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The course and connections of the Facial Nerve in the Temporal Bone
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The 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 .
Its main function is motor control of most of the
Facial Muscles and the stapedius muscle of the middle
Ear . It also supplies
Parasympathetic fibres to the
Submandibular Gland and
Sublingual Gland s via
Chorda Tympani Nerve and the
Submandibular Ganglion , and to the
Lacrimal Gland via the
Pterygopalatine Ganglion . In addition, it receives
Taste sensations from the anterior two-thirds of the
Tongue and sends them to the nucleus of solitary tract. There is also a small amount of cutaneous sensation carried by the
Nervus Intermedius from the skin in and around the
Auricle (earlobe).
Fig. 788 - Plan of the facial and intermediate nerves and their communication with other nerves.]]
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 Acoustic Canal (intimately close to the
Inner Ear ) then runs a tortuous course (including two tight turns) through the
Fallopian Canal , emerges from the
Stylomastoid Foramen and passes through the
Parotid Gland , where it divides into five major branches. Though it passes through the paratid 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.
The five main branches of the facial nerve are, from top to bottom:
- temporal 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 helpful mnemonic device for remembering the major branches is the phrase, "To Zanzibar By Motor Car".
Aside from the five main branches, the facial nerve also gives rise to the
Posterior Auricular Nerve which controls movements of some of the scalp muscles around the ear.
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.
See
Facial Nucleus .
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).
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.
