When they hit or pinched, they lost a token. The children could then exchange specified amounts of tokens for minutes of playtime.
Behavior Modification in Children
Parents and teachers often use behavior modification to change a child’s behavior. Behavior modification uses the principles of operant conditioning to accomplish behavior change so that undesirable behaviors are switched for more socially acceptable ones. Some teachers and parents create a sticker chart, in which several behaviors are listed (Figure). Sticker charts are a form of token economies, as described in the text. Each time children perform the behavior, they get a sticker, and after a certain number of stickers, they get a prize, or reinforcer. The goal is to increase acceptable behaviors and decrease misbehavior. Remember, it is best to reinforce desired behaviors, rather than to use punishment. In the classroom, the teacher can reinforce a wide range of behaviors, from students raising their hands, to walking quietly in the hall, to turning in their homework. At home, parents might create a behavior chart that rewards children for things such as putting away toys, brushing their teeth, and helping with dinner. In order for behavior modification to be effective, the reinforcement needs to be connected with the behavior; the reinforcement must matter to the child and be done consistently.
Time-out is another popular technique used in behavior modification with children. It operates on the principle of negative punishment. When a child demonstrates an undesirable behavior, she is removed from the desirable activity at hand (Figure). For example, say that Sophia and her brother Mario are playing with building blocks. Sophia throws some blocks at her brother, so you give her a warning that she will go to time-out if she does it again. A few minutes later, she throws more blocks at Mario. You remove Sophia from the room for a few minutes. When she comes back, she doesn’t throw blocks.
There are several important points that you should know if you plan to implement time-out as a behavior modification technique. First, make sure the child is being removed from a desirable activity and placed in a less desirable location. If the activity is something undesirable for the child, this technique will backfire because it is more enjoyable for the child to be removed from the activity. Second, the length of the time-out is important. The general rule of thumb is one minute for each year of the child’s age. Sophia is five; therefore, she sits in a time-out for five minutes. Setting a timer helps children know how long they have to sit in time-out. Finally, as a caregiver, keep several guidelines in mind over the course of a time-out: remain calm when directing your child to time-out; ignore your child during time-out (because caregiver attention may reinforce misbehavior); and give the child a hug or a kind word when time-out is over.
REINFORCEMENT SCHEDULES
Remember, the best way to teach a person or animal a behavior is to use positive reinforcement. For example, Skinner used positive reinforcement to teach rats to press a lever in a Skinner box. At first, the rat might randomly hit the lever while exploring the box, and out would come a pellet of food. After eating the pellet, what do you think the hungry rat did next? It hit the lever again, and received another pellet of food. Each time the rat hit the lever, a pellet of food came out. When an organism receives a reinforcer each time it displays a behavior, it is called continuous reinforcement. This reinforcement schedule is the quickest way to teach someone a behavior, and it is especially effective in training a new behavior. Let’s look back at the dog that was learning to sit earlier in the chapter. Now, each time he sits, you give him a treat. Timing is important here: you will be most successful if you present the reinforcer immediately after he sits, so that he can make an association between the target behavior (sitting) and the consequence (getting a treat).
Watch this video clip where veterinarian Dr. Sophia Yin shapes a dog’s behavior using the steps outlined above.
Once a behavior is trained, researchers and trainers often turn to another type of reinforcement schedule—partial reinforcement. In partial reinforcement, also referred to as intermittent reinforcement, the person or animal does not get reinforced every time they perform the desired behavior. There are several different types of partial reinforcement schedules (Table). These schedules are described as either fixed or variable, and as either interval or ratio. Fixed refers to the number of responses between reinforcements, or the amount of time between reinforcements, which is set and unchanging. Variable refers to the number of responses or amount of time between reinforcements, which varies or changes. Interval means the schedule is based on the time between reinforcements, and ratio means the schedule is based on the number of responses between reinforcements.
| Reinforcement Schedule | Description | Result | Example |
|---|---|---|---|
| Fixed interval | Reinforcement is delivered at predictable time intervals (e.g., after 5, 10, 15, and 20 minutes). | Moderate response rate with significant pauses after reinforcement | Hospital patient uses patient-controlled, doctor-timed pain relief |
| Variable interval | Reinforcement is delivered at unpredictable time intervals (e.g., after 5, 7, 10, and 20 minutes). | Moderate yet steady response rate | Checking Facebook |
| Fixed ratio | Reinforcement is delivered after a predictable number of responses (e.g., after 2, 4, 6, and 8 responses). | High response rate with pauses after reinforcement | Piecework—factory worker getting paid for every x number of items manufactured |
| Variable ratio | Reinforcement is delivered after an unpredictable number of responses (e.g., after 1, 4, 5, and 9 responses). | High and steady response rate | Gambling |
Now let’s combine these four terms. A fixed interval reinforcement schedule is when behavior is rewarded after a set amount of time. For example, June undergoes major surgery in a hospital. During recovery, she is expected to experience pain and will require prescription medications for pain relief. June is given an IV drip with a patient-controlled painkiller. Her doctor sets a limit: one dose per hour. June pushes a button when pain becomes difficult, and she receives a dose of medication. Since the reward (pain relief) only occurs on a fixed interval, there is no point in exhibiting the behavior when it will not be rewarded.
With a variable interval reinforcement schedule, the person or animal gets the reinforcement based on varying amounts of time, which are unpredictable. Say that Manuel is the manager at a fast-food restaurant. Every once in a while someone from the quality control division comes to Manuel’s restaurant. If the restaurant is clean and the service is fast, everyone on that shift earns a $20 bonus. Manuel never knows when the quality control person will show up, so he always tries to keep the restaurant clean and ensures that his employees provide prompt and courteous service. His productivity regarding prompt service and keeping a clean restaurant are steady because he wants his crew to earn the bonus.
With a fixed ratio reinforcement schedule, there are a set number of responses that must occur before the behavior is rewarded. Carla sells glasses at an eyeglass store, and she earns a commission every time she sells a pair of glasses. She always tries to sell people more pairs of glasses, including prescription sunglasses or a backup pair, so she can increase her commission. She does not care if the person really needs the prescription sunglasses, Carla just wants her bonus. The quality of what Carla sells does not matter because her commission is not based on quality; it’s only based on the number of pairs sold. This distinction in the quality of performance can help determine which reinforcement method is most appropriate for a particular situation. Fixed ratios are better suited to optimize the quantity of output, whereas a fixed interval, in which the reward is not quantity based, can lead to a higher quality of output.
In a variable ratio reinforcement schedule, the number of responses needed for a reward varies. This is the most powerful partial reinforcement schedule. An example of the variable ratio reinforcement schedule is gambling. Imagine that Sarah—generally a smart, thrifty woman—visits Las Vegas for the first time. She is not a gambler, but out of curiosity she puts a quarter into the slot machine, and then another, and another. Nothing happens. Two dollars in quarters later, her curiosity is fading, and she is just about to quit. But then, the machine lights up, bells go off, and Sarah gets 50 quarters back. That’s more like it! Sarah gets back to inserting quarters with renewed interest, and a few minutes later she has used up all her gains and is $10 in the hole. Now might be a sensible time to quit. And yet, she keeps putting money into the slot machine because she never knows when the next reinforcement is coming. She keeps thinking that with the next quarter she could win $50, or $100, or even more. Because the reinforcement schedule in most types of gambling has a variable ratio schedule, people keep trying and hoping that the next time they will win big. This is one of the reasons that gambling is so addictive—and so resistant to extinction.
In operant conditioning, extinction of a reinforced behavior occurs at some point after reinforcement stops, and the speed at which this happens depends on the reinforcement schedule. In a variable ratio schedule, the point of extinction comes very slowly, as described above. But in the other reinforcement schedules, extinction may come quickly. For example, if June presses the button for the pain relief medication before the allotted time her doctor has approved, no medication is administered. She is on a fixed interval reinforcement schedule (dosed hourly), so extinction occurs quickly when reinforcement doesn’t come at the expected time. Among the reinforcement schedules, variable ratio is the most productive and the most resistant to extinction. Fixed interval is the least productive and the easiest to extinguish (Figure).
Gambling and the Brain
Skinner (1953) stated, “If the gambling establishment cannot persuade a patron to turn over money with no return, it may achieve the same effect by returning part of the patron's money on a variable-ratio schedule” (p. 397).
Skinner uses gambling as an example of the power and effectiveness of conditioning behavior based on a variable ratio reinforcement schedule. In fact, Skinner was so confident in his knowledge of gambling addiction that he even claimed he could turn a pigeon into a pathological gambler (“Skinner’s Utopia,” 1971). Beyond the power of variable ratio reinforcement, gambling seems to work on the brain in the same way as some addictive drugs. The Illinois Institute for Addiction Recovery (n.d.) reports evidence suggesting that pathological gambling is an addiction similar to a chemical addiction (Figure). Specifically, gambling may activate the reward centers of the brain, much like cocaine does. Research has shown that some pathological gamblers have lower levels of the neurotransmitter (brain chemical) known as norepinephrine than do normal gamblers (Roy, et al., 1988). According to a study conducted by Alec Roy and colleagues, norepinephrine is secreted when a person feels stress, arousal, or thrill; pathological gamblers use gambling to increase their levels of this neurotransmitter. Another researcher, neuroscientist Hans Breiter, has done extensive research on gambling and its effects on the brain. Breiter (as cited in Franzen, 2001) reports that “Monetary reward in a gambling-like experiment produces brain activation very similar to that observed in a cocaine addict receiving an infusion of cocaine” (para. 1). Deficiencies in serotonin (another neurotransmitter) might also contribute to compulsive behavior, including a gambling addiction.
It may be that pathological gamblers’ brains are different than those of other people, and perhaps this difference may somehow have led to their gambling addiction, as these studies seem to suggest. However, it is very difficult to ascertain the cause because it is impossible to conduct a true experiment (it would be unethical to try to turn randomly assigned participants into problem gamblers). Therefore, it may be that causation actually moves in the opposite direction—perhaps the act of gambling somehow changes neurotransmitter levels in some gamblers’ brains. It also is possible that some overlooked factor, or confounding variable, played a role in both the gambling addiction and the differences in brain chemistry.
COGNITION AND LATENT LEARNING
Although strict behaviorists such as Skinner and Watson refused to believe that cognition (such as thoughts and expectations) plays a role in learning, another behaviorist, Edward C. Tolman, had a different opinion. Tolman’s experiments with rats demonstrated that organisms can learn even if they do not receive immediate reinforcement (Tolman & Honzik, 1930; Tolman, Ritchie, & Kalish, 1946). This finding was in conflict with the prevailing idea at the time that reinforcement must be immediate in order for learning to occur, thus suggesting a cognitive aspect to learning.
In the experiments, Tolman placed hungry rats in a maze with no reward for finding their way through it. He also studied a comparison group that was rewarded with food at the end of the maze. As the unreinforced rats explored the maze, they developed a cognitive map: a mental picture of the layout of the maze (Figure). After 10 sessions in the maze without reinforcement, food was placed in a goal box at the end of the maze. As soon as the rats became aware of the food, they were able to find their way through the maze quickly, just as quickly as the comparison group, which had been rewarded with food all along. This is known as latent learning: learning that occurs but is not observable in behavior until there is a reason to demonstrate it.
Latent learning also occurs in humans. Children may learn by watching the actions of their parents but only demonstrate it at a later date, when the learned material is needed. For example, suppose that Ravi’s dad drives him to school every day. In this way, Ravi learns the route from his house to his school, but he’s never driven there himself, so he has not had a chance to demonstrate that he’s learned the way. One morning Ravi’s dad has to leave early for a meeting, so he can’t drive Ravi to school. Instead, Ravi follows the same route on his bike that his dad would have taken in the car. This demonstrates latent learning. Ravi had learned the route to school, but had no need to demonstrate this knowledge earlier.
This Place Is Like a Maze
Have you ever gotten lost in a building and couldn’t find your way back out? While that can be frustrating, you’re not alone. At one time or another we’ve all gotten lost in places like a museum, hospital, or university library. Whenever we go someplace new, we build a mental representation—or cognitive map—of the location, as Tolman’s rats built a cognitive map of their maze. However, some buildings are confusing because they include many areas that look alike or have short lines of sight. Because of this, it’s often difficult to predict what’s around a corner or decide whether to turn left or right to get out of a building. Psychologist Laura Carlson (2010) suggests that what we place in our cognitive map can impact our success in navigating through the environment. She suggests that paying attention to specific features upon entering a building, such as a picture on the wall, a fountain, a statue, or an escalator, adds information to our cognitive map that can be used later to help find our way out of the building.
Watch this video to learn more about Carlson’s studies on cognitive maps and navigation in buildings.
Summary
Operant conditioning is based on the work of B. F. Skinner. Operant conditioning is a form of learning in which the motivation for a behavior happens after the behavior is demonstrated. An animal or a human receives a consequence after performing a specific behavior. The consequence is either a reinforcer or a punisher. All reinforcement (positive or negative) increases the likelihood of a behavioral response. All punishment (positive or negative) decreases the likelihood of a behavioral response. Several types of reinforcement schedules are used to reward behavior depending on either a set or variable period of time.
Review Questions
________ is when you take away a pleasant stimulus to stop a behavior.
- positive reinforcement
- negative reinforcement
- positive punishment
- negative punishment
Hint:
D
Which of the following is not an example of a primary reinforcer?
- food
- money
- water
- sex
Hint:
B
Rewarding successive approximations toward a target behavior is ________.
- shaping
- extinction
- positive reinforcement
- negative reinforcement
Hint:
A
Slot machines reward gamblers with money according to which reinforcement schedule?
- fixed ratio
- variable ratio
- fixed interval
- variable interval
Hint:
B
Critical Thinking Questions
What is a Skinner box and what is its purpose?
Hint:
A Skinner box is an operant conditioning chamber used to train animals such as rats and pigeons to perform certain behaviors, like pressing a lever. When the animals perform the desired behavior, they receive a reward: food or water.
What is the difference between negative reinforcement and punishment?
Hint:
In negative reinforcement you are taking away an undesirable stimulus in order to increase the frequency of a certain behavior (e.g., buckling your seat belt stops the annoying beeping sound in your car and increases the likelihood that you will wear your seatbelt). Punishment is designed to reduce a behavior (e.g., you scold your child for running into the street in order to decrease the unsafe behavior.)
What is shaping and how would you use shaping to teach a dog to roll over?
Hint:
Shaping is an operant conditioning method in which you reward closer and closer approximations of the desired behavior. If you want to teach your dog to roll over, you might reward him first when he sits, then when he lies down, and then when he lies down and rolls onto his back. Finally, you would reward him only when he completes the entire sequence: lying down, rolling onto his back, and then continuing to roll over to his other side.
Personal Application Questions
Explain the difference between negative reinforcement and punishment, and provide several examples of each based on your own experiences.
Think of a behavior that you have that you would like to change. How could you use behavior modification, specifically positive reinforcement, to change your behavior? What is your positive reinforcer?
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Observational Learning (Modeling)
Overview
By the end of this section, you will be able to:
- Define observational learning
- Discuss the steps in the modeling process
- Explain the prosocial and antisocial effects of observational learning
Previous sections of this chapter focused on classical and operant conditioning, which are forms of associative learning. In observational learning, we learn by watching others and then imitating, or modeling, what they do or say. The individuals performing the imitated behavior are called models. Research suggests that this imitative learning involves a specific type of neuron, called a mirror neuron (Hickock, 2010; Rizzolatti, Fadiga, Fogassi, & Gallese, 2002; Rizzolatti, Fogassi, & Gallese, 2006).
Humans and other animals are capable of observational learning. As you will see, the phrase “monkey see, monkey do” really is accurate (Figure). The same could be said about other animals. For example, in a study of social learning in chimpanzees, researchers gave juice boxes with straws to two groups of captive chimpanzees. The first group dipped the straw into the juice box, and then sucked on the small amount of juice at the end of the straw. The second group sucked through the straw directly, getting much more juice. When the first group, the “dippers,” observed the second group, “the suckers,” what do you think happened? All of the “dippers” in the first group switched to sucking through the straws directly. By simply observing the other chimps and modeling their behavior, they learned that this was a more efficient method of getting juice (Yamamoto, Humle, and Tanaka, 2013).
Imitation is much more obvious in humans, but is imitation really the sincerest form of flattery? Consider Claire’s experience with observational learning. Claire’s nine-year-old son, Jay, was getting into trouble at school and was defiant at home. Claire feared that Jay would end up like her brothers, two of whom were in prison. One day, after yet another bad day at school and another negative note from the teacher, Claire, at her wit’s end, beat her son with a belt to get him to behave. Later that night, as she put her children to bed, Claire witnessed her four-year-old daughter, Anna, take a belt to her teddy bear and whip it. Claire was horrified, realizing that Anna was imitating her mother. It was then that Claire knew she wanted to discipline her children in a different manner.
Like Tolman, whose experiments with rats suggested a cognitive component to learning, psychologist Albert Bandura’s ideas about learning were different from those of strict behaviorists. Bandura and other researchers proposed a brand of behaviorism called social learning theory, which took cognitive processes into account. According to Bandura, pure behaviorism could not explain why learning can take place in the absence of external reinforcement. He felt that internal mental states must also have a role in learning and that observational learning involves much more than imitation. In imitation, a person simply copies what the model does. Observational learning is much more complex. According to Lefrançois (2012) there are several ways that observational learning can occur:
- You learn a new response. After watching your coworker get chewed out by your boss for coming in late, you start leaving home 10 minutes earlier so that you won’t be late.
- You choose whether or not to imitate the model depending on what you saw happen to the model. Remember Julian and his father? When learning to surf, Julian might watch how his father pops up successfully on his surfboard and then attempt to do the same thing. On the other hand, Julian might learn not to touch a hot stove after watching his father get burned on a stove.
- You learn a general rule that you can apply to other situations.
Bandura identified three kinds of models: live, verbal, and symbolic. A live model demonstrates a behavior in person, as when Ben stood up on his surfboard so that Julian could see how he did it. A verbal instructional model does not perform the behavior, but instead explains or describes the behavior, as when a soccer coach tells his young players to kick the ball with the side of the foot, not with the toe. A symbolic model can be fictional characters or real people who demonstrate behaviors in books, movies, television shows, video games, or Internet sources (Figure).
Latent learning and modeling are used all the time in the world of marketing and advertising. This commercial played for months across the New York, New Jersey, and Connecticut areas, Derek Jeter, an award-winning baseball player for the New York Yankees, is advertising a Ford. The commercial aired in a part of the country where Jeter is an incredibly well-known athlete. He is wealthy, and considered very loyal and good looking. What message are the advertisers sending by having him featured in the ad? How effective do you think it is?
STEPS IN THE MODELING PROCESS
Of course, we don’t learn a behavior simply by observing a model. Bandura described specific steps in the process of modeling that must be followed if learning is to be successful: attention, retention, reproduction, and motivation. First, you must be focused on what the model is doing—you have to pay attention. Next, you must be able to retain, or remember, what you observed; this is retention. Then, you must be able to perform the behavior that you observed and committed to memory; this is reproduction. Finally, you must have motivation. You need to want to copy the behavior, and whether or not you are motivated depends on what happened to the model. If you saw that the model was reinforced for her behavior, you will be more motivated to copy her. This is known as vicarious reinforcement. On the other hand, if you observed the model being punished, you would be less motivated to copy her. This is called vicarious punishment. For example, imagine that four-year-old Allison watched her older sister Kaitlyn playing in their mother’s makeup, and then saw Kaitlyn get a time out when their mother came in. After their mother left the room, Allison was tempted to play in the make-up, but she did not want to get a time-out from her mother. What do you think she did? Once you actually demonstrate the new behavior, the reinforcement you receive plays a part in whether or not you will repeat the behavior.
Bandura researched modeling behavior, particularly children’s modeling of adults’ aggressive and violent behaviors (Bandura, Ross, & Ross, 1961). He conducted an experiment with a five-foot inflatable doll that he called a Bobo doll. In the experiment, children’s aggressive behavior was influenced by whether the teacher was punished for her behavior. In one scenario, a teacher acted aggressively with the doll, hitting, throwing, and even punching the doll, while a child watched. There were two types of responses by the children to the teacher’s behavior. When the teacher was punished for her bad behavior, the children decreased their tendency to act as she had. When the teacher was praised or ignored (and not punished for her behavior), the children imitated what she did, and even what she said. They punched, kicked, and yelled at the doll.
Watch this video clip to see a portion of the famous Bobo doll experiment, including an interview with Albert Bandura.
What are the implications of this study? Bandura concluded that we watch and learn, and that this learning can have both prosocial and antisocial effects. Prosocial (positive) models can be used to encourage socially acceptable behavior. Parents in particular should take note of this finding. If you want your children to read, then read to them. Let them see you reading. Keep books in your home. Talk about your favorite books. If you want your children to be healthy, then let them see you eat right and exercise, and spend time engaging in physical fitness activities together. The same holds true for qualities like kindness, courtesy, and honesty. The main idea is that children observe and learn from their parents, even their parents’ morals, so be consistent and toss out the old adage “Do as I say, not as I do,” because children tend to copy what you do instead of what you say. Besides parents, many public figures, such as Martin Luther King, Jr. and Mahatma Gandhi, are viewed as prosocial models who are able to inspire global social change. Can you think of someone who has been a prosocial model in your life?
The antisocial effects of observational learning are also worth mentioning. As you saw from the example of Claire at the beginning of this section, her daughter viewed Claire’s aggressive behavior and copied it. Research suggests that this may help to explain why abused children often grow up to be abusers themselves (Murrell, Christoff, & Henning, 2007). In fact, about 30% of abused children become abusive parents (U.S. Department of Health & Human Services, 2013). We tend to do what we know. Abused children, who grow up witnessing their parents deal with anger and frustration through violent and aggressive acts, often learn to behave in that manner themselves. Sadly, it’s a vicious cycle that’s difficult to break.
Some studies suggest that violent television shows, movies, and video games may also have antisocial effects (Figure) although further research needs to be done to understand the correlational and causational aspects of media violence and behavior. Some studies have found a link between viewing violence and aggression seen in children (Anderson & Gentile, 2008; Kirsch, 2010; Miller, Grabell, Thomas, Bermann, & Graham-Bermann, 2012). These findings may not be surprising, given that a child graduating from high school has been exposed to around 200,000 violent acts including murder, robbery, torture, bombings, beatings, and rape through various forms of media (Huston et al., 1992). Not only might viewing media violence affect aggressive behavior by teaching people to act that way in real life situations, but it has also been suggested that repeated exposure to violent acts also desensitizes people to it. Psychologists are working to understand this dynamic.
View this video to hear Brad Bushman, a psychologist who has published extensively on human aggression and violence, discuss his research.
Summary
According to Bandura, learning can occur by watching others and then modeling what they do or say. This is known as observational learning. There are specific steps in the process of modeling that must be followed if learning is to be successful. These steps include attention, retention, reproduction, and motivation. Through modeling, Bandura has shown that children learn many things both good and bad simply by watching their parents, siblings, and others.
Review Questions
The person who performs a behavior that serves as an example is called a ________.
- teacher
- model
- instructor
- coach
Hint:
B
In Bandura’s Bobo doll study, when the children who watched the aggressive model were placed in a room with the doll and other toys, they ________.
- ignored the doll
- played nicely with the doll
- played with tinker toys
- kicked and threw the doll
Hint:
D
Which is the correct order of steps in the modeling process?
- attention, retention, reproduction, motivation
- motivation, attention, reproduction, retention
- attention, motivation, retention, reproduction
- motivation, attention, retention, reproduction
Hint:
A
Who proposed observational learning?
- Ivan Pavlov
- John Watson
- Albert Bandura
- B. F. Skinner
Hint:
C
Critical Thinking Questions
What is the effect of prosocial modeling and antisocial modeling?
Hint:
Prosocial modeling can prompt others to engage in helpful and healthy behaviors, while antisocial modeling can prompt others to engage in violent, aggressive, and unhealthy behaviors.
Cara is 17 years old. Cara’s mother and father both drink alcohol every night. They tell Cara that drinking is bad and she shouldn’t do it. Cara goes to a party where beer is being served. What do you think Cara will do? Why?
Hint:
Cara is more likely to drink at the party because she has observed her parents drinking regularly. Children tend to follow what a parent does rather than what they say.
Personal Application Question
What is something you have learned how to do after watching someone else?
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Public Opinion
Overview
Public Opinion
Learning Objective
By the end of this section, you will be able to:
- Explain why public opinion is important and the beliefs and ideologies that shape public opinion
Introduction: What Is Public Opinion?
Public opinion is a collection of popular views about something, perhaps a person, a local or national event, or a new idea. For example, each day, a number of polling companies call Americans at random to ask whether they approve or disapprove of the way the president is guiding the economy.
When situations arise internationally, polling companies survey whether citizens support U.S. intervention in places like Syria or Ukraine. These individual opinions are collected together to be analyzed and interpreted for politicians and the media. The analysis examines how the public feels or thinks, so politicians can use the information to make decisions about their future legislative votes, campaign messages, or propaganda.
But where do people’s opinions come from? Most citizens base their political opinions on their beliefs and their attitudes, both of which begin to form in childhood and develop through political socialization.
