Cranial nerves
Cranial nerves are
nerves that emerge from the
brainstem instead of the
spinal cord.
In
human anatomy, there are 12 pairs of cranial nerves, traditionally abbreviated by the corresponding
Roman numerals. They are numbered according to where their nucleii lie in the brain stem, i.e Cranial Nerve I (the Olfactory nerve) leaves the brainstem at a higher position then Cranial nerve XII, whose origin is located more caudally (lower) than the other cranial nerves.
All cranial nerves except for the olfactory and optic nerves belong to the
peripheral nervous system, having axons that are
myelinated by
Schwann cells (myelinating cells of the peripheral nervous system) rather than
oligodendrocytes (myelinating cells of the central nervous system). The olfactory and optic nerves are named as such, but are technically not nerves, and are continuations of the
central nervous system.
Note: technically the
accessory nerve splits into the
spinal accessory nerve and the
cranial accessory nerve, but the latter quickly combines with the
vagus nerve.
| # | Name | Nuclei | Function | | I ¦¦ Olfactory nerve | Anterior olfactory nucleus | Sense of smell |
| II ¦¦ Optic nerve | Lateral geniculate nucleus | Transmits visual information to the brain |
| III ¦¦ Oculomotor nerve | Oculomotor nucleus, Edinger-Westphal nucleus | Controls most of the eye movements |
| IV ¦¦ Trochlear nerve | Trochlear nucleus | Rotates the eye away or down from the nose |
| V ¦¦ Trigeminal nerve | Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus | Gives sensations to the face |
| VI ¦¦ Abducent nerve (or abducens nerve) | Abducens nucleus | Controls each eye's ability to move away from the midline |
| VII ¦¦ Facial nerve (VII) | Facial nucleus, Solitary nucleus, Superior salivary nucleus | Controls facial expression and taste to two-thirds of the tongue, salivary glands |
| VIII ¦¦ Vestibulocochlear nerve (or auditory nerve) | Vestibular nuclei, Cochlear nuclei | Senses sound, rotation and gravity (essential for balance & movement) |
| IX ¦¦ Glossopharyngeal nerve | Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus | Controls various sensations, glands, and muscles |
| X ¦¦ Vagus nerve | Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus | Supplies sensory parasympathetic fibers to nearly all internal organs |
| XI ¦¦ Accessory nerve (or cranial accessory nerve or spinal accessory nerve) | Nucleus ambiguus, Spinal accessory nucleus | Controls muscles of the neck and overlaps with functions of the vagus |
| XII ¦¦ Hypoglossal nerve | Hypoglossal nucleus | Controls most of the tongue muscles as well as others |
Human cranial nerves are
evolutionarily
homologous to those found in many other
vertebrates. The first ten pairs of cranial nerves arose in the common ancestor of
tetrapods (
amphibians,
reptiles including
birds, and
mammals). Cranial nerves XI and XII evolved in the common ancestor to
amniotes (non-amphibian tetrapods) thus totalling twelve pairs. These characters are
synapomorphies for their respective
clades. In some primitive cartilagenous fishes, such as the
dogfish (
Squalos acanthos), there is a terminal nerve numbered 0 (as it exits the brain before the first cranial nerve).
As the list is important to keep in mind during the examination of the nervous system, there are many
mnemonic devices in circulation to help remember the names and order of the cranial nerves.
*
Oliver the
optimistic
octopus
trots
triumphantly
about
facing
audiances
glossily
vaguely
spinning
hippos.
** (Note that the accessory nerve is referred to by its alternate name
Spinal accessory nerve, and the Vestibulocochlear nerve by its former name,
Auditory, in this mnemonic.)
* "
Old
Opticians
Occasionally
Too
Try
And
Feel
Audrey
Glossop's
Vagina
AcH!"
*
On
Old
Olympus'
Towering
Top
A Fin
And
German
Viewed
Some
Hops
** (Note that the accessory nerve is referred to by its alternate name
Spinal accessory nerve, and the Vestibulocochlear nerve by its former name,
Auditory, in this mnemonic.)
*
Ooh,
Ooh,
Ooh
To
Touch
And
Feel
Virgin
Girls
Vaginas,
Ahh
Heaven!
*
Ooh,
Ooh,
Ooh
To
Touch
And
Feel
Virgin
Girls
Vaginas
And
Hymens!
*
Ooh,
Ooh,
Ooh
To
Touch
And
Feel
Very
Good
Velvet.
Such
Heaven!
** (Note that the accessory nerve is referred to by its alternate name
Spinal accessory nerve in this mnemonic.)
*
Ooh,
Ooh,
Ooh
Toppless
Tiffany
And
Fat
Valerie
Got
Vaganitis
And
Hepatitis
*
Oh
Once
One
Takes
The
Anatomy
Final
Very
Good
Vacations
Are
Heavenly
* Another to help remember the types of information these nerves carry (sensory, motor, or both) is thus:
Some
Say
Marry
Money,
But
My
Brother
Says
Big
Brains
Matter
More.
See mnemonic for more mnemonic devices to aid remembering the cranial nerves.Although twelve nerves are classically described in humans, there is a theory that finds favour with some authors, that humans really have thirteen cranial nerves (Andy Lelli , 1999). If the C1 spinal nerve were considered the thirteenth cranial nerve, C2 through C8 would be renamed as the first through seventh cervical nerves (though anatomists might change the term 'cervical' to 'nuchal' or some other term to avoid confusion between the two nomenclatures). This would make the numbering system consistent all the way through the spinal column - every nerve would exit below its corresponding vertebra, and the number of vertebrae would equal the number of spinal nerves.
Alternatively, C1 could be considered the spinal root of the hypoglossal nerve (CN XII). This would, again, make the numbering system consistent.
*
Cranial nerve nucleus*
Examination of the cranial nerves -
University of Toronto Medicine
*
Diagram of all 12 cranial nerves*
Modalities and pathways
