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 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 death, resulting in rigor mortis. What is the primary reason for this phenomenon?

Accepted Answer

ATP is unavailable, so myosin heads cannot detach from actin.

Question 4

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 glycolysis, which produces lactic acid and less ATP per glucose.

Question 5

A weightlifter holds a heavy barbell stationary above their head. Which type of muscle contraction is primarily occurring in the deltoid muscles?

Accepted Answer

Isometric contraction

Question 6

Which of the following statements about the neuromuscular junction (NMJ) is correct?

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 describes the difference between isotonic and isometric contractions?

Accepted Answer

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

Question 8

A marathon runner is able to maintain muscle activity for hours. Which muscle fiber type is most active during this endurance event?

Accepted Answer

Slow oxidative fibers

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 connective tissue layer surrounds individual muscle fibers?

Accepted Answer

Endomysium

Question 11

During a sustained muscle contraction, what is the primary reason for the development of muscle fatigue?

Accepted Answer

Relative deficit of ATP and accumulation of metabolic byproducts such as lactic acid

Question 12

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 13

A patient is experiencing muscle weakness due to a defect in acetylcholinesterase at the neuromuscular junction. What is the most likely effect?

Accepted Answer

Prolonged muscle contraction due to continued presence of acetylcholine

Question 14

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 15

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

Accepted Answer

A muscle generates maximum force when it is slightly stretched, allowing optimal overlap of thick and thin filaments.

Question 16

Which energy source is used first to regenerate ATP during the initial seconds of intense muscle activity?

Accepted Answer

Creatine phosphate

Question 17

Which of the following is a unique feature of cardiac muscle compared to skeletal and smooth muscle?

Accepted Answer

It has a pacemaker that sets the rate of contraction.

Question 18

A person is running a 100-meter sprint. Which metabolic pathway is primarily supplying ATP to their skeletal muscles during this activity?

Accepted Answer

Anaerobic glycolysis

Question 19

Which of the following best explains why eccentric isotonic contractions are more likely to cause delayed-onset muscle soreness than concentric contractions?

Accepted Answer

Eccentric contractions generate more force and cause greater mechanical stress on muscle fibers.

Physiology of Muscle: Structure, Function, and Comparison of Muscle Types

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