XX An Experimental Study of Central Motor Innervation of the Laryngeal Muscles in the Cat

Abstract

Electrical stimulation was given to certain points in the central nervous system of the cat under Nembutal anesthesia and evoked activity in the laryngeal muscles was electromyographically recorded. A circumscribed part of the anterior sigmoid gyrus was defined as a cortical motor center for the laryngeal muscles. Repetitive stimulation at 3V, 60[long dash]100 cps in frequency, with a pulse duration of 1 msec was effective in evoking myographic changes in the laryngeal muscles. The subcortical region from which the effect could be evoked was mapped by the use of the stereotaxic instrument and verified by subsequent histological examination. This region extended throughout the internal capsule, pes pedunculi cerebri, midbrain reticular formation and medulla oblongata. The optimum frequency of subcortical stimulation was 10 cps, the electro-myogram obtained showed a muscle twitch corresponding to each stimulating impulse. However, correspondence disappeared when the stimulating frequency was over 50 cps. Bilateral motor innerva-tion to the laryngeal muscle was electromyographically demonstrated in the cat. Descending fibers to the contralateral side were assumed to cross the median raphe near the level of the medullary motor nuclei. Judging from latency of evoked potential of the laryngeal muscle, it appears that there is an indirect cortical projection to the bulbar cranial motoneurons innervating laryngeal muscles. It was also suggested that the bulbar respiratory center has great influence on the activity of laryngeal montoneurons.