The major role of the facial nerve is to innervate
the muscles of facial expression. These can be observed
while taking the history and then more formally assessed
during the neurological examination.
- observe for asymmetry widening of the palpebral
fissure or flattening of the nasolabial fold.
- observe for involuntary facial movements (e.g. hemifacial
spasm, orofacial dyskinesia, myokymia, or synkinesis).
- ask the patient to wrinkle their forehead by raising
their eyebrows and close their eyes tightly. Observe
for asymmetry of ability to burry the eyelashes and
palpate for differences of ability to resist eye opening.
Ask the patient to show their teeth, puff out their
cheeks and appose their lips.
- recall that the efferent limb of the corneal reflex
(see trigeminal nerve) is through the 7th cranial
- although patients may have an asymmetric face, there
should be no facial weakness.
- lower motor neuron weakness causes weakness of the
entire side of the face with equal involvement of
upper and lower facial muscles.
- an upper motor neuron lesion of the contralateral
supranuclear pathway results in weakness primarily
of lower muscles of facial expression. The upper muscles
of facial expression (frontalis and orbicularis oculi)
are much less affected because the facial nucleus
that innervates them receives partial input from the