Question 1

Which of the following best describes the role of troponin in skeletal muscle contraction?

Accepted Answer

Troponin binds calcium ions, causing a conformational change that moves tropomyosin away from actin's myosin-binding sites.

Question 2

During the depolarization phase of an action potential in a muscle fiber, which ion is primarily responsible for the rapid change in membrane potential?

Accepted Answer

Na$$^+$$ ions entering the cell

Question 3

What is the correct sequence of events at the neuromuscular junction leading to muscle fiber contraction?

Accepted Answer

Action potential arrives at axon terminal → ACh released → ACh binds to sarcolemma receptors → Na$$^+$$ influx → Action potential in muscle fiber

Question 4

Which structure in a skeletal muscle fiber stores and releases calcium ions to trigger contraction?

Accepted Answer

Sarcoplasmic reticulum

Question 5

If a muscle fiber is unable to remove Ca$$^{2+}$$ from the cytosol after contraction, what is the most likely consequence?

Accepted Answer

The muscle fiber will remain contracted and be unable to relax.

Question 6

Which of the following best explains the difference between the A band and the I band in a sarcomere?

Accepted Answer

The A band contains both thick and thin filaments, while the I band contains only thin filaments.

Question 7

A patient is exposed to a toxin that blocks acetylcholine (ACh) receptors at the neuromuscular junction. What is the most likely effect on muscle contraction?

Accepted Answer

Muscle contraction will be inhibited because the action potential cannot be generated in the muscle fiber.

Question 8

Which phase of a muscle twitch corresponds to the time when cross bridges are actively cycling and tension is increasing?

Accepted Answer

Period of contraction

Question 9

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

Accepted Answer

To conduct action potentials deep into the muscle fiber

Question 10

During the cross-bridge cycle, what event directly triggers the power (working) stroke of the myosin head?

Accepted Answer

Release of ADP and inorganic phosphate (Pi) from the myosin head

Question 11

Which of the following best describes the relationship between a motor unit and muscle control?

Accepted Answer

A small motor unit allows for fine, precise control of muscle contraction.

Question 12

Which of the following changes occur in the sarcomere during muscle contraction?

Accepted Answer

The I band shortens, while the A band remains the same length.

Question 13

A muscle fiber is stimulated by a single action potential. Which of the following best describes the resulting contraction?

Accepted Answer

An isometric twitch with three phases: latent, contraction, and relaxation

Question 14

Which of the following best explains why ATP is required for muscle relaxation?

Accepted Answer

ATP is needed to detach myosin heads from actin and to pump Ca$$^{2+}$$ back into the sarcoplasmic reticulum.

Question 15

Which of the following is a key difference between skeletal muscle and smooth muscle?

Accepted Answer

Skeletal muscle fibers are multinucleated and striated, while smooth muscle fibers are uninucleated and non-striated.

Question 16

A researcher measures the membrane potential of a muscle fiber and finds it is at +30 mV. Which phase of the action potential is the muscle fiber most likely experiencing?

Accepted Answer

Peak depolarization

Question 17

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

Accepted Answer

Tropomyosin blocks myosin-binding sites on actin in a relaxed muscle.

Question 18

Which of the following best explains why a muscle fiber can generate more force when stimulated at optimal sarcomere length?

Accepted Answer

There is maximal overlap between thick and thin filaments, allowing for the greatest number of cross-bridges.

Question 19

Which of the following events occurs first during excitation-contraction coupling in skeletal muscle?

Accepted Answer

An action potential travels along the sarcolemma and down the T tubules.

Question 20

A patient with a genetic defect in their sarcolemma sodium channels would most likely experience which of the following symptoms?

Accepted Answer

Impaired ability to generate action potentials, leading to muscle weakness

Muscle Tissue: Structure, Function, and Physiology

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