Question 1

During the depolarization stage of an action potential in a skeletal muscle fiber, which of the following events occurs?

Accepted Answer

Voltage-gated sodium channels open and sodium ions enter the cell.

Question 2

Which structure is responsible for storing and releasing calcium ions during excitation-contraction coupling in skeletal muscle fibers?

Accepted Answer

Sarcoplasmic reticulum

Question 3

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

Accepted Answer

To degrade acetylcholine in the synaptic cleft, terminating the signal.

Question 4

Which of the following best describes the sequence of events at the neuromuscular junction leading to muscle fiber excitation?

Accepted Answer

Calcium influx into the axon terminal → exocytosis of synaptic vesicles → acetylcholine release → binding to receptors on the motor end plate

Question 5

If a drug blocked voltage-gated sodium channels on the sarcolemma, what would be the most immediate effect on muscle contraction?

Accepted Answer

The muscle fiber would be unable to generate an action potential.

Question 6

Which of the following equations best represents the change in membrane potential during the depolarization stage?

Accepted Answer

$$V_m = V_{rest} + \Delta V_{Na^+}$$

Question 7

A patient is exposed to a toxin that prevents the breakdown of acetylcholine in the synaptic cleft. What is the most likely physiological outcome?

Accepted Answer

Continuous stimulation of the muscle fiber, leading to muscle spasms.

Question 8

Which of the following best explains why only a few ions need to cross the sarcolemma to cause large changes in membrane potential?

Accepted Answer

The membrane potential is determined by the relative difference in ion concentrations across the membrane, not the absolute number of ions.

Question 9

During the contraction phase, what is the role of ATP in the crossbridge cycle?

Accepted Answer

ATP hydrolysis cocks the myosin head into its high-energy position.

Question 10

Which of the following events occurs immediately after acetylcholine binds to its receptor on the motor end plate?

Accepted Answer

Ligand-gated cation channels open, allowing sodium to enter the muscle fiber.

Question 11

Which of the following best describes the propagation of an action potential along the sarcolemma?

Accepted Answer

Depolarization of one region triggers opening of voltage-gated sodium channels in adjacent regions.

Question 12

A mutation causes the ligand-gated cation channels on the motor end plate to become nonfunctional. What is the most immediate effect?

Accepted Answer

The muscle fiber cannot generate an end-plate potential.

Question 13

Which of the following is the correct order of events in excitation-contraction coupling?

Accepted Answer

End-plate potential → action potential propagation → T-tubule depolarization → calcium release from SR

Question 14

Which of the following best explains why multiple end-plate potentials are necessary for a functional muscle contraction?

Accepted Answer

Each end-plate potential only depolarizes a small region of the sarcolemma.

Question 15

Which of the following is a direct result of calcium ions binding to troponin during the contraction phase?

Accepted Answer

Tropomyosin moves, exposing the active sites on actin.

Skeletal Muscle Contraction: Action Potentials, Neuromuscular Junction, and Excitation-Contraction Coupling

Study Guide - Practice Questions