Neuroglia or glial cells are the "nerve glue" that provides a support network for the central nervous system and can be thought of as neural connective tissue. Glial cells surround and insulate nerve cells with the exception of where they are in contact with another nerve cell (synaptic contact). Glial cells also produce myelin sheath.
Glial cells can be subclassified as:
- Oligodendroglia: Primarily responsible for producing the myelin sheath surrounding axons in the central nervous system (CNS). These are the most numerous of all glial cells.
- Astroglia (astrocytes): Primarily responsible for scar formation after injury to the CNS; also part of exchanges of fluids, gases, and metabolites between blood, cerebrospinal fluid, and nervous tissue.
- Microglia: Phagocytic cells primarily responsible for the active immune defense of the CNS.
- Ependymal cells: Cells that line the spinal canal and in doing so also provide a barrier between cerebrospinal fluid and nervous tissue.