Question

During the majority of the process of repolarization, the cardiac cell is unable to respond to a new electrical stimulus; the cardiac cell cannot spontaneously depolarize, and this period is referred to as the

Answer 1

Repolarization (phase 3 of the action potential) occurs because of an increase in potassium permeability. At the SA node, potassium permeability can be further enhanced by vagal stimulation. This has the effect of hyperpolarizing the cell and reducing the rate of firing. Sympathetic stimulation has the opposite effect.