$$\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$$

Question 1

According to the sliding filament theory, what happens to the sarcomere during skeletal muscle contraction?

Accepted Answer

The thin filaments (actin) slide over the thick filaments (myosin), causing the sarcomere to shorten.

Question 2

Which of the following best describes the role of ATP in the muscle contraction cycle?

Accepted Answer

ATP hydrolysis by myosin heads provides energy to 'cock' the myosin head into its extended position.

Question 3

What is the primary function of acetylcholinesterase at the neuromuscular junction?

Accepted Answer

It breaks down acetylcholine, terminating neural stimulation of the muscle fiber.

Question 4

A patient is exposed to a toxin that prevents acetylcholine from binding to its receptors on the motor end plate. What is the most likely result?

Accepted Answer

Flaccid paralysis due to inability of muscles to contract.

Question 5

During excitation-contraction coupling, what triggers the release of calcium ions from the sarcoplasmic reticulum?

Accepted Answer

Depolarization of T tubules by the action potential.

Question 6

Which of the following events directly causes the power stroke during muscle contraction?

Accepted Answer

Release of ADP and phosphate from the myosin head.

Question 7

What is the effect of organophosphorus pesticide poisoning on muscle contraction?

Accepted Answer

It inhibits acetylcholinesterase, causing spastic paralysis.

Question 8

Which of the following best explains why rigor mortis occurs after death?

Accepted Answer

Calcium accumulates in the sarcoplasm and ATP is unavailable to break cross-bridges.

Question 9

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

Accepted Answer

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

Question 10

Which of the following is NOT a component of the neuromuscular junction?

Accepted Answer

Sarcoplasmic reticulum terminal cisternae

Question 11

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

Accepted Answer

Failure of calcium ion pumps in the sarcoplasmic reticulum due to lack of ATP

Question 12

Which process is responsible for the reuptake of calcium ions into the sarcoplasmic reticulum during muscle relaxation?

Accepted Answer

Active transport using ATP-dependent calcium pumps

Question 13

During the contraction cycle, what event immediately follows the binding of myosin to actin?

Accepted Answer

Release of ADP and phosphate, resulting in the power stroke

Question 14

Which of the following best describes the graded potential at the motor end plate?

Accepted Answer

It is caused by the influx of sodium ions through ligand-gated channels after acetylcholine binds to its receptor.

Question 15

Which of the following factors does NOT affect the duration of muscle contraction?

Accepted Answer

Amount of acetylcholinesterase in the sarcoplasmic reticulum

Question 16

Which step in the contraction cycle requires the direct input of ATP?

Accepted Answer

Detachment of myosin heads from actin after the power stroke

Question 17

A patient presents with muscle weakness and inability to contract muscles. Which of the following could explain this condition?

Accepted Answer

A toxin that blocks acetylcholine receptors at the neuromuscular junction

Question 18

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

Accepted Answer

Troponin binds calcium ions, causing a conformational change that exposes active sites on actin.

Question 19

Which of the following equations best represents the depolarization of the sarcolemma due to sodium influx?

Accepted Answer

$$\mathrm{Na}^+_{	ext{outside}} ightarrow \mathrm{Na}^+_{	ext{inside}}$$

Physiology of Skeletal Muscle Contraction: Sliding Filament Theory and Neuromuscular Junction

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