Question 1

Which of the following best describes the role of the sodium-potassium pump ($$\mathrm{Na^+/K^+}$$ ATPase) in skeletal muscle fibers?

Accepted Answer

It moves three sodium ions out of the cell and two potassium ions in, using ATP hydrolysis to maintain resting membrane potential.

Question 2

A patient presents with muscle weakness and a waddling gait. Genetic testing reveals a mutation in the gene encoding dystrophin. Which of the following best explains the pathophysiology of this condition?

Accepted Answer

Dystrophin mutation disrupts the anchoring of the sarcolemma to the endomysium, resulting in muscle fiber death and replacement by connective tissue.

Question 3

During the contraction of a sarcomere, which of the following changes occur?

Accepted Answer

The I band and H zone narrow, while the A band remains unchanged.

Question 4

Which of the following is the correct sequence of events in the crossbridge cycle during skeletal muscle contraction?

Accepted Answer

ATP binds to myosin, myosin detaches from actin, ATP hydrolysis cocks the myosin head, myosin binds to actin, power stroke occurs.

Question 5

A toxin blocks the release of acetylcholine at the neuromuscular junction. What is the most likely effect on skeletal muscle?

Accepted Answer

Muscle paralysis due to inability to generate end-plate potentials.

Question 6

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, resulting in sustained muscle contraction.

Question 7

Which of the following statements about the energy sources for muscle contraction is correct?

Accepted Answer

Creatine phosphate provides immediate ATP for about 10 seconds of maximal activity.

Question 8

A muscle fiber is stimulated 100 times per second, resulting in a sustained contraction with maximal tension. Which phenomenon is being observed?

Accepted Answer

Fused (complete) tetanus

Question 9

Which of the following best describes the difference between single-unit and multi-unit smooth muscle?

Accepted Answer

Single-unit smooth muscle cells are connected by gap junctions and contract together, while multi-unit smooth muscle cells contract independently.

Question 10

Which of the following is a property unique to cardiac muscle tissue compared to skeletal muscle tissue?

Accepted Answer

Presence of intercalated discs with gap junctions and desmosomes

Question 11

A marathon runner is able to sustain muscle activity for hours. Which muscle fiber type is most responsible for this endurance, and why?

Accepted Answer

Type I fibers, because they have abundant myoglobin, mitochondria, and use oxidative catabolism.

Question 12

Which of the following best explains the physiological basis for delayed-onset muscle soreness (DOMS) after unaccustomed exercise?

Accepted Answer

Minor structural damage to myofilaments, especially from isotonic eccentric contractions.

Question 13

Which of the following is true regarding the length-tension relationship in skeletal muscle?

Accepted Answer

Maximum tension is produced at optimal sarcomere length, where there is maximal overlap between thick and thin filaments.

Question 14

Which of the following best describes the process of excitation-contraction coupling in skeletal muscle?

Accepted Answer

An action potential travels down the T-tubules, triggering calcium release from the sarcoplasmic reticulum.

Question 15

Which of the following is a function of muscle tone in the body?

Accepted Answer

It maintains posture, stabilizes joints, and keeps muscles ready to respond.

Question 16

Which of the following best explains why creatine supplementation may not always enhance athletic performance?

Accepted Answer

Skeletal muscle fibers have a maximal storage capacity for creatine, and excess is excreted in urine.

Question 17

Which of the following is the primary reason why muscle fibers fatigue during intense exercise?

Accepted Answer

Depletion of key metabolites such as creatine phosphate, glycogen, and blood glucose reduces ATP production.

Question 18

Which of the following best describes the difference between isotonic concentric and isotonic eccentric muscle contractions?

Accepted Answer

Isotonic concentric contractions shorten the muscle as force exceeds the load, while isotonic eccentric contractions lengthen the muscle as the load exceeds the force generated.

Muscle Tissue and Physiology: Structure, Function, and Mechanisms

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