SOME FUNCTIONAL CHARACTERISTICS OF MECHANORECEPTORS IN THE LARYNX OF THE CAT

Abstract

Sensory discharges from laryngeal mechanoreceptors were recorded from superior and recurrent laryngeal nerve (SLN and RLN) fibers which supplied the sensory innervation of the larynx. Mechanoreceptors under study fell into two general categories: touch receptors, located in the laryngeal mucosa, and mechanoreceptors, located deep in laryngeal structures. Touch receptors were particularly sensitive to light touch and to jets of air, and showed considerable variation on their baseline discharge. They were readily activated by vibratory stimuli applied to the mucosa and some units followed input frequencies as high as 400 cps. Following was dependent on both frequency and amplitude of the vibratory stimuli. Touch receptors had an optimum temperature-sensory frequency value, departures from which decreased sensory frequency. Deep mechanoreceptor activity was modified by displacement of either the vocal cords or laryngeal segments. Most units showed a "resting" background discharge which was synchronous with either inspiration or expiration when the homolateral RLN was intact. Warming usually increased, while cooling decreased the activity of deep mechanoreceptors. The baseline discharge of both types of units was appreciably influenced by either normally occurring motor discharges in RLN''s or single shocks applied to the peripheral stump of a severed homolateral RLN. These effects were abolished by intravenous injections of gallamine triethiodide. The results obtained were discussed in connection with reflexes involved in normal respiration, cough and phonation.