Beliefs are closely held ideas that support our values and expectations about life and politics. For example, the idea that we are all entitled to equality, liberty, freedom, and privacy is a belief most people in the United States share. We may acquire this belief by growing up in the United States or by having come from a country that did not afford these valued principles to its citizens.
Our attitudes are also affected by our personal beliefs and represent the preferences we form based on our life experiences and values. A person who has suffered racism or bigotry may have a skeptical attitude toward the actions of authority figures, for example.
While attitudes and beliefs are slow to change, ideology can be influenced by events. A student might leave college with a liberal ideology but become more conservative as she ages. A first-year teacher may view unions with suspicion based on second-hand information but change his mind after reading newsletters and attending union meetings. These shifts may change the way citizens vote and the answers they give in polls. For this reason, political scientists often study when and why such changes in ideology happen, and how they influence our opinions about government and politicians.
Political Socialization
At the same time that our beliefs and attitudes are forming during childhood, we are also being socialized; that is, we are learning from many information sources about the society and community in which we live and how we are to behave in it. Political socialization is the process by which we are trained to understand and join a country’s political world, and, like most forms of socialization, it starts when we are very young. We may first become aware of politics by watching a parent or guardian vote, for instance, or by hearing presidents and candidates speak on television or the Internet, or seeing adults honor the American flag at an event. As socialization continues, we are introduced to basic political information in school. We recite the Pledge of Allegiance and learn about the Founding Fathers, the Constitution, the two major political parties, the three branches of government, and the economic system.
By the time we complete school, we have usually acquired the information necessary to form political views and be contributing members of the political system. A young man may realize he prefers the Democratic Party because it supports his views on social programs and education, whereas a young woman may decide she wants to vote for the Republican Party because its platform echoes her beliefs about economic growth and family values.
Accounting for the process of socialization is central to our understanding of public opinion, because the beliefs we acquire early in life are unlikely to change dramatically as we grow older.
Our political ideology, made up of the attitudes and beliefs that help shape our opinions on political theory and policy, is rooted in who we are as individuals. Our ideology may change subtly as we grow older and are introduced to new circumstances or new information, but our underlying beliefs and attitudes are unlikely to change very much, unless we experience events that profoundly affect us. For example, family members of 9/11 victims became more Republican and more political following the terrorist attacks.
Similarly, young adults who attended political protest rallies in the 1960s and 1970s were more likely to participate in politics in general than their peers who had not protested.
Today, polling agencies have noticed that citizens’ beliefs have become far more polarized, or widely opposed, over the last decade. According to some scholars, these shifts led partisanship to become more polarized than in previous decades, as more citizens began thinking of themselves as conservative or liberal rather than moderate.
Public Opinion and Elections
Elections are the events on which opinion polls have the greatest measured effect. Public opinion polls do more than show how we feel on issues or project who might win an election. The media use public opinion polls to decide which candidates are ahead of the others and therefore of interest to voters and worthy of interview. From the moment President Obama was inaugurated for his second term, speculation began about who would run in the 2016 presidential election. Within a year, potential candidates were being ranked and compared by a number of newspapers.
The speculation included favorability polls on Hillary Clinton, which measured how positively voters felt about her as a candidate. The media deemed these polls important because they showed Clinton as the frontrunner for the Democrats in the next election.
Polling is also at the heart of horserace coverage, in which, just like an announcer at the racetrack, the media calls out every candidate’s move throughout the presidential campaign. Horserace coverage can be neutral, positive, or negative, depending upon what polls or facts are covered. During the 2012 presidential election, the Pew Research Center found that both Mitt Romney and President Obama received more negative than positive horserace coverage, with Romney’s growing more negative as he fell in the polls.
Horserace coverage is often criticized for its lack of depth; the stories skip over the candidates’ issue positions, voting histories, and other facts that would help voters make an informed decision. Yet, horserace coverage is popular because the public is always interested in who will win, and it often makes up a third or more of news stories about the election.
Exit polls, taken the day of the election, are the last election polls conducted by the media. Announced results of these surveys can deter voters from going to the polls if they believe the election has already been decided.
During presidential primary season, we see examples of the bandwagon effect, in which the media pays more attention to candidates who poll well during the fall and the first few primaries. Bill Clinton was nicknamed the “Comeback Kid” in 1992, after he placed second in the New Hampshire primary despite accusations of adultery with Gennifer Flowers. The media’s attention on Clinton gave him the momentum to make it through the rest of the primary season, ultimately winning the Democratic nomination and the presidency.
Public opinion polls also affect how much money candidates receive in campaign donations. Donors assume public opinion polls are accurate enough to determine who the top two to three primary candidates will be, and they give money to those who do well. Candidates who poll at the bottom will have a hard time collecting donations, increasing the odds that they will continue to do poorly.
Presidents running for reelection also must perform well in public opinion polls, and being in office may not provide an automatic advantage. Americans often think about both the future and the past when they decide which candidate to support.
They have three years of past information about the sitting president, so they can better predict what will happen if the incumbent is reelected. That makes it difficult for the president to mislead the electorate. Voters also want a future that is prosperous. Not only should the economy look good, but citizens want to know they will do well in that economy.
For this reason, daily public approval polls sometimes act as both a referendum of the president and a predictor of success.
Public Opinion and Government
The relationship between public opinion polls and government action is murkier than that between polls and elections. Like the news media and campaign staffers, members of the three branches of government are aware of public opinion. But do politicians use public opinion polls to guide their decisions and actions?
The short answer is “sometimes.” The public is not perfectly informed about politics, so politicians realize public opinion may not always be the right choice. Yet many political studies, from the American Voter In the 1920s to the American Voter Revisited in the 2000s, have found that voters behave rationally despite having limited information. Individual citizens do not take the time to become fully informed about all aspects of politics, yet their collective behavior and the opinions they hold as a group make sense. They appear to be informed just enough, using preferences like their political ideology and party membership, to make decisions and hold politicians accountable during an election year.
Overall, the collective public opinion of a country changes over time, even if party membership or ideology does not change dramatically. As James Stimson’s prominent study found, the public’s mood, or collective opinion, can become more or less liberal from decade to decade. While the initial study on public mood revealed that the economy has a profound effect on American opinion.
Further studies have gone beyond to determine whether public opinion, and its relative liberalness, in turn affect politicians and institutions. This idea does not argue that opinion never affects policy directly, rather that collective opinion also affects the politician’s decisions on policy.
Individually, of course, politicians cannot predict what will happen in the future or who will oppose them in the next few elections. They can look to see where the public is in agreement as a body. If public mood changes, the politicians may change positions to match the public mood. The more savvy politicians look carefully to recognize when shifts occur. When the public is more or less liberal, the politicians may make slight adjustments to their behavior to match. Politicians who frequently seek to win office, like House members, will pay attention to the long- and short-term changes in opinion. By doing this, they will be less likely to lose on Election Day. Presidents and justices, on the other hand, present a more complex picture.
Link to Learning
Policy Agendas Project
The website of the Policy Agendas Project details a National Science Foundation-funded policy project to provide data on public opinion, presidential public approval, and a variety of governmental measures of activity. All data are coded by policy topic, so you can look for trends in a policy topic of interest to you to see whether government attention tracks with public opinion.
References and Further Reading
Gallup. 2015. Gallup Daily: Obama Job Approval Gallup: News; Rasmussen Reports. 2015. Daily Presidential Tracking Poll. Ras Reports; Roper Center (2015). Obama Presidential Approval. Roper Center.
V. O. Key, Jr. 1966. The Responsible Electorate. Harvard University: Belknap Press.
John Zaller. 1992. The Nature and Origins of Mass Opinion. Cambridge: Cambridge University Press.
Eitan Hersh. 2013. "Long-Term Effect of September 11 on the Political Behavior of Victims’ Families and Neighbors." Proceedings of the National Academy of Sciences of the United States of America 110 (52): 20959–63.
M. Kent Jennings. 2002. "Generation Units and the Student Protest Movement in the United States: An Intra- and Intergenerational Analysis." Political Psychology 23 (2): 303–324.
Pew Research Center (2014). Political Polarization in the American Public. Pew Research Center.
Joseph Bafumi & Robert Shapiro (2009). A New Partisan Voter. The Journal of Politics 71 (1): 1–24.
Hitlin, P. (2013). The 2016 Presidential Media Primary Is Off to a Fast Start. Pew Research Center. Retrieved October 22, 2019.
Kiley, J. (2015). A Clinton Candidacy: Voters' Early Impressions. Pew Research Center. Retrieved October 22, 2019.
Texas Politics Project (2018). Ted Cruz Favorability (2018) - by Party ID. Retrieved October 29, 2019.
Pew Research Center. (2012). Winning the Media Campaign. Pew Research Center.
Pew Research Center (2012). Fewer Horserace Stories-and Fewer Positive Obama Stories-Than in 2008. Pew Research Center.
Erikson, R. S., MacKuen, M. B., and Stimson, J. A. (2000). Bankers or Peasants Revisited: Economic Expectations and Presidential Approval. Electoral Studies 19: 295–312. Retrieved October 22, 2019.
MacKuen, M. B., Erikson, R. S., & Stimson, J. A. (1989). Macropartisanship. American Political Science Review 83(4). 1125–1142.
Stimson, J. A., Mackuen, M. B. & Erikson, R. S. (1995). Dynamic Representation. American Political Science Review 89 (3): 543–565
Licensing and Attribution
CC LICENSED CONTENT, ORIGINAL
Revision and Adaptation. Authored by: Daniel M. Regalado. License: CC BY: Attribution
CC LICENSED CONTENT, SHARED PREVIOUSLY
American Government. Authored by: OpenStax. Provided by: OpenStax; Rice University. Located at: http://cnx.org/contents/5bcc0e59-7345-421d-8507-a1e4608685e8@18.11. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/5bcc0e59-7345-421d-8507-a1e4608685e8@18.11
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oercommons
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05/05/2020
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"url": "https://oercommons.org/courseware/lesson/66353/overview",
"title": "Texas Government 2.0, Public Opinion and the Media in Texas, Public Opinion",
"author": "Kris Seago"
}
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https://oercommons.org/courseware/lesson/66300/overview
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Voting and Political Participation in Texas
Overview
Voting and Political Participation in Texas
Chapter Learning Objective
By the end of this chapter, you should be able to:
- Identify the voting rights and responsibilities of Texas' citizens
Introduction: Voting and Political Participation in a Changing Texas
Fort Bend County covers an area along the Brazos River southwest of Houston. For most of the 20th Century, it was a rural area known for ranching and cotton farming, and as the home of Imperial Sugar and several large state prisons. As Texas shifted from a predominantly Democratic to a predominantly Republican state in the 1970s, Fort Bend County’s rural, conservative roots brought it enthusiastically along with the trend. In 1976, only 39 percent of Fort Bend voters selected Jimmy Carter for President in a race in which he carried Texas over President Gerald Ford.
In the 2000s, Republican majorities began to shrink. Mitt Romney won Fort Bend County with only 53 percent in 2012, and Hillary Clinton carried Fort Bend County in 2016, even as 52 percent of Texas voters chose Donald Trump.
In the 2018 election, every countywide election was won by a Democrat, with challenger Beto O’Rourke outpolling incumbent Republican Senator Ted Cruz by more than 11 points, even as Cruz was reelected statewide. How did rural/suburban Fort Bend County become what appears to be at least a Democratic-leaning, if not solidly Democratic, county?
The answer lies at least partly in demographics. The population of Fort Bend grew almost 30 percent from 2010 to the 2018 election, and the 19 percent growth in Anglos was far outpaced by Asians (56%), Hispanics (33%) and African Americans (22%). The latest Census data shows Fort Bend as the most diverse county in Texas – meaning that it has the most closely equal percentages of the four major racial groups at 35% Anglo, 24% Hispanic, 20% African American and 21% Asian and other.
For better or worse, race is a strong predictor of political party preferences. As non-Anglo races become a larger percentage of the population and – more importantly – a larger percentage of the electorate throughout Texas, many predict that Texas’ days as a reliably Republican state are numbered.
How and why do Texans participate in politics?
License and Attribution
CC LICENSED CONTENT, ORIGINAL
Voting and Political Participation in Texas: Introduction. Authored by: Andrew Teas. License: : CC BY: Attribution
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"url": "https://oercommons.org/courseware/lesson/66300/overview",
"title": "Texas Government 2.0, Voting and Political Participation in Texas, Voting and Political Participation in Texas",
"author": "Kris Seago"
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https://oercommons.org/courseware/lesson/66356/overview
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Glossary
Overview
Glossary
Glossary: Public Opinion and the Media in Texas
agenda setting: the media’s ability to choose which issues or topics get attention
agent of political socialization: a person or entity that teaches and influences others about politics through use of information
attitudes: represent the preferences we form based on our life experiences and values; affected by our personal beliefs
bandwagon effect: occurs when the media pays more attention to candidates who poll well during the fall and the first few primaries
beliefs: closely held ideas that support our values and expectations about life and politics
Bradley effect: theory concerning observed discrepancies between voter opinion polls and election outcomes in government elections where a white candidate and non-white candidate run against one another; the theory proposes that some voters who intend to vote for the white candidate would nonetheless tell pollsters that they are undecided or likely to vote for the non-white candidate
covert content: ideologically slanted information presented as unbiased information in order to influence public opinion
cultivation theory: hypothesizes that media develops a person’s view of the world by presenting a perceived reality
episodic framing: occurs when a story focuses on isolated details or specifics rather than looking broadly at a whole issue
favorability polls: a public opinion poll that measures a public's positive feelings about a candidate or politician
mass media: the collection of all media forms that communicate information to the general public
media: the number of different communication formats, from television media to print media
overt content: political information whose author makes clear that only one side is presented
pack journalism: journalists follow one another rather than digging for their own stories, often leading to shallow press coverage
political socialization: the process by which we are trained to understand and join a country’s political world
public opinion: a collection of popular views about something. For example, a person, a local or national event, or a new idea
public relations: biased communication intended to improve the image of people, companies, or organizations
racial framing: a type of media framing in which socially constructed frames about specific racial groups are repackaged and circulated through newspapers, magazines, billboards, music, social media, television, film, and radio; these frames influence media audiences to recall, evaluate, and interpret an issue in particular ways
social media: a set of applications or web platforms that allow users to immediately communicate with one another
thematic framing: takes a broad look at an issue and skips numbers or details; it looks at how the issue has changed over a long period of time and what has led to it
Licenses and Attributions
CC LICENSED CONTENT, SHARED PREVIOUSLY
American Government. What is the Media? Glossary Authored by: OpenStax. Provided by: OpenStax; Rice University. Located At: https://cnx.org/contents/W8wOWXNF@12.1:Y1CfqFju@5/Preface. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/9e28f580-0d1b-4d72- 8795-c48329947ac2@1.
CC LICENSED CONTENT, ORIGINAL
Public Opinion and the Media in Texas: Glossary. Authored by: panOpen. License: CC BY: Attribution
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oercommons
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05/05/2020
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"url": "https://oercommons.org/courseware/lesson/66356/overview",
"title": "Texas Government 2.0, Public Opinion and the Media in Texas, Glossary",
"author": "Kris Seago"
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https://oercommons.org/courseware/lesson/82675/overview
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"Abnormal Psychology"
Overview
This is an Abnormal Psychology course at a community college. The syllabus outlines how the course is broken down by modules and possible discussion questions that could be used each week as students work through the material.
Abnormal Psychology
PSY 150-30 (Online)
Fall 2021 Course Syllabus
Instructor: Jennifer Pisarik
Bedford House 201
Contact: 781-280-3804 voice mail
pisarikj@middlesex.mass.edu *this is the preferred method of communication
Office hours: T/Th 12:30-1:30 and by appointment
Course Description: This course covers the history of mental illness and its treatment, modern classification, diagnosis, the theoretical causes of disorders, and treatments. The range of psychopathy extends from anxiety disorder, mood disorders, disorders of stress, personality disorders, to psychosis and schizophrenia.
General Education Elective: Behavioral Science.
Prerequisite: Completion of PSY 101.
Student Learning Outcomes: Upon successful completion of this course, students will be able to:
- Classify the different types of Psychological Disorders
- Differentiate between the Major Models of Abnormality and their approach to etiology and therapy
- Identify the signs of Abnormal Behavior
- Identify and describe methods that are used to classify and evaluate psychological disorders
- Develop empathy for the mentally distressed
Apply distinguishing features and diagnostic criteria for various types of mental disorders using the current DSM
This course uses a free online textbook: Abnormal Psychology, 2nd edition by Alexis Bridley and Lee w. Daffin https://opentext.wsu.edu/abnormal-psych/
Weekly Assignments: Each week you will be take a test on a module from the text, write a 1-2 page paper demonstrating your understanding of specific content areas, and participate at least twice in a discussion forum. To prepare for this work, you will have readings from the text, videos and activities within a designated module activity folder. Additionally, you will write an annotated bibligraphy and take a final exam.
Class Meeting Times: This is an asynchronous online class. This means that we will not be meeting on campus at any specific time, but it does not mean that you won't need to find a regular time and place to work on your course. Research has shown that students who do the best in online courses are the ones that set up a schedule and stick to it. If you just try to "fit it in" to your already busy life without planning specific times to work, you will undoubtedly fall behind, so one of the first things you should do is to figure out where and when you will work on this course each week and include it in your schedule!
Late Work: Assignments must be completed by assigned due dates. After a very short “grace period” assignments are automatically taken down from the site and can no longer be turned in for credit. Late work (when allowed) will not be given full credit.
Academic Honesty: Plagiarism will not be tolerated. Any work that is plagiarized will receive a grade of zero on the assignment and not be allowed to be made up. While I realize it is tempting to copy and paste information from the web onto papers, you are expected to take the extra step and put information into your own words before passing it in. This helps to ensure that you really understand the points being made. In the instances when you find you can’t say it any better, be sure to cite your source. Cheating on tests or papers will result in an F.
Plagiarism Statement: “Plagiarism is representing, intentionally or unintentionally, the words or ideas of another as one’s own work without correctly acknowledging the source, in any educational setting. It is the responsibility of the student to learn and use the correct methods of avoiding plagiarism in each class.” (Adapted from UMass Lowell Handbook)
Technology Help Available 24/7
PHONE OR E-MAIL
>> Contact us at 978-656-3301 for phone support 24/7
>> Via e-mail at servicedesk@middlesex.mass.edu
Credit Hour Policy
Middlesex Community College follows the Carnegie Unit for credit. Students are expected to spend a minimum of 45 hours of work for each credit. The most common breakdown for one credit is one hour of class instruction and two hours of homework for 15 weeks each semester. A three credit course demands nine hours each week.
Student Conduct: In this class, you are expected to behave in ethically and ways that are consistent with the requirements of the MCC Student Handbook and MCC Honor Code.
You can find the MCC Student Handbook at http://www.middlesex.mass.edu/studenthandbook/
MCC also has an Honor Code you can view at
http://www.middlesex.mass.edu/deanofstudents/downloads/hcodeflyer.pdf
Course Communication Policies: Discussion is an important part of the learning experience for this course. You should be prepared to become involved in every class discussion and provide feedback to others, understanding that the class will be more interesting, enriching and rewarding when we have each person’s contributions and perspectives to learn from.
Each week there will be discussion board activities. You will be asked to post a response to a question, article or video clip, and you will also be expected to reply to at least one other classmate's post. After the required posts are made, you are free to make as many additional posts as you like.
Keep in mind that in a collegial atmosphere discussion and collaboration are encouraged. I will require you to adhere to proper etiquette on the discussion board. Please do not say anything that may be offensive or inappropriate. Foul language and slang are not acceptable.
The discussion boards are incorporated your grade. Grades are based on the frequency and content of your posts.
Feel free to email me with individual questions, but be sure to review the unit folder before emailing. I will make every attempt to respond to your email within 24-48 hours. Be sure to use correct email protocol:
1. identify yourself and your course/section in the subject line
2. write clearly
3. use proper spelling and grammar (including capitalization)
I know all of this may sound picky, but since we will communicate mainly through writing, taking short cuts in spelling and grammar may confuse what you mean to say.
How to Get Help: If you need help working on your assignments, Middlesex provides free academic tutoring both face-to-face and online. You can find more information at the Academic Support website (http://www.middlesex.mass.edu/tutoringservices )
Students with documented disabilities who believe they may need accommodation(s) in this class are encouraged to contact Disability Support Services in order to ensure that such accommodations are accomplished in a timely manner. Bedford: Enrollment Center 2nd floor (781-280-3636); Lowell CC 3rd floor 314 (978-656-3258)
If you are experiencing technical problems, call 978- 656 3301. Or contact: https://www.middlesex.mass.edu/technologycenter/ Help is available 24 hours a day, 7 days a week.
Grading weights:
Chapter Reading Tests: 9 at 20 points each = 180 points
Discussion Board Participation 10 at 10 points each= 100 points
Writing Assignments 10 at 20 points each= 200 points
Annotated Bibliography 20 points
Final Exam: 50 points
Total 550 points
A = 495-550
B = 440-494
C = 385-439
D = 330-384 below 330 is not passing
Plus or minus grades are according to college policy (ex. B+ is 87% -89%; B- is 80%-82%)
Course Schedule Outline – Tentative dates – I reserve the right to make changes as needed
Sept. 9-13 Introductions
September 13-20 Module 1: What is Abnormal Psychology?
September 21-27 Module 2: Models in Abnormal Psychology
Sept.28 –Oct. 4 Module 3: Clinical Assessment, Diagnosis and Treatment
Oct. 5-11 Module 7: Anxiety Disorders
Oct 12-18 Module 9: Obsessive-Compulsive and Related Disorders
Oct 19-25 Module 5: Trauma and Stressor Related Disorders Modules - 5.1. 5.2, 5.3, 5.5, 5.6 and Module 6: Dissociative Disorders: Modules -6.1, 6.4, 6.5
Oct 26-Nov 1 Annotated Bibliography
Nov 2- 8 Module 4: Mood Disorders
Nov 9 – 15 Module 8: Somatic Symptom and Related Disorders
Nov 16 – 22 Module of your choice: choose from Eating Disorders, Substance-Related and Addictive Disorders or Neurocognitive Disorders
Thanksgiving Holiday
Nov 29-Dec 6 Module12: Schizophrenia
Dec 7-13 Module 13: Personality Disorders
Dec 14-20 Final Exam
Module 1: What is Abnormal Psychology?
This week's topic lays a good foundation in terms of introducing you to the field of Abnormal Psychology. Included in this topic is the difficulty in producing a clear definition of abnormal psychology as well as a brief look at psychological disorders over the years. It is through understanding the way that society has perceived abnormal behavior throughout history that we can get a clearer picture of how we have come to our perception of abnormal psychology today. Finally, because psychology is a science, it is necessary to understand the research methods that are used to study abnormal behavior both from a clinical perspective and as a societal phenomenon.
Learning Objectives:
- Discuss the difficulties in defining a person's behavior as abnormal
- Describe the history of how abnormal behavior was viewed in the past from ancient times to the present
- Compare and contrast current common theories in abnormal psychology
- Compare and contrast the professions that study and treat abnormal behavior
- Describe the case study and its role and limitations
- Describe the correlational method. What is meant by a positive versus a negative versus a null correlation?
- Describe the experiment as well as alternative research experimental designs
Possible Discussion Question: After reading your text and the resources provided in your activity folder, what do you think are important considerations in determining if a psychological disorder is present? Are the "4 D's" a good guideline? Why is it important to consider cultural context?
Module 2: Models in Abnormal Psychology
Just as the story of the blind men trying to describe an elephant goes, the lens through which you view a psychological disorder has an impact on your perception, understanding and of the treatment for the disorder. This unit will explore the six most prominent models that psychologists use today.
Learning Objectives:
- Define and describe the biological model including various therapies used by this model.
- Summarize the origins of Freud's model. Describe abnormal functional according to this model including descriptions of the id, ego and superego, defense mechanisms and psychosexual stages.
- Summarize the behavioral model including the main features of classical and operant conditioning and how they are used to describe abnormal behavior
- Summarize the cognitive model. Give examples of maladaptive assumptions, and illogical thinking processes. Describe cognitive therapy.
- Summarize Rogers' theory and therapy including unconditional positive regard and conditions of worth. Describe Gestalt theory and therapy.
- Summarize sociocultural models and various sociocultural therapies.
- Compare and contrast the various models of abnormal functioning.
Possible Discussion Question: Give an example of at least one defense mechanism you have used or seen in action. Do you agree with the psychodynamic explanation?
Module 3: Clinical Assessment, Diagnosis and Treatment
Up until this point you have been learning about how researchers build a general understanding of abnormal functioning in psychology. The goal of this unit is to better understand how clinicians work to use this knowledge to fully understand the client and his/her problems in order to better help them overcome them. This week you will be learning about various assessment methods and how clinicians use idiographic information to build a diagnosis and develop treatment strategies.
Learning Objectives:
- Define clinical assessment and discuss the various roles of clinical interviews, tests and observations
- Compare and contrast the values and limitations of various assessments used to determine abnormal functioning.
- Describe the process of diagnosis using DSM-5. which requires both categorical and dimensional information.
