BILATERALITY OF THE JAW-OPENING REFLEX IN THE CAT

The response of digastric muscles of both sides to unilateral electrical stimulation of teeth, lips and inferior dental nerves was studied with small EMG electrodes. Suprathreshold stimulation of the right lower canine caused contraction of the right digastric after 6-9 ms and of the left after 7-12 ms. Stimulation of the inferior dental nerve excited the right digastric muscle after 5 ms and the left after 6 ms. The peak ipsilateral response amplitude was three times as large as the contralateral. The threshold was 1-4 V for the ipsilateral reflex and 2-7 V for the contralateral. The ipsilateral EMG could follow the stimuli up to 16/s and the contralateral for up to 7.5/s. This suggests that there is at least one more synapse between the afferent and the efferent branches of the crossed opening reflex than in the ipsilateral reflex. Subthreshold tooth and lip stimuli together produced digastric contraction. The digastric response was greatest at wide initial angles of opening and persisted bilaterally when the mandible was divided at the suture. © 1979.