Question 1

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

Accepted Answer

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

Question 2

During the depolarization phase of an action potential in a muscle fiber, which ions move and in which direction?

Accepted Answer

$\mathrm{Na^+}$ ions move into the cell, making the inside more positive.

Question 3

Which structure in a skeletal muscle fiber is primarily responsible for propagating the action potential deep into the cell?

Accepted Answer

T-tubules

Question 4

What is the immediate effect of calcium ions binding to troponin during muscle contraction?

Accepted Answer

Tropomyosin shifts, exposing myosin-binding sites on actin.

Question 5

If acetylcholinesterase is inhibited at the neuromuscular junction, what is the expected effect on muscle contraction?

Accepted Answer

Muscle contraction will increase due to prolonged action of acetylcholine.

Question 6

Which of the following correctly sequences the steps of excitation-contraction coupling?

Accepted Answer

Action potential propagates along sarcolemma and T-tubules $\rightarrow$ Voltage-gated channels release $\mathrm{Ca^{2+}}$ $\rightarrow$ $\mathrm{Ca^{2+}}$ binds to troponin $\rightarrow$ Tropomyosin moves $\rightarrow$ Cross bridges form and muscle contracts.

Question 7

A patient is exposed to a toxin that blocks voltage-gated sodium channels in the sarcolemma. What is the most likely effect on muscle contraction?

Accepted Answer

The muscle will not contract because the action potential cannot propagate.

Question 8

Which of the following structures has the greatest total surface area in a skeletal muscle fiber?

Accepted Answer

Sarcolemma

Question 9

During repolarization of a muscle fiber, which ion movement restores the resting membrane potential?

Accepted Answer

$\mathrm{K^+}$ ions move out of the cell.

Question 10

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

Accepted Answer

Depolarization of the T-tubule membrane by the action potential.

Question 11

A drug blocks the binding of acetylcholine to its receptor at the neuromuscular junction. What is the most likely outcome?

Accepted Answer

Muscle contraction will be inhibited due to lack of action potential initiation.

Question 12

Which of the following best explains the function of tropomyosin in muscle contraction?

Accepted Answer

Tropomyosin prevents myosin heads from binding to actin in the absence of calcium.

Question 13

Which of the following is the correct formula for the change in membrane potential ($\Delta V$) during depolarization?

Accepted Answer

$\Delta V = V_{final} - V_{rest}$

Question 14

Which of the following statements about excitation-contraction coupling is correct?

Accepted Answer

It converts the electrochemical signal to the mechanical movement of contraction.

Question 15

Which of the following would most likely result from blocking the acetylcholine receptor at the neuromuscular junction?

Accepted Answer

Inhibit contraction

Question 16

What is the primary function of the sarcoplasmic reticulum in muscle fibers?

Accepted Answer

Store and release $\mathrm{Ca^{2+}}$ ions to regulate contraction.

Question 17

Which of the following best describes the role of the motor neuron in muscle contraction?

Accepted Answer

It forms a synapse with the muscle fiber at the neuromuscular junction to pass the electrical signal.

Question 18

Which of the following events occurs first during the process of muscle contraction?

Accepted Answer

Action potential arrives at the axon terminal.

Question 19

A patient is given a drug that increases the activity of acetylcholinesterase at the neuromuscular junction. What is the expected effect?

Accepted Answer

Decrease muscle contraction due to rapid breakdown of acetylcholine.

Muscle Contraction and Neuromuscular Junction: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards