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Chapter 6 Short Answer/Critical Application

Terms in this set (26)

What is the major function of muscle?
To contract or shorten. To cause movement.
Compare skeletal, smooth, and cardiac muscles in regard to their microscopic anatomy, location and arrangement in body organs, and function in the body
Skeletal muscle: Long, cylindrical, striated, multinucleate cells; attached to bones and crossing joints; forms the "flesh" of the body and is responsible for all voluntary movement. Cardiac muscle: Branching, striated cells containing a single nucleus; interdigitate with one another at tight junctions called intercalated disks; found only in the heart, arranged in spiral bundles; contraction of the heart propels blood into the blood vessels. Involuntary
movement. Smooth muscle: Fusiform, uninucleate cells, no striations; generally found in cell layers (or sheets) arranged at right angles to one another (one running longitudinally and the other circularly) within the walls of hollow organs; causes substances to move through internal body tracts (digestive, urinary, reproductive, respiratory). Involuntary movement.
What two types of muscle tissue are striated?
Skeletal and cardiac muscle.
Why are the connective tissue wrappings of skeletal muscles important? Name these connective tissue coverings, beginning with the finest and ending with the coarsest.
They protect, reinforce, and strengthen the delicate muscle tissue. Endomysium, perimysium, and epimysium.
What is the function of tendons?
Tendons attach muscle to bone.
Define neuromuscular junction, motor unit, tetanus, graded response, aerobic respiration, anaerobic glycolysis, muscle fatigue, and neurotransmitter.
Neuromuscular junction: The junction of a motor neuron's axon terminals and the sarcolemma of a muscle cell.
Motor unit: One motor neuron and all the muscle cells it stimulates.
Tetanus: The smooth, sustained contractions of a muscle with no evidence of relaxation.
Graded response: Different degrees of contraction in response to different levels of stimulation (changes in both the stimuli frequency and number of muscle cells stimulated).
Aerobic respiration: Metabolic pathways that use O2 to generate ATP.
Anaerobic glycolysis: Metabolic pathway that breaks down glucose into pyruvic acid (without using O2) to generate ATP.
Muscle fatigue: The inability of a muscle to contract even though it is still being stimulated; usually a result of a lack of oxygen and the accumulation of lactic acid in the muscle tissue.
Neurotransmitter: A chemical substance released by a neuron when the nerve impulse reaches its axon terminals.
Describe the events that occur from the time calcium ions enter the axon terminal at the neuromuscular junction until muscle cell contraction occurs.
Acetylcholine is released; it diffuses through the synaptic cleft and attaches to receptors on the sarcolemma; sarcolemma permeability to sodium ions increases briefly; sodium ions rush into the muscle cell, reversing the electrical conditions of the resting sarcolemma (depolarization of the membrane); the action potential is initiated and sweeps over the entire sarcolemma eventually reaching the sarcoplasmic reticulum deep inside the cell; calcium ions are released from the sarcoplasmic reticulum; attachment of calcium ions to the thin/actin filaments exposes binding sites for myosin. Myosin heads bind to actin, triggering their inward sliding; contraction occurs.
How do isotonic and isometric contractions differ?
Isotonic contractions: Muscle tension remains the same, and the muscle shortens. Isometric contractions: Muscle tension increases, but the muscle cannot shorten.
Muscle tone keeps muscles healthy. What is muscle tone, and what causes it? What happens to a muscle that loses its tone?
Muscle tone is a state of continuous, partial contraction of muscles resulting from discontinuous but systematic stimulation of different motor units by the nervous system . A muscle without tone is paralyzed (unable to contract) due to destruction of the nerve supply, and becomes flaccid and can eventually atrophy.
A skeletal muscle is attached to bones at two points. Name each of these attachment points, and indicate which is movable and which is immovable.
Origin: Immovable (or less movable) end. Insertion: Movable end; when contraction occurs, the insertion moves toward the origin.
List the 12 body movements studied in this chapter, and demonstrate each.
Flexion, extension, abduction, adduction, rotation, circumduction, pronation, supination, inversion, eversion, dorsiflexion, plantar flexion.
How is a prime mover different from a synergist muscle? How can a prime mover also be considered an antagonist?
A prime mover is a muscle that has major responsibility for causing a particular movement; for example, the gastrocnemius is the prime mover of plantar flexion. Synergist muscles aid prime movers by causing the same movement (but less effectively) or by stabilizing joints or bones over which the prime mover acts; for example, the peroneus muscles (which promote plantar flexion) are synergists of the gastrocnemius muscle. The tibialis anterior muscle causes dorsiflexion of the foot; thus, the gastrocnemius (prime mover for plantar flexion) is its antagonist.
If you were alternately contracting and relaxing your masseter muscle, what would you be doing? Name three other muscles of the face, and give the location and function of each.
