A dielectric (electrically insulating) material consisting of protein and fat that forms a layer, the myelin sheath, usually around only the axon of a neuron. Myelin is about 40 % water; the dry mass of myelin is about 70 - 85 % lipids and about 15 - 30 % proteins. Some of the proteins that make up myelin are myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG), and proteolipid protein (PLP). The primary lipid of myelin is a glycolipid called galactocerebroside (GalC). The intertwining hydrocarbon chains of sphingomyelin serve to strengthen the myelin sheath. [ http://en.wikipedia.org/wiki/Myelin ]