What serves to insulate the axon and increase the speed of impulses conducted?

Myelin is a fatty substance that wraps around the axon of neurons, forming an insulating layer known as the myelin sheath. This insulation is crucial because it increases the speed at which electrical impulses, or action potentials, are conducted along the axon. The presence of myelin allows for saltatory conduction, where the action potential jumps from one node of Ranvier (gaps in the myelin sheath) to the next, significantly speeding up signal transmission compared to unmyelinated axons.

In contrast, neuroglia, axon terminals, and dendrites each have distinct roles in the nervous system that do not involve the insulation of axons or increasing impulse speed. Neuroglia, for example, support and protect neurons rather than act as insulation. Axon terminals are involved in transmitting signals to other neurons or target cells, while dendrites receive incoming signals. None of these components contribute to the rapid conduction of impulses in the way that myelin does.