Editing Cranial nerves (section)

==Function==
The cranial nerves provide motor and sensory supply mainly to the structures within the head and neck.  The sensory supply includes both "general" sensation such as temperature and touch, and "special" senses such as [[taste]], [[Visual perception|vision]], [[Olfaction|smell]], balance and [[hearing]].<ref name=Fitzgerald>{{cite book|last=Mtui|first=M.J. Turlough FitzGerald, Gregory Gruener, Estomih|title=Clinical neuroanatomy and neuroscience|year=2012|publisher=Saunders/Elsevier|location=[Edinburgh?]|isbn=978-0-7020-3738-2|page=198|edition=6th}}</ref> The vagus nerve (X) provides sensory and autonomic (parasympathetic) supply to structures in the neck and also to most of the organs in the chest and abdomen.<ref name = Vilensky/><ref name="Kandel" />

===Terminal nerve (0)===
The [[terminal nerve]] (0) may not have a role in humans,<ref name = Vilensky/> although it has been implicated in hormonal responses to smell, sexual response and mate selection.<ref name = Sonne>{{cite journal |last1=Sonne |first1=J |last2=Lopez-Ojeda |first2=W |title=Neuroanatomy, Cranial Nerve 0 (Terminal Nerve) |journal=StatPearls [Internet] |date=January 2019 |pmid=29083731}}</ref>

===Smell (I)===
The [[olfactory nerve]] (I) conveys information giving rise to the sense of smell.<ref name=TC2018 />

Damage to the olfactory nerve (I) can cause an inability to smell ([[anosmia]]), a distortion in the sense of smell ([[parosmia]]), or a distortion or lack of taste.<ref name=TC2018 /><ref name="Kandel Appendix B">{{cite book|last=Kandel|first=Eric R.|title=Principles of neural science|year=2013|publisher=McGraw Hill|location=Appleton and Lange|isbn=978-0-07-139011-8|pages=1533–1549|edition=5.}}</ref>

===Vision (II) ===
The [[optic nerve]] (II) transmits visual information.<ref name="Kandel"/>

Damage to the optic nerve (II) affects specific aspects of vision that depend on the location of the damage. A person may not be able to see objects on their left or right sides ([[homonymous hemianopsia]]), or may have difficulty seeing objects from their outer visual fields ([[bitemporal hemianopsia]]) if the [[optic chiasm]] is involved. Inflammation ([[optic neuritis]]) may impact the sharpness of vision or color detection<ref name=TC2018 />

===Eye movement (III, IV, VI)===
[[File:Lawrence 1960 14.13.png|thumb|The oculomotor (III), troclear (IV) and abducens (VI) nerves supply the muscle of the eye. Damage will affect the movement of the eye in various ways, shown here.|alt=]]

The [[oculomotor nerve]] (III), [[trochlear nerve]] (IV) and [[abducens nerve]] (VI) coordinate [[eye movement]]. The oculomotor nerve (III) controls all muscles of the eye except for the [[superior oblique muscle]] controlled by the trochlear nerve (IV), and the [[lateral rectus muscle]] controlled by the abducens nerve (VI). This means the ability of the eye to look down and inwards is controlled by the trochlear nerve (IV), the ability to look outwards is controlled by the abducens nerve (VI), and all other movements are controlled by the oculomotor nerve (III)<ref name=TC2018 />

Damage to these nerves may affect the movement of the eye. Damage may result in double vision ([[diplopia]]) because the movements of the eyes are not synchronized. Abnormalities of visual movement may also be seen on examination, such as jittering ([[nystagmus]]).<ref name="Kandel Appendix B" />

Damage to the oculomotor nerve (III) can cause double vision and inability to coordinate the movements of both eyes ([[strabismus]]), also eyelid drooping ([[ptosis (eyelid)|ptosis]]) and pupil dilation ([[mydriasis]]).<ref name=Netter2007>{{cite book|first=Neil |last=Norton|title=Netter's head and neck anatomy for dentistry|year=2007|publisher=Saunders Elsevier|location=Philadelphia, Pa.|isbn=978-1-929007-88-2|page=78}}</ref> Lesions may also lead to inability to open the eye due to paralysis of the [[levator palpebrae]] muscle. Individuals suffering from a lesion to the oculomotor nerve, may compensate by tilting their heads to alleviate symptoms due to paralysis of one or more of the eye muscles it controls.<ref name="Kandel Appendix B" />

