Which structure is coated with myelin to increase speed of nerve impulse transmission?

The structure coated with myelin to increase the speed of nerve impulse transmission is the axon. Myelin is a fatty substance that forms a protective sheath around the axon, facilitating faster electrical signal conduction through a process called saltatory conduction. This allows the nerve impulses to jump between the gaps in the myelin sheath, known as nodes of Ranvier, significantly enhancing transmission speed.