Oligodendrocytes are glia of the central nervous system named from Greek words for cells with a few branches. They have a soma and up to a few dozen processes.
The membrane of the end of each process wraps thinly around an axon many times like a roll of tape. This membrane is a material called myelin that is composed mostly of lipid, which insulates the axon like the rubber coating on a wire.
Each oligodendrocyte process forms one segment of myelin on one axon, and each process may myelinate different axons.
In addition to the function of myelination, oligodendrocytes also appear to influence neurons and other glia, and vice versa, through exchange of a variety of substances. There are also some oligodendroctyes, called nonmyelinating because they do not appear to myelinate axons. These are variably shaped, and their function is not clear.