Q: Which of the following equations correctly represents the reaction catalyzed by creatine kinase during immediate ATP regeneration in muscle fibers?

$$\mathrm{ADP} + \mathrm{CP} \xrightarrow{\text{CK}} \mathrm{ATP} + \mathrm{Creatine}$$

Question 1

During the power stroke of the crossbridge cycle, what event directly causes the myosin head to pivot and pull the actin filament toward the center of the sarcomere?

Accepted Answer

Release of phosphate from the myosin head

Question 2

Which of the following best explains why the thin filaments do not slide backward during muscle contraction, even though ATP breaks the actin-myosin attachment?

Accepted Answer

Some myosin heads remain attached while others detach and recock

Question 3

Which process is responsible for returning calcium ions to the sarcoplasmic reticulum during muscle relaxation?

Accepted Answer

Active transport using ATP

Question 4

A patient presents with muscle spasms after intense exercise. Which of the following is the most likely explanation based on muscle physiology?

Accepted Answer

Inability to relax muscle fibers due to impaired calcium reuptake

Question 5

What is the primary immediate source of ATP for muscle contraction during the first few seconds of intense activity?

Accepted Answer

Creatine phosphate reaction

Question 6

Which of the following best describes the role of acetylcholinesterase (AChE) in muscle relaxation?

Accepted Answer

It degrades acetylcholine, stopping muscle fiber stimulation

Question 7

Which of the following equations correctly represents the reaction catalyzed by creatine kinase during immediate ATP regeneration in muscle fibers?

Accepted Answer

$$\mathrm{ADP} + \mathrm{CP} \xrightarrow{	ext{CK}} \mathrm{ATP} + \mathrm{Creatine}$$

Question 8

Rigor mortis occurs after death because:

Accepted Answer

ATP is no longer available to detach myosin heads from actin

Question 9

Which of the following is NOT a function of ATP in skeletal muscle contraction and relaxation?

Accepted Answer

Binding to troponin to expose active sites on actin

Question 10

A muscle fiber is unable to relax after contraction. Which of the following is the most likely cause?

Accepted Answer

Continuous stimulation by acetylcholine due to lack of acetylcholinesterase

Question 11

Which of the following best describes the sliding-filament mechanism during muscle contraction?

Accepted Answer

Thin filaments slide past thick filaments, increasing the zone of overlap

Question 12

Which of the following statements about creatine supplementation is supported by research?

Accepted Answer

It mildly improves short bursts of muscle activity

Question 13

Which of the following is a potential negative effect of massive creatine supplementation?

Accepted Answer

Kidney damage

Question 14

Which of the following best explains why excess creatine supplementation is a waste of money?

Accepted Answer

Skeletal muscle fibers have a maximal storage capacity for creatine

Question 15

Which of the following is the correct sequence of events during muscle relaxation?

Accepted Answer

Acetylcholine is degraded, sarcolemma repolarizes, calcium is pumped into the sarcoplasmic reticulum, troponin shifts

Question 16

Which of the following best describes the analogy of sailors pulling on a rope as it relates to the crossbridge cycle?

Accepted Answer

Some sailors pull while others reposition, preventing backward movement

Skeletal Muscle Contraction, Relaxation, and Energy Sources

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