Renal and acid–base: neurogenic bladder: 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 · Renal and acid–base: neurogenic bladder

Sample item

A woman with a prolapsed lumbar disc has saddle anaesthesia and a painless distended bladder with continuous dribbling. Which reflex arc is interrupted?

ASacral S2-S4 parasympathetic efferents to the detrusorBThoracolumbar sympathetic outflow to the internal sphincterCPontine micturition centreDFrontal micturition centre in the cortex

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

The answer and the reasoning

A. Sacral S2-S4 parasympathetic efferents to the detrusor

The sacral micturition reflex needs S2-S4 afferents and parasympathetic efferents to contract the detrusor. When these are interrupted the bladder becomes atonic, fills until the pressure overcomes the sphincter, and overflow incontinence follows.

Option by option

A. Sacral S2-S4 parasympathetic efferents to the detrusor (correct)
Correct. Loss of the sacral reflex arc produces an atonic, overfilled bladder.
B. Thoracolumbar sympathetic outflow to the internal sphincter
Sympathetic outflow relaxes the detrusor and closes the sphincter, so loss would not cause retention.
C. Pontine micturition centre
Pontine lesions above the sacral cord produce detrusor-sphincter dyssynergia.
D. Frontal micturition centre in the cortex
Cortical lesions cause urgency and incontinence without a distended bladder.

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, Sacral S2-S4 parasympathetic efferents to the detrusor. The sacral micturition reflex needs S2-S4 afferents and parasympathetic efferents to contract the detrusor.

Why is "Thoracolumbar sympathetic outflow to the internal sphincter" not the answer?

Sympathetic outflow relaxes the detrusor and closes the sphincter, so loss would not cause retention.

Why is "Pontine micturition centre" not the answer?

Pontine lesions above the sacral cord produce detrusor-sphincter dyssynergia.

Why is "Frontal micturition centre in the cortex" not the answer?

Cortical lesions cause urgency and incontinence without a distended bladder.

What concept does this question test?

It tests Renal and acid–base: neurogenic bladder in Physiology. When these are interrupted the bladder becomes atonic, fills until the pressure overcomes the sphincter, and overflow incontinence follows.

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 Renal and acid–base: neurogenic bladder?

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.