Final answer:
White matter consists mainly of myelinated axons surrounded by a myelin sheath, which is created by neuroglial cells. The high lipid content of myelin gives white matter its characteristic glossy white appearance.
Step-by-step explanation:
White matter is mainly composed of myelinated axons, which are covered by a myelin sheath. The myelin sheath is created by the tightly wrapped plasma membrane of neuroglial cells called oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS). Due to the high lipid content of myelin, white matter appears glossy and white in color.