n. nonneuronal tissue in the nervous system that provides structural, nutritional, and other kinds of support to neurons. It may consist of very small cells (microglia) or relatively large ones (macroglia). The latter include astrocytes, ependymal cells, and the two types of cells that form the myelin sheath around axons: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Also called neuroglia. —glialadj.