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The vestibular system modulates masseter muscle activity
No full textThe aim of this study was to investigate whether, and in what way, the vestibular input may influence the activity of the masseter muscles. The variations in the spontaneous electrical activity and the evoked responses in the masseter motor units to natural or electrical activation of the vestibular afferents were recorded in anesthetized guinea pigs. The effects of a unilateral lesion of the labyrinth on the firing rate of the masseter motor units were also studied. Results show that: 1) vestibular input elicited an excitatory tonic control on masseter muscle activity; 2) a faster labyrinthine control is driven to the contralateral than the homolateral masseter muscles; 3) vestibular macular input does exert an asymmetrical control on masseteric muscles of both sides, in relation to the head displacement in space. The latencies of responses recorded from the masseter motor units suggest that polysynaptic pathways are involved in connecting the vestibular system to the trigeminal compl..
RESPONSES OF HYPOGLOSSAL MOTONEURONS TO MECHANICAL STIMULATION OF THE TEETH IN RATS
No full textReflex discharges were evoked in the XIIth nerve single fibers and in the genioglossal muscle following mechanical stimulation of the homolateral incisor tooth in rats. The tooth mechanoreceptors affected the firing rate of 70% of the tested motoneurons mainly localized in the ventral region of the hypoglossal nucleus. Different types of response in relation to stimulus direction were recorded. Type A responded with excitation to labio-lingual and with inhibition to linguo-labial stimulus direction. Opposite effects were observed in type B motoneurons. However, these neurons did not respond to mechanical stimuli applied in medio-distal or disto-medial directions. Type C showed excitatory or inhibitory responses to mechanical stimulation in all directions. Type D only responded to one direction of stimulation. The stimulus was often able to excite motoneurons previously silent (type E). Some motoneurons showed complex responses to one stimulus direction. The results demonstrate that sti..
Galvanic vestibular stimulation evokes short-latency EMG responses in human masseter muscles
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A monosynaptic vestibule-trigeminal pathway innervating masseter muscle motoneurons in rats
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