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Path of the Facial Nerve- Top: Innervation of superficial muscles by the facial nerve (CN

VII) (green), and also some branches of the trigeminal nerve (sensory nerve in this view);

2nd: facial, trigeminal, and other nerves with some muscle tissues removed; 3rd: schematic

course of facial nerve through brainstem and through skull; Bottom: Course of facial nervethrough the temporal bone of skull.

The facial nerve (or seventh cranial nerve, CN VII) carries the signals thatcontrol the movements of the facial muscles, which are the most significantof the muscles that produce facial expressions. Some anatomists identifythe "muscles of facial expression" as those innervated by the facial nerve,but psychologically, eye muscles innervated by third, fourth, fifth, and sixthcranial nerves, orbital muscles partly innervated by CN III, jaw musclesinnervated by the trigeminal nerve (fifth cranial nerve), and some other

relatively minor motor connections of cervical nerves to muscles affectingfacial appearance also play a role in production of facial expressions.

The origin of the facial nerve is a nucleus in the brainstem. According to ananatomy textbook:

The motor nucleus of the facial nerve is located in the ventrolateral part ofthe reticular formation of the pons near its caudal border. Its constituentcells are arranged so as to form a varying number of sub-groups whichmay possibly be concerned with the innervation of individual facial muscles.

From the dorsal aspect of this nucleus there emerge a large number of finebundles of fibers, directed dorsomedially through the reticular formation.These rather widely separated bundles constitute the first part of the root ofthe facial nerve. Beneath the floor of the fourth ventricle the fibers turnsharply rostrad and are assembled into a compact strand of longitudinalfibers, often called the ascending part of the facial nerve. This ascendsalong the medial longitudinal bundle for a considerable distance (5 mm).The nerve then turns sharpy lateralward over the dorsal surface of the

nucleus of the abducens nerve, and helps to form the elevation in therhomboid fossa, known as the facial colliculus. This bend around theabducens nucleus, including the asceding part of the facial nerve, is knownas the genu. The second part of the root of the facial nerve is directedventrolaterally and at the same time somewhat caudally, passing close tothe lateral side of its own nucleus, to make its exit from the lateral part ofthe caudal border of the pons.

The facial nerve courses its way from the brainstem through someproblematic human tissues, which can cause trouble for the functioning of

this nerve. According to Gray's:

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The facial nerve, firmer, rounder, and smaller than the auditory, passesforward and outward upon the middle peduncle of the cerebellum, andenters the internal auditory meatus with the auditory nerve. Within themeatus the facial nerve lies in a groove along the upper and anterior part of

the auditory nerve, and the pars intermedia is placed between the two, andjoins the inner angle of the geniculate ganglion. Occasionally a few of itsfibres pass into the auditory nerve. Beyond he ganglion its fibres aregenerally regarded as forming the chorda tympani.

At the bottom of the meatus, the facial nerve enters the aquaeductusFallopii, and follows the course of that canal through the petrous portion ofthe temporal bone, from its commencement at the internal meatus, to itstermination at the stylo-mastoid foramen. it is at first directed outwardbetween the cochlea and vestibule toward the inner wall of the tympanum;

it then bends suddenly backward and arches downward behind thetympanum to the stylo-mastoid foramen. At the point where it changes itsdirection, it presents a reddish gangliform swelling (intumescentiaganglioformis, or geniculate ganglion). On emerging from the stylo-mastoidforamen it runs forward in the substance of the parotid gland, crosses theexternal carotid artery, and divides behind the ramus of the lower jaw intotwo primary branches, temporo-facial and cervico-facial from whichnumerous offsets are distributed over the side of the head, face, and upperpart of the neck, supplying the superficial muscles in these regions.

Disease organisms attacking tissues through which the facial nerve runscan disorder its funtion. Bell's Palsy is a fairly common facial hemiparalysiscaused by damage to this peripheral nerve, usually by a disease in theinternal meatus or foramen that affects the nerve tract. It usually strikesovernight and gravely frightens its victim who wakes with one side of theface unable to move. Prognosis is for some recovery over several months,and often recovery is complete. A very rare congenital condition is absenceof a functioning facial nerve, which results in a lack of facial expressionsand has catastrophic social consequences. Many other named clinical

abnormalities of the facial nerve are known, all of which, though interestingto the neurologist, have an impact on the life of the victim that is out ofproportion to the small physical damage done, due to the importance offacial expression in normal interpersonal activities.