Gliae

Gliae, or glial cells, are non-neuronal cells that support and protect neurons in the central and peripheral nervous systems. The term glial comes from the Greek glia meaning glue; gliae is the Latin plural form. Glia outnumber neurons in many brain regions and play essential roles in maintenance, signaling, and repair.

In the central nervous system, the main glial types are astrocytes, oligodendrocytes, microglia, and ependymal cells. Astrocytes regulate the blood-brain barrier and ion and neurotransmitter balance, provide metabolic support to neurons, and participate in scar formation after injury. Oligodendrocytes form myelin sheaths around axons, increasing conduction speed. Microglia act as resident immune cells, surveying for pathogens and debris. Ependymal cells line the ventricular system and contribute to cerebrospinal fluid production and circulation. In the peripheral nervous system, Schwann cells perform myelination of peripheral axons, while satellite glial cells surround neuron cell bodies in ganglia, supplying nutrients and cushioning.

Developmentally, glial cells arise from neural stem and progenitor cells. Radial glia serve as scaffolding for migrating neurons and later differentiates into astrocytes and oligodendrocytes, among others. Glia participate in synaptic regulation and plasticity and contribute to waste clearance via glymphatic pathways, especially during sleep.

Clinical relevance includes gliomas, tumors of glial origin, and demyelinating diseases such as multiple sclerosis. Glial activation and gliosis are common responses to CNS injury and disease, reflecting their integral role in nervous system health and pathology.