ACTIVATION AND COORDINATION PATTERNS OF THE SUPRAHYOID MUSCLES DURINGSWALLOWING

This study was undertaken to determine the activation and coordination patterns of the three suprahyoid muscles-geniohyoid, mylohyoid, and a nterior belly of the digastric muscle-in elevating the larynx during s wallowing. Electromyographic activity was also recorded from two intri nsic laryngeal muscles (vocalis and lateral cricoarytenoid) and the an terior genioglossus. Ten adults served as participants. Each participa nt produced 15 swallows of 15 mL of tap water both normally and with a 12-mm bite block placed between the molars. The electromyographic dat a were ensemble averaged with a laboratory computer. Analyses showed t hat the three suprahyoid muscles were used selectively by different pa rticipants. Some participants used all three muscles for hyoid elevati on, while others used different pairs of two of the muscles. The activ ation patterns of the suprahyoid muscles during swallowing also varied with respect to each other and the onset of the laryngeal constrictor muscles; however, use of at least one suprahyoid muscle always preced ed the onset of the laryngeal adductors, indicating that larynx elevat ion consistently preceded glottal adduction. The way in which the musc les responded to the bite block varied considerably both within and am ong participants. Some maintained temporal stability but increased ove rall muscle activity; others reorganized temporal relations either wit h or without corresponding muscle activity adjustments. These findings suggest that the laryngeal elevation system is an adaptive function r ather than an immutable action.