Mandibular joint control of genioglossus muscle activity in the cat ( Felis domesticus) and monkey ( Macaca irus)

Abstract

Jaw position had a profound influence on genioglossus (GG) muscle activity, the amount of activity varying with the amount of jaw opening. Mandibular rotations of 21 from tooth contact position increased the GG activity which was maintained as long as the jaw was opened. The response could be abolished by bilateral local anaesthesia of the mandibular joint (MJ). Bipolar stimulation of the small branches of the auriculotemporal nerve which supply the joint elicited a reproducible reflex response in the ipsilateral GG muscle with a latency of approximately 10 ms. The reflex could be abolished by administering a muscle relaxant or by severing or anaesthetizing the branches of the auriculotemporal nerve central to the stimulating electrode. Anaesthetizing or severing the nerves supplying the masseter or temporalis muscles did not abolish the GG reflex response to the nerve stimulus or the response to jaw opening. A prior threshold glossopharyngeal (IX) or superior laryngeal (SL) nerve stimulus produced an early facilitation of the GG reflex elicited by threshold MJ stimulation. In contrast, a supra-threshold lingual, IX or SL nerve stimulus resulted in a long-lasting inhibition of the GG reflex. A number of functional relationships may explain the significance of these excitatory and inhibitory responses in the GG muscle.