Question 1

Which structure in a skeletal muscle fiber is responsible for storing and releasing calcium ions ($$Ca^{2+}) $$during muscle contraction?

Accepted Answer

Sarcoplasmic reticulum

Question 2

During the sliding filament model of muscle contraction, what happens to the length of the thick and thin filaments?

Accepted Answer

Both filaments remain the same length

Question 3

Which protein blocks the myosin binding sites on actin when intracellular $$Ca^{2+} is $$low?

Accepted Answer

Tropomyosin

Question 4

A patient presents with muscle rigidity several hours after death. Which physiological process best explains the development of rigor mortis?

Accepted Answer

ATP is no longer synthesized, preventing $$Ca^{2+}$$ reuptake and cross bridge detachment

Question 5

Which of the following best describes the role of the T-tubules in skeletal muscle fibers?

Accepted Answer

They transmit action potentials deep into the muscle fiber

Question 6

What is the primary function of the neuromuscular junction?

Accepted Answer

To transmit nerve impulses from the motor neuron to the muscle fiber

Question 7

Which event directly triggers the exposure of myosin binding sites on actin during excitation-contraction coupling?

Accepted Answer

Release of $$Ca^{2+}$$ from the sarcoplasmic reticulum

Question 8

A muscle twitch consists of which three phases?

Accepted Answer

Latent period, contraction period, relaxation period

Question 9

Which of the following best explains why only a fraction of myosin heads are actively pulling at one time during muscle contraction?

Accepted Answer

To prevent muscle fatigue and allow continuous contraction

Question 10

If the sarcoplasmic reticulum fails to reclaim $$Ca^{2+}$$ after contraction, what would be the most likely outcome?

Accepted Answer

Muscle would remain in a contracted state

Question 11

Which of the following is true regarding the structure of a sarcomere?

Accepted Answer

It is the region between two Z-lines

Question 12

What is the effect of acetylcholine binding at the motor end plate of a skeletal muscle fiber?

Accepted Answer

It initiates an action potential in the muscle fiber

Question 13

Which of the following best describes a motor unit?

Accepted Answer

A motor neuron and all the muscle fibers it innervates

Question 14

Which of the following statements about the cross bridge cycle is correct?

Accepted Answer

ATP is required for both attachment and detachment of myosin heads

Question 15

A muscle fiber is stimulated by a single action potential and contracts quickly before relaxing. This response is best described as:

Accepted Answer

A muscle twitch

Question 16

Which of the following is a direct consequence of $$Ca^{2+}$$ binding to troponin?

Accepted Answer

Tropomyosin moves away from myosin binding sites on actin

Question 17

Which of the following would most likely result from a defect in the acetylcholine receptor at the neuromuscular junction?

Accepted Answer

Muscle fibers would not respond to nerve stimulation

Question 18

Which of the following best explains why large, fleshy muscles (such as calf muscles) contract more slowly and hold contraction longer than small, rapid muscles?

Accepted Answer

They have different metabolic properties and enzyme compositions

Question 19

Which of the following is NOT a component of the triad in skeletal muscle fibers?

Accepted Answer

One Z-line

Question 20

If a muscle fiber's sarcolemma fails to propagate an action potential, which of the following would most likely occur?

Accepted Answer

No $$Ca^{2+}$$ would be released from the sarcoplasmic reticulum

Skeletal Muscle Fiber Microanatomy and Neuromuscular Junction: Structure, Function, and Physiology

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