A ganglion is any structure containing a collection of nerve cell bodies in the central nervous system (CNS) or peripheral nervous system (PNS) and often also numbers of synapses. Plural: ganglia.

 

The CNS of many invertebrates consists largely of ganglia, connected by nerve cords, variously arranged but usually well developed in the head (cerebral ganglia). In vertebrates the CNS has a different structure but ganglia occur in the PNS (see nerve root) and autonomic nervous system.

 

A ganglion is also the name of a benign lump, often at the wrist, found close to tendons and containing jelly-like fluid.