Nerve cells communicate with each other when the synaptic end bulb on the axon of one cell makes contact with a dendrite or cell body of another. Nerve cell impulses are conducted from one cell to another across this connection, called a synapse.
The end bulb contains synaptic vesicles which are filled with a neurotransmitter substance. When a nerve impulse travels down the axon and reaches the end bulb the neurotransmitter is released into a small space, the synaptic cleft. Here it interacts with the membrane of the adjoining cell initiating a new impulse in that cell.
Many diseases of the brain and psychiatric disorders result from a disruption of synaptic communication. Synapses are also the sites of action for many drugs that affect the brain.