Jaw opening and jaw closing reflexes in the cat

Abstract

In decerebrated unanaesthetized cats the reflex mechanical response of the jaw and the reflex EMG activity in digastric and temporalis muscles were recorded following electrical stimulation of the exposed infraorbital nerve. Single shocks elicited rapid transient jaw opening associated with digastric activity (5–6 msec latency) and simultaneous weak temporalis activity; under isotonic conditions this was followed by temporalis activity (12–20 msec latency) corresponding to jaw movement. Reflex jaw opening elicited by a moderate strength stimulus was converted into jaw closing if it was elicited during an opening movement; reflex opening in response to a strong stimulus was not reversible. Reflex jaw closing was also elicited at rest by short trains of stimuli individually subthreshold for digastric activity; closing was characterised by temporalis activity with 5–6 msec latency. Maintained opening was elicited by trains of afferent volleys in slowly conducting fibres and was characterised by temporalis inhibition alone. The results were explicable on the basis of separate afferent pathways for digastric excitation, temporalis excitation and temporalis inhibition.