Ch. 20

Question 1

1. A striated muscle fiber is made up of many parallel _______, each containing a series of _______.
   a. fascicles; fibrils
   b. myofibrils; sarcomeres
   c. fascicles; z-lines
   d. sarcomeres; myotomes
   e. cross-bridges; myosin ladders

Answer 1

B

Question 2

2. According to the sliding filament theory of muscle contraction, myosin heads pull on _______ filaments and _______.
   a. thick; move the z-lines apart
   b. thick; move the z-lines together
   c. thin; move the z-lines apart
   d. thin; move the z-lines together
   e. thin; shorten the thin filaments

Answer 2

D

Question 3

3. The smallest unit of a skeletal muscle that shortens during a muscle contraction is the
   a. myosin molecule.
   b. thin filament.
   c. sarcomere.
   d. myofibril.
   e. muscle fiber.

Answer 3

C

Question 4

4. In striated muscle, phosphate is released from the myosin head at the same instant that
   a. the myosin head binds to actin.
   b. the myosin head releases from actin.
   c. troponin T changes conformation and exposes myosin binding sites on actin.
   d. the myosin head returns to the cocked position.
   e. the myosin head starts the power stroke.

Answer 4

E

Question 5

5. In relaxed skeletal muscle, myosin heads are
   a. bound to actin with no ADP or phosphate bound.
   b. bound to actin with ADP and phosphate bound.
   c. bound to actin with ATP bound.
   d. dissociated from actin with ATP bound.
   e. dissociated from actin with ADP and phosphate bound.

Answer 5

E

Question 6

6. In skeletal muscle cells, cytoplasmic Ca2+ is bound by
   a. actin.
   b. myosin.
   c. troponin.
   d. tropomyosin.
   e. ryanodine receptors.

Answer 6

C

Question 7

7. What happens when Ca2+ increases in the cytoplasm of a striated muscle cell?
   a. Myosin binding sites on actin are exposed, allowing a single cross-bridge cycle to occur.
   b. Myosin binding sites on actin are exposed, allowing cross-bridge cycles to occur until Ca2+ drops again.
   c. Actin binding sites on myosin are exposed, allowing a single cross-bridge cycle to occur.
   d. Actin binding sites on myosin are exposed, allowing cross-bridge cycles to occur until Ca2+ drops again.
   e. Actin binding sites on myosin are blocked, preventing a cross-bridge cycle from occurring until Ca2+ rises again.

Answer 7

B

Question 8

8. In resting skeletal muscle, contraction does not occur because
   a. there is very little ATP in the cytoplasm.
   b. most of the ATP is bound to other molecules for storage.
   c. there is very little myosin in the cell.
   d. there is very little calcium in the cytoplasm.
   e. myosin is inactivated.

Answer 8

D

Question 9

9. Running mice are capable of moving their legs back and forth much more quickly than elephants. Thus, compared to an elephant muscle cell, a mouse muscle cell likely contains more
   a. actin.
   b. myosin.
   c. troponin C.
   d. tropomyosin.
   e. SR Ca2+-ATPase.

Answer 9

E

Question 10

10. When the cell membrane of a vertebrate skeletal muscle is depolarized, ryanodine receptors change configuration and permit passage of Ca2+
    a. passively, from the extracellular fluid to the cytoplasm.
    b. passively, from the sarcoplasmic reticulum to the cytoplasm.
    c. actively, from the extracellular fluid to the cytoplasm.
    d. actively, from the sarcoplasmic reticulum to the cytoplasm.
    e. actively, from the cytoplasm to the sarcoplasmic reticulum.

Answer 10

B

Question 11

11. In striated muscle, _______ before the sarcomere can generate force.
    a. Ca2+ must dissociate from troponin C
    b. Ca2+ must be pumped by the SR Ca2+-ATPase
    c. Ca2+ must bind to the ryanodine receptor
    d. the SR calcium channel must open
    e. calcium must bind to tropomyosin

Answer 11

D

Question 12

12. During the latent period of an isometric twitch,
    a. myosin hydrolyzes ATP and releases from actin.
    b. Ca2+ binds to troponin C.
    c. ryanodine receptors open and conduct Ca2+ into the SR.
    d. tropomyosin moves to block myosin-binding sites on actin.
    e. dihydropyridine receptors open and conduct Ca2+ into the cytoplasm.

