Final answer:
White matter is the part of the nervous system composed of mostly myelinated axons, appearing white due to the high lipid content of myelin. Myelin is the fatty layer that insulates the axon, and nodes of Ranvier are gaps in the myelin sheath that facilitate faster transmission of signals along the axon.
Step-by-step explanation:
White matter refers to the regions of the nervous system that contain mostly myelinated axons, making the tissue appear white due to the high lipid content of myelin. Myelin is a fatty layer that insulates the axon and allows electrical signals to travel more quickly. Nodes of Ranvier are regularly spaced gaps in the myelin sheath along the axon that expose the axon, allowing even faster transmission of a signal.