Question

Which of the following is an example of multiunit smooth muscles?
A. Smooth muscles in uterine wall
B. Smooth muscle with the intestine
C. Masseter muscle of the jaw
D. Arrector pili muscle of skin

Answer 1

Hint: Smooth muscle is a non-striated, involuntary muscle that lacks sarcomeres and hence no striations. Smooth muscle is split into two types: single-unit and multiunit. The whole bundle or sheet of smooth muscle cells contracts as a syncytium in a single-unit muscle. Smooth muscles can be found in the walls of hollow organs like the stomach, intestines, bladder, and uterus; in passageways like blood and lymph arteries; and in the respiratory, urinary, and reproductive systems' tracts.

Complete answer:
Option:A – Smooth muscles in uterine walls are single units and work as one single unit which aids in parturition and uterine contractions.
Thus, Option:A is not the correct answer.
Option:B – Smooth muscles of intestine are also single unit type and as single unit smooth muscles are myogenic the intestinal muscles are always in a state of muscle tonus.
Thus, Option:B is not the correct answer.
Option:C – Masseter muscles of jaw are also single units and are involved in masticating the food during chewing.
Thus, Option:C is also not correct.
Option:D – the Arrector pili muscle of skin is an example of multi unit smooth muscle and these muscles are stimulated to contract at particular muscle cells only.
Thus, Option:D is the correct answer.

Therefore, Option D) Arrector pili muscle of skin is the correct answer.

Note:
Smooth muscle cells of multi-unit smooth muscle function independently of one another, contracting and relaxing on their own. Multi-unit smooth muscle has fewer gap junctions than other kinds of smooth muscle on a histological level. Because each smooth muscle cell is self-contained, there is no need to use a gap junction to electrically connect the cells.