Answer 12

B

Question 13

13. Lengthening of a muscle occurs
    a. as a result of an external load that acts on the muscle.
    b. when myosin completes the cross-bridge cycle in reverse.
    c. as the muscle cell action potential repolarizes.
    d. as Ca2+ levels drop following a contraction.
    e. only when the muscle is generating negative force.

Answer 13

A

Question 14

14. During an eccentric muscle contraction,
    a. the length of the sarcomeres is unchanged, but the length of the elastic component increases.
    b. the sarcomeres shorten, but the length of the elastic component is unchanged.
    c. the muscle produces force and its length is unchanged.
    d. the muscle produces force and its length decreases.
    e. the muscle produces force and its length increases.

Answer 14

E

Question 15

15. During an isometric tetanic contraction,
    a. neither the sarcomeres nor the elastic components of the muscle change in length.
    b. the sarcomeres shorten, but the elastic components lengthen.
    c. the sarcomeres shorten, but the elastic components stay the same length.
    d. the sarcomeres and the elastic components shorten.
    e. the sarcomeres lengthen, but the elastic components shorten.

Answer 15

B

Question 16

16. Cross-bridges generate force in a skeletal muscle cell any time
    a. the muscle is shortened.
    b. the muscle is lengthened.
    c. Ca2+ levels in the cytoplasm are high.
    d. ATP levels are high enough.
    e. the antagonistic muscle is relaxed.

Answer 16

C

Question 17

17. During an isotonic muscle twitch, the presence of elastic elements causes the latent period to be _______ than during an isometric twitch, and the peak force transmitted through the tendon to be _______.
    a. shorter; lower
    b. shorter; higher
    c. longer; higher
    d. longer; lower
    e. unaffected; equally unaffected

Answer 17

D

Question 18

18. The elastic component of the gastrocnemius
    a. is composed of the epimysium, perimysium, and endomysium surrounding the muscle.
    b. is composed of actin and myosin proteins within the muscle cells.
    c. must be fully stretched before the gastrocnemius can exert any external force.
    d. must be fully stretched in order for the muscle to exert maximum tetanic force.
    e. is fully stretched during an isotonic muscle twitch.

Answer 18

D

Question 19

19. How can summation of skeletal muscle twitches occur if the motor neuron’s refractory period prevents multiple action potentials from being transmitted to the neuromuscular junction at the same time?
    a. The motor neuron’s absolute refractory period is much shorter than the time it takes for calcium release and reuptake from the SR.
    b. The motor neuron’s absolute refractory period is much longer than the time it takes for calcium release and reuptake from the SR.
    c. The motor neuron’s absolute refractory period is much shorter than the muscle action potential.
    d. The motor neuron’s absolute refractory period is much longer than the muscle action potential.
    e. The muscle action potential does not have an absolute refractory period.

Answer 19

A

Question 20

20. A muscle produces less force during a twitch than during a tetanic contraction because during a twitch
    a. peak cytoplasmic Ca2+ is lower.
    b. the membrane voltage during the action potential is lower.
    c. tropomyosin does not have time to unblock all of the actomyosin binding sites.
    d. myosin does not have time to bind to as many actin molecules.
    e. the elastic components of the muscle are not fully stretched.

Answer 20

E

Question 21

21. In skeletal muscle, an unfused tetanus results from
    a. action potentials arriving at a rate fast enough for the intracellular Ca2+ levels to rise much higher than they would in a muscle twitch.
    b. action potentials arriving at a rate fast enough for sarcomeres to generate force while the elastic components of the muscle are still stretched.
    c. action potentials arriving so quickly that there is no fluctuation in intracellular Ca2+ levels.
    d. many, but not all, of the motor units in the muscle being recruited at once.
    e. many, but not all, of the thin filaments being activated to permit cross-bridge formation.

