Question 1

Which of the following best describes the role of acetylcholine (ACh) at the neuromuscular junction?

Accepted Answer

ACh binds to receptors on the sarcolemma, increasing its permeability to Na+ ions and initiating an action potential in the muscle fiber.

Question 2

During the sliding filament theory of muscle contraction, what happens to the sarcomere?

Accepted Answer

The sarcomere shortens as actin filaments slide past myosin filaments toward the M line.

Question 3

What is the function of acetylcholinesterase (AChE) at the neuromuscular junction?

Accepted Answer

AChE breaks down acetylcholine in the synaptic cleft, terminating the signal and allowing muscle relaxation.

Question 4

Which event directly triggers the release of calcium ions from the sarcoplasmic reticulum during muscle contraction?

Accepted Answer

An action potential traveling down the T-tubules.

Question 5

What is the role of troponin in the muscle contraction cycle?

Accepted Answer

Troponin binds to Ca2+, causing tropomyosin to move and expose active sites on actin.

Question 6

A patient is exposed to a toxin that blocks voltage-gated calcium channels in the axon terminal of a motor neuron. What is the most likely effect on muscle contraction?

Accepted Answer

Acetylcholine will not be released, so the muscle fiber will not contract.

Question 7

Which of the following correctly describes the power stroke in the cross-bridge cycle?

Accepted Answer

The myosin head pivots toward the M line, pulling actin filaments and releasing ADP and P.

Question 8

Which of the following is required for the detachment of the myosin head from actin during muscle relaxation?

Accepted Answer

Binding of a new ATP molecule to the myosin head.

Question 9

If a muscle fiber is unable to remove Ca2+ from the sarcoplasm after contraction, what will most likely occur?

Accepted Answer

The muscle fiber will remain contracted and unable to relax.

Question 10

Which of the following best explains why ATP is necessary for muscle contraction and relaxation?

Accepted Answer

ATP is required both for the detachment of myosin from actin and for the re-cocking of the myosin head.

Question 11

A drug that inhibits acetylcholinesterase (AChE) would have which of the following effects on skeletal muscle?

Accepted Answer

Prolonged muscle contraction due to continued presence of ACh in the synaptic cleft.

Question 12

Which of the following sequences correctly represents the order of events in excitation-contraction coupling?

Accepted Answer

Action potential travels along sarcolemma → T-tubules → Ca2+ released from sarcoplasmic reticulum → Ca2+ binds troponin → Cross-bridge formation

Question 13

A patient with a genetic defect in troponin that prevents it from binding Ca2+ would experience which of the following?

Accepted Answer

Inability to expose active sites on actin, resulting in no muscle contraction.

Question 14

Which of the following best describes the function of T-tubules in skeletal muscle fibers?

Accepted Answer

They conduct action potentials deep into the muscle fiber, ensuring the entire fiber contracts simultaneously.

Question 15

Which of the following equations best represents the hydrolysis of ATP by myosin during the contraction cycle?

Accepted Answer

$$\mathrm{ATP} + \mathrm{H}_2\mathrm{O} ightarrow \mathrm{ADP} + \mathrm{P}_i + 	ext{energy}$$

Question 16

A patient is given a drug that prevents the reuptake of Ca2+ into the sarcoplasmic reticulum. What is the most likely physiological effect?

Accepted Answer

Sustained muscle contraction due to continued cross-bridge cycling.

Question 17

Which of the following is the correct sequence of the cross-bridge cycle?

Accepted Answer

Cross-bridge formation → Power stroke → Cross-bridge detachment → Myosin reactivation

Question 18

Which of the following would most likely occur if ATP were suddenly unavailable in a contracting muscle fiber?

Accepted Answer

Myosin heads would remain attached to actin, preventing muscle relaxation (rigor mortis).

Question 19

Which of the following best explains why muscle fibers rarely reach maximum shortening during contraction?

Accepted Answer

Joints usually limit movement before full filament overlap occurs.

Muscle Tissue: Muscle Contraction and the Neuromuscular Junction

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