Muscles and Walls of the Pharynx
- the oropharynx
- the nasopharynx
- the laryngopharynx
All three of these cavities open posteriorly into the pharyngeal tube.
This article will highlight the anatomical structures, namely the muscles the make up the pharyngeal walls, with regards to their origins, insertions, innervation, main functions, blood supply and lymphatic drainage. Lastly, some common pathological alterations will be mentioned.
The muscles that make up the pharyngeal walls run both circularly on the outside and longitudinally on the inside.
The three pharyngeal constrictor muscles make up the outer layer of the wall while the inner layer is comprised of paired muscles. The superior, middle and inferior pharyngeal constrictor muscles form a muscular sleeve that has a strong internal lining on its fascial aspect known as the pharyngobasilar fascia. These muscles contract involuntarily in a sequence known as peristalsis which helps push the food bolus down from the oral cavity and into the esophagus which occurs during and immediately after swallowing.
The three paired muscles of the inner pharynx act as a group in order to elevate the larynx, shorten the pharynx and act during swallowing and speaking. These muscles are known as the stylopharyngeus, the palatopharyngeus and the salpingopharyngeus.
There are several gaps that exist between the folds of the pharyngeal constrictor muscles which allow structures to enter and exit the pharynx. Between the superior constrictor muscle and the skull, the levator palatini muscle, the auditory tube and the ascending palatine artery pass through. Between the superior and middle pharyngeal constrictor muscles, the stylopharyngeus muscle, the glossopharyngeal nerve and the stylohyoid muscle pass through. Between the middle and inferior pharyngeal constrictor muscles, the internal laryngeal nerve and the superior laryngeal artery and vein pass through. Lastly, below the inferior pharyngeal constrictor muscle, the recurrent laryngeal nerve and the inferior laryngeal artery pass through.
The musculature of the pharynx will now be discussed. Firstly, the muscles that make up the outer pharyngeal wall will be mentioned, followed by the inner paired muscles.
The superior pharyngeal constrictor muscle originates from the pterygoid hamulus, the pterygomandibular raphe, the retromolar trigone of the mandible and the side of the tongue. It inserts into the pharyngeal tubercle and the pharyngeal raphe. Its function is to constrict the upper portion of the pharynx.
The middle pharyngeal constrictor muscle proximally attaches to the stylohyoid ligament and the greater and lesser cornu of the hyoid bone. It distally attaches to the pharyngeal raphe, as does the inferior pharyngeal constrictor muscle. It constricts the middle portion of the pharynx.
The inferior pharyngeal constrictor muscle arises from the oblique line of the thyroid cartilage of the larynx and the lateral aspect of the cricoid cartilage of the larynx. It acts by constricting the lower portion of the pharynx.
The palatopharyngeus muscle starts at the posterior border of the hard palate on the palatine aponeurosis and finishes on the posterior aspect of the lamina of the thyroid cartilage of the larynx, as do the other paired muscles. It elevates the pharynx in order to close off the nasopharynx during swallowing.
The salpingopharyngeus muscle originates from the cartilage of the auditory tube and eleveates the superior and lateral aspects of the pharynx.
Lastly, the stylopharyngeus muscle comes from the medial aspect of the base of the styloid process and functions by elevating the pharynx and expanding it laterally.
Innervation, Blood Supply and Lymphatic Drainage
The pharyngeal plexus is the main nervous plexus that supplies the pharynx.
The sensory branches originate from the glossopharyngeal nerve (CN IX) which runs into the plexus. The maxillary nerve (CN V/II) supplies the anterior and superior nasopharynx, while the tonsillar nerves carry fibers from both the glossopharyngeal nerve (CN XI) and the vagus nerve (CN X).
The motoric branches come from the pharyngeal plexus and carry fibers from the vagus nerve (CN X) from the cranial root of the accessory nerve (CN XI) to all the pharyngeal muscles, save the stylopharyngeus muscle. The inferior constrictor muscles are supplied by the external and recurrent branches of the vagus nerve (CN X).
The arterial supply of the pharyngeal region comes from the facial artery, which gives the tonsillar artery and supplies the tonsils. Other branches include the ascending pharyngeal artery, the lingual artery and the ascending and descending palatine arteries.
The venous drainage is governed by the external palatine vein that drains into the pharyngeal venous plexus and from there into the internal jugular vein.
Lastly, the lymphatic drainage occurs in general to the deep cervical nodes. The tonsillar tissues however, drain to the nodes at the angle of the mandible and to the jugulodigastric node.
Obstructive sleep apnea is a disorder that occurs while patients are asleep and their breathing cycle is somewhat inhibited. This ailment has more than one cause however oropharyngeal collapse during sleep is one of the most common. The etiology behind it has been linked to smoking and obesity. Incessant smoking had been proven to increase the edematous swelling of the mucosa, whereas obesity increases the fat deposits around the pharynx. These two factors together cause a lack of longitudinal traction within the pharynx which makes the muscular walls droop towards one another, narrowing the tube and making it more difficult for the air to pass in and out during breathing, when in the supine position.