In anatomy, a ganglion (// GANG-glee-ən; plural ganglia) is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells.
In neurological contexts, ganglia are composed mainly 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 two major groups of ganglia:
- Dorsal root ganglia (also known as the spinal ganglia) contain the cell bodies of sensory (afferent) nerves.
- Autonomic ganglia contain the cell bodies of autonomic nerves.
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.
However, in the brain (part of the central nervous system), the "basal ganglia" is a group of nuclei interconnected with the cerebral cortex, thalamus and brainstem, associated with a variety of functions: motor control, cognition, emotions, and learning.
Partly due to this ambiguity, the Terminologia Anatomica recommends using the term basal nuclei instead of basal ganglia.