White matter is one of the three main solid components of the central nervous system. White matter tissue of the freshly cut brain appears white to the naked eye because of being composed largely of lipid. The other two components of the brain are grey matter and substantia nigra. White matter is composed of bundles of myelinated nerve cell processes (or axons), which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other, and carry nerve impulses between neurons. Cerebral- and spinal white matter do not contain dendrites, which can only be found in grey matter along with neural cell bodies, and shorter axons. The white matter is the tissue through which messages pass between different areas of gray matter within the nervous system. Using a computer network as an analogy, the gray matter can be thought of as the actual computers themselves, whereas the white matter represents the network cables connecting the computers together. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is important because it allows the messages to pass quickly from place to place. The brain in general (and especially a child's brain) can adapt to white-matter damage by finding alternative routes that bypass the damaged white-matter areas, and can therefore maintain good connections between the various areas of gray matter. Unlike gray matter, which peaks in development in a person's twenties, the white matter continues to develop, and peaks in middle age.