Question 1

According to the sliding-filament model, which of the following structures shortens during skeletal muscle contraction?

Accepted Answer

I band

Question 2

During the crossbridge cycle, what directly triggers the power stroke of the myosin head?

Accepted Answer

Release of inorganic phosphate (Pi)

Question 3

Which enzyme is responsible for breaking down acetylcholine in the synaptic cleft after it is released at the neuromuscular junction?

Accepted Answer

Acetylcholinesterase

Question 4

What is the primary function of the sarcoplasmic reticulum (SR) in skeletal muscle fibers?

Accepted Answer

Storing and releasing calcium ions

Question 5

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

Accepted Answer

It binds calcium ions, causing a conformational change that moves tropomyosin and exposes myosin-binding sites on actin.

Question 6

A patient is experiencing muscle cramps due to sustained contraction. Which of the following is a likely cause based on the mechanism of muscle contraction?

Accepted Answer

Elevated cytosolic calcium concentration

Question 7

What would happen to the crossbridge cycle if ATP were suddenly unavailable in a muscle cell?

Accepted Answer

Myosin heads would remain bound to actin, resulting in rigor.

Question 8

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

Accepted Answer

The thick filaments slide past the thin filaments without changing length.

Question 9

During excitation-contraction coupling, what is the role of the DHP receptor in the T-tubule membrane?

Accepted Answer

It functions as a voltage sensor that triggers the opening of ryanodine receptors in the sarcoplasmic reticulum.

Question 10

Which of the following events occurs first during the process of skeletal muscle contraction?

Accepted Answer

Acetylcholine is released from the motor neuron.

Question 11

If a mutation caused the ryanodine receptor to remain open, what would be the most likely effect on muscle cells?

Accepted Answer

Continuous release of calcium, leading to sustained contraction or cramping.

Question 12

Which of the following best describes the relationship between cytosolic calcium concentration and the strength of muscle contraction?

Accepted Answer

Higher cytosolic calcium increases the number of exposed myosin-binding sites on actin, resulting in stronger contraction.

Question 13

Which of the following steps in the crossbridge cycle requires the hydrolysis of ATP?

Accepted Answer

Cocking of the myosin head into the high-energy conformation

Question 14

A drug that blocks the calcium pumps in the sarcoplasmic reticulum would have which of the following effects?

Accepted Answer

Prolong muscle contraction by preventing the removal of calcium from the cytosol

Question 15

Which of the following is true regarding the orientation of crossbridges at opposite ends of a thick filament?

Accepted Answer

They are oriented in opposite directions, pulling thin filaments toward the center of the sarcomere.

Question 16

Which of the following best explains why muscle contraction ceases when neural input stops?

Accepted Answer

Calcium is actively transported back into the sarcoplasmic reticulum, causing troponin and tropomyosin to block myosin-binding sites on actin.

Question 17

Which of the following is a direct result of acetylcholine binding to its receptor on the motor end plate?

Accepted Answer

Depolarization of the muscle cell membrane, leading to an action potential

Mechanism of Force Generation in Skeletal Muscle

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