Medical Definition of antioxidant. : any of various substances (as beta-carotene, vitamin C, and alpha-tocopherol) that inhibit oxidation or reactions promoted by oxygen and peroxides and that include many held to protect the living body from the deleterious effects of free radicals.
An action potential is a very rapid change in membrane potential that occurs when a nerve cell membrane is stimulated. Specifically, the membrane potential goes from the resting potential (typically -70 mV) to some positive value (typically about +30 mV) in a very short period of time (just a few milliseconds).
Structure of axon membrane changes, tiny openings (channels) allow ions outside cell to move inside cell (changing the ratio of P. to N. ions). Channels first open near soma then down length of axon as action potential sweeps along. Period in which neuron is not ready to fire again.