Ganglion

A ganglion (pl.: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively. A pseudoganglion looks like a ganglion, but only has nerve fibers and has few nerve cell bodies. The restriction of the ganglion to refer to structures in the peripheral nervous system postdates the naming of brain structures such as the basal ganglia, which has remained as a historical artifact in vertebrate terminology. Among invertebrates the restriction is disregarded: for example, the main part of the insect brain is called the cerebral ganglion.