Tongue movements--brainstem mechanisms and clinical postulates.

Specific excitatory and inhibitory influences on protrusive (P) and retrusive motoneurons in the hypoglossal nucleus of cat have been documented. Stimuli delivered to peripheral branches of the auriculotemporal nerve which innervate the temporomandibular joint activate both genioglossus (GG) single units and synaptically-evoked responses in P motoneurons. Similarly, stimuli delivered to the glossopharyngeal (IX) and superior laryngeal nerves activate P motoneurons. Any one of these three stimuli may contribute to the various responses in which the GG muscle is known to participate. In contrast, stimuli applied to the tongue itself (lingual and IX nerves) result in a retrusive tongue movement. These brainstem mechanisms suggest specific therapy regimens for the treatment of skeletal open-bite malocclusions where resting tongue posture appears to be a primary etiological factor.