Final answer:
White matter in the brain and spinal cord is composed of myelinated axons, which facilitate communication within the CNS.
Step-by-step explanation:
White matter is composed of axons, which provide for communication between different parts of the brain, as well as with CNS centers.
These axons are insulated by myelin, a lipid-rich substance that gives white matter its characteristic white color due to the high lipid content. In contrast, gray matter primarily consists of neuron and glial cell bodies, along with dendrites.
The myelinated axons of the white matter allows for efficient transmission of electrical impulses within the central nervous system (CNS).