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 mechanism of skeletal muscle contraction, which event directly triggers the exposure of myosin-binding sites on actin?

Accepted Answer

Calcium ions ($$\mathrm{Ca$$^{2+}$$}) $$bind to troponin, causing a conformational change that moves tropomyosin.

Question 3

A patient is unable to relax their muscles after contraction, resulting in a state similar to rigor mortis. Which of the following best explains this phenomenon?

Accepted Answer

ATP is unavailable, preventing the detachment of myosin heads from actin.

Question 4

Which of the following best distinguishes between isotonic and isometric muscle contractions?

Accepted Answer

Isotonic contractions involve a change in muscle length, while isometric contractions generate tension without changing muscle length.

Question 5

A sprinter running a 100-meter dash primarily relies on which energy source for muscle contraction?

Accepted Answer

Anaerobic glycolysis

Question 6

Which of the following is TRUE regarding the neuromuscular junction (NMJ)?

Accepted Answer

Acetylcholine is released from the motor neuron and binds to receptors on the sarcolemma, initiating an action potential.

Question 7

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

Accepted Answer

They rely primarily on anaerobic metabolism, which produces less ATP and more lactic acid.

Question 8

A muscle is stretched to 120% of its resting length and then stimulated to contract. According to the length-tension relationship, what is the expected outcome?

Accepted Answer

The muscle will generate less force because there is less overlap between actin and myosin filaments.

Question 9

Which of the following events occurs first during excitation-contraction coupling in skeletal muscle?

Accepted Answer

An action potential travels along the sarcolemma and down the T-tubules.

Question 10

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

Accepted Answer

It stores oxygen for use during aerobic metabolism.

Question 11

A patient is holding a heavy box without moving it. Which type of muscle contraction is primarily occurring in their biceps?

Accepted Answer

Isometric contraction

Question 12

Which of the following is a characteristic unique to smooth muscle compared to skeletal muscle?

Accepted Answer

Smooth muscle uses calmodulin instead of troponin to bind calcium ions ($$\mathrm{Ca$$^{2+}$$}).$$

Question 13

Which of the following best explains the physiological basis of muscle tone?

Accepted Answer

It is due to the continuous, partial contraction of some motor units, even at rest.

Question 14

During a sustained, high-frequency stimulation of a skeletal muscle, which phenomenon is most likely to occur?

Accepted Answer

Tetanus, where contractions fuse and no relaxation is observed.

Question 15

Which of the following best describes the role of creatine phosphate in muscle contraction?

Accepted Answer

It donates a phosphate group to ADP to rapidly regenerate ATP during the initial seconds of intense activity.

Question 16

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

Accepted Answer

Opening of ligand-gated sodium channels, leading to depolarization of the sarcolemma.

Question 17

Which of the following best explains why smooth muscle can maintain contractions for long periods with minimal fatigue?

Accepted Answer

Smooth muscle has slow, sustained contractions and primarily uses aerobic metabolism.

Question 18

Which of the following is the correct sequence of events in the cross-bridge cycle during muscle contraction?

Accepted Answer

Myosin binds to actin, power stroke occurs, ATP binds to myosin, myosin detaches from actin, ATP is hydrolyzed, myosin returns to high-energy state.

Question 19

Which of the following best describes the effect of increasing the load on a skeletal muscle during contraction?

Accepted Answer

The velocity of contraction decreases and the duration of contraction shortens.

Physiology of Muscle: Structure, Function, and Types

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