The inferior pharyngeal constrictor muscle is a skeletal muscle of the neck. It is the thickest of the three outer pharyngeal muscles. It arises from the sides of the cricoid cartilage and the thyroid cartilage. It is supplied by the vagus nerve (CN X). It is active during swallowing, and partially during breathing and speech. It may be affected by Zenker's diverticulum. Structure The inferior pharyngeal constrictor muscle is composed of two parts. The first part (and more superior) arises from the thyroid cartilage (thyropharyngeal part), and the second part arises from the cricoid cartilage (cricopharyngeal part). On the thyroid cartilage, it arises from the oblique line on the side of the lamina, from the surface behind this nearly as far as the posterior border and from the inferior horn of the thyroid cartilage. From the cricoid cartilage, it arises in the interval between the cricothyroid muscle in front, and the articular facet for the inferior horn of the thyroid cartilage behind. From these origins, the fibers spread backward and medially to insert with the muscle of the opposite side into the fibrous pharyngeal raphe in the posterior median line of the pharynx. The thyropharyngeal part mainly uses type 2 fibres (anaerobic), while the cricopharyngeal part mainly uses type 1 fibres (aerobic). Fibre type may change after birth. The inferior fibers are horizontal and continuous with the circular fibers of the esophagus; the rest ascend, increasing in obliquity, and overlap the middle pharyngeal constrictor muscle. The cricopharyngeal part is synonymous with the upper esophageal sphincter (UES), which controls the opening of the cervical esophagus. It is sometimes referred to as the cricopharyngeal inlet. Nerve supply The inferior pharyngeal constrictor muscle is supplied by branches from the pharyngeal plexus, and the recurrent laryngeal nerve. These come from the vagus nerve (CN X). This is similar to the superior pharyngeal constrictor muscle and the middle pharyngeal constrictor muscle. Variation The inferior pharyngeal constrictor muscle can merge with superior pharyngeal constrictor, or posterior part of pharyngobasilar fascia. Function The inferior pharyngeal constrictor muscle has a broad role in moving the lower part of the pharynx. Swallowing As soon as a bolus of food is received in the pharynx, elevator muscles relax, and the pharynx descends. The inferior pharyngeal constrictor muscle, along with the other constrictors, contract upon the bolus, and convey it downward into the esophagus. During swallowing, they contract and cause peristalsis