Question 1

Which of the following best describes a motor unit in skeletal muscle physiology?

Accepted Answer

All muscle fibers innervated by the same axon from a single somatic motor neuron.

Question 2

During the generation of an action potential in a skeletal muscle fiber, what is the primary ion responsible for the initial depolarization phase?

Accepted Answer

Sodium ($$Na^+)$$

Question 3

What is the role of acetylcholinesterase (AChE) at the neuromuscular junction?

Accepted Answer

It hydrolyzes acetylcholine, terminating the signal at the synaptic cleft.

Question 4

Which of the following events directly triggers the release of calcium ions from the sarcoplasmic reticulum during excitation-contraction coupling?

Accepted Answer

Propagation of the action potential along the sarcolemma and into T tubules.

Question 5

A patient is exposed to a toxin that blocks voltage-gated sodium channels in skeletal muscle. Which phase of the action potential would be directly affected?

Accepted Answer

Depolarization

Question 6

What is the typical resting membrane potential ($$RMP) of a $$skeletal muscle fiber?

Accepted Answer

$$-90\ \mathrm{mV}$$

Question 7

Which of the following best explains why muscle fibers cannot be stimulated during the refractory period?

Accepted Answer

Voltage-gated sodium channels are inactivated and cannot reopen until repolarization is complete.

Question 8

In smooth muscle contraction, which enzyme is activated by the calcium-calmodulin complex to initiate cross-bridge formation?

Accepted Answer

Myosin light-chain kinase (MLCK)

Question 9

Which of the following is TRUE regarding the source of calcium for contraction in smooth muscle?

Accepted Answer

Most calcium comes from the extracellular fluid via caveolae.

Question 10

During the contraction cycle in skeletal muscle, what is the immediate consequence of ATP binding to the myosin head?

Accepted Answer

Myosin head detaches from actin.

Question 11

A patient with a genetic defect in the sodium-potassium ATPase pump would most likely have problems with which aspect of muscle physiology?

Accepted Answer

Restoring the resting membrane potential after an action potential.

Question 12

Which of the following best describes the role of tropomyosin in skeletal muscle contraction?

Accepted Answer

It covers myosin binding sites on actin, preventing cross-bridge formation until moved by troponin.

Question 13

What is the threshold potential required to trigger an action potential in a skeletal muscle fiber?

Accepted Answer

$$-65\ \mathrm{mV}$$

Question 14

Which of the following is a correct sequence of events in excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential → Calcium release from SR → Cross-bridge formation → Muscle contraction

Question 15

Which type of receptor is found at the neuromuscular junction and is responsible for binding acetylcholine?

Accepted Answer

Nicotinic cholinergic receptor ($$nAChR)$$

Question 16

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

Accepted Answer

The sarcomere shortens as thin filaments are pulled toward the M line.

Question 17

Which of the following best explains why smooth muscle can contract in response to stretch and autonomic nervous system stimulation?

Accepted Answer

Smooth muscle cells have caveolae and varicosities that allow for widespread neurotransmitter release and calcium influx.

Question 18

Which process is responsible for restoring the ionic conditions of the resting state after a muscle action potential?

Accepted Answer

Active transport by the $$Na^+-K^+$$ ATPase pump.

Question 19

A patient is given a drug that inhibits acetylcholine release at the neuromuscular junction. What is the most likely effect on muscle contraction?

Accepted Answer

Muscle contraction will be inhibited due to lack of end plate potential formation.

Question 20

Which of the following is TRUE regarding the difference between skeletal and smooth muscle innervation?

Accepted Answer

Skeletal muscle fibers are individually innervated by somatic motor neurons, while smooth muscle fibers are innervated by the autonomic nervous system via varicosities.

Muscle Physiology

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