The pharynx is an intercommunicating pathway situated in the cervical region of the human body. The lower two segments of the pharynx facilitate the passage of food inferiorly into the lower digestive tract. Superior movement of the bolus from the oropharynx to the nasopharynx is limited by synergistic action of Passavant’s ridge (palatopharyngeal sphincters), muscles of the velum (soft palate) and the uvula.
This article will review the muscles associated with Passavant’s ridge, their neurovascular supply and lymphatic drainage as well as the physiology associated with the closure of the nasopharyngeal isthmus during swallowing.
Muscles of Passavant’s Ridge
The palatopharyngeal sphincter consists of skeletal muscle fibers of the most superior aspect of the palatopharyngeus muscle. The fibers form an incomplete circle along the lateral and posterior walls of the nasopharyngeal isthmus at the level of the C1 vertebra.
In vivo, the ridge can be observed just inferior to the pharyngeal tonsils and posterior and inferior to the pharyngeal opening of the Eustachian tube (ostium pharyngeum).
Superior Constrictor Muscle
The superior constrictor muscle of the pharynx originates from the posteromedial border of the pterygoid plate to the apex of the hamulus, as well as from the pterygomandibular fascia. The superior fibers attach to the pharyngeal tubercle of the basilar part of the occiput of the skull, by way of the pharyngeal raphe. The inferior fibers blend with the middle constrictors to the level of the vocal folds.
Salpingopharyngeus originates from the inferomedial apex of the cartilaginous part of the pharyngotympanic tube. The muscle then courses inferoposteriorly to merge with palatopharyngeus in the submucosa, giving rise to the salpingopharyngeal fold (the anterior border of the fossa of Rosenmüller).
Soft Palate Muscles
The bilateral muscles of the soft palate that aid in the closure of the nasopharyngeal isthmus are:
- The palatoglossus muscle originates from the inferior surface of the palatine aponeurosis and inserts by interdigitating with styloglossus.
- The anterior head of palatopharyngeus originates from the posterior part of the hard palate as well as the anterosuperior surface of the palatine aponeurosis; while the posterior head arises from the posterosuperior aspect of the palatine aponeurosis. They each insert in the posterior and anterior borders of the thyroid lamina, respectively.
- Tensor veli palatini has its origin at the superomedial aspect of the pterygoid plate, as well as the cartilaginous part of the pharyngotympanic tube. It inserts on the medial aspect of the pterygoid hamulus.
- Levator veli palatini originates from both the inferior apical part of the petrous bone and the medial side of the cartilaginous part of the pharyngotympanic tube. It inserts on the nasal part of the palatine aponeurosis.
Neurovascular Supply & Lymphatic Drainage
The muscles associated with the closure of the nasopharyngeal isthmus receive arterial supply from the facial, maxillary artery and ascending pharyngeal arteries. Venous drainage is accomplished by the pharyngeal and pterygoid venous plexuses.
They are innervated by fibers of the pharyngeal plexus, with the exception of tensor veli palatini, which is innervated by the mandibular nerve. Lymphatic fluid is drained by way of the retropharyngeal and upper deep cervical lymph nodes.
Closure of the Nasopharyngeal Isthmus
The superior pharyngeal constrictors contract to narrow the nasopharyngeal space. While the tensor veli palatini muscle tenses the soft palate to prevent distortion, the levator veli palatini, palatopharyngeus and salpingopharyngeus elevate it posterosuperiorly. The lateral and posterior walls around the nasopharyngeal isthmus are then made taut by contraction of the palatopharyngeal sphincter muscle fibers. The latter action forms Passavant’s ridge. These series of actions prevents communication between the nasopharynx and the oropharynx during swallowing.
Failure to close the naso-oropharyngeal communication results in a condition known as velopharyngeal insufficiency. Parents usually bring in infants with this complication due to food and liquids coming through the nose during feeding and vomiting. Older individuals may present with recurrent sinus and ear infections due to ingested contents flowing back into the nasal sinuses and the ostium pharyngeum, respectively.