When most people talk about brain cells, they're talking about
neurons. There's another kind of cell in the brain, though, and
they're known as glia (they're also called glial cells or
neuroglia), and they're actually more numerous than neurons are. Glia aren't as sexy as neurons are--they don't seem to play major roles in
the transmission of information--but they do play several vital roles. In the central nervous system,
oligodendrocytes (spell THAT five times fast) create the myelin sheath that
insulates axons. (In the peripheral nervous system, Schwann cells myelinate axons). Microglia help repair damage to the
nervous system after a stroke or some similar event. Astrocytes make up
the blood-brain barrier and also maintain homeostasis by helping to
regulate the concentration of ions that play a role in the action
potential. Radial glial cells help guide developing neurons into the
proper locations. Thus, they're vital to brain function, even though you don't hear about them very much.