L58. GA - Pharynx

• The pharynx is a fibromuscular tube connecting the nasal and oral cavities with the respiratory and gastrointestinal systems.
• It extends ~15 cm from the base of the skull to the C6 level.
• The pharynx is widest at the hyoid bone(C3) and narrowest at the entrance to the esophagus.

Divisions, Boundaries, Layers

• There are 3 divisions of the pharynx: nasopharynx, oropharynx, and laryngopharynx.
• The nasopharynx is located posterior to the nasal cavity and superior to the soft palate.
• The oropharynx sits posterior to the tongue and superior to the epiglottis.
• The laryngopharynx is located posterior to the larynx and superior to the esophagus.
• The layers of the pharynx include the mucosa, pharyngobasilar fascia, muscular layer, and buccopharyngeal fascia.
• The mucosa is the same covering as the oral and nasal cavities.
• The pharyngobasilar fascia is the thick fascia that fills in gaps between pharyngeal muscles.
• The pharyngobasilar fascia attaches the pharynx to the base of the skull superiorly.
• The muscular layer includes inner longitudinal and outer circular muscles.
• The buccopharyngeal fascia is the posterior part of pretracheal fascia that permits movements of the pharynx and contains the pharyngeal plexus of CN IX & X.
• The retropharyngeal space is located between the pretrachial fascia anteriorly and the prevertebral fascia posteriorly and communicates with the superior mediastinum of the thorax.

Muscles of the Pharynx

• The external (outer) constrictors include the superior, middle, and inferior constrictors.
• The superior constrictor originates from the pterygoid hamulus, pterygomandibular raphe, and mandible.
• The middle constrictor originates from the hyoid bone and stylohyoid ligament.
• The inferior constrictor originates from the thyroid and cricoid cartilages.
• All constrictors overlap and insert posteriorly as a tendinous seam (pharyngeal raphe).
• The superior constrictor is the innermost, and the inferior constrictor is the outermost.
• The internal (inner) longitudinal muscles include the stylopharyngeus, palatopharyngeus, and salpingopharyngeus.
• The stylopharyngeus originates from the styloid process and inserts into the pharyngeal wall between the superior and middle constrictor muscles.
• The palatopharyngeus originates from the soft palate (palatine aponeurosis) and inserts into the pharyngeal wall.
• The salpingopharyngeus originates from the auditory tube and blends with the palatopharyngeus muscle to insert into the pharyngeal wall.

Gaps for Structures of Passage

• The oropharyngeal triangle is a triangular area bounded by the superior and middle constrictor muscles posteriorly and the mylohyoid muscle anteriorly.
• Structures pass through the oropharyngeal triangle between the neck/infratemporal fossa and the oral cavity.
• Lingual artery, lingual nerve, and hypoglossal nerve pass through the oropharyngeal triangle.
• CN IX enters the oropharynx through the oropharyngeal triangle along with the stylopharyngeus muscle.
• There are 3 other gaps related to the lateral regions of the constrictor muscles: superior, middle, and inferior.
• Superior to the superior constrictor muscle is a gap that contains the opening of the auditory tube, levator veli palatini, tensor veli palatini, and salpingopharyngeus muscles.
• Between the middle and inferior constrictor muscles is a gap that transmits the superior laryngeal artery and the internal laryngeal nerve into the laryngopharynx region.
• Inferior to the inferior constrictor muscle is a gap that contains the recurrent laryngeal nerve and associated vessels entering the larynx.

Location of Tonsils

• Lymphoid tissue collections (tonsils) are in the nasopharynx, oropharynx, and oral cavity.
• The pharyngeal (adenoids) tonsils are located in the roof of the nasopharynx.
• Tubal tonsils are near the opening of the auditory tube in the nasopharynx.
• Palatine tonsils are located between the palatoglossal and palatopharyngeal folds.
• Lingual tonsils are in the pharyngeal tongue mucosa.

Blood Supply of the Pharynx

• The ascending pharyngeal artery supplies blood to the pharynx.
• Branches from the facial artery (ascending palatine & tonsillar) supply blood to the pharynx.
• Branches from the maxillary & lingual arteries supply blood to the pharynx.
• Branches from the inferior thyroid artery.

