Middle pharyngeal constrictor

Origin and insertion

The pharyngeal constrictor muscles encircle the pharynx and larynx. They run from an anterior origin to meet posteriorly in the midsagittal plane, forming a semi-circular tube.

The middle pharyngeal constrictor is a fan-shaped muscle that has two points of origin. Some fibers arise from the hyoid bone (the whole length of the greater horn and the posterolateral aspect of the lesser horn), while the remaining fibers arise from the stylohyoid ligament. From these origin points the muscle fibers run in a posterior direction, diverging in a fan-shaped manner. Taking a semi-circular path, the fibers eventually meet with those from the opposite side, inserting at the posterior median pharyngeal raphe. Based on their arrangements and direction, the fibers of this muscle can be divided into three groups:

• The anterosuperior group - fibers ascend from the stylohyoid ligament and lesser horn, overlapping with the superior pharyngeal constrictor
• The middle group - fibers run horizontally from the greater horn
• The posteroinferior group - fibers descend from the greater horn, beneath the inferior pharyngeal constrictor

Relations:

The middle pharyngeal constrictor is located on the lateral and posterior sides of the neck. It is found anterior to the prevertebral muscles, such as longus coli and longus capitis, and posterior to the muscles of the mouth floor, most notably the hyoglossus muscle.

Within the pharynx the middle pharyngeal constrictor sits between the superior and inferior pharyngeal constrictor muscles. Stylopharyngeus muscle extends between the superior and middle pharyngeal muscles and is sometimes used to separate these two muscles. Passing on the lateral aspect of the middle pharyngeal muscle is the lingual artery.

The middle pharyngeal muscle originates on the greater horn of the hyoid bone just medial to the attachment of the hyoglossus muscle. By extending in a fan-shaped manner, the fibers of this muscle overlap on the posterior side of the pharynx with the fibers of superior and inferior pharyngeal constrictors. Before they overlap, these muscles leave gaps on the lateral sides of the pharynx due to the different orientation of their muscle fibers, allowing the passage of various structures:

• The superior gap between the superior and middle pharyngeal constrictors allows passage of the stylopharyngeal muscle and glossopharyngeal nerve, as well as the passage of stylohyoid ligament into the internal aspect of the pharynx.
• The inferior gap between the middle and inferior pharyngeal constrictors allows the internal laryngeal nerve, superior laryngeal artery and accompanying vein to pass towards the larynx.

This region around the pharynx, also called the parapharyngeal space, is very sensitive due to its important neurovascular contents. Be sure to master this region with the help of the following resources:

Innervation

All three pharyngeal constrictors receive their innervation from the pharyngeal plexus. The motor fibers of this plexus are derived from the pharyngeal branch of the vagus nerve (CN X), while sensory fibers arise from the glossopharyngeal nerve (CN IX).

Blood supply

The middle pharyngeal constrictor receives its arterial supply from the pharyngeal branch of ascending pharyngeal artery, as well as the tonsillar branch of the facial artery. Venous blood is drained by the pharyngeal venous plexus, a tributary of the internal jugular vein.

Function

Contraction of the middle pharyngeal muscle, in coordination with the superior and inferior pharyngeal constrictors, constricts and closes the pharynx during deglutition to propel the food bolus from the oropharynx downward to the esophagus. The middle pharyngeal constrictor works specifically on the mid-portion of the pharynx.