STUDIES ON THE NERVE PATHWAYS INVOLVED IN THE LARYNGEAL REFLEX (LARYNGOSPASM) EN THE CAT BY

The receptor sites and nerve pathways involved in the reflex production of laryngospasm have been investigated in the cat. The trigeminal nerves and the internal branch of the superior laryngeal nerves were shown to provide an afferent pathway for the reflex when the nasopharynx and larynx were exposed to ether vapour. Evidence was obtained suggesting that the recurrent laryngeal nerves may form part of the afferent innervation of the trachea involved in this reflex response. The vagus nerves provide an afferent pathway from receptors in the trachea and lungs. The literature on laryngeal structure and function reviewed previously (Rex, 1970a) indicated the nerve pathways which are probably involved in the stimulation of laryngospasm. Murtagh and Campbell (1954), in particular, considered that the afferent pathways involved are those from the surface of the pharynx and larynx (trigeminal, hypoglossal and vagus nerves). However, they drew attention to the possibility that stimulation of receptors in many areas of the body may produce laryngospasm. They considered the motor pathways to be in the vagus nerve and its branches, including the superior laryngeal nerves and recurrent laryngeal nerves. They stated that the external branch of the superior laryngeal nerve provides the motor innervation to the cricothyroid muscle and that the recurrent laryngeal nerve has motor branches to the other intrinsic laryngeal muscles. In a previous paper (Rex, 1970b) evidence was provided for the existence of receptors which are stimulated by volatile anaesthetic agents not only in the nasopharynx and larynx, but also in the trachea and lungs. Stimulation of these receptors when they are exposed to ether vapour may result in laryngospasm and apnoea or other changes in the respiratory rhythm. The work reported here is a series of experi-ments carried out to determine the effect of exposure of regions of the respiratory tract t