AN ACTION POTENTIAL
Information moves along the axon of a neuron in the form of an electrochemical change known as an action potential. At rest, there is a potential difference across the cell membrane of -70 mV due to the unequal distribution of charged particles on the inside and outside of the membrane. The inside of the membrane is negatively charged due to the presence of negatively charged proteins associated with the membrane. The outside of the membrane is positively charged relative to the inside because of the large number of positively charged ions attracted to the outer surface by the negative charge on the inside.

There are more Na⁺ outside of the cell than inside, and more K⁺ inside the cell than outside. When a small stimulus is applied to the cell membrane, a few sodium channels open. Na⁺ diffuse into the cell along their concentration gradient. As a result, there is a local change in the potential in a relatively small region of the plasma membrane.