What is the fatty tissue layer that encases axons and speeds up neural impulses?

The fatty tissue layer that encases axons and significantly increases the speed of neural impulses is known as myelin. Myelin is a substance composed primarily of lipids and proteins that forms a protective and insulating sheath around the axons of many neurons. This insulation is crucial because it allows for the rapid transmission of electrical signals, or action potentials, along the axon.

The process by which myelin enhances the speed of neural impulses is called saltatory conduction. In this process, the action potential jumps from one node of Ranvier (gaps in the myelin sheath) to the next, rather than traveling continuously along the axon. This jumping mechanism allows for much faster communication between neurons compared to unmyelinated axons where the action potential must propagate continuously along the entire length of the axon.

The presence of myelin is critical for the proper functioning of the nervous system, and disruptions in myelin can lead to neurological diseases such as multiple sclerosis, where the immune system attacks the myelin sheath, leading to impaired neural function.