Abstract
Several investigators on their clinical and experimental studies have indicated that velar function might be effected by the tongue position. The present study was designed to analyse a neuro physiological relation between the tongue and velar movement.
An experimental model usin g anesthetized dog was established. The afferents of the glossopharyngeal nerve (IX) was exposed at the level of the cricothyroid cartilage. Twin platium wire electrodes were placed perorally into the levator veli palatini muscle of ipsilateral side. It was ascertained that a single stimulus generated by an electrical amplifier to the IXth afferent induced the levator reflex of an amplitude of 80-360μV with a latency of 16-28 m ec. That kind of stimulation did not elicite a swallowing reflex in th e series of the present experiment.
After the exp erimental model was provided, the lingual and hypoglossal nerves of the ipsilateral side were stimulated electrically to clarify an intricate function of those nerves to the levator contracture. The results were summarized as followings:
1) When conditionin g stimulus to the peripheral end of the dissected hypoglossal nerve 100-200m sec prio- toasingle stimulus to the IXth afferent, the levator reflex was inhibited.
2) The protrusion and retractor nerves were divided at the peripheral end of the hypoglossal nerve. The same inhibition to the reflex mentioned above was observed when a conditioning stimulus was given to the protrusion nerve. The finding of inhibition did not occur when a stimulus was given to the retractor nerve.
3) An inhibition of the reflex elicited by the protrusion nerve stimulation was eliminated when the lingual nerve was cut.
It is concluded that the levator reflex induced by the IXth afferent stimulation was controlled by the protrusion nerve of the hypoglossal nerve via the lingual nerve. In the control mechanism, the protrusion nerve seems to be an antagonist to the levator contracture.
