The superior constrictor pharyngeal muscle (SCPM) originates at the lateral base of tongue, medial pterygoid plate, pterygomandibular raphe, pterygoid hamulus, and the posterior end of the mylohyoid line. It inserts onto the pharyngeal raphe and contracts during deglutition to move the soft palate to the posterior pharyngeal wall, thus preventing the bolus from moving upward.[2][9]

The middle constrictor pharyngeal muscle (MCPM) originates from the stylohyoid ligament and the greater and lesser horns of the hyoid bone. It fans out to attach along the pharyngeal raphe, but this muscle rarely reaches the top of the pharynx (superiorly) or thyroid cartilage (inferiorly). The contraction of these fibers constrict and close the pharynx during deglutition to propel the bolus downward.[1]

The inferior constrictor pharyngeal muscle (ICPM) originates from the cricoid and thyroid cartilages and crosses the cricothyroid muscle. It inserts onto the pharyngeal raphe and constricts in coordination with the SCPM and MCPM during deglutition to propel the bolus towards the esophagus. Due to the finding that some of the inferior ICPM fibers merge with fibers of the cricothyroid muscle, the belief is that the ICPM serves as part of the functional UES.[10][11] 

The cricopharyngeus muscle attaches at the cricoid cartilage and wraps around the pharynx. In contrast to the constrictor muscles, it maintains a contracted state during resting physiology to maintain the UES and thus helps to prevent pharyngeal reflux of esophageal contents. During deglutition, the cricopharyngeus relaxes as the bolus descends through the pharynx to allow passage into the esophagus. The coordination of the constrictor muscle peristalsis with this opening of the UES also creates a negative pressure to propel the bolus further.[2][12]

The palatopharyngeus originates from both the oral and nasal side of the soft palate and inserts along the pharyngeal wall. It functions to elevate the pharynx and moves the lateral pharyngeal wall toward the midline, which propels a bolus downward during deglutition.[13]

The stylopharyngeus muscle originates from the styloid process and inserts along the pharyngeal wall. It functions along with the PP and SLP to elevate the pharynx during deglutition.

The SLP originates from the Eustachian tube and inserts along the pharyngeal wall. It functions along with the PP and STP to elevate the pharynx during deglutition.[3]

Minor anatomic and physiologic variations can occur in these pharyngeal muscles, due to the proximity to other structures and a rich neurovascular supply. Additional attachments by the longitudinal muscle group is a common occurrence, with insertions into the palatine tonsil, epiglottis, arytenoid and thyroid cartilage, among others. In one study, the SLP muscle was found to be present in only 63% of cadavers, with the majority being very thin.[3][14]

The pharyngeal muscles have many surgical implications regarding dysphagia, breathing, and cancer resection. Patients undergoing significant resection of pharyngeal muscles during oncologic surgery should have an assessment for dysphagia and aspiration in the postoperative period. Feeding tubes and swallowing therapy may be required. Another example is the importance of preservation of the STP muscle during lateral pharyngoplasty for obstructive sleep apnea.[15] 

Swallowing requires precise coordination between many different nerves and muscles, and many problems can arise. As noted above, a common important clinical problem is dysphagia. The prevalence of dysphagia is around 50% in the very elderly and is also 50% in those with neurologic dysfunction. Many severe complications can arise from dysphagia, such as malnutrition or pulmonary aspiration of food or saliva. The prevalence of dysphagia makes it a highly prioritized area of research.[16][17][18] 

The pharyngeal muscles also can be implicated in other processes such as sleep apnea. During sleep, these muscles may become hypotonic and are unable to prevent the collapse of the airway if increased airway resistance/narrowing are present from factors such as generalized hypotonia, obesity, macroglossia (large tongue), tonsillar hypertrophy, retrognathia (short jaw), etc.).[19]

Failure of relaxation of the cricopharyngeus muscle during swallowing (cricopharyngeal achalasia) can lead to both dysphagia and a pathologic outpouching of the pharynx called Zenker's diverticulum. Since the cricopharyngeus does not relax in the usual fashion, pressure from the constrictor muscles and the bolus builds up in the pharynx causing an outpouching of the pharynx that fills with food. Since the cricopharyngeus is innervated by the pharyngeal plexus and the recurrent laryngeal nerve, a thorough workup including complete head, neck, and chest exam are indicated. If possible malignancy is suspected, esophagoscopy, laryngoscopy, and bronchoscopy are required. MRI or CT of the neck and chest may also be necessary since the vagus and recurrent laryngeal nerves pass through the neck and chest.