Glia

The support cells of the nervous system — also called neuroglia. They do not carry impulses themselves, but they make the neurons’ work possible, and they outnumber neurons.

Main types

• Astrocytes — nourish neurons, regulate their chemical environment, and help form the blood–brain barrier.
• Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) — wrap axons in myelin, an insulating sheath that speeds signals.
• Microglia — the nervous system’s resident immune cells.
• Ependymal cells — line the brain’s cavities and help produce cerebrospinal fluid.

Key idea

Once dismissed as mere “glue,” glia are now known to be active partners in signaling, protection, and repair — not passive packing.