Electromyography of intrinsic laryngeal muscles.

Abstract

In man during phonation, an increased electrical activity was found in all the intrinsic adductor muscles of the larynx investigated. The change in electrical activity started one‐third to one‐half of a second before audible sound could be recorded by microphone. This latency probably reflects the time necessary to build up a minimum air current and pressure. Whenever it could be discriminated, the maximum frequency of single motor unit discharges was of the order of 20‐50 per second during phonation. This is in contradiction to Husson's theory that the frequency of vibration of the vocal cord during a tone of a given pitch is the result of a corresponding number of impulses to the muscle fibres.During phonation with increasing pitch the electrical activity increased considerably, as long as the increase in pitch occurred within the same register. The increase in electrical activity was adjusted to the level corresponding to a given pitch before the onset of audible sound. The pronounced electrical activity in the adductor muscle in the absence of phonation was inhibited 0 3 sec. before the onset of phonation. This complete inhibition persisted throughout the entire period of voice production.In the abductor muscles also there was a slight activity in the absence of phonation. This activity persisted even when breathing stopped. It was enhanced during inspiration and remained unaltered during expiration.Electromyographical findings are consistent with the assumptions (1) that the vibrational frequency of the vocal cords, and thereby the pitch of the sound produced, is determined by the active and passive tension exerted by the intrinsic laryngeal muscles, and (2) that the active force of sound production is the air pressure, which separates the margins of the glottis with periodic recoil of the vocal cords.