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'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.

Contents

Names of Nerves

Cranial nerves in non-human vertebrates

Mnemonic devices

See also

External links

References

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''.

'#'	'Name'	'Nuclei'	'Function'
0	Cranial nerve zero (''CN0 is not traditionally recognized.'')[1]	olfactory trigone, medial olfactory gyrus, and lamina terminalis	Still controversial New research indicates CN0 may play a role in the detection of pheromones [2][3]
I	Olfactory nerve	Anterior olfactory nucleus	Transmits the sense of smell
II	Optic nerve	Lateral geniculate nucleus	Transmits visual information to the brain
III	Oculomotor nerve	Oculomotor nucleus, Edinger-Westphal nucleus	Innervates the superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements
IV	Trochlear nerve	Trochlear nucleus	Innervates the superior oblique muscle, which depresses, pulls laterally, and intorts the eyeball
V	Trigeminal nerve	Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus	Receives sensation from the face and innervates the muscles of mastication
VI	Abducent nerve (or ''abducens nerve'')	Abducens nucleus	Innervates the lateral rectus, which abducts the eye
VII	Facial nerve	Facial nucleus, Solitary nucleus, Superior salivary nucleus	Provides motor innervation to the muscles of facial expression and stapedius, receives the special sense of taste from the anterior 2/3 of the tongue, and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland
VIII	Vestibulocochlear nerve (or ''auditory-vestibular nerve'' or ''statoacustic nerve'')	Vestibular nuclei, Cochlear nuclei	Senses sound, rotation and gravity (essential for balance & movement)
IX	Glossopharyngeal nerve	Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus	Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus
X	Vagus nerve	Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus	Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles; provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure; and receives the special sense of taste from the epiglottis
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	Provides motor innervation to the intrinsic muscles of the tongue and other glossal muscles

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.
'O'n 'O'ld 'O'lympus' 'T'owering 'T'ops 'A' 'F'riendly 'V'iking 'G'rew 'V'ines 'a'nd 'H'ops

★ '''OL'd 'OP'ie 'OC'casionally 'TR'ies 'TRIG'onometry 'A'nd 'F'eels 'VE'ry 'GLO'omy, 'VAGU'e, 'A'nd 'HYPO'active''

★ 'O'n 'O'ccasion 'O'ur 'T'rusty 'T'ruck 'A'cts 'F'unny. 'V'ery 'G'ood 'V'ehicle 'A'ny 'H'ow.

★ '''O'n 'O'ld 'O'lympus' 'T'owering 'T'op 'A' 'F'inely 'V'ested 'G'erman 'V'iewed 'A' 'H'awk''

★ '''O'n 'O'ld 'O'lympus' 'T'owering 'T'op 'A' 'F'inn 'A'nd 'G'erman 'V'iewed 'S'ome 'H'ops''

★ 'O'nly 'O'n 'O'ccasion, 'T'ouching 'T'he 'A'morous 'F'emale 'V'irgin 'G'oat 'V'acillates 'A' 'H'and

★ 'OL'ympic 'OP'ium 'OC'cupies 'TR'oubled 'TR'iathletes 'A'fter 'F'inishing 'VE'gas 'G'ambling 'VA'cations 'S'till 'H'igh

★
★ (Note that the Vestibulocochlear nerve is referred to by its former name, 'A'uditory, in this mnemonic.)

★ '''Ol'iver the 'opti'mistic 'oc'topus 'tro'ts 'tri'umphantly 'ab'out 'faci'ng 'audi'ences 'gloss'ily 'vag'uely 'spin'ning 'hippo's.''

★
★ (Note that the accessory nerve is referred to by its alternate name 'S'pinal accessory nerve, and the Vestibulocochlear nerve by its former name, 'A'uditory, in this mnemonic.)

★ '''O'range 'o'rangutans 'o'ften 'tr'y 't'o 'a'void 'f'eeding 'a'ngry 'g'orillas 'v'ery 'a'ncient 'h'otdogs.''

★
★ (Note that the Vestibulocochlear nerve is referred to by its former name, 'A'uditory, in these mnemonics.)

★ '''OL'd 'OPTIC'ians 'OCC'asionally 'T'oo 'TR'y 'A'nd 'F'eel 'AUD'rey 'GLOSSO'p's 'VAG'ina 'AcH!'''

★ '''O'n 'O'ld 'O'lympus' 'T'ufted 'T'op 'A' 'F'at 'A'rmed 'G'erman 'V'iewed 'A'n 'H'op''

★ '''O'h, 'O'h, 'O'h 'T'o 'T'ouch 'A'nd 'F'eel 'V'arious 'G'irls' 'V'aginas 'A'nd 'H'ymens''

★ '''O'h, 'O'h, 'O'h 'T'o 'T'ouch 'A'nd 'F'eel a ''V'ery 'G'ungy' 'V'agina 'A'nd 'H'ymen''

★ '''O'h, 'O'h, 'O'h 'T'o 'T'ouch 'A'nd 'F'eel 'A' 'G'irl's 'V'agina 'A'nd 'H'ymen''

★
★ (Note that the Vestibulocochlear nerve is referred to by its former name, 'A'uditory, in this mnemonic.)

