Masseteric reflex inhibition induced by afferent impulses in the hypoglossal nerve
ABSTRACT Summary1.Effects of stimulation of the central cut end of the hypoglossal nerve on the masseteric reflex were studied in cats (spinal cord sectioned between C2 and C3). Hypoglossal stimulation with 1–3 pulses induced a prolonged suppression of the ipsilateral and contralateral masseteric reflex, with or without a facilitatory phase following the peak of suppression.2.The threshold of suppression was 2–3 times higher than the threshold for firing axons of hypoglossal motor neurons and maximal suppression was obtained when the hypoglossal nerve was stimulated with pulses supramaximal for these axons. Pulses of longer duration than necessary to induce suppression were usually required to induce facilitation.3.Hypoglossal influences on the masseteric reflex were almost completely abolished following section of the hypoglossal roots on the stimulated side, whereas the effects still remained following section of the glossopharyngeal, vagal and accessory nerve roots and the dorsal roots of C1 and C2 when the hypoglossal roots were left intact.4.Dihydro-β-erythroidine did not alter the hypoglossal effects on the masseteric reflex.5.Neither precollicular nor medullo-spinal transection altered these hypoglossal influences, whereas ponto-medullary transection completely abolished them.6.From these results it was concluded that afferent impulses in the hypoglossal nerve enter the brain stem primarily through the hypoglossal roots, ascend bilaterally in the brain stem via a polysynaptic route to the trigeminal motor nucleus and induce inhibition and facilitation of the masseteric monosynaptic reflex.
- SourceAvailable from: nih.govJournal of Anatomy 12/1971; 110(Pt 2):215-20. · 2.23 Impact Factor
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ABSTRACT: The effect of intraoral stimuli on the lip musculature was studied in healthy subjects and in patients with an unilateral retrogasserian neurotomy. A brisk tap of the tongue surface, predominantly near its tip, evoked in the m. orbicularis oris an uncrossed reflex response with a latency of 11–15 msec. It was not affected by anesthesia of the tongue surface but abolished after lingual nerve anesthesia. It was concluded that deep submucosal mechanoreceptors of the tongue are responsible for this reflex. During voluntary activation of the m. orbicularis oris, a powerful facilitation of this reflex was noticed, which seemed not attributable to the cortical depolarization of the corresponding motoneurons. It was postulated therefore that the cortical inputs excite interneurons of the reflex path. Lingual nerve anesthesia failed to produce a substantial alternation of the pattern of activation of the m. orbicularis oris during chewing. Besides this early reflex response, a crossed reflex, with a variable latency of between 28 and 80 msec, was elicitable in the m. orbicularis oris upon nociceptive stimulation of the intraoral mucosa especially in areas exposed to external noxious stimuli.Experimental Neurology 11/1972; 37(1):179-87. DOI:10.1016/0014-4886(72)90234-8 · 4.62 Impact Factor
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ABSTRACT: The hypoglossal nerve of the cat contains some afferent fibers, but the role of these afferents in controlling hypoglossal motoneuron activity has not yet been analyzed. The effect of hypoglossal nerve stimulation on activity of hypoglossal motoneurons was investigated using microelectrode technique. Spontaneous discharges of hypoglossal motoneurons were inhibited by hypoglossal nerve stimulation, and during the period of this inhibition IPSP were recorded intracellularly. Threshold for evoking these IPSP was much higher than that for evoking antidromic action potentials in hypoglossal motoneurons. The mean latency of these IPSP was 14.4 msec and it was about twice as long as those of IPSP induced by lingual nerve stimulation. Therefore, these inhibitory effects by hypoglossal nerve stimulation are possibly due to excitation of high-threshold afferent fibers in the hypoglossal nerve and are not due to current spread to the lingual nerve. IPSP evoked by hypoglossal nerve stimulation were strychnine insensitive and picrotoxin sensitive. These hypoglossal IPSP were inhibited by lingual nerve stimulation, and this inhibition lasted for about 500 msec when supramaximal stimulation was applied to the lingual nerve. From these results we conclude that afferent fibers in the cat hypoglossal nerve exert inhibitory effects on hypoglossal motoneurons.Experimental Neurology 11/1972; 37(1):188-98. DOI:10.1016/0014-4886(72)90235-X · 4.62 Impact Factor