The cranial nerves are part of the peripheral nervous system (as distinct from the central nervous system, which consists of the brain and spinal cord). In addition, five of the cranial nerves contain important autonomic functions and hence are part of the autonomic nervous system.
Cranial nerves supply the sense organs and muscles of the head, neck, and viscera. Like spinal nerves, cranial nerves have dorsal and ventral roots (see nerve root) and each root is numbered and named as a separate nerve.
Twelve cranial nerves are conventionally recognized in humans. They are designated both by name and by numerals (Roman I–XII), or Arabic 1–12) according to the order (from front to back) in which they appear on the inferior surface of the brain, as shown in the table below. (Click on a link to learn more about a specific nerve.)
Most of the nerves have both sensory and motor components (see the section below). Three of the nerves are associated with the special senses of smell, vision, hearing, and equilibrium and have only sensory fibers. Five other nerves are primarily motor in function but do have some sensory fibers for proprioception. The remaining four nerves consist of significant amounts of both sensory and motor fibers.
Sensory, motor, and mixed nervesNerves which carry sensations from the skin and the sense organs to the brain and the spinal cord are called sensory nerves. Their messages travel towards the central nervous system. Nerves which carry impulses telling muscles how to work are called motor nerves. Their messages travel away from the central nervous system. Besides these purely sensory and purely motor nerves, there are many nerves which contain fibers of both kinds. These are called mixed nerves.
Related category• ANATOMY AND PHYSIOLOGY
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