CVS Practice Test 2026 – The All-In-One Guide to Exam Success!

Spontaneous depolarization in pacemaker cells, such as those found in the sinoatrial node of the heart, is primarily associated with slow Na+ currents. These currents contribute to the gradual increase in the membrane potential until the threshold for an action potential is reached.

In pacemaker cells, the depolarization phase does not rely on the rapid influx of sodium ions typical in fast action potentials, but instead involves a more gradual process. During this phase, sodium ions slowly leak into the cell through specific channels, which helps to create a pacemaker potential.

While calcium currents also play a role in the depolarization of pacemaker cells after reaching threshold, the primary characteristic of spontaneous depolarization is indeed the activation of slow sodium currents. Therefore, recognizing the role of slow Na+ currents is crucial in understanding how heart rhythms are generated and maintained in these specialized conductive tissues.