Nerve physiology: regeneration: 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 physiology: regeneration

Sample item

A 30-year-old woman has a clean transection of the ulnar nerve at the elbow, repaired surgically within hours. The first intrinsic hand muscle to be reinnervated lies about 24 cm from the repair site. Assuming regrowth at the usual rate of about 1 mm per day and ignoring delays, when is reinnervation expected?

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

The answer and the reasoning

A. About 8 months

After transection the distal axon undergoes Wallerian degeneration, and the proximal axon sprouts and advances along the Schwann cell tubes at about 1 mm per day. A distance of 24 cm is 240 mm, so 240 mm divided by 1 mm per day gives about 240 days, or roughly 8 months. Muscles that are denervated for too long develop irreversible fibrosis, so distance matters for prognosis.

Option by option

  • A. About 8 months (correct)

    240 mm at 1 mm per day is 240 days, about 8 months.

  • B. About 3 weeks

    Three weeks would need regrowth of about 11 mm per day, ten times the real rate.

  • C. About 2 years

    Two years would apply to a rate of about 0.3 mm per day, much slower than the usual rate.

  • D. About 2 months

    Two months would need about 4 mm per day, which is not achievable.

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, About 8 months. After transection the distal axon undergoes Wallerian degeneration, and the proximal axon sprouts and advances along the Schwann cell tubes at about 1 mm per day.

Why is "About 3 weeks" not the answer?

Three weeks would need regrowth of about 11 mm per day, ten times the real rate.

Why is "About 2 years" not the answer?

Two years would apply to a rate of about 0.3 mm per day, much slower than the usual rate.

Why is "About 2 months" not the answer?

Two months would need about 4 mm per day, which is not achievable.

What concept does this question test?

It tests Nerve physiology: regeneration in Physiology. A distance of 24 cm is 240 mm, so 240 mm divided by 1 mm per day gives about 240 days, or roughly 8 months. Muscles that are denervated for too long develop irreversible fibrosis, so distance matters for prognosis.

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 physiology: regeneration?

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.