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Glial cells, or glia, are non-neuronal cells of the nervous system that provide essential support for neurons. They participate in a wide range of functions that help neurons develop, survive, and communicate. In the central nervous system (CNS) and peripheral nervous system (PNS), the major glial cell types differ, with astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS, and Schwann cells and satellite cells in the PNS.

The principal roles of glial cells include structural support and guidance for developing neurons, maintenance of extracellular ion balance and neurotransmitter levels, and the formation and maintenance of barriers and insulation. Oligodendrocytes in the CNS and Schwann cells in the PNS form myelin sheaths around axons, increasing the speed of electrical signaling. Astrocytes regulate synaptic environments and contribute to the blood-brain barrier, while microglia act as resident immune cells. Ependymal cells line brain ventricles and contribute to cerebrospinal fluid dynamics.

Glial cells arise from neural progenitor cells during development, with most CNS glia originating from radial glia, and microglia arising from yolk sac–derived macrophages. After injury, glial cells can participate in repair through processes such as gliosis, which can support healing but may also impede regeneration if excessive. In disease, glial cells can contribute to pathology, as seen in gliomas—tumors that originate from glial lineages—and in various neurodegenerative conditions where glial dysfunction or activation plays a role.

Research on glia uses diverse approaches, including glial cultures, induced pluripotent stem cell–derived glia, and brain organoids, to study neuron–glia interactions and glial contributions to health and disease.