Electrical synapses are different from chemical synapses because they couple neurons electrically. Electrical synapses contain numerous *gap junctions. At these synapses, the presynaptic and postsynaptic cell membranes are separated by a space of only 2–3 nanometers, and membrane proteins called connexins link the two neurons by forming pores that connect the cytoplasm of the two cells (see Figure 7.16A). Electrical current as well as ions and small molecules can pass directly from cell to cell through these pores. As a result, transmission at electrical synapses is very fast and can proceed in either direction. In comparison, transmission at chemical synapses is slow and unidirectional.

The properties of electrical synapses make them especially well adapted for processes that have to be fast–for example, escape from danger. They are also effective means of achieving synchronous activity of populations of cells. Electrical synapses are less common in the nervous systems of vertebrates than are chemical synapses. The major reason is that they offer fewer means for integration of information. Electrical synapses are almost exclusively excitatory whereas chemical synapses are both excitatory and inhibitory. Electrical synapses are not well suited for temporal summation of inputs. Also, because of their relative simplicity of structure and function, electrical synapses offer fewer possible mechanisms for plasticity which is the foundation of learning and memory. One advantage they do have is the ability to synchronize large numbers of cells.