AP PSYCHOLOGY

Detailed explanation-1: -The repolarization or falling phase is caused by the slow closing of sodium channels and the opening of voltage-gated potassium channels. As a result, the membrane permeability to sodium declines to resting levels.

Detailed explanation-2: -The sodium–potassium pump is found in many cell (plasma) membranes. Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, three sodium ions are extruded from and two potassium ions are imported into the cell.

Detailed explanation-3: -After hyperpolarization the potassium channels close and the natural permeability of the neuron to sodium and potassium allows the neuron to return to its resting potential of –70 mV.

Detailed explanation-4: -The sodium-potassium pump system moves sodium and potassium ions against large concentration gradients. It moves two potassium ions into the cell where potassium levels are high, and pumps three sodium ions out of the cell and into the extracellular fluid.