Pharyngeal Muscles: Actions and Innervations
Overview of Pharyngeal Muscle Groups
The pharyngeal muscles are organized into four functional groups based on their innervation patterns: Group 1 (glossopharyngeal nerve), Groups 2-3 (pharyngeal plexus from vagus and accessory nerves), and Group 4 (pharyngeal plexus plus laryngeal nerves). 1
Constrictor Muscles (Circular Layer)
Superior Pharyngeal Constrictor
Actions:
- Constricts the upper pharynx during swallowing 2
- Maintains pharyngeal wall stiffness during respiration and speech articulation 3
- Coordinates smooth movements from mastication to swallowing through its attachment to the buccinator muscle 2
Innervation:
- Slow inner layer