Cricopharyngeus Muscle Classification
The cricopharyngeus muscle is part of the inferior pharyngeal constrictor group, though it functions as a distinct anatomical and functional unit within the upper esophageal sphincter. 1
Anatomical Classification
The cricopharyngeus represents the most inferior portion of the pharyngeal constrictor muscle system and is specifically associated with the inferior pharyngeal constrictor muscle complex. 2 However, it maintains distinct characteristics that set it apart:
The cricopharyngeus has three distinct muscular bundles: superior oblique fibers joining the inferior pharyngeal constrictor, horizontal circular fibers (11-12mm high, 3mm thick), and inferior oblique fibers joining the external layer of the superior esophagus. 3
Anatomically, the cricopharyngeus sits at the pharyngoesophageal junction at the level of the cricoid cartilage, forming the primary muscular component of the upper esophageal sphincter. 4
Functional Distinction from Other Constrictors
While grouped with the inferior constrictor, the cricopharyngeus functions differently:
The cricopharyngeus is tonically contracted at rest (unlike other pharyngeal constrictors) and relaxes during swallowing, belching, and vomiting. 4
Muscle fiber composition differs markedly: the cricopharyngeus shows 89% type I (slow-twitch) fibers, while the inferior pharyngeal constrictor shows 62% type II (fast-twitch) predominance. 2
Neural Innervation Pattern
The cricopharyngeus has unique dual innervation that distinguishes it from typical pharyngeal constrictors:
The recurrent laryngeal nerve provides motor innervation to the posterior cricopharyngeus through its dorsal branch, along with the inferior constrictor and all intrinsic laryngeal muscles except the cricothyroid. 1, 5
The superior laryngeal nerve supplies the anterior cricopharyngeus via its lateral branch, creating a double vagal innervation pattern. 3
This dual innervation contrasts with the inferior pharyngeal constrictor, which receives innervation primarily from the pharyngeal plexus, though the recurrent laryngeal nerve functionally contributes to the inferior constrictor in most patients. 2, 5
Clinical Relevance
During thyroid surgery, the cricopharyngeus can be identified by its relationship to the tracheoesophageal groove where the RLN travels, positioned posterior to the thyroid gland and adjacent to the esophagus. 1
Recognition that the RLN innervates the cricopharyngeus is critical to maintaining cricopharyngeal function during neck surgery. 1
The cricopharyngeus corresponds to only the distal one-third of the manometric high-pressure zone of the upper esophageal sphincter, with the peak pressure zone located proximal to the anatomic cricopharyngeus muscle. 6