Final answer:
Oligodendrocytes and Schwann cells produce myelin, a lipid-rich sheath that facilitates the transmission of electrical signals along the axon in both the CNS and PNS, respectively.
Step-by-step explanation:
Oligodendrocytes and Schwann cells generate a fatty substance called myelin. Schwann cells are responsible for producing the myelin sheath that insulates axons in the peripheral nervous system (PNS), while oligodendrocytes do the same within the central nervous system (CNS). Myelin is crucial because it enhances the transmission of electrical signals along the axon, increasing the speed and efficiency of nerve impulse conduction. It comprises not just the phospholipids of the glial cell membrane but also essential proteins that help to maintain the structural integrity of the myelin sheath.