The motor nerve supply of the velopharyngeal muscles.

The present study attempted to clarify the motor nerve supply of the velopharyngeal muscles. Experiments were carried out on 20 anesthetized rhesus monkeys. Evoked EMG responses of the levator veli palatini, uvula, and superior constrictor pharyngeus muscles, which seem to contribute to velopharyngeal closure, were analyzed by stimulating the cranial nerves within the skull. Results were as follows: 1. Muscle action potentials (M-waves) from the selected muscles could be recognized on stimulating the facial, glossopharyngeal, and vagus nerves at the petrosal area of the temporal bone but were not noted upon accessory nerve stimulation. 2. At maximal stimulation, the vagus gave a greater increase in muscle amplitude than the other nerves studied. This was followed by the glossopharyngeal with the facial nerve producing the least increase in amplitude. 3. Also at maximal stimulation, latencies in the response of the levator veli palatini and uvula muscles were reduced to the greatest degree by stimulation of the vagus, to a lesser extent for the glossopharyngeal, and least for the facial nerve. 4. On stimulating the facial nerve below the stylomastoid foramen, M-waves could not be recognized. From the present study, it was concluded that the levator veli palatini, uvula, and superior constrictor pharyngeus muscles are double innervated by the facial nerve and branches of the pharyngeal plexus derived from the glossopharyngeal and vagus nerves and that the facial nerve plays an important role as one of the motor nerves in movements responsible for velopharyngeal closure.