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 presents with muscle weakness and drooping eyelids. Laboratory tests reveal a decrease in acetylcholine receptors at the neuromuscular junction. Which disease is most likely responsible?

Accepted Answer

Myasthenia gravis

Question 3

During the sliding filament model of contraction, which event directly causes the shortening of the sarcomere?

Accepted Answer

The thin filaments slide past the thick filaments, increasing their overlap.

Question 4

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

Accepted Answer

Action potential travels along sarcolemma $$\rightarrow T $$tubules $$\rightarrow Ca$^{2+}$$ released from SR $$\rightarrow Ca$^{2+}$$ binds to troponin $$\rightarrow$$ cross bridge formation

Question 5

Which energy system provides the majority of ATP during a marathon run?

Accepted Answer

Aerobic respiration (oxidative phosphorylation)

Question 6

A muscle is stimulated so rapidly that no evidence of relaxation is seen and contractions fuse into a smooth, sustained plateau. This is called:

Accepted Answer

Fused (complete) tetanus

Question 7

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 8

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

Accepted Answer

Striated and involuntary

Question 9

A weightlifter attempts to lift a very heavy barbell but cannot move it. Which type of muscle contraction is occurring?

Accepted Answer

Isometric contraction

Question 10

Which protein anchors thin filaments to the sarcolemma and is defective in Duchenne muscular dystrophy?

Accepted Answer

Dystrophin

Question 11

Which of the following best describes the role of ATP in the cross bridge cycle?

Accepted Answer

ATP binds to myosin, causing it to detach from actin.

Question 12

Which muscle fiber type is most resistant to fatigue and is best suited for maintaining posture?

Accepted Answer

Slow oxidative fibers

Question 13

Which of the following is true regarding smooth muscle contraction?

Accepted Answer

Calcium binds to calmodulin, which activates myosin light chain kinase.

Question 14

Which of the following best explains the size principle of motor unit recruitment?

Accepted Answer

Smaller motor units are recruited first, followed by larger ones as stimulus intensity increases.

Question 15

Which of the following is a function of muscle tone?

Accepted Answer

Maintaining posture and stabilizing joints

Question 16

Which of the following is a direct result of acetylcholine binding to its receptor on the sarcolemma?

Accepted Answer

Opening of chemically gated Na$$^+$$ channels and generation of an end plate potential

Question 17

Which of the following best describes the effect of aerobic (endurance) exercise on skeletal muscle?

Accepted Answer

Increases capillaries, mitochondria, and myoglobin content, especially in slow oxidative fibers

Question 18

Which of the following is a unique feature of multi-unit smooth muscle compared to unitary (visceral) smooth muscle?

Accepted Answer

Each muscle fiber is innervated and contracts independently.

Question 19

Which of the following is NOT a characteristic shared by all muscle tissue types?

Accepted Answer

Ability to divide and regenerate extensively after injury

Question 20

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

Accepted Answer

Ionic imbalances and accumulation of inorganic phosphate interfere with excitation-contraction coupling.

Muscles and Muscle Tissue: Structure, Function, and Contraction Mechanisms

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