GI physiology: enteric nervous system: 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 · GI physiology: enteric nervous system

Sample item

A newborn has not passed meconium for 48 hours and has abdominal distension. Anorectal manometry shows absence of the normal fall in internal sphincter pressure when the rectum is distended with a balloon. What is the underlying defect?

AAbsence of enteric ganglion cells in the distal bowel, so the inhibitory reflex cannot be relayedBExcessive inhibitory neuron activity causing tonic relaxation of the sphincterCFailure of the gastrocolic reflex from lack of gastrinDSpinal cord transection above the sacral segments

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

The answer and the reasoning

A. Absence of enteric ganglion cells in the distal bowel, so the inhibitory reflex cannot be relayed

In Hirschsprung disease, neural crest cells fail to migrate to the distal bowel, leaving an aganglionic segment starting at the rectum. Without the intrinsic neurons that relay the rectoanal inhibitory reflex, the internal sphincter does not relax and the segment remains contracted, causing functional obstruction. Diagnosis is confirmed by rectal biopsy showing absent ganglion cells.

Option by option

A. Absence of enteric ganglion cells in the distal bowel, so the inhibitory reflex cannot be relayed (correct)
Absent ganglion cells remove the intrinsic pathway of the reflex.
B. Excessive inhibitory neuron activity causing tonic relaxation of the sphincter
Excess inhibition would cause incontinence, not obstruction.
C. Failure of the gastrocolic reflex from lack of gastrin
The gastrocolic reflex is not the reflex tested, and it does not depend on gastrin alone.
D. Spinal cord transection above the sacral segments
The rectoanal inhibitory reflex is intrinsic and persists after spinal transection.

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, Absence of enteric ganglion cells in the distal bowel, so the inhibitory reflex cannot be relayed. In Hirschsprung disease, neural crest cells fail to migrate to the distal bowel, leaving an aganglionic segment starting at the rectum.

Why is "Excessive inhibitory neuron activity causing tonic relaxation of the…" not the answer?

Excess inhibition would cause incontinence, not obstruction.

Why is "Failure of the gastrocolic reflex from lack of gastrin" not the answer?

The gastrocolic reflex is not the reflex tested, and it does not depend on gastrin alone.

Why is "Spinal cord transection above the sacral segments" not the answer?

The rectoanal inhibitory reflex is intrinsic and persists after spinal transection.

What concept does this question test?

It tests GI physiology: enteric nervous system in Physiology. Without the intrinsic neurons that relay the rectoanal inhibitory reflex, the internal sphincter does not relax and the segment remains contracted, causing functional obstruction. Diagnosis is confirmed by rectal biopsy showing absent ganglion cells.

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 GI physiology: enteric nervous system?

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.