A ganglion is a nerve cell cluster[1] or a group of nerve cell bodies located in the autonomic nervous system and sensory system, mostly outside the central nervous system except certain nuclei.[2][3] Ganglia house the cell bodies of afferent nerves (input nerve fibers) and efferent nerves (output/motor nerve fibers).

A pseudoganglion looks like a ganglion, but only has nerve fibers and has no nerve cell bodies.

Ganglia are primarily made up of somata and dendritic structures which are bundled or connected. Ganglia often interconnect with other ganglia to form a complex system of ganglia known as a plexus. Ganglia provide relay points and intermediary connections between different neurological structures in the body, such as the peripheral and central nervous systems.

Among vertebrates there are three major groups of ganglia:

In the autonomic nervous system, fibers from the central nervous system to the ganglia are known as preganglionic fibers, while those from the ganglia to the effector organ are called postganglionic fibers.