Damage to the trochlear nerve (IV) can also cause double vision with the eye adducted and elevated.<ref name=Netter2007/> The result will be an eye which can not move downwards properly (especially downwards when in an inward position). This is due to impairment in the superior oblique muscle.<ref name="Kandel Appendix B" />

Damage to the abducens nerve (VI) can also result in double vision.<ref name=Netter2007 /> This is due to impairment in the lateral rectus muscle, supplied by the abducens nerve.<ref name="Kandel Appendix B" />

===Trigeminal nerve (V)===
The [[trigeminal nerve]] (V) and its three main branches the ophthalmic (V1), maxillary (V2), and mandibular (V3) provide sensation to the skin of the face and also controls the muscles of [[mastication|chewing]].<ref name=TC2018 />

{{Trigeminal nerve}}

Damage to the trigeminal nerve leads to loss of sensation in an affected area. Other conditions affecting the trigeminal nerve (V) include [[trigeminal neuralgia]], herpes zoster, sinusitis pain, presence of a [[dental abscess]], and [[cluster headache]]s.<ref name=Nesbitt2012>{{cite journal|author=Nesbitt AD, Goadsby PJ|title=Cluster headache|journal=BMJ (Clinical Research Ed.)|date=Apr 11, 2012|volume=344|pages=e2407|pmid=22496300 |type=Review|doi=10.1136/bmj.e2407|s2cid=5479248}}</ref><ref name=TC2018 />
{{clear}}
[[File:Bellspalsy.JPG|alt=|thumb|The facial nerve (VII) supplies the muscles of facial expression. Damage to the nerve causes a lack of muscle tone on the affected side, as can be seen on the right side of the face here.]]

===Facial expression (VII)===
The [[facial nerve]] (VII) controls most muscles of facial expression, supplies the sensation of taste from the front two-thirds of the tongue, and controls the [[stapedius muscle]].<ref name=TC2018 /> Most muscles are supplied by the cortex on the opposite side of the brain; the exception is the [[frontalis muscle]] of the forehead, in which the left and the right side of the muscle both receive inputs from both sides of the brain.<ref name=TC2018 />

Damage to the facial nerve (VII) may cause [[facial palsy]]. This is where a person is unable to move the muscles on one or both sides of their face.<ref name=TC2018 /> The most common cause of this is [[Bell's palsy]], the ultimate cause of which is unknown.<ref name=TC2018 /> Patients with Bell's palsy often have a drooping mouth on the affected side and often have trouble chewing because the [[buccinator muscle]] is affected.<ref name="Vilensky" /> The facial nerve is also the most commonly affected cranial nerve in [[blunt trauma]].<ref name="pmid29861376">{{cite journal |vauthors=Cools MJ, Carneiro KA |title=Facial nerve palsy following mild mastoid trauma on trampoline |journal=Am J Emerg Med |volume= 36|issue= 8|pages= 1522.e1–1522.e3|date=April 2018 |pmid=29861376 |doi=10.1016/j.ajem.2018.04.034 |s2cid=44106089 }}</ref>

===Hearing and balance (VIII)===
The [[vestibulocochlear nerve]] (VIII) supplies information relating to balance and hearing via its two branches, the [[vestibular nerve|vestibular]] and [[cochlear nerve]]s. The vestibular part is responsible for supplying sensation from the [[vestibules (inner ear)|vestibules]] and [[semicircular canal]] of the [[inner ear]], including information about [[balance (ability)|balance]], and is an important component of the [[vestibuloocular reflex]], which keeps the head stable and allows the eyes to track moving objects. The cochlear nerve transmits information from the [[cochlea]], allowing sound to be heard.<ref name="Kandel"/>

When damaged, the vestibular nerve may give rise to the sensation of spinning and dizziness ([[vertigo]]).  Function of the vestibular nerve may be tested by putting cold and warm water in the ears and watching eye movements [[caloric stimulation]].<ref name = Vilensky/><ref name="Kandel Appendix B"/> Damage to the vestibulocochlear nerve can also present as repetitive and involuntary eye movements ([[nystagmus]]), particularly when the eye is moving horizontally.<ref name="Kandel Appendix B" /> Damage to the cochlear nerve will cause partial or complete [[deafness]] in the affected ear.<ref name="Kandel Appendix B"/>

