Corpus: Ganglion
from Greek: γαγγγλιον - swelling, lump
1. Definition
A ganglion is a collection of nerve cell bodies that creates a thickening along a nerve cord. In the peripheral nervous system (PNS), these are specifically referred to as ganglia. In the central nervous system (CNS), similar collections of nerve cell bodies are typically called nuclei.
In surgery and orthopedics, the term "ganglion" is also used to describe benign soft tissue tumors (synovial cysts) that arise from tendon sheaths or joint capsules. These are commonly referred to as "ganglion cysts" in layman's terms.
2. Classification
2.1. ...by nervous system
There are two main groups of ganglia:
- Spinal ganglia: These are formed from nerve cells of the somatic nervous system, whose afferent, sensitive fibres conduct stimuli from the periphery to the spinal cord.
- Autonomic ganglia: They consist of nerve cells of the autonomic nervous system. Before reaching the ganglion, the fibres here are called "preganglionic", after the changeover there they are called "postganglionic".
2.2. ...by anatomical region
- Head ganglia (parasympathetic head ganglia)
- Cervical ganglia
- Thoracic ganglia
- Lumbar ganglia
- Sacral ganglia
3. Physiology
Ganglia are not merely passive relay stations, but are autonomous neuronal structures capable of simple signal processing. This functionality, particularly in parasympathetic ganglia, allows for localized and independent signal processing near the target organ, without requiring central nervous system involvement. However, the detailed mechanisms behind these processes remain largely unexplored.
4. Examples
- Otic ganglion (ganglion oticum)
- Stellate ganglion
- Submandibular ganglion
- Pterygopalatine ganglion
- Superior ganglion of the vagus nerve (ganglion jugulare)
- Inferior ganglion of the vagus nerve (ganglion nodosum)
- Superior ganglion of the glossopharyngeal nerve
- Inferior ganglion of the glossopharyngeal nerve (ganglion petrosum)