Form major portion of the white matter of the brain and spinal cord and all nerves. Most fibers in peripheral nerves are myelinated.

Fibers that extend from the body of a nerve cell that transmit electrical pulses as part of the information handling in the nervous system. - A bundle of nerve fibers (axons). The fibers are either afferent - leading towards the brain and serving in the perception of sensory stimuli of the skin, joints, muscles, and inner organs; or efferent - leading away from the brain and mediating contractions and relaxsations of muscles or organs.

Slender processes of neurons, especially the prolonged axons that conduct nerve impulses.