Corpus: Inferior pharyngeal constrictor muscle
from Latin: constringere - to constrict; from ancient Greek: φάρυγξ ("pharynx") - throat
1. Definition
The inferior pharyngeal constrictor muscle is a striated skeletal muscle and the most caudal constrictor of the pharyngeal musculature, connecting to the esophagus inferiorly.
2. Embryology
The inferior pharyngeal constrictor muscle primarily develops from the muscle system of the 6th pharyngeal (gill) arch, which fuses with the 4th pharyngeal arch.
3. Anatomy
3.1. Classification
The inferior pharyngeal constrictor muscle consists of two parts:
- the thyropharyngeal part
- the cricopharyngeal part
Some authors consider the cricopharyngeal part a separate muscle, referring to it as the "cricopharyngeus muscle". This part can be further subdivided into the oblique and fundiform parts.
3.2. Origin
The thyropharyngeal part originates from the oblique line of the thyroid cartilage, while the cricopharyngeal part originates from the lateral edge of the cricoid cartilage.
3.3. Attachment
The fibers of the inferior pharyngeal constrictor muscle run obliquely upward, medially, and dorsally, merging with the fibers from the opposite side at the pharyngeal raphe. These fibers overlap the caudal fibers of the middle pharyngeal constrictor muscle.
4. Innervation
The inferior pharyngeal constrictor muscle is innervated by the pharyngeal plexus, a network of nerves that includes contributions from the glossopharyngeal nerve (cranial nerve IX) and the vagus nerve (cranial nerve X). The external branch of the superior laryngeal nerve also contributes fibers to the pharyngeal plexus and plays a role in innervating this muscle.[1][2]
5. Function
5.1. Swallowing
The inferior pharyngeal constrictor muscle constricts the hypopharynx, pushing the food bolus toward the esophagus during swallowing.
5.2. Phonation
During phonation, the muscle has a dual role. The cricopharyngeal part acts antagonistically to the cricothyroid muscle, which stretches the vocal folds, and synergistically with the vocalis muscle, which shortens the vocal folds. This is achieved by rotating the cricoid cartilage and pulling the larynx backward, causing the vocal folds to shorten. This effect is more pronounced with lower pitch tones, where a low larynx position enhances the effect by passively tensing the pharyngeal wall. Overactivity of this muscle may result in a rough and strained voice.
In contrast, the thyropharyngeal part contributes to the lengthening and increased tension of the vocal folds by bringing the thyroid cartilage plates closer together. This action is observed during transitions from soft to loud sounds and from the falsetto to the chest voice register. The elevation of the larynx, which this muscle contributes to during swallowing, also increases its tone.
6. Clinic
Between the oblique and fundiform parts of the cricopharyngeal lies the Killian triangle, a region of muscle weakness that is prone to the formation of Zenker's diverticula. Additionally, Killian-Jamieson diverticula can form ventrolaterally beneath the fundiform part.
7. Sources
8. Literature
- Anderhuber et al, Waldeyer - Human Anatomy: Textbook and Atlas in One Volume (De Gruyter Studium) (19th totaly rev. ed.), De Gruyter, 2012