Question 1

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

Accepted Answer

It stores and releases $$\mathrm{Ca$$^{2+}$$}$$ ions necessary for muscle contraction.

Question 2

During the sliding filament mechanism of muscle contraction, which of the following statements is correct?

Accepted Answer

The A band remains the same length while the I band and H zone shorten.

Question 3

A patient is exposed to curare, a toxin that binds to acetylcholine (ACh) receptors at the neuromuscular junction. What is the most likely physiological effect?

Accepted Answer

Skeletal muscle paralysis due to blocked ACh receptor activation.

Question 4

Which of the following is a characteristic unique to cardiac muscle tissue?

Accepted Answer

Presence of intercalated discs for synchronized contraction.

Question 5

What is the primary source of ATP during the first 15 seconds of intense muscle activity, such as sprinting?

Accepted Answer

Creatine phosphate breakdown

Question 6

Which of the following best explains why slow oxidative (Type I) muscle fibers are more resistant to fatigue than fast glycolytic (Type IIb) fibers?

Accepted Answer

They have abundant mitochondria and rely primarily on aerobic respiration.

Question 7

A muscle cell is unable to contract even when stimulated. Which of the following is the most likely explanation for this muscle fatigue?

Accepted Answer

Depletion of ATP and accumulation of lactic acid.

Question 8

Which of the following events occurs immediately after acetylcholine binds to its receptor on the motor end plate?

Accepted Answer

Sodium ions ($$\mathrm{Na^+}) $$rapidly enter the muscle cell, causing depolarization.

Question 9

Which of the following best describes the 'all-or-none' principle in muscle physiology?

Accepted Answer

An individual muscle fiber contracts to its full extent when stimulated above threshold.

Question 10

A person is experiencing muscle cramps after running a marathon. Which of the following is the most likely cause?

Accepted Answer

Electrolyte imbalances in the extracellular fluid.

Question 11

Which of the following statements about smooth muscle is correct?

Accepted Answer

It contracts slowly and is highly resistant to fatigue.

Question 12

What is the role of troponin in skeletal muscle contraction?

Accepted Answer

It binds $$\mathrm{Ca$$^{2+}$$}$$ and moves tropomyosin to expose myosin binding sites on actin.

Question 13

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.

Question 14

Which of the following is true regarding the recruitment of motor units during muscle contraction?

Accepted Answer

Smaller motor units are activated before larger ones to allow fine control.

Question 15

A muscle fiber is observed to have a large diameter, few mitochondria, and little myoglobin. Which type of muscle fiber is this most likely to be?

Accepted Answer

Fast glycolytic (Type IIb)

Question 16

Which of the following best describes the function of the sodium-potassium pump in muscle cells?

Accepted Answer

It maintains the resting membrane potential by moving $$3\ \mathrm{Na^+}$$ out and $$2\ \mathrm{K^+} in$$, using ATP.

Question 17

Which of the following changes would you expect in the muscles of a person who has had their arm in a cast for several weeks?

Accepted Answer

Disuse atrophy resulting in decreased muscle fiber size.

Question 18

Which of the following best explains why chickens have white breast meat and dark leg meat, while ducks have dark breast meat?

Accepted Answer

Chickens use their legs for sustained activity (more slow oxidative fibers), while ducks use their breast muscles for sustained flight (more slow oxidative fibers).

Question 19

Which of the following is a direct result of the crossbridge cycle during muscle contraction?

Accepted Answer

The actin filaments are pulled toward the center of the sarcomere.

Question 20

Which of the following best describes the process of temporal (wave) summation in muscle contraction?

Accepted Answer

Increasing the frequency of stimulation before the muscle can fully relax, resulting in greater force.

Chapter 9: The Muscular System – Structure, Function, and Physiology

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