<P> White matter is named for its relatively light appearance resulting from the lipid content of myelin . However, the tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries . Its white color in prepared specimens is due to its usual preservation in formaldehyde . </P> <P> White matter is composed of bundles, which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other, and carry nerve impulses between neurons . Myelin acts as an insulator, which allows electrical signals to jump, rather than coursing through the axon, thus increasing the speed of transmission of all nerve signals . </P> <P> The total number of long range fibres within a cerebral hemisphere is 2% of the total number of cortico - cortical fibers (across cortical areas) and is roughly the same number as those that communicate between the two hemispheres in the brain's largest white tissue structure, the Corpus callosum . According to Schüz and Braitenberg note "As a rough rule, the number of fibres of a certain range of lengths is inversely proportional to their length ." </P> <P> White matter in nonelderly adults is 1.7--3.6% blood . </P>

Where is white matter located in the brain