gliaal

Glial cells, or glia, are non-neuronal cells of the nervous system that provide support and protection for neurons. They contribute to tissue structure, metabolic support, insulation, and modulation of synaptic activity. The term glia, from Greek for glue, reflects their historical role as the supportive scaffolding of the nervous system. In the vertebrate brain, glia outnumber neurons and help maintain homeostasis.

In the central nervous system, the major glial types are astrocytes, oligodendrocytes, microglia, and ependymal cells. Astrocytes regulate the extracellular ion and neurotransmitter environment, contribute to the blood–brain barrier, and support metabolism. Oligodendrocytes myelinate CNS axons. Microglia act as resident immune cells, clearing debris and mediating inflammation. Ependymal cells line ventricles and help circulate cerebrospinal fluid. Radial glia guide neuronal migration during development.

In the peripheral nervous system, Schwann cells myelinate peripheral nerves, while satellite glial cells envelop dorsal root and autonomic ganglia, helping regulate the neuronal microenvironment.

Glial cells originate from neural progenitors and differentiate under signaling cues. Oligodendrocyte precursor cells populate the CNS; astrocytes are widespread; Schwann cells and satellite cells support the peripheral nerves. Glial pathology is linked to several diseases: gliomas are tumors derived from glial cells; multiple sclerosis involves demyelination in the CNS; microglial activation is associated with neuroinflammatory and neurodegenerative conditions. Ongoing research highlights glia in synaptic regulation, neuroprotection, and brain repair.