- Discuss the dangers of diagnosing and labeling in classifying mental disorders.
- Discuss types and effectiveness of treatments for mental disorders.
Possible Discussion Question: Discuss your thoughts about the importance of considering cultural factors in assessing and diagnosing mental illness. What are some ways that you believe that cultural context can influence a diagnosis?
Module 7: Anxiety Disorders
In the United States, anxiety disorders are the most common of all of the psychological disorders. It is estimated that approximately 18% of all adults suffer from at least one of the anxiety disorders in a given year. Many people who suffer from one anxiety disorder will also experience another disorder.
In this unit, you will read about several disorders that the DSM-5 has classified in this category. You will learn more about how the model you use to understand the origin of the disorder can inform the treatment techniques that are used. You will also learn more about the important cultural influences within this category.
Learning Objectives:
- Describe each of the anxiety disorders and how common these disorders are.
- Discuss the major theories and treatments for generalized anxiety disorder.
- Define phobia; then distinguish between specific phobias and agoraphobia; discuss the major theories and treatments for each type.
- Discuss the characteristics, theories and treatment of social anxiety disorder.
- Discuss cultural impact on etiology and presentation of anxiety disorders.
Possible Discussion Question: Why do you think so many professional performers suffer from performance anxiety (social anxiety disorder)? Be sure to demonstrate a clear understanding of the characteristic features of this disorder.
Module 9 Obsessive-Compulsive and Related Disorders
Module 9 focuses on a relatively new categorical update in DSM-5. This group of disorders was formerly considered part of the Anxiety disorders chapter but in this edition was moved to its own chapter to better reflect increasing knowledge and awareness of the relatedness of the disorders within this special category. The close relationship between these disorders and the Anxiety disorders is reflected in the sequencing within DSM-5. In addtion to Obsessive-compulsive disorder (OCD) the DSM-5 groups Body Dysmorphic disorder (BDD) and hoarding disorder as represented in the textbook, but also trichotillomania, excoriation, substance/medication induced OCD, OCD adue to another medical condtion, other specified OCD, and unspecified OCD.
Learning Objectives:
- Distinguish between obsessions and compulsions. Descrbe how they present.
- Describe the etiology of obsessive-compiulsive disorders
- Discuss the major theories and treatment options for obsessive-compulsive disorder.
- Describe the new Obsessive -Compulsive Related Disorder in DSM-5
Possible Discussion Question: To what extent do you think that social media sites contribute to disorders like Body Dysmorphic Disorder? If you think they are at risk, what can be done to prevent younger children from developing them?
Modules 5 & 6
The focus of this week's study will be a group of disorders that are caused by trauma and stress. This DSM-5 category lists several disorders that are triggered by extraordinary stress and share many of the same symptoms like heightened physiological arousal, anxiety and mood problems, severe memory difficulties and orientation problems. Our study begins with a better understanding of stress on the body and brain and then continues to explore acute stress disorder, PTSD, and finally the dissociative disorders. For this week you should read Module 5 - 5.1. 5.2, 5.3, 5.5, 5.6 and Module 6 -6.1, 6.4, 6.5
Learning Objectives:
- Distinguish between fear and anxiety and describe the fight or flight response.
- Define acute stress disorder and posttraumatic stress disorder, list typical symptoms and discuss treatment for these disorders
- Discuss the various triggers for psychological stress disorders.
- Describe the various factors that put people at a greater risk for developing a stress disorder and various treatment approaches for these disorders
- Describe the general characteristics of dissociative amnesia and dissociative identity disorder.
- Describe treatment for the dissociative disorders.
Possible Discussion Question: While there is no "one size fits all' treatment for acute stress disorder or PTSD, a number of effective treatment procedures were mentioned in the text and in the videos. Discuss one treatment that you learned about this week explaining why you think it may be particularly effective.
Annotated Bibiliography
Annotated Bibliography Assignment for Abnormal Psychology
Annotated bibliographies provide brief accounts of available research materials on a given topic. An annotation is a concise paragraph or two that informs the reader of the relevance, accuracy and quality of the source cited. The purpose of this assignment is to improve your research skills and to ensure that you understand your research materials.
Guidelines:
- Choose three journal articles about your chosen psychological disorder from our library’s database. The college librarians would be happy to work with you if you need help accessing psychological journals.
- One of the articles must address the disorder from the perspective of another culture. There are no restrictions on how the disorder is addressed in the other culture, I simply want to expand your awareness that psychopathology is not always viewed the same way.
- Cite the source in APA format.
- Beneath each citation include a few sentences summarizing the source. Use your own words.
- Who are the authors? If there is information about the authors’ credentials you can include that.
- What is the purpose of the article? What is the topic covered? Does the article reflect current understanding of the subject? Be sure to demonstrate to me that you have some understanding of the work you are citing.
- How is this work useful in better understanding the disorder?
Module 4: Mood Disorders
One's emotional state can have a powerful influence on motivation, behavior, cognitions and even physical well-being. This next category of disorders is sometimes referred to as Disorders of Affect, and includes both the low, sad state of Depression and the opposite breathless, frenzied state of Mania. Mood disorders, especially Depression, are among the most common of the psychological disorders.This week's focus will examine the various types of Depression and Bipolar disorder, including the etiology, characteristic symptoms and treatment approaches for each of these disorders.
Learning Objectives
- Contrast depression and mania while discussing the symptoms of each
- Compare major depressive disorder,persistent depressive disorder and seasonal affective disorder
- Describe the biological, psychological and sociocultural perspectives of depression
- Describe the major psychological approaches to the treatment of unipolar depression
- Discuss the biological theory of bipolar disorder
- Describe the current treatment approaches and best practices for the treatment of bipolar disorder
Possible Discussion Question: It seems that everyone feels depressed at some time or another, although not everyone experiences depression that meets the criteria for a DSM-5 diagnosis. After reading the chapter, watching videos and becoming more informed about this disorder how would you determine when one should seek help for depression? Include what you have learned about duration for clinical diagnosis as well as your own thoughts on this guideline.
Module 8: Somatic Symptom and Related Disorders
Psychological factors can contribute to somatic and bodily illnesses in a variety of ways. This chapter will focus on how stress and related psychosocial factors may contribute to physical illnesses. This DSM-5 category includes factitious disorders, conversion disorders, somatic disorders, as well as illness anxiety disorder. The chapter ends with a review of psychophysiological disorders, or psychological factors affecting medical conditions.
Learning Objectives:
- Describe the criteria for diagnosing factitious disorder
- Define conversion disorder and somatic symptom disorder and discuss the primary theories of causality and major treatment approaches
- Explain how physicians distinguish between conversion disorder and true medical problems
- Describe illness anxiety disorder, its diagnosis, theories of causality and treatment approaches
- Describe the traditional psychophysiological disorders
- Discuss how perceptions of control, personality, mood, and social support affect immune system functioning
Possible Discussion Question: After having read about how psychological factors can be involved in physical illnesses as well as psychological illnesses, it is important to think about how to best practice self care. What are some strategies that you may have tried? How helpful would you rate them to be? What are some new strategies that you would like to try?
Module of your choice
This week is your opportunity to learn about one of the modules from the text that has not/will not be covered this semester. Choose from: Eating Disorders, Substance-Related and Addictive Disorders, Neurocognitive disorders.
Possible Discussion Question: Which category of disorders did you choose to read about on your own? What is the most surprising thing that you learned?
Schizophrenia Spectrum and other psychotic disorders
Schizophrenia is a serious mental illness that affects approximately 1% of Americans. It interferes with a person's ability to think clearly, make decisions, manage emotions and have healthy interpersonal relationships. It is one of the most complex of all the psychological disorders and while we don't know specifically what causes it, researchers have identified several possible factors that you will read about this week. There are many characteristic symptoms but the defining feature is the presence of psychosis, or a break with reality such as hallucinations, delusions or disorganized speech.
Learning Objectives:
- Describe what is meant by a positive and negative symptom of schizophrenia
- Compare and contrast delusions of persecution, reference, grandeur and control
- Describe what is meant by psychomotor symptoms associated with schizophrenia
- Compare and contrast Type I and Type II schizophrenia
- Summarize the characteristics of the prodromal, active and residual phases of schizophrenia
- Summarize evidence to support a biological perspective in the research of schizophrenia
- Discuss various approaches in the treatment of schizophrenia
Possible Discussion Question: How has this chapter changed your understanding of schizophrenia? In your post describe two new things you have learned about schizophrenia and how this has changed your way of thinking.
Personality Disorders
Personality disorders are defined as inflexible, maladaptive patterns of behavior that impair one's sense of self, emotional experience, goals, capacity for empathy and relationships. These patterns of behavior often lead to psychological pain for the individual and others, but because many sufferers are unaware that they have a problem they are very difficult to treat. DSM-5 identifies 10 personality disorders and separates them into three groups: Odd or Eccentric Personality Disorders; Dramatic Personality Disorders; and Anxious Personality Disorders.
Learning Objectives
- Discuss the issues in classifying personality disorders
- Define and discuss explanations and treatments for odd personality disorders, including schizoid, schizotypal and paranoid
- Define and discuss explanations and treatments for dramatic personality disorders, including antisocial, borderline, histrionic and narcissistic
- Define and discuss explanations and treatments for anxious personality disorder including avoidant, dependent and obsessive-compulsive personality disorder.
Possible Discussion Question: Pick one of the personality disorders and discuss how this week's reading has changed your understanding of that disorder.
Final exam
Your final exam will be an essay exam for which you will have the opportunity to describe, explain and apply information that you have learned over the course of the semester. Details will follow as the semester nears the end.
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06/22/2021
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"url": "https://oercommons.org/courseware/lesson/82675/overview",
"title": "\"Abnormal Psychology\"",
"author": "Jennifer Pisarik"
}
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https://oercommons.org/courseware/lesson/65285/overview
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Writing
Overview
Daily writing assignments. Please see activities folder for activities mentioned for Monday, Tuesday, Thursday, and Friday.
Writing
| Monday | Hottest and coldest places on Earth Click the link above and read. When finished, go to activities folder and choose a writing prompt. You may type or write your response. If typing your response, be sure to share with Melissa at melissa@stepaheadacademy.org. Group A: Ask an adult to record your answer via phone camera or type your response for you. Text your video response to Melissa aat 919-741-1007 or share via Google Docs at melissa@stepaheadacademy.org |
| Tuesday | See activities folder |
| Wednesday | Read and watch video |
| Thursday | See activities folder |
| Friday | Read the interview then go to activities folder and choose a writing prompt activity |
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oercommons
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2025-03-18T00:38:22.342536
|
04/15/2020
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/65285/overview",
"title": "Writing",
"author": "Julie Cronin"
}
|
https://oercommons.org/courseware/lesson/87204/overview
|
Graphic Design
Overview
The main content of this topic is to teach graphic design by focusing on common design methods.
8 Types of Graphic Design
In the content of this section, I would like to introduce you to the common four of the eight types of graphic design. Graphic design is a kind of visual communication and impact. Whether we go shopping in a mall or sit in an office to work, there are all kinds of design products all around us. So I want to show students the four types of graphic design that I prepared today.
1. Marketing & Advertising Graphic Design
Marketing graphic design is a design method used to promote and communicate products, allowing more people to understand the brand, visually allowing people to recognize and familiarize themselves with the product or service. However, there is still a difference between the two. Advertising design focuses more on the concept of advertising and how to highlight the theme of the product or service. But graphic design focuses on showing richer visual effects with graphics, text, colors, etc.
2. Package Design
Product packaging design, as the name suggests, is the design on the packaging. Another important way for a brand to promote their products is to attract people from the packaging. By linking products and designs through structure, color, image, layout, etc., the uniqueness of packaging design will attract customers and become the most eye-catching product on the shelf.
3. Illustration Graphic Design
Illustration design is a relatively new art creation technique, which is mainly displayed in flyers, posters and other items to help express brand promotion, visual creativity, and so on. This is an artistic technique that can be used for communication or decoration. It first appeared in mural paintings in caves in Europe and Asia, and later appeared in religious sites, scroll paintings, and Buddhist murals. In today's society, computer software or manual drawing is also used to help customers convey the information they want to express.
4. Web Graphic Design
Web design focuses on websites that are made up of good-looking appearance, layout, images and text. According to the needs of customers and the convenience of users to rationalize the web design. However, there are still some challenges for graphic designers, such as the need to consider the impact of image and file size and resolution on website usage (including loading speed).
|
oercommons
|
2025-03-18T00:38:22.358540
|
10/29/2021
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/87204/overview",
"title": "Graphic Design",
"author": "Xiaoyun Lu"
}
|
https://oercommons.org/courseware/lesson/79722/overview
|
Education Standards
https://www.odin.nodak.edu/databases
Author Research using Databases & Google Slides
Overview
In this lesson the students will be creating a collaborative Google Slide using Online Databases focusing on a Biography (Author) Research
Step 1: Database Review
The first part of this lesson is for the students to get a quick review of the databases available to them.
- This would be a REVIEW of how to get to the databases- the students would already have a basic understanding of the databases available to them.
For this lesson, my students will have a review of our databases available at www.odin.nodak.edu
- They will only use databases labeled K-12, and decide which one they like best based on what was used during previous projects.
Step 2: Google Slide Review
- Before starting this project, the teacher will have to create a Google Slide or use the one provided with this lesson. The teacher will have to copy & paste enough slides for each student in the class.
- Next, the teacher will share the Google Slide with the class.
- This is a collaborative lesson, so the whole class will be working on the same document.
- After they all have opened up the shared Google Slide, the teacher will assign each student a slide number. That will be the ONLY slide they will be working on during this project.
- The teacher will go over each part of what they need to fill out on their Google Slide. ALL of this information needs to come from one or more of the databases from ODIN. They are to NOT copy and paste this information they are to type it.
- This lesson is intended for grades 2-4, they will not specifically be citing their sources but I do expect them to write which database they got their information from. The next step would be for them to cite their source. All of these databases give you an option to cite where they can just copy and paste it.
Step 3: Completing the Google Slide
5. The students now should have time to go on to the database/s of their choosing. In each database they are to go to the "people" section, click on authors, and then choose on they want to research.
*** This step will change depending on what databases are available to you and your school.
6. If the students complete their research and have extra time, they can edit their slide any way they would like. Backgrounds, fonts, etc.
|
oercommons
|
2025-03-18T00:38:22.387639
|
Homework/Assignment
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/79722/overview",
"title": "Author Research using Databases & Google Slides",
"author": "Elementary Education"
}
|
https://oercommons.org/courseware/lesson/122580/overview
|
Research Outline Guiding Tool for M & D Studies
Overview
This resource is guide for M & D candidates who wish to design a research outline to submit when applying for a Masters or Doctoral qualification.
This Open Educational Resource (OER) is provided only for informational and educational purposes. The content contained within this resource is intended to be used as a starting point for further learning and exploration. This OER is licensed under share alike, meaning others can freely repurpose and share it for non-commercial purposes. However, any modifications or adaptations made to this resource must be clearly indicated and attributed back to the original source. I make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability of the OER or the information, products, services, or related graphics contained within the OER for any purpose. Every effort has been made to ensure this OER complies with copyright and other intellectual property laws. If you believe any part of this OER infringes upon your intellectual property rights, please contact me immediately. By using this OER, you agree to the terms and conditions outlined in this disclaimer.
|
oercommons
|
2025-03-18T00:38:22.404854
|
12/04/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/122580/overview",
"title": "Research Outline Guiding Tool for M & D Studies",
"author": "Ramashego Shila Mphahlele"
}
|
https://oercommons.org/courseware/lesson/17902/overview
|
Group Slideshow
Shutter Speed Quizlet
Shutter Speed
Overview
Students will be able to take images implying motion by applying fast/slow shutter speeds techniques *try and keep the 10 rules of photography in mind when shooting these pictures*
Group Slide Show
Students will work in small groups to take the following types of images:
-1 image that shows motion (Slow Shutter Speed)
-1 image where you apply panning
-1 image when elements are Frozen (Fast Shutter Speed)
- 1 Light Painting
Each group will evaluate all of the photos of that group took and each team member will then edit the same set of photos.
Individually you will upload your 4 edits and then as a group descide which edited pictures are the strongest for each category and inserted them into the slideshow.
-1 image that shows motion (Slow Shutter Speed)
-1 image where you apply panning
-1 image when elements are Frozen (Fast Shutter Speed)
- 1 Light Painting
Save your image as a Jpeg by going to: File > Save As > Change Format from Photoshop to Jpeg > Save
After you click save, say Ok to any other dialog boxes that may pop up
Homework
Homework Assignment:
Homework Assignment:
Shoot 50 - 75 images showing each of the examples of how to use shutter speed
-Apply Panning
- Motion Frozen
-Showing Motion
Extra Credit: Night Shots
Quizlet
Formative Assesment
Use the form below to answer a few shutter speed questions
Individual Shutter Speed Photos
Students take and edit their own shutter speed photos
Students will be able to take images implying and freezing motion by applying fast/slow shutter speeds techniques, while continuing to apply the rules of photography.
_______________________________________________________________________________
-1 image that shows motion (Slow Shutter Speed)
-1 image where you apply panning
-1 image when elements are Frozen (Fast Shutter Speed)
- Extra Credit: Night Shot
Save your image as a Jpeg by going to: File > Save As > Change Format from Photoshop to Jpeg > Save
After you click save, say Ok to any other dialog boxes that may pop up
|
oercommons
|
2025-03-18T00:38:22.427078
|
10/17/2017
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/17902/overview",
"title": "Shutter Speed",
"author": "Alyssa Taranto"
}
|
https://oercommons.org/courseware/lesson/108900/overview
|
Brutalist Campuses—OER on Brutalism
Canvas as a Tool for OER Remixing
remixing-oer-in-canvas-demo-export
Remixing OER Content: Using Brutalist Architecture on Campus as an OER Remixing Case Study
Overview
This module uses sample remixed content on brutalist architecture to demonstrate how to use Canvas to remix OER content, and how to use the OERizona OER Commons Template to remix OER content.
This can also be used in any event in which someone is looking for resources on brutalist architecture.
Brutalist Architecture on College Campuses
Material Description
This is a PowerPoint that contains links to open access resources that help explore how and why some college campuses have examples of brutalist architecture on them.
This also contains an mp4 video file that explores how to use Canvas as a tool for OER Remixing.
Context for sharing:
I'm sharing this as an example submission to demonstrate some remixing best practices.
Additional information about the resource:
The sources here are OER but this is really just for demo purposes.
PowerPoint
This PowerPoint attachment contains links to open educational resources about brutalist archut
Canvas Course
Common Cartridge file
Use this file to use the course in a non-Canvas LMS.
|
oercommons
|
2025-03-18T00:38:22.450390
|
Micah Weedman
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/108900/overview",
"title": "Remixing OER Content: Using Brutalist Architecture on Campus as an OER Remixing Case Study",
"author": "Unit of Study"
}
|
https://oercommons.org/courseware/lesson/127857/overview
|
remixing-oer-in-canvas-demo-export_N9eACll
Remixing Template Demo
Overview
This is a demo course on brutalist architecture.
Some Powerpoints.
Here are some powerpoints.
Canvas Commons Link
Use this link to access the course in Canvas Commons. http://www.canvas.com
Common Cartridge file
Use this common cartridge file to load this course in your LMS.
|
oercommons
|
2025-03-18T00:38:22.470222
|
Lecture
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/127857/overview",
"title": "Remixing Template Demo",
"author": "Full Course"
}
|
https://oercommons.org/courseware/lesson/66271/overview
|
The Structure and Function of the Texas Legislature
Overview
The Structure and Function of the Texas Legislature
Learning Objectives
By the end of this section, you should be able to:
- Describe the function and structure of the Texas legislature
Introduction
This section examines the structure and functions of the Texas State Legislature.
Structure
The structure of any institution or organization matters a great deal. The structure can determine how well an institution fulfills its duties and responsibilities. Article 3 of the Texas Constitution describes the legislative department (branch) of Texas. Texas Legislature utilizes a bicameral (two branches or chambers) system with the Texas Senate being the upper house, and the Texas House of Representatives the lower house. Every other state has a bicameral legislature except for Nebraska. One of the benefits of a bicameral legislature is the is forces either chamber to compromise on legislation before passing it onto the government.
Much like the Framers of the U.S. Consitution, the men who wrote the Texas constitution recognizes the benefit of slowing down the legislative process. Moreover, there are a total of 181 members of the Texas Legislature: 31 Senators, and 150 members of the House. There will be more in the text about them later; however, for now, understand that the different sizes of each chamber also plays a role in how well they function.
Texas uses single-member districts, meaning each member of the Texas Legislature represents one legislative district. This is also true of congressional seats. Every ten years, after the U.S. census, the state legislative districts and congressional districts are redrawn to maintain proportional representation. This is also called reapportionment when it is done at the national level because all 435 seats have to be approximately equal in size. This causes some states to lose or gain seats every ten years based on their changing population.
Texas State House District Map
Texas State Senate District Map
Who Represents Me?
Look on the district maps above, or visit the Texas Redistricting website to find out the state house and senate representatives who represent you.
Duties and Roles
The duties of the legislature include consideration of proposed laws and resolutions, consideration of proposed constitutional amendments for submission to the voters, and appropriation of all funds for the operation of state government. All bills for raising revenue considered by the legislature must originate in the house of representatives. The House alone can bring impeachment charges against a statewide officer, which charges must be tried by the senate. All bills for raising revenue considered by the Legislature must originate in the House of Representatives. The House alone can bring impeachment charges against a statewide officer, impeachment charges are tried by the Senate.
The Legislature is the constitutional successor of the Congress of the Republic of Texas after Texas’s 1845 entrance into the Union. The Legislature held its first regular session from February 16 to May 13, 1846.
Organization and Leadership
Although members are elected on partisan ballots, both houses of the Legislature are officially organized on a nonpartisan basis, with members of both parties serving in leadership positions such as committee chairmanships. As of the 2019 Legislative Session, a majority of the members of each chamber are members of the Republican Party.
The Lieutenant Governor (currently Dan Patrick), elected statewide separately from the governor, presides over the Senate, while the Speaker of the House (currently Dade Phelan from the Beaumont area) is elected from that body by its members. Both have wide latitude in choosing committee membership in their respective houses and have a large impact on lawmaking in the state.
Legislative Sessions
Regular Sessions
The Texas Legislature uses biennial sessions which means they meet once every odd-numbered years, for 140 days.
The Texas Legislature meets in regular session on the second Tuesday in January of each odd-numbered year. The Texas Constitution limits the regular session to 140 calendar days.
Special Sessions
Only the governor may call the legislature into special sessions, unlike other states where the legislature may call itself into session. The governor may call as many sessions as he or she desires. For example, Governor Rick Perry called three consecutive sessions to address the 2003 Texas congressional redistricting. The Texas Constitution limits the duration of each special session to 30 days; lawmakers may consider only those issues designated by the governor in his “call,” or proclamation convening the special session (though other issues may be added by the Governor during a session).
Redistricting
What is Redistricting?
Redistricting is the process by which new congressional and state legislative district boundaries are drawn. Each of Texas’ 36 United States Representatives, 31 state senators, and 181 state legislators are elected from political divisions called districts. United States Senators are not elected by districts, but by the states at large. District lines are redrawn every 10 years following completion of the United States census. The federal government stipulates that districts must have nearly equal populations and must not discriminate on the basis of race or ethnicity based on the U.S. Supreme Court case of Reynolds v. Sims (1964).
Why does Texas Have to Redistrict?
The federal constitution calls for reapportionment of congressional seats according to population from a decennial census (Section 2, Article I). Reapportionment is the division of a set number of districts among established units of government. For example, the 435 congressional seats are reapportioned among the 50 states after each decennial census according to the method of equal proportions. The boundaries of the congressional districts are then redrawn by state legislatures in accordance with state and federal law.
Redistricting is the revision or replacement of existing districts, resulting in new districts with different geographical boundaries. The basic purpose of decennial redistricting is to equalize population among electoral districts after publication of the United States census indicates an increase or decrease in or shift of population.
The Texas Constitution requires the legislature to redistrict Texas house and senate seats during its first regular session following publication of each United States decennial census (Section 28, Article III). After each census, State Board of Education seats also must be redistricted to bring them into compliance with the one-person, one-vote requirement.
Although the formal redistricting process under the Texas Constitution may remain the same, every decade sees a different, often unpredictable, path for state redistricting plans, depending on legislative, gubernatorial, Legislative Redistricting Board, and judicial action. The history of the redistricting process during the 1980s, 1990s, 2000s, and 2010s illustrates some of the different courses decennial redistricting can take. The timing and legal requirements, however, dictate that the basic process generally takes the following course, which is described in more detail in the associated sections.
Federal census population data is delivered to the legislature no later than April 1 of the year following the decennial census, and the data is usually provided several weeks earlier. As soon as the census data is verified and loaded in the computer systems, the members of the legislature and other interested parties begin drawing plans. Bills to enact new state redistricting plans follow the same path through the legislature as other legislation.
