Editing Cranial nerves (section)

==Anatomy==
{{See also|Table of cranial nerves}}Most typically, humans are considered to have twelve pairs of cranial nerves (I–XII), with the [[terminal nerve]] (0) more recently canonized.<ref name="Kandel" /><ref name="Sonne" /> The nerves are: the [[olfactory nerve]] (I), the [[optic nerve]] (II), [[oculomotor nerve]] (III), [[trochlear nerve]] (IV), [[trigeminal nerve]] (V), [[abducens nerve]] (VI), [[facial nerve]] (VII), [[vestibulocochlear nerve]] (VIII), [[glossopharyngeal nerve]] (IX), [[vagus nerve]] (X), [[accessory nerve]] (XI), and the [[hypoglossal nerve]] (XII).
{{Cranial nerves}}{{multiple image
| align             = right
| direction         = vertical
| width             = 250
| image1            = Human brain anterior-inferior view description.JPG
| caption1          = View of the human brain from below showing the cranial nerves on an autopsy specimen
| image2            = Brain human normal inferior view with labels en-2.svg
| caption2          = View from below of the [[Human brain|brain]] and [[brainstem]] showing the cranial nerves, numbered from olfactory to hypoglossal after the order in which they emerge
| image3            = Brain stem sagittal.svg
| caption3          = The brainstem, with [[Cranial nerve nucleus|cranial nerve nuclei]] and tracts shown in red
| total_width       = 
| alt1              = 
}}
===Terminology===

Cranial nerves are generally named according to their structure or function. For example, the olfactory nerve (I) supplies smell, and the facial nerve (VII) supplies the muscles of the face. Because [[Latin]] was the ''[[lingua franca]]'' of the study of [[anatomy]] when the nerves were first documented, recorded, and discussed, many nerves maintain Latin or [[Greek language|Greek]] names, including the trochlear nerve (IV), named according to its structure, as it supplies a muscle that attaches to a pulley ({{langx|el|trochlea}}). The trigeminal nerve (V) is named in accordance with its three components ({{langx|la|trigeminus}} meaning [[wikt:triplet|triplet]]s),<ref>{{cite web|last=Harper|first=Douglas|title=Trigeminal Nerve|url=http://www.etymonline.com/index.php?search=trigeminalnerve|work=Online Etymology Dictionary|access-date=2 May 2014}}</ref> and the vagus nerve (X) is named for its wandering course ({{langx|la|vagus}}).<ref name=Davis2014 />

Cranial nerves are numbered based on their position from front to back ([[anatomical terminology#skull and brain|rostral-caudal]]) of their position on the brain,<ref name=Marieb>{{cite book|last=Mallatt|first=Elaine N. Marieb, Patricia Brady Wilhelm, Jon|title=Human anatomy|year=2012|publisher=Benjamin Cummings|location=Boston|isbn=978-0-321-75327-4|pages=431–432|edition=6th ed. media update.}}</ref> as, when viewing the forebrain and brainstem from below, they are often visible in their numeric order. For example, the olfactory nerves (I) and optic nerves (II) arise from the base of the [[forebrain]], and the other nerves, III to XII, arise from the brainstem.<ref name=Marieb/>

Cranial nerves have paths within and outside the [[Human Skull|skull]]. The paths within the skull are called "intracranial" and the paths outside the skull are called "extracranial". There are many holes in the skull called "foramina" by which the nerves can exit the skull. All cranial nerves are ''paired'', which means they occur on both the right and left sides of the body. The muscle, skin, or additional function supplied by a nerve, on the same side of the body as the side it originates from, is an ''ipsilateral'' function. If the function is on the opposite side to the origin of the nerve, this is known as a ''contralateral'' function.<ref>{{cite book|last1 = Albert|first1=Daniel|title=Dorland's Illustrated Medical Dictionary.|date=2012|publisher=Saunders/Elsevier|location=Philadelphia, PA|isbn=978-1-4160-6257-8|edition=32nd}}</ref>

===Intracranial course===
====Nuclei====

{{main|Cranial nerve nuclei}}
[[Gross anatomy|Grossly]], all cranial nerves have a [[Nucleus (neuroanatomy)|nucleus]]. With the exception of the olfactory nerve (I) and optic nerve (II), all the nuclei are present in the brainstem.<ref name="Kandel" />

