Depolarization and hyperpolarization occur when ion channels in the membrane open or close, altering the ability of particular types of ions to enter or exit the cell. For example: The opening of channels that let positive ions flow out of the cell (or negative ions flow in) can cause hyperpolarization.
How does a cell Repolarize?
Repolarization typically results from the movement of positively charged K+ ions out of the cell. The repolarization phase of an action potential initially results in hyperpolarization, attainment of a membrane potential, termed the afterhyperpolarization, that is more negative than the resting potential.
What ion Depolarizes the cell?
Sodium ions continue to diffuse into the cells of SA node. When the membrane potential becomes greater than the threshold potential, it causes the opening of Ca+2 channels. The calcium ions then rush in, causing depolarization. depolarization and contraction of ventricles.
