Cranial nerves
Cranial nerves are nerves that emerge directly from the brain in contrast to spinal nerves which emerge from segments of the spinal cord. Although thirteen cranial nerves in humans fit this description, twelve are conventionally recognized. The nerves from the third onward arise from the brain stem.
Except for the tenth and the eleventh nerve, they primarily serve the motor and sensory systems of the head and neck region. However, unlike peripheral nerves which are separated to achieve segmental innervation, cranial nerves are divided to serve one or a few specific functions in wider anatomical territories.
Names of Nerves
The 12 pairs of cranial nerves are traditionally abbreviated by the corresponding Roman numerals. They are numbered according to where their nuclei lie in the brain stem, e.g. Cranial Nerve III (the Oculomotor nerve) leaves the brainstem at a higher position than 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.
Cranial nerves in non-human vertebrates
Human cranial nerves are evolutionarily homologous to those found in many other vertebrates.
The 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 zero (as it exits the brain before the first cranial nerve).
Mnemonic devices
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.
- OLd OPie OCcasionally TRies TRIgonometry And Feels VEry GLoomy, VAGUe, Acutely HYPOactive
- On Occasion Our Trusty Truck Acts Funny. Very Good Vehicle Any How.
- On Old Olympus' Towering Top A Finely Vested German Viewed A Hawk
- On Old Olympus' Towering Top A Finn And German Viewed Some Hops
Only On Occasion, Touching The Amorous Female Virgin Goat Vacillates A Hand
OLympic OPium OCcupies TRoubled TRiathletes After Finishing VEgas Gambling VAcations Still High
- (Note that the Vestibulocochlear nerve is referred to by its former name, Auditory, in this mnemonic.)
- Oliver the optimistic octopus trots triumphantly about facing audiences 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.)
- Orange orangutans often try to avoid feeding angry gorillas very ancient hotdogs.
- (Note that the Vestibulocochlear nerve is referred to by its former name, Auditory, in these mnemonics.)
- OLd OPTICians OCCasionally Too TRy And Feel AUDrey GLOSSOp's VAGina AcH!
- On Old Olympus' Tufted Top A Fat Armed German Viewed An Hop
- Oh, Oh, Oh To Touch And Feel Various Girls' Vaginas And Hymens
- Oh, Oh, Oh To Touch And Feel a 'Very Gungy' Vagina And Hymen
- Oh, Oh, Oh To Touch And Feel A Girl's Vagina And Hymen
- (Note that the Vestibulocochlear nerve is referred to by its former name, Auditory, in this mnemonic.)
- Oh Oh Oh To Touch And Feel Very Good Velvet, Ah Heaven
- Oh, Oh, Oh, 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.)
- Oh, Oh, Oh, To Touch And Feel Very Gross Vagina, So Awesomely Hairy!
- Ooh, Ooh, Ooh Topless Tiffany And Fat Valerie Got Vaginitis And Hepatitis
- Oh Once One Takes The Anatomy Final Very Good Vacations Are Heavenly
- OOO Truely There Are Five Very Gorgeous Vixens Awaiting Him
- Ooh, Ooh, Ooh To Touch And Feel Veronica's Gaping Vagina And Hymen
- Oh, Oh, Oh To Touch And Feel Virgin Girls' Vaginas And Hymens
- Oh, Oh, Oh, To Touch A Females Vagina, Gives Verne A Hardon
- Only Older Octogenarians That Take A Free Viagra Get Very Aroused Here
- Oh, Oh, Onward Through The Airy Facade Viewing Gorgeous Vixens Acessorizing Hopelessly
- You have 1 nose, 2 ears, and 3,4,6 makes my eyes do tricks!
- Another to help remember the types of information these nerves carry (sensory, motor, or both) is thus:
- Some Say Money Matters, But My Brother Says Big Brains Matter More.
- Some Say Marry Money, But My Brother Says Bad Business Marry Money.
- Some Say Marry Money, But My Brother Says Big Brains Matter More.
- Some Say Marry Money, But My Brother Says Big Boobs Matter More.
- Some Say Marry Money, But My Brother Says Big Butts Matter More.
- Small Ships Make Money, But My Brother Says Big Boats Make More.
- Some Say Marilyn Monroe, But My Brother Says Bridgette Bardot Mmmm Mmmmm.
- Some Students Make More Bs More Boys Say Bs Bring More Master.
- Some Say Marry Money But My Brother Says Be Brave Marry Merry.
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