Electrophysiology Unit (EPU) 26.19 Practice Test

The resting potential of nodal cells is primarily maintained by which type of channels?

Fast Sodium Channels Potassium Leak Channels Slow Calcium Channels Chloride Channels

Correct Answer:

Slow Calcium Channels

Explanation:

Nodal (pacemaker) cells rely on slow calcium influx to set and progress toward threshold. In these cells there aren’t many fast sodium channels, so there isn’t a quick, Na+-driven upstroke like in ventricular tissue. Instead, the inward current through slow calcium channels slowly depolarizes the membrane during diastole, driving the pacemaker activity that maintains their characteristic resting/pacemaker potential. Chloride channels aren’t the main driver here, and potassium leak channels provide only a background set point rather than the depolarizing force.

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