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 Ca$$^{2+}$$ ions, which are essential for initiating muscle contraction.

Question 2

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, pulling the Z discs closer together.

Question 3

Which connective tissue sheath surrounds individual muscle fibers?

Accepted Answer

Endomysium

Question 4

A patient is exposed to a toxin that blocks acetylcholinesterase at the neuromuscular junction. What is the most likely physiological effect?

Accepted Answer

Prolonged muscle contraction due to continuous stimulation by acetylcholine

Question 5

Which of the following is NOT a characteristic of cardiac muscle?

Accepted Answer

Voluntary control

Question 6

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

Accepted Answer

To conduct action potentials deep into the muscle fiber, ensuring every myofibril is activated simultaneously

Question 7

Which protein forms the thick filaments in a sarcomere and acts as a cross-bridge during muscle contraction?

Accepted Answer

Myosin

Question 8

A muscle biopsy reveals elongated, multinucleated, striated cells under voluntary control. Which muscle type is this?

Accepted Answer

Skeletal muscle

Question 9

Which event occurs first during the excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential travels along the sarcolemma

Question 10

Which of the following best explains why skeletal muscle fibers are multinucleated?

Accepted Answer

They are formed by the fusion of multiple myoblasts during development.

Question 11

Which of the following is a function of skeletal muscle that is NOT shared by smooth muscle?

Accepted Answer

Maintaining posture and body position

Question 12

Which of the following statements about the I band in a sarcomere is correct?

Accepted Answer

It contains only thin filaments and shortens during muscle contraction.

Question 13

A patient presents with muscle weakness. Laboratory tests reveal a defect in the voltage-gated Ca$$^{2+}$$ channels at the neuromuscular junction. Which step in muscle contraction is most directly affected?

Accepted Answer

Release of acetylcholine from the axon terminal

Question 14

Which of the following best describes the function of titin in the sarcomere?

Accepted Answer

It provides elasticity and helps the muscle fiber recoil after being stretched.

Question 15

Which of the following is the correct sequence of events at the neuromuscular junction leading to muscle contraction?

Accepted Answer

Action potential arrives at axon terminal → Ca$$^{2+}$$ enters terminal → ACh released → ACh binds to receptors → Na$$^+$$ enters muscle fiber → End plate potential generated

Question 16

Which property of muscle tissue allows it to return to its original length after being stretched?

Accepted Answer

Elasticity

Question 17

Which of the following best explains why more Na$$^+$$ enters the muscle fiber than K$$^+$$ exits when ACh binds to its receptor?

Accepted Answer

The electrochemical gradient for Na$$^+ is $$greater than that for K$$^+ at $$the resting membrane potential.

Question 18

Which of the following is a regulatory protein found in thin filaments that binds Ca$$^{2+}$$ during muscle contraction?

Accepted Answer

Troponin

Question 19

A muscle fiber is unable to relax after contraction. Which structure is most likely malfunctioning?

Accepted Answer

Sarcoplasmic reticulum (SR)

Question 20

Which of the following best describes the arrangement of myofibrils within a skeletal muscle fiber?

Accepted Answer

They are densely packed, rod-like structures that run parallel to the length of the cell.

Muscle Tissue and Physiology: Structure, Function, and Contraction

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