Answer 21

B

Question 22

22. Which of the following contributes to the length‒tension relationship observed in skeletal muscle?
    a. When sarcomere lengths are long, thin filaments overlap.
    b. When sarcomere lengths are short, thick and thin filaments do not overlap fully.
    c. When sarcomere lengths are short, the elastic elements in the muscle are not fully stretched.
    d. When sarcomere lengths are long, thick and thin filaments do not overlap optimally.
    e. When sarcomere lengths are long, less Ca2+ reaches the thin filaments than when the sarcomeres lengths are near the resting length.

Answer 22

D

Question 23

23. The sarcomeres of vertebrate skeletal muscles are all about the same length, but squid have different sarcomere lengths in different muscles in the body. If all other factors are equal, the muscle with shorter sarcomeres
    a. will shorten more slowly.
    b. will shorten more rapidly.
    c. will generate more force.
    d. will generate less force.
    e. will have a length‒tension relationship with a broader plateau.

Answer 23

B

Question 24

24. The force‒velocity relationship for skeletal muscle indicates that a muscle
    a. produces maximum force when contracting at its maximum velocity.
    b. shortens at maximum velocity when contracting against the maximum load it can move.
    c. produces maximum power when producing its maximum force at its maximum velocity.
    d. produces maximum power when contracting isometrically.
    e. shortens at maximum velocity when contracting against no load.

Answer 24

E

Question 25

25. Suppose that muscle A is long with a narrow diameter and muscle B is short with a large diameter. Compared to muscle A, muscle B is capable of producing _______ maximum force and _______ maximum velocity.
    a. a lower; a lower
    b. a higher; a higher
    c. a lower; a higher
    d. a higher; a lower
    e. the same; the same

Answer 25

D

Question 26

26. Suppose that each cross-bridge cycle moves the thin filament 10 nanometers relative to the thick filament. If myosin in a particular muscle can go through the cross-bridge cycle at 250 cycles per second, what is the rate at which a muscle that is 30 cm long can shorten?
    a. 75 µm/s
    b. 75 mm/s
    c. 0.30 m/s
    d. 0.60 m/s
    e. 2.5 m/s

Answer 26

D

Question 27

27. Muscle A has a volume of 200 cm3, a length of 20 cm, and a cross-sectional area of 10 cm2. Muscle B has a volume of 200 cm3, a length of 10 cm, and a cross-sectional area of 20 cm2. Which of the following statements about these muscles is true?
    a. Both muscles can produce the same power, but they will shorten at different speeds.
    b. Both muscles will shorten at the same speed, but they can produce different amounts of power.
    c. Both muscles can exert the same force, but they can produce different amounts of power.
    d. Both muscles can exert the same force, but one will shorten more quickly than the other.
    e. Both muscles can produce the same power and the same force.

Answer 27

A

Question 28

28. Which of the following muscles can generate the most power per cubic centimeter of muscle?
    a. A muscle containing mostly slow oxidative fibers contracting at its Vmax
    b. A muscle containing mostly slow oxidative fibers contracting against a moderate load
    c. A muscle containing mostly fast glycolytic fibers contracting at its Vmax
    d. A muscle containing mostly fast glycolytic fibers contracting against a moderate load
    e. A muscle containing equal numbers of all three fiber types contracting isometrically

Answer 28

D

Question 29

29. When muscle is suddenly activated to perform contractions at a rapid rate, most of the ATP to fuel the first 3‒5 seconds of exercise comes from
    a. the aerobic breakdown of glycogen.
    b. the aerobic breakdown of lipid.
    c. creatine phosphate hydrolysis.
    d. anaerobic glycolysis.
    e. ATP stored in the cell.

Answer 29

C

Question 30

30. Fast glycolytic muscle fibers dependent on carbohydrate as a fuel, whereas slow oxidative fibers are capable of metabolizing carbohydrates, lipids, or amino acids. What is the physiological reason for this difference?
    a. Anaerobic glycolysis can produce ATP from glucose much more quickly than lipid or amino acid oxidation can take place.
    b. The myosin in FG fibers can only bind to glycogen.
    c. FG fibers cannot produce lactic acid.
    d. Compared to FG fibers, SO fibers need to metabolize a wider variety of fuels to meet a higher ATP demand.
    e. SO fibers need to metabolize lipid because they have less creatine kinase.

