In a neuron, the myelin sheath serves to insulate

and protect the axon. It is composed of specialized glial cells called Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. The myelin sheath helps increase the speed at which electrical impulses travel along the axon, allowing for faster and more efficient communication between neurons. It also helps to prevent signal loss or interference, and protects the axon from damage.