★ '''O'h 'O'h 'O'h 'T'o 'T'ouch 'A'nd 'F'eel 'V'ery 'G'ood 'V'elvet, 'A'h 'H'eaven'''

★ '''O'h, 'O'h, 'O'h, 'T'o 'T'ouch 'A'nd 'F'eel 'V'ery 'G'ood 'V'elvet. 'S'uch 'H'eaven!''

★
★ (Note that the accessory nerve is referred to by its alternate name 'S'pinal accessory nerve in this mnemonic.)

★ '''O'h, 'O'h, 'O'h, 'T'o 'T'ouch 'A'nd 'F'eel 'A' 'G'irl's 'V'agina, 'S'o 'H'ot!''

★ '''O'h, 'O'h, 'O'h, 'T'o 'T'ouch 'A'nd 'F'eel 'V'ery 'G'ross 'V'agina, 'S'o 'A'wesomely 'H'airy!''

★ '''O'oh, 'O'oh, 'O'oh 'T'opless 'T'iffany 'A'nd 'F'at 'V'alerie 'G'ot 'V'aginitis 'A'nd 'H'epatitis''

★ '''O'h 'O'nce 'O'ne 'T'akes 'T'he 'A'natomy 'F'inal 'V'ery 'G'ood 'V'acations 'A're 'H'eavenly''

★ '''OOO' 'T'ruely 'T'here 'A're 'F'ive 'V'ery 'G'orgeous 'V'ixens 'A'waiting 'H'im''

★ '''O'oh, 'O'oh, 'O'oh 'T'o 'T'ouch 'A'nd 'F'eel 'V'eronica's 'G'aping 'V'agina 'A'nd 'H'ymen''

★ '''O'h, 'O'h, 'O'h 'T'o 'T'ouch 'A'nd 'F'eel 'V'irgin 'G'irls' 'V'aginas 'A'nd 'H'ymens''

★ 'O'h, 'O'h, 'O'h, 'T'o 'T'ouch 'A' 'F'emales 'V'agina, 'G'ives 'V'erne 'A' 'H'ardon

★ 'O'nly 'O'lder 'O'ctogenarians 'T'hat 'T'ake 'A' 'F'ree 'V'iagra 'G'et 'V'ery 'A'roused 'H'ere

★ 'O'h, 'O'h, 'O'nward 'T'hrough 'T'he 'A'iry 'F'acade 'V'iewing 'G'orgeous 'V'ixens 'A'cessorizing 'H'opelessly

★ You have '1' nose, '2' eyes, 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:

★ '''S'ome 'S'ay 'M'oney 'M'atters, 'B'ut 'M'y 'B'rother 'S'ays 'B'ig 'B'rains 'M'atter 'M'ore.''

★ '''S'ome 'S'ay 'M'arry 'M'oney, 'B'ut 'M'y 'B'rother 'S'ays 'B'ad 'B'usiness 'M'arry 'M'oney.''

★ '''S'ome 'S'ay 'M'arry 'M'oney, 'B'ut 'M'y 'B'rother 'S'ays 'B'ig 'B'rains 'M'atter 'M'ore.''

★ '''S'ome 'S'ay 'M'arry 'M'oney, 'B'ut 'M'y 'B'rother 'S'ays 'B'ig 'B'oobs 'M'atter 'M'ore.''

★ '''S'ome 'S'ay 'M'arry 'M'oney, 'B'ut 'M'y 'B'rother 'S'ays 'B'ig 'B'utts 'M'atter 'M'ore.''

★ '''S'mall 'S'hips 'M'ake 'M'oney, 'B'ut 'M'y 'B'rother 'S'ays 'B'ig 'B'oats 'M'ake 'M'ore.''

★ '' 'S'ome 'S'ay 'M'arilyn 'M'onroe, 'B'ut 'M'y 'B'rother 'S'ays 'B'ridgette 'B'ardot 'M'mmm 'M'mmmm.''

★ '' 'S'ome 'S'tudents 'M'ake 'M'ore 'B's 'M'ore 'B'oys 'S'ay 'B's 'B'ring 'M'ore 'M'aster.''

★ '' 'S'ome 'S'ay 'M'arry 'M'oney 'B'ut 'M'y 'B'rother 'S'ays 'B'e 'B'rave 'M'arry 'M'erry.''

See also

★ Cranial nerve nucleus

External links

★ Examination of the cranial nerves - University of Toronto Medicine

★

★ CN Medical Notes on rahulgladwin.com

References

1. Fuller GN, Burger PC. "Nervus terminalis (cranial nerve zero) in the adult human." ''Clin Neuropathol'' 9, no. 6 (Nov-Dec 1990): 279-283.
2. Merideth, Michael. "Human Vomeronasal Organ Function." ''Oxford Journals: Chemical Senses'', 2001.
3. Fields, R. Douglas. "Sex and the Secret Nerve." ''Scientific American Mind'', February 2007.