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Morphological Features Of The Nerve Endings And Muscle Spindles In The Intrinsic Laryngeal Muscles
Published 1990 · Medicine
The larynx performs fine adjustments as the eye balls do. Motions of the vocal folds are, therefore, supposed to be regulated by the afferent and efferent innervation more precisely than many other skeletal muscles. The purposes of this paper were to investigate morphological features of the laryngeal muscles, muscle spindles and sensory nerveendings in different species which might explain the ability of fine laryngeal adjustments. Histochemical studies of muscle fibers and morphometrical analyses of subneural apparatus at the neuromuscular junctions of the canine larynges showed that the intrinsic laryngeal muscles consisted ofthree types of muscle fibers : type 1, 2 A and 2 C. Each type had a specific subneural apparatus. The postnatal differentiation of the muscle fibers of the larynx of rats was completed prior to the development of the subneural apparatus. The muscle spindles in the intrinsic muscles of human larynges contained rich collagenous fibrils in a narrow periaxial space. The density of muscle spindles was low. The same morphological features of the muscle spindle were also observed in monkeys. The sensory nerve endings on the intrafusal fibers were not of the annulo-spiral type, which had been generally observed in mammalian muscle spindles, but of a varicose type. The sensory nerve endings on the laryngeal muscles were richer more multiform in human beings than in monkeys. It is considered that a few muscle spindles regulate laryngeal motions in cooperation with rich sensory nerve endings.