Question 1

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

Accepted Answer

It is the synapse where a motor neuron communicates with a muscle fiber, triggering muscle fiber excitation.

Question 2

During the depolarization phase of an action potential in a muscle fiber, which ion primarily moves into the cell, and what is the resulting change in membrane potential?

Accepted Answer

Sodium ions ($Na^+$) move into the cell, causing the membrane potential to become more positive.

Question 3

What is the primary function of the Na$^+$/K$^+$ pump in maintaining the resting membrane potential ($RMP$) of excitable cells?

Accepted Answer

It actively transports 3 sodium ions out and 2 potassium ions in, maintaining a negative $RMP$.

Question 4

Which step in muscle contraction directly leads to the formation of cross bridges between actin and myosin?

Accepted Answer

Excitation-contraction coupling

Question 5

A patient is unable to generate sufficient muscle tension to lift a heavy object. Which physiological principle explains why increasing the number of recruited motor units increases muscle tension?

Accepted Answer

Size principle of recruitment

Question 6

Which of the following best describes the difference between isometric and concentric muscle contractions?

Accepted Answer

Isometric contractions generate force without changing muscle length, while concentric contractions shorten the muscle to produce movement.

Question 7

During a muscle twitch, which phase is characterized by the time between stimulus and the onset of contraction, and what is occurring at the cellular level?

Accepted Answer

Latent period; excitation-contraction coupling is occurring.

Question 8

Which process produces ATP the fastest during skeletal muscle contraction?

Accepted Answer

Direct phosphorylation by creatine phosphate

Question 9

A marathon runner relies on which primary pathway for ATP production during prolonged exercise, and what is a key limitation of this pathway?

Accepted Answer

Aerobic respiration; it requires a continuous supply of oxygen.

Question 10

Which of the following equations correctly represents the overall reaction for aerobic cellular respiration in muscle cells?

Accepted Answer

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP$

Question 11

Which event occurs during repolarization of the muscle fiber membrane after an action potential?

Accepted Answer

Potassium channels open, allowing $K^+$ efflux, restoring negative membrane potential.

Question 12

Which of the following best explains why the resting membrane potential ($RMP$) is necessary for muscle and nerve cell function?

Accepted Answer

It creates a state of readiness so cells can be excited and respond to stimuli.

Question 13

Which process is responsible for clearing lactic acid produced during anaerobic glycolysis in muscle cells?

Accepted Answer

Aerobic respiration in the mitochondria

Question 14

A muscle fiber is stimulated repeatedly at a high frequency, resulting in sustained contraction. Which phenomenon is being demonstrated?

Accepted Answer

Temporal (wave) summation

Question 15

Which of the following is a direct result of excitation-contraction coupling in skeletal muscle fibers?

Accepted Answer

Release of calcium ions from the sarcoplasmic reticulum

Question 16

Which energy source is used first during short-duration, high-intensity exercise, such as a 100-meter sprint?

Accepted Answer

Direct phosphorylation by creatine phosphate

Question 17

Which of the following statements about motor unit size is correct?

Accepted Answer

Muscles requiring precise movements have smaller motor units.

Question 18

Which of the following is a limitation of the anaerobic pathway for ATP production in muscle cells?

Accepted Answer

It produces lactic acid, which can lead to muscle fatigue.

Question 19

Which process must occur in the mitochondria and relies on the cardiovascular system to deliver necessary substrates?

Accepted Answer

Aerobic respiration

Muscles and Muscle Tissue: Contraction, Membrane Potentials, and ATP Regeneration

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