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 Ca$^{2+}$ ions, which are necessary for the initiation of the cross-bridge cycle.

Question 2

A competitive antagonist of the nicotinic acetylcholine receptor (nAChR) at the neuromuscular junction would most likely:

Accepted Answer

Prevent acetylcholine from binding, thereby reducing or blocking the excitatory postsynaptic potential (EPSP).

Question 3

Which protein is responsible for coupling the depolarization of the T-tubule membrane to the release of Ca$^{2+}$ from the sarcoplasmic reticulum?

Accepted Answer

Dihydropyridine receptor (DHP)

Question 4

During the cross-bridge cycle, what event directly triggers the power stroke of the myosin head?

Accepted Answer

Release of ADP and Pi from the myosin head

Question 5

Which of the following best explains why fast-twitch glycolytic muscle fibers fatigue more quickly than slow-twitch oxidative fibers?

Accepted Answer

They rely primarily on anaerobic glycolysis, which produces less ATP per glucose molecule.

Question 6

A patient with myasthenia gravis experiences muscle weakness because:

Accepted Answer

Their immune system attacks nAChRs, reducing the effectiveness of neuromuscular transmission.

Question 7

Which of the following equations correctly represents the relationship between ionic current, permeability, membrane potential, and equilibrium potential?

Accepted Answer

$I_{ion} = P_{ion}(V_m - E_{ion})$

Question 8

What is the primary function of the SERCA pump in skeletal muscle?

Accepted Answer

To actively transport Ca$^{2+}$ back into the sarcoplasmic reticulum, promoting muscle relaxation.

Question 9

Which of the following best describes the force-length relationship in skeletal muscle?

Accepted Answer

Force generation is maximal at an optimal overlap between thick and thin filaments, allowing the greatest number of cross-bridges.

Question 10

Which of the following is a direct result of acetylcholine binding to the nicotinic acetylcholine receptor at the neuromuscular junction?

Accepted Answer

Depolarization of the muscle fiber membrane due to influx of Na$^+$ ions.

Question 11

Which of the following best explains why the sarcomere shortens during muscle contraction?

Accepted Answer

Thick and thin filaments slide past each other, increasing their overlap.

Question 12

Which protein is mutated in Duchenne muscular dystrophy, leading to instability of the muscle cell membrane?

Accepted Answer

Dystrophin

Question 13

What is the immediate source of energy for the power stroke during the cross-bridge cycle?

Accepted Answer

Hydrolysis of ATP by myosin ATPase

Question 14

Which of the following best describes the size principle of motor unit recruitment?

Accepted Answer

Small motor units are recruited first, allowing fine control at low force levels.

Question 15

Which of the following is true regarding the difference between slow-twitch (Type I) and fast-twitch (Type II) muscle fibers?

Accepted Answer

Type II fibers fatigue more quickly due to reliance on anaerobic metabolism.

Question 16

Which of the following best explains why ATP is required for muscle relaxation?

Accepted Answer

ATP is needed to detach myosin heads from actin and to power the SERCA pump for Ca$^{2+}$ reuptake.

Question 17

Which of the following metabolic pathways provides the fastest but least sustainable source of ATP during intense muscle activity?

Accepted Answer

Direct phosphorylation by creatine phosphate

Question 18

A non-competitive antagonist of the nAChR would most likely:

Accepted Answer

Bind to a different site on the receptor, changing its conformation and reducing the EPSP even if ACh is present.

Question 19

Which of the following best describes the role of titin in the sarcomere?

Accepted Answer

It maintains the structural alignment and elasticity of thick and thin filaments.

Skeletal Muscle Physiology: Structure, Function, and Excitation-Contraction Coupling

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