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).
I. An action potential is a momentary change in the membrane potential caused by a transient change in the membrane's permeability to sodium and potassium. A. It can be observed with an oscilloscope that monitors the electrical potential (or voltage) recorded by a microelectrode inserted into a cell.Figure 1.. The action potential is initiated when an excitable cell such as a nerve or muscle fiber is depolarized to threshold. 1. The upstroke, or depolarization phase, is caused by the flow of sodium ions into the cell. 2.