Nerve and muscle: depolarising versus non-depolarising block: 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: depolarising versus non-depolarising block

Sample item

During neuromuscular monitoring after a drug, train-of-four stimulation shows each twitch smaller than the last, and the response improves after a tetanic burst. Which type of agent has been given?

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

The answer and the reasoning

A. A competitive non-depolarising blocker

A competitive antagonist such as rocuronium occupies receptors, so as acetylcholine mobilisation falls with repeated stimulation each twitch is weaker (fade). Tetanic stimulation increases acetylcholine release, producing post-tetanic facilitation. A phase I depolarising block shows reduced twitches without fade and no post-tetanic facilitation.

Option by option

  • A. A competitive non-depolarising blocker (correct)

    Correct. Fade with post-tetanic facilitation is typical of non-depolarising block.

  • B. Botulinum toxin given locally

    Botulinum toxin acts presynaptically over days and is not used for intraoperative monitoring.

  • C. A depolarising agent producing a phase I block

    A phase I depolarising block shows no fade and no post-tetanic facilitation.

  • D. An anticholinesterase

    An anticholinesterase would reverse, not produce, a block.

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, A competitive non-depolarising blocker. A competitive antagonist such as rocuronium occupies receptors, so as acetylcholine mobilisation falls with repeated stimulation each twitch is weaker (fade).

Why is "Botulinum toxin given locally" not the answer?

Botulinum toxin acts presynaptically over days and is not used for intraoperative monitoring.

Why is "A depolarising agent producing a phase I block" not the answer?

A phase I depolarising block shows no fade and no post-tetanic facilitation.

Why is "An anticholinesterase" not the answer?

An anticholinesterase would reverse, not produce, a block.

What concept does this question test?

It tests Nerve and muscle: depolarising versus non-depolarising block in Physiology. Tetanic stimulation increases acetylcholine release, producing post-tetanic facilitation. A phase I depolarising block shows reduced twitches without fade and no post-tetanic facilitation.

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: depolarising versus non-depolarising block?

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.