Innervation of the Pharynx

• The pharyngeal nerve plexus is in the buccopharyngeal fascia.
• CN X, inferior ganglia, & superior laryngeal branch form the pharyngeal nerve plexus.
• CN IX & branches to the oropharynx forms the pharyngeal nerve plexus.
• The sensory nerve distribution to the 3 divisions of the pharynx:
• Nasopharynx CN V2
• the Oropharynx CN IX
• and the Laryngopharynx CN X

Sympathetic Ganglia & Trunk

• Superior cervical ganglion & sympathetic trunk are in the prevertebral fascia on the anterolateral surface of the vertebral bodies.
• Trace the trunk inferiorly to find middle and inferior cervical ganglia and note vertebral levels and surrounding structures.
• There may be a fusion of the inferior cervical ganglion with the 1st thoracic ganglion (stellate ganglion).
• Preganglionic cell bodies for head/neck SANS function at the superior part of the intermediolateral cell column.
• Sources vary from T1-2, T1-3, T1-4
• Neurons send VE axons into spinal nerves and enter the sympathetic trunk using white rami communicans.
• Preganglionic SANS axons ascend in the trunk until they reach the superior cervical sympathetic ganglion where they synapse onto postganglionic neurons of the ganglion.
• Postganglionic SANS fibers travel in gray rami communicantes to get into cervical spinal nerves (C2-C4).
• These cervical spinal nerves deliver SANS axons to neck targets.
• Other fibers form a plexus around the internal & external carotid arteries associated with the carotid body & sinus.
• Postganglionic SANS fibers for the head/skull form the carotid nerve which exits the top region of the superior cervical ganglion and forms a nerve plexus around the internal carotid artery as it enters the carotid canal.
• These fibers deliver postganglionic SANS axons that to become the deep petrosal nerve.

Swallowing Mechanism

• The oral phase involves movements of the intrinsic and extrinsic tongue muscles to prepare the bolus for entry into the oropharynx.
• The soft palate is elevated to prevent the bolus from entering the nasopharynx and forms a seal with the palatopharyngeal sphincter, and a bulge in the pharyngeal mucosa is known as Passavant's ridge.
• In the pharyngeal phase, breathing ceases.
• The pharynx is elevated by the inner longitudinal muscles.
• This action pulls the walls of the pharynx superiorly over the food bolus as the constrictor muscles move it inferiorly toward the esophagus.
• The cricopharyngeus m. is a part of the inferior constrictor m. considered the upper esophageal sphincter and represents the superior site of esophageal constriction.
• The cricopharyngeus muscle relaxes as food passes from the pharynx to the esophagus.
• CN X supplies motor innervation to 2 of the inner longitudinal pharyngeal muscles (palatopharyngeus and salpingopharyngeus).
• The stylopharyngeus muscle is innervated by a motor branch of CN IX.
• Dysphagia is difficulty in swallowing and can occur when the motor fibers of CN IX & X are damaged, such as in bulbar palsy (degeneration in the medulla), or because of a physical object that impedes the swallowing process (e.g., tumor).

Tonsil Infections & Tonsillectomy

• Enlargement of the pharyngeal tonsils (adenoids) can obstruct airflow through the nasopharynx and cause mouth-breathing; common in children with recurring infections that require surgery to remove pharyngeal tonsils.
• The position of the pharyngeal and tubal tonsils near the opening of the auditory tube can cause the spread of infection into the middle ear cavity, causing otitis media.
• Chronic infections that require removal of palatine tonsils must be performed carefully because the tonsillar bed houses palatine tonsils as well as the glossopharyngeal n. and vessels that must be isolated during surgery.

Gag reflex

• The glossopharyngeal nerve (CN IX) innervates the oropharynx and posterior tongue; touching these areas activates the afferent limb of the gag reflex.
• The efferent limb is the vagus nerve (CN X) that causes pharyngeal muscle contractions.

Piriform Recess

• The laryngopharynx communicates with the larynx via the aditus (inlet) of the larynx; on each side of the aditus is the piriform recess, a pear-shaped depression where food must travel to enter the esophagus.
• Objects can lodge in the piriform recess of the laryngopharynx, and sensory fibers from CN X give the feeling that “something is caught in the throat."

Retropharyngeal Space

• The retropharyngeal space (RS) is located between the pretrachial and prevertebral fascia.
• The RS contains the pharyngeal plexus of nerves (IX, X).
• The loose connective tissue (buccopharyngeal fascia) of the RS permits movements of the pharynx during phonation and swallowing.
• The RS communicates inferiorly with the superior mediastinum of the thorax.
• Retropharyngeal Space infections (or tumors) interfere with swallowing and speaking and may spread inferiorly to the thorax.

Test your knowledge of pharynx anatomy. This quiz covers the origin and spatial relationship of the pharyngeal constrictor muscles and buccopharyngeal fascia. Also tests knowledge of the oropharyngeal triangle.