A ganglion is a cluster of nerve cells found in the peripheral nervous system. The cells that are specific to a ganglion are called ganglion cells. However, the term is sometimes used to describe the retinal ganglion cells.
Structure of the ganglion
The main components of the ganglion are a cell body called the somata and associated dendritic structures. Ganglia often connect with each other to form a complex network called the plexus. The ganglia form networks that interconnect different structures in the body including the central nervous system and the peripheral nervous system.
Among vertebrate animals or those with spinal cords, there are three major groups of ganglia. These include:
- Cranial nerve ganglia that contain the neurons of the cranial nerves
- Dorsal root ganglia or spinal ganglia where the cell bodies of sensory or afferent nerves are located
- Autonomic ganglia, which contain the cell bodies of the autonomic nervous system. In this system, nerve fibers that run from the central nervous system to the ganglia are called the preganglionic fibers. The nerve fibers originating in the ganglia that connect to effector organs are termed postganglionic fibers.
In addition to the ganglion of the peripheral nervous system, there are also parts of the brain that contains a cluster of interconnected nuceli called the “basal ganglia” or “basal nuclei”. Basal ganglia is found in the cerebral cortex, thalamus and brainstem and is associated with several key functions including motor control, emotions, cognition and learning.
A pseudoganglion refers to a nerve trunk which has become thickened, giving the appearance of a ganglion, even though only nerve fibres and not nerve cells are present. These are found in the radial nerve and in the teres minor muscle.