Reflex Responses and Recurrent Discharges Evoked by Stimulation of Laryngeal Nerves

Proprioceptive mechanisms in the laryngeal musculature were investigated and it was concluded that the secondary response represented a recurrent discharge from the motoneurons, whereas no response exhibiting the properties of a monosynaptic reflex was observed.

Abstract

Abstract Reflex responses in intrinsic laryngeal muscles to stimulation of the internal laryngeal nerve were studied with a view to elucidating the mechanism of the protective reflex closure of the glottislpsilateral stimulation evoked reflex discharges of multisynaptic character in all four vocal cord adductors studied but never in the abductor in which only inhibition of pre‐existent activity was observed. Contralateral stimulation evoked similar reciprocal effects but the discharges in the adductors were smaller and of longer latencies and did not appear in all muscles; latent contralateral reflex connections could, however, be demonstrated in all muscles. The reciprocal innervation pattern and the difference in transmitter potentiality of different reflex connections are discussed. 2/ Proprioceptive mechanisms in the laryngeal musculature were investigated. Stimulation of individual muscle nerves evoked, in nerve and muscle, in addition to the direct response, a secondary response amounting to a few per cent of the primary response. By performing an analysis in analogy with previous work on the spinal cord it was concluded that the secondary response represented a recurrent discharge from the motoneurons, whereas no response exhibiting the properties of a monosynaptic reflex was observed. Attempts to record afferent impulses from muscle spindles gave negative results. The findings are discussed in relation to earlier results from morphological and physiological studies of proprioceptive systems in the larynx.