A lateral jaw movement reflex

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Abstract

Pressure of at least 300 g, when applied rapidly to the labial or lingual surface of a maxillary central incisor of lightly anesthetized decerebrate rabbits, caused the mandible to swing to the opposite side, where it would remain for 2–10 sec if the pressure were maintained. On the contralateral side, the zygomaticomandibular and anterior temporal muscles showed the highest levels of maintained activity. The digastric muscle was sometimes active at the start of stimulation while the superficial masseter became active later and returned the mandible to the midline. The external pterygoid muscles of both sides fired at the start of stimulation. Other muscles ipsilateral to the applied stimulus were inhibited. Section of the infraorbital nerve above, but not below, its union with the anterior superior alveolar nerves abolished the reflex response when pressing on the incisor of that side. A similar reflex could be elicited by electrical stimulation of the pericoronal incisal gingivae or adjacent palatal mucosa if the stimulus frequency was greater than 7 Hz. Using a stimulus of 30 Hz, 6–15 v, 1 or 2 msec, reflex activity began in the zygomaticomandibular and anterior temporal EMG 80–210 msec from the beginning of the pulse train. Evoked activity followed each stimulus with a latency of 9.0–16.0 msec. This reflex could act during chewing to modify the basic central masticatory pattern.

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    This study was supported by the Medical Research Council of Canada, a Fellowship to J. P. Lund and a Research Grant to P. G. Dellow.

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