Synapse. Coloured Transmission Electron Micrograph (TEM) of a synapse. These transmit one-way signals from one nerve cell to the next. The end of the nerve cell (known as a terminal bouton) that transmits the signal is seen at upper centre (green). This is a roughly triangular shape and contains cell-organelles. At centre, a multitude of small circular synaptic vesicles are seen (red) which contain a neurotransmitter. When a signal is transmitted, these vesicles are released and cross the microscopic gap (known as the synaptic cleft) to the next cell (seen at lower right). In this way the nerve signal is passed on from cell to cell. Magnification: x14,400 at 6x7cm size.