Which of the following statements describes phase 4 of the action potential of cells in the ...

Ans:
A

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During phase 4 in the cells of the SA node, a slow leakage of current through the slow channels of the cellular membrane leads to spontaneous depolarization; this slow response enables pacemaker function. Answer B describes the relative refractory period of the action potential curve, which occurs at the end of phase 3 in cardiac cells, and answer C describes phase 1 of the action potential, which signals the end of depolarization. The sodium-potassium pump transports sodium out of the cell and a smaller amount of potassium into it, contributing to the negative intracellular charge of the resting membrane potential in phase 4.