The bioelectric current– basis for signal transmission

As living cells are unable to utilise a metallic conductor for communication, they have chosen other means: (1) extracellular for fluid metabolic products; (2) vascular transport for hormones; and (3) ionic generation of propagated membrane potentials. Cells can accumulate negatively charged molecules inside as a result of having a selectively permeable outer membrane. Thus, a potential difference exists between the cell's interior and the outside medium, and can be used for processes of de- and repolarisation. Electrical transmission of signals by the nervous system was investigated in the first half of the nineteenth century by eminent physiologists such as Dubois-Reymond (1843) and later by Hermann (1883) and Bernstein (1902). Galvani and Volta in Italy had already recognised the presence of electric currents in frog muscle, although Volta believed that the muscle only produced a current when metals were in contact with the moisture and salt of the muscle, rather like a battery. Galvani's work was carried on by Valli and eventually it was commonly agreed that the resting muscle had an electrical potential difference across it, with a negative charge within the muscle and a positive charge on its outside. The presence of a potential difference across an inactive muscle (the resting potential) was well demonstrated by the actual flow of current which was released when the muscle was injured. Nobili (1825) for instance, recorded a marked flow of current in a frog muscle preparation, which he, not unnaturally, called the ‘frog current’.