Illustration of synapses, the junction between nerve cells. Synapses transmit electrical signals from one nerve cell to the next. When the signal reaches the synapse it triggers the release of chemicals called neurotransmitters (red spheres) from vesicles in the terminal swelling (bulb-shaped) of the presynaptic cell. The neurotransmitters cross a microscopic gap called the synaptic cleft and bind to the receptor nerve cell, where they trigger an electrical impulse.