Question 1

Which of the following best describes the initial event that triggers skeletal muscle contraction at the neuromuscular junction?

Accepted Answer

Binding of acetylcholine to receptors on the muscle cell membrane

Question 2

After acetylcholine is released from the motor neuron, what is the next step in the sequence leading to muscle contraction?

Accepted Answer

Acetylcholine binds to receptors on the sarcolemma

Question 3

Which structure is responsible for facilitating the spread of the action potential deep into the muscle fiber?

Accepted Answer

T tubules

Question 4

What is the direct result of the action potential reaching the sarcoplasmic reticulum?

Accepted Answer

Release of calcium ions into the cytoplasm

Question 5

In the sliding filament model, what is the role of calcium ions after they are released into the cytoplasm?

Accepted Answer

They bind to troponin, causing a conformational change

Question 6

Which molecular event allows myosin to perform the power stroke during muscle contraction?

Accepted Answer

Release of energy from ATP hydrolysis by myosin

Question 7

What happens to the myosin head after it completes the power stroke in the sliding filament model?

Accepted Answer

It unbinds from actin

Question 8

A patient is exposed to a toxin that blocks acetylcholine receptors at the neuromuscular junction. Which of the following would most likely occur?

Accepted Answer

No action potential would be generated in the muscle cell

Question 9

Which of the following best explains why ATP is necessary for muscle contraction?

Accepted Answer

ATP provides energy for the myosin head to move during the power stroke

Question 10

If the sarcoplasmic reticulum fails to release calcium, which step in the sliding filament model would be directly affected?

Accepted Answer

Calcium binding to troponin

Question 11

Which of the following sequences correctly describes the order of events from acetylcholine release to calcium release in skeletal muscle contraction?

Accepted Answer

Acetylcholine release → Action potential in muscle cell → T tubule depolarization → Calcium release from sarcoplasmic reticulum

Question 12

A mutation prevents troponin from binding calcium. What is the most likely consequence for muscle contraction?

Accepted Answer

Tropomyosin will continue to block myosin binding sites on actin

Question 13

Which of the following best describes the function of T tubules in skeletal muscle contraction?

Accepted Answer

They transmit the action potential deep into the muscle fiber

Question 14

During the sliding filament model, which protein does calcium bind to in order to initiate contraction?

Accepted Answer

Troponin

Question 15

Which of the following is a direct effect of calcium binding to troponin?

Accepted Answer

Tropomyosin shifts to expose myosin binding sites on actin

Question 16

A patient with a genetic defect in myosin ATPase activity would most likely experience which symptom?

Accepted Answer

Reduced ability to perform power strokes during contraction

Question 17

Which equation best represents the hydrolysis of ATP by myosin during muscle contraction?

Accepted Answer

$$ \mathrm{ATP} + \mathrm{H}_2\mathrm{O} ightarrow \mathrm{ADP} + \mathrm{P}_i + 	ext{energy} $$

Question 18

Which of the following is NOT a step in the sequence from acetylcholine release to calcium release in skeletal muscle contraction?

Accepted Answer

Myosin binds to actin and performs a power stroke

Question 19

A patient is diagnosed with a disease that prevents the release of acetylcholine from motor neurons. Which of the following would be the most immediate effect?

Accepted Answer

No action potential would be generated in the muscle cell

Skeletal Muscle Contraction: Neuromuscular Junction and Sliding Filament Model

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