Alternate Innervations of Facial Musculature

There have been several case reports in which spontaneous return of facial function has occurred without grafting or other surgical intervention. This implies that there may be alternate pathways to explain this phenomenon. Using the technique of retrograde axonal transport with chromogens tagged to the marker enzyme horseradish peroxidase, selected facial muscles of the monkey were injected to demonstrate CNS representation. The facial nucleus was identified, exhibiting topographic arrangement in the CNS. More importantly, in several specimens, nuclear cells of the mesencephalic tract also were stained. This is part of the trigeminal system, normally associated with proprioception, whose axons travel with other fifth cranial nerve branches. The trigeminal motor nucleus did not exhibit any pickup of the enzyme marker, indicating that there was no contamination from facial musculature innervated by the fifth cranial nerve. This finding suggests that the facial musculature, normally innervated by the seventh cranial nerve, has an additional nerve supply.