cranial nerve
1. Olfactory nerve. A sensory
nerve which carries the sensations of smell from the olfactory mucosa in the nose.
2. Optic nerve. A sensory nerve which carries
the sensations of vision from the retina at the back of the eye.
3. Oculomotor nerve.
4. Trochlear nerve.
5. Trigeminal nerve. This is a mixed nerve. It
contains the sensory fibers from the face and the motor fibers
which control the muscles of mastication.
6. Abducens nerve. Nerves 3, 4, and 6 are all motor nerves. They supply
the muscles around the eyeball and carry the impulses which move
the eye.
7. Facial nerve. A mixed nerve. The motor fibers
supply the facial muscles of expression and several muscles in
the neck. The sensory fibers carry taste sensations from the front
of the tongue.
8. Auditory nerve. In effect the auditory nerve
consists of two quite separate parts, both of which have sensory
functions. One part is the cochlear nerve which carries the sensation
of hearing from the cochlea.
The other part is the vestibular nerve which carries, from the
vestibule of the ear, information
concerning the position and movements of the head.
9. Glossopharyngeal nerve. A mixed nerve. It supples
a single muscle in the neck and carries sensations from the tongue
and pharynx.
10. Vagus nerve. This important nerve is part of
the autonomic nervous system. It is a mixed nerve which supplies
the heart, lungs, intestines, and larynx.
11. Accessory nerve. Motor fibers in this nerve
supply muscles in the neck.
12. Hypoglossal nerve. A motor nerve which controls
the tongue muscles.
A cranial nerve (CN) is a nerve that emerges directly from the brain of vertebrates, as distinct from a spinal nerve, which emerges from the spinal cord. All the cranial nerves, except the vagus nerve, pass through the foramina of the skull to innervate structures in the head, neck, and facial region.
The cranial nerves are generally part of the peripheral nervous system (as distinct from the central nervous system, which consists of the brain and spinal cord). Exceptions are cranial nerve II, which is unequivocally part of the central nervous system and CN I (or at least some of its important associated structures), which is traditionally considered to be part of the central nervous system as well. 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.)
Note that cranial nerve 0 (aka CN XIII), the nervous terminalis, is not commonly mentioned in textbooks as part of the classic twelve. It used to be thought that it was a vestigial remnant and not very common in most adult brains. However, it is now known to be unequivocally a normal and common part of the adult human brain and does serve physiological functions, likely related to reproductive behavior.
| I | olfactory nerve |
| II | optic nerve |
| III | oculomotor nerve |
| IV | trochlear nerve |
| V | trigeminal nerve |
| VI | abducens nerve |
| VII | facial nerve |
| VIII | auditory nerve |
| IX | glossopharyngeal nerve |
| X | vagus nerve |
| XI | accessory nerve |
| XII | hypoglossal 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 nerves
Nerves 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.