If Texas senate or house districts are not enacted during the first regular session following the publication of the decennial census, the Texas Constitution requires that the Legislative Redistricting Board (LRB), a five-member body of state officials including the lieutenant governor and speaker, meet and adopt its own plan. The LRB has jurisdiction only in the months immediately following that regular session.
If congressional or State Board of Education districts are not enacted during the regular session, the governor may call a special session to consider the matter. If the governor does not call a special session, then a state or federal district court likely will issue court-ordered plans. Similarly, if the legislature and LRB fail to adopt a state senate or state house plan, a court will likely issue a plan to fill the void.
A suit challenging an adopted redistricting plan may be brought at any time under the federal or state constitution or federal law. Before 2013, Texas and certain other states were required to obtain federal preclearance of any redistricting plans before they could be implemented. In 2013, the applicable provision of the federal Voting Rights Act was held invalid by the U.S. Supreme Court in Shelby County v. Holder.
The filing deadline for primary elections established by the Texas Election Code allows approximately six and one-half months from the end of the regular legislative session for the governor to act on any redistricting legislation passed, for the LRB to meet if necessary, for any special session called to consider redistricting if necessary, for court action, and for counties to make necessary changes in county election precincts.
Controversies
There are conflicting opinions regarding the correlation between partisan gerrymandering and electoral competitiveness. In 2012, Jennifer Clark, a political science professor at the University of Houston, said, “The redistricting process has important consequences for voters. In some states, incumbent legislators work together to protect their own seats, which produces less competition in the political system. Voters may feel as though they do not have a meaningful alternative to the incumbent legislator. Legislators who lack competition in their districts have less incentive to adhere to their constituents’ opinions.
Section 2 of the Voting Rights Act of 1965 mandates that electoral district lines cannot be drawn in such a manner as to “improperly dilute minorities’ voting power.” No voting qualification or prerequisite to voting, or standard, practice, or procedure shall be imposed or applied by any State or political subdivision to deny or abridge the right of any citizen of the United States to vote on account of race or color.
States and other political subdivisions may create majority-minority districts in order to comply with Section 2 of the Voting Rights Act. A majority-minority district is a district in which minority groups compose a majority of the district’s total population. As of 2015, Texas was home to 18 congressional majority-minority districts.
Proponents of majority-minority districts maintain that these districts are a necessary hindrance to the practice of cracking, which occurs when a constituency is divided between several districts in order to prevent it from achieving a majority in any one district. In addition, supporters argue that the drawing of majority-minority districts has resulted in an increased number of minority representatives in state legislatures and Congress.
Critics, meanwhile, contend that the establishment of majority-minority districts can result in packing, which occurs when a constituency or voting group is placed within a single district, thereby minimizing its influence in other districts. Because minority groups tend to vote Democratic, critics argue that majority-minority districts ultimately present an unfair advantage to Republicans by consolidating Democratic votes into a smaller number of districts.
Current District Maps
View current district maps at Texas Redistricting website, where you can use the DistrictViewer software.
Senate Elections at the Beginning of a New Decade
Each senator serves a four-year term and one-half of the Senate membership is elected every two years in even-numbered years, with the exception that all the Senate seats are up for election for the first legislature following the decennial census in order to reflect the newly redrawn districts.
After the initial election, the Senate is divided by lot into two classes, with one class having a re-election after two years and the other having a re-election after four years. This process protects the Senate’s membership and the Senate as an institution serving as the more elite legislative chamber during normal (i.e., not at the beginning of new decade) election cycles.
Licenses and Attributions
CC LICENSED CONTENT, ORIGINAL
Revision and Adaptation. Authored by: Kris S. Seago. License: CC BY: Attribution
Revision and Adaptation: Structure and Function of the Texas Legislature. Authored by: John Osterman. License: CC BY: Attribution
|
oercommons
|
2025-03-18T00:38:22.503537
|
05/05/2020
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/66271/overview",
"title": "Texas Government 2.0, The Texas Legislature, The Structure and Function of the Texas Legislature",
"author": "Kris Seago"
}
|
https://oercommons.org/courseware/lesson/66337/overview
|
The Criminal Justice System in Texas
Overview
The Criminal Justice System in Texas
Chapter Learning Objective
By the end of this chapter, you will be able to:
- Explain the purpose, structure, and behavior of the criminal justice system in Texas
Introduction
Criminal justice is the delivery of justice to those who have committed crimes. In Texas, the criminal justice system is a series of government agencies and institutions whose goals are to identify and catch unlawful individuals to inflict a form of punishment on them.
Insider Perspective: Theory Meets Practice
Typically a person charged with a serious crime will have a brief hearing before a judge to be informed of the charges against him or her, to be made aware of the right to counsel, and to enter a plea. Other hearings may be held to decide on the admissibility of evidence seized or otherwise obtained by prosecutors.
If the two sides cannot agree on a plea bargain during this period, the next stage is the selection of a jury. A pool of potential jurors is summoned to the court and screened for impartiality, with the goal of seating twelve (in most states) and one or two alternates. All hear the evidence in the trial; unless an alternate must serve, the original twelve decide whether the evidence overwhelmingly points toward guilt or innocence beyond a reasonable doubt.
In the trial itself, the lawyers for the prosecution and defense make opening arguments, followed by testimony by witnesses for the prosecution (and any cross-examination), and then testimony by witnesses for the defense, including the defendant if he or she chooses. Additional prosecution witnesses may be called to rebut testimony by the defense. Finally, both sides make closing arguments. The judge then issues instructions to the jury, including an admonition not to discuss the case with anyone outside the jury room. The jury members leave the courtroom to enter the jury room and begin their deliberations (Figure 12.1).
The jurors pick a foreman or forewoman to coordinate their deliberations. They may ask to review evidence or to hear transcripts of testimony. They deliberate in secret and their decision must be unanimous; if they are unable to agree on a verdict after extensive deliberation, a mistrial may be declared, which in effect requires the prosecution to try the case all over again.
A defendant found not guilty of all charges will be immediately released unless other charges are pending (e.g., the defendant is wanted for a crime in another jurisdiction). If the defendant is found guilty of one or more offenses, the judge will choose an appropriate sentence based on the law and the circumstances; in the federal system, this sentence will typically be based on guidelines that assign point values to various offenses and facts in the case. If the prosecution is pursuing the death penalty, the jury will decide whether the defendant should be subject to capital punishment or life imprisonment.
The reality of court procedure is much less dramatic and exciting than what is typically portrayed in television shows and movies. Nonetheless, most Americans will participate in the legal system at least once in their lives as a witness, juror, or defendant.
| Have you or any member of your family served on a jury? If so, was the experience a positive one? Did the trial proceed as expected? If you haven’t served on a jury, is it something you look forward to? Why or why not? |
References and Further Reading
Texas Department of Criminal Justice (2019). Texas Board of Criminal Justice. Retrieved September 10, 2019.
Licensing and Attribution
CC LICENSED CONTENT, ORIGINAL
The Criminal Justice System in Texas: Introduction. Authored by: Andrew Teas. License: CC BY: Attribution
CC LICENSED CONTENT, SHARED PREVIOUSLY
The Criminal Justice System: Theory Meets Practice. Authored by: Rice University. Provided by: OpenStax. Located at: https://cnx.org/contents/W8wOWXNF@15.7:7SLLEy8U@2/The-Rights-of-Suspects. License: CC BY: Attribution
|
oercommons
|
2025-03-18T00:38:22.524705
|
05/05/2020
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/66337/overview",
"title": "Texas Government 2.0, The Criminal Justice System in Texas, The Criminal Justice System in Texas",
"author": "Kris Seago"
}
|
https://oercommons.org/courseware/lesson/123703/overview
|
NSG 140 Nursing Theory I (Fundamentals)
Overview
Introduction to the fundamentals of nursing care for clients with selected alterations in health, utilizing the nursing process as a framework for care. Presents a holistic approach to assessment using QSEN competencies, and /or related nursing concepts. Introduces the competencies of nursing knowledge to include patient-centered care, professionalism, informatics and technology, teamwork and collaboration, safety, quality improvement, and evidence-based practice.
NSG 140 Nursing Theory I
Introduction to the fundamentals of nursing care for clients with selected alterations in health, utilizing the nursing process as a framework for care. Presents a holistic approach to assessment using QSEN competencies, and /or related nursing concepts. Introduces the competencies of nursing knowledge to include patient-centered care, professionalism, informatics and technology, teamwork and collaboration, safety, quality improvement, and evidence-based practice.
Use the attached IMSCC file to access the course in an LMS other than Canvas.
|
oercommons
|
2025-03-18T00:38:22.543547
|
01/10/2025
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/123703/overview",
"title": "NSG 140 Nursing Theory I (Fundamentals)",
"author": "BAMBI PISH-DERR"
}
|
https://oercommons.org/courseware/lesson/58415/overview
|
Animated Sprite
Piskelapp
Swirl
Pixel Art and Sprites with Piskelapp
Overview
Learn how to create and animate art one pixel at a time with Piskelapp!
Supplies & Products
You will need a computer with a mouse and the Piskelapp website.
Piskelapp
Head to the Piskelapp website.
If you'd like to save your creation to work on later, create an account before you begin drawing and animating!
If you'd rather jump right in, click "Create Sprite" to get started.
Pixel Art
"Pixel art" is art created by coloring individiual sqaures, or "pixels", on a "bitmap". "Bitmaps" are basic image files comprised of colored pixels. In this activity, pixels will be your medium and bitmaps will be your canvas!
Use the various paint and brush tools on the left to fill in the bitmap squares and create a picture made entirely of pixels!
When you're finished, use the "save" and "export" tools on the right to save the image to your Piskelapp account, or to create a finished product in the form of an image file.
Sprites
A "sprite" is a series of pixel art images, or "frames", played in succession at a high rate of speed, or "framerate". If drawn correctly, the frames will appear animated and convey motion!
Start by drawing a simple picture or shape using the tools on the left.
Once you complete your first image, hover your mouse over frame #1 on the left and click the "duplicate this frame" button on the right corner of the frame.
Select your duplicated frame and make a small, subtle change to one of the elements of your drawing. The smaller the change, the better. Once you've made a change, use the "duplicate this frame button" and make a copy.
Continue making subtle changes to the elements of your drawings, duplicating your frames as you go.
When you feel like you've made enough changes to create an animation, adjust the "FPS" slider on the right to control how quickly your frames are looped. Use the tool above the slider to preview your work.
Use the "save" and "export" tools on the right to copy your project to your Piskelapp account, or to greate a .GIF of your sprite to share!
Share your work
Proud of your pixel art or your sprite? You can save it to a public or private gallery right on the piskelapp site.
|
oercommons
|
2025-03-18T00:38:22.567943
|
Alexandra Houff
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/58415/overview",
"title": "Pixel Art and Sprites with Piskelapp",
"author": "Lesson Plan"
}
|
https://oercommons.org/courseware/lesson/128111/overview
|
S6 UNIT 10
Overview
this unit 10 aims to equip learners with ability to evaluate the success of sustainable development projects in power and energy production in different parts of the world.
UNIT 10: POWER AND ENERGY PRODUCTION IN THE WORLD
UNIT 10: POWER AND ENERGY PRODUCTION IN THE WORLD
Power refers to the capacity to do work or make things much easier.
Energy refers to any source of usable power such as solar, hydroelectric power, wind, petrol and others.
10.1. Sources and forms of energy used in the world
Classification of energy resources
- Renewable energy resources: these are natural resources which ae not exhausted when they are used. They are continuously replaced by nature. These are land, soil, water, animals and wildlife, sunshine.
- Non-renewable resources: these are resources which diminish and get exhausted when used or exploited. For example, Crude oil and natural gas
10.1.2. Non-renewable energy sources
Non-renewable energy resources are available in limited supplies. This is usually due to the long time it takes for them to be replenished.
a) Nuclear energy (Uranium)
Nuclear energy is energy obtained from uranium through a chain reaction. When it was realized that when the nucleus of an atom is bombarded by electron it disintegrates and releases enormous quantity of energy, two thoughts came in the mind of rational man:
- to build an atomic weapon, and;
- to generate electricity.
Thus, mankind has developed the art of both. The release of energy by this process is known as fission. Based on this process scientists build reactors in which controlled fission went on to produce energy (heat) and this heat generated electricity.
b) Coal
Coal is a sedimentary deposit formed by the slow action of heat and pressure on plant remain buried in the long past. It is a mechanical mixture of carbon, hydrogen, nitrogen, Sulphur.
i)Types of coal
The amount of fixed carbon and hydrocarbons forms the basis of classification of coal into various types.
- Anthracite: It is a hard and dense coal which is relatively free from iron compounds and moisture. It is made by 95 % of carbon.
- Bituminous: The moisture content is relatively low. The fixed carbon content ranges from about 50 to over 80% and that volatile matter from 40 to 15%.
- Lignite: It is also known as brown coal. The higher grades vary from dark brown to almost black. It is characterized by high moisture content, generally about 40%. The fixed carbon content is also 40%. The structure is fibrous, and sometimes woody.
- Peat: It occurs in bogs(swamps), especially in areas of cool temperate climates. This is young coal which consists of partly decomposed vegetation.
ii. Uses of coal
- in thermal generators to produce thermal electricity.
- as a domestic fuel for heating and indirectly in the form of a gas and electricity.
- in iron smelting e.g. through use of metallurgical coke in blast furnaces.
- to provide a number of raw materials for the chemical industries like coal gas, coal tar, benzele and sulphate of ammonia.
c)Petroleum (oil)
Petroleum is an inflammable mixture of oil hydrocarbons with very complex properties. Petroleum literally means ‘rock oil.’ It exists underground in solid, liquid and gaseous form. Accumulations of petroleum are found in underground fields, pools or reservoirs of sedimentary rock formations.
Three grades of crude oil according to gasoline yields
- Paraffin: base oil has high percentage of methane (highest yields)
- Mixed-base: oil has high percentage of naphthene (intermediate yields)
- Asphalt - base oil has heavier hydrocarbons (lowest yield)
Uses of petroleum
- for heating homes and hearths;
- as industrial power to drive/move engines and for heating furnaces and producing thermal electricity;
- as transport power for driving railways, motorcars, ships and aeroplanes;
- as lubricants of machines especially high-speed machines;
- as a raw material in various petro-chemicals industries, such as synthetic rubber, synthetic fibres, fertilizers, medicines.
10.1.3. Renewable energy resources
Renewable energy is the energy which comes from natural resources that are naturally replenished such as sunlight, wind, water from rivers, biogas, geothermal heat and tides which naturally replenish themselves.
a) Hydroelectric power(water energy)
This is the energy produced from running water. Usually a dam is constructed across a river to store water. China is the largest producer of HEP, followed by Canada, Brazil and USA. The water is then made to fall over a steep gradient. It then passes through a turbine hence spinning the blades of the turbine. Rotation of th e blades cause the turbine to turn an electric generator that produces electricity.
Hydro-electrical power energy requires the following physical and economic conditions:
i. Physical conditions
- A seismological less sensitive area.
- High quantity of water supplied by fairly heavy rainfall distributed throughout the year.
- Great altitude with steep slope to enhance water velocity.
- Existence of rapids and falls favour the development of power by increasing the velocity of stream.
- Narrow steep-sided valley to facilitate dam construction.
- A hard rock for firm foundation.
- Existence of lakes or space for water reservoir.
- The absence of coal, petroleum, etc., expedites the development of waterpower.
ii. Economic Conditions
- Market: Large demand for hydroelectric power;
- Huge capital outlay;
- Technological knowledge and skill and
- Transport facility.
Advantages
-Once built, the supply of electricity is relatively cheap
-Large dams become tourist attractions
-The reservoirs (lakes) that form behind the dam can be used for water sports, leisure and pleasure activities,
-The water in the reservoir can be used for used for irrigation purpose and fishing.
-Power dams control flooding.
Disadvantages
-Dams are very expensive to build
-The buildings of large dams, floods large areas and destroys existing wild life and causes the damage to habitats of any creatures living in the area.
-Changing the flow of a river will affect the water supply to lands nearer the sea. The may cause problems of irrigation for crops.
-The fertile silt that usually flows down to the floodplains and deltas is blocked by the dams
-Damming destroys the beauty of rivers and affects tourism.
b) Solar energy: is a form of power tapped from direct rays of the sun using solar panels. A greenhouse uses panels of transparent glass to trap solar energy. Another way of tapping solar energy is by use of solar cells. This transforms sunlight directly into electricity.
c) Wind energy: wind energy is renewable form of energy generated from wind. This is widely used in Europe (Denmark, Portugal, Spain, Ireland and Germany), Asia, United States. the process of the production of energy from the wind is the following: usually a propeller blade is mounted on a tower. The blade is connected onto an electric generator. As wind blows, the blade spins and turns the generator which produces electricity by converting the kinetic energy of the wind into electric energy. A suitable site for a wind turbine depends on the local wind conditions.
d) Energy from biomass: is the oldest source of renewable energy, used since our ancestors learned the secret of fire. This is the energy produced from materials of living things. This could be plant material, animal material. The generation of energy starts through the process of photosynthesis. Through this process, chlorophyll in plants captures the sun’s energy by converting carbon dioxide from the air and water from the ground into carbohydrates—complex compounds composed of carbon, hydrogen, and oxygen. When these carbohydrates are burned, they turn back into carbon dioxide and water and release the energy they captured from the sun. Bio-mass energy includes: wood fuel, Bio-gas and Gasohol.
- Wood fuel: This is a very important source of energy in third world countries. The wood obtained from forests is either used directly or converted to charcoal.
- Waste products (Bio-gas): This is a flammable gas produced by microorganisms, when organic matter is fermented under specific temperatures, moisture content and acidity.
- Gasohol: Plant material may be converted to alcohol which is a fuel.
Wood, wood wastes and garbage can be heated to produce methanol. Most plants containing starch and sugar like sugarcane and cassava can be converted to ethanol. Corn, corn stalks, manure and sewerage can be fermented and distilled to give ethanol. Both methanol and ethanol are directly burned as a fuel.
e) Geothermal energy: Geothermal energy is produced when rocks lying deep below the earth’s surface are heated to high temperatures by energy from the decay of the radioactive elements in the earth and from magma. Geothermal energy can be considered as renewable source of energy if deep underground heat flows can be tapped.
Geothermal energy can either be used for heating water, directly and space heating needs in agriculture and for domestic purposes or it can be converted into electricity.
f) Tidal energy: is a form of hydropower that converts the energy obtained from tides into useful forms of power, mainly electricity. Although not yet widely used, tidal energy has potential for future electricity generation.
As the tide rises and falls water flows into and out of bays and estuaries. If the bays and the estuaries can be closed by a dam the energy in the tidal flow can be extracted four times a day and used to spin a turbine to produce electricity.
Although all coastal areas are subject to some tidal changes, only those few areas with a large enough tidal range of some four to five meters are potential sites for tidal power plants.
10.2. Factors favouring power and energy production in the world
There are:
- Availability of market
- Availability of capital
- A high degree of technical knowledge and skills
- The amount of energy to be produced
- Presence of waterfalls
- Natural environment area where the energy will be produced.
10.2.2. IMPORTANCE OF POWER IN THE DEVELOPMENT OF THE WORLD
- It is used in industries and settlements for lighting and heating purposes
- It is a source of income to the government/earn foreign exchange: it can be exported
- It is a source of employment opportunities to many people directly or indirectly
- There are tourist potentials as they attract different tourists and foreign investors
- They facilitate the growth and development of industries
- They facilitate the growth of towns and other urban centers
- They help in the development of trade and commerce.
- It improves the standard of people
10.3.1. Problems hindering power production and supply in the world
- There is high demand for power due to rapid growth of heavy industries and urbanization
- Many waterfalls are not yet exploited due to seasonal changes
- Inadequate capital to invest in power production and maintenance
- No feasibility study in accessibility, exploitation and marketing of power services
- Lack of technical knowledge
- Over dependence on oil and its products
- Economic and political embargoes fixed by the rich countries
- Increase in oil prices imposed by Oil Producing and Exporting Countries (OPEC)
- Wastage and misuse of energy
- Depletion of wood fuel due to over exploitation of forests
- Exhaustion and deepening of coal mines.
- Environmental pollution
- To seed alternative sources of energy
- Development of renewable sources of energy like solar power, wind energy, geothermal, biogas, water energy.
- The government may come in and improve on public transport efficiency so as to reduce the need to use personal vehicle to reduce the use of petroleum.
- Switching off electricity gadgets when not in use.
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oercommons
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2025-03-18T00:38:22.637172
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03/05/2025
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"url": "https://oercommons.org/courseware/lesson/128111/overview",
"title": "S6 UNIT 10",
"author": "NIYONKURU SELEMAN"
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https://oercommons.org/courseware/lesson/62290/overview
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Chapter 16 Endocrine System
Chapter 17--Blood
Chapter 18--The Heart
Chapter 19--Blood Vessels
Chapter 20--Lymphatic System
Chapter 21--Immune System
Chapter 22--Respiratory System
Chapter 23--Digestive System
Chapter 24 Nutrition Concepts, Deep Dive into the Liver, Review of Organic Compounds
Chapter 25 Urinary System
Chapter 27 The Reproductive System (selected concepts)
Digestive Models Labeling Practice (Word)
Kahoot Questions for Ch 17 Blood
Kahoot Questions for Ch 18 (in addition to what's already in Kahoot) Heart
Kahoot Questions for Ch 19 Blood Vessels
Kahoot Questions for Ch 20 Lymphatic System
Kahoot Questions for Ch 21
Kahoot Questions for Ch 22
Kahoot Questions for Ch 26 Fluids & Electrolytes
Kahoot Questions for Review of A&P 1 Concepts
Practice for Blood Vessel in Models (Word)
Practice Reading Blood Typing Plates
Respiratory Models Labeling Practice (Word)
Video Lectures for A&P 2 (Compilation List)
Anatomy & Physiology 2 Resources
Overview
Teaching and learning resources for A&P 2. Please check back as I intend to add more.
Video Lectures for A&P 2
This is a compilation of video lectures used in my A&P 2 courses. Some videos were made by me; others were acquired from youtube, Khan Academy, and other instructors. Some videos may include "embedded questions"; my students often use these as a study tool, but I do not have an answer key to share (sorry!).
Kahoot Reviews for A&P 2
I use Kahoots in class as a fun way to review with students and/or check understanding on a video homework assignment. I also share the links with them at the end of class. A little competition usually creates a lively environment! I've also included the excel files that correspond to these links, so you can remix questions as suits your course. Then, you can do a batch upload of all questions at once to Kahoot. I suggest you play through yourself to double check answers before playing with students.
- Review of Key A&P 1 Concepts: https://create.kahoot.it/share/a-p-2-review-of-some-a-p-1-concepts/91322996-3e89-4a5b-8f40-e7cd594bd7d1
- Cardiovascular System-Blood: https://create.kahoot.it/share/ch-17-blood/f44df12c-c1cd-4d40-96f1-06df9579d2de
- Cardiovascular System-The Heart: https://create.kahoot.it/share/ch-18-the-heart/2037d723-87ab-4802-9388-07f98e5f64ad
- Cardiovascular System-Blood Vessels: https://create.kahoot.it/share/ch-19-cadiovascular-system-blood-vessels/c66a1c57-6ce8-4b3f-aeeb-aea2d1a7cc34
- Lymphatic System: https://create.kahoot.it/share/ch-20-lymphatic-system/acea1a40-2bf8-4630-b2a9-36dd59fa5161
- Immune System (limited to ): https://create.kahoot.it/share/ch-21-slides-19-31/e6eb2060-865e-4761-84a1-d6e5f9d55519
- Respiratory System: https://create.kahoot.it/share/ch-22-respiratory-anatomy/b94e274f-d250-44bb-a73c-ad5987c48bef
- Fluids & Electrolytes: https://create.kahoot.it/share/ch-26-fluids-electrolytes/78b2cf5f-2a0c-4413-bbb2-3e2b9d74433d
Notes for A&P 2
As you'll see, I started teaching A&P with powerpoints associated with the Marieb A&P text. Over the years, I've integrated more and more resources (e.g. pictures, links to articles and studies, graphics). Notes are always a work in progress for me. These are samples of my notes, so remix away!
Lab Manual: Supplemental Materials
For instructors: I also have lab assignments that are, for the most part, self grading and lab practicals built on pools of questions. If you're interested in these, please email me (jrobinson@ccsnh.edu) from a verifiable instructor account.
For everyone: The "Supplemental Lab Manual" contains the following supplemental materials:
- a study guide for each lab (the objectives)
- weblinks for a plethora of website where students can practice lab content
- weblinks for many videos to help students review lab content
- "practice documents" at the end which are pictures of models and other lab content formatted similar to a lab practical; you can always add or delete arrow or letters as you see fit
- I've also uploaded the individual "practice" documents as well for easier viewing
For instructors: I have most of this information formatted into Lab Modules (as pages ans quizzes in Canvas). If you'd like the Canvas pages, please email me (jrobinson@ccsnh.edu), so I can send you a Canvas download.
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oercommons
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2025-03-18T00:38:22.678412
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Interactive
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"title": "Anatomy & Physiology 2 Resources",
"author": "Game"
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https://oercommons.org/courseware/lesson/92546/overview
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Anxiety Countdown
Overview
Strategy for reducing anxiety that may cause inattention and zoning out in triggering situations.
