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 The human airway consists of two openings: the nose, which leads to the nasopharynx, and the mouth, which leads to the oropharynx. These passages are separated anteriorly by the palate and they join posteriorly, although still separated via an imaginary horizontal line extending posteriorly from the palate. Inferiorly past the base of the tongue, the epiglottis separates the oropharynx from the laryngopharynx, or hypopharynx. The epiglottis serves to protect against aspiration by covering the opening of the larynx (the glottis) during swallowing. The larynx is a cartilaginous skeleton comprised of nine cartilages as well as ligaments and muscles. The thyroid cartilage functions partly to shield the vocal cords. Inferior to the cricoid cartilage lies the trachea, which extends to the carina at approximately T5 where it branches into the right and left mainstem bronchi. The right mainstem bronchus takeoff is more straight and vertical, making it the most likely path taken by a deep endotracheal tube placement.

 Innervation of the upper airway is from the cranial nerves. Sensation to mucous membranes of the nose is supplied by the ophthalmic division (V1) of the trigeminal nerve anteriorly and the maxillary division of the same nerve posteriorly. The glossopharyngeal nerve provides sensation to the posterior third of the tongue as well as the tonsils and undersurface of the soft palate.

 Below the epiglottis, sensation is supplied by branches of the vagus nerve. The superior laryngeal branch divides into external and internal segments. The internal branch provides sensation to the larynx between the epiglottis and the vocal cords. Another branch of the vagus nerve, the recurrent laryngeal nerve, provides laryngeal sensation below the vocal cords as well as the trachea.

 Motor supply to the muscles of the larynx is from the recurrent laryngeal nerve, with the exception of the cricothyroid muscle (vocal cord tensor), which is innervated by the external branch of the superior laryngeal nerve. All vocal cord abductors are controlled by the recurrent laryngeal nerve.