Neurophysiology: clonus: 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 · Neurophysiology: clonus

Sample item

A patient after a stroke has rhythmic, repeated contractions of the calf when the foot is briskly dorsiflexed and held. Which mechanism underlies this sign?

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

The answer and the reasoning

D. Lost descending inhibition of the stretch reflex

In an upper motor neuron lesion, descending inhibition of the gamma loop and alpha motor neurons is lost, so the stretch reflex is hyperactive. A sustained stretch triggers repeated reflex contraction and relaxation (clonus).

Option by option

  • A. Loss of dorsal column position sensation

    Dorsal column loss causes sensory ataxia and does not generate rhythmic contraction.

  • B. Destruction of anterior horn cells in the cord

    Anterior horn cell destruction gives flaccid weakness with reduced reflexes.

  • C. Failure of neuromuscular junction transmission

    Neuromuscular junction failure causes fatigable weakness, not rhythmic contraction.

  • D. Lost descending inhibition of the stretch reflex (correct)

    Correct. A hyperexcitable stretch reflex arc with loss of descending inhibition produces clonus.

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 D, Lost descending inhibition of the stretch reflex. In an upper motor neuron lesion, descending inhibition of the gamma loop and alpha motor neurons is lost, so the stretch reflex is hyperactive.

Why is "Loss of dorsal column position sensation" not the answer?

Dorsal column loss causes sensory ataxia and does not generate rhythmic contraction.

Why is "Destruction of anterior horn cells in the cord" not the answer?

Anterior horn cell destruction gives flaccid weakness with reduced reflexes.

Why is "Failure of neuromuscular junction transmission" not the answer?

Neuromuscular junction failure causes fatigable weakness, not rhythmic contraction.

What concept does this question test?

It tests Neurophysiology: clonus in Physiology. A sustained stretch triggers repeated reflex contraction and relaxation (clonus).

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 Neurophysiology: clonus?

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.