Answer 30

A

Question 31

31. Lactate produced by muscle cells
    a. is produced only during very intense exercise.
    b. is the primary cause of muscle fatigue.
    c. is always broken down to yield ATP within the muscle cell that produced it.
    d. is always used to produce glucose by gluconeogenesis in the cell that produced it.
    e. can be exported into the bloodstream and used by other cells.

Answer 31

E

Question 32

32. Tonic muscle
    a. conducts action potentials rapidly.
    b. is a form of smooth muscle.
    c. has large amounts of sarcoplasmic reticulum.
    d. is found primarily in postural muscles.
    e. consumes no ATP.

Answer 32

D

Question 33

33. One reason that fast glycolytic muscle fibers fatigue more rapidly than slow oxidative muscle fibers is that
    a. the myosin in FG fibers cannot use ATP as fast as SO fibers can.
    b. FG fibers contain lower amounts of ATP than SO fibers.
    c. FG fibers have a lower capacity for glycolysis than SO fibers.
    d. FG fibers have a higher capacity for oxidative phosphorylation than SO fibers.
    e. FG fibers use ATP more rapidly than SO fibers.

Answer 33

E

Question 34

34. The diffusion rate of which factor best explains why vertebrates evolved to have slow oxidative muscle fibers that are smaller in diameter than fast glycolytic fibers?
    a. Lipid
    b. Oxygen
    c. Ca2+
    d. Lactate
    e. Glucose

Answer 34

B

Question 35

35. A skeletal muscle fiber with high myosin ATPase activity, a high rate of Ca2+ reuptake by the SR, and large number of mitochondria would be classified as a
    a. slow oxidative fiber.
    b. fast oxidative glycolytic fiber.
    c. fast glycolytic fiber.
    d. slow glycolytic fiber.
    e. tonic fiber.

Answer 35

B

Question 36

36. Fast oxidative-glycolytic fibers in skeletal muscle are used
    a. only for motions requiring maximum power output, such as jumping.
    b. constantly, for postural activities such as standing and sitting.
    c. intermittently, for activities requiring more force output than the FG fibers alone can produce.
    d. intermittently, for activities requiring more force output than the SO fibers alone can produce.
    e. only when the other fiber types are not used.

Answer 36

D

Question 37

37. Slow oxidative fibers in skeletal muscle have
    a. few mitochondria but abundant sarcoplasmic reticulum.
    b. few mitochondria but numerous capillaries.
    c. large diameters, to hold many mitochondria.
    d. low levels of glycolytic enzymes but high levels of oxidative enzymes.
    e. a low maximum shortening velocity but high rates of glycolysis.

Answer 37

D

Question 38

38. The small diameter of slow oxidative muscle fibers is particularly advantageous for minimizing the distance over which
    a. calcium diffuses from the sarcolemma to the myofibrils.
    b. oxygen diffuses from the sarcolemma to the mitochondria.
    c. glycogen diffuses from the sarcolemma to the myofibrils.
    d. myofibrils generate force.
    e. lactate diffuses from the myofibrils to the sarcolemma.

Answer 38

B

Question 39

39. The extraocular muscles that move the mammalian eyeball can contract and relax at much higher frequencies than the muscles of the limbs, but they produce relatively low force as they rotate the eye. These characteristics tell us that extraocular muscles have
    a. high levels of myosin.
    b. high levels of actin.
    c. a high volume fraction of myofibrils.
    d. a high volume fraction of sarcoplasmic reticulum.
    e. troponin C with high Ca2+ affinity.

Answer 39

D

Question 40

40. A vertebrate motor unit consists of
    a. a single motor neuron and all of the muscle fibers that it innervates.
    b. all of the muscles that contract to complete a particular body movement.
    c. a particular muscle and all of its synergistic and antagonistic muscles.
    d. all of the fibers of a particular fiber type in a given muscle.
    e. a small group of contiguous muscle fibers.

Answer 40

A

Question 41

41. The force that a particular vertebrate skeletal muscle produces can be changed by a change in the
    a. size of the action potentials in motor neurons.
    b. number of motor units recruited.
    c. order in which motor units are recruited.
    d. amount of calcium released in response to each action potential.
    e. proportion of myofibrils activated per muscle fiber.

