Question 1

Which of the following best describes the sequence of events at the neuromuscular junction (NMJ) leading to muscle cell depolarization?

Accepted Answer

An action potential reaches the synaptic bulb, acetylcholine is released into the synaptic cleft, binds to receptors on the sarcolemma, and opens sodium channels.

Question 2

During the refractory period, why can't a muscle cell immediately generate another action potential?

Accepted Answer

The sodium-potassium pump has not yet restored the original ion concentrations across the membrane.

Question 3

Which of the following events occurs during the latent period of muscle contraction?

Accepted Answer

The action potential travels down the T-tubules, triggering calcium release from the terminal cisternae.

Question 4

A patient is exposed to a toxin that inhibits acetylcholinesterase. What is the most likely effect on skeletal muscle contraction?

Accepted Answer

Muscles will remain contracted due to continuous stimulation by acetylcholine.

Question 5

Which of the following best explains why rigor mortis occurs after death?

Accepted Answer

ATP is no longer produced, so myosin heads cannot detach from actin.

Question 6

Which equation best represents the change in membrane potential during depolarization of a muscle cell?

Accepted Answer

$$V_{m} : -70\ \mathrm{mV} \rightarrow +30\ \mathrm{mV}$$

Question 7

Which of the following is the correct sequence of events in the cross-bridge cycle (CBC)?

Accepted Answer

Myosin binds to actin, power stroke occurs, ATP binds to myosin causing detachment, myosin re-cocks.

Question 8

A muscle cell is unable to contract even though it is being stimulated by the nervous system. Which of the following is the most likely explanation?

Accepted Answer

There is insufficient calcium available for release from the sarcoplasmic reticulum.

Question 9

Which muscle fiber type would be most active in a marathon runner, and what is a key characteristic of this fiber type?

Accepted Answer

Slow oxidative; high myoglobin concentration

Question 10

Which of the following best describes the role of the sodium-potassium pump in muscle physiology?

Accepted Answer

It restores the resting ion concentrations after an action potential by moving sodium out and potassium in.

Question 11

A person is exercising intensely and experiences muscle fatigue. Which of the following best explains this phenomenon?

Accepted Answer

The sarcoplasmic reticulum is damaged or there is insufficient calcium available.

Question 12

Which of the following is TRUE regarding the process of muscle relaxation?

Accepted Answer

Calcium is pumped back into the sarcoplasmic reticulum, and acetylcholine is broken down by acetylcholinesterase.

Question 13

Which of the following best defines a motor unit?

Accepted Answer

A motor neuron and all the muscle fibers it innervates.

Question 14

Which of the following best describes muscle tone?

Accepted Answer

A state of constant, slight contraction in muscle fibers.

Question 15

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

Accepted Answer

Tropomyosin moves, exposing binding sites on actin.

Question 16

A normal dad plays basketball against an NBA player and quickly tires. Which muscle fiber type is primarily being used, and what is a key metabolic feature?

Accepted Answer

Fast glycolytic; relies on anaerobic metabolism

Question 17

Which of the following best describes oxygen debt?

Accepted Answer

The extra oxygen needed to restore ATP, creatine phosphate, and glycogen reserves after exercise.

Question 18

Which of the following is TRUE regarding the role of ATP in skeletal muscle contraction?

Accepted Answer

ATP is required for both the attachment and detachment of myosin heads to actin.

Question 19

Which of the following best explains why sodium influx is critical for generating an action potential in the muscle cell?

Accepted Answer

Sodium influx depolarizes the membrane, shifting the voltage from $$-70\ \mathrm{mV} to$$ $$+30\ \mathrm{mV}$$, which triggers the action potential.

Skeletal Muscle Contraction: Mechanisms and Key Concepts

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