The course and connections of the facial nerve in the temporal bone.
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|colspan="2"|n. facialis
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|colspan="2"|[subject #202 ]
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|Innervates
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|MeSH
|colspan="2"|[A08.800.800.120.250]
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|Dorlands/Elsevier
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The facial nerve is seventh 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.
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.
No other nerve in the body travels such a long distance through a bony canal.
A helpful mnemonic device for remembering the major branches is the phrase, "To Zanzibar By Motor Car".
Two divisions occur in the parotid gland - temporofacial and cervicofacial divisions. The temporofacial division is made up of: temporal branch, zygomatic branch and buccal branch. Cervicofacial branch is made up of cervical branch, marginal mandibular branch and buccal branch. The two buccal branches later join.
Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly, pursing the lips and puffing out the cheeks, all test the facial nerve. There should be no noticeable asymmetry.
In an upper motor neuron lesion, only the lower part of the face will be affected, due to the bilateral control to the upper facial muscles.
Taste can be tested on the anterior 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).
Facial nerve 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.
