What material surrounds and insulates the axons of some neurons, accelerating the transmission of electrical signals?

Myelin serves the essential role of surrounding and insulating the axons of certain neurons, which greatly enhances the speed of electrical signal transmission along those axons. This fatty substance is composed of lipids and proteins, and it forms a sheath around the axon in segments, with intervals known as nodes of Ranvier.

When an electrical impulse travels along a myelinated axon, the signal jumps from one node to the next, a process called saltatory conduction. This allows for much faster transmission compared to unmyelinated axons, where the signal must travel continuously along the entire length of the axon. The presence of myelin is crucial for the efficient functioning of the nervous system, especially in areas where rapid response is necessary, such as reflex actions.

In contrast, the other options do not relate to the insulation of axons in this way. Arachnoid refers to a layer of the meninges that protect the brain and spinal cord but has no insulating properties for axons. Dendrites are the structures that receive signals from other neurons and do not facilitate electrical transmission along axons. Neuroglia comprises various support cells in the nervous system but does not specifically insulate axons like myelin does.