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 triggers 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. What is the most likely diagnosis?

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 lift the weight, your biceps muscle shortens. What type of contraction is this?

Accepted Answer

Concentric isotonic contraction

Question 8

Which metabolic pathway provides the greatest yield of ATP per glucose molecule during muscle activity?

Accepted Answer

Aerobic respiration ($$\sim 32$$ ATP per glucose)

Question 9

A sprinter running a 100-meter dash relies primarily on which source of ATP during the first few seconds of the race?

Accepted Answer

Phosphocreatine system

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

A weightlifter performs a heavy lift and holds the weight steady without moving it. Which type of muscle contraction is primarily occurring?

Accepted Answer

Isometric contraction

Question 12

Which of the following best explains why muscle fatigue occurs during prolonged, intense exercise?

Accepted Answer

Depletion of glycogen and accumulation of extracellular potassium reduce muscle excitability.

Question 13

Which of the following changes occurs in muscle fibers as a result of endurance (aerobic) training?

Accepted Answer

Increased number of mitochondria and capillary density

Question 14

Which of the following is true regarding resistance training (such as weight lifting)?

Accepted Answer

Muscle fibers increase in size but not in number.

Question 15

Which of the following best describes the power stroke during cross bridge cycling?

Accepted Answer

The myosin head pivots and pulls the actin filament toward the M line.

Question 16

Which of the following is required for the detachment of the myosin head from actin during muscle contraction?

Accepted Answer

Binding of ATP to the myosin head

Question 17

Which of the following is a direct result of the accumulation of potassium ions in the extracellular fluid during intense muscle activity?

Accepted Answer

Reduced excitability of the muscle fiber

Question 18

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

Accepted Answer

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

Question 19

Which of the following is a distinguishing feature of eccentric isotonic contractions?

Accepted Answer

The muscle lengthens while generating force.

Question 20

A marathon runner is able to maintain muscle activity for several hours. Which of the following adaptations is most important for this endurance?

Accepted Answer

High density of capillaries and mitochondria in muscle fibers

The Muscular System: Skeletal Muscle Contraction and Physiology

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