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

A patient is unable to relax their muscles after contraction, resulting in a state similar to rigor mortis. Which of the following best explains this phenomenon?

Accepted Answer

There is a lack of ATP, preventing detachment of myosin heads from actin.

Question 3

During the sliding filament mechanism of muscle contraction, which event occurs immediately after calcium ions bind to troponin?

Accepted Answer

Tropomyosin shifts, exposing myosin-binding sites on actin.

Question 4

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

Accepted Answer

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

Question 5

A sprinter running a 100-meter dash primarily relies on which energy source for ATP regeneration during the race?

Accepted Answer

Anaerobic glycolysis

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 explains why fast glycolytic muscle fibers fatigue more quickly than slow oxidative fibers?

Accepted Answer

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

Question 8

A muscle is stretched to 120% of its resting length and then stimulated to contract. According to the length-tension relationship, what is the expected outcome?

Accepted Answer

The muscle will generate less force because fewer cross-bridges can form.

Question 9

Which of the following events occurs during the latent period of a muscle twitch?

Accepted Answer

Excitation-contraction coupling, including calcium release from the SR, but no visible shortening.

Question 10

Which of the following is a characteristic unique to smooth muscle compared to skeletal muscle?

Accepted Answer

Presence of calmodulin instead of troponin for calcium binding.

Question 11

A weightlifter holds a heavy barbell stationary above their head without moving it. Which type of muscle contraction is primarily occurring in the deltoid muscles?

Accepted Answer

Isometric contraction

Question 12

Which of the following best describes the function of myoglobin in skeletal muscle fibers?

Accepted Answer

It stores oxygen for use during aerobic metabolism.

Question 13

During a sustained, high-frequency stimulation of a skeletal muscle, the muscle produces a smooth, sustained contraction with no evidence of relaxation. This phenomenon is known as:

Accepted Answer

Tetanus

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, ADP and $\mathrm{P_i}$ are released, ATP binds to myosin, myosin detaches from actin.

Question 15

Which of the following best explains why smooth muscle can maintain contractions for long periods with minimal fatigue?

Accepted Answer

Smooth muscle has slow ATPase activity and relies primarily on aerobic metabolism.

Question 16

Which of the following is the primary reason why muscle tone is important in the human body?

Accepted Answer

It helps maintain posture and stabilize joints.

Question 17

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

Accepted Answer

Slow oxidative fibers

Question 18

Which of the following best describes the effect of increasing load on the velocity and duration of skeletal muscle contraction?

Accepted Answer

As load increases, contraction velocity decreases and duration shortens.

Question 19

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

Accepted Answer

Direct phosphorylation of ADP by creatine phosphate ($\mathrm{CP} + \mathrm{ADP} \rightarrow \mathrm{creatine} + \mathrm{ATP}$)

Question 20

After vigorous exercise, which of the following processes occurs during the repayment of oxygen debt (excess post-exercise oxygen consumption, EPOC)?

Accepted Answer

Lactic acid is converted back to pyruvic acid.

Physiology of Muscle: Structure, Function, and Types

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