Chewing food, grinding your teeth, or just opening and closing the jaw.
Frontalis: covers the frontal bone; allows you to raise your eyebrows and wrinkle your forehead.
Orbicularis oculi: found in circles around eyes; functions to close eyes, squint, blink, and wink. Orbicularis oris: circular muscle of the lips; closes mouth and protrudes lips (kissing motion).
Buccinator: runs horizontally across the cheek and inserts into the orbicularis oris; flattens cheek and aids in chewing. Zygomaticus: extends from corner of mouth to cheekbone; raises corners of mouth upward for smiling. Temporalis: overlies the temporal bone; closes jaw.
The sternocleidomastoid muscles help to flex the neck. What are their antagonists?
Trapezius muscles.
Name two muscles that reverse the movement of the deltoid muscle.
Anteriorly, the pectoralis major. Posteriorly, the latissimus dorsi.
Name the prime mover of elbow flexion. Name its antagonist.
Prime mover: Biceps brachii. Antagonist: Triceps brachii.
Other than acting to flex the spine and compress the abdominal contents, the abdominal muscles are extremely important in protecting and containing the abdominal viscera. What is it about the arrangement of these muscles that makes them so well suited for their job?
The four muscles (or muscle pairs) are arranged so their fibers run in different directions, much as sheets of different wood grains are compressed together to make plywood. Like plywood, the abdominal wall musculature is extremely strong for its thickness; it is well constructed for its function as an abdominal girdle.
The hamstring and quadriceps muscle groups are antagonists of each other, and each group is a prime mover in its own right. What action does each muscle group perform?
Hamstrings: Extend hip and flex knee. Quadriceps: Flex hip (rectus femoris only) and extend knee.
What two-bellied muscle makes up the calf region of the leg? What is its function?
Gastrocnemius: Plantar flexion.
What happens to muscles when they are exercised regularly? Exercised vigorously as in weight lifting? Not used?
Muscles that are exercised regularly are healthy (with increased endurance), firm and free of superficial fat, and perhaps larger in size (depending on the type of exercise). Resistance- type exercises, such as weight lifting, cause muscles to hypertrophy to meet the increased demands placed on them. Muscles that are not used will atrophy (lose mass) and become weak.
What is the effect of aging on skeletal muscles?
With aging, skeletal muscle tissue mass decreases and the relative amount of connective tissue in the muscles increases, causing the muscles to become sinewy. As the muscles decrease in mass, they also decrease in strength. Loss in muscle mass may be partially prevented by regular exercise.
Should a triathlete engage in aerobic or resistance training? Explain.
He or she should engage in aerobic training. Training aerobically increases the amount and activity of enzymes within the aerobic metabolic pathways to make ATP for repeated muscular contractions whereas anaerobic training increases the amount and activity of enzymes within the glycolytic metabolic pathways. Muscles that are stronger, more resistant to fatigue, and flexible are the result of aerobic types of exercise.
Name three muscles or muscle groups used as sites for intramuscular injections. Which is most often used in babies?
Deltoid, gluteus maximus, gluteus medius, vastus lateralis, and rectus femoris. The vastus lateralis and rectus femoris is used more often for babies because their gluteus muscles are poorly developed.
While jogging, Mr. Ahmadi was forced to jump out of the way of a speeding car. He heard a snapping sound that was immediately followed by pain in his right lower calf. A gap was visible between his swollen calf and his heel, and he was unable to plantar flex that foot. What do you think happened?
He ruptured his Achilles tendon, which attaches the gastrocnemius to the heel bone. This accounts for the gap between the calf and the heel, as well as the inability to plantar flex the foot.
Susan fell off her bicycle and fractured her right clavicle. Treatment prescribed by the emergency room physician included using a sling to immobilize the clavicle and speed its healing. What muscles are temporarily "out of business" as a result of this injury?
Any muscle that inserts on the clavicle-trapezius. The muscles of her arm would also be immobilized by the sling.
When Eric returned from jogging, he was breathing heavily and sweating profusely, and he complained that his legs ached and felt weak. On the basis of what you have learned about muscle energy metabolism, respond to the following questions:

Why is Eric breathing heavily?

What ATP-harvesting pathway have his working muscles been using that leads to such a breathing pattern?

What metabolic product(s) might account for his sore muscles and his feeling of muscle weakness?
Eric's oxygen intake has not been adequate to keep his muscles supplied with the oxygen they needed to support prolonged aerobic activity. His heavy breathing will supply oxygen to repay the oxygen deficit. His muscle cells were relying on aerobic metabolism, and their oxygen consumption led to breathlessness. When the oxygen ran out, anaerobic metabolism took place, leading to lactic acid accumulation, short-term muscle fatigue, and muscle soreness.
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