Anxiety/Sustaining Attention
Introduce the activity when he’s not zoning out, in a neutral environment in order for him to get a grasp of it before using it as a strategy. When using it as a strategy, use it in a playful manner in order to make a fun activity instead.
This is a calming and grounding technique when in triggering situations. Ask the child to notice 5 things they can see, 4 things they can feel or touch, 3 things they can hear, 2 things they can smell, and 1 thing they can taste. Queue them for him and ask him about each one to grab his attention back to the present moment and stop him from zoning out.
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oercommons
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2025-03-18T00:38:22.691638
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Activity/Lab
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"url": "https://oercommons.org/courseware/lesson/92546/overview",
"title": "Anxiety Countdown",
"author": "Special Education"
}
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https://oercommons.org/courseware/lesson/65711/overview
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504 Accommodations Checklist
Accommodations
ADHS Work Sample
Ants in Their Pants
CAST website - UDL
Choice Boards
choice-boards-primary-example-length
Communication Disorders What to Do
electricity-Think-Tac-Toe1
How Difficult Can This Be?
Introduction to Special Ed
Layered Curriculum Example
Learners with Communication Disorders
Learners with Intellectual and Developmental Disabilities
Learners with Specific Learning Disabilities
Learning Contract
learning styles
lesson plan differentiation
Lesson plan differentiation2
MENU2
PPT Differentiation
Principles of Differentiation
Reg Ed Work Sample II
Speech and Language Patterns by Age
Task analysis
Teaching Strategies_ID
THE MAIN IDEA -- Driven by Data
tic_tac_toe_book_report
Universal Design for Learning video
Using Bloom’s Taxonomy to Differentiate
High-incidence Disabilities
Overview
High-Incidence Disabilities are disabilities that are more often seen in the regular education classroom. This resource is intended to be used by pre-service teacher who are learning about disabilities in the classroom and how to make accommodations for all learners.
High Incidence Disabilities and Universal Design for Learning (UDL)
High-incidence disabilities are disabilities that are more commonly seen in regular education classrooms. Students with high incidence disabilities typically are able to participate in regular education with some additional learning and support.
“High-incidence” disabilities may include:
- Communication disorders
- Intellectual disabilities
- Specific learning disabilities
- Autism Spectrum Disorder recently considered high-incidence.
See the PPT in the resource section, Introduction to Special Ed for an overview along with the resource, 13 Categories of Disabilities, which notes the areas of disabilities for which an individual may have an Individualized Education Program (IEP).
One way to support all learners is to plan lessons using Universal Design for Learning (UDL). See introductory video on Universal Design for Learning in resource section. The CAST website explains the three common areas for UDL: Engagement, Representation, and Action and Expresssion. Visit the website and view the UDL Guidelines for how to build access, build, and internalize each of the areas.
Learners with Communication Disorders
Assignment:
Writing IEP Goals for Speech
Open and analyze the two (2) documents from the Speech Evaluation Report (ER). There is one for Early Childhood titled Preschool_Sample Speech ER and one for secondary titled Middle School_Speech ER. From the information in the reports, write at least two goals for each students’ Individualized Education Report (IEP). IEP goals are annual --- something to work on for one year – and follow a particular format:
ABCD.
A-Audience: Determine who will achieve the objective. (THE STUDENT)
B-Behavior: Use action verbs (Bloom’s taxonomy) to write observable and measurable behavior that shows mastery of the objective.
C-Condition: State the condition under which behavior is to be performed.
D-Degree: State the criterion for acceptable performance, speed, accuracy, quality, etc.
Example:
Given a diagram of the eye, students will be able label the 9 extra-ocular muscles and describe at least 2 of their actions.
Write two IEP goals for each student using the ABCD format. The goals should be things that you as the regular education or special education teacher will develop over a year. Think about things that will take a year, not a short term – one is done – goal. For example, develop comprehension skills by increasing fluency would be a long-term goal where memorize three sight words would be short term.
Grading: 24 points
Each IEP goal will be worth 6 points:
4 points: Each part of the ABCD goal is obvious and highlighted as in the example above.
1 point: Goal matches the needs of the student.
1 point: Goal is long-term.
Speech-Language Diagnostic Evaluation Report
NAME: Joe Speaks NAME OF SCHOOL: Say Something Preschool
DATE OF BIRTH: 00/00/0000 CHRONOLOGICAL AGE: 3.8
TEACHER: Ms. Heythere GRADE: Preschool
EXAMINER: Ms. Talker EVALUATION DATE: 00/00/0000
HISTORY INFORMATION:
Joe, a –year three, eight-month-old male, was seen for a speech and language assessment at
the Say Something Preschool on 00/00/0000.
Additional information from Joe’s family, teacher, or medical history was not attained.
ASSESSMENT FINDINGS
HEARING SCREENING:
Joe’s hearing was not screened at the time of assessment.
ORAL MOTOR STRUCTURE/FUNCTION:
A thorough oral-facial examination was not completed; however, Joe’s face, mouth, and mandible (jaw) appeared symmetrical. His lips remained closed at rest, and there was no evidence of a repaired cleft lip or additional inhibitory scar tissue.
ARTICULATION EVALUATION:
The Goldman-Fristoe Test of Articulation was administered as a formal assessment of Joe’s articulation of consonant sounds at word level. During the GFTA, the student spontaneously or imitatively produces a single-word label after looking at pictures. Performance on this measure aids in diagnosis of a speech sound disorder, which is difficulty with sound production or delayed phonological processes. The former affects a specific speech sound in all word positions. In example, an individual with a phonetic error during the production of “s” will present this error in initial (“soft”), medial (“blessing”), and final position (“looks”). A phonological process simplifies adult speech through errors in patterns of sounds. Examples include consistently substituting difficult consonants (“r”) with ones that are easier to produce (“w”) or reducing/deleting the consonant cluster, or blend (“str” to just “t”). The speech sounds are produced accurately but are not organized correctly within the individual’s speech. While most of these types of errors are considered normal during language acquisition, all are typically suppressed gradually in children’s speech during the ages of 3-5 years.
The GFTA provides standardized scores with a mean score of 100, and a standard deviation of 15. Standard scores between 85 and 115 are considered to be within the typical range. A standard score of 100 was obtained for Joe, which falls within normal limits.
The following errors were noted:
Initial Medial Final
“p” – pig, pajamas “g” - tiger “s” - house
“q” - quack “r” - giraffe “sh” - fish
“d” - drum “t” - vegetable “f” - leaf
“v” - vacuum “l” - yellow “ch” - watch
“l” - lion “th” - brother
“r” – ring, red
“sl” - slide
“sh” - shovel
“tr” - truck
“pl” – plate
None of these speech sound errors were present consistently in Joe’s speech. These sounds were elicited correctly in other opportunities during the assessment. The most common phonological process was gliding: substituting “y” or “w” for “r” or “l.”
LANGUAGE EVALUATION:
Formal and informal evaluation measures were used to evaluate Joe’s language skills.
Language was informally assessed during a 5-minute play sample.
The Peabody Picture Vocabulary Test, Fourth Edition (PPVT-4) was administered to assess receptive vocabulary. This formal evaluation measures only words that Joe comprehends. The student is asked to point to the appropriate visual representation of the target word from a field of four on a stimulus book. The PPVT-4 provides standardized scores with a mean score of 100, and a standard deviation of 15. Standard scores between 85 and 115 are considered to be within the typical range. A standard score of 68 was obtained for Joe, falling more than 2 standard deviations below the mean. Joe incorrectly identified vocabulary from all categories: nouns, attributes, and present participles (-ing ending that accompanies a form of “to be”). The results from the PPVT-4 indicated below-average receptive vocabulary skills.
VOICE EVALUATION:
Informal evaluation measures were used to assess the student’s voice quality, and Joe exhibited normal voice quality.
FLUENCY EVALUATION:
An informal evaluation of fluency indicated a normal speaking rate for Joe during the evaluation.
SOCIAL SKILLS/BEHAVIORAL:
Despite STUDENT’s articulation delays, he is eager to share ideas in class. He needs occasional cues to use articulation strategies: “close the gate” for /s/ production. STUDENT also benefits from being allowed a second repetition of his/her expressions. This strategy increases intelligibility and his/her ability to express ideas clearly to teachers and peers. STUDENT does need assistance to keep work/things organized. He often misplaces things. STUDENT is well liked by peers and makes friends easily. He is functioning independently with age appropriate personal care and independent living skills.
DIAGNOSTIC IMPRESSIONS:
Joe demonstrated appropriate articulation skills as evidenced by a standard score within normal limits on the GFTA-3. He exhibited impaired receptive vocabulary skills characterized by a score of more than 2 standard deviations below the mean on the PPVT-4. Therefore, Joe is able to produce intelligible speech, but understanding core vocabulary words is an area of need.
PROGNOSIS:
Prognosis for Joe’s improvement in language abilities with treatment is good, provided his continued participation and motivation. In addition to intervention, he will also have a language-rich learning environment at school and extensive support from his classroom teachers.
__________________________________ __________________________________
The following paragraph is information from the Evaluation Report of a 7th grader.
In direct speech sessions, JENNIFER is working on naming, defining, comparing and categorizing 5th grade level vocabulary. Jennifer is also working on improving her ability to cohesively convey thoughts and ideas in the academic setting. JENNIFER still requires moderate cues to add details to definitions. JENNIFER is able to provide 4-5 details with those support cues. JENNIFER’s decreased vocabulary skills impact both writing skills and success on language arts assessments. JENNIFER needs moderate cues (50-70% of the time) to use vocabulary strategies. JENNIFER’S expressions often lack organization and critical details. This negatively impacts her ability to demonstrate what she has learned in class.
A communication disorder is any disorder that affects an individual's ability to understand, detect, or apply language and speech to speak and communicate with others. The delays and disorders can range from simple sound substitution to the inability to understand or use language.
This module includes the following for your review:
PPT_Learners with Communication Disorders
Speech and Language Patterns by Age
PPT_Communication Disorders: What is Expected? What to Do?
Learners with Specific Learning Disabilities
Assignment_CASE STUDY
Analyze the following description about Robert, a student identified with a Specific Learning Disability in Reading. After reviewing the PPT_Accommodations, describe at least 8 accommodations that you as the classroom teacher would provide for Robert and WHY. WHY – explain your reasoning for each of the accommodations that you have suggested.
Robert, aged 14, is the eldest son and the second child of a family of seven. He has always been a bright and intelligent boy, quick at games, and in no way inferior to others of his age. His great difficulty is his inability to learn to read. He has been at school or under tutors since he was 7 years old, and the greatest efforts have been made to teach him to read, but, in spite of this laborious and persistent training, he can only with difficulty spell out words of one syllable.
He seems to have no power of preserving and storing up the visual impression produced by words‐hence the words, though seen, have no significance for him. His visual memory for words is defective or absent.
Robert is bright and of average intelligence in conversation. His eyes are normal and his eyesight is good. His teacher says that he would be the smartest lad in the school if the instruction were entirely oral.
His father informs me that the greatest difficulty was found in teaching the boy his letters, and they thought he never would learn them.
Grading = 16 points total
Each accommodation 8 maximum points (1 point each)
Explanation of WHY you think the accommodation will benefit Robert
8 maximum points (1 point each)
Specific learning disabilities can be defined by a disorder in one or more of the basic psychological processes involved in understanding or using spoken or written language.Included in this section are the following:
PPT_Learners with Specific Learning Disabilities
PPT_Accommodations
Workshop Video_How Difficult Can This Be? -- This is a dated video, but so very helpful in understanding SLD. Worth watching!!
Learners with Intellectual or Developmental Disabilities
Learners with Intellectual or Developmental Disabilities - Intellectual disability is a disability characterized by significant limitations in both intellectual functioning and in adaptive behavior, which covers many everyday social and practical skills. This disability originates before the age of 18. An Intellegence Quotient (IQ) of 70 or below typically indicates an Intellectual Disability.
The following resources are available for your review:
PPT_Learners with Intellectual and Developmental Disabilities
PPT_Teaching Strategies_ID
Task Analysis
Differentiation
Assignment: Differentiating an Assignment
Review the assignment below and provide differentiation for content, process, and product for 3 learners with special needs: Intellectual Disability, Specific Learning Disability in Reading, Gifted. Use the chart to show your answers. Consider the entire lesson plan leading up to this assignment for the students, what content you are covering in the lesson and how you teach based on each learner’s needs. Then, think about how you would change this particular assignment as the product. An example is provided.
Example of Differentiation
Math 3-5
Mrs. Forest wanted to plan how to contact her students by phone in case the field trip they were going on the next day needed to be canceled. She decided to call one student who would then call 2 other students. Each of these students would then call 2 other students. This would continue until all students had been called. Mrs. Forest has 31 students. How many students will need to make phone calls if Mrs. Forest calls the first student?
Suggested Grade Span
Grades 3-5
Grade(s) in Which Task Was Piloted
Grade 4
Alternative Versions of Task
More Accessible Version:
Mrs. Forest wanted to plan how to contact her students by phone in case the field trip they were going on the next day needed to be canceled. She decided to call one student who would then call 2 other students. Each of these students would then call 2 other students. This would continue until all students had been called. Mrs. Forest has 15 students. How many students will need to make phone calls if Mrs. Forest calls the first student?
More Challenging Version:
Mrs. Forest wanted to plan how to contact her students by phone in case the field trip they were going on the next day needed to be canceled. She decided to call one student who would then call 2 other students. Each of these students would then call 2 other students. This would continue until all students had been called. Mrs. Forest has 31 students. How many students will need to make phone calls if Mrs. Forest calls the first student? Find a rule for determining how many phone calls will be made for any number of students.
Assignment that you will differentiate:
Name: ___________________________________________
Objective: I can identify examples of how writers use grammar in fiction.
DIRECTIONS: For each grammar concept listed below, find a sentence from ANY fiction book that correctly uses the concept.
| Topic | Example Sentences: | Complete: |
Punctuation | Semicolons
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|
Colons |
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| |
Dialogue |
|
| |
Commas (in a list) |
|
| |
Commas (nonessential clauses/ phrases) |
|
| |
Commas (after an introductory clause or phrase) |
|
|
| Intellectual Disability | Specific LD in Reading | Gifted |
Content – How would you change WHAT you are teaching?
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|
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Process – How would you change HOW you are teaching?
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Product – How would you change what the student is turning in for this assignment?
|
|
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Other???
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Points – Each of the responses within the chart will be based on the following rubric:
5 points | 3 | 1 or 0 |
Uses depth with details and examples in response; knowledge on disability is evident; focuses on learning the objective; adaptations for the disability or ability are appropriate and thorough. | Uses some explanation with details or examples in response; knowledge on disability is somewhat evident; focuses on learning the objective; adaptations for the disability or ability are somewhat appropriate. | Lack of explanation with details or examples in response; lack of knowledge on disability; does not focus on learning the objective; adaptations for the disability or ability are inappropriate. |
Other – can earn up to 3 bonus points total for additional information.
Total points – 45 with possible 3 bonus points
Differentiation is a way to adjust the content, process, and products of instruction so that students may participate. There are a variety of things to consider when differentiating and a variety of ways to differentiate.
- Content
- Process
- Product
- Readiness Levels
- Interests
- Learning Profiles
- Affect
- Learning Environment
- Grouping
- VAK (Visual, Auditory, Kinesthetic)
- Multiple Intelligences
- Universal Design for Learning
- Bloom's Taxonomy
- Assessment
- Using data
Included in this section are the following:
PPT_Principles of Differentiation
PPT_Differentiation
Example of planning for differentiation in a lesson (2)
VAK
PPT_Using Bloom's Taxonomy to Differentiate Instruction
The MAIN IDEA - Driven by Data
Choice Boards
CHOICE BOARD
Choice boards are a means of offering students a choice in assignments. Easier work is worth less points, so more assignments are completed. Conversely, more challenging work is worth more points if completed well. Students often choose what suits them best. Most importantly, all of the choices assess the objective and meet the learner’s needs.
The focus of this assignment is for you to be exposed to and experienced making a variety choice boards.
Please choose 15 points worth of options. You must choose 2 different choices. Use a lesson plan that you previously designed in another course.
CHOICES
Tic-tac-toe Board | 7 points |
Learning contract | 7 points |
Layered curriculum | 8 points |
Menu | 8 points |
Choice boards offer a series of acticities that focus on students' specific learning needs, interests, and abilities. Students decide which activities they are most comfortable completing. Included in this section are the following:
PPT_Choice Boards
Examples: Tic-tac-toe boards, Learning contracts, Menus, Layered curriculum
Students decide which activity they are most comfortable completing first, and once they master it, they can move on to more challenging activities.Choice boards offer a series of activities that focus on students’ specific learning needs, interests, and abilities. Students decide which activity they are most comfortable completing first, and once they master it, they can move on to more challenging activities.
Attention Deficit/Hyperactivity Disorder
ADHD Behavioral Intervention Plan
– each area worth 5 points based on quality of responses
Targeted Behavior:
Intervention Plan
Objectives:
Preventative Strategies:
Teaching Alternative Behaviors:
Positive Reinforcement:
Consequences for Non-compliance:
Home Interventions:
Attention Deficit /Hyperactivity Disorder (ADHD) is a highly genetic, brain-based syndrome that has to do with the regulation of a particular set of brain functions and related behaviors.
Included in this section are the following:
PPT_Ants in Their Pants
504 Accommodations
Work samples from regular education student compared to a student with ADHD
Resources
AAC: Augmentative and Alternative Communication. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=zmsdLzQW5G0
American Association on Intellectual and Developmental Disabilities. Retrieved on 5.6.20 from https://www.aaidd.org/intellectual-disability/definition
American Speech-Language-Hearing Association. Retrieved on 4.29.20 from https://www.asha.org/public/speech/development/01/
Austrailian Disability Clearinghouse on Education and Training. Retrieved on 5.11.20 from https://www.adcet.edu.au/inclusive-teaching/specific-disabilities/intellectual-disability/
Bambrick-Santoyo, P. (2010). Driven by Data: A Practical Guide to Improve Instruction. Jossey-Bass: San Francisco.
Bloom's in the Classroom. Retrieved on 5.12.20 from http://www.bloomsintheclassroom.com/2012/05/blooms-taxonomy-sample-products-and.html
Centers for Disease Control and Prevention. Retrieved on 5.13.20 from https://www.cdc.gov/ncbddd/adhd/school-success.html
Daniel - Speech Delay 4.5 Years Old. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=1mMmK-FyHds
Dysarthria. Retrrived on 4.29.20 from https://www.youtube.com/watch?v=SriryvkbU9c
Dyslexia and ADHD - Dyslexia Connect. Retrieved on 5.5.20 from https://www.youtube.com/watch?v=1WD4tNMaFyI
Dyslexia for a Day- Writing Simulation. Retrieved on 5.5.20 from https://www.youtube.com/watch?v=ZznFCz6V1cM
Examples of Different Levels of Severity in Childhood Apraxia of Speech. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=cEOy3APLA-g
Facts About Down Syndrome. Centers for Disease Control and Prevention. Retrieved on 5.6.20 from https://www.cdc.gov/ncbddd/birthdefects/downsyndrome.html
How Difficult Can This Be? Retrieved on 5.6.20 from https://www.youtube.com/watch?v=Q3UNdbxk3xs&t=22s
Introduction to Augmentative and Alternative Communication (AAC). Retrieved on 4.29.20 from https://www.youtube.com/watch?v=zmsdLzQW5G0
Learning Disabilies: What are the Different Types? Retrieved on 5.5.20 from https://www.youtube.com/watch?v=yG_xSBsFMPQ
Looney Tunes and Communication Disorders. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=UASW6zSuXaE
Mayo Clinic. Retrived on 5.6.20 from https://www.mayoclinic.org/diseases-conditions/prader-willi-syndrome/symptoms-causes/syc-20355997?utm_source=Google&utm_medium=abstract&utm_content=Prader-Willi-syndrome&utm_campaign=Knowledge-panel
Revised Bloom's Taxonomy Process Verbs, Assessments, and Questioning Strategies. Retrieved on 5.12.20 from https://www.cloud.edu/Assets/pdfs/assessment/revised-blooms-chart.pdf
See Dyslexia Differently. Retrieved on 5.5.20 from https://www.youtube.com/watch?v=11r7CFlK2sc
Specific Learning Disabilities. Project Ideal: Informing and Designing Education for All Students. Retrieved on 5.5.20 from http://www.projectidealonline.org/v/specific-learning-disabilities/
Supporting Developmental Language Disorders in the Classroom. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=PKegRlHFqH4
Teachers TV: Speech and Language Strategies. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=CUw1zkZkzhk
UDL at a Glance. Retrieved on 4.28.20 from http://www.cast.org/our-work/about-udl.html?utm_source=udlguidelines&utm_medium=web&utm_campaign=none&utm_content=homepage#.XqiNtchKhPY
Using Speak Screen in iOS 8. Retrieved on 4.29.20 from https://www.youtube.com/watch?v=6E59bJfv75U
We Are Teachers. Retrieved on 04.13.2020 from https://www.weareteachers.com/what-is-an-iep/
What are Learning Disabilities? Retrieved on 5.5.20 from https://www.youtube.com/watch?v=_3ONz6TaKIk
What is Developmental Disability? Retrieved on 5.6.20 from https://www.youtube.com/watch?v=QCk0Iq_Pwug&t=30s
Williams Syndrome: What You Need to Know. Medical News Today. Retrieved on 5.6.20 from https://www.medicalnewstoday.com/articles/220139
|
oercommons
|
2025-03-18T00:38:22.817350
|
Higher Education
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/65711/overview",
"title": "High-incidence Disabilities",
"author": "Elementary Education"
}
|
https://oercommons.org/courseware/lesson/105679/overview
|
Palo Alto College - IHE Accessibility in OER Implementation Guide
Overview
In this section, you and your team will engage in a Landscape Analysis to uncover key structures and supports that can guide your work to support Accessibility in OER. You may or may not answer all of these questions, but this is an offering.
Part One: Initial Thoughts
What is your team's initial goal for this series?
To make some sort of meaningful, measurable change to accessibility in our current and future OER offerings.
Part Two: Introductory probing questions
What does accessibility look like in our organization? How do we measure accessibility?
Physical accessibility is addressed via campus-level committee. We have a DSS office which handles course modifications for students and distributes/communicates those to instructors.
We also currently assess accessibility issues in electronic environments (Canvas courses) in a limited form, via the APPQMR process/rubric (which the district has trained a number of faculty in already), but we do not have a standardized approach to OER.
What does OER look like in our organization? How do we measure access to OER?
At PAC in recent years, we have leveraged grant funding to support a multi-year/multi-level training program for faculty who wish to incorporate OER into courses or author their own OER.
We currently track faculty who have been trained in OER, as well as courses which are coded for OER in Banner; I do not believe we have developed a universalized metric for assessing access beyond these.
Part Three: Clarifying questions for accessibility
What is the organizational structure that supports accessibility?
DSS office and a campus-level accessibility committee. TLC sometimes takes up some of this conversation, as does district-level faculty development.
Who generates most of the accessibility structures/conversation in our organization?
The DSS office, the Teaching and Learning Center…
Where do most educators get support with accessibility?
The most visible place for instructors to see accessibility support is often the modification sheets that DSS sends out as a means of accommodation at the beginning of each semester. However, we can do better – adopting UD as a faculty-led pedagogical stance could stave off access issues before they begin.
What content areas might have the largest gaps in access to accessibility?
Historically, government courses have far fewer OR-listed sections than other disciplines. We suspect this may indicate an accessibility gap as well.
Part Four: Clarifying questions for OER
What is our organizational structure that supports OER?
We have a college advisory committee and a campus-level OER team (S. Molina and M. Elston - faculty, S. Puccio - library).
Who generates most of the curricular resources in our organization?
Faculty have enthusiastically embraced OER at our campus, and almost 70% have received training to select or generate OER. A large proportion of these faculty are actively using OER. This is complemented by department-level support.
Where do most educators get support with curricular resources?
See previous answer.
What content areas might have the largest gaps in access to curricular resources/OER?
Government has the biggest historical gap. (History and Government are our developmental focus for the upcoming AY in OER.)
New CTE programs are catching up rapidly.
Part Five: Clarifying questions for Faculty learning and engagement
What Professional Learning (PL) structures have the best participation rates for our educators?
Faculty development sessions are offered at the district and campus level (through AC District Faculty Development and the PAC Teaching and Learning Center). There are also some department-level faculty development sessions, but these are uneven across departments. (For example, our English department hosts a series of Teaching Circles each year that have high participation rates. Not every department does this.) We also have a very well-attended, multi-session Faculty Symposium every year that frequently focuses on teaching issues.
What PL structures have the best "production" rates for our educators?
Professional development offerings that are developed by faculty for faculty have the best production and retention rate at Palo Alto College.
What incentive do we have to offer people for participating in learning and engagement?
OER Professional Development courses offer within Canvas (paid incentive)
Introduction to OER (1.17 WLU)
OER for the Zealot (2.34 WLU)
OER for Textbook Publication (3.0 WLU)
Who are the educators that would be most creative with accessibility and OER?
In September 2023, the PAC OER Advisory Committee will begin discussing developing professional development accessibility courses. We expect some of our early adopters to be the most creative with this aspect of OER.
Who are the educators that would benefit the most from accessibility and OER?
All educators and students will benefit from accessibility and OER.
Part Six: Final Probing questions
What is our current goal for Accessibility in OER and why is that our goal?
Create Accessibility professional development course: Modules: Empathy, Usability, Accessibility
Incorporate Universal Design into our “OER for Textbook Publication” course so that textbook authors do not have to go back and retrofit their work – but design these textbooks with accessibility in mind from the start.
Create Accessibility Review Committee for OER produced at PAC, to support goal #2 and add oversight/a “second set of eyes.”
Who have we not yet included while thinking about this work?
PAC DSS Staff (Director: Cindy Morgan)
What barriers remain when considering this work?
Funding for additional professional development
Faculty feeling “overwhelmed” by taking on access work
Limited prep time, administrative expectations vs. actual faculty workload
What would genuine change look like for our organization for this work?
Embrace of Universal Design at the Course/Department level when working with or planning OER, plus committed institutional support ($$) for faculty development toward this purpose, and to compensate faculty for time/labor.
Perhaps an additional position in the organizational chart – like a Director of Universal Design? Housed in TLC? DSS Office? (There are several options that would make sense.)
|
oercommons
|
2025-03-18T00:38:22.849103
|
Alba De Leon
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/105679/overview",
"title": "Palo Alto College - IHE Accessibility in OER Implementation Guide",
"author": "Susan Puccio"
}
|
https://oercommons.org/courseware/lesson/112814/overview
|
201_Part2_Implementation
301_Part1
Webinar Two Slidedeck
Home Base document - Accessibility in OER - Higher Education - Spring 2024 Cohort
Overview
This resource will contain all of the links and resources from the Accessibility in OER - IHE Spring 2024 Cohort webinar series.
Session One - February 15, 2024
In this section, you will find all of the links and resources from the "Accessibility in OER Spring 2023 IHE Cohort" Session One.
Links to resources from the pre-work:
Links to resources from Session One's webinar:
Video Recording of the series embedded below
Links to resources for after the webinar:
Attendance document - Please see this document for the Discussion Board links.
Breakout Rooms by Institution
Institution Name | Point Person Name | Breakout Room Number |
|---|---|---|
UMGC | Sonja Strahl | 1 |
NETC | Ron Stafford | 2 |
MCCEDU | Manisha Khetarpal | 3 |
UMBC | Michael Canale | 4 |
Alamo | Suzel Molina | 5 |
Alleghany | Working on it | 6 |
Midlands Tech | Bonnie Alger | 7 |
Pikes Peak | Jacqueline Tomrdle | 8 |
Hiram | Brittany Jackson | 9 |
Kirkwood | Kate Cameron | 10 |
Ohio Dominican | Joshua Byerly | 11 |
RTC | Di Zhang | 12 |
Siena Heights | Ashley Harris | 13 |
CCCS | Rachel Meisner | 14 |
Institution | Point Person Name | Breakout Room Number |
|---|---|---|
UNOH | Randy Blank | 15 |
UMB | George Anagnostou | 16 |
CLTCC | Kelly Kingrey-Edwards | 17 |
UNAL | Rossana Cuervo Botero | 18 |
UNG | Bonnie Robinson | 19 |
NVCC | Jeff Prater | 20 |
TAMU | Kalani Pattison | 21 |
Marymount | Brianna Chatmon | 22 |
Kutztown | Daniel Stafford | 23 |
Mt. Mary | Jennifer Kinkade | 24 |
CCCS | Kathy Sindt | 25 |
EGCC | Vanessa Birney | 26 |
EGCC | Carolyn Stevenson | 27 |
Siena Heights | Gail Ryder | 28 |
Norquest College | Kari Ubels | 29 |
Session Two - February 22, 2024
In this section, you will find all of the links and resources from the "Accessibility in OER Spring 2023 IHE Cohort" Session Two.
Links to resources from Session Two's webinar:
Text transcript of the Webinar Two Zoom Chat
Video Recording of the series embedded below
Links to resources for after the webinar:
Attendance document - Please see this document for the Discussion Board links.
Session Three - February 29, 2024
In this section, you will find all of the links and resources from the "Accessibility in OER Spring 2024 IHE Cohort" Session Three.
Links to resources from the Session Three webinar:
Video Recording (embedded below)
Links to resources for after the webinar:
Attendance document - Please see this document for the Discussion Board links.
Additional links to support teams:
Session Four - March 7, 2024
In this section, you will find all of the links and resources from the "Accessibility in OER Spring 2024 IHE Cohort" Session Four.
Links to resources from the Session Four webinar:
Video Recording One (Main Session and OER Breakout room with Joanna)
Video Recording Two (Styles Breakout with Luis)
Video Recording Three (UDL and Tables Breakout with Alison)
Links to resources for after the webinar:
Attendance document - Please see this document for the Discussion Board links.
Additional links to support teams:
Session Five - March 14, 2024
In this section, you will find all of the links and resources from the "Accessibility in OER Spring 2024 IHE Cohort" Session Five.
Links to resources from the Session Five webinar:
Links to resources for after the webinar:
Attendance document - Please see this document for the Discussion Board links.
Additional links to support teams:
Session Six - March 21, 2024
In this section, you will find all of the links and resources from the "Accessibility in OER Spring 2024 IHE Cohort" Session Six.
Links to resources from the Session Six webinar:
Links to resources for after the webinar:
Attendance document - Please see this document for the Discussion Board links.
Additional links to support teams:
Collaborative Breakout Rooms for March 21
Below are the breakout rooms for collaborative feedback during our Webinar Six.
Institution Name | Point Person Name | Breakout Room Number |
|---|---|---|
UMGC | Sonja Strahl | 1 |
NETC | Ron Stafford | 1 |
MCCEDU | Manisha Khetarpal | 2 |
UMBC | Michael Canale | 2 |
Alamo | Suzel Molina | 3 |
Midlands Tech | Bonnie Alger | 3 |
Pikes Peak | Jacqueline Tomrdle | 4 |
Hiram | Brittany Jackson | 4 |
CCCS | Rachel Meisner | 4 |
Kirkwood | Kate Cameron | 5 |
Ohio Dominican | Joshua Byerly | 5 |
RTC | Di Zhang | 6 |
Siena Heights | Ashley Harris | 6 |
| Institution Name | Point Person's Name | Breakout Room Number |
|---|---|---|
UNOH | Randy Blank | 7 |
UMB | George Anagnostou | 7 |
CLTCC | Kelly Kingrey-Edwards | 8 |
UNAL | Rossana Cuervo Botero | 8 |
UNG | Bonnie Robinson | 9 |
NVCC | Jeff Prater | 9 |
TAMU | Kalani Pattison | 10 |
Marymount | Brianna Chatmon | 10 |
Kutztown | Daniel Stafford | 11 |
Mt. Mary | Jennifer Kinkade | 11 |
CCCS | Kathy Sindt | 12 |
EGCC | Vanessa Birney | 12 |
EGCC | Carolyn Stevenson | 13 |
Siena Heights | Gail Ryder | 13 |
Norquest College | Kari Ubels | 14 |
|
oercommons
|
2025-03-18T00:38:22.915376
|
Luis Perez
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/112814/overview",
"title": "Home Base document - Accessibility in OER - Higher Education - Spring 2024 Cohort",
"author": "Joanna Schimizzi"
}
|
https://oercommons.org/courseware/lesson/113026/overview
|
Open Prompt Book from CampGPT
Overview
In CampGPT, educators experimented with generative AI-enabled tools like chatbots and image generators to learn and explore together. Their work and insights have been compiled in the Open Prompt Book from CampGPT. Throughout this prompt book, you’ll learn more about generative AI, what educators use it for, and key tips and tricks. The “Try It Out” links enable you to try the prompts in your own account (links for ChatGPT and Bard are provided). This means that, if you like an idea, you can start with the prompt in the book and then continue interacting with a chatbot to further adapt the output to your needs. In addition to the open prompts, we’ve included quotes from the educators from whom the ideas and prompts in this book were crowdsourced.
Introduction
At World Education, we believe in the power of open. We aim to share resources with educators that are reusable and adaptable. Throughout this prompt book, you’ll find “Try It Out” links that enable you to try a prompt in your own account. This means that, if you like an idea, you can start with the prompt in the book and then continue interacting with a chatbot to further adapt the output to your needs. In addition to the open prompts, we’ve included quotes from the educators from whom the ideas and prompts in this book were crowdsourced.
|
oercommons
|
2025-03-18T00:38:22.928348
|
02/18/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/113026/overview",
"title": "Open Prompt Book from CampGPT",
"author": "Rebecca Henderson"
}
|
https://oercommons.org/courseware/lesson/112664/overview
|
State Guidance for Understanding Artificial Intelligence in K-12 Schools: North Carolina
Overview
Several State Departments of Education have published guides for understanding issues around AI in education, including privacy, security, transparency, accessibility, and keeping humans at the center of learning. These and related resources are being curated on the #GoOpen Hub and are freely available and openly licensed.
Introduction
These generative AI implementation recommendations and considerations have been created as a way to
share information and resources to help direct responsible implementation of generative AI tools and guide AI
Literacy in North Carolina Public Schools.
These guidelines have been organized around the five focus areas of the North Carolina Digital Learning Plan,
which guides digital teaching and learning for North Carolina public schools. The Digital Learning Plan
encourages the safe use of innovative technology to prepare students for future school and work to improve
student outcomes and support the appropriate use of
technology to advance learning.
|
oercommons
|
2025-03-18T00:38:22.941093
|
02/12/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/112664/overview",
"title": "State Guidance for Understanding Artificial Intelligence in K-12 Schools: North Carolina",
"author": "Rebecca Henderson"
}
|
https://oercommons.org/courseware/lesson/112660/overview
|
State Guidance for Understanding Artificial Intelligence in K-12 Schools: California
Overview
Several State Departments of Education have published guides for understanding issues around AI in education, including privacy, security, transparency, accessibility, and keeping humans at the center of learning. These and related resources are being curated on the #GoOpen Hub and are freely available and openly licensed.
Introduction
Emerging technologies often lead to new and exciting learning opportunities for students, particularly in increasing personalization and accessibility options. While Artificial Intelligence (AI) can be a valuable learning tool for educators and students, it must be evaluated according to usage terms, and clear guidelines for data collection should prioritize student safety.
The California Department of Education (CDE) considers human relationships crucial in education, particularly when incorporating generative AI tools such as ChatGPT into schools. This is particularly vital in light of school closures that occurred in the recent past due to the COVID19 pandemic and other natural disasters, that left many educators and students physically isolated. AI or any other technology cannot replace the value of a student’s relationship with a caring educator who can connect on a human level.
|
oercommons
|
2025-03-18T00:38:22.953971
|
02/12/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/112660/overview",
"title": "State Guidance for Understanding Artificial Intelligence in K-12 Schools: California",
"author": "Rebecca Henderson"
}
|
https://oercommons.org/courseware/lesson/112665/overview
|
State Guidance for Understanding Artificial Intelligence in K-12 Schools: Washington
Overview
Several State Departments of Education have published guides for understanding issues around AI in education, including privacy, security, transparency, accessibility, and keeping humans at the center of learning. These and related resources are being curated on the #GoOpen Hub and are freely available and openly licensed.
Introduction
The integration of Artificial Intelligence (AI) in education starts with the fundamental understanding that AI is not a replacement for human intelligence or humanitarian presence in education. According to UNESCO, AI in education is expected to be a $6 billion worldwide industry in 20241 with estimates of growth reaching $19.9 billion by 20282. LinkedIn’s Economic Graph Research Institute estimates that, by 2030, the skill sets needed for jobs will change by 65%, affecting not just tech, but all industries. Corporate entities are moving fast to meet the need and demand for products that streamline the delivery of education, but not all products are the same. It is the responsibility of the education community to carefully and strategically understand how these products work, what data is collected, and where information is sourced.
While AI is an emerging innovation in education, Local Education Agencies (LEAs) can utilize and build on existing policies that are based on educational integrity, student safety, and proven instructional practices. In conversation, AI tools are often discussed as a holistic, outside influence on education, yet policy regarding AI should not be separately written. Key facets of these tools already apply to concerns such as student data privacy, plagiarism, cyberbullying, and digital literacy, and can be called out within existing and corresponding policies.
|
oercommons
|
2025-03-18T00:38:22.966398
|
02/12/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/112665/overview",
"title": "State Guidance for Understanding Artificial Intelligence in K-12 Schools: Washington",
"author": "Rebecca Henderson"
}
|
https://oercommons.org/courseware/lesson/113027/overview
|
Using AI to Keep Your ELL Program’s Content Ready, Relevant, and Sustainable
Overview
World Education's AI for Learning and Work initiative is dedicated to exploring the intersection of artificial intelligence and education, and how it can shape the future of the way we live and work. This blog post discusses the ways in which AI can support ELL programs for Adult Learners.
Introduction
In their latest blog post, World Education explores the role of generative AI in enhancing English Language Learning (ELL) programs, and explores how these programs can transform the creation of content, making it more relevant, engaging, and sustainable for adult learners.
|
oercommons
|
2025-03-18T00:38:22.978755
|
02/18/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/113027/overview",
"title": "Using AI to Keep Your ELL Program’s Content Ready, Relevant, and Sustainable",
"author": "Rebecca Henderson"
}
|
https://oercommons.org/courseware/lesson/88150/overview
|
Getting the Facts Straight Worksheet_Digital Version
Getting the Facts Straight Worksheet_Printable Version
GW_quote
Hospital
https://answergarden.ch/2235532
Image Verification Example 1
Image Verification Example 2
Jane Doe OSPI Twitter Post_We Do
Jane Doe OSPI Twitter post_You Do
John Doe Census Data Facebook Post_Opener
MLK_quote
Picture Verification Worksheet Digital Version
Picture Verification Worksheet- Printable
Social Media Image Quiz Digital Version
Social Media Image Quiz Printable version
Social Media Verification Worksheet_Digital Version
Social Media Verification Worksheet_Printable Version
Who Said What_Worksheet Digital version
Who Said What_Worksheet Printable version
Verifying Social Media Posts
Overview
Verifying social media posts is quickly becoming a necessary endeavor in everyday life, let alone in the world of education. Social media has moved beyond a digital world which connects with friends and family and has become a quick and easy way to access news, information, and human interest stories from around the world. As this state of media has become the "new normal," especially for our younger generations, we, educators, find ourselves charged with a new task of teaching our students how to interact with and safely consume digital information.
The following three modules are designed to be used as stand-alone activities or combined as one unit, in which the lessons can be taught in any order. "Who Said What?!" is a module focusing on author verification. "A Picture is Worth a Thousand Words'' is a module devoted to image verification. "Getting the Facts Straight" is a module designed to dive into information verification. Lastly, there are assessment suggestions to be utilized after completing all three modules.
Who said What?!
Who Said What?!
A Practice in Author Verification
We have all seen, and most likely have posted, an inspirational quote that is fitting for the poster’s current mood, attitude, outlook on life, or the issues of the day. A common practice is to simply Google a portion of a quote, click on images, and find one that is most appealing. But do we always verify that the person the quote is attributed to is correct, or that the quote itself is accurate, or even that the quote means what we think it means within the broader context of when it was stated?
Most likely, the answer is no. This activity is meant to open up conversations around the authenticity, accuracy, and context of reposted quotes on social media.
OPENER:
Display this image (provided as a jpg file) and ask students if the statement is authentic. Ask them to explain how they know it is or isn’t authentic, accurate, attributed properly, etc. Use this misattributed quote to spur conversation around if and how students determine elements of authenticity.
This quote came from John F. Kennedy's Inaugural Address, January 20, 1961.
- SCAFFOLD:
- Take the first paragraph of JFK's Inaugural Address and have students think-pair-share what do they know about the context in which this statement was made. Annotate the paragraph together (e.g., think aloud) and use an online resource such as the JFK library to explain.
EXTENSION:
Open up the full transcript of JFK’s Inaugural Address and discuss the context in which this statement was made.
Display this image (provided as a jpg file) and ask students the same questions as before.
This quote is partially accurate and went viral on social media causing quite a controversy.
The following articles discuss the life of this fake quote and how easily a quote can be misrepresented, misattributed, and cause offense when it is reposted without verification.
Use the articles as discussion starters regarding the importance of proper attribution.
I DO:
Model for your students how to verify quotes for accuracy, correct attribution, and context. This works best if you can project your computer screen for students to watch as you sift the internet for information (use a think aloud).
Choosing a quote:
Have students offer suggestions for a random quote.
Use a site like Brainy Quote’s Quote of the Day to provide a random quote.
Choose a quote based on your current class content so that it is relevant to the work your students are already doing.
Google your chosen quote and begin the work of searching for the original publication in which the quote was given. This can be a messy and drawn-out process, but one that allows students to see how you determine where, and how, to search for the truth.
WE DO:
Have students work in groups to verify quotes using similar tactics that you modeled.
Groups can select their own quote to investigate.
You could also preselect quotes if you want students to work on a particular topic.
For older students you could intentionally give them quotes that are misattributed, but seem legitimate, allowing them to show how deeply they must dig for the truth.
Provide the Who Said What Worksheet for students to fill out as they work through the verification process.
Have the groups share out how they determined the authenticity of their group’s quote.
EXTENSION:
For younger students, give all the groups the same quote to verify and make it a race to see who can accurately verify the quote first. Then chart their reponses and analyze the processes that were successful.
For older students, have them challenge other groups by finding challenging quotes to verify. Include some that are accurate and others that are specious.
YOU DO:
Have students work independently, using the Who Said What Worksheet, to verify a quote using the tactics modeled and practiced.
For younger students, preselect a quote that allows for an easier/simpler path to verification.
For older students, have them open their own social media accounts and choose a recently posted quote to verify.
A Picture Is Worth A Thousand Words
A Picture is Worth a Thousand Words
A Practice in Image Verification
In today’s world, people want to take in information faster than ever before. As the old adage goes, a picture is worth a thousand words. So what better way to get information out quickly and ensure it is consumed than to post a captivating, emotion-inducing image with a short caption. That almost guarantees that people will read, comment, and share the post thus furthering your message. People, companies, governments, and the media are using images to catch our eye, hold our attention, and share their messages in a fast, convenient, and powerful way. We often assume the pictures are undoctored and shown accurately portraying the actual situation. However, more and more images are being reused, mistitled, altered, and used to mislead. This activity is meant to open up conversation around the authenticity, accuracy, and context of images and provide tools to determine an image's veracity.
OPENER:
Give students the Social Media Image Quiz (provided as a jpeg file) and have them answer the questions for each image. The quiz can be done individually or as a whole class. Two “posts” and questions have been provided so one may be used as a model for younger students. Questions can also be altered to fit individual students’ needs.
Do you think this post is authentic? What makes you think that?
Does this post make you think or feel a certain way? What does it make you feel? Do you think the creator wants you to feel that way?
Why do you think it was posted?
Would somebody else have a different opinion about this post?
Do you think this post is authentic? What makes you think that?
Does this post make you think or feel a certain way? What does it make you feel? Do you think the creator wants you to feel that way?
Why do you think it was posted?
What type of person or organization may have published this post?
Go over images and questions as a class and share your findings and answers to the questions. Explain that these “posts” were created using random pictures and were designed to sway opinions on controversial topics such as protests and diseases. Discuss what the students looked for to determine accuracy and authenticity and whether or not these images produced an intended effect.
I DO:
Model for your students how to verify images for accuracy, correct attribution, and context. This works best if you can project your computer screen for students to watch as you sift through the internet for information.
There are two example images included below you can use (provided as jpeg files). Both can be used as an example or one can be used for the “We Do” activity below.
This is an image of medical tents assembled at the "Emergency" entrance of Kiang Wu Hospital, Macau, China. The post claims that it is at the Sanford South University Medical Center in Fargo, North Dakota. Some aspects to point out would be the language on the signage on the tent and the building, the tropical foliage in the background, and the vehicle parked in the background. None of those elements would normally be found in North Dakota.
You can also look up images of the actual Sanford South University Medical Center in Fargo, North Dakota and see that it looks nothing like the image.
Look up the hashtags as well to check for credibility
This image was taken in the Great Otway National Park, Victoria, Australia. The post claims that it is the rainforest in Brazil, and it was posted by Marcus Andrews, the Environmental Minister of Brazil. Some aspects to point out may include the type of trees, the dry soil on the ground, the title, and the name of the minister, the website and hashtag.
You can also research the quote to check if it was stated by Marcus Andrews.
WE DO:
Have students work in groups to verify images using similar tactics that you have modeled.
Groups can select their own image to investigate.
You could also preselect images if you want students to work on a particular topic.
For older students, you could intentionally giving them images that are misattributed or misrepresented, but seem legitimate, (along with some creditble ones) allowing them to show how deeply they must dig for the truth.
Provide the Picture Verification Worksheet for students to fill out as they work through the verification process.
Have the groups share how they determined the authenticity of their group’s image in a brainstorming sessions using chart paper to catalog their methods.
EXTENSION:
For younger students, give all the groups the same image to verify and make it a race to see who can accurately verify the image first. (Again, use chart paper to note the processes that work well.)
For older students, have them challenge other groups by finding challenging images to verify.
YOU DO:
Have students work independently, using the Picture Verification Worksheet, to verify an image using the tactics modeled and practiced.
For younger students, preselect an image that allows for an easier/simpler path to verification.
For older students, have them open their own social media accounts and choose a recently posted image to verify.
Getting the Facts Straight
Getting the Facts Straight
A Practice in Information Verification
We are living in the information age where statistics and data are available with the click of button, giving most everyone the capability of being a “fact checker.” But do we actually take the time to search out and verify the data being promoted, or do we accept it without much checking? Should we trust information just because it is accompanied by numbers and statistics, or should we seek to find the original source to see the data in its entirety in order to understand it within its context? This student activity is designed to begin inquiries into data verification, triangulaition, and analysis of data for verification.
OPENER:
Display this image (provided as a jpg file) and ask students for their initial “Facebook” reaction (Like, Love, Wow, etc.). Based on their responses, begin a conversation as to why they reacted that way. This should prompt questions/comments around believability, accuracy of statistics, and how to verify information.
I DO:
Model for your students how to verify the information in the above post for accuracy, and context. This works best if you can project your computer screen for students to watch as you sift the internet for information. Using the U.S. Census Data for Educational Attainment, you can begin the work of considering the claim made in the post.
The claim is not entirely false, but does take some liberties with the interpretation of data and assumptions of cause and effect.
WE DO:
Display this image (provided as a jpg file)
Direct students to the OSPI website and show them how to search for this data.
Have students work in groups to verify data using similar tactics you modeled.
Provide the Getting the Facts Straight Worksheet for students to fill out as they work through the verification process.
Have the groups share out how they determined the authenticity of their group’s data.
EXTENSION:
Groups can select their own post with data to investigate.
You could also preselect a post if you want students to work on a particular topic.
For older students, you could intentionally mislead them by creating a “fake” post, giving them data that is correct, but is written in a misleading way, allowing them to illustrate deep analysis for the truth. This website is a helpful resource in creating “fake” social media posts. (https://zeoob.com/)
ADDITIONAL OPTIONS:
For younger students, give all the groups the same data post to verify and make it a race to see who can accurately verify the data first. Chart the successful processes as for future research.
For older students, have them challenge other groups by finding challenging data to verify.
YOU DO:
Have students work independently, using the Getting the Facts Straight Worksheet, to verify data using the tactics modeled and practiced.
For younger students, use this pre-made post below (provided as a jpg file), preselect a current real social media post, or create a post that allows for an easier/simpler path to verification. This website is a helpful resource in creating “fake” social media posts. (https://zeoob.com/)
This post uses the same data source as the “We Do” activity which could make it easier for younger students to navigate. OSPI website
For older students, have them open their own social media accounts and choose a recent post with data in it to verify.
** These activities were intentionally created without a focus on the authorship of the posts as the purpose is to focus on data verification. However, if this module is taught last in the series, you could create posts that incorporate the need for author and/or image verification as well.
Assessment Suggestions
Assessment Suggestions
After completing all three modules, the following are a few assessment suggestions that can be used as a summative assessment to gage individual understanding and skill development regarding social media verification, or used as group or class projects.
Create a social media post using https://zeoob.com/ and have students complete the Social Media Verification Worksheet.
The post can incorporate all three types of verification (author, image, and information), or can focus on whichever combination works best for your class of students.
The post can be created using content relevant to your specific course and/or learning unit.
The post can be created in a variety of social media platforms (Snapchat, Twitter, Facebook, Whatsapp, Instagram). Choose the platform(s) that your students most connect with.
Find a current real social media post and have students complete the Social Media Posts Verification Worksheet.
Choose a post that incorporates the elements of verification you want students to focus on.
Author verification: Choose a post by a well known public figure (local/state/national government officials, celebrities, athletes, reporters etc.).
Image verification: Choose a post that includes a detailed image with a description/caption.
