The Facial Nerve

 

The cranial nerve injured in Bell's Palsy is CN-VII (7th cranial nerve). It originates in an area of the brain stem known as the Pons. The 7th nerve passes through the stylomastoid foramen and enters the parotid gland. It divides into its main branches inside the parotid gland. These branches then further divide into 7000 smaller nerve fibers that reach into the face, neck, salivary glands and the outer ear. The nerve controls the muscles of the neck, the forehead and facial expressions, as well as perceived sound volume. It also stimulates secretions of the lower jaw, the tear glands and the salivary glands in the front of the mouth. Taste sensations at the front 2/3 of the tongue and sensations at the outer ear are transmitted by the 7th nerve.

Bells Palsy is caused by an inflammation within a small bony tube called the fallopian canal. The canal is an extremely narrow area. An inflammation within it is likely to exert pressure on the nerve, compressing it. Likewise, if the nerve itself becomes inflamed within this small canal, it can encounter pressure, with the same result of compression. The nerve has not yet exited the skull and divided into its several branches, resulting in impairment of all functions controlled by the 7th nerve. If only part of the face is affected, the condition is not Bell's palsy. (See Comparison of Bellís and Stroke) If, for example, the mouth area is weak but the forehead moves, Bells palsy is ruled out. Trauma induced by tumor, surgery, etc. can occur at a location where the nerve has already divided into its main branches. This type of trauma may spare one or more branches and allow some muscles to remain functional.

 

 

 

FIGURE LEGEND 1. Facial nerve nucleus 2. Trigeminal nerve: Spinal nucleus 3. Superior salivary nucleus 4. Solitary tract 5. Porus acusticus internus 6. Meatal foramen 7. Greater petrosal nerve 8. Sphenopalatine ganglion 9. Maxillary nerve 10. Lacrimal gland 11. Deep petrosal nerve 12. Vidian nerve 13. Nerve to glands of nose and palate   (motor fibers to levator palati muscles) 14.Minor petrosal nerve anastamosis 15. Stapedial nerve 16. Chorda tympani 17. Auricular branch 18. Stylomastoid foramen 19. Lingual nerve 20. Submandibular ganglion 21. Submandibular gland 22. Sublingual gland

 

 

 

Region of the Facial Nerve

The facial nerve takes an interesting course from both a teleological as well as an anatomic perspective.  Anatomically the course of the facial nerve is fascinating for its long canal in the petrous temporal bone (above right) alongside the labyrinth.

 

 

Facial Nerve Anatomy:

http://www.neuro.wustl.edu/neuromuscular/pathol/diagrams/viianat.htm