Stylopharyngeus muscle

Origin and insertion

Stylopharyngeus muscle is a long, thin muscle that is shaped like a cylinder superiorly and becomes flat inferiorly. It originates from the medial base of the styloid process of temporal bone. The muscle extends inferiorly, traveling along the sides of the pharynx between the superior and middle pharyngeal constrictor muscles. It then spreads out underneath the mucous membrane of the pharynx before finally inserting into three distinct sites. Fibers of stylopharyngeus may:

• Blend with the other pharyngeal constrictors.
• Join the lateral glossoepiglottic fold.
• Attach to the posterior border of thyroid cartilage after joining the palatopharyngeus muscle.

Relations

Stylopharyngeus is covered superficially by the external, circular pharyngeal constrictor muscles (superior, middle and inferior). These contain an internal fascial lining (pharyngobasilar fascia) which is closely related to stylopharyngeus. 

As the stylopharyngeus muscle passes between the superior pharyngeal constrictor (laterally) and middle pharyngeal constrictor (medially) muscles, it is accompanied by the glossopharyngeal nerve (cranial nerve IX) and stylohyoid ligament. The glossopharyngeal nerve courses around the posterior border of the stylopharyngeus muscle and then curves forward on the lateral aspect of the muscle on its way towards the tongue. 

Along its course, the stylopharyngeus muscle crosses the ascending pharyngeal artery right after it branches from the external carotid artery. Then, stylopharyngeus travels anterolaterally in relation to palatopharyngeus muscle until the level of the digastric muscle. Superior to the digastric, stylopharyngeus separates the external carotid artery from the internal carotid artery. At the level of the head, the external carotid artery ascends through the parotid gland. Here, the stylopharyngeus muscle separates this artery from several deeper structures that lie underneath; internal carotid artery, internal jugular vein and vagus nerve (cranial nerve X). 

Stylopharyngeus is also interposed between the medial pterygoid muscle and the superior pharyngeal constrictor muscle at the level of the tensor veli palatini muscle. 

Innervation

Stylopharyngeus muscle receives innervation from the glossopharyngeal nerve (cranial nerve IX).

Blood supply

Stylopharyngeus muscle receives arterial blood via the pharyngeal branch of ascending pharyngeal artery. The latter stems from the external carotid artery.

Functions

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Stylopharyngeus is involved in elevating the pharynx and larynx. These movements are important during swallowing and speaking. The swallowing reflex is triggered once the food bolus touches the pharyngeal wall. Firstly, the pharyngeal constrictor muscles propel the bolus through the pharynx towards the esophagus. Then the internal pharyngeal longitudinal muscles, including stylopharyngeus, elevate the pharynx and in order to receive the food bolus.

More details about the stylopharyngeus muscle and other pharyngeal muscles are included below: