[The activity of the supraglottal sphincter during phonation]

By means of the measurement of the aperture of the upper laryngeal sphincter it is shown that the sphincter constriction increases when the pitch is lowered and/or the voice intensity is raised. The sphincter movement does not result from the action of extrinsic laryngeal muscles. Moreover, the action of the adductor muscles results in a constriction of the supraglottal sphincter. Out of this group of muscles the lateral thyroarytenoid muscle is dominant. Since it is the strongest muscle of the group of adductors, it also activates the glottal and the supraglottal sphincters, and only this muscle guarantees glottal closure at a relaxed vocalis muscle (low pitch) and/or high subglottal pressure (high intensity). EMG data acquired from the lateral thyroarytenoid muscle at phonation at various pitch levels and different voice intensities confirm the assumed muscular function. The EMG activity increases with descending pitch level and/or with increasing voice intensity.