Nerve and muscle: degrees of nerve injury: 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: degrees of nerve injury

Sample item

After a crush injury to the radial nerve, a man has wrist drop. The axons are interrupted but the endoneurial tubes and connective tissue sheaths remain intact. Which outcome is expected?

AAxonal regrowth along the intact tubes, with usually good functional recoveryBRecovery with aberrant regrowth and neuroma formation in most casesCRecovery within days to weeks without any axonal regrowthDNo recovery without surgery because the gap prevents regrowth

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

The answer and the reasoning

A. Axonal regrowth along the intact tubes, with usually good functional recovery

In axonotmesis the axon and myelin degenerate distally, but the endoneurium remains, so regenerating axons are guided to their targets and recovery is usually good over weeks to months at a rate of roughly a millimetre a day. In neurapraxia, conduction block recovers without Wallerian degeneration, and in neurotmesis the whole nerve is divided.

Option by option

A. Axonal regrowth along the intact tubes, with usually good functional recovery (correct)
Correct. Intact endoneurial tubes guide axonal regrowth, so recovery is usually good.
B. Recovery with aberrant regrowth and neuroma formation in most cases
Aberrant regrowth and neuroma are the typical result when the endoneurial tubes are disrupted.
C. Recovery within days to weeks without any axonal regrowth
Recovery without axonal regrowth describes neurapraxia, where the axon is not interrupted.
D. No recovery without surgery because the gap prevents regrowth
Needing surgery because of a gap describes neurotmesis, where the whole nerve is divided.

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 A, Axonal regrowth along the intact tubes, with usually good functional recovery. In axonotmesis the axon and myelin degenerate distally, but the endoneurium remains, so regenerating axons are guided to their targets and recovery is usually good over weeks to months at a rate of roughly a millimetre a day.

Why is "Recovery with aberrant regrowth and neuroma formation in most cases" not the answer?

Aberrant regrowth and neuroma are the typical result when the endoneurial tubes are disrupted.

Why is "Recovery within days to weeks without any axonal regrowth" not the answer?

Recovery without axonal regrowth describes neurapraxia, where the axon is not interrupted.

Why is "No recovery without surgery because the gap prevents regrowth" not the answer?

Needing surgery because of a gap describes neurotmesis, where the whole nerve is divided.

What concept does this question test?

It tests Nerve and muscle: degrees of nerve injury in Physiology. In neurapraxia, conduction block recovers without Wallerian degeneration, and in neurotmesis the whole nerve is divided.

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: degrees of nerve injury?

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.