glial cell (neuroglia)

Glial cells, also called neuroglia, are the nervous system's non-neuronal cells — the crew that surrounds, supports, and protects neurons, the cells that actually fire off signals. For a long time scientists thought of them as little more than packing material; in fact the name comes from a Greek word for glue, because they seemed to be the stuff holding the brain together. We now know they are far busier than that. If a neuron is a performer on stage, glia are the whole backstage team: the electricians, the cleaners, the security guards, and the caterers who keep the show running.

There are several kinds, each with a day job. Astrocytes, named for their star-like shape, mop up chemical waste, balance the salts and fluids around neurons, and help feed them with nutrients drawn from nearby blood vessels. Oligodendrocytes in the brain and spinal cord, and Schwann cells out in the body's nerves, wrap axons (the long signal-carrying fibres of neurons) in a fatty insulating sheath called myelin, which lets electrical messages race along far faster. Microglia are the resident immune cells: they patrol the tissue, swallow up germs and debris, and prune away weak or unused connections. Glia even outnumber neurons in much of the brain, so the nervous system is as much their territory as it is the neurons'.

Because glia maintain, insulate, and defend nervous tissue, they sit at the center of both health and disease. When their support falters, neurons struggle: damage to myelin slows or blocks signals, as in multiple sclerosis, while overactive microglia can drive harmful inflammation that contributes to many brain disorders. Studying glia has shifted the picture of the brain from a wiring diagram of neurons alone to a living community in which the supporting cells are essential partners, not just background.