7th Cranial Nerve (Facial Nerve) has motor, sensory and autonomic components
·
A
large motor component supplies all the muscles of facial expression
·
A
small sensory component carries taste sensations from the anterior 2/3rd of the
tongue
·
Parasympathetic
efferent supplies salivary glands
Tests for motor functions
·
Inspection
of facial expression
·
Tests
for facial movements, comparing on both the sides
For upper face
·
Ask
the subject to frown, raise the eyebrows and wrinkle the forehead, and to close
the eyes as strongly as possible. In case of facial nerve palsy, the eye on the
affected side cannot be closed completely.
·
Attempt
to open the subject’s eyes while he is forcibly closing them. If the
orbicularis oculi is functioning normally it is almost impossible to do so.
For Lower face
Instruct
the patient to
·
Show
the teeth (in patient of 7th cranial nerve paralysis, the mouth is drawn to the
healthy side)
·
Blow
out the cheeks (a tap on the inflated cheek will cause air to easily escape on
the paralyzed side)
·
Ask
the subject to depress his chin against resistance of your hand, observe the
skin under the chin for contraction of the Platysma muscle.
Tests for Sensory functions
·
Examine
the sense of taste over the anterior 2/3of the tongue, subserved by fibers that
pass from the 5th cranial nerve into the facial nerve through the chorda
tympani. The primary tastes - sweet, salt, bitter and sour should be tested
using sugar, salt, quinine and vinegar respectively.
·
With
the eyes closed ask the subject to protrude the tongue. With a glass rod, place
small quantities of the test solution on each side of the tongue. Ask the
patient to open his eyes and identify the taste.
Note:
·
The
patient should be instructed not to speak because this will cause movement of
the tongue and therefore flow of saliva, carrying taste to both sides and the
posterior third of the tongue.
·
Rinse
the subject’s mouth after each test.
·
Apply
quinine last as its effect is longer lasting than that of the others.
Lesions
Unilateral upper motor neuron lesions
(above the level of pons)
·
Weakness
in movements of the lower part of the face more than those of the upper face.
This is because the upper facial structures are innervated by fibers from both
cerebral hemispheres, while the lower facial movements are controlled largely
by the fibers from the contralateral motor cortex only.
Lower motor neuron lesions (eg. Bell’s
palsy)
·
Occurs
when the nerve is affected anywhere along its pathway from the pons to the
peripheral branches. These lesions involve the whole of one side of the face,
i.e., the same side of the face as the nerve lesion.