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.