of the 7th Cranial Nerve
is the 7th Cranial Nerve located?
7th Cranial Nerves are located on either side of the brainstem, at the
top of the medulla.
is the function of the 7th Cranial Nerve?
function of each of the two 7th cranial nerves is facial movement on the
same side (ipsilateral). Left sided forehead wrinkle, left
eyelid closure, and movement of the left half of the face is stimulated
by the left 7th cranial nerve. Lacrimation (tearing) and salivation
is also stimulated by the 7th cranial nerve.
cranial nerve also has some sensory component including the sense of taste
(anterior 2/3 of the tongue).
are the symptoms of 7th Cranial Nerve injury?
facial movement occurs when a message is sent from the right cerebral
cortex (from the motor strip) crossing over to stimulate the left
7th cranial nerve. Activation of the 7th cranial nerve causes the
entire left side of the face to move.
Palsy, or a true left 7th cranial nerve paralysis causes paralysis
of the entire left side of the face. This includes loss of
the ability to wrinkle the left forehead on the affected side.
Other symptoms include an inability to close the eyelid on the affected
side, ipsilateral dryness of the eye (with risk for corneal ulceration),
dryness of the mouth, and decreased sense of taste.
of the close proximity to the 8th cranial nerve, balance and hearing should
also be assessed when the 7th cranial nerve is damaged.
findings - upper versus lower motor neuron dysfunction.
paralysis can also occur as a result of damage to the cerebral cortex or
motor nerves that carry the message to the 7th cranial nerve on the opposite
side (upper motor neuron injury). Thus, right cerebral
cortex injury prevents the left 7th cranial nerve from being stimulated,
causing left sided facial weakness.
wrinkle is the one clinical feature that can differentiate the cause of
a facial weakness. The forehead receives duel innervation....one
pathway from the right cerebral cortex and another from the left cerebral
cortex. These messages then stimulate the forehead wrinkle.
If a left sided facial weakness is caused by an injury to the right cerebral
cortex, the duel innervation of the forehead will result in facial weakness
below the forehead, with preservation of bilateral forehead wrinkle.
With facial weakness that is caused by a 7th cranial nerve injury, the
weakness will extend to include the forehead on the affected side (making
it look "ironed out" on the side of the 7th cranial nerve injury).