When the facial nerve is paralyzed, the patient loses what Ballance and Duel have so aptly named "the language of facial expression." Emotional movements and the power of voluntary movement are both destroyed.
Only when absolutely symmetrical impulses reach the facial muscles on both sides at exactly the same moment will a patient exposed to emotional stimulation be able to react normally. Such impulses can only originate in the facial nuclei, because the symmetry and synchronism of the emotional movements of the face are dependent on the close cooperation of the cortical facial centers of both hemispheres.
Voluntary movements on the other hand can be performed if only nervous impulses from any suitable center in the brain reach the muscles concerned.
This is illustrated in Figure 1. During a mastoidectomy performed elsewhere, the facial nerve had been cut and the distal end of the facial nerve had been anastomosed to
KETTEL K. Surgical Repair Versus Expectant Treatment in Traumatic Facial Palsy. AMA Arch Otolaryngol. 1960;71(4):623–627. doi:10.1001/archotol.1960.03770040023004
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