Question 1

Which of the following best describes the role of the sarcoplasmic reticulum during skeletal muscle contraction?

Accepted Answer

It stores and releases calcium ions ($$\mathrm{Ca$$^{2+}$$}) in $$response to depolarization.

Question 2

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

Accepted Answer

Calcium ions ($$\mathrm{Ca$$^{2+}$$}) $$bind to troponin, causing tropomyosin to shift.

Question 3

What is the primary function of T-tubules in skeletal muscle fibers?

Accepted Answer

To conduct action potentials deep into the muscle fiber.

Question 4

Which of the following correctly describes the sequence of events leading to cross-bridge formation in skeletal muscle?

Accepted Answer

Depolarization → $$\mathrm{Ca$$^{2+}$$}$$ release → Troponin activation → Tropomyosin shift → Myosin binds actin

Question 5

A patient is given a drug that blocks voltage-gated sodium ($$\mathrm{Na^+}) $$channels in skeletal muscle. Which step in muscle contraction will be directly affected?

Accepted Answer

Initiation of the action potential along the sarcolemma.

Question 6

Which of the following best explains why ATP is necessary for muscle relaxation?

Accepted Answer

ATP binds to myosin, causing it to detach from actin after the power stroke.

Question 7

If a mutation prevents troponin from binding calcium ions ($$\mathrm{Ca$$^{2+}$$}$$), what would be the most immediate effect on muscle contraction?

Accepted Answer

Tropomyosin would not move, preventing myosin from binding to actin.

Question 8

Which of the following equations best represents the sodium-potassium pump activity during the resting state of a muscle cell?

Accepted Answer

$$3\ \mathrm{Na^+_{(in)}} + 2\ \mathrm{K^+_{(out)}} + \mathrm{ATP} \rightarrow 3\ \mathrm{Na^+_{(out)}} + 2\ \mathrm{K^+_{(in)}} + \mathrm{ADP} + \mathrm{P_i}$$

Question 9

A toxin prevents the reuptake of calcium ions ($$\mathrm{Ca$$^{2+}$$}) $$into the sarcoplasmic reticulum. What is the most likely physiological consequence?

Accepted Answer

Prolonged muscle contraction (tetanus) due to sustained cross-bridge formation.

Question 10

Which of the following best describes the function of tropomyosin in skeletal muscle contraction?

Accepted Answer

It blocks the myosin-binding sites on actin when the muscle is at rest.

Question 11

A patient with a genetic defect in their acetylcholine receptors at the neuromuscular junction would most likely experience which of the following symptoms?

Accepted Answer

Muscle weakness due to impaired depolarization of the sarcolemma.

Question 12

Which of the following steps requires the hydrolysis of ATP during the cross-bridge cycle?

Accepted Answer

Cocking of the myosin head into its high-energy position.

Question 13

If the voltage-gated potassium ($$\mathrm{K^+}) $$channels in a muscle cell are blocked, what is the most immediate effect on the action potential?

Accepted Answer

Repolarization of the membrane will be delayed.

Question 14

Which of the following best explains why a lack of ATP after death leads to rigor mortis?

Accepted Answer

Myosin heads cannot detach from actin without ATP, causing sustained cross-bridge formation.

Question 15

Which of the following is the correct order of events in excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential in sarcolemma → T-tubule depolarization → $$\mathrm{Ca$$^{2+}$$}$$ release → Troponin activation → Cross-bridge formation

Question 16

A muscle fiber is exposed to a drug that keeps the sodium ($$\mathrm{Na^+}) $$channels open. What is the most likely effect on the muscle cell's membrane potential?

Accepted Answer

The membrane will remain depolarized, preventing repolarization and further action potentials.

Question 17

Which of the following best describes the relationship between depolarization and calcium release in skeletal muscle fibers?

Accepted Answer

Depolarization of the T-tubules triggers the opening of calcium channels in the sarcoplasmic reticulum.

Question 18

Which of the following would most likely occur if tropomyosin is unable to return to its resting position after contraction?

Accepted Answer

Myosin-binding sites on actin would remain exposed, leading to continuous cross-bridge cycling.

Muscle Contraction: Mechanisms and Key Components

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