One of the Functions of the Larynx is Respiration, and Hypercapnia can result in structural changes dictated by the Brain Stem to open the airway

” The larynx (voice box) is the area that connects the throat to the windpipe (trachea). Without it, we would hardly be able to sing or speak. It also keeps food and drink out of the windpipe.

The structure of the larynx

The larynx is located about half way down our neck. It can be thought of as a short tube. At the top it is connected to the throat, and at the bottom it is attached to the windpipe, so it’s a part of our respiratory system.

The inside of the larynx is lined with mucous membrane tissue. Its walls are made of connective tissue, muscles and cartilage. The cartilage provides support and also keeps the larynx elastic. In men, it is clearly visible from outside the body and known as the “Adam’s apple.”

Illustration: Structure of the larynx

Structure of the larynx ” https://www.ncbi.nlm.nih.gov/books/NBK534630/ InformedHealth.org [Internet].

Abstract

The larynx has three functions: phonation, airway protection, and respiration. Few studies have dealt with laryngeal respiratory function. To elucidate respiratory regulation by the larynx, we studied the changes in the activity of the intrinsic laryngeal muscles during hypercapnia in decerebrated cats. The electromyographic activities of the posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were recorded simultaneously with an electromyogram of the diaphragm, endotracheal pressure, and concentrations of O2and CO2. The activity of the intrinsic laryngeal muscles during hypercapnia (end-tidal CO2, 8% to 10%) was analyzed in comparison with that during eucapnia. In hypercapnia, both the PCA and TA muscles increased their activities, and the endotracheal pressure during expiration was elevated to a higher level than that in eucapnia. TA muscle activities returned to the level during eucapnia after ligation of the common carotid arteries. These findings suggest that hypercapnia causes a further widening of the glottis during inspiration to decrease inspiratory resistance and a further narrowing of the glottis during expiration to prevent alveolar collapse. Thus it may be concluded that the larynx actively participates in respiratory regulation under the control of the brain stem through a process of peripheral inputs from the carotid receptors. Otolaryngol Head Neck Surg. 1998 Apr;118(4):537-44. doi: 10.1177/01945998981180041 Changes in Laryngeal Muscle Activities During Hypercapnia in the Cat T Adachi 1T UmezakiT MatsuseT Shin

Abstract

Experiments were conducted in adult dogs to determine the respiratory activity of laryngeal muscles during wakefulness and sleep. We studied the EMG activity of three laryngeal muscles in five trained dogs, two of which were completely intact, and three of which had a previously-formed side-hole tracheal stoma. Pairs of electrodes were implanted chronically into the posterior cricoarytenoid muscle (PCA), a laryngeal dilator, cricothyroid (CT), and thyroarytenoid (TA), a laryngeal adductor. EMG electrodes were also inserted into the costal portion of the diaphragm. In wakefulness (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep the EMGs of the PCA and CT muscles increased in intensity during diaphragm activation, with varying levels of basal activity during expiration. However, the greatest levels of inspiratory activity in PCA and CT during sleep were found in REM sleep, usually in the absence of augmented diaphragm EMG activity. This laryngeal muscle activity was associated with laryngeal dilation. There were also marked state-related changes in the level of activity of CT [cricothyroid]during expiration, suggestive of changes in the degree of expiratory adduction of the larynx. The adductor muscles (TA) were not active during expiration, except during alert W. [Wakefulness]. There were no consistent differences in respiratory activity of the laryngeal muscles between the two intact dogs and those with a tracheal stoma (whether or not an endotracheal tube was in place), nor was laryngeal muscle activity affected by the subsequent creation of a tracheal stoma in the two intact dogs. The findings indicate that sleep-wakefulness state exerts important influences on the respiratory activity of laryngeal muscles in the adult dog. Respiratory Activity of Laryngeal Muscles in Awake and Sleeping Dogs R HardingS J EnglandJ R StradlingL F KozarE A Phillipson PMID: 3797846 DOI: 10.1016/0034-5687(86)90083-6

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