The action potential of the sinoatrial node

The action potential of the sinoatrial node and atrioventricular node results from the opening of the slow Ca2+ channels and the influx of Ca2+ (some Na+ may also enter through these slow Ca2+ channels). An action potential is elicited when the membrane potential reaches threshold. Spontaneous depolarization is an intrinsic propey of nodal tissue and can occur in the absence of nerves. The low resting potential results in a small action potential that propagates slowly. The rapid Na+ channels are inactivated in nodal tissue. An increase in the conductance to K+ would hyperpolarize the membrane.