REFLEX RESPONSES INDUCED BY STIMULATION OF HYPOGLOSSAL AFFERENTS

On stimulation of the central end of the cut hypoglossal nerve, multisynaptic reflex discharges were set up in the intrinsic laryngeal muscles and in certain muscles innervated by the facial nerve; by contrast, reflex responses were never observed in tongue muscles. Activation of the fibers mediating the reflex responses required a stimulus strength 2–4 times that required for activation of the hypoglossal motor fibers. On the basis of earlier data on the caliber spectrum of the hypoglossal nerve fibers and on the relation between the threshold values for afferent fibers and motor fibers it is concluded that the hypoglossal afferents belong to the group III fibers. The threshold differences also eliminate the possibility of the centrally relayed responses being set up by activation of recurrent collaterals from hypoglossal alpha motor fibers.—The possibility that synchronized impulses in the hypoglossal afferents might depolarize central afferent terminals in other nerves to firing level and thus open up reflex connections not operative under physiological conditions is considered and excluded.—The rypes of receptors connected to the high‐threshold hypoglossal afferents and their functional role are briefly discussed. © 1969 Scandinavian Physiological Society