The response of laryngeal afferent fibres to mechanical and chemical stimuli

Abstract

1. We have recorded afferent activity from ‘single fibres’ dissected from the superior laryngeal nerve of anaesthetized cats. 2. Units which responded to gentle mechanical stimulation of the larynx epithelium were chosen for study. 3. Receptors with myelinated fibres were grouped according to their spontaneous activity. Group 1 fibres had little or no spontaneous activity: group 2 fibres had constant and continuous spontaneous activity. 4. Group 1 fibres had a wide range of adaptation rates. Their conduction velocities lay between 3·0 and 30 m/sec. The receptors were generally stimulated by ammonia and distilled water and often by CS riot control agent, 5 and 10% CO 2, 200 ppm SO 2, and cigarette smoke. Histamine, phenyl diguanide, graphite dust, 100 ppm SO 2 and saline drops did not generally excite the fibres. 5. Group 2 fibres were slowly adapting. Their conduction velocities ranged between 8·0 and 26·5 m/sec. Ammonia usually, and distilled water sometimes, excited these fibres while 5 and 10% CO 2 mixtures inhibited them. A minority of group 2 fibres were pH sensitive, inhibited by acids and stimulated by alkaline buffers. Cigarette smoke had complex actions, either excitation, inhibition or, at different times, both. Histamine, P.d.g., CS, SO 2, saline drops and dust had no action on these fibres. 6. Recordings were made from one unmyelinated fibre (conduction velocity 1·9 m/sec) which responded to stroking of the epithelium with a thread and to histamine, P.d.g. and ammonia vapour applied to the epithelium. 7. We consider the site, method of excitation and reflex actions of the different receptors described.