Sensory receptors of the larynx

doi:10.1016/S0002-9343(99)00339-3

The American Journal of Medicine

Volume 108, Issue 4, Supplement 1, 6 March 2000, Pages 47-50

https://doi.org/10.1016/S0002-9343(99)00339-3 Get rights and content

Abstract

The larynx is a highly reflexogenic area, and stimulation with mechanical and chemical stimuli results in a number of protective reflexes. Investigators have used anatomical, behavioral, and neurophysiological techniques to examine the receptors responsible for initiating these reflex responses. Histologic examination has revealed the presence of free nerve endings, Merkel cells, Meissner corpuscles, and taste buds. Mechanoreceptors have been classified in several different ways and are located either in the superficial mucosa or in muscles and laryngeal joints. Recordings from afferent fibers innervating laryngeal mechanoreceptors have revealed that some of them are spontaneously active whereas others are silent until stimulated. Laryngeal mechanoreceptors respond to stimulation with either a rapidly adapting or a slowly adapting response pattern. Often the mechanoreceptors respond to respiratory movement of the larynx, giving bursts of action potentials during inspiration. A large number of taste buds that are anatomically similar to lingual taste buds populates the laryngeal surface of the epiglottis. Taste buds of the larynx respond to a number of chemical stimuli and to water. They do not respond to NaCl solutions close to physiological concentrations (0.154 M) but do respond at both a lower and higher concentration. When water is the solvent for the chemical stimuli, most chemicals initiate a response in laryngeal taste buds. However, when 0.154 M saline is used as a solvent, chemicals that taste bitter or sweet when applied to the tongue are ineffective stimuli. Taste buds of the larynx tend to be stimulated by the pH and tonicity of the stimulating solution and not by the gustatory properties. These results reveal a fundamental difference between the chemoreceptors of the oral cavity and larynx and result in the conclusion that chemoreceptors of the larynx do not play a role in gustation but are adapted to detect chemicals that are not saline-like in composition.

Section snippets

Mechanoreceptors

Histologic investigations using light and electron microscopy have revealed a number of neural structures that include “free nerve endings,” corpuscular endings, Merkel cells, and encapsulated endings resembling Meissner corpuscles.3, 4 Because free nerve endings are either nociceptors or thermal receptors, the Merkel cells, and Meissner corpuscles are probably the receptors responsible for responding to mechanical stimulation of the larynx and epiglottis.

Investigators recording from the SLN

Chemoreceptors

The presence of taste-bud–like structures on the larynx has been known for some time. As early as 1876, Schofield described taste buds on the epiglottis of the dog and cat.9 Since that time, many authors have described the morphology, development, innervation, and distribution of these structures at the light microscopic level.10, 11, 12, 13, 14, 15, 16, 17 These investigations have shown that taste buds located at the entrance to the larynx are only found on the epithelium of the laryngeal

Water receptors

Because reflex responses to water in the larynx can be recorded from locations that do not have taste buds, some investigators have claimed that the laryngeal response to water does not originate with stimulation of taste buds but another receptor of unknown morphology called a water receptor.28 However, analysis of the receptive fields of cat SLN chemosensitive fibers has shown that these receptive fields correspond to the distribution of taste buds on the laryngeal surface of the epiglottis

Acknowledgements

This work was supported by the National Institute of Deafness and Other Communicative Disorders Grant DC 00288.

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Sensory Organization of the Pharynx and LarynxSensory receptors of the larynx