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MCAT Question A Day - 9/7/14 - Answer!

Which of the following muscular actions is controlled by the autonomic nervous system?

A.  the knee-jerk reflex
B.  conduction of cardiac muscle action potential from cell to cell
C.  peristalsis of the gastrointestinal tract
D.  contraction of the diaphragm

C is correct. Peristalsis is a smooth-muscle activity, and smooth muscle is innervated by the autonomic nervous system. The skeletal muscles are innervated by the somatic nervous system, so interruption of the autonomic nervous system would not affect the knee-jerk reflex or the diaphragm. An action potential in cardiac muscle is conducted from cell to cell by gap junctions.

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