Question:medium
Multi-unit smooth muscle is present at all of the following except?
Multi-unit smooth muscle is present at all of the following except?
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Gut is single-unit (syncytial) smooth muscle; iris, vessels and vas deferens are multi-unit.
Updated On: Jun 24, 2026
- Blood vessels
- Iris
- Gut
- Ductus deferens
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Sort smooth muscle into its two functional categories. Multi-unit fibres behave like separate motor units with little coupling, while single-unit fibres are joined by gap junctions and fire as one sheet.
Step 2: Tissues needing precise, independent control use multi-unit muscle: the iris (pupil size), the large arteries, the piloerector muscles, and the ductus deferens. All of these appear among the answer choices as multi-unit sites.
Step 3: The gastrointestinal tract is the classic example of single-unit visceral smooth muscle. Its cells are electrically connected so that a wave of depolarisation spreads across the whole sheet to generate coordinated peristaltic contractions, the opposite of independent multi-unit behaviour.
Step 4: Since the gut is single-unit and not multi-unit, it is the exception asked for.
\[\boxed{\text{Gut (single-unit smooth muscle)}}\]
Step 2: Tissues needing precise, independent control use multi-unit muscle: the iris (pupil size), the large arteries, the piloerector muscles, and the ductus deferens. All of these appear among the answer choices as multi-unit sites.
Step 3: The gastrointestinal tract is the classic example of single-unit visceral smooth muscle. Its cells are electrically connected so that a wave of depolarisation spreads across the whole sheet to generate coordinated peristaltic contractions, the opposite of independent multi-unit behaviour.
Step 4: Since the gut is single-unit and not multi-unit, it is the exception asked for.
\[\boxed{\text{Gut (single-unit smooth muscle)}}\]
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