Neural communication is based on electrophysiology – cellular mechanisms that produce electrical potentials and currents. Plasma membrane of all cells have a large number of ion channels that are made up of membrane proteins. Some of the channels are passive or ‘leak’ and are always open. Some are active or ‘gated’ – they have a molecular gate that changes shape in response to a signal. The signal can be chemical (transmitter gated channels – respond to chemical neurotransmitters) or voltage gated or dependent channels (respond to changes in membrane electrical potential).