Answer 41

B

Question 42

42. Which of the following is true of most arthropod and vertebrate skeletal muscle?
    a. Muscle fibers are innervated by multiple neurons.
    b. Muscle fibers receive both EPSPs and IPSPs.
    c. Resting sarcomere lengths vary within the same animal and within the same muscle.
    d. Different myosin isoforms in adjacent fibers produce different maximum shortening velocities.
    e. Ca2+ is released from the sarcoplasmic reticulum in response to depolarization of the fiber.

Answer 42

E

Question 43

43. Which of the following is the most likely explanation for the differing patterns of innervation in arthropod skeletal muscle (polyneuronal) and vertebrate skeletal muscle (single innervation)?
    a. Arthropods need to modulate muscle force, whereas a vertebrate always exerts the same force with a given muscle.
    b. Vertebrates need to modulate muscle force, whereas an arthropod always exerts the same force with a given muscle.
    c. Action potentials in vertebrate neurons are all-or-nothing, whereas arthropod neurons fire action potentials of varying magnitude.
    d. Action potentials in arthropod neurons are all-or-nothing, whereas vertebrate neurons fire action potentials of varying magnitude.
    e. The two patterns are products of the evolutionary history of the two taxa and each one allows effective control of muscle contraction.

Answer 43

E

Question 44

44. Smooth muscle cells possess which of the following components?
    a. Sarcoplasmic reticulum
    b. T-tubules
    c. Multiple nuclei
    d. Sarcomeres
    e. Striations

Answer 44

A

Question 45

45. Single-unit smooth muscle differs from multiunit smooth muscle in that multiunit smooth muscle
    a. contains gap junctions that link the cells as an electrical syncytium.
    b. is often spontaneously active.
    c. is usually stretch-activated.
    d. does not require calcium to contract.
    e. has cells that function as independent units.

Answer 45

E

Question 46

46. For contraction to occur in smooth muscle,
    a. myosin light chains must be phosphorylated.
    b. myosin light-chain kinase must be phosphorylated.
    c. calcium must bind to troponin C.
    d. calcium must bind to tropomyosin.
    e. DHPR must interact physically with ryanodine receptor calcium channels.

Answer 46

A

Question 47

47. ATP use is lower in smooth muscle than in skeletal muscle in part because
    a. there is no sarcoplasmic reticulum calcium ATPase in smooth muscle.
    b. smooth muscle myosin does not require an ATP molecule for each cross-bridge cycle.
    c. smooth muscle myosin completes the cross-bridge cycle more slowly than skeletal muscle myosin does.
    d. calcium removal from the cytoplasm does not require ATP in smooth muscle.
    e. smooth muscle myosin takes longer “steps” along the thin filaments than skeletal muscle myosin does.

Answer 47

C

Question 48

48. Which of the following could increase the force produced by a smooth muscle cell?
    a. A reduction in cytosolic Ca2+
    b. Inhibition of myosin light-chain kinase
    c. Inhibition of myosin light-chain phosphatase
    d. Inhibition of calmodulin
    e. An increase in the amount of Ca2+ binding to troponin C

Answer 48

C

Question 49

49. In tonic smooth muscle that contracts continuously for long periods, the highly efficient “latch state” depends on
    a. rapid Ca2+ cycling by the sarcoplasmic reticulum.
    b. high myosin ATPase activity.
    c. very slow turnover of ATP bound to myosin.
    d. slow release of Ca2+ by troponin C.
    e. high activity of myosin light-chain phosphatase.

Answer 49

D

Question 50

50. In contrast to skeletal muscle, nervous signaling to smooth muscle cells
    a. does not occur, because hormones regulate smooth muscle contraction.
    b. is always inhibitory.
    c. can be excitatory or inhibitory.
    d. is all-or-nothing.
    e. can regulate frequency, but not force, of contraction.

Answer 50

C

Question 51

51. Mammalian cardiac muscle cells are stimulated to contract by
    a. action potentials arriving from somatic motor neurons.
    b. hormonal signals that trigger Ca2+ release and myosin light-chain phosphorylation.
    c. electrical signals transmitted through gap junctions from other autorhythmic cardiac muscle cells.
    d. action potentials from excitatory autonomic neurons.
    e. ion channels that open in response to stretch of the cardiac muscle cell membranes.

