History And Definitions

The first significant contribution to facial nerve anatomy was the description of its course through the temporal bone by Gabriel Fallopius in 1550. The British neurologist Sir Charles Bell made the next important discovery in 1829, when he described that the sensory innervation to the face was provided by cranial nerve V (CN V), whereas the motor function was supplied by cranial nerve VII (CN VII). [ji Over the years, much more has been learned about the anatomy and function of the facial nerve.

The facial nerve has a mixed function, primarily motor, but also sensory and parasympathetic. Consisting of approximately 10,000 fibers, CN VII has two segments, a skeletal motor root (contributing about 70 percent of the axons) and the nervus intermedius, which carries the sensory and autonomic fibers (the remaining 30 percent).[2] A lesion may involve the facial nerve anywhere along its course, and based upon specific signs and symptoms, the location of the pathology can be deduced. A distinction can be made between central and peripheral facial weakness. Because of bilateral supranuclear innervation of the upper facial musculature, a central palsy spares forehead and brow motion. A peripheral palsy, however, involves both upper and lower facial muscles. In addition, with a central palsy, there may be preservation of emotional or involuntary facial motion, which is not seen with a peripheral paralysis. y , [4

The most common cause of facial nerve dysfunction is Bell's palsy, an idiopathic peripheral facial weakness. Named after Sir Charles Bell, Bell's palsy is a diagnosis of exclusion, applied only after other causes of facial paralysis are ruled out.


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