Synapse. Coloured transmission electron micrograph (TEM) of a synapse, a junction between two nerve cells, in the brain. At a synapse an electrical signal is transmitted from one cell to the next in only one direction. The nerve cells are pink, with the presynaptic cell at left and the postsynaptic cell at right. Mitochondria, supplying the cells with energy, are yellow. When an electrical signal reaches a synapse it triggers the release of neurotransmitter chemicals from vesicles (red) at the end of the presynaptic cell. The neurotransmitters cross a microscopic gap and bind to receptors on the post synaptic cell. Magnification: 50,000x when printed 10 centimetres across.
