Synapses are the junctions between two neurones and there are approximately 1014 of them in the human brain. Synapses are the means by which neurones communicate with each other. The point of contact may be between the axon terminal of one neurone and the cell body of another, or between the axon terminal of one neurone and the axon of a neighbouring neurone.
Synapses do not simply pass on the information, but play a crucial role in processing the information. Chemical synapses rely on a chemical transmitter substance called a neurotransmitter. This neurotransmitter travels from one neurone, across a small gap, and attaches to receptors on the surface of the second neurone. This binding leads to intracellular changes that will either stimulate or inhibit firing of the second neurone.
There are two types of synapse: electrical and chemical. Most synapses are chemical and will therefore be the focus of the learning activities in this course. Electrical synapses are able to transmit nerve signals very fast and directly across a very small gap between two nerve cells. Direct connections between cells are called gap junctions. In electrical synapses gap junctions enable the electrical signal to pass from one nerve cell to another without any significant change to the signal.