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MCAT Question A Day - 9/12/14

When left alone, certain specialized cardiac muscle cells have the capacity for self-excitation. The SA node is collection of such cellsThe SA node is innervated by the vagus nerve. The frequency of self excitation of the cardiac cells of the SA Node ilikely to be:

A.  slower than a normal heartbeat because excitation by the vagus nerve decreases the heart rate.
B.  slower than normal heartbeat because excitation by the vagus nerve increases the heart rate.
C.  faster than normal heartbeabecause excitation bthvagus nerve decreasethe heart rate.
D.  faster than a normal heartbeat because excitation bthe vagunervincreases thheart rate.

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