Q: Which equation correctly represents the recycling of acetylcholine in the presynaptic neuron?

$$\mathrm{Acetate} + \mathrm{Choline} \xrightarrow{\text{Choline acetyltransferase}} \mathrm{Acetylcholine}$$

Question 1

Which of the following best describes the role of the alpha (lower) motor neuron in the somatic motor pathway?

Accepted Answer

It carries signals from the spinal cord or brainstem directly to the muscle fibers.

Question 2

A patient presents with progressive muscle weakness and atrophy. Genetic testing reveals a mutation in the gene encoding superoxide dismutase. Which condition is most likely?

Accepted Answer

Amyotrophic lateral sclerosis (ALS)

Question 3

At the neuromuscular junction, which event directly triggers the release of acetylcholine from the presynaptic neuron?

Accepted Answer

Influx of calcium ions through voltage-gated calcium channels

Question 4

Which of the following best explains the effect of acetylcholinesterase inhibitors in the treatment of myasthenia gravis?

Accepted Answer

They prevent the degradation of acetylcholine, prolonging its action at the neuromuscular junction.

Question 5

Which structure increases the surface area of the postsynaptic membrane at the neuromuscular junction, enhancing the response to acetylcholine?

Accepted Answer

Junctional folds of the sarcolemma

Question 6

Which of the following is TRUE regarding the nicotinic acetylcholine receptor at the neuromuscular junction?

Accepted Answer

It requires binding of two acetylcholine molecules to open.

Question 7

What is the primary intracellular signal that triggers muscle contraction in all muscle types?

Accepted Answer

Increase in intracellular calcium $$[Ca$$^{2+}$$]$$

Question 8

During excitation-contraction coupling in skeletal muscle, which event occurs immediately after the action potential propagates along the sarcolemma?

Accepted Answer

Opening of voltage-gated calcium channels in the T-tubules

Question 9

Which equation correctly represents the recycling of acetylcholine in the presynaptic neuron?

Accepted Answer

$$\mathrm{Acetate} + \mathrm{Choline} \xrightarrow{	ext{Choline acetyltransferase}} \mathrm{Acetylcholine}$$

Question 10

A patient with myasthenia gravis has antibodies against acetylcholine receptors. What is the most direct effect of these antibodies?

Accepted Answer

Decreased activation of postsynaptic ion channels

Question 11

Which of the following best describes the process of excitation-contraction coupling in skeletal muscle?

Accepted Answer

Electrical excitation of the sarcolemma triggers an increase in $$[Ca$$^{2+}$$] in $$the muscle fiber, leading to contraction.

Question 12

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

Accepted Answer

Sarcoplasmic reticulum

Question 13

Which of the following statements about the corticospinal tract is correct?

Accepted Answer

It consists of upper motor neurons descending from the cortex to the spinal cord.

Question 14

Which of the following best explains why muscle fibers in a motor unit contract simultaneously?

Accepted Answer

All muscle fibers in a motor unit are innervated by branches of the same alpha motor neuron.

Question 15

Which of the following is the correct sequence of events at the neuromuscular junction leading to muscle contraction?

Accepted Answer

Action potential arrives at axon terminal → Calcium influx → Acetylcholine release → Acetylcholine binds to nicotinic receptors → End plate potential → Muscle action potential

Question 16

Which of the following is TRUE regarding calcium-induced calcium release in skeletal muscle?

Accepted Answer

It is not vital for skeletal muscle contraction; most $$Ca^{2+} is $$released from the sarcoplasmic reticulum via mechanical coupling.

Question 17

Which of the following best describes the function of the T-tubules in skeletal muscle fibers?

Accepted Answer

They transmit action potentials deep into the muscle fiber, facilitating excitation-contraction coupling.

Question 18

A patient is exposed to a toxin that blocks voltage-gated calcium channels in the presynaptic motor neuron terminal. What is the most likely effect?

Accepted Answer

Decreased acetylcholine release and muscle paralysis

Question 19

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

Accepted Answer

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

Muscles 2: Somatic Motor Division, Neuromuscular Junction, and Excitation-Contraction Coupling

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