Information verification: Choose a post that includes specific data/statistics that can potentially be verified.
*Tip - Social media pages for news outlets are the most likely to have recent posts that incorporate all three elements (post by a public figure, with a meaningful image, along with data).
Have students/student groups use https://zeoob.com/ to create their own “fake” posts with information to be verified by other students/groups.
Students can create posts based on a particular topic relevant to your current learning unit or a current event.
Students can incorporate both real and fake data, or intentionally misinterpret the data to make it challenging for other students to verify.
They can use their own images to challenge their classmates to accurately verify the location.
*Note - This process of having students create “fake” posts should also open their eyes to how easy it is to mislead people through social media, both intentionally and unintentionally.
Answer Garden
Click on the link below and add an answer to the answer garden!
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oercommons
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2025-03-18T00:38:23.046744
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Reading Informational Text
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{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/88150/overview",
"title": "Verifying Social Media Posts",
"author": "Political Science"
}
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https://oercommons.org/courseware/lesson/68056/overview
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Washington Models for the Evaluation of Bias Content in Instructional Materials
Overview
Developed in 2009, this framework was designed for Washington educators to evaluate instructional content for bias using five dimensions: Gender/Sex, Multicultural, Persons with Disabilities, Socio-Economic Status, and Family.
Visit the updated 2020 version: Screening for Biased Content in Instructional Materials | OSPI
Guidelines for Identifying Bias
Visit the updated 2020 version: Screening for Biased Content in Instructional Materials | OSPI
As schools work to increase success for all students, it is important to recognize the impact of bias in classrooms, instructional materials and teaching strategies. Bias in general may be identified by determining whose interest is being portrayed and whose interest is being excluded. Evaluating for bias requires us to learn about others and to respect and appreciate the differences and similarities.
A Bias Review should consider the following elements*: | ||
Gender | Race | Ethnicity |
Sexual Orientation | Religion | Socio-economic Status |
Gender Expression & Identity | Physical Disability | Age |
Family Structure | Native Language | Occupation |
Body Shape/Size | Culture | Geographic Setting |
*This list is intended to serve as a starting point.
Instructional Materials Selection Committee
Washington State RCW 28A.320.230 requires school districts to establish an instructional materials committee to support the selection of instructional materials aswell as to provide a system for receiving written complaints in regards to materials used by the school district (Appendix B).
As teachers select classroom materials they must first be aware of their own biases and experiences which
may influence their choice of instructional materials and examples. District training should help staff and instructional materials committee members identify bias.
Involving Parents
The process of evaluating instructional materials should be inclusive and involve parent participation. Districts must provide reasonable notice to parents of the opportunity to serve on the committee and should consider the major language other than English, spoken in the community.
Challenges to Selection of Instructional Materials
District policies and procedures should include how individuals may make a complaint and how the district will receive and respond to complaints about instructional materials. By adopting clear policies and procedures, school districts can assure they are following RCW 28A.320.230.
Ten Quick Ways to Analyze Children's Books for Racism and Sexism
Adapted from the Council on Interracial Books for Children
Both in school and out, young children are exposed to racist and sexist attitudes. These attitudes—expressed over and over in books and in other media—gradually distort their perceptions until stereotypes and myths about minorities and women are accepted as reality. It is difficult for a librarian or teacher to convince children to question society’s attitudes.
But if a child can be shown how to detect racism and sexism in a book or other multimedia materials, the child can proceed to transfer the perception to wider areas. The following ten guidelines are offered as a starting point in evaluating children’s books from this perspective.
1. Check the illustrations. | Look for stereotypes. A stereotype is an oversimplified generalization about a particular group, race or sex which usually carries derogatory implications. Some stereotypes can be overt – for example, depicting a male Latino teenager as a gang member. While stereotypes may not be this obvious, look for variations which may demean or ridicule characters because of their race or sex. Look for tokenism. If there are non-white characters in the illustrations, do they look like whites except for being tinted or colored in? Do all faces look stereotypically alike, or are they depicted as genuine individuals with distinctive features? Who’s doing what? Do the illustrations depict non-whites in subservient and passive roles or in leadership and action roles? Are males the active “doers” and females the inactive observers? |
2. Check the story line. | Standard for success. Does it take “white” behavior standards for a minority person to “get ahead”? Is “making it” in the dominant white society projected as the only ideal? To gain acceptance and approval, do persons of color have to exhibit extraordinary qualities—excel in sports, get A’s, etc.? In friendships between white and children from developing countries, is it the child from the developing country who does most of the understanding and forgiving? Resolution of problems. How are problems presented, conceived and resolved in the story? Are minority people considered to be “the problem”? Are the oppressions faced by minorities and women represented as related to social injustice? Are the reasons for poverty and oppression explained, or are they accepted as inevitable? Does the story line encourage passive acceptance or active resistance? Is a particular problem that is faced by a racial minority person or a female resolved through the benevolent intervention of a white person or a male? Role of women. Are the achievements of girls and women based on their own initiative and intelligence, or are they due to their good looks or to their relationship with boys? Are sex roles incidental or critical to characterization and plot? Could the same story be told if the sex roles were reversed. |
3. Look at the lifestyles. |
Are persons from developing countries and their setting depicted in such a way that they contrast unfavorably with the unstated norm of white middle-class suburbia? If the minority group in question is depicted as “different,” are negative value judgments implied? Are minorities depicted exclusively in ghettoes or migrant camps? Look for inaccuracy and inappropriateness in the depiction of other cultures. Watch for instances of the “quaint-natives-in costume” syndrome (most noticeable in areas like costume and custom, but extending to behavior and personality traits as well). |
4. Weigh the relationships between people. |
Do the whites in the story possess the power, take the leadership, and make the important decisions? Do racial minorities and females function in essentially supporting roles? How are family relationships depicted? In black families, is the mother always dominant? In Latino families, are there always lots of children? If the family is separated, are societal conditions—unemployment, poverty, for example—cited among the reasons for the separation? |
5. Note the heroes. |
For many years, books showed only “safe” minority heroes—those who avoided serious conflict with the white establishment of their time. Minority groups today are insisting on the right to define their own heroes (of both sexes) based on their own concepts and struggles for justice. When minority heroes do appear, are they admired for the same qualities that have made white heroes famous or because what they have done have benefited white people? Ask this question: “Whose interest is a particular hero really serving?” |
6. Consider the effects on a child’s self-image. |
Are norms established which limit the child’s aspirations and self-concepts? What effect can it have on black children to be continuously bombarded with images of the color white as the ultimate in beauty, cleanliness, virtue, etc., and the color black as evil, dirty, menacing, etc.? Does the book counteract or reinforce this positive association with the color white and negative association with black? What happens to a girl’s self-image when she reads that boys perform all of the brave and important deeds? What about a girl’s self-esteem if she is not “fair” of skin and slim of body? In a particular story, are there one or more persons with whom a minority child can readily identify to a positive and constructive end? |
7. Consider the author’s or illustrator’s background. |
Analyze the biographical material on the jacket flap or the back of the book. If a story deals with a minority theme, what qualifies the author or illustrator to deal with the subject? If the author and illustrator are not members of the minority being written about, is there anything in their background that would specifically recommend them as the creators of this book? |
8. Check out the author’s perspective. |
No author can be wholly objective. All authors write out of a cultural as well as a personal context. Children’s books in the past have traditionally come from authors who are white and who are members of the middle class, with one result being that a single ethnocentric perspective has dominated American children’s literature in the United States. With the book in question, read carefully to determine whether the direction of the author’s perspective substantially weakens or strengthens the value of his/her written work. Is the perspective patriarchal or feminist? Is it solely Eurocentric or do minority cultural perspectives also receive respect? |
9. Watch for loaded words. |
A word is loaded when it has insulting overtones. Examples of loaded adjectives (usually racist) are savage, primitive, conniving, lazy, superstitious, treacherous, wily, crafty, inscrutable, docile, and backward.
Look for sexist language and adjectives that exclude or ridicule women. Look for use of the male pronoun to refer to both males and females. While the generic use of the word “man” was accepted in the past, its use today is outmoded. The following examples show how sexist language can be avoided: ancestors instead of forefathers; chairperson instead of chairman; community instead of brotherhood; firefighters instead of firemen; manufactured instead of manmade; the human family instead of the family of man. |
10. Look at the copyright date. |
Books on minority themes—usually hastily conceived—suddenly began appearing in the mid-1960s. There followed a growing number of “minority experience” books to meet the new market demand, but most of these were still written by white authors, edited by white editors and published by white publishers. They therefore reflected a white point of view. Not until the early 1970s did the children’s book world began to even remotely reflect the realities of a pluralistic society. The new direction resulted from emergence of third world authors writing about their own experiences in an oppressive society. This promising direction has been reversing in the late 1970s. Nonsexist books, with rare exceptions, were not published before 1972 to 1974. The copyright dates, therefore, can be a clue as to how likely the book is to be overtly racist or sexist, although a recent copyright d ate, of course, is no guarantee of a book’s relevance or sensitivity. The copyright date only means the year the book was published. It usually takes about two years—and often much more than that—from the time a manuscript is submitted to the publisher to the time it is actually printed and put on the market. This time lag meant very little in the past, but in a time of rapid change and changing consciousness, when children’s book publishing is attempting to be “relevant,” it is becoming increasingly significant. |
Stereotype Examples and Alternatives
STEREOTYPE EXAMPLES AND ALTERNATIVES | ||
EXAMPLES | ALTERNATIVE | |
RACE/ETHNICITY/RELIGION | ||
African Americans are depicted as employed only as athletes, or as unemployed. Native Americans are depicted as people of the past. Japanese Americans are depicted only as participants in World War II. Latinos are depicted only in the context of migrant farm work. Non-Christian religions are depicted as extreme. | All ethnic groups are portrayed as equally independent/dependent, leaders/subordinates, peaceable/ militant, open/secretive, thoughtful/impulsive etc. Religions are not presented as either right or wrong. | |
SEX /GENDER | ||
Boys are depicted as doing; girls as watching. Women are depicted only in relationship to men (husbands, sons, and bosses); as timid, silly and interested in trivial things. Men and boys must be fearless, confident, competitive, and controlling their emotions. | Members of both sexes are depicted in nontraditional as well as traditional roles in the family, at work, and in leisure activities. Members of both sexes are depicted as independent/dependent, positive/fearful, active/passive, intelligent, emotional, gentle and caring for others. | |
OTHER AREAS | ||
Gay, lesbian, bisexual and transgender people are portrayed only as angry protestors; only in Mardi- Gras type parade costumes; or only in the context of HIV/AIDS. | All identity groups are portrayed in different settings and emotions – with different ranges of dress, activity and health. | |
Only nuclear family groups are portrayed, with young, able-bodied, heterosexual parents – the father works outside the home, the mother works inside the home, and there are two to four children. | In addition to the traditional nuclear family model, family groups are depicted in which there are single parents, adopted and foster children, stepparents, same-sex parents, and/or relatives living with the family, including relatives as surrogate parents.
Extended family models are depicted, where emphasis is placed on roles and relationships rather than physical proximity. | |
All illustrations and photos are of young, able- bodied, thin, traditionally-attractive individuals. | Examples of all different ages and body types are visible, including people of size, people with wheel chairs and people with birth marks and other physical “differences”. All identity groups are portrayed in different settings and emotions – with different ranges of health - sometimes as able- bodied, sometimes as healthy, sometimes as ill and sometimes with disabilities. | |
OMISSION | ||
When non-majority and women’s contributions to humankind are included, they are segregated in special chapters, sections, units or bordered boxes, and do not appear in context. | Non-majority and women’s contributions are interwoven with the rest of the text, as they are in life. |
Appendix A: SAMPLE Evaluation Form
GENERAL CRITERIA FOR EVALUATING INSTRUCTIONAL MATERIALS |
Recommended Instructional Material:
- Type of material:
Textbook Novel (Fiction) Video (DVD/Movie) Music (CD) Computer Software Novel (Non-Fiction) Script (Play)
- Title: Copyright Date:
- Author: Publisher:
- Course or subject area: Grade level (s):
- Is this material part of a Series? Yes No Title of Series:
Gender/Sex | ||||
| Standard is clearly articulated or inferred 3 | Standard is present, but limited in presentation and/or explanation 2 | Limited presentation of standard 1 | Standard is not present N/A |
Male and female characters reflect qualities such as leadership, intelligence, imagination and courage. |
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Male and females are represented as central characters in story and illustrations. |
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Male and females are shown performing similar work in related fields |
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People are referred to by their names and roles as often as they are referred to as someone’s spouse, parent or sibling. |
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Stereotyping language as “women chatting/men discussing” is avoided. |
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Biographical or historical materials include a variety of male and female contributions to society. |
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Groups which include male and females are referred to in neutral languages such as people, mail carriers, firefighters, or legislators. |
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TOTAL SCORE: |
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Comments/Suggestions to address scores of 2 or 1:
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Multicultural | ||||
| Standard is clearly articulated or inferred 3 | Standard is present, but limited in presentation and/or explanation 2 | Limited presentation of standard 1 | Standard is not present N/A |
Materials contain racial/ethnic balance in main characters and in illustrations. |
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Minorities are represented as central characters in story and illustrations. |
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Minority characters are shown in a variety of lifestyles in active, decision- making and leadership roles. |
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Materials provide an opportunity for a variety of racial, ethnic, and cultural perspectives. |
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The vocabulary of racism is avoided. |
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Stereotyping language is avoided. |
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Biographical or historical materials include minority characters and their discoveries and contributions to society. |
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One religion is not perceived as superior to others. |
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Oversimplified generalizations about different religions are avoided in text and illustrations. |
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TOTAL SCORE: |
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Comments/Suggestions to address scores of 2 or 1: |
Persons with Disabilities | ||||
| Standard is clearly articulated or inferred 3 | Standard is present, but limited in presentation and/or explanation 2 | Limited presentation of standard 1 | Standard is not present N/A |
People are sometimes portrayed as able-bodied, healthy, ill, and having disabilities. |
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Qualities of character such as leadership, imagination, courage, and integrity are distributed among non- handicapped persons and persons with disabilities. |
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Non-handicapped persons and persons with disabilities are represented as central characters in story and illustrative materials |
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Non-handicapped persons and persons with disabilities are shown performing similar work in related fields. |
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Non-handicapped persons and persons with disabilities are shown working and playing together as colleagues |
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Persons with disabilities are referred to by their names and roles rather than their disability |
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Biographical and historical materials include contributions to society by persons with disabilities |
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TOTAL SCORE: |
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Comments/Suggestions to address scores of 2 or 1: |
| Socio-Economic Status | ||||
| Standard is clearly articulated or inferred 3 | Standard is present, but limited in presentation and/or explanation 2 | Limited presentation of standard 1 | Standard is not present N/A | |
Social class groupings portray all individuals in a variety of roles (positive and negative) and situations displaying positive and negative characteristics of integrity, humility, valor, and intelligence. |
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Oversimplified generalizations about social classes and groups are avoided in text and illustrations. |
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All individuals are judged by their strength of character rather than their socio-economic status. |
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Characters are described by their behaviors, beliefs, and values rather than unnecessary socio-economic descriptors. |
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Contributions of individuals are valued for their benefit to all peoples of society. |
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Materials provide an opportunity for dialogue which considers a variety of socioeconomic perspectives. |
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TOTAL SCORE: |
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Comments/Suggestions to address scores of 2 or 1: |
| Family | ||||
| Standard is clearly articulated or inferred 3 | Standard is present, but limited in presentation and/or explanation 2 | Limited presentation of standard 1 | Standard is not present N/A | |
In addition to the traditional nuclear family model, family groups are depicted in which there are single parents, adopted and foster children, step-parents, same-sex parents, and/or relatives living with the family. |
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A variety of life’s experiences are depicted. |
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People of all groups are depicted in a variety of clothing and with a variety of eating habits and activities. |
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Males and females are depicted in non-traditional as well as traditional roles in the family, at work, in leisure activities, and in attitude. |
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Do you recommend the use of this instructional material within the classroom? yes no Comments:
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Appendix B: Washington State Law
RCW 28A.320.230 Instructional Materials – Instructional Materials Committee
Every board of directors, unless otherwise specifically provided by law, shall:
(1) Prepare, negotiate, set forth in writing and adopt, policy relative to the selection or deletion of instructional materials. Such policy shall:
- State the school district's goals and principles relative to instructional materials;
- Delegate responsibility for the preparation and recommendation of teachers' reading lists and specify the procedures to be followed in the selection of all instructional materials including text books;
- Establish an instructional materials committee to be appointed, with the approval of the school board, by the school district's chief administrative officer. This committee shall consist of representative members of the district's professional staff, including representation from the district's curriculum development committees, and, in the case of districts which operate elementary school(s) only, the educational service district superintendent, one of whose responsibilities shall be to assure the correlation of those elementary district adoptions with those of the high school district(s) which serve their children. The committee may include parents at the school board's discretion: PROVIDED, That parent members shall make up less than one-half of the total membership of the committee;
- Provide for reasonable notice to parents of the opportunity to serve on the committee and for terms of office for members of the instructional materials committee;
- Provide a system for receiving, considering and acting upon written complaints regarding instructional materials used by the school district;
- Provide free text books, supplies and other instructional materials to be loaned to the pupils of the school, when, in its judgment, the best interests of the district will be sub served thereby and prescribe rules and regulations to preserve such books, supplies and other instructional materials from unnecessary damage.
Recommendation of instructional materials shall be by the district's instructional materials committee in accordance with district policy. Approval or disapproval shall be by the local school district's board of directors.
Districts may pay the necessary travel and subsistence expenses for expert counsel from outside the district. In addition, the committee's expenses incidental to visits to observe other districts' selection procedures may be reimbursed by the school district.
Districts may, within limitations stated in board policy, use and experiment with instructional materials for a period of time before general adoption is formalized.
Within the limitations of board policy, a school district's chief administrator may purchase instructional materials to meet deviant needs or rapidly changing circumstances.
RCW 28A.640.020 Regulations, guidelines to eliminate discrimination--Scope. (1) The superintendent of public instruction shall develop regulations and guidelines to eliminate sex discrimination as it applies to public school employment, counseling and guidance services to students, recreational and athletic activities for students, access to course offerings, and in textbooks and instructional materials used by students.
- (e) Specifically with respect to textbooks and instructional materials, which shall also include, but not be limited to, reference books and audio-visual materials, they shall be required to adhere to the guidelines developed by the superintendent of public instruction to implement the intent of this chapter: PROVIDED, That this subsection shall not be construed to prohibit the introduction of material deemed appropriate by the instructor for educational purposes.
WAC 392-190-055 Textbooks and instructional materials—Scope—Elimination of sex bias— Compliance timetable.
- It is the intent of this section to eliminate sex bias in connection with any form of instruction provided by a school district.
- The instructional materials policy of each school district required by RCW 28A.320.230 shall incorporate therein, as part of the selection criteria, a specific statement requiring the elimination of sex bias in all textbooks and instructional materials including reference materials and audio-visual materials.
- The instructional materials committee of each school district shall establish and maintain appropriate screening criteria designed to identify and eliminate sex bias in all textbooks and instructional materials including reference materials and audio-visual materials: Provided, That such selection criteria shall be consistent with the selection criteria endorsed by the state board of education dated December 6, 1974, WAC 180-48-010, as now or hereafter amended, and WAC 180-46-005 through WAC 180-46-060, as now or hereafter amended. One of the aids to identification of sex bias in instructional materials consists of the Washington Models for the Evaluation of Bias Content in Instructional Materials published by the superintendent of public instruction.
- In recognition of the fact that current instructional materials which contain sex bias may not be replaced immediately, each school district should acquire supplemental instructional materials or aids to be used concurrent with existing materials for the purpose of countering the sex bias content thereof.
- Nothing in this section is intended to prohibit the use of assignment of supplemental instructional materials such as classic and contemporary literary works, periodicals and technical journals which, although they contain sex bias, are educationally necessary or advisable.
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oercommons
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2025-03-18T00:38:23.178067
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Barbara Soots
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"title": "Washington Models for the Evaluation of Bias Content in Instructional Materials",
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https://oercommons.org/courseware/lesson/64073/overview
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Trading on Equity
Overview
Trading on equity occurs when a company incurs new debt (such as from bonds, loans, or preferred stock) to acquire assets on which it can earn a return greater than the interest cost of the debt. If a company generates a profit through this financing technique, its shareholders earn a greater return on their investments. In this case, trading on equity is successful. If the company earns less from the acquired assets than the cost of the debt, its shareholders earn a reduced return because of this activity. Many companies use trading on equity rather than acquiring more equity capital, in an attempt to improve their earnings per share.
Given:
Defination
Meaning
Examples and illustrations
Types
Advantages
Limitations
Financial Concepts
Definition:
Trading on equity, which is also referred to as financial leverage, occurs when a corporation uses bonds, other debt, and preferred stock to increase its earnings rather than equity on its common stock.
Meaning:
Equity means equity capital or capital of the owners, whereas trading means earning of profits. In composite form, the method of earning profits by equity capital is known as trading on equity. In a narrow sense, when trading in any business institution is done on the basis of debt capital, rather than equity capital, then it is known as trading on equity.
The term owes its name also to the fact that the creditors are willing to advance funds on the strength of the equity supplied by the owners. Trading feature here is simply one of taking advantage of the permanent stock investment to borrow funds on reasonable basis.
When the amount of borrowing is relatively large in relation to capital stock, a company is said to be ‘trading on this equity’ but where borrowing is comparatively small in relation to capital stock, the company is said to be trading on thick equity.
However, in a broader sense, when the managers/directors of any company depend upon debt or debentures or issue of preference shares to fulfill the financial requirements of the company, aiming at earning maximum profits on equity shares held by them, it is known as trading on equity.
Example of Trading on Equity:
To illustrate trading on equity, let's assume that a corporation uses long term debt to purchase assets that are expected to earn more than the interest on the debt. The earnings in excess of the interest expense on the new debt will increase the earnings of the corporation's common stockholders. The increase in earnings indicates that the corporation was successful in trading on equity. If the newly purchased assets earn less than the interest expense on the new debt, the earnings of the common stockholders will decrease.
Example 1:
Izhaan Company is capitalized with Rs. 10, 00,000 dividends in 10,000 common shares of Rs. 100 each. The management wishes to raise another Rs. 10, 00,000 to finance a major programme of expansion through one of four possible financing plans.
A) May finance the company with all common stock,
B) Rs. 5 lakhs in common stock and Rs. 5 lakhs in debt at 5% interest,
C) All debt at 6% interest or
D) Rs. 5 lakhs in common stock and Rs. 5 lakhs in preferred stock with 5% dividend.
The company’s existing earnings before interest and taxes (EBIT) amounted to Rs. 1,20,000 corporation tax is assumed to be 50%
Solution:
Impact on trading on equity, will be reflected in earnings per share available to common stock holders. To calculate the EPS in each of the four alternatives EBIT has to be first of all calculated.
| Proposal A Rs. | Proposal B Rs. | Proposal C Rs. | Proposal D Rs. |
EBIT | 1,20,000 | 1,20,000 | 1,20,000 | 1,20,000 |
Less interest |
| 25,000 | 60,000 |
|
Earnings before taxes | 1,20,000 | 95,000 | 60,000 | 1,20,000 |
Less taxes @ 50% | 60,000 | 47,500 | 30,000 | 60,000 |
Earnings after taxes | 60,000 | 47,500 | 30,000 | 60,000 |
Less Preferred stock dividend |
|
| 25,000 | |
Earnings available to common stock holders | 60,000 | 47,500 | 30,000 | 35,000 |
No. of common shares | 20,000 | 15,000 | 10,000 | 15,000 |
EPS | Rs. 3.00 | 3.16 | 3.00 | 2.33 |
Thus, when EBIT is Rs. 1,20,000 proposal B involving a total capitalisation of 75% common stock and 25% debt, would be the most favourable with respect to earnings per share. It may further be noted that proportion of common stock in total capitalisation is the same in both the proposals B and D but EPS is altogether different because of induction of preferred stock.
While preferred stock dividend is subject to taxes whereas interest on debt is tax deductible expenditure resulting in variation in EPS in proposals B and D, with a 50% tax rate the explicit cost of preferred stock is twice the cost of debt.
Thus, the meaning of trading on equity is the technique, by which attempt is made to earn more income on equity capital getting capital through fixed cost securities. There is a limit to the proportion of debt that can be added before the corporation's financial future is jeopardized.
Following are the important points regarding trading on equity:
- Trading on equity is a technique to earn profits.
- In equity capital, the amount of both equity shares and free reserves and Debt capital are included.
- The proportion of debt capital is higher in it, as compared to owners capital.
- Operation of own regular trade is done in it by taking the capital, along with owners capital.
- This policy is adopted only when the owners feel confident on the basis of certain and sufficient Grounds that the amount of interest payable on loans was taken will be less than the income to accrue on account of the Debt capital.
2 Types of Trading on Equity
1. Trending on Low or Tiny Equity
When the quantity of share capital of the company is less than the debt capital than that situation is known as trading on Low or thin equity. In other words, when the share of fixed cost securities (Debt, Debentures or Preference shares) is more than equity capital, it is said that the company is trading on low or thin equity.