===Oral sensation, taste, and salivation (IX)===
[[File:Lawrence 1960 16.9.png|thumb|164x164px|A damaged glossopharyngeal nerve (IX) may cause the uvula to deviate to the affected side.|alt=]]
The [[glossopharyngeal nerve]] (IX) supplies the [[stylopharyngeus muscle]] and provides sensation to the [[oropharynx]] and back of the tongue.<ref name = Vilensky/> The glossopharyngeal nerve also provides parasympathetic input to the [[parotid gland]].<ref name = Vilensky />

Damage to the nerve may cause failure of the [[gag reflex]]; a failure may also be seen in damage to the vagus nerve (X).<ref name=TC2018 />

===Vagus nerve (X)===
The [[vagus nerve]] (X) provides sensory and parasympathetic supply to structures in the neck and also to most of the organs in the chest and abdomen.<ref name="Kandel" />

Loss of function of the vagus nerve (X) will lead to a loss of parasympathetic supply to a very large number of structures. Major effects of damage to the vagus nerve may include a rise in blood pressure and heart rate. Isolated dysfunction of only the vagus nerve is rare, but – if the lesion is located above the point at which the vagus first branches off – can be indicated by a hoarse voice, due to dysfunction of one of its branches, the [[recurrent laryngeal nerve]].<ref name="Moore's"/>

Damage to this nerve may result in difficulties swallowing.<ref name="Kandel Appendix B"/>

===Shoulder elevation and head-turning (XI)===
{{multiple image
| image1            = Lawrence 1960 14.14.png
| caption1          = The accessory nerve (XI) supplies the sternocleidomastoid and trapezius muscles. Damage to the nerve may cause a [[winged scapula]], shown here.
| image2            = Unilateral hypoglossal nerve injury.jpeg
| caption2          = The hypoglossal nerve (XII) supplies the muscles of the tongue. A damaged hypoglossal nerve will result in an inability to stick the tongue out straight; here seen in an injury resulting from [[branchial cyst]] surgery.<ref>{{Cite journal|title = A case with unilateral hypoglossal nerve injury in branchial cyst surgery|journal = Journal of Brachial Plexus and Peripheral Nerve Injury|date = 2014-01-01|pmc = 3395866|pmid = 22296879|volume = 7|issue = 1|doi = 10.1186/1749-7221-7-2|first1 = Sudipta|last1 = Mukherjee|first2 = Chandra|last2 = Gowshami|first3 = Abdus|last3 = Salam|first4 = Ruhul|last4 = Kuddus|first5 = Mohshin|last5 = Farazi|first6 = Jahid|last6 = Baksh|page=2 | doi-access=free }}</ref>
| align             = right
| direction         = horizontal
| height1           = 200
}}

The [[accessory nerve]] (XI) supplies the [[sternocleidomastoid muscle|sternocleidomastoid]] and [[trapezius muscle]]s.<ref name=TC2018 />

Damage to the accessory nerve (XI) will lead to weakness in the trapezius muscle on the same side as the damage. The trapezius lifts the shoulder when [[shrug]]ging, so the affected shoulder will not be able to shrug and the shoulder blade ([[scapula]]) will protrude into a [[winged scapula|winged]] position.<ref name = Vilensky /> Depending on the location of the lesion there may also be weakness present in the sternocleidomastoid muscle, which acts to turn the head so that the face points to the opposite side.<ref name=TC2018 />

===Tongue movement (XII)===
The [[hypoglossal nerve]] (XII) supplies the intrinsic muscles of the tongue, controlling tongue movement.<ref name=TC2018 /> The hypoglossal nerve (XII) is unique in that it is supplied by the [[motor cortex|motor cortices]] of both hemispheres of the brain.<ref name="Kandel Appendix B"/>

Damage to the nerve may lead to fasciculations or wasting ([[atrophy]]) of the muscles of the tongue. This will lead to weakness of tongue movement on that side. When damaged and extended, the tongue will move towards the weaker or damaged side, as shown in the image.<ref name="Kandel Appendix B"/> The fasciculations of the tongue are sometimes said to look like a "bag of worms". Damage to the nerve tract or nucleus will not lead to atrophy or fasciculations, but only weakness of the muscles on the same side as the damage.<ref name="Kandel Appendix B"/>