AP PSYCHOLOGY

Detailed explanation-1: -The rising phase is a rapid depolarization followed by the overshoot, when the membrane potential becomes positive. The falling phase is a rapid repolarization followed by the undershoot, when the membrane potential hyperpolarizes past rest. Finally, the membrane potential will return to the resting membrane potential.

Detailed explanation-2: -After the action potential peak is reached, the neuron begins repolarization (3), where the sodium channels close and potassium channels open, allowing potassium ions to cross the membrane into the extracellular fluid, returning the membrane potential to a negative value.

Detailed explanation-3: -At the onset of the action potential, Na+ sodium channels open and allow up to a 5000-fold increase in Na+ conductance. The inactivation process then closes the Na+ channels. The onset of the action potential also triggers voltage gating of the K+ channels, causing them to open at the time the Na+ channels close.

Detailed explanation-4: -At the peak action potential, K+ channels open and K+ begins to leave the cell. At the same time, Na+ channels close. The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire.