CVS Practice Test

The end result of combined ionic movements during phase 4 of the cardiac action potential is a stable resting membrane potential. During phase 4, particularly in cardiac cells, there is a balance of various ionic currents, specifically the inward rectifier potassium current (I_K1) that helps to maintain a negative resting membrane potential. This phase is critical as it prepares the cardiac cells for the next action potential.

Spontaneous depolarization, often observed in pacemaker cells, occurs due to a gradual increase in membrane potential due to specific channels like the funny current (I_f) associated with sodium, which allows for the heart's intrinsic rhythm. However, this is not directly related to the ionic movements in phase 4 of non-pacemaker cells where a stable resting state is achieved instead.

Thus, the correct understanding points to the fact that phase 4 is primarily about resting potential stabilization rather than spontaneous electrical activity that would lead to depolarization or arrhythmias.