Question 1

Which of the following statements is TRUE regarding skeletal-muscle contraction?

Accepted Answer

A)  Only one cross-bridge cycle can occur when the [Ca2+] is elevated in the cytosol; in order to undergo a second cycle,[Ca2+] must be sequestered in the sarcoplasmic reticulum and released again.
B)  ATP hydrolysis products must be removed from myosin before it can bind to actin.
C)  Binding of myosin to actin takes place when [Ca2+] increases in the cytosol.
D)  A single twitch in skeletal muscle lasts the same length of time as the action potential that causes it.
E)  The powerstroke of the cross-bridge cycle occurs simultaneously with ATP being hydrolyzed into ADP and Pi.

Question 2

During an isometric twitch in a skeletal muscle:

Accepted Answer

A)  tension generated by the muscle always exceeds the load on the muscle.
B)  tetanus occurs.
C)  sarcomeres do not significantly shorten.
D)  the whole muscle shortens.
E)  the load on the muscle is always greater than the tension generated.

Question 3

Myasthenia gravis is an autoimmune disease in which the immune system gradually destroys the receptors for acetylcholine at the neuromuscular junction.Which of the following drugs might initially be useful in treating the symptoms of this disease?

Accepted Answer

A)  a drug that inhibits acetylcholinesterase
B)  a drug that inhibits release of acetylcholine
C)  curare
D)  atropine (a muscarinic acetylcholine receptor antagonist) 
E)  a nicotinic acetylcholine receptor antagonist

Question 4

The shortening velocity of a skeletal muscle fiber increases with decreasing load because the rate at which the cross-bridge cycle can occur increases with decreasing load.

Accepted Answer

A) True 
 B)False

Question 5

The step of the cross-bridge cycle that immediately follows the attachment of ATP to the myosin head is referred to as the "powerstroke."

Accepted Answer

A) True 
 B)False

Question 6

Which of the following statements regarding whole-muscle contraction is TRUE?

Accepted Answer

A)  The order of recruitment of motor units in a muscle is such that the last units recruited are those that fatigue most readily.
B)  The order of recruitment of motor units in a muscle is such that the first units recruited generate the most tension
C)  Motor units whose motor neurons have large-diameter cell bodies are recruited first,while motor units with smaller-diameter motor neurons are only activated as the level of activation in the spinal cord increases.
D)  The order of motor unit recruitment is independent of the size of the alpha motor neuron that innervates them.
E)  Recruitment of one fast-glycolytic motor unit provides a smaller increment in whole-muscle tension than recruitment of one slow-oxidative motor unit.

Question 7

The binding of ATP to myosin causes an allosteric change in myosin's actin-binding site such that the affinity of myosin for actin is decreased.

Accepted Answer

A) True 
 B)False

Question 8

In general,activating a slow-oxidative motor unit in a muscle will generate more tension than activating a fast-glycolytic motor unit.

Accepted Answer

A) True 
 B)False

Question 9

Recruitment of different types of motor units in a muscle is one means of varying the amount of tension generated in that muscle.

Accepted Answer

A) True 
 B)False

Question 10

Which occurs FIRST as a result of ATP binding to myosin?

Accepted Answer

A)  cross-bridge heads are cocked into an "energized" state
B)  actin dissociates from from myosin
C)  Ca2+ is released from the sarcoplasmic reticulum
D)  actin binds to myosin
E)  cross-bridges rotate,sliding past the thin filament

Question 11

Which of the following is FALSE regarding single-unit smooth-muscle cells?

Accepted Answer

A)  They have an individual neuron innervating of each individual smooth-muscle cell.
B)  They have many gap junctions between cells.
C)  They may have pacemaker activity.
D)  They may respond to stretch by contracting.
E)  They exhibit tone.

Question 12

Which of the following statements regarding skeletal muscle is TRUE?

Accepted Answer

A)  Skeletal muscle fibers have pacemaker activity.
B)  Skeletal muscle fibers are joined together by gap junctions.
C)  A given skeletal muscle fiber will contract when excitatory nervous stimuli sufficiently exceed inhibitory nervous stimuli at the motor end plate
D)  A given skeletal muscle fiber will contract if excitatory synaptic inputs sufficiently exceed inhibitory synaptic inputs on the motor neuron that innervates that fiber and the motor neuron fires an action potential.
E)  Skeletal muscle contraction is inhibited by inhibitory motor neurons that synapse onto skeletal muscle fibers.

Question 13

Which best describes a "myofibril?"

