The cardiac electrical impulse normally begins spontaneously in the SA node because
A. of the superior location of the SA node in the right atrium.
B. of action potentials from the cardioregulatory center.
C. the SA node is the only area of the heart capable of spontaneous depolarization.
D. of the rich sympathetic innervation of the SA node.
E. this area produces action potentials more rapidly than any other portion of the conduction system.
Answer: E
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