Nerve and muscle: acetylcholine synthesis: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Nerve and muscle: acetylcholine synthesis

Sample item

A drug blocks the rate-limiting step in acetylcholine production at the motor nerve terminal, so stores run down during repeated firing. Which step is blocked?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. High-affinity uptake of choline into the terminal

Choline entering the terminal by a sodium-dependent high-affinity transporter is the rate-limiting step for acetylcholine synthesis by choline acetyltransferase. Hemicholinium blocks this uptake. Vesamicol blocks vesicle filling, and acetylcholinesterase breaks down transmitter in the cleft.

Option by option

  • A. Packaging of acetylcholine into vesicles by a vesicular transporter

    Vesicular loading is blocked by vesamicol but is not the rate-limiting step.

  • B. High-affinity uptake of choline into the terminal (correct)

    Correct. Choline uptake limits acetylcholine synthesis and is blocked by hemicholinium.

  • C. Breakdown of acetylcholine in the cleft

    Breakdown in the cleft removes transmitter and does not limit synthesis.

  • D. Release of acetylcholine by calcium

    Calcium-dependent release is exocytosis, which comes after synthesis.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, High-affinity uptake of choline into the terminal. Choline entering the terminal by a sodium-dependent high-affinity transporter is the rate-limiting step for acetylcholine synthesis by choline acetyltransferase.

Why is "Packaging of acetylcholine into vesicles by a vesicular transporter" not the answer?

Vesicular loading is blocked by vesamicol but is not the rate-limiting step.

Why is "Breakdown of acetylcholine in the cleft" not the answer?

Breakdown in the cleft removes transmitter and does not limit synthesis.

Why is "Release of acetylcholine by calcium" not the answer?

Calcium-dependent release is exocytosis, which comes after synthesis.

What concept does this question test?

It tests Nerve and muscle: acetylcholine synthesis in Physiology. Hemicholinium blocks this uptake. Vesamicol blocks vesicle filling, and acetylcholinesterase breaks down transmitter in the cleft.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Nerve and muscle: acetylcholine synthesis?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.