Each subdivision of the pharynx has a different sensory innervation:
The nasopharynx is innervated by a pharyngeal branch of the maxillary nerve [V2] that originates in the pterygopalatine fossa and passes through the palatovaginal canal in the sphenoid bone to reach the roof of the pharynx.
The oropharynx is innervated by the glossopharyngeal nerve [IX] via the pharyngeal plexus.
The laryngopharynx is innervated by the vagus nerve [X] via the internal branch of the superior laryngeal nerve.
The glossopharyngeal nerve [IX] is related to the pharynx throughout most of its course outside the cranial cavity.
After exiting the skull through the jugular foramen, the glossopharyngeal nerve [IX] descends on the posterior surface of the stylopharyngeus muscle (Fig. 8.208B), passes onto the lateral surface of the stylopharyngeus, and then passes anteriorly through the gap (oropharyngeal triangle) between the superior constrictor, middle constrictor, and mylohyoid muscles to eventually reach the posterior aspect of the tongue.
As the glossopharyngeal nerve [IX] passes under the free edge of the superior constrictor, it is just inferior to the palatine tonsil lying on the deep surface of the superior constrictor.
Pharyngeal branches to the pharyngeal plexus and a motor branch to the stylopharyngeus muscle are among branches that originate from the glossopharyngeal nerve [IX] in the neck. Because sensory innervation of the oropharynx is by the glossopharyngeal nerve [IX], this nerve carries sensory innervation from the palatine tonsil and is also the afferent limb of the gag reflex (see “In the clinic” on p. 889).
The larynx is a hollow musculoligamentous structure with a cartilaginous framework that caps the lower respiratory tract.
The cavity of the larynx is continuous below with the trachea, and above opens into the pharynx immediately posterior and slightly inferior to the tongue and the posterior opening (oropharyngeal isthmus) of the oral cavity (Fig. 8.209A,B).
The larynx is both a valve (or sphincter) to close the lower respiratory tract, and an instrument to produce sound. It is composed of: three large unpaired cartilages (cricoid, thyroid, and epiglottis), three pairs of smaller cartilages (arytenoid, corniculate, and cuneiform), and a fibro-elastic membrane and numerous intrinsic muscles.
The larynx is suspended from the hyoid bone above and attached to the trachea below by membranes and ligaments. It is highly mobile in the neck and can be moved up and down and forward and backward by the action of extrinsic muscles that attach either to the larynx itself or to the hyoid bone.
During swallowing, the dramatic upward and forward movements of the larynx facilitate closing the laryngeal inlet and opening the esophagus.
Motor and sensory innervation of the larynx is provided by the vagus nerve [X].
The cricoid cartilage is the most inferior of the laryngeal cartilages and completely encircles the airway (Fig. 8.210). It is shaped like a signet ring with a broad lamina of cricoid cartilage posterior to the airway and a much narrower arch of cricoid cartilage circling anteriorly.
The posterior surface of the lamina is characterized by two shallow oval depressions separated by a vertical ridge. The esophagus is attached to the ridge and the depressions are for attachment of the posterior crico-arytenoid muscles.
The cricoid cartilage has two articular facets on each side for articulation with other laryngeal cartilages: