Nerve and muscle: extrajunctional receptors: 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: extrajunctional receptors

Sample item

A burns victim is paralysed with succinylcholine for surgery three weeks after injury. Within minutes serum potassium rises sharply and arrhythmia follows. Which change in the muscle explains this?

AIncreased release of acetylcholine from nerve terminalsBUpregulated extrajunctional acetylcholine receptors across the muscle membraneCBlockade of voltage-gated sodium channelsDLoss of acetylcholinesterase from the junction

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

The answer and the reasoning

B. Upregulated extrajunctional acetylcholine receptors across the muscle membrane

After burns, denervation or immobilisation, acetylcholine receptors spread across the entire muscle membrane. Succinylcholine depolarises all of them, releasing a large potassium load into plasma. Avoid it from about 24 to 48 hours after such injury.

Option by option

A. Increased release of acetylcholine from nerve terminals
Succinylcholine acts postsynaptically and does not increase acetylcholine release.
B. Upregulated extrajunctional acetylcholine receptors across the muscle membrane (correct)
Correct. Widespread receptors cause massive depolarisation and potassium efflux.
C. Blockade of voltage-gated sodium channels
Sodium channel blockade would cause paralysis without potassium release.
D. Loss of acetylcholinesterase from the junction
Succinylcholine is cleared by plasma cholinesterase, and junctional acetylcholinesterase is not the issue.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Upregulated extrajunctional acetylcholine receptors across the muscle membrane. After burns, denervation or immobilisation, acetylcholine receptors spread across the entire muscle membrane.

Why is "Increased release of acetylcholine from nerve terminals" not the answer?

Succinylcholine acts postsynaptically and does not increase acetylcholine release.

Why is "Blockade of voltage-gated sodium channels" not the answer?

Sodium channel blockade would cause paralysis without potassium release.

Why is "Loss of acetylcholinesterase from the junction" not the answer?

Succinylcholine is cleared by plasma cholinesterase, and junctional acetylcholinesterase is not the issue.

What concept does this question test?

It tests Nerve and muscle: extrajunctional receptors in Physiology. Succinylcholine depolarises all of them, releasing a large potassium load into plasma. Avoid it from about 24 to 48 hours after such injury.

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: extrajunctional receptors?

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.