Inferior pharyngeal constrictor

At a glance

English

Inferior pharyngeal constrictor

Latin (TA2)

Constrictor inferior pharyngis

System

Muscle

Region

Whole body

Side

Paired, left and right

About the inferior pharyngeal constrictor

This muscle forms the lower part of the outer muscular coat of the pharynx, at the level of the larynx. It is the thickest of the three overlapping constrictors and is curved like a cupped hand, its fibres sweeping backwards from each side of the larynx to meet those of the opposite muscle at the back. Its lowest fibres pass without a break into the circular muscle of the oesophagus.

It has two parts. The upper thyropharyngeal part springs from the thyroid lamina's oblique line, from the area just behind it and from the inferior horn of the thyroid cartilage, with a slip from a tendinous arch over cricothyroid. Its fibres rise as they run backwards, overlapping the middle constrictor, and insert into the pharyngeal raphe in the posterior midline. The lower cricopharyngeal part arises from the side of the cricoid cartilage, between cricothyroid and the facet for the inferior thyroid horn. Its fibres run horizontally round the back of the pharynx without a raphe, forming a sling.

In swallowing, once the food has passed into the pharynx, the constrictors squeeze in sequence from above down and drive it towards the oesophagus. The cricopharyngeal part behaves differently: it stays tonically contracted between swallows as the upper oesophageal sphincter, keeping air out of the oesophagus and limiting backflow, and it relaxes briefly to let each mouthful through.

Both parts are supplied from the pharyngeal plexus, chiefly vagal fibres, with extra branches from the external and recurrent laryngeal nerves, especially to the cricopharyngeal part. Blood comes from the superior and inferior thyroid arteries and the ascending pharyngeal artery. Between the two parts at the back lies a thin, weak triangle of wall with few muscle fibres. If the sphincter fails to relax properly, pressure can push the lining out through this gap to form a pouch, a Zenker diverticulum, in which food collects. Poor relaxation also causes difficulty swallowing and, in some people, an inability to belch; muscle injections or division of the sphincter can help.

Attachments, action and supply

Origin

Thyropharyngeal part: oblique line and inferior horn of the thyroid cartilage; cricopharyngeal part: side of the cricoid cartilage.

Insertion

Posterior pharyngeal raphe, meeting its partner; lowest fibres continuous with the circular muscle of the oesophagus.

Action

Constricts the lower pharynx to push food into the oesophagus; the cricopharyngeal part acts as the upper oesophageal sphincter.

Nerve supply

Pharyngeal plexus (vagus nerve), with branches of the external and recurrent laryngeal nerves.

Blood supply

Superior and inferior thyroid arteries and the ascending pharyngeal artery.