Coordination of the Levator Veli Palatini and Intrinsic Laryngeal Muscles: An Evoked Electromyographic Study in the Dog

Abstract

Fourteen dogs anesthetized with sodium pentobarbital were used as experimental animals in an electromyographic study of the functional relationships among the levator veli palatini and the intrinsic laryngeal muscles. The following results were obtained: 1. A single pulse stimulation to the afferent fibers of the pharyngeal branches of the glossopharyngeal nerve evoked ipsilateral reflexes from the levator veli palatini and laryngeal adductor muscles. The laryngeal abductor muscle, however, did not respond to this stimulation. 2. A repetitive pulse stimulation (3—5 Hz) to the afferent fibers of the pharyngeal branches of the glossopharyngeal nerve decreased the level of amplitude of the respiratory discharge from the laryngeal abductor muscle. 3. The reflex discharges in the levator veli palatini muscle were decreased when the respiratory discharges in the laryngeal abductor muscle were enhanced. The present study indicates that there are relationships between the palatal and glottal movements and that the coordinate actions in these regions are influenced by two types of relationships among the palatal and laryngeal muscles. One is the relationship between the levator veli palatini and laryngeal adductor muscles, and the other is that between the levator veli palatini and laryngeal abductor muscle. Velar movement is one of the most important components of swallowing and phonation. In swallowing and vomiting, both the velopharynx and the glottis are closed. During normal inspiration , both the velopharynx and glottis are open. Iwashita (1965) and Fritzell et a1 (1976) studied the relationship between velar and glottal move— ments. However, questions remain unanswered. All authors are affiliated with the First This study was designed to investigate the func— tional relations among the levator veli palatini and the intrinsic laryngeal muscles, which are asso— ciated with velar and glottal movements, respec— tively. Electromyographic analysis of the levator and intrinsic laryngeal muscle activities in the dog was carried out in conjunction with electri— cal stimulation of the afferent fibers of the pharyngeal branches of the glossopharyngeal nerve. MATERIALS AND METHODS Fourteen adult dogs weighing 7.0 to 9.0 kg were used. Anesthesia was induced by intraperitoneal injection of 35 mg per kilogram body weight of sodium pentobarbital, and it was maintained by repeated intravenous injections of sodium pen— tobarbital.