Question 1

Which structure in a skeletal muscle fiber is responsible for storing and releasing calcium ions during muscle contraction?

Accepted Answer

Sarcoplasmic reticulum

Question 2

During the sliding filament mechanism of muscle contraction, what happens to the I band and the A band?

Accepted Answer

The I band shortens, but the A band remains unchanged

Question 3

Which protein directly binds to calcium ions to initiate muscle contraction?

Accepted Answer

Troponin

Question 4

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

Accepted Answer

They transmit action potentials deep into the muscle fiber

Question 5

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

Accepted Answer

It stabilizes the myofibril and resists excessive stretching

Question 6

A patient is exposed to a toxin that blocks ligand-gated Na$$^+$$ channels at the motor end plate. What is the most immediate effect on muscle contraction?

Accepted Answer

The muscle fiber cannot depolarize in response to acetylcholine

Question 7

Which of the following is TRUE regarding the crossbridge cycle in skeletal muscle contraction?

Accepted Answer

Binding of ATP to myosin causes the myosin head to release from actin

Question 8

Which of the following best describes the resting membrane potential of a skeletal muscle fiber?

Accepted Answer

The inside of the membrane is 85 mV more negative than the outside

Question 9

Which event directly triggers the release of calcium ions from the sarcoplasmic reticulum?

Accepted Answer

Arrival of an action potential at the triad

Question 10

Which of the following statements about the neuromuscular junction (NMJ) is correct?

Accepted Answer

The NMJ is the synapse between a motor neuron and a muscle fiber

Question 11

Which molecule blocks the active sites on actin, preventing myosin binding in a relaxed muscle?

Accepted Answer

Tropomyosin

Question 12

A mutation causes the sarcolemma to become impermeable to Na$$^+$$ ions. What is the most likely consequence?

Accepted Answer

The muscle fiber cannot generate an action potential

Question 13

Which of the following is a regulatory protein found in the thin filament of a sarcomere?

Accepted Answer

Tropomyosin

Question 14

Which of the following best describes excitation-contraction coupling?

Accepted Answer

The sequence of events linking the action potential to muscle contraction

Question 15

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

Accepted Answer

ACh binds to ligand-gated channels → Na$$^+$$ enters the cell → Action potential generated

Question 16

Which of the following is a function of the Z disc in a sarcomere?

Accepted Answer

Anchors thin filaments and serves as an attachment point for elastic filaments

Question 17

A drug prevents the release of acetylcholine from the axon terminal at the NMJ. What is the most immediate effect?

Accepted Answer

The muscle fiber cannot depolarize and will not contract

Question 18

Which of the following best explains why the A band does not change length during muscle contraction?

Accepted Answer

Thin filaments move but do not change length, and the thick filaments remain stationary

Question 19

Which of the following is the correct formula for the resting membrane potential of a muscle fiber?

Accepted Answer

$$V_{rest} = -85\ \mathrm{mV}$$

Question 20

Which of the following best describes the role of the triad in skeletal muscle fibers?

Accepted Answer

It coordinates the release of calcium ions in response to an action potential

Muscle Tissue: Structure and Contraction Mechanisms

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