Question 1

Which of the following best describes the role of calcium ions ($$Ca^{2+}) in $$skeletal muscle contraction?

Accepted Answer

Calcium ions bind to troponin C, causing a conformational change that moves tropomyosin and exposes the myosin binding sites on actin.

Question 2

During the crossbridge cycle, what event triggers the power stroke?

Accepted Answer

Release of inorganic phosphate ($$P_i) $$from the myosin head

Question 3

Which process is responsible for muscle relaxation after contraction?

Accepted Answer

Removal of $$Ca^{2+}$$ from the sarcoplasm by the SERCA pump into the sarcoplasmic reticulum

Question 4

What is the primary function of calsequestrin and calreticulin in skeletal muscle cells?

Accepted Answer

They bind $$Ca^{2+} in $$the sarcoplasmic reticulum, allowing for maximal $$Ca^{2+}$$ uptake and delaying inhibition of the SERCA pump.

Question 5

Which of the following correctly describes the sequence of events in the crossbridge cycle?

Accepted Answer

ATP binds to myosin, myosin releases actin, ATP is hydrolyzed, myosin binds actin, $$P_i is $$released, power stroke occurs, ADP is released.

Question 6

Which enzyme is responsible for degrading acetylcholine in the synaptic cleft?

Accepted Answer

Acetylcholinesterase

Question 7

What would happen to muscle contraction if ATP were suddenly unavailable?

Accepted Answer

Myosin would remain tightly bound to actin, resulting in rigor mortis.

Question 8

Which of the following is NOT a source of ATP for skeletal muscle contraction?

Accepted Answer

ATP produced by hydrolysis of tropomyosin

Question 9

During muscle contraction, which band(s) of the sarcomere shorten?

Accepted Answer

The H zone and I band

Question 10

Which of the following best explains the latent period observed between muscle fiber action potential and contraction?

Accepted Answer

Time required for $$Ca^{2+}$$ release and binding to troponin

Question 11

A patient with a mutation in the gene encoding the SERCA pump would most likely experience which of the following?

Accepted Answer

Prolonged muscle contraction due to impaired $$Ca^{2+}$$ reuptake into the sarcoplasmic reticulum

Question 12

Which of the following statements about the sliding filament theory is correct?

Accepted Answer

Actin and myosin filaments slide past each other, causing sarcomere shortening without changing the length of the filaments.

Question 13

Which of the following is required for the removal of $$Ca^{2+}$$ from the sarcoplasm to terminate muscle contraction?

Accepted Answer

ATP hydrolysis by the SERCA pump

Question 14

Which of the following events occurs immediately after acetylcholine binds to its receptor on the motor end plate?

Accepted Answer

Opening of ion channels and influx of $$Na^+$$

Question 15

Which of the following best describes the effect of high $$Ca^{2+}$$ concentration in the sarcoplasmic reticulum (SR) on the SERCA pump?

Accepted Answer

High $$Ca^{2+}$$ inhibits the SERCA pump, but calsequestrin and calreticulin delay this inhibition by binding $$Ca^{2+}.$$

Question 16

Which of the following is a direct consequence of acetylcholine degradation at the neuromuscular junction?

Accepted Answer

Termination of muscle fiber action potential initiation

Question 17

Which of the following is TRUE regarding the role of ATP in muscle contraction and relaxation?

Accepted Answer

ATP is required for both contraction (myosin ATPase activity) and relaxation ($$Ca^{2+}$$ ATPase activity in the SERCA pump).

Question 18

Which of the following best explains why muscle cells store glycogen?

Accepted Answer

Glycogen provides a rapid source of glucose for ATP production during muscle activity.

Question 19

Which of the following metabolic pathways produces the most ATP per glucose molecule in skeletal muscle?

Accepted Answer

Aerobic metabolism (oxidative phosphorylation)

Skeletal Muscle Contraction: Mechanisms and ATP Supply

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