2. Trading on High or Thick Equity
When the share capital of the company is more than the debt capital, that situation is known as trading on high or thick equity. In other words, when a company collects more funds from equity shares and less by the fixed cost securities, then it is said that the company is trading on high or thick equity.
Importance or Advantages of Trading on Equity
Following are the advantages or importance of trading on equity to the company and its several parties:
1. Continuous Operation of Trading
The most important advantages of trading on equity to the company are that its trade operates quite regularly, because the company also rises the debt capital, along with ownership capital.
2. Payment of Dividend on High Rate
The company may increase its income by using the policy of trading on equity and may make payment of dividend at a higher rate on the equity capital. As a result, the income of shareholders also increases.
3. Minimize Tax Burden
The tax burden on the company gets minimized, by trading on equity, because the tax is levied only on profits accruing after payment of interest on loans and debentures.
4. Increase in Goodwill of Company
Since as a result of trading on equity, the dividend is paid at high rates, it has good effects on the Goodwill of the company, as well. With the increase in Goodwill of the company, the per share price of the company also goes high. As a result, the company is able to easily obtain loans from the market and owners of the company become capable to expand their trade with the help of Debt capital.
5. Control on Financial Sources
The company may gain control over maximum financial sources, even with the investment of very low capital, by using the policy of trading on equity.
6. Control on Business
By trading on equity, the promoters or establishers of the business may exercise control on the business, because if the quantity of equity capital gets reduced, then it is issued to a small group. As a result, the voting power gets centralized in the hands of a small group and control over the business may be gained, easily.
Limitations of Trading on Equity
Along with various advantages of a policy of trading on equity, it has some limitations or disadvantages also, which are as follows:
1. Uncertainty of Income
The policy of trading on equity may be profitable only when the income of the business has certainty, stability, and continuity
2. Low Rate of Return
When the rate of return received on invested capital goes on decreasing and rate of return becomes even lower than the rate of interest and rate of preference dividend, then the company is not in a position to carry out trading on equity. Hence, the company will get deprived of the benefits of trading on equity on reduction in the rate of return.
3. Limitations Relating to Management Support
If the financial position of the company is so good that it may arrange funds by issuing debentures or mortgage deeds and this debt capital is economical, in comparison to the share capital. Even then, its management may decline to support this policy.
4. Loan on High Rate of Interest
The rate of interest on the amount taken on loan gradually goes on rising, as a result of the policy of trading on equity, because every fresh loan increases the risks.Hence, the investor taking high risks wants its reward also. As a result, the company has to reduce the rate of the dividend of the shareholders.
5. Legal and Contractual Difficulties
Many times, trading on equity is beneficial. But, obstacles arise in taking loans, due to restrictions by the existing legal provisions, like – Company act, and other Nation act, and also according to the contract.
6. Fear of Over Capitalisation
Trading on equity is operated on the strength of debt, but it may be the to a certain limit only, reason being that due to interest not decided rates the burden of expenses on the company becomes so heavy that after some time, the business becomes overcapitalization. It reduces the loan taking capacity of the company and the market value of the shares also starts declining due to a reduction in the rate of dividend.
7. Under Intervention of Loan Givers
Besides other economic reasons the influence and intervention of the loan givers increases, while adopting the policy of “Trading on Equity”.In such a situation, whenever the need for additional capital arises, the business faces difficulty because for each such scheme of increasing the capital requires the approval of the loan givers.
8. Difficulty in Extra Capital
If the activities of the company are directed by Finance Corporation, Industrial Development Bank, and other specific financial institutions, then such Institutions may even limit the maximum amount of loan which may be taken by the company and may stop the issue of next debentures and Mortgage Loans.
Limitations of Debt
Now, the question arises, to what extent debt should be availed by the management to take profit of trading and increasing the utility.
In response, it may be said that the debt capital should be used until the additional income generated by Debt capital is more than the cost of the debt capital.
When the additional cost and additional income are equal, that is the maximum limit of the debt capital. At this level, Earning per share (EPS) will always be the same, irrespective of the debt-equity mix.
This is known as the abstract point of earning before tax and interest (EBIT).
Abstract point is that point where the rate of return on investment of debt capital is equal to the rate of interest of this capital.
If the probable income of the companies is much above this point, It will be beneficial to arrange funds through the debentures.
On the contrary, if the income is expected to be less than this point, The use of equity share capital will be beneficial, because in such condition, Earning per share will be high.
If the expected income is less than even the fixed costs, the company will incur losses.
In addition to it, use of equity shares will also not prove useful for the company and hence, the closer of the business will be worthwhile, keeping in view of safeguarding the interests of the owners.
Thus, the best form of the capital structure may be determined with the help of abstract point analysis.
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oercommons
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2025-03-18T00:38:23.268301
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Reading
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https://oercommons.org/courseware/lesson/92450/overview
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Labor Equity in Open Science Lesson Plan - PDF
Labor Equity in Open Science Lesson Plan - Word
Labor Equity in Open Science - Presentation
Persona 1 Handout
Persona 2 Handout
Persona 3 Handout
Persona 4 Handout
Persona 5 Handout
Scenario 1 - Printable
Scenario 2 - Printable
Scenario 3 - Printable
Scenario 4 - Printable
Scenario 5 - Printable
Scenario 6 - Printable
Scenario 7 - Printable
Labor Equity in Open Science
Overview
Labor Equity in Open Science is an interactive lesson plan designed to introduce students to labor equity issues in open science practices. The lesson is designed for MLIS students, and assumes no prior knowledge. During the lesson, students are given a persona representing a researcher, encompassing various professional and personal identities. Students are then given multiple scenarios and asked to predict how their persona would respond and why. Through group discussion and personal reflection, students consider the ways that researchers in different positions engage with open science in different ways.
Labor Equity in Open Science - Lesson Plan
Lesson Plan
Labor Equity in Open Science
Summary
This lesson plan is an interactive, experiential learning activity for MLIS students with an interest in scholarly communication. This lesson gives students the opportunity to consider scholarly communication issues from an equity lens. Using personas and scenarios, students are invited to consider the ways that different people with different professional identities are affected by common open science activities. This personal exploration is supplemented by background readings, a guided group discussion, a personal reflection, and a short writing exercise that encourages students to consider how they can address inequity in their own work as information professionals.
Table of Contents
| Summary | Pg. 1 |
| Table of Contents | Pg. 1 |
| Learning Objectives | Pg. 2 |
| Lesson Overview | Pg. 3 |
| Pre-activity Reading Assignment | Pg. 4 |
| Personas | Pg. 5-7 |
| Scenarios | Pg. 8-9 |
| Discussion Activity | Pg. 10 |
| Post-Activity Assessment | Pg. 10 |
| Alternate Assignment | Pg. 11 |
| Photo Attribution | Pg. 12 |
Learning Objectives
- Students will be able to recognize common open science activities and best practices.
- Students will compare and contrast the barriers that different researchers face in following best practices in open science.
- Students will explain the ways that varying levels of privilege affect open science practice
- Students will develop a strategy for reducing barriers researchers face in following best practices in open science.
Lesson Overview
Pre-activity Reading Assignment
- 4 readings: two short web articles and 2 academic articles. These readings provide an introduction to open science for students who are new to the topic, and introduce the equity issues that they will evaluate during the in-class activity.
In-Class Activity (60 minutes)
- Can be completed in-person or virtually via synchronous learning tools.
Introduction (10 minutes)
- This is time for the instructor to introduce the activity, hand out materials, and answer any questions about the pre-activity readings. A short slide deck for this section is included in the instructional materials.
Individual Persona/Scenario Assignments (20 minutes)
- Provide each student with one persona and 3 scenarios. They will have 20 minutes to think through their scenarios. Students should determine what their persona’s actions will be in different scenarios and be prepared to explain their reasoning. Student handouts with persona and scenario details are included in the instructional materials.
Group Discussion (30 minutes)
- The class will have 30 minutes to come together as a group, share their experiences, and connect their individual persona assessments to wider trends and structural issues.
Post-Activity Assessment
- Students will be given two short writing assignments as homework. The first is a one-page reflection asking students to reflect on their persona, what barriers affected them, and how they relate to wider social justice issues. The second assignment asks students to identify one of these barriers and briefly conceive of a way they might reduce that barrier as librarians.
Instructor Guideline: We recommend displaying a timer for students during the individual persona/scenario assignment to ensure students stay on track and have enough time for the group discussion.
Pre-activity Reading Assignment
Instructor Guideline: Have students complete these readings before the in-class activity so they have background information on open science practices, barriers, and issues before applying that knowledge in the persona activity. All of the articles are freely available online.
de la Fuente, G. B. (n.d.). What is Open Science? Introduction. FOSTER Open Science. https://www.fosteropenscience.eu/content/what-open-science-introduction
Crotty, D. (2021, August 19). The curse of more, or, does anybody have any time left to do research? The Scholarly Kitchen. https://scholarlykitchen.sspnet.org/2021/08/19/the-curse-of-more-or-does-anybody-have-any-time-left-to-do-research/
Gownaris, N. J., Vermeir, K., Bittner, M.-I., Gunawardena, L., Kaur-Ghumaan, S., Lepenies, R., Ntsefong, G. N., & Zakari, I. S. (2022). Barriers to full participation in the open science life cycle among early career researchers. Data Science Journal, 21(1), 2. https://doi.org/10.5334/dsj-2022-002
Instructor Guideline: Students can skip the “Survey Design and Results” section.
Olejiniczak, A., & Wilson, M. (2020). Who’s writing open access (OA) articles? Characteristics of OA authors at Ph.D.-granting institutions in the United States. Quantitative Science Studies, 1(5), 1429–1450. https://doi.org/10.1162/qss_a_00091
Instructor Guideline: Students only need to read Section 1: Introduction, and Section 5: Discussion and Conclusions.
Personas
Instructor Guideline: Each student should be given one persona to work with for the instruction activity. Each student should be given a unique persona unless there are more students in the class than there are personas. Students with the same persona should be given different combinations of scenarios.
Persona 1
Jerry is a tenured professor in the chemistry department at a well-known, elite private university. He has already achieved tenure and teaches one class per semester. Conducting research is a significant part of his job description. His library has staff that helps him manage the publishing workflow, including assistance with data management plans, open lab notebooks, and uploading his research articles and data to the institutional repository on his behalf. His university has a fund dedicated to article processing charges when faculty publish open access.
STEM
Persona 2
Kate is an early-career researcher at a small, little-known private university. She is a new adjunct faculty member in the sustainability department, and will only have her position for two years. She has a full teaching load of 4 classes per semester and has no dedicated time for research in her job description. The library at her institution is small and has no dedicated staff or funding that can help her practice open science.
STEM
Persona 3
Thomas is a tenure-track professor in the geological science department at a large, comprehensive public university. He teaches 2 courses per semester, with the rest of his time dedicated to research. He is only one year away from his tenure review, and his employment will be terminated if he does not pass it. The library at this institution provides a variety of online guides and resources to support open science, but has limited staff for direct assistance. The university has agreements with a select few publishers to allow their authors to publish open access for free but provides no financial support for open access publication with other publishers.
STEM
Persona 4
Cath is a tenured professor in the english department at a large, comprehensive public university. They have already achieved tenure and teach one class per semester. Conducting research is a significant part of their job description. The library at this institution provides a variety of online guides and resources to support open science, but has limited staff for direct assistance. The university has agreements with a select few publishers to allow their authors to publish open access for free, but provides no financial support for open access publication with other publishers.
Humanities
Persona 5
Carl is an early-career researcher at a well-known, elite private university. He is a new adjunct faculty member in the philosophy department, and will only have his position for two years. He has a full teaching load of 4 classes per semester and has no dedicated time for research in his job description. His library has staff that helps him manage the publishing workflow. His university has a fund dedicated to author processing fees when faculty publish open access.
Humanities
Scenarios
Instructor Guideline: Each student should be given three scenarios. Note that some scenarios are labeled as being STEM- or humanities-specific. These scenarios should only be matched with personas in their same disciplines. If there is no label, the scenario applies to all personas.
Scenario 1
The institution your persona works for has adopted a new open access policy stating that all faculty at the institution are required to upload a copy of the final accepted version of their published articles to the institutional repository. The policy, while supported by the administration and the faculty, has no clear method of enforcement. Your persona has already had their work accepted by a prestigious journal that does not allow work published in the journal to be uploaded to a repository. What options do they have, and what will their next course of action be?
Scenario 2
The institution your persona works for has adopted a new open access policy stating that all faculty at the institution are required to upload a copy of the final accepted version of their published articles to the institutional repository. The policy, while supported by the administration and the faculty, has no clear method of enforcement. The researcher is finalizing their manuscript but has not yet submitted it to any journals. What options do they have, and what will their next course of action be?
Scenario 3
Your persona has secured grant funding for a major research project. As part of the grant requirements, they are required to publish their article open access immediately upon publication. What options do they have, and what actions might they take?
Scenario 4
Your persona is undertaking a major, high-profile, experimental research project. The head of their department is asking them to pre-register their experiment and keep an open lab notebook, to ensure the validity of the results in such high-profile research. What options do they have, and what actions might they take?
STEM only
Scenario 5
Your persona has secured grant funding for an exciting new project. One of the conditions of this grant funding is that they must make a research data management plan to be submitted to the grant agency and followed during the course of the research. In addition, they are required to make a version of the research publication open access, in any form, immediately upon publication of the article. What options do they have, and what actions might they take?
STEM only
Scenario 6
Your persona has received an email from a publisher that wants to publish their work. The publisher claims they will publish their article open access in less than a month, so long as they pay a $3000 publishing fee. In addition, the publisher has also invited them to sit on their editorial board! What might your persona do next, and why?
Scenario 7
Your persona is interested in open science but does not publish many articles as part of their research. They are in a monograph-heavy discipline, and aren't sure that open access has any relevance to their discipline. What options do they have, and what actions might they take?
Humanities only
Discussion Activity
Instructor Guideline: After working through their persona/scenario combinations, the class should come together as a group to discuss the systematic barriers that they noticed their personas working through. In particular, students should be encouraged to compare how their personas handled the same scenarios differently and start to think beyond their individual personas in order to consider the wider, structural barriers to open science practice.
Guiding Questions:
- Have students compare how two different personas handled the same scenario. Did the two personas handle the situation differently, and if so, why?
- If students came to different conclusions about the same persona/scenario combination, give them the opportunity to discuss their reasoning. There is not necessarily a correct answer!
- Have students briefly share the barriers their persona faced across their scenarios. What wider, structural issues emerge from that comparison?
Post-activity Assessment
Instructor Guideline: These short writing assignments are intended to be completed outside of class, following the in-class persona activity. This is the student’s opportunity to think individually and holistically about structural barriers, as well as begin to move from identifying barriers to eliminating them. This is also the best opportunity to collect work for a grade.
- Please write a one-page reflection that discusses the barriers (or lack thereof) that your persona faced in their scenarios. How did their barriers differ between scenarios? What was easy for them and what was hard? How do their identities, demographics, and professional status affect the barriers they face?
- Identify one common open science activity from the article “Barriers to full participation in the open science life cycle among early career researchers”, and then identify one significant barrier your persona faces in doing that activity. Briefly outline a strategy you could implement as a librarian for eliminating or reducing that barrier.
Alternate Assignment
Instructor Guideline: This is an alternate (or additional) assignment that incorporates an open pedagogy approach. This assignment explores the same themes as the primary assignment while also introducing students to the OER ecosystem and inviting them to contribute to this OER as a living resource. It can be used in place of the primary assignment for a class with an open pedagogy focus, or can be assigned in addition to the primary lesson to reinforce the main concepts while engaging students with a different instruction style. Note that while this assignment is designed for small groups, it can also be done individually for smaller class sizes.
Assignment Outline
The personas and scenarios in this lesson plan were chosen to highlight the major demographic and professional differences that affect open science practices, as well as to reflect the most common open science practices. Of course, the small number of personas does not fully capture the scope of professional or personal identity a researcher may have, and the small number of scenarios does not encompass all the situations and barriers researchers may face.
For this assignment, students should, in small groups, develop their own personas and scenarios. Each group should develop at least 2 personas and at least 2 scenarios, and consider the different lessons that could be learned if they are matched in different ways. Whenever possible, these personas and scenarios should be compatible with the existing personas and scenarios in the lesson plan.
In a brief, one-page, writing assignment, each group should briefly describe why they chose to develop the personas and scenarios that they did, with particular attention paid to how the additional content they developed contributes to the conversation around labor equity in open science.
Learning Objectives
- Students will identify researcher identities and open science practices not included in the original lesson plan.
- Students will design new personas and scenarios that match the gaps they identified and integrate them with the existing lesson plan.
- Students will justify why they chose to develop specific personas and scenarios, and explain their rationale.
Photo Attribution
Photographs used in this lesson plan are courtesy of:
Christina @ wocintechchat.com on Unsplash
"Open Science 우산" by eotls4387 is marked with CC BY 2.0.
Labor Equity in Open Science - Additional Resources
The files attaches in this section are additional resources to assist instructors in using the lesson plan. These include:
- A instructor presentation that goes over the main points of the reading and introduces the lesson
- Student handouts that give persona details and re-iterate the lesson instructions
- Printable scenario handouts that can be cut up and handed out for an in-person lesson
- A digital scenario handout to be distributed for virtual lessons
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oercommons
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2025-03-18T00:38:23.325497
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Lesson Plan
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https://oercommons.org/courseware/lesson/98716/overview
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Video: Development Perspectives from Kelly Hammond
Overview
Kelly Hammond, Open Educational Resources (OER) and Instructional Technology Adjust at CUNY School of Professional Studies, talks about the importance of developing a strategic introduction to the OER-DEIA Action Plan for K-12 District Implementation that provides users with critical information that gives them a solid foundation when beginning their OER-DEIA journey. As she developed this section of the guide she reflected on her own OER journey and asked herself the guiding question, "What would I have needed to know in order to get there faster and more comfortably?"
Video: Kelly Hammond talks about the importance of developing a strategic introduction for users
OER-DEIA Action Plan for K-12 District Implementation
About This Guide
The guide contains a series of informational sections and reusable templates aimed at supporting district leaders and their educators in creating structures, making decisions and plans, and advancing new strategies for integrating open educational resources (OER) and diversity, equity, inclusion, and accessibility (DEIA), as a comprehensive approach to improving teaching and learning for all.
The creation of the guide relied on the groundwork, advisement, and authorship of the following contributors:
Rebecca M. Henderson, Westmoreland Intermediate Unit, Pennsylvania; Tracy Rains, Appalachia Intermediate Unit, Pennsylvania; Kelly Hammond, CUNY Graduate Center and CUNY School of Professional Studies, New York, Amee Evans Godwin, ISKME, California; An-Me Chung, New America, Washington, D.C.
Acknowledgments
This guide was collaboratively developed by members of K-12 Voices for Open, a group of 50 plus educators and leaders working together to support OER implementation in K-12 classrooms across the country. This community-led effort is facilitated by the Institute for the Study of Knowledge Management in Education (ISKME, www.iskme.org) and with support from the William and Flora Hewlett Foundation.
The authors are grateful for the input and encouragement from K-12 Voices for Open. More information: https://sites.google.com/iskme.org/k-12voicesforopen
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oercommons
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2025-03-18T00:38:23.341257
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Amee Godwin
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/98716/overview",
"title": "Video: Development Perspectives from Kelly Hammond",
"author": "Rebecca Henderson"
}
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https://oercommons.org/courseware/lesson/86111/overview
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Five-Whys-Group Work
High School Posters-OLD
https://docs.google.com/forms/d/1BH1CjCos7IQowbUXqgh8-YG_kXhU97aDKHQsvF4LigM/edit
https://docs.google.com/forms/d/1kdGYuCL9yrxJvB644SatqKnKmD2-xZ54ggJ2n9dVkJw/edit
https://drive.google.com/file/d/1u3-1oLQNOMQKa5JrBdatzpuqBE-H-hsU/view?usp=sharing_eil&ts=60b03493
JHS2
TIPS & TRICKS
WBL Simulated Experience Survey
WHS Poster
Special Populations Tips and Tricks
Overview
The information within this resource are techniques that we have used to address gaps in CTE equity. These techniques have assisted us in to beginning address inequity and we continue to use as part of a continous improvement process.
Tips and Tricks Flow Chart
Greetings the following module will share how we first recognized the inequity that existed in CTE, and the steps we have taken to continously improve equity. Please review our "Tips and Tricks" sheet that provides a breakdown of how we originally viewed the problem of inequity around CTE, how we have explored the problem, and steps we have taken to adrress the issue of inequity.
Student and Educator Surveys
In order to explore our root cause theory that students were unaware of the CTE and STEM opportunties we created a student survey. The survey findings verified that a majority of students were unaware of the opportunities. We provide this survey to our secondary schools annually until the disruption caused by COVID 19. We have provided a sample of our survey.
We also expanded our research to include an educator survey. We wanted to gauge whether teachers at the secondary schools were aware of the CTE opportunites. The survey included all programs available at every secondary school.
CTE Needs Assessment and Grant Planning
Special populations became a key point in newly required CTE Needs Assessment, and as part of our CTE Needs Assessment. Our consortia chose to meet as a team and review the data provided by ODE and broke it down into by categories by our ODE colleagues. This information identified our specific goals for the next 4 years. The CTE needs assessment process also highlighted an important lesson in equity. Three of our larger schools identified an increasing Hispanic population as being an area that influenced student support, but three of our smaller schools identified students with lower economic status as being their greatest concern. The lessen that emerged overall from this exercise was that we need to be prepared to meet our schools where they are at, and begin to work on increasing equity from the level they are starting at.
While the CTE Needs Assessment allowed our consortium to recognize themes in who was not participating we did not just share this information with the administration. We chose to follow up individually with our Program of Study CTE Teachers. Each teacher was provided their own ODE data to review, and we shared the shared themes that we recognized in the CTE Needs Assessment. By providing this information to the CTE teachers we are asking them to question why the special population gap exists, and to be part of the solution. One way that we are attempting to do this is by holding POS meetings with the CTE Teachers to discuss root cause analysis. We completed a first session in Spring with our Ag/Natural resource POS opportunities. Attached in this module is the example of the five why activity we completed. On the Tips and Trick sheet we provided a link to a video that explains how you can use this technique. We are providing the document that we completed during this session.
Work Based Learning and Place Matters Webinar
In this section we are sharing a survey that we created in hopes of identifying how our CTE teachers are implementing WorkBased Learning opportunities. As a rural consortia we recognized that the majority of our students would not be able to benefit from a CWE/Internship because of travel barriers, family commitments, or necessity of work. To ensure that students are receiving WBL our teachers are looking at simulated learning experiences into their class offerings. We are sharing a survey that we will be reviewing teacher practices, and we hope to share what is working throughout our consortia. Laslty, we are also sharing a webinar that we were asked to particpate in around Education, Health, and Equity. Please note that our portion of the webinar begins at 37 minutes and 38 seconds in.
Education Material Created to Highlight the Benefits for Students Who Take CTE
Another way we combated the lack of advising was to create educational posters that highlight the positive graduation rate for 4 year cohorts and identify the Program of Study Opportunities (POS) available at each secondary school. Previously, the Regional Coordinator (RC) had been trained in the Positive Community Norms (PCN). PCN was a technique that focused on using data and messaging to change the culture of public health issues . For example, instead of highlighting a concerning statistic on underage alcohol or drug use, the PCN method would focus in highlighting the percentage of youth not participating in drug or alcohol use, and instead focus on positive healthy activity (The Montana Institute LLC, 2012) . Messaging in this manner has been found to change the culture of public health problems. Using the understanding from the training that had occurred, the RC chose to highlight the consortia 4 year graduation cohort rate which identifies that students who participate in a CTE as graduating at 93.07% (Oregon Department of Education, 2021).
This module includes the very 1st posters we created to educates schools about the CTE Programs availble. The 1st file includes student represtation in school POS opportunities. The updated shares the same message but has less focus of student participation due to COVID 19.
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oercommons
|
2025-03-18T00:38:23.371504
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09/24/2021
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/86111/overview",
"title": "Special Populations Tips and Tricks",
"author": "Mary Jackson"
}
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https://oercommons.org/courseware/lesson/118023/overview
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AI Design Tool Integration
Overview
The arrival of artificial intelligence has sent shockwaves through numerous industires. Instructional design and education, like many other fields, are bracing for impact. The conversation around AI in instructional design and education has ranged from doomsday scenarios to claims of a new savior. The only constraint in these projects is a general lack of data supporting either scenario. To inform our strategy plan for the utilization and adoption of AI tools, the AI working group at Emeritus Institute of Management conducted a pilot study, assaying the impacts of two tools, ChatGPT and Blue Willow, on the efficiency and effectiveness of these tools in completing common design tasks. This paper describes our study design and the results of our experiment.
Please select the following link to find our Artificial Intelligence in Executive Education paper.
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oercommons
|
2025-03-18T00:38:23.384549
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07/16/2024
|
{
"license": "Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/",
"url": "https://oercommons.org/courseware/lesson/118023/overview",
"title": "AI Design Tool Integration",
"author": "Nolan Williams"
}
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