chapter  4
11 Pages

Electrical signals

The mechanism by which the signal is transmitted along the cell membrane is referred to as

local current flow

or the movement of positively charged ions. In the area of a stimulus causing a depolarization, the inside of the cell becomes positive (less negative) relative to the outside of the cell. Because opposite charges attract, the (+) charges in this area are attracted to and move toward the negative charges on the adjacent areas of the internal surface of the cell membrane. As a result, these adjacent areas become depolarized due to the presence of these (+) charges. This process continues and the electrical signal travels along the cell membrane away from the initial site of the stimulus; however, these graded or local potentials travel only short distances. The cell membrane is not well insulated and the current (positive charges) tends to drift away from the internal surface of the cell membrane. Consequently, as the signal travels along the membrane, the number of (+) charges causing the depolarization of the next region of membrane continually decreases and the magnitude of the depolarization therefore decreases. The further away from the initial site of stimulation, the smaller the magnitude of the signal is until it eventually dies out.