The middle pharyngeal constrictor muscle is one of the three pharyngeal constrictor muscles that form the circular muscular layer of the pharynx.[7] It assists in swallowing by contracting sequentially to move food from the oropharynx to the esophagus.
Location
The middle pharyngeal constrictor muscle is located in the middle portion of the pharynx, overlapping the inferior portion of the superior pharyngeal constrictor and the superior portion of the inferior pharyngeal constrictor.[5] It originates from the stylohyoid ligament and the greater and lesser horns of the hyoid bone, and inserts into the pharyngeal raphe, a fibrous midline structure at the back of the pharynx.
Anatomy
The middle pharyngeal constrictor muscle is the intermediate muscle of the three pharyngeal constrictors that form the circular layer of the pharyngeal wall. Below is a detailed description of its anatomy:
Structure
- The middle pharyngeal constrictor is a thin, fan-shaped muscle that contributes to the walls of the pharynx.[3]
- It overlaps both the superior pharyngeal constrictor (above) and the inferior pharyngeal constrictor (below), ensuring a continuous muscular tube for swallowing.
Origin
The muscle arises from two main sites:
Stylohyoid Ligament:
A fibrous band connecting the styloid process to the lesser horn of the hyoid bone.
Hyoid Bone:
Specifically, the greater and lesser horns of the hyoid bone.
Insertion
- The fibers of the middle pharyngeal constrictor course posteriorly and medially to insert into the pharyngeal raphe, a fibrous midline structure at the back of the pharynx.[1]
- The superior fibers overlap with the inferior fibers of the superior pharyngeal constrictor.
- The inferior fibers blend with the superior fibers of the inferior pharyngeal constrictor.
Layers and Orientation
- The middle pharyngeal constrictor is part of the outer circular muscle layer of the pharynx.
- It lies superficial to the inner longitudinal muscle layer, which includes muscles like the stylopharyngeus, palatopharyngeus, and salpingopharyngeus.
Blood Supply
Arterial Supply:
Supplied by branches of the:
- Ascending pharyngeal artery (from the external carotid artery).
- Facial artery (ascending palatine branch).
- Lingual artery.
Venous Drainage:
Drains into the pharyngeal venous plexus, which ultimately empties into the internal jugular vein.
Nervous Supply
Innervated by the pharyngeal plexus, which is formed by:
- Vagus nerve (cranial nerve X) providing motor innervation.
- Contributions from the glossopharyngeal nerve (cranial nerve IX) for sensory input.[8]
Lymphatic Drainage
Lymph from the middle pharyngeal constrictor drains into the deep cervical lymph nodes.
Relationships to Adjacent Structures
Superiorly:
Overlaps with the inferior fibers of the superior pharyngeal constrictor.
Inferiorly:
Overlapped by the superior fibers of the inferior pharyngeal constrictor.
Anteriorly:
Related to the hyoid bone and the stylohyoid ligament.
Posteriorly:
Inserts into the pharyngeal raphe and is covered by pharyngeal mucosa.
Functional Integration
Although primarily circular, its fibers blend seamlessly with the other pharyngeal constrictors to form a continuous muscular tube that facilitates the coordinated movement of food during swallowing.[6]
Functions
The middle pharyngeal constrictor muscle plays a crucial role in swallowing (deglutition) by contributing to the sequential contraction of the pharyngeal constrictor muscles, ensuring efficient movement of food and liquids from the oropharynx into the esophagus. Below is a detailed explanation of its functions:
Sequential Constriction of the Pharynx
The middle pharyngeal constrictor muscle contracts in a coordinated manner after the superior pharyngeal constrictor and before the inferior pharyngeal constrictor during the pharyngeal phase of swallowing:
- This sequential contraction creates a peristaltic wave that propels the bolus (food or liquid) downward toward the esophagus.
- The wave of contraction narrows the pharyngeal lumen, forcing the bolus in a single direction.
Narrowing of the Pharyngeal Lumen
By contracting, the middle pharyngeal constrictor reduces the diameter of the pharynx:
- This narrowing ensures the bolus is directed smoothly and efficiently through the oropharynx to the laryngopharynx.
- Prevents food or liquid from remaining in the pharynx or moving backward.
Coordination with Other Pharyngeal Muscles
The middle pharyngeal constrictor works in tandem with:
- Superior pharyngeal constrictor: To propel the bolus from the nasopharynx and oropharynx.
- Inferior pharyngeal constrictor: To guide the bolus into the esophagus.
- This coordination ensures a smooth and efficient swallowing process, avoiding interruptions or misdirection of the bolus.[4]
Stabilization of the Pharyngeal Wall
The muscle provides structural support to the pharyngeal wall during swallowing and breathing:
Its contraction helps maintain the integrity and tone of the pharyngeal tube, preventing collapse during bolus transit or respiration.
Prevention of Bolus Misdirection
By forming part of the pharyngeal constrictor system, the middle pharyngeal constrictor aids in ensuring the bolus is directed toward the esophagus and not into the nasal cavity or airway:
Works indirectly with the soft palate and epiglottis to ensure proper closure of the nasopharynx and laryngeal inlet, respectively.
Functional Integration in Swallowing Phases
The middle pharyngeal constrictor muscle is active during the pharyngeal phase of swallowing:
- This phase is involuntary and controlled by the swallowing center in the brainstem (medulla oblongata).
- The muscle’s action is triggered reflexively as the bolus enters the pharynx.
Clinical Significance
The middle pharyngeal constrictor muscle plays a critical role in swallowing, and its dysfunction can contribute to several clinical conditions:
- Dysphagia (Difficulty Swallowing):
- Impaired contraction or coordination of the middle pharyngeal constrictor may result in incomplete bolus propulsion, leading to food retention in the pharynx or misdirection into the airway.[2]
- Aspiration Risk:
- Weakness or uncoordinated contraction can allow food or liquids to enter the airway, increasing the risk of aspiration pneumonia.
- Pharyngeal Weakness:
- Neurological conditions like stroke, Parkinson’s disease, or multiple sclerosis can affect the pharyngeal constrictor muscles, including the middle constrictor, causing swallowing disorders.
- Surgical Landmark:
- The muscle is a key landmark during neck surgeries, particularly in procedures involving the pharynx, hyoid bone, or surrounding vascular structures.