Reflex control of discharge in motor fibres to the larynx.

1. Action potentials have been recorded from single laryngeal motor fibres, with expiratory or inspiratory phases, in cats anaesthetized with pentobarbitone and breathing through a tracheal cannula.2. Pneumothorax increased the discharge of both inspiratory and expiratory units, the inspiratory response being greatly reduced by bilateral vagotomy below the origin of the recurrent laryngeal nerves.3. Addition of a ;viscous' resistance to breathing, or asphyxial rebreathing through an added dead space, increased the activity of inspiratory units and decreased that of expiratory units.4. Induction of pulmonary oedema decreased the discharge of inspiratory units and increased that of expiratory units. After vagotomy the response of inspiratory units was reversed.5. Intravenous injections of potassium cyanide increased the activity of both types of unit.6. Chemical irritation of the laryngeal mucosa decreased the discharge of inspiratory units and increased that of expiratory units, whether the vagi were intact or cut.7. It is concluded that expiratory unit discharge can be correlated with expiratory laryngeal resistance, but that inspiratory unit discharge does not correlate so well with inspiratory laryngeal resistance.8. The relationship between laryngeal motor-fibre activity and the contractions of the inspiratory and expiratory muscles of breathing is discussed.