The [[midbrain]] has the nuclei of the oculomotor nerve (III) and trochlear nerve (IV); the [[pons]] has the nuclei of the trigeminal nerve (V), abducens nerve (VI), facial nerve (VII) and vestibulocochlear nerve (VIII); and the [[Medulla oblongata|medulla]] has the nuclei of the glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI) and hypoglossal nerve (XII).<ref name="Moore's">{{cite book|author1=Keith L. Moore |author2=Anne M.R. Agur |author3=Arthur F. Dalley|title=Clinically oriented anatomy|year=2010|publisher=Lippincott Williams & Wilkins, Wolters Kluwer|location=Philadelphia|isbn=978-1-60547-652-0|pages=1055–1082|edition=6th}}</ref> The olfactory nerve (I) emerges from the [[olfactory bulb]], and depending slightly on division the optic nerve (II) is considered to emerge from the [[lateral geniculate nucleus|lateral geniculate nuclei]].<ref name="Moore's"/>

Because each nerve may have several functions, the [[nerve fibre]]s that make up the nerve may collect in more than one [[Nucleus (neuroanatomy)|nucleus]]. For example, the trigeminal nerve (V), which has a sensory and a motor role, has [[Trigeminal nerve nuclei|at least four nuclei]].<ref name="Moore's"/><ref name="Fitzgerald"/>

====Exiting the brainstem====
With the exception of the olfactory nerve (I) and optic nerve (II), the cranial nerves emerge from the [[brainstem]]. The oculomotor nerve (III) and trochlear nerve (IV) emerge from the [[midbrain]], the trigeminal (V), abducens (VI), facial (VII) and vestibulocochlear (VIII) from the [[pons]], and the glossopharyngeal (IX), vagus (X), accessory (XI) and hypoglossal (XII) emerge from the [[Medulla oblongata|medulla]].<ref name=OBER1998>{{cite book|last2=Ober|first1=Frederic H. |last1=Martini |first2=William C.|title=Fundamentals of anatomy and physiology|year=1998|publisher=Prentice Hall International|location=London|isbn=978-0-13-010436-6|pages=474–485|edition=4th | others=coordinator, art; photographer, illustrator, Claire W. Garrison, illustrator, Kathleen Welch, clinical consultant, Ralph T. Hutchings, biomedical}}</ref>

The olfactory nerve (I) and optic nerve (II) emerge separately. The olfactory nerves emerge from the [[olfactory bulb]]s on either side of the [[crista galli]], a bony projection below the [[frontal lobe]], and the optic nerves (II) emerge from the lateral colliculus, swellings on either side of the [[temporal lobe]]s of the brain.<ref name=OBER1998 />

====Ganglia====
{{main|Cranial nerve ganglia}}
The cranial nerves give rise to a number of [[ganglia]], collections of the [[cell body|cell bodies]] of neurons in the nerves that are outside of the brain. These ganglia are both parasympathetic and sensory ganglia.<ref name="Moore's"/>

The sensory ganglia of the cranial nerves, directly correspond to the [[dorsal root ganglia]] of [[spinal nerve]]s and are known as [[cranial nerve ganglia]].<ref name="Marieb"/> Sensory ganglia exist for nerves with sensory function: V, VII, VIII, IX, X.<ref name="Kandel" /> There are also a number of [[parasympathetic ganglion|parasympathetic]] [[cranial nerve ganglion|cranial nerve ganglia]]. [[sympathetic ganglion|Sympathetic ganglia]] supplying the head and neck reside in the upper regions of the [[sympathetic trunk]], and do not belong to the cranial nerves.<ref name="Moore's"/>

The ganglion of the sensory nerves, which are similar in structure to the dorsal root ganglion of the [[spinal cord]], include:<ref name=GRAYS2005 />
* The [[trigeminal ganglia]] of the trigeminal nerve (V), which occupies a space in the [[dura mater]] called [[Meckel's cave]]. This ganglion contains only the sensory fibres of the trigeminal nerve.
* The [[geniculate ganglion]] of the facial nerve (VII), which occurs just after the nerve enters the [[facial canal]]. 
* A superior and inferior ganglia of the glossopharyngeal nerve (IX), which occurs just after it passes through the [[jugular foramen]].

