Myelin is a lipid-rich extramembranous structure found on the axons and dendrites of neuron in many bilaterian animals, mainly vertebrates, as well as some arthropods and annelids. A circumferential wrapping of myelin, known as a myelin sheath, increases the conduction speed of electrical impulses passing along the axon by generating saltatory conductions, which are much faster than conduction along an unmyelinated axon , and also reduce signal loss due to extrinsic disturbances.