عدد المساهمات : 6676
تاريخ التسجيل : 06/08/2009
|موضوع: Muscle Physiology Self Assessment الأربعاء نوفمبر 10, 2010 5:53 am|| |
I. SKELETAL MUSCLES
Skeletal muscles are composed of individual muscle fibers that contract when they are stimulated by a motor neuron. Each motor neuron branches to innervate a number of muscle fibers, and all of these fibers contract when their motor neuron is activated. Activation of varying numbers of motor neurons, and thus varying numbers of muscle fibers, results in gradations in the strength of contraction of the whole muscle.
A. Multiple Choice
___ 1. In a skeletal muscle contraction
a. the origin is pulled toward the insertion
b. flexor muscles increase the angle of a joint
c. extensors and flexors may be found at the same joint
d. abductor muscles move limbs inward toward the midline
e. None of these statements regarding skeletal muscle contractions is correct.
___ 2. The “string” in cooked, stringy stew meat best describes this part of the muscle anatomy.
___ 3. The actual muscle cell, a syncytium of several embryonic myoblast cells with such components as nuclei, mitochondria, glycogen, and sarcoplasm, is also known as a
e. None of these terms describe the actual muscle cell.
___ 4. In the body (in vivo), each muscle fiber receives __________ axon(s) from a (an) __________ motor neuron, which always liberates the specific neurotransmitter __________.
a. one; somatic; ACh
b. many; autonomic; norepinephrine (NE)
c. many; somatic; norepinephrine (NE)
d. one; autonomic; ACh
___ 5. Which of the following muscles is controlled by the greatest number of small motor units, resulting in fine neural control over the strength of muscle contraction?
b. biceps brachii
B. True or False/Edit
___ 6. Antagonistic muscle action occurs when flexors and extensors act on the same joint.
___ 7. A muscle that is contracting is called the agonist muscle.
___ 8. The connective tissue tendons, epimysium, perimysium, and endomysium are one continuous noncontractile unit within muscle.
___ 9. Like most other cells in the body, skeletal muscles have a single, centrally located nucleus as a control center.
___ 10. Unlike other cells in the body, skeletal muscle fibers contain multiple nuclei because they are formed during embryonic development from the union of several immature myoblasts cells.
___ 11. A single motor unit is composed of one somatic motor neuron and all of the muscle fibers innervated (excited) by the axon branches.
___ 12. All motor units to a given muscle (for example, gastrocnemius) innervate the same number of muscle fibers.
___ 13. Recruitment of larger motor units (with more fibers per unit) occurs when greater strength is needed.
II. MECHANISMS OF CONTRACTION
The A bands within each muscle fiber are composed of thick filaments and the I bands contain thin filaments. Movement of cross bridges that extend from the thick to the thin filaments causes sliding of the filaments, and thus muscle tension and shortening. The activity of the cross bridges is regulated by the availability of Ca2+, which is increased by electrical stimulation of the muscle fiber. Electrical stimulation produces contraction of the muscle through the binding of Ca2+ to regulatory proteins within the thin filaments.
A. Multiple Choice
___ 14. The cytoplasm (sarcoplasm) of each muscle fiber (or cell) contains small, densely-packed parallel arrangements of subunits known as
e. None of these terms is correct.
___ 15. The I bands within a longitudinal section of a myofibril are seen as the __________ bands, composed primarily of the protein __________.
a. dark; actin
b. dark; myosin
c. light; actin
d. light; myosin
___ 16. That part of the myofibril striation pattern where actin and myosin filaments overlap is known as the
a. A band.
b. I band.
c. H band.
d. Z line (disc).
___ 17. During an isotonic muscle contraction, which statement about the shortening of adjoining sarcomeres is false?
a. The distance between the two Z lines of each sarcomere appears to shorten.
b. The A bands of adjoining sarcomeres appear to shorten in length.
c. The I bands of adjoining sarcomeres appear to shorten in length.
d. The H bands of adjoining sarcomeres appear to shorten.
___ 18. Which statement about the thin actin filaments is false?
a. They are polymers of hundreds of globular G actin subunits.
b. They are also known as filament actin or F actin.
c. They are arranged in a double row of subunits and twisted to form a helix.
d. The grooves within the actin filaments contain the regulatory protein called troponin.
e. All of these statements about actin filaments are true.
___ 19. Normal relaxation of skeletal muscle is most directly the result of
a. a decrease in ATP concentrations within the sarcomere
b. fewer action potentials on the muscle fiber membrane
c. more acetylcholine (ACh) neurotransmitter molecules broken down in the synapse
d. active transport of calcium ion (Ca2+) out of the sarcoplasm and into the sarcoplasmic reticulum
___ 20. The strength of a muscle’s contraction is affected by the
a. number of muscle fibers within the muscle that are stimulated to contract
b. thickness of each muscle fiber within the muscle
c. initial length of the muscle fibers when they are at rest
d. Only a and b are correct.
e. All of these factors affect the strength of contraction.
B. True or False/Edit
___ 21. In the center of each A band is a thin, dark Z line (disc).
___ 22. The basic or smallest subunit of striated muscle contraction is the sarcomere.
___ 23. Shortening of the sarcomere is produced by shortening of the protein filaments called actin and myosin.
___ 24. Cross bridges are actually the globular “heads” of the myosin protein molecules that extend out toward the actin molecules.
___ 25. Splitting of ATP is required before myosin cross bridges attach to actin; and at the end of the power stroke, a new ATP must be attached to release the cross bridge.
___ 26. Each tropomyosin molecule covers a distance of approximately seven G-actin subunits within the groove of the longer F actin molecule.
___ 27. When a muscle fiber is stimulated to contract, calcium ions (Ca2+) are released that will bind directly to tropomyosin molecules located in the sacrcoplasm.
