Nerve and muscle: occlusion in neuronal pools: 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: occlusion in neuronal pools

Sample item

Stimulating afferent A alone discharges 6 neurones in a pool, and afferent B alone discharges 6 neurones, some of them the same ones. Stimulating A and B together discharges only 9 neurones. Which phenomenon explains the result?

ATemporal summation, because stimuli arrive in quick successionBPresynaptic inhibition, because the afferent terminals suppress each otherCSpatial facilitation, because subthreshold inputs summateDOcclusion, because some neurones receive suprathreshold input from both afferents

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

The answer and the reasoning

D. Occlusion, because some neurones receive suprathreshold input from both afferents

When two inputs share target neurones that are already fired by either alone, combined stimulation discharges fewer neurones than the sum of the separate responses. This is occlusion. In facilitation, subthreshold inputs from the two sources summate and the combined response exceeds the sum.

Option by option

A. Temporal summation, because stimuli arrive in quick succession
Temporal summation concerns timing of successive stimuli from one source.
B. Presynaptic inhibition, because the afferent terminals suppress each other
The result is explained by shared targets, and presynaptic inhibition is not required.
C. Spatial facilitation, because subthreshold inputs summate
Facilitation would give more than the sum, not less.
D. Occlusion, because some neurones receive suprathreshold input from both afferents (correct)
Correct. Shared neurones are fired by either input alone, so the combined count is less than 12.

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 D, Occlusion, because some neurones receive suprathreshold input from both afferents. When two inputs share target neurones that are already fired by either alone, combined stimulation discharges fewer neurones than the sum of the separate responses.

Why is "Temporal summation, because stimuli arrive in quick succession" not the answer?

Temporal summation concerns timing of successive stimuli from one source.

Why is "Presynaptic inhibition, because the afferent terminals suppress each…" not the answer?

The result is explained by shared targets, and presynaptic inhibition is not required.

Why is "Spatial facilitation, because subthreshold inputs summate" not the answer?

Facilitation would give more than the sum, not less.

What concept does this question test?

It tests Nerve and muscle: occlusion in neuronal pools in Physiology. This is occlusion. In facilitation, subthreshold inputs from the two sources summate and the combined response exceeds the sum.

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: occlusion in neuronal pools?

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.