Several large nerves branch from the brain and the spinal cord to various parts of the body.

A typical nerve contains thousands of axons. These axons are wrapped in bundles called fascicles. Together with their surroundings supporting cells, the axons form a nerve cell bundle. Because nerve cells are living cells, they need oxygen and nutrients in order to function. Therefore, there are also blood vessels in the nerve.

In the central nervous system, axon bundles form tracts, whereas in the peripheral nervous system, axon bundles form nerves.