Nerve and muscle: multi-unit smooth muscle: 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: multi-unit smooth muscle

Sample item

A smooth muscle preparation has fibres that each receive their own nerve ending, few gap junctions, and graded contraction depending on how many fibres are stimulated. From which tissue was it most likely taken?

AWall of the small intestineBMyometrium of the pregnant uterusCSphincter pupillae of the irisDDetrusor of the urinary bladder

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

The answer and the reasoning

C. Sphincter pupillae of the iris

Multi-unit smooth muscle has fibres that act independently, each with its own innervation, and it is found in the iris, ciliary body, vas deferens and piloerector muscles. Single-unit (visceral) smooth muscle in the gut, uterus and bladder has many gap junctions and contracts as a syncytium, often with pacemaker activity.

Option by option

A. Wall of the small intestine
Intestinal smooth muscle is single-unit and spreads slow waves through gap junctions.
B. Myometrium of the pregnant uterus
The uterine myometrium is a syncytium with abundant gap junctions, especially near term.
C. Sphincter pupillae of the iris (correct)
Correct. The iris muscles are multi-unit, with fine graded control.
D. Detrusor of the urinary bladder
Detrusor muscle is single-unit and contracts as a whole during voiding.

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 C, Sphincter pupillae of the iris. Multi-unit smooth muscle has fibres that act independently, each with its own innervation, and it is found in the iris, ciliary body, vas deferens and piloerector muscles.

Why is "Wall of the small intestine" not the answer?

Intestinal smooth muscle is single-unit and spreads slow waves through gap junctions.

Why is "Myometrium of the pregnant uterus" not the answer?

The uterine myometrium is a syncytium with abundant gap junctions, especially near term.

Why is "Detrusor of the urinary bladder" not the answer?

Detrusor muscle is single-unit and contracts as a whole during voiding.

What concept does this question test?

It tests Nerve and muscle: multi-unit smooth muscle in Physiology. Single-unit (visceral) smooth muscle in the gut, uterus and bladder has many gap junctions and contracts as a syncytium, often with pacemaker activity.

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 Nerve and muscle: multi-unit smooth muscle?

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.