Final answer:
Myelin is a lipid-rich insulating substance and acts as a protective covering for nerve fibers, enabling faster transmission of electrical signals along neurons. It is produced by oligodendrocytes in the CNS and Schwann cells in the PNS.
Step-by-step explanation:
The best description of the waxy-appearing material called myelin is a protective covering for nerve fibers. Myelin is a lipid-rich insulating substance that surrounds the axons of many neurons, which is crucial in allowing for faster transmission of electrical signals.
In the central nervous system (CNS), myelin sheaths are produced by oligodendrocytes, while in the peripheral nervous system (PNS), they are formed by Schwann cells. This myelin sheath acts as an electrical insulator in a similar way to the plastic or rubber that encases an electrical cord. Regularly spaced nodes, known as nodes of Ranvier, allow nerve impulses to jump rapidly along the axon, enhancing the speed of signal transmission. Myelin includes important proteins that are integral to the glial cell membrane and help hold the layers closely together.