Functions of Pharyngeal Muscles During Deglutition (Swallowing)

The Pharyngeal Muscles and Their Roles

Group 1: Pharyngeal Constrictors (all insert into the median pharyngeal raphe)

Group 2: Pharyngeal Elevators (shorten the pharynx - longitudinal muscles)

Group 3: Cricopharyngeus - The Upper Esophageal Sphincter (UES)

• Composed primarily of the cricopharyngeus muscle, along with the cervical esophagus and inferior pharyngeal constrictor
• At rest: tonically contracted, preventing air entry into the esophagus and reflux upward
• During swallowing: actively dilated by laryngeal elevation (hyoid and larynx pulled up by suprahyoid muscles) - relaxes to allow bolus passage into the esophagus
• The Killian dehiscence is a weakness between the cricopharyngeus and inferior constrictor; with age this can lead to a Zenker's diverticulum

Step-by-Step Events in the Pharyngeal Phase

1. Velopharyngeal sealing: The superior constrictor contracts at its upper border, forming Passavant's ridge. The soft palate is elevated against this ridge, sealing off the nasopharynx and preventing nasal regurgitation.
2. Laryngeal elevation and airway protection: Suprahyoid muscles (mylohyoid, digastric) and thyrohyoid elevate the hyoid bone and larynx. The laryngeal inlet approaches the epiglottis. The epiglottis is pulled down by the base-of-tongue muscles and aryepiglottic muscles. The rima glottidis closes. Respiration is briefly interrupted - the lower airways are sealed.
3. Pharyngeal expansion: As the larynx elevates, the pharynx expands anteriorly and superiorly, creating a low-pressure receiving chamber.
4. Bolus transport: The tongue is drawn posteriorly (styloglossus, hyoglossus), pushing the bolus through the fauces into the enlarged pharynx. Most food travels through the piriform recesses on either side; fluid courses over the epiglottis. Sequential contraction of the superior → middle → inferior constrictors propels the bolus downward.
5. UES opening: Laryngeal elevation physically dilates the cricopharyngeus (UES), and the sphincter reflexly relaxes, allowing the bolus into the esophagus.
6. Recovery: The larynx descends, glottis reopens, respiration resumes (typically during expiration), and the constrictors return to resting tone.

Neural Control Summary

• Afferent trigger: Receptors in the posterior upper pharyngeal wall, soft palate, and oropharyngeal mucosa send signals via CN IX and X to the swallowing center in the medulla (nucleus tractus solitarius + nucleus ambiguus)
• Efferent output: Motor commands via the pharyngeal plexus (CN IX + X) to all constrictors; CN IX exclusively to stylopharyngeus; XII to tongue
• Central pattern generator: Located in the caudal NTS and medullary reticular formation adjacent to nucleus ambiguus; controls the entire involuntary sequence without requiring continuous peripheral feedback

• Cummings Otolaryngology: Head and Neck Surgery - Oral Phase of Deglutition
• Ganong's Review of Medical Physiology (26th ed.) - Swallowing, pp. 499
• Color Atlas of Human Anatomy Vol. 2 - The Act of Swallowing, pp. 286-287
• K.J. Lee's Essential Otolaryngology - Pharyngeal Walls
• Gray's Anatomy for Students - Constrictor Muscles

Functions of Pharyngeal Muscles During Deglutition

• Contract sequentially in a peristaltic wave to propel the bolus from oropharynx into the esophagus
• Superior constrictor forms Passavant's ridge to seal the nasopharynx (prevents nasal regurgitation)

• Elevate and widen the pharynx, pulling it upward over the descending bolus
• Salpingopharyngeus also opens the Eustachian tube to equalize middle ear pressure

• Tonically contracted at rest (prevents reflux/air entry)
• Relaxes during swallowing (aided by laryngeal elevation) to let the bolus enter the esophagus

1. Seal nasopharynx (velopharyngeal closure)
2. Protect airway (epiglottis down, glottis closed, respiration briefly stopped)
3. Propel bolus downward via peristaltic constriction
4. Open UES to allow esophageal entry