Mono- and polysynaptic reflexes of the trigeminal muscles in human beings

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Abstract
Since the tension (Golgi) and length (muscle spindles) receptors run separately in the sensory and motor roots, respectively, of the trigeminal nerve, the masseter muscle lends itself to studies of the "silent period" of contraction. The monosynaptic reflex was observed in four patients with unilateral mesencephalic disease, four patients recovering after a Frazier-Spiller operation, two patients in whom the Gasserian ganglion had been infiltrated with alcohol and in 10 control patients. An increase in both tension and length of the masseter muscles produces a monosynaptic reflex followed by a silent period of the masseters and temporal muscles. Increase in tension of the masseters alone produces a "pure" inhibitory reflex of the muscles of mastication without monosynaptic discharge. Contraction of one masseter leads to inhibition of all masticatory musculature. The monosynaptic reflex is absent on the side of the lesion in unilateral mesencephalic diseases and the inhibitory polysynaptic reflexes are absent on the operated side when the sensory root is sectioned. It is shown that the silent period after monosynaptic reflexes and after direct muscular stimulation is an autogenetic inhibition from the muscle.