Additional ganglia for nerves with [[Parasympathetic system|parasympathetic]] function exist, and include the [[ciliary ganglion]] of the oculomotor nerve (III), the [[pterygopalatine ganglion]] of the maxillary nerve (V2), the [[submandibular ganglion]] of the [[lingual nerve]], a branch of the facial nerve (VII), and the [[otic ganglion]] of the glossopharyngeal nerve (IX).<ref name="Purves" >{{cite book | author1 = Purves, Dale |author2=George J. Augustine |author3=David Fitzpatrick |author4=William C. Hall |author5=Anthony-Samuel LaMantia |author6=James O. McNamara |author7=Leonard E. White | title = Neuroscience. 4th ed. | publisher = Sinauer Associates | pages = 12–13 | year = 2008 | isbn = 978-0-87893-697-7}}</ref>

====Exiting the skull and extracranial course====
{| class="wikitable" style="float:right;margin-left:15px"
|+ Exits of cranial nerves from the skull.<ref name="Moore's"/><ref name=GRAYS2005>{{cite book|last=Drake|first=Richard L.|title=Gray's anatomy for students|year=2005|publisher=Elsevier/Churchill Livingstone|location=Philadelphia|isbn=978-0-8089-2306-0|author2=Vogl, Wayne |author3=Tibbitts, Adam W.M. Mitchell  |author4=illustrations by Richard |author5= Richardson, Paul |pages=800–807}}</ref>
|-
! Location !! Nerve
|-
| [[cribriform plate]] || Terminal nerve (0) 
|-
| [[cribriform plate]] || Olfactory nerve (I) 
|-
| [[optic foramen]] || Optic nerve (II)
|-
| [[superior orbital fissure]] || Oculomotor (III)<br/>Trochlear (IV)<br/>Abducens (VI)<br/>Trigeminal V1<br/>     ''([[Ophthalmic nerve|ophthalmic]])''
|-
| [[foramen rotundum]]|| Trigeminal V2 <br/>     ''([[maxillary nerve|maxillary]])''
|-
| [[foramen ovale (skull)|foramen ovale]]|| Trigeminal V3 <br/> ''([[Mandibular nerve|mandibular]])''
|-
| [[stylomastoid foramen]]|| Facial nerve (VII)
|-
| [[internal auditory canal]]|| Vestibulocochlear (VIII)
|-
| [[jugular foramen]] || Glossopharyngeal (IX) <br/>Vagus (X)<br/>Accessory (XI)
|-
| [[hypoglossal canal]] || Hypoglossal (XII)
|}

After emerging from the brain, the cranial nerves travel within the [[skull]], and some must leave it in order to reach their destinations.  Often the nerves pass through holes in the skull, called [[foramen|foramina]], as they travel to their destinations. Other nerves pass through bony canals, longer pathways enclosed by bone. These foramina and canals may contain more than one cranial nerve and may also contain blood vessels.<ref name=GRAYS2005 />
*The terminal nerve (0) is a thin network of fibers associated with the dura and lamina terminalis running rostral to the olfactory nerve, with projections through the cribriform plate.
* The olfactory nerve (I) passes through perforations in the [[cribriform plate]] part of the [[ethmoid bone]].  The nerve fibres end in the upper nasal cavity.
* The optic nerve (II) passes through the [[optic foramen]] in the [[sphenoid bone]] as it travels to the eye.
* The oculomotor nerve (III), trochlear nerve (IV), abducens nerve (VI) and the ophthalmic branch of the trigeminal nerve (V1) travel through the [[cavernous sinus]] into the [[superior orbital fissure]], passing out of the skull into the [[Orbit (anatomy)|orbit]].
* The maxillary division of the trigeminal nerve (V2) passes through [[foramen rotundum]] in the sphenoid bone.
* The mandibular division of the trigeminal nerve (V3) passes through [[foramen ovale (skull)|foramen ovale]] of the sphenoid bone.
* The facial nerve (VII) and vestibulocochlear nerve (VIII) both enter the [[internal auditory canal]] in the [[temporal bone]].  The facial nerve then reaches the side of the face by using the stylomastoid foramen, also in the temporal bone.  Its fibers then spread out to reach and control all of the muscles of facial expression.  The vestibulocochlear nerve reaches the organs that control balance and hearing in the temporal bone and therefore does not reach the external surface of the skull.
* The glossopharyngeal (IX), vagus (X) and accessory nerve (XI) all leave the skull via the jugular foramen to enter the neck. The glossopharyngeal nerve provides sensation to the upper throat and the back of the tongue, the vagus supplies the muscles in the [[larynx]] and continues downward to supply parasympathetic supply to the chest and abdomen.  The accessory nerve controls the trapezius and sternocleidomastoid muscles in the neck and shoulder.
*[[File:Cranial Nerves Anatomy in Schematic 3D.ogg|thumb|Schematic 3D model of the cranial nerves]]The hypoglossal nerve (XII) exits the skull using the hypoglossal canal in the [[occipital bone]].