Some Aspects of the Control of Cricothyroid Muscle Activity

Abstract

The effects of stretching the cricothyroid (CT) muscle were small (fig. 1) and mainly decreased the activity of tonically discharging units (fig. 2). Excitatory effects were rare, and when they occurred only an increase in the firing rate of the already active units, but not the recruitment of new ones was observed (fig. 3A and B). However, other types of afferent stimulation (heavy pressure to the skin and direct stimulation of the laryngeal mucosa) were more effective for the induction of reflex discharges (fig. 3C and D). Deformation of the CT muscle belly (fig. 4) or its active and passive shortening (fig. 5) did not substantially affect the discharge patterns of the muscle. It is therefore concluded that the tension-length changes imposed to the CT muscle do not initiate reflex discharges opposing to these changes. The discharge patterns of both CT muscles were highly synchronized and this was unaffected by deafferentation of the larynx (fig. 6). Only a transient depression of activity was produced which is assumed to be due to the suppression of a tonic action that facilitates expiratory activity and depresses the inspiratory one (fig. 8). The sources of these tonic influences probably are the movement induced by the contraction of the intrinsic laryngeal muscles (fig. 7) and the air flow through the larynx.