The Excitability of Cells

Abstract

In 1868 Bernstein developed the hypothesis that living cells are composed of an electrolytic interior surrounded by a thin membrane relatively impermeable to ions. Different ionic concentrations on both sides of the membrane cause a difference in electrical potential or ‘voltage’. While at rest, the inside of the cell is about 70mV more negative than the extracellular fluid. This state is called ‘polarized’. Whenever nerve cells or muscle fibers are active the voltage across the membrane changes from this ‘resting voltage’ of −70mV up to +50mV — they become ‘depolarized’ for a short time. The voltage comes down again (repolarization), commonly with an overshoot to values less than —70mV, which is called ‘hyperpolarization’.