Figure 1.

Electron micrograph showing a small area of cortical neuropil from the brain of a rat. The ECS has been roughly outlined by hand in red. A typical synapse is shown between a presynaptic neuronal terminal (with clear, round vesicles containing neurotransmitter) and a dendritic spine of a postsynaptic neuron (displaying a dark electron-dense region called the postsynaptic density) - a narrow synaptic cleft may be identified between them. Adapted with permission from Nicholson and Sykova (1998).