MEDICAL PHYSIOLOGY

Detailed explanation-1: -In neurons, the rapid rise in potential, depolarization, is an all-or-nothing event that is initiated by the opening of sodium ion channels within the plasma membrane. The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels.

Detailed explanation-2: -They are the first channels to open in response to changes in voltage, allowing positively charged sodium ions to accumulate in the interior of the cell.

Detailed explanation-3: -This lets positively charged sodium ions flow into the negatively charged axon, and depolarize the surrounding axon. We can think of the channels opening like dominoes falling down-once one channel opens and lets positive ions in, it sets the stage for the channels down the axon to do the same thing.

Detailed explanation-4: -Once the sodium channels open, the neuron completely depolarizes to a membrane potential of about +40 mV. Action potentials are considered an “all-or nothing” event, in that, once the threshold potential is reached, the neuron always completely depolarizes.