Conjugate Deviation
8. Clench your teeth and pull the corners of your mouth forcefully downward with a grimace, revealing your platysma
At rest, the patient with a seventh nerve lesion has, on the paretic side,
• An eye open wider than on the normal side; it does not blink; increased tears are stimulated by the dry and irritated cornea and flow over the paretic cheek.
• A flat, creaseless forehead
• A flat, sometimes drooping cheek
• The corner of the mouth lower than on the normal side
• A “flappy,” loose cheek as he talks
• The midsagittal line of the mouth pulled over to the normal side
At rest, the patient with a facial weakness may look perfectly normal or show a minor flattening and asymmetry.
Remember that normal elderly people may have an asymmetrical lower face at rest. This is because of an asymmetrical loss of teeth, a lifetime habit of talking out of the corner of the mouth, or simple passage of time. (Look carefully at the next 12 people over 65 years of age that you meet. Most of them have some asymmetry about the mouth and difference in the depth of the two nasolabial folds.)
The patient with a seventh nerve lesion is equally unable to perform vol-untary, reflex, or emotional movements of half of the face.
In contrast, the patient with a facial weakness has paresis and slowness, mostly of the lower half of the face, for voluntary movements but smiling is normal and symmetrical. If you can make him laugh, the paretic side of the face seems to move as well or more than the normal side. Why? Either emo-tional facial movements have bilateral supranuclear connections (which is probably correct) or the upper motor neuron for voluntary movements is completely different from the supranuclear fibers concerned with smiling, frowning, laughing, and crying. A patient with a hemifacial defect for emo-tional movements only, but a normal face for voluntary movements and a solitary lesion in the opposite thalamus, has been described (See N Engl J Med 1998; 338(21):1515).
Blinking
Watch the patient blink. If he blinks less often than you do, he may have parkinsonism or may be abusing some sedative. The eyes blink at exactly the same moment and the eye is completely covered with each blink. If he
Eye lashes
"tucked in"
Wrinkling
Nasolabial folds
Corner of the mouth:
distance from midline and rate of retraction
Figure 8-6. A. Testing the frontalis muscle and seventh nerve function by asking the pa-tient to repeatedly wrinkle and relax the forehead in the direction of the arrows.
B. Forceful eye closing reveals the symmetry of eyelash tucking, wrinkling around the eyes, depth of the nasolabial folds, and retraction of the corners of the mouth. {Continued)
CRANIAL NERVES 1,5, AND 7 / 101
Platysma
Figure 8-6 (continued). C. The patient purses his iips together and distends his cheel<s by biowing into them. Tap one cheel< and then the other Air wiii escape between the iips on the weai< side. D. Cienching the teeth and forcefuiiy puiiing the corners of the mouth downward reveais the symmetry of mouth movement and the piatysma.
blinks less often on the right side or does not cover the entire right eye with each blink, he has a partial right seventh nerve lesion, new or old. This is never the result of an upper motor neuron facial weakness or a fifth cranial nerve lesion. Asynchronous blinking is most often seen in the patient with a partially recovered Bell’s palsy.
Sensory and Autonomic
The intermediate nerve or sensory root of cranial nerve 7 emerges from the brain stem between the facial motor root and the vestibular (eighth) nerve.
If it had its own cranial nerve number, it would be 71/2. Its functions are
• Taste—From the anterior two thirds of the tongue, cells are in the genicu-late ganglion, and central termination is on the rostral part of the solitary nucleus. The peripheral pathway is via the chorda tympani and lingual nerves.
• Saliva—The cells are in the dorsolateral reticular formation, called the su-perior salivatory nucleus. Fibers that are preganglionic and parasympa-thetic travel in the intermediate nerve, then in the chorda tympani and lin-gual nerves to the submandibular ganglion. Postganglionic fibers go to the submandibular and sublingual salivary glands.
• Tears—Have the same reticular formation cells of origin as described above for saliva. Parasympathetic preganglionic fibers leave the intermedi-ate nerve to enter the greintermedi-ater superficial petrosal nerve to the pterygopala-tine ganglion. Postganglionic fibers go to the lacrimal gland, and secretory and vasomotor fibers proceed to the mucous membrane of the nose and mouth.
• Pain fibers—Are from the external auditory canal and behind the ear. The fibers are part of the intermediate nerve, and the nucleus is part of the spinal trigeminal tract. Most patients with a seventh nerve palsy complain of numbness over the cheek but have no demonstrable sensory loss to touch, pain, or temperature examination on the cheek or anywhere else.
Taste, Tears, and Saliva Taste from the anterior two thirds of the tongue is an afferent function of the seventh nerve. Taste from the posterior tongue and palate is via the glossopharyngeal nerve, which is more important than the seventh nerve in this function.
From the anterior two thirds of the tongue the pathway is complex as fol-lows: (a) the fibers are first in the lingual nerve, which is a branch of the mandibular (the third division of the trigeminal); (b) they are then in the chorda tympani nerve (a branch of cranial nerve 7) to their cell station, which is the geniculate ganglion; and (c) from here are in the intermediate nerve, which is the sensory root of the seventh cranial nerve.
CRANIAL NERVES 1,5, AND 7 / 103
Centrally, the fibers connect with the nucleus of the solitary tract and prob-ably to both ipsilateral and contralateral thalamus and sensory cortex.
How to Test Taste
1. Ask the patient to protrude his tongue. Place the dorsal surface of your left index finger horizontally against his chin. Hold a tissue draped over your index finger. When the tongue comes out over your finger, grasp it between your index finger and thumb, using the tissue to improve your grip (Figure 8-7). Tell the patient not to try to answer but to hold up his hand if he tastes something.
2. Use a slightly damp applicator stick dipped in granulated sugar or