Neurophysiological Studies on the Mechanisms of the Jaw Tongue Reflex in the Cat

Abstract

Tongue was reflexly retracted by passive depression of the mandible in adecerebrate cat. The purpose of this study is to clarify the mechanisms of this “Jaw-Tongue Reflex”. Electromyographic activities of jaw closing muscles and of extrinsic tongue muscles were recorded during this reflex. Results obtained were as follows.1) The styloglossal and the genioglossal muscles were activated by passive depression of the mandible, while the hyoglossal muscle was not.2) These tongue muscle activities were elicited when the mouth was opened beyond 10deg;, while activities of the masticatory muscle were induced by only 2deg; of opening.3) The Jaw-tongue reflex was not affected by neither masseter nerve sectioning noranesthetization of the temporomandibular joint capsule.4) Exfoliation of the temporal muscle from the attachment to the temporal bone greatly reduced tongue muscle activities at the jaw-tongue reflex. Extension of the temporal muscle induced by downward stretch of the isolated coronoid process of the mandible elicited the tongue muscle activities.5) Repetitive electrical stimulation (100Hz, 0.1msec) of the temporal nerve activated tongue muscle activities, and the threshold of this activation was between 1.3 and 1.7 times threshold of the temporal nerve.6) Vibratory stimuli applied to the mandible at a frequency of less than 130Hz were also effective in evoking the jaw-tongue reflex, and most effective frequency of stimulationwas 70Hz. However, vibratory frequency more than 130Hz was ineffective and tongue muscle was not activated at all. In contrast, jaw closing muscle was followed to such high frequency vibratory stimuli and activated through tonic vibration reflex.7) Time course of adaptation to sustained mouth opening was different between tongue muscle activities and those of masticatory muscle. The former sustained their activities longer than the latter.8) The Jaw-tongue reflex was diminished by rostrocaudal section between the mesencephalic trigeminal nucleus and the motor trigeminal nucleus.These results indicate that receptors of the Jaw-tongue reflex are mainly located in the tempo