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In anatomy, a ganglion (// GANG-glee-ən; plural ganglia) is a nerve cell cluster or a group of nerve cell bodies located in the peripheral nervous system. 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 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.
However, in the brain (part of the central nervous system), the "basal ganglia", or basal nuclei, 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; this usage though has not been generally adopted.
A pseudoganglion is a localized thickening of the main part or trunk of a nerve that has the appearance of a ganglion but has only nerve fibres and no nerve cells.