Facial nerve

The facial nerve is the seventh (VII) of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and taste to the anterior two-thirds of the tongue. It also supplies preganglionic parasympathetic fibers to several head and neck ganglia.

Course

The motor part of the facial nerve arises from the facial nerve nucleus in the pons while the sensory part of the facial nerve arises from the nervus intermedius.

The motor part of the facial nerve enters the petrous temporal bone into the internal auditory meatus (intimately close to the inner ear) then runs a tortuous course (including two tight turns) through the facial canal, emerges from the stylomastoid foramen and passes through the parotid gland, where it divides into five major branches. Though it passes through the parotid gland, it does not innervate the gland. This action is the responsibility of cranial nerve IX, the glossopharyngeal nerve.

The facial nerve forms the geniculate ganglion prior to entering the facial canal.

No other nerve in the body travels such a long distance through a bony canal.

Branches

Inside the internal acoustic meatus

Greater petrosal nerve - provides parasympathetic innervation to lacrimal gland, sphenoid sinus, frontal sinus, maxillary sinus, ethmoid sinus, nasal cavity, as well as special sensory taste fibers to the palate via the Vidian nerve.
Nerve to stapedius - provides motor innervation for stapedius muscle in middle ear
Chorda tympani - provides parasympathetic innervation to submandibular gland and sublingual gland and special sensory taste fibers for the anterior 2/3 of the tongue.
branch to the tympanic plexus

Outside skull (distal to stylomastoid foramen)

Posterior auricular nerve - controls movements of some of the scalp muscles around the ear
Branch to Posterior belly of Digastric and Stylohyoid muscle
Five major facial branches (in parotid gland) - from top to bottom:
Temporal (frontal) branch of the facial nerve
Zygomatic branch of the facial nerve
Buccal branch of the facial nerve
Marginal mandibular branch of the facial nerve
Cervical branch of the facial nerve

A traditional mnemonic device for the five major branches of the facial nerve is, "The Zebra Bit My Cat." Another mnemonic for this is, "Today Zoe Broke My Car", or "To Zanzibar By Motor Car" and "The Zoo Bought Monkey Clothes", or more commonly among medical students "Ten Zebras Buggered My Cunt".

Embryology

The facial nerve is developmentally derived from the hyoid arch (second pharyngeal branchial arch).

Function

Efferent

Its main function is motor control of most of the muscles of facial expression. It also innervates the posterior belly of the digastric muscle, the stylohyoid muscle, and the stapedius muscle of the middle ear. All of these muscles are striated muscles of branchiomeric origin developing from the 2nd pharyngeal arch.

The facial also supplies parasympathetic fibers to the submandibular gland and sublingual glands via chorda tympani. Parasympathetic innervation serves to increase the flow of saliva from these glands. It also supplies parasympathetic innervation to the nasal mucosa and the lacrimal gland via the pterygopalatine ganglion.

The facial nerve also functions as the efferent limb of the corneal reflex and the blink reflex.

Afferent

In addition, it receives taste sensations from the anterior two-thirds of the tongue and sends them to the nucleus of solitary tract. The facial nerve also supplies a small amount of afferent innervation to the oropharynx above the palatine tonsil. There is also a small amount of cutaneous sensation carried by the nervus intermedius from the skin in and around the auricle (earlobe).

Location of Cell Bodies

The cell bodies for the facial nerve are grouped in anatomical areas called nuclei or ganglia. The cell bodies for the afferent nerves are found in the geniculate ganglion for both taste and general afferent sensation. The cell bodies for muscular efferent nerves are found in the facial motor nucleus whereas the cell bodies for the parasympathetic efferent nerves are found in the superior salivatory nucleus.

Pathology

People may suffer from acute facial nerve paralysis, which is usually manifested by facial paralysis. Bell's palsy is one type of idiopathic acute facial nerve paralysis, which is more accurately described as a multiple cranial nerve ganglionitis that involves the facial nerve, and most likely results from viral infection and also sometimes as a result of Lyme disease. Iatrogenic Bell's Palsy may also be as a result of an incorrectly placed dental local-anesthetic (Inferior alveolar nerve block). Although giving the appearance of a hemi-plegic stroke, effects dissipate with the drug.

Testing the facial nerve

Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly (lagophthalmos) , pursing the lips and puffing out the cheeks, all test the facial nerve. There should be no noticeable asymmetry.

In an UMN lesion, called central seven, only the lower part of the face on the contralateral side will be affected, due to the bilateral control to the upper facial muscles (frontalis and orbicularis oculi).

Lower motor neuron lesions can result in a CNVII palsy (Bell's palsy is the term used to describe the idiopathic form of facial nerve palsy), manifested as both upper and lower facial weakness on the same side of the lesion.

Taste can be tested on the anterior 2/3 of the tongue. This can be tested with a swab dipped in a flavoured solution, or with electronic stimulation (similar to putting your tongue on a battery).

Translation of "Facial nerve"

Arabic: عصب وجهي, Catalan: Nervi facial, German: Nervus facialis, Spanish: Nervio facial, French: Nerf facial, Galician: Nervio facial, Italian: Nervo faciale, Lithuanian: Veidinis nervas, Hungarian: Arcideg, Dutch: Nervus facialis, Japanese: 顔面神経, Norwegian (Bokmål): Nervus facialis, Polish: Nerw twarzowy, Portuguese: Nervo facial, Russian: Лицевой нерв, Serbian: Живац лица, Finnish: Kasvohermo, Swedish: Ansiktsnerven, Thai: เส้นประสาทเฟเชียล, Chinese: 顏面神經.