Nerve and muscle: compound action potential: 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: compound action potential

Sample item

During a nerve conduction study of the median nerve, the recorded compound action potential grows larger as stimulus intensity is increased and then stops growing. What explains this behaviour?

AEach fibre generates a larger action potential as stimulus strength risesBRefractory periods shorten with stimulus strengthCFibres have different thresholds, and more are recruited until all are activatedDConduction velocity rises with stimulus strength

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

The answer and the reasoning

C. Fibres have different thresholds, and more are recruited until all are activated

A single axon obeys the all-or-none law, but a nerve contains many fibres with different thresholds. Stronger stimuli recruit more fibres until all fire, giving a maximal compound potential.

Option by option

A. Each fibre generates a larger action potential as stimulus strength rises
Single action potentials are all-or-none and do not grow with stimulus strength.
B. Refractory periods shorten with stimulus strength
Refractory periods are intrinsic to channel kinetics and do not shorten with stimulus strength.
C. Fibres have different thresholds, and more are recruited until all are activated (correct)
Correct. The summed response rises with fibre recruitment until all fibres fire.
D. Conduction velocity rises with stimulus strength
Conduction velocity depends on fibre diameter and myelination, not stimulus strength.

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 C, Fibres have different thresholds, and more are recruited until all are activated. A single axon obeys the all-or-none law, but a nerve contains many fibres with different thresholds.

Why is "Each fibre generates a larger action potential as stimulus strength r…" not the answer?

Single action potentials are all-or-none and do not grow with stimulus strength.

Why is "Refractory periods shorten with stimulus strength" not the answer?

Refractory periods are intrinsic to channel kinetics and do not shorten with stimulus strength.

Why is "Conduction velocity rises with stimulus strength" not the answer?

Conduction velocity depends on fibre diameter and myelination, not stimulus strength.

What concept does this question test?

It tests Nerve and muscle: compound action potential in Physiology. Stronger stimuli recruit more fibres until all fire, giving a maximal compound potential.

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: compound action potential?

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.