Question 1

Which of the following best describes the role of the sarcoplasmic reticulum (SR) in skeletal muscle contraction?

Accepted Answer

It stores and releases calcium ions ($$\mathrm{Ca$$^{2+}$$}) $$necessary for muscle contraction.

Question 2

During the sliding filament model of muscle contraction, what happens to the A band of the sarcomere?

Accepted Answer

The A band remains the same length.

Question 3

Which event directly triggers the release of acetylcholine (ACh) from the axon terminal at the neuromuscular junction?

Accepted Answer

Influx of $$\mathrm{Ca$$^{2+}$$}$$ into the axon terminal through voltage-gated channels.

Question 4

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

Accepted Answer

Prolonged muscle contraction due to continued presence of ACh in the synaptic cleft.

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 step in the cross bridge cycle is directly powered by the hydrolysis of ATP?

Accepted Answer

Cocking of the myosin head into the high-energy position.

Question 7

A mutation causes the voltage-gated Na+ channels in the sarcolemma to remain closed. What is the most immediate effect on muscle contraction?

Accepted Answer

The muscle fiber will not depolarize and will not contract.

Question 8

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

Accepted Answer

Action potential arrives at axon terminal → $$\mathrm{Ca$$^{2+}$$}$$ enters terminal → ACh released → ACh binds to receptors → Na+ enters muscle fiber

Question 9

In a patient with myasthenia gravis, which of the following is most directly responsible for muscle weakness?

Accepted Answer

Destruction of ACh receptors by the immune system.

Question 10

Which of the following best describes the function of T tubules in skeletal muscle fibers?

Accepted Answer

They conduct action potentials deep into the muscle fiber to trigger calcium release.

Question 11

During muscle contraction, which of the following changes occur in the sarcomere?

Accepted Answer

I bands shorten, H zones disappear, Z discs move closer together.

Question 12

Which of the following is the correct formula for the sodium-potassium pump that restores ionic conditions after an action potential?

Accepted Answer

$$3\ \mathrm{Na^+}$$ out, $$2\ \mathrm{K^+} in$$, using 1 ATP

Question 13

A drug that blocks voltage-gated K+ channels in the sarcolemma would have which effect on the action potential?

Accepted Answer

It would delay repolarization, prolonging the action potential.

Question 14

Which of the following is required for cross bridge detachment during the cross bridge cycle?

Accepted Answer

Binding of ATP to the myosin head.

Question 15

In the context of excitation-contraction coupling, what is the immediate consequence of an action potential traveling down the T tubules?

Accepted Answer

Release of $$\mathrm{Ca$$^{2+}$$}$$ from the sarcoplasmic reticulum.

Question 16

Which of the following best explains why muscle fibers are unable to contract during the refractory period?

Accepted Answer

Voltage-gated Na+ channels are inactivated and cannot reopen until repolarization is complete.

Ch 9B Skeletal Muscle Contraction: Structure, Function, and Mechanisms

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