Reflex control of discharge in motor fibres to the larynx

Abstract

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.

Studies on laryngeal calibre during stimulation of peripheral and central chemoreceptors, pneumothorax and increased respiratory loads

“…For the inspiratory phase, asphyxia due to rebreathing increases the discharge of inspiratory laryngeal motor fibres in the cat (Glogowska, Stransky & Widdicombe, 1974). Breathing carbon dioxide rich gas mixtures increases the inspiratory-phasic discharge of recurrent laryngeal 357 M. DIXON AND OTHERS fibres (Eyzaguirre & Taylor, 1963) and of those with inspiratory rhythm entering the posterior cricoarytenoid muscle (Suzuki & Kirchner, 1969).…”

“…The results are consistent with the observation that in the cat with intact vagi a 50 ml. pneumothorax increases the discharge of both inspiratory and expiratory motor fibres; the former response is greatly reduced by vagotomy (Glogowska et al 1974). With very large pneumothoraces (100 ml.)…”

“…Similar loads have been shown to increase the discharge of inspiratory units in the cricothyroid and posterior cricoarytenoid muscles (Suzuki et al 1970;Fukuda & Kirchner, 1972;Fukuda et al 1973), and to dilate the larynx of man (Rattenborg, 1961), although negative results have also been described for man (Spann & Hyatt, 1971). Recordings from inspiratory motor fibres (in the vagotomized rabbit) show an increase in discharge on resistance breathing (Dziewanowska & Szereda-Przestaszewska, 1974) and in the cat with intact or cut vagi (Glogowska et al 1974), and expiratory laryngeal fibres cease their discharge under similar conditions (Glogowska et al 1974).…”

“…In the cat with intact vagi, intravenous injections of cyanide increase the discharge of both inspiratory and expiratory laryngeal motor fibres (Glogowska et al 1974). Pneumothorax Pneumothorax (50 ml.)…”

Lung Reflexes Affecting the Larynx in the Pig, and the Effect of Pulmonary Microembolism

“…The calibre of the larynx shows respiratory variations and is also affected by lung reflexes that change the discharge of inspiratory and expiratory laryngeal motoneurones, as shown for the cat, rabbit and dog (Stransky, Szereda-Przestaszewska & Widdicombe, 1973;Dixon, Szereda-Przestaszewska, Widdicombe & Wise, 1974;Glogowska, Stransky & Widdicombe, 1974;Jammes, Davies & Widdicombe, 1985). Furthermore, Bartlett and co-workers (Bartlett, ; Remmers & Bartlett, 1977) showed that the larynx can control breathing pattern by regulating expiratory time and flow.…”