Glia are specialized cells of the nervous system whose main function is to "glue" neurons together. Specialized glia called Schwann cells secrete myelin sheaths around particularly long axons. Glia of the various types greatly outnumber the actual neurons.

Glia cells are also known as neuroglia. There are three main types of glia cells in the central nervous system: microglia, astrocytes, and oligodendrocytes, each of which perform different functions. Glia cells are specialized to support and nourish the neurons and have many regulatory functions.