___ 28. Transverse tubules (or T tubules) are formed from, and continuous with, the muscle cell membrane and, therefore are capable of conducting action potentials.
___ 29. Perhaps with the help of the second messenger called inositol triphosphate (IP3), action potentials along the transverse tubules cause the release of Ca2+ from the sarcoplasmic reticulum.
___ 30. Excitation-contraction coupling refers to the opening of voltage-regulated Ca2+ channels along the transverse tubules by action potentials that lead to the opening of other calcium channels in the sarcoplasmic reticulum and to the release of Ca2+ to stimulate muscle contraction.
C. Sequencer — Muscle Excitation-Contraction Coupling
31. Arrange the numbers the following events involved in stimulation of muscle contraction and
relaxation (excitation contraction coupling) in proper order from 1 to 10. Note: The first event has
been done for you. If you get stuck, sneak a peek at table 12.3 in the text.
action potentials are conducted along transverse tubules
cross bridges are exposed as the troponin complex moves tropomyosin
action potentials in the T tubules promote Ca2+ release
1 somatic neuron action potentials release ACh molecules
with ATP, cross bridges pull the thin over the thick filaments
without action potentials, Ca2+ is pumped away from troponin and into the sarcoplasmic reticulum
released Ca2+ binds to troponin, changing its structure
ACh binds to its sarcolemma receptors and produces new action potentials
contraction cycles continue as long as Ca2+ and fresh ATP are present in the sarcomere
ATP activated myosin cross bridges attach to actin
III. CONTRACTIONS OF SKELETAL MUSCLES
Contraction of muscles generates tension, which allows muscles to shorten and thereby perform work. The contraction strength of skeletal muscles must be sufficiently great to overcome the load on a muscle in order for that muscle to shorten.
___ 32. When an isolated muscle is electrically stimulated outside of the body (in vitro), which of the following events does not occur?
a. Increasing the stimulus voltage increases the strength of the twitch.
b. Increasing the stimulus frequency may lead to consecutive twitches that “ride piggyback” and summate.
c. Increasing the stimulus frequency may lead to tetanus.
d. All of these events occur during electrical stimulation of an isolated muscle.
___ 33. Which of the following best demonstrates an isometric contraction?
a. lifting a chair up and over your head
b. sliding the chair horizontally across the room
c. sitting in the chair reading (and enjoying!) this text
d. gluing together the chair that just broke
e. None of these statements demonstrates an isometric contraction.
___ 34. Which statement about skeletal muscle fibers in the body (in vivo) is false?
a. The membranes of skeletal muscle fibers conducts action potentials just like those of neurons.
b. When activated, each individual muscle fiber contraction is an all or none twitch.
c. Activation of a single somatic motor neuron will activate every single muscle fiber in that motor unit only.
d. Contractions of whole muscles are produced with varying strength (graded) by increasing or decreasing the number of motor units that are activated.
e. All of these statements about skeletal muscle fibers are true.
___ 35. Which of the following statements regarding the muscle contraction phenomenon known as treppe is false?
a. It may represent a warmup effect, perhaps due to an increase in intracellular calcium ions.
b. It assumes that all the fibers in the muscle are stimulated maximally.
c. Twitches in fresh muscle will be successively stronger when maximally stimulated up to a new maximum.
d. Treppe is also known as the staircase effect.
e. All of these statements about treppe are true.
___ 36. When examining a force-velocity curve made from a contracting muscle,
a. an inverse relationship between load and velocity of shortening is shown
b. the force (load) is always greater than the muscle tension generated
c. the contraction strength varies at each load
d. as the load increases the velocity of muscle shortening increases
e. with an isotonic contraction, the velocity of contraction is zero
___ 37. Complete muscle tetanus is the same as muscle tetany.
___ 38. The process of lifting a barbell up and over one’s head is an example of an isometric muscle contraction.
___ 39. A muscle contraction with shortening that moves a load is called isotonic.
___ 40. At the far right of the force-velocity curve where there is a maximum load with the muscle unable to shorten, the muscle contraction is now isometric.
___ 41. Series elastic component refers to noncontractile connective tissues of the muscle that are pulled tight first before muscles can shorten.
___ 42. An example of the series elastic component of muscle contraction is demonstrated by the elastic recoil of the thoracic structures during expiration.
___ 43. Maximum muscle tension is produced at 100% of its normal (or “ideal”) resting length, such that at 60% or less of this resting length, further contraction cannot occur.
IV. ENERGY REQUIREMENTS OF SKELETAL MUSCLES
Skeletal muscles generate ATP through aerobic and anaerobic respiration and through the use of phosphate groups donated by creatine phosphate. The aerobic and anaerobic abilities of skeletal muscle fibers differ according to muscle fiber type. Slow twitch (type I) fibers are adapted for aerobic respiration; fast twitch (type II) fibers are adapted for anaerobic respiration.
A. Multiple Choice
___ 44. Skeletal muscle at rest obtains most of its energy from the breakdown, or catabolism of
a. stored glycogen molecules within the muscle fiber
b. imported glucose molecules extracted from the blood
c. aerobic respiration of fatty acid molecules within the muscle fiber
d. All of these sources of energy are used by resting muscle.
___ 45. During sustained muscle activity, the rapid regeneration of ATP molecules is accomplished mainly by the
a. transfer of phosphate from high energy phosphocreatine molecules in the muscle fiber
b. hydrolysis of stored glycogen in the muscle fiber
c. uptake and aerobic combustion of glucose molecules from the blood
d. uptake and oxidation of free fatty acid molecules from the blood
___ 46. Slow twitch skeletal muscle fibers
a. are also
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