Neurons contact and communicate with their target cells at structures called synapses, named from Greek words for clasping together.
The target cell of a neuron may be another neuron, a muscle cell, or a gland cell.
A few neurons act as gland cells by having axons terminals on capillaries to secrete substances called hormones into the bloodstream. Most synapses are chemical, meaning that molecules communicate information across the synapse.
Very few synapses are electrical, meaning that the cells are physically connected through gap junctions that allow ions to flow directly from the neuron to the target cell; these will not be discussed further.
A typical human neuron receives information from thousands of synapses, and sends information through synapses to thousands of target cells. Synapses between neurons most often occur between an axon terminal and a dendritic spine, although axon terminals also contact somas or other axon terminals.
Chemical synapses contain a small gap called the synaptic cleft that separates the membranes of the neuron and its target cell.
The membranes separated by the synaptic cleft are called the presynaptic and postsynaptic membranes. Inside the presynaptic membrane of the neuron are vesicles, called synaptic vesicles, which are filled with molecules called neurotransmitter.
The postsynaptic membrane of the target cell has receptors for the neurotransmitter molecules in the presynaptic vesicles.
Most synapses in the central nervous system are covered by astrocyte end feet.
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Introduction to Neurology 