Answer 51

C

Question 52

1. Which of the following statements about skeletal muscle is true?
   a. Proteins in thick filaments pull on thin filaments, while intermediate filaments hold sarcomeres together.
   b. Proteins in thin filaments pull on intermediate filaments, while thick filaments hold sarcomeres together.
   c. Proteins in thin filaments pull on thick filaments, while intermediate filaments hold sarcomeres together.
   d. Proteins in intermediate filaments pull on thin filaments, while thick filaments hold sarcomeres together.
   e. Proteins in thick filaments pull on intermediate filaments, while thin filaments hold sarcomeres together.

Answer 52

A

Question 53

2. The power stroke of the myosin head occurs in conjunction with what other event of the cross-bridge cycle?
   a. ATP hydrolysis to ADP and inorganic phosphate
   b. ATP binding to the myosin head
   c. ATP binding to the actin filament
   d. Release of ADP from the myosin head
   e. Release of inorganic phosphate from the myosin head

Answer 53

E

Question 54

3. In the absence of _______, muscle can contract but cannot relax
   a. Ca2+
   b. myosin
   c. lactate
   d. ATP
   e. oxygen

Answer 54

D

Question 55

4. In a vertebrate skeletal muscle cell, depolarization of the t-tubule membrane causes dihydropyridine receptors to
   a. open and conduct Ca2+ into the t-tubule.
   b. open and conduct Ca2+ into the cytoplasm.
   c. open and conduct Ca2+ into the sarcoplasmic reticulum.
   d. change conformation and interact with ryanodine receptors.
   e. bind dihydropyridines and change configuration.

Answer 55

D

Question 56

5. A hypothetical skeletal muscle cell with no t-tubules would probably
   a. contract and relax more quickly during twitch contractions.
   b. contract and relax more slowly during twitch contractions.
   c. shorten more quickly during tetanic contractions.
   d. have a lower rate of aerobic ATP production.
   e. generate more force during twitch contractions.

Answer 56

B

Question 57

6. During an isometric tetanic contraction,
   a. the sarcomeres generate no force.
   b. the sarcomeres generate force but cannot stretch the elastic component of the muscle.
   c. the sarcomeres generate force and stretch the elastic component of the muscle, but they cannot move the load.
   d. the sarcomeres generate force but do not transmit it to the elastic component of the muscle.
   e. the elastic component of the muscle generates force and pulls on the sarcomeres.

Answer 57

C

Question 58

7. Why is the latent period of an isotonic twitch different from that of an isometric twitch?
   a. The motoneuron sends a longer action potential if there is an isotonic load on the muscle.
   b. The motoneuron sends a longer action potential if there is an isometric load on the muscle.
   c. An isotonic twitch does not begin until the muscle develops enough force to lift the load.
   d. An isometric twitch does not begin until the muscle develops enough force to lift the load.
   e. The isometric load inhibits the twitch.

Answer 58

C

Question 59

8. Which of the following factors would increase the stimulation frequency at which a muscle shifts from twitch to tetanic contractions?
   c. Lactate dehydrogenase with faster kinetics
   d. Voltage-gated sodium channels with faster kinetics
   a. A larger volume fraction of mitochondria
   b. A larger volume fraction of myofibrils
   e. A larger number of SR Ca2+-ATPase proteins

Answer 59

E

Question 60

9. On the plateau of the length‒tension curve,
   a. all myosin heads are in proximity to actin.
   b. all actin monomers are in proximity to myosin heads.
   c. the width of the I-band is maximized.
   d. the width of the A-band is minimized.
   e. the distance between Z-lines is minimized.

Answer 60

A

Question 61

10. If a muscle contains 10,000 sarcomeres in a series (i.e., end-to-end along its length), each sarcomere is ~2.5 µm in length, and each sarcomere can shorten by 2.5 µm/s, how fast can the muscle shorten?
    a. 2.5 µm/s
    b. 2.5 mm/s
    c. 2.5 cm/s
    d. 25 cm/s
    e. 2.5 m/s

Answer 61

C

Question 62

11. Muscle A has a volume of 200 cm3, a length of 10 cm, and a cross-sectional area of 20 cm2. Muscle B has a volume of 100 cm3, a length of 5 cm, and a cross-sectional area of 20 cm2. Which of the following statements about the muscles is true?
    a. Both muscles can produce the same power, but they can shorten at different speeds.
    b. Both muscles can shorten at the same speed, but they can produce different amounts of power.
    c. Both muscles can exert the same force and can produce the same amount of power.
    d. Both muscles can exert the same force, but one can shorten more quickly than the other.
    e. The two muscles can exert different forces and shorten at different speeds.

