Anatomy, Head and Neck, Pharyngeal Muscles

The outer circular layer consists of the superior, middle, and inferior constrictor muscles. The superior constrictor muscle originates from the pterygoid process, posterior end of the mylohyoid line of mandible, and the pterygomandibular ligament/raphe. This superior constrictor muscle inserts into the base of the skull at the pharyngeal tubercle and the pharyngeal raphe. The pharyngeal raphe is a midline tendinous seam where the constrictor muscles meet. When the superior constrictor muscle contracts, it constricts the upper portion of the pharynx. The middle constrictor muscle originates from the greater and lesser horn of the hyoid bone and stylohyoid ligament. The middle constrictor inserts into the median pharyngeal raphe as well as blending in with fibers of the superior and inferior constrictors. The middle constrictor muscle contracts to constrict the middle portion of the pharynx. The inferior pharyngeal constrictor muscle further divides into two muscles, the thyropharyngeus, and the cricopharyngeus muscle. The thyropharyngeus muscle originates from the thyroid cartilage and inserts into the median pharyngeal raphe. The cricopharyngeus muscle originates from the cricoid cartilage and blends into the esophageal muscle. When the inferior constrictors contract, they constrict the lower portion of the pharynx. These constrictor muscles work together and contract to push food after swallowing to propel it from the oral cavity into the esophagus.[7]  

The inner longitudinal layer consists of the palatopharyngeus, salpingopharyngeus, and stylopharyngeus muscles. The palatopharyngeus muscle originates from the posterior hard palate, the palatine aponeurosis, and inserts into the thyroid cartilage. When the palatopharyngeus muscle contracts, it elevates the pharynx superiorly.  The salpingopharyngeus muscle originates from the inferior auditory tube and inserts into the palatopharyngeus muscle. This muscle contracts to elevate the pharynx superiorly as well as opening the auditory tube when swallowing. The stylopharyngeus muscle origin is from the styloid process of the temporal bone and it inserts into the posterior thyroid cartilage as well as merging with muscle fibers of the palatopharyngeal muscle. When the stylopharyngeus muscle contracts, it elevates the pharynx and larynx. As previously mentioned, this muscle is different from the other pharyngeal muscle in that it is the only muscle innervated by the glossopharyngeal nerve.[8] These longitudinal muscles work to elevate the pharynx and larynx superiorly during swallowing.[9][10]

There are multiple physiologic variants of the pharyngeal constrictor muscles. The superior constrictor can merge with the muscle of the middle and inferior constrictor. The inferior constrictor merges with the superior constrictor or the posterior part of the pharyngobasilar fascia.[11] Longitudinal muscle groups can have different insertion points, including into the palatine tonsil, epiglottis, and arytenoid.[1][10]

Cricopharyngeal myotomy can be performed to improve bolus transport for a patient experiencing symptoms of block dysphagia at the cricoid level. This procedure requires cutting into the muscle of the upper esophagus and cricopharyngeus muscle.[12]

Zenker diverticulum

The inferior pharyngeal constrictor muscle subdivides into the thyropharyngeus and cricopharyngeus muscle. The thyropharyngeus muscle is superior to the cricopharyngeus muscle, and during normal swallowing, the thyropharyngeus contracts while the cricopharyngeus relaxes to propel the food into the esophagus. If there is incoordination of contraction and relaxation of these two muscles, intrapharyngeal pressure can rise and form a diverticulum between the weak spot of the two muscles. This structure is called Zenker diverticulum, and it can cause an accumulation of food into the pouch and can lead to dysphagia. Other complication includes gurgling, aspiration, foul breath, and neck mass.[13] 

Pharyngitis

The pharynx can become inflamed and present with pain, irritation, discomfort, and dysphagia of the throat. This condition can be the result of bacteria or viral infections. If a viral infection is suspected, treatment is often supportive and given NSAIDs for pain. If a bacterial infection is suspected, antibiotics are the therapeutic intervention. Pharyngitis caused by Streptococcus Pyogenes is promptly treated to prevent the sequela of rheumatic fever and glomerulonephritis.

Dysphagia

Dysphagia is difficulty swallowing foods or liquids, and some etiology can be due to dysmotility of the pharyngeal muscles. Stroke patients can present with dysphagia due to its effect on the pharyngeal muscle.[14][15] Dysphagia is a common issue in the elderly and is primarily of oropharyngeal or esophageal origin.[16] 

Cricopharyngeal achalasia

Cricopharyngeal achalasia is when the cricopharyngeal muscle fails to open adequately enough to allow the passage of bolus into the esophagus. The patient can present with symptoms of choking, regurgitation, coughing, and recurrent pneumonia. A patient diagnosed with cricopharyngeal achalasia can have it treated with cricopharyngeal myotomy or with botulinum toxin injection.[17] 

Glossopharyngeal neuralgia

Glossopharyngeal neuralgia is a disorder presenting with the repeated episodes of pain lasting from a few seconds to minutes in the tongue, throat, ear, and tonsils and is usually unilateral. The pain can worsen or triggered by swallowing, speaking, and chewing. The etiology is thought to be due to irritation of the glossopharyngeal nerve, but the source of irritation is often not found. Glossopharyngeal neuralgia is often misdiagnosed as trigeminal neuralgia since the presentation of pain can overlap and looks similar.[18]