Testing The Facial Nerve
Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly (inability to do so is called 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 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).
Corneal reflex. The afferent arc is mediated by the General Sensory afferents of the Trigeminal Nerve. The efferent arc occurs via the Facial Nerve. The reflex involves consensual blinking of both eyes in response to stimulation of one eye. This is due to the Facial Nerve's innervation of the muscles of facial expression, namely Orbicularis oculi, responsible for blinking. Thus, the corneal reflex effectively tests the proper functioning of both Cranial Nerves V and VII.
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