Answer 62

D

Question 63

12. Lactate produced by muscle cells
    a. is produced only during very intense exercise.
    b. is the primary cause of muscle fatigue.
    c. is always broken down to yield ATP within the muscle cell that produced it.
    d. is always used to produce glucose by gluconeogenesis in the cell that produced it.
    e. can be exported into the bloodstream and used by other cells.

Answer 63

E

Question 64

13. Which of the following statements about slow oxidative and fast glycolytic muscle fibers is false?
    a. They have isoforms of many muscle proteins that have different properties.
    b. Their thick and thin filaments are arranged differently.
    c. They have differing numbers of organelles such as mitochondria and sarcoplasmic reticulum.
    d. They have different amounts of metabolic enzymes such as hexokinase or citrate synthase.
    e. They have different amounts of certain EC-coupling proteins, such as SR Ca2+-ATPase.

Answer 64

B

Question 65

14. Which of the following factors best explains why vertebrates evolved to have FG muscle fibers that are larger than SO fibers?
    a. SO fibers rely on aerobic metabolism, whereas FG fibers rely on anaerobic metabolism.
    b. SO fibers can oxidize a variety of fuels, whereas FG fibers primarily oxidize glucose/glycogen.
    c. FG fibers must be larger to generate larger action potentials and greater force.
    d. FG fibers must be larger to exchange glucose across the sarcolemma more quickly.
    e. SO fibers must be smaller in order to exchange Ca2+ across the sarcolemma more rapidly.

Answer 65

A

Question 66

15. Slow oxidative fibers in skeletal muscle are used
    a. only for motions requiring maximum power output, such as jumping.
    b. constantly, for postural activities such as standing and sitting.
    c. intermittently, for activities requiring more force output than the FG fibers alone can produce.
    d. intermittently, for activities requiring more force output than the FG and FOG fibers alone can produce.
    e. only when the other fiber types are not used.

Answer 66

B

Question 67

16. Compared to a typical avian leg muscle, hummingbird flight muscle
    a. produces more force per cross-sectional area.
    b. has an exceptionally high volume fraction of mitochondria.
    c. has very high numbers of muscle fibers per capillary.
    d. has a very high glycolytic capacity.
    e. has very high levels of SR Ca2+-ATPase, but low levels of mitochondria.

Answer 67

B

Question 68

17. Muscles of the larynx that help mammals to produce complex sounds can contract and relax at much higher frequencies than the muscles of the limbs, but they produce relatively low force as they act on the vocal cords. Based on these characteristics, one would predict that laryngeal muscles have
    a. high levels of myosin.
    b. myosin that binds ADP very tightly.
    c. high levels of parvalbumin.
    d. high levels of troponin T.
    e. unusually long sarcomeres.

Answer 68

C

Question 69

18. Calcium enters the cytoplasm of a smooth muscle cell by
    a. active transport from the extracellular space only.
    b. active transport from the sarcoplasmic reticulum only.
    c. active transport from the extracellular space and the sarcoplasmic reticulum.
    d. diffusion from the sarcoplasmic reticulum only.
    e. diffusion from the extracellular space and the sarcoplasmic reticulum.

Answer 69

E

Question 70

19. Which of the following cannot modulate force production in smooth muscle?
    a. Ca2+
    b. Inhibition of myosin light chain kinase.
    c. Inhibition of myosin light chain phosphatase.
    d. Binding of Ca2+ to troponin C
    e. Hormonal stimuli

Answer 70

D

Question 71

20. In smooth muscle, calcium must bind to _______ to initiate contraction.
    a. calmodulin
    b. calcineurin
    c. troponin C
    d. myosin
    e. ryanodine receptor

Answer 71

A