Q: Which equation best represents the change in membrane potential during muscle cell depolarization?

Resting membrane potential: $$V_{rest} = -70\ \text{mV}$$; Depolarization: $$V_{depol} \approx +30\ \text{mV}$$

Question 1

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

Accepted Answer

ACh binds to receptors on the sarcolemma, opening sodium channels and initiating depolarization.

Question 2

During the refractory period of a muscle cell, which process is responsible for restoring the original ion concentrations?

Accepted Answer

The sodium-potassium pump actively transports sodium out and potassium in.

Question 3

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

Accepted Answer

Sustained muscle contraction due to prolonged presence of acetylcholine.

Question 4

Which sequence correctly represents the events leading to muscle contraction, starting from the arrival of an action potential at the synaptic bulb?

Accepted Answer

Release of acetylcholine → sodium influx → depolarization → action potential in muscle cell → calcium release → cross-bridge formation

Question 5

If ATP is unavailable in a muscle cell, which step of the cross-bridge cycle will be directly affected, and what is the physiological consequence?

Accepted Answer

Myosin cannot detach from actin, resulting in sustained contraction (rigor mortis).

Question 6

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

Accepted Answer

Resting membrane potential: $$V_{rest} = -70\ 	ext{mV}$$; Depolarization: $$V_{depol} \approx +30\ 	ext{mV}$$

Question 7

During excitation-contraction coupling, what is the primary function of the T-tubules?

Accepted Answer

To transmit the action potential deep into the muscle fiber, triggering calcium release from the terminal cisternae.

Question 8

Which of the following best explains the role of calcium in the cross-bridge cycle?

Accepted Answer

Calcium binds to troponin, causing exposure of actin binding sites for myosin attachment.

Question 9

A muscle cell is unable to repolarize after contraction. Which ion movement is most likely impaired?

Accepted Answer

Potassium efflux from the cell is impaired.

Question 10

Which of the following is TRUE regarding the latent period in skeletal muscle contraction?

Accepted Answer

It is the brief delay between the arrival of the action potential and the release of calcium from the sarcoplasmic reticulum.

Question 11

Which of the following best describes the function of acetylcholinesterase in muscle relaxation?

Accepted Answer

It breaks down acetylcholine in the synaptic cleft, preventing continued stimulation of the muscle cell.

Question 12

Which of the following statements about the sodium-potassium pump is correct?

Accepted Answer

It moves sodium out of the cell and potassium into the cell, restoring resting ion concentrations.

Question 13

A muscle cell receives an action potential, but no calcium is released from the sarcoplasmic reticulum. Which step of contraction will be directly affected?

Accepted Answer

Myosin will not bind to actin, preventing cross-bridge formation.

Question 14

Which formula best represents the action of the sodium-potassium pump during the refractory period?

Accepted Answer

$$3\ 	ext{Na}^+ 	ext{out} : 2\ 	ext{K}^+ 	ext{in}$$

Question 15

Which of the following is a direct consequence of the power stroke in the cross-bridge cycle?

Accepted Answer

The actin filament is pulled toward the center of the sarcomere, causing muscle shortening.

Question 16

Which scenario would most likely result in muscle relaxation?

Accepted Answer

The brain stops sending action potentials, acetylcholine is broken down, and calcium is pumped back into the sarcoplasmic reticulum.

Question 17

Which of the following best explains why the cross-bridge cycle cannot continue without ATP?

Accepted Answer

ATP is required for myosin to detach from actin and re-cock for another cycle.

Question 18

Which of the following is NOT a function of the sarcoplasmic reticulum in skeletal muscle contraction?

Accepted Answer

Breaking down acetylcholine in the synaptic cleft.

Question 19

A muscle cell is exposed to a drug that blocks ligand-gated sodium channels on the sarcolemma. What is the most immediate effect?

Accepted Answer

The muscle cell will not depolarize, preventing contraction.

Skeletal Muscle Contraction: From Neural Signal to Muscle Movement

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