$$\text{Na}^+_{\text{outside}} \rightarrow \text{Na}^+_{\text{inside}}$$

Question 1

Which of the following best describes the function of a motor neuron in skeletal muscle contraction?

Accepted Answer

It releases acetylcholine at the neuromuscular junction to initiate muscle fiber excitation.

Question 2

What is the primary role of chemically gated ion channels at the neuromuscular junction?

Accepted Answer

They open in response to neurotransmitter binding, allowing Na+ to enter the muscle fiber.

Question 3

During the generation of an action potential across the sarcolemma, which event occurs first?

Accepted Answer

ACh binds to its receptors, causing chemically gated ion channels to open.

Question 4

Which equation best represents the movement of ions during depolarization at the neuromuscular junction?

Accepted Answer

$$	ext{Na}^+_{	ext{outside}} ightarrow 	ext{Na}^+_{	ext{inside}}$$

Question 5

What is the function of acetylcholinesterase at the neuromuscular junction?

Accepted Answer

It breaks down acetylcholine, terminating its effects on the muscle fiber.

Question 6

Which of the following best describes the process of repolarization in a muscle fiber?

Accepted Answer

Voltage-gated K+ channels open, allowing K+ to exit the cell and restore the negative membrane potential.

Question 7

A patient is exposed to a toxin that blocks voltage-gated Ca2+ channels in motor neurons. What is the most likely effect on muscle contraction?

Accepted Answer

Acetylcholine release will be inhibited, preventing muscle fiber excitation.

Question 8

Which of the following is TRUE regarding the refractory period in muscle fibers?

Accepted Answer

The muscle fiber cannot be stimulated again until repolarization is complete.

Question 9

Which structure contains millions of acetylcholine receptors and is critical for muscle fiber excitation?

Accepted Answer

Junctional folds of the sarcolemma

Question 10

What is the correct sequence of events leading to muscle contraction at the neuromuscular junction?

Accepted Answer

Action potential arrives → Ca2+ enters axon terminal → ACh released → ACh binds receptors → Na+ enters muscle fiber

Question 11

Which formula best represents the restoration of ionic conditions after an action potential?

Accepted Answer

$$	ext{Na}^+_{	ext{inside}} ightarrow 	ext{Na}^+_{	ext{outside}}$$ and $$	ext{K}^+_{	ext{outside}} ightarrow 	ext{K}^+_{	ext{inside}}$$

Question 12

Which of the following best defines a motor unit?

Accepted Answer

A motor neuron and all the muscle fibers it innervates

Question 13

Recruitment in muscle contraction refers to:

Accepted Answer

The activation of additional motor units to increase muscle force

Question 14

Which event directly triggers the release of acetylcholine from the axon terminal?

Accepted Answer

Influx of Ca2+ into the axon terminal

Question 15

ACh binding to its receptor on the sarcolemma results in:

Accepted Answer

Opening of ion channels that allow Na+ to enter and K+ to exit the muscle fiber

Question 16

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

Accepted Answer

Sarcoplasmic reticulum

Question 17

Excitation-contraction coupling involves which sequence of events?

Accepted Answer

Propagation of action potential along sarcolemma → Down T tubules → Ca2+ release from SR → Contraction

Question 18

If acetylcholinesterase is inhibited at the neuromuscular junction, what is the most likely outcome?

Accepted Answer

Prolonged muscle contraction due to persistent ACh activity

Question 19

Which of the following best explains why more Na+ enters the muscle fiber than K+ exits during end plate potential?

Accepted Answer

The driving force for Na+ entry is greater due to its higher concentration gradient and membrane potential.

Motor Neurons and the Neuromuscular Junction: Mechanisms of Muscle Contraction

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