Evolution of Nervous Systems and Brains

Abstract

To exchange and process information cells rely mostly on biochemical signalling pathways. Since these pathways are not well suited to rapidly transmit signals over larger distances, neurons use electrical activity in addition, exploiting the energy stored in the electrical gradients across cellular membranes. These gradients result from the uneven distribution of ions between the intra- and extracellular space due to the ongoing activity of ion transporters and pumps and the fact that the membrane is semipermeable for certain ions. The resulting membrane potential allows for fast flow of ions across cellular membranes via specialized classes of membrane-spanning proteins, namely ion channels. In neurons, some of these channels are voltage-gated, creating an electrical feedback loop that can generate stereotyped, regenerative depolarizing responses. Voltage-gated channels mediate the generation and conduction of action potentials and the release of transmitters at the synapse.