Inferior pharyngeal constrictor

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 further divided into two parts: pars oblique (superior part) and pars fundiformis (inferior part). The pars oblique is oriented posteromedially, inserting onto the median pharyngeal raphe. The pars fundiformis courses horizontally forming a semicircular band that fuses with the circular muscle fibers of the proximal esophagus.

Relations

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.

Buccopharyngeal fascia lies posterior to the muscle and separates the whole pharynx from the posteriorly located retropharyngeal space and vertebral compartment of the neck.

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.

Innervation

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.

Blood supply

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.

Function

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).

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