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. the SA node is the only area of the heart capable of spontaneous depolarization.
C. of the rich sympathetic innervation of the SA node.
D. this area produces action potentials more rapidly than any other portion of the conduction system.
E. of action potentials from the cardioregulatory center.
D
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Fill in the blank(s) with the appropriate word(s).
Which of the following statements is correct concerning the variation of voltage-gated ion channels?
A) Na+ channels have much greater diversity than K+ channels. B) Typically, a more complex nervous system also contains a greater diversity of channels. C) There is a great diversity of channels, but within a single organism, only one isoform of a channel can exist. D) There is a large diversity of channels, but they show no physiological significance.
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