in the pharynx. Breathing The inferior pharyngeal constrictor muscle is partially used during breathing and speech. It helps to keep the pharynx open, particularly during sleep. Clinical significance Zenker's diverticulum Uncoordinated muscle contraction, cricopharyngeal spasm, or impaired relaxation of the inferior pharyngeal constrictor muscle are currently considered the main factors in development of a Zenker's diverticulum. Zenker's diverticulum develops between the two muscular bellies (the thyropharyngeal part and the cricopharyngeal part) in a small gap called Killian's dehiscence. A diverticulum can form where a balloon of mucosa becomes trapped outside the pharyngeal boundaries. Food or other materials may reside here, which may lead to infection. Motor incoordination of the cricopharyngeal part can cause difficulty swallowing. In extreme cases, this can be related to retrograde cricopharyngeus dysfunction (R-CPD) which causes the inability to burp; this is in part due to the muscle not being able to relax. Botox or a cricopharyngeal myotomy are used to treat the condition. Radiological damage The inferior pharyngeal constrictor muscle may be damaged by chemotherapy-intensity modulated radiotherapy. This may lead to dysphagia, causing continued use of a feeding tube rather than independent swallowing. Additional images See also Upper esophageal sphincter References External links () Muscles of the head and neck Pharynx