Nerve and muscle: edrophonium test: 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: edrophonium test

Sample item

A 30-year-old woman with fatigable ptosis has her eyelid droop reverse for a few minutes after an intravenous dose of edrophonium. How does the drug produce this improvement?

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

The answer and the reasoning

A. Inhibits acetylcholinesterase so acetylcholine remains in the cleft and binds the remaining receptors repeatedly

In myasthenia gravis, antibody-mediated loss of nicotinic receptors lowers the end-plate potential. A short-acting cholinesterase inhibitor lets acetylcholine persist in the cleft, so it can bind the remaining receptors repeatedly and the end-plate potential rises, giving a brief improvement in strength.

Option by option

  • A. Inhibits acetylcholinesterase so acetylcholine remains in the cleft and binds the remaining receptors repeatedly (correct)

    Correct. Slower acetylcholine breakdown raises the end-plate potential at the diminished receptor pool.

  • B. Replaces the lost acetylcholine receptors on the end plate

    It does not replace receptors; their number recovers only with treatment of the autoimmune process.

  • C. Increases presynaptic release of acetylcholine by opening calcium channels

    Edrophonium acts on the enzyme in the cleft and does not act on presynaptic calcium channels.

  • D. Blocks the antibodies directed against the receptor

    It does not neutralise antibodies; immunotherapy does that more slowly.

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 A, Inhibits acetylcholinesterase so acetylcholine remains in the cleft and binds the remaining receptors repeatedly. In myasthenia gravis, antibody-mediated loss of nicotinic receptors lowers the end-plate potential.

Why is "Replaces the lost acetylcholine receptors on the end plate" not the answer?

It does not replace receptors; their number recovers only with treatment of the autoimmune process.

Why is "Increases presynaptic release of acetylcholine by opening calcium cha…" not the answer?

Edrophonium acts on the enzyme in the cleft and does not act on presynaptic calcium channels.

Why is "Blocks the antibodies directed against the receptor" not the answer?

It does not neutralise antibodies; immunotherapy does that more slowly.

What concept does this question test?

It tests Nerve and muscle: edrophonium test in Physiology. A short-acting cholinesterase inhibitor lets acetylcholine persist in the cleft, so it can bind the remaining receptors repeatedly and the end-plate potential rises, giving a brief improvement in strength.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: edrophonium test?

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.