Depolarisation
Nerve-, muscle- and heart cells at rest have a positive electrical charge of about 70 mV on the outside of their cell membrane, matched by a negative charge on the inside of the cell membrane. When a cell is stimulated (e.g. by a chemical or nerve impulse) the charges on a small area of the cell surface are reversed, becoming negative on the outside and positive on the inside. The area where the charges are reversed then moves along the cell surface at high speed until it reaches another cell, which can then be stimulated. The process of reversing the charges is called depolarisation. When the depolarisation starts moving along the cell surface, the charges return to the resting state, the outside once again becoming positively and the inside negatively charged. This return to the resting state is called repolarisation.
GE Healthcare Glossary