Accepted Answer

A)  It is a single skeletal-muscle cell.
B)  It is a cylindrical cellular organelle composed of myofilaments.
C)  It is a hollow membranous structure that stores calcium.
D)  It is composed of a single type of protein and forms cross-bridges.
E)  It is a fibrous junction between a muscle cell and a tendon.

Question 14

Which type of skeletal muscle fibers fatigues most quickly?

Accepted Answer

A)  Type I
B)  Type II

Question 15

Sustained contraction and tension in a skeletal muscle is called tetanus.

Accepted Answer

A) True 
 B)False

Question 16

Which of these is a major difference between smooth muscle and skeletal muscle?

Accepted Answer

A)  Myosin is the main regulatory protein in smooth muscle.
B)  Myosin is the main regulatory protein in skeletal muscle.
C)   Skeletal muscle usually exhibits spontaneous activity,while smooth muscle cannot contract spontaneously.
D)  Only skeletal muscle requires increased calcium ion concentration in the cytosol for contraction.
E)  Only skeletal muscle has both actin and myosin.

Question 17

A Ca2+-binding protein in smooth muscle is calmodulin.

Accepted Answer

A) True 
 B)False

Question 18

Which of these occurs during an isometric contraction of a skeletal muscle?

Accepted Answer

A)  The I bands shorten and the A bands stay the same length.
B)  The thick and thin filaments slide past each other.
C)  Sarcomere length does not change.
D)  The A bands shorten and the I bands stay the same length.
E)  Cross-bridges lock onto actin,similar to what occurs in rigor mortis.

Question 19

What protein is the principle component of skeletal muscle thick filaments?

Accepted Answer

A)  actin
B)  myosin
C)  troponin
D)  calmodulin
E)  tropomyosin

Question 20

The fiber type intermediate between the two extremes of fast-glycolytic and slow-oxidative is slow-glycolytic.

Accepted Answer

A) True 
 B)False

Exam 9: Muscle

Which of the following statements regarding skeletal muscle is TRUE?

Correct AnswerverifiedShow Answer

Which occurs FIRST as a result of ATP binding to myosin?

Correct AnswerverifiedShow Answer

In general,activating a slow-oxidative motor unit in a muscle will generate more tension than activating a fast-glycolytic motor unit.

Correct AnswerverifiedShow Answer

Which of these occurs during an isometric contraction of a skeletal muscle?

Correct AnswerverifiedShow Answer

The shortening velocity of a skeletal muscle fiber increases with decreasing load because the rate at which the cross-bridge cycle can occur increases with decreasing load.

Correct AnswerverifiedShow Answer

Which best describes a "myofibril?"

Correct AnswerverifiedShow Answer

Sustained contraction and tension in a skeletal muscle is called tetanus.

Correct AnswerverifiedShow Answer

Which of the following is FALSE regarding single-unit smooth-muscle cells?

Correct AnswerverifiedShow Answer

During an isometric twitch in a skeletal muscle:

Correct AnswerverifiedShow Answer

Which of the following statements is TRUE regarding skeletal-muscle contraction?

Correct AnswerverifiedShow Answer

Which of these is a major difference between smooth muscle and skeletal muscle?

Correct AnswerverifiedShow Answer

A Ca2+-binding protein in smooth muscle is calmodulin.

Correct AnswerverifiedShow Answer

The step of the cross-bridge cycle that immediately follows the attachment of ATP to the myosin head is referred to as the "powerstroke."

Correct AnswerverifiedShow Answer

Recruitment of different types of motor units in a muscle is one means of varying the amount of tension generated in that muscle.

Correct AnswerverifiedShow Answer

The fiber type intermediate between the two extremes of fast-glycolytic and slow-oxidative is slow-glycolytic.

Correct AnswerverifiedShow Answer

The binding of ATP to myosin causes an allosteric change in myosin's actin-binding site such that the affinity of myosin for actin is decreased.

Correct AnswerverifiedShow Answer

Myasthenia gravis is an autoimmune disease in which the immune system gradually destroys the receptors for acetylcholine at the neuromuscular junction.Which of the following drugs might initially be useful in treating the symptoms of this disease?

Correct AnswerverifiedShow Answer

Which of the following statements regarding whole-muscle contraction is TRUE?

Correct AnswerverifiedShow Answer

What protein is the principle component of skeletal muscle thick filaments?

Correct AnswerverifiedShow Answer

Which type of skeletal muscle fibers fatigues most quickly?

Correct AnswerverifiedShow Answer

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A Ca²⁺-binding protein in smooth muscle is calmodulin.

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