Question 1

Which of the following best describes the role of acetylcholine (ACh) at the neuromuscular junction?

Accepted Answer

ACh binds to receptors on the sarcolemma, initiating an action potential in the muscle fiber.

Question 2

During excitation-contraction coupling, what is the primary function of the T-tubules?

Accepted Answer

They propagate the action potential deep into the muscle fiber, triggering calcium release from the sarcoplasmic reticulum.

Question 3

Which event directly causes the exposure of myosin-binding sites on actin during muscle contraction?

Accepted Answer

Calcium ions bind to troponin, causing tropomyosin to move away from the binding sites.

Question 4

A patient presents with muscle weakness and drooping eyelids. Laboratory tests reveal antibodies against acetylcholine receptors. Which condition is most likely?

Accepted Answer

Myasthenia gravis

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, resulting in sustained contraction.

Question 6

Which type of muscle contraction occurs when muscle tension increases but the muscle does not change length?

Accepted Answer

Isometric contraction

Question 7

During a biceps curl, as you slowly lower the weight back down, which type of contraction is occurring in the biceps muscle?

Accepted Answer

Eccentric contraction

Question 8

Which metabolic pathway provides the greatest yield of ATP per glucose molecule for muscle contraction?

Accepted Answer

Aerobic respiration

Question 9

A sprinter running a 100-meter dash primarily relies on which energy system for ATP production?

Accepted Answer

Anaerobic fermentation

Question 10

Which of the following is a characteristic of slow-twitch muscle fibers?

Accepted Answer

They are highly resistant to fatigue and adapted for aerobic respiration.

Question 11

Which of the following best describes the sliding filament model of muscle contraction?

Accepted Answer

Thin filaments slide past thick filaments, increasing the overlap between actin and myosin.

Question 12

Which of the following is NOT a cause of muscle fatigue?

Accepted Answer

Increased synthesis of ATP in mitochondria

Question 13

Which of the following equations correctly represents the net ATP yield from aerobic respiration of one glucose molecule?

Accepted Answer

$$C_6H_{12}O_6$ + 6O_2 \rightarrow 6CO_2 + 6H_2O + 32ATP$$

Question 14

Which of the following best explains why resistance training increases muscle strength but not fatigue resistance?

Accepted Answer

It causes existing muscle fibers to increase in size, but does not increase the number of mitochondria or capillaries.

Question 15

A muscle fiber is unable to relax after contraction. Which of the following is the most likely explanation?

Accepted Answer

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

Question 16

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

Accepted Answer

Concentric contractions shorten the muscle, while eccentric contractions lengthen the muscle under tension.

Question 17

Which of the following is a direct result of ATP hydrolysis during the cross-bridge cycle?

Accepted Answer

The myosin head is cocked into a high-energy state, ready to bind actin.

Question 18

Which of the following factors does NOT contribute to increased endurance in skeletal muscle?

Accepted Answer

Increased number of muscle fibers

Question 19

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

Accepted Answer

Slow-twitch fibers

Question 20

Which of the following best explains why muscle contraction ceases when nervous stimulation stops?

Accepted Answer

Calcium is pumped back into the sarcoplasmic reticulum, and myosin-binding sites on actin are covered.

The Muscular System: Mechanisms of Skeletal Muscle Contraction

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