Anatomy of the Pharynx
Boundaries and Divisions of the Pharynx
§ The pharynx is a muscular tube, which serves as an upward extension of the digestive tube.
§ It also has regions in common with the respiratory systems.
§ It is generally divided into three parts:
(1) nasopharynx, behind the nasal cavity
§ The nasopharynx extends from the pharyngeal recess superiorly to the palatopharyngeal arch.
§ Often, the roof, which is essentially the basal portions of the sphenoid bones, is called the fornix.
§ The soft palate forms the floor the anterior portion of the nasopharynx.
§ The posterior portion is open through a passageway called the isthmus.
§ The is this is closed during swallowing, by the action of several muscles, to prevent the passage of food and liquid into the nasopharynx.
(2) oropharynx behind the oral cavity
§ The oropharynx runs from the tonsillar arches to the epiglottis inferiorly.
§ The oropharynx contains the root of the tongue.
(3) laryngopharynx, behind the larynx.
§ The laryngopharynx lies posterior to the larynx, and is continuous with the esophagus.
Features
§ The opening of the auditory tube is perhaps the most prominent landmark of the nasopharynx.
§ It is surrounded by two elevations that descend to the soft palate and oropharynx as the salpingopalatine and salpingopharyngeal folds, respectively.
§ Associated with the auditory tube, especially in the young, are collections of lymphoid tissue – known as the tubal tonsil.
§ On the posterior wall is another collection of lymphoid tissue, known as the pharyngeal tonsil.
§ When the tubal and pharyngeal tonsils are enlarged, they are known as adenoids may be of sufficient size to obstruct breathing through the nose.
§ Also, as ‘adenoids’ may prevent the opening of the auditory tube, they may affect hearing because of the gradual absorption of air in the middle ear.
§ Prominent features of the oropharynx are the palatine tonsils and the root of the tongue.
§ The palatine tonsil
lies in a ‘bed’ between two well-developed folds in the oropharynx: (1) palatoglossal and (2) palatopharyngeal.
The folds are named for the underlying muscles that form the folds.
Collectively, these folds are referred to as the ‘pillars of the fauces (throat).’
The palatine tonsil, the tonsil, is only anchored to fascia of the superior constrictor muscle by loose connective tissue, thus easy to remove.
The tonsil lies in a bed, formed in part by the superior constrictor.
The surface of tonsillar tissue, especially the palatine tonsil, presents with a typical appearance.
For instance, the surface is covered by epithelium with numerous ‘crypts’ that pass inward to the lymphoid tissue.
The blood supply to the palatine tonsil is the tonsillar artery, which is a major branch off the facial artery.
An important relationship for the palatine tonsil is CN IX because it runs nearby and may be affected during the surgical removal of the tonsil and also by edema that may be a sequelae of a tonsillectomy.
§ The posterior one-third of the tongue
is another important constituent of the oropharynx, but best discussed in conjunction with the anterior two-thirds of the tongue.
§ Important in the laryngopharynx are the piriform recesses.
These are lateral extensions of the aryepiglottic folds, and form the course for the passage of food and liquid around to opening of the larynx.
§ The upward regions of the pharynx are blessed with an abundance of lymphatic tissue, and distributed in a more-or-less ring-like manner and is thought to be an obstacle for the spread of infection.
This is called Waldeyer’s ring, and is the circle of lymphoid tissue that ‘protects’ the opening of the pharynx. It consists of the pharyngeal tonsils, palatine tonsil, and lingual tonsils.
Muscles
§ The musculature within the nasopharynx are those related to the soft plate, and form two prominent folds: (1) salpingopalatine and (2) salpingopharyngeus.
§ The salpingopharyngeal fold essentially formed by the mucosal covering over the muscle of the same name, i.e., formed by the mucosal covering over the levator veli palatini and tensor veli palatini. These muscles function to elevate and flatten the soft palate during swallowing and also to open the auditory tube.
§ There are three constrictor muscles that are arranged by one cone within another, so that they overlap with one another. The overlay is incomplete, however, so that there are ‘gaps’ through which various structures pass.
o The superior constrictor the uppermost and is attached to the skull and to the pterygomandibular raphe, which is one point of origin. However, the superior constrictor does not complete the posterior wall of the pharynx posteriorly. There are gaps which is covered by the pharyngobasilar fascia. The auditory tube passes the gap above the superior constrictor muscle. The lower portion of the superior constrictor is covered by the middle constrictor, but at their interface there is another pharyngeal gap, which allows passage of the stylopharyngeus muscle. The superior constrictor forms much of the posterior wall of the pharynx behind the nasopharynx, and runs down to form part of the tonsillar bed in the oropharynx.
o The middle constrictor arises from the hyoid bone like the superior constrictor meets its fellow from the opposite side in the posterior midline at the pharyngeal raphe.
o The inferior constrictor arises from the thyroid and cricoid cartilages, overlaps with the middle constrictor above and blends in with the esophagus below. The lowermost portion of the inferior constrictor is specialized as a sphincter, and is referred to as the cricopharyngeus muscle. This muscle is tonically closed, and only opens to allow boluses of food and liquid to enter the esophagus.
§ In addition to the constrictors, there is a stylopharyngeus arises from the styloid process and inserts in the superior and posterior border of the thyroid cartilage. This latter muscle functions to elevate the laryngeal apparatus during swallowing, but the paralysis of this muscle due to damage to IX has no dramatic affect on swallowing.
§ The clinically important retropharyngeal space lies behind the three constrictors and before the prevertebral musculature. This space contains an abundance of loose connective tissue, but no other anatomical features that would impede the spread of disease. Consequently, this zone allows for the spread of infection from the paratonsillar region into the thorax. Please consult your textbook for the details of the origins and insertions.
Nerve Supply
§ Innervation to the pharynx is provided by, in part, by the pharyngeal plexus,
which is an complex or network from cranial nerves IX and X.
§ The functional responsibilities are also divided along these lines.
§ For instance, fibers donated by X are the motor component,
§ whereas IX generally provides the sensory component in the oropharynx and laryngopharynx,
§ but X is sensory to the lowermost portion of the pharynx.
§ An exception is that IX supplies the stylopharyngeus.
§ However, the motor fibers running with IX and X are derived from XI.
| Muscle | Action | Innervation |
| Stylopharyngeus | Elevate the thyroid cartilage | IX |
| Superior constrictor | Sequential constriction | X, via the pharyngeal plexus |
| Middle constrictor | Sequential constriction | X, via the pharyngeal plexus |
| Inferior constrictor | Sequential constriction | X, via the pharyngeal plexus |
Blood Supply
§ The arterial supply to the pharynx arises indirectly from various branched off the external carotid artery.
§ For example, the structures of the oropharynx are supplied by branches off the lingual artery and also the tonsillar branch off the facial artery.
§ The nasopharynx is supplied largely by branches of the maxillary artery; e.g., ascending and descending palatine arteries.
§ Lastly, the laryngopharynx is supplied by branches from the ascending pharyngeal artery.
Swallowing
§ Swallowing (deglutition) is a complex act that has both voluntary and involuntary stages.
§ Once, a bolus reaches the level oropharynx, the actions become automatic.
§ The complete act of swallowing will be summarized with the discussion of the oral cavity.
§ Suffice it to say, that swallowing involves the sequential contraction of the pharyngeal constrictors starting with the superior constrictor through the inferior constrictor.
§ In addition, as the bolus enters the oropharynx, the whole pharynx is elevated by other muscles in an effort to protect the larynx.
§ The larynx is further protected by the sphincter action of muscles at its inlet and also by the fact that boluses tend to pass around the inlet in the piriform recesses, rather than directly over the inlet. T
§ he process of constriction and relaxation continues downward to the cricopharyngeus, which starts to relax once the process of swallowing is initiated.
Clinical Correlates
§ As alluded to above, the competency of the auditory tube is often affected by infections that enlarge the tubal and pharyngeal tonsils.
§ As tonsillar tissues tend to shrink after puberty, it is of most concern in children.
§ Also, the nerve and arterial relations of the palatine tonsils are important due to the relative frequency of surgical procedures.
§ Furthermore, the relationship between the paratonsillar region and the retropharyngeal space is very important for the understanding and anticipating the spread of infection.
§ Finally, with respect to neurological considerations, the integrity of the pharyngeal portions of IX and X are typically tested by movement of the soft palate and the ‘gag’ reflex.
Tags: adenoids, auditory tube, cranial nerves, cricoid cartilage, cricopharyngeus, deglutition, esophagus, fornix, isthmus, laryngopharynx, nasopharynx, oropharynx, palatine tonsils, paratonsillar, pharyngeal, pharynx, respiratory systems, retropharyngeal space, soft palate, stylopharyngeus, tonsillectomy, Waldeyer's ring
