Question 1

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

Accepted Answer

It binds to receptors on the sarcolemma, initiating an action potential in the muscle fiber.

Question 2

During excitation-contraction coupling, what is the primary function of calcium ions ($$\mathrm{Ca$$^{2+}$$}$$)?

Accepted Answer

To bind to troponin, causing a conformational change that exposes myosin-binding sites on actin.

Question 3

Which sequence correctly represents the events at the neuromuscular junction leading to muscle fiber excitation?

Accepted Answer

Action potential arrives at axon terminal → Acetylcholine released → Acetylcholine binds to receptors → Sarcolemma depolarizes

Question 4

What is the correct order of events in the contraction cycle of a skeletal muscle fiber?

Accepted Answer

Cross-bridge formation → Power stroke → Cross-bridge detachment → Reactivation of myosin head

Question 5

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

Accepted Answer

Depolarization of the T-tubule membrane

Question 6

A patient is exposed to a toxin that blocks acetylcholinesterase at the neuromuscular junction. What is the most likely effect on muscle contraction?

Accepted Answer

Prolonged muscle contraction due to continuous stimulation by acetylcholine

Question 7

Which of the following best explains the process of skeletal muscle fiber relaxation?

Accepted Answer

Calcium ions are actively transported back into the sarcoplasmic reticulum, and acetylcholine is broken down in the synaptic cleft.

Question 8

Which structure is responsible for transmitting the action potential deep into the muscle fiber?

Accepted Answer

Transverse (T) tubules

Question 9

If the sarcolemma fails to repolarize after an action potential, what is the most likely consequence?

Accepted Answer

The muscle fiber will remain in a contracted state.

Question 10

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

Accepted Answer

$$\mathrm{ATP \rightarrow ADP + P_i + energy}$$

Question 11

A drug that blocks voltage-gated sodium channels on the sarcolemma would have what effect on muscle contraction?

Accepted Answer

It would prevent the initiation of an action potential, inhibiting muscle contraction.

Question 12

Which of the following is NOT a component of the neuromuscular junction?

Accepted Answer

Sarcoplasmic reticulum

Question 13

Which step in the contraction cycle requires the direct use of ATP?

Accepted Answer

Detachment of the myosin head from actin

Question 14

What would happen if calcium ions were not removed from the cytosol of the muscle fiber after contraction?

Accepted Answer

The muscle would remain contracted and not relax.

Question 15

Which of the following best describes the function of the motor end plate?

Accepted Answer

It contains receptors for acetylcholine that initiate an action potential in the muscle fiber.

The Process of Skeletal Muscle Contraction and Relaxation

Study Guide - Practice Questions