Neuroanatomy: autonomic nervous system: practice question

A Anatomy 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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Anatomy · Neuroanatomy: autonomic nervous system

Sample item

After a fracture-dislocation at the conus medullaris, a man has an atonic bladder, overflow incontinence and loss of the defecation reflex. Which outflow is mainly interrupted?

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

The answer and the reasoning

C. Sacral parasympathetic outflow (S2 to S4) through the pelvic splanchnic nerves

The parasympathetic system has a craniosacral outflow. Pelvic splanchnic nerves from S2 to S4 supply the bladder detrusor, the descending and sigmoid colon, rectum and erectile tissue. Their loss removes detrusor contraction and distal colonic motility, producing an atonic bladder and constipation. Sympathetic outflow arises from the T1 to L2 segments.

Option by option

  • A. Thoracolumbar sympathetic outflow (T1 to L2)

    Sympathetic fibres relax the detrusor and close the sphincter, so their loss would not abolish bladder emptying.

  • B. Somatic outflow through the femoral nerve

    The femoral nerve supplies the thigh and has no role in bladder or bowel function.

  • C. Sacral parasympathetic outflow (S2 to S4) through the pelvic splanchnic nerves (correct)

    Correct. S2 to S4 parasympathetic fibres drive the bladder and hindgut.

  • D. Vagal parasympathetic outflow

    The vagus supplies the gut only as far as the proximal two thirds of the transverse colon.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Sacral parasympathetic outflow (S2 to S4) through the pelvic splanchnic nerves. The parasympathetic system has a craniosacral outflow.

Why is "Thoracolumbar sympathetic outflow (T1 to L2)" not the answer?

Sympathetic fibres relax the detrusor and close the sphincter, so their loss would not abolish bladder emptying.

Why is "Somatic outflow through the femoral nerve" not the answer?

The femoral nerve supplies the thigh and has no role in bladder or bowel function.

Why is "Vagal parasympathetic outflow" not the answer?

The vagus supplies the gut only as far as the proximal two thirds of the transverse colon.

What concept does this question test?

It tests Neuroanatomy: autonomic nervous system in Anatomy. Pelvic splanchnic nerves from S2 to S4 supply the bladder detrusor, the descending and sigmoid colon, rectum and erectile tissue. Their loss removes detrusor contraction and distal colonic motility, producing an atonic bladder and constipation. Sympathetic outflow arises from the T1 to L2 segments.

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 Neuroanatomy: autonomic nervous system?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.