Neuroglia

Neuroglia, commonly referred to as glial cells, are non-neuronal cells that support, protect, and modulate the activity of neurons. They populate the central and peripheral nervous systems and contribute to metabolic support, homeostasis, insulation, immune defense, and repair responses. Unlike neurons, glia are not primarily responsible for transmitting electrical impulses, but they participate in signaling and synaptic regulation.

In the central nervous system, the major glial cell types are astrocytes, oligodendrocytes, microglia, and ependymal cells. Astrocytes maintain the extracellular ionic and metabolic environment, regulate neurotransmitter levels, and contribute to the blood-brain barrier and energy supply to neurons. Oligodendrocytes myelinate axons, increasing conduction speed, with a single oligodendrocyte extending processes to many axons in the CNS. Microglia act as resident immune cells, surveying the tissue and performing phagocytosis in development and disease. Ependymal cells line the ventricular system and help produce and circulate cerebrospinal fluid.

In the peripheral nervous system, Schwann cells form myelin around peripheral axons and assist in regeneration after injury. Satellite cells surround neuron cell bodies in ganglia, providing metabolic support and helping regulate the local microenvironment.

During development, radial glia guide migrating neurons and can act as progenitors. Other glial progenitors, such as NG2-glia, persist into adulthood and can generate oligodendrocytes. Glial dysfunction or neoplastic transformation gives rise to gliomas; glia are also implicated in various neurodegenerative and repair processes.