"White matter" is the portions of the brain
and spinal cord
which are white and composed of the long, thin extensions (called axon
s and dendrite
s) of neuron
s. This is in contrast to gray matter
, which is the portions that are gray and composed of the cyton
s (main bodies) of neurons. In the spinal cord, the white matter borders the gray matter, making up the outer layers of nerve tissue
. In the brain, the white matter carries the nerve impulses originating in the gray matter.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.