We also have the exxon terminal. Now, the exxon usually contains myelination. And what the myelin is, it is basically a special type of substance that's composed of protein and fats. And these myelin sheaths or simply myelin, help insulate our axon. And that means that increases the speed of propagation of the action potential along our axon. Now, within our central nervous system the cells responsible for actually creating the myelin around the axon are the liga denticides.