Intraoral mechanoreceptor activity during jaw movement in the anesthetized rabbit.

Abstract

The extracellular activity was recorded of single primary afferent neurons in the mandibular division of the Gasserian ganglion of hemidecerebrate rabbits anesthetized with urethane. Intraoral mechanoreceptors (84) were identified by their receptive-field characteristics; 24 appeared to innervate the periodontal ligament, 31 the tongue, 23 the mucosa of the floor of the mouth and the cheek, and 6 the mandibular symphysis. Their activity patterns were recorded as the jaw was moved by hand and during masticatory movements. None were spontaneously active. Of the 9 incisor periodontal receptors, 8 were slowly adapting, whereas of the 16 molar periodontal afferents, 14 were rapidly adapting. Of lingual and other mucosal mechanoreceptors, 65% were rapidly adapting and were similarly distributed within the mouth. The 6 neurons were classified as sutural receptors because they responded to any stimulus that distorted the mandibular symphysis. With the exception of the latter group, none of the intraoral mechanoreceptors appeared to discharge during imposed movements or mastication unless their receptive fields were contacted. This usually occurs only in the late stages of jaw closure during mastication. A major role of intraoral receptors during mastication is evidently to signal the position of the food bolus within the mouth. It is doubtful that they could make any contribution to the awareness of the jaw position or movement . The modulation of the reflex effects of these afferent neurons by central motor programs is discussed.