The motor innervation of the soft palate. An anatomical study in guinea pigs and monkeys.

In an effort to gain a more precise understanding of the motor innervation of the soft palate, a neuroanatomical tracer (horseradish peroxidase) was injected into the vela of nine guinea pigs and four monkeys. After 48 h the animals were sacrificed and frozen frontal sections were appropriately reacted with tetramethylbenzidine and counterstained with neutral red, and then evaluated by means of light microscopy. In all specimens retrogradely labeled neurons appeared in the brain stem. The distribution patterns of these labeled cells were to a large degree comparable in both the guinea pigs and the monkeys. The complex motor innervation of the soft palate was found to involve at least five different centers, with the strongest staining seen in the nucleus ambiguus and the motor nucleus of the trigeminal nerve. Additional cells of origin were discernible in the retrofacial nucleus. Facial neurons, however, were labeled only occasionally. Findings also showed that a previously undescribed component from the hypoglossal nerve appears to be essential for lateral soft palate movement in both animal models.