An Investigation of the Protective Reflex Mechanism of the Larynx.

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The larynx participates in protective reflex during second stage of the swallowing. In this study, morphological and electrophysiological investigations were performed to clarify the neural organization of the swallowing in the cat.The free nerve ending, taste buds and beaded nerve terminals were observed in the pharyngolaryngeal mucosa. It is proposed that mechanoreceptors, chemoreceptors and polymodal receoptors exist in the laryngeal mucosa. The strucures and characteristics of these receptors are appropriate for elicitation of the swallowing. The majority of the impulses from the pharyngolaryngeal region are carried into the interstitial subnucleus of the nucleus tractus solitarius. The sensory informations, which are essential for elicitaion of the protective reflex, are converged and processed in the interstitial subnucleus. The swallowing related neurons which burst during swallowing are classified into three types. A part of type II neurons constitute the central pattern generator for swallowing. The region of the cortex related to the swallowing was located in the orbital gyrus. This region may modulate the excitability in the elicitation of the swallowing. LSEP (laryngeal sensory evoked potential), which was consisted of short latent potentials in the brainstem and cortex evoked by electrical stimulation of the superior laryngeal nerve, was recorded from the scalp and generator sources were determined.