Inferior pharyngeal constrictor
The function of this muscle is to facilitate food propagation towards the esophagus by constricting the wall of pharynx during deglutition. In addition, the inferior part of this muscle forms the upper esophageal sphincter. Along with the external urethral and anal sphincters, this is one of the only three sphincters in the body comprised of skeletal muscle tissue.
This article will discuss the anatomy and function of the inferior pharyngeal constrictor.
|Origin||Thyropharyngeal part: Oblique line of thyroid cartilage
Cricopharyngeal part: Cricoid cartilage
|Insertion||Thyropharyngeal part: Median pharyngeal raphe
Cricopharyngeal part: Blends inferiorly with circular esophageal fibers
|Action||Constricts wall of pharynx during swallowing|
|Innervation||Both parts: Branches of pharyngeal plexus (CN X)
Cricopharyngeal part: also receives branches of external and/or recurrent laryngeal branches of vagus nerve (CN X)
|Blood supply||Pharyngeal branch of ascending thyroid artery, muscular branches of inferior thyroid artery.|
Origin and insertion
The inferior pharyngeal constrictor consists of two parts; thyropharyngeal and cricopharyngeal. The thyropharyngeal part is located superiorly and it comprises most of the muscle.
It originates from the oblique line of thyroid cartilage, courses posteromedially and inserts to the median pharyngeal raphe, meeting with the insertion of its contralateral counterpart.
The cricopharyngeal part originates from the anterolateral parts of cricoid cartilage. It is divided into two parts; pars oblique (superior part of the muscle) and pars fundiformis (inferior part).
Pars oblique is oriented posteromedially, inserting onto the median pharyngeal raphe. Pars fundiformis courses horizontally forming a semicircular band that fuses with the circular muscle fibers of the proximal esophagus.
The muscle is located inferior to the middle pharyngeal constrictor and superior to the esophagus. Its superior fibers overlap with the inferior fibers of the middle pharyngeal constrictor. As the middle constrictor overlaps in the same way with superior constrictor, all three constrictors create a continuous, semicircular muscular wall of the pharynx.
The apices of the thyroid gland lobes, common carotid artery and sternothyroid muscle are lateral to the inferior constrictor. The external branch of superior laryngeal nerve courses over the external surface of the thyropharyngeal part and pierces it on its way to the larynx.
The specific orientation of muscle fibers defines a triangular gap between the thyropharyngeal and cricopharyngeal parts of the muscle called Killian’s dehiscence (or triangle). This is a weak spot of the pharyngeal wall through which the pharyngeal diverticulum (Zenker’s diverticulum) may prolapse.
Both parts of the muscle are innervated by branches of vagus nerve (CN X) via the pharyngeal plexus of nerves. The cricopharyngeal part receives additional vagus supply via the branches of external and/or recurrent laryngeal nerves.
The muscle is supplied by the pharyngeal branch of ascending thyroid artery and muscular branches of inferior thyroid artery. Venous blood is conveyed by the pharyngeal venous plexus (tributaries of the internal jugular vein).Solidify your knowledge with our quiz.
The thyropharyngeal part constricts the inferior part of the pharynx, pushing the bolus towards the esophagus.
The cricopharyngeal part makes up most of the upper esophageal sphincter (UES). Depending on the physiological state, it intermittently contracts and relaxes to prevent or allow content passage between the esophagus and pharynx.
- Except in deglutition and in some reflexes, the UES is constantly contracted, preventing esophageal air insufflation during breathing and laryngopharyngeal reflux of food during normal esophageal peristalsis.
- UES relaxes in two situations; to allow the bolus to pass to the esophagus, and to allow reflexive responses in retrograde direction, such as vomiting (emesis).
For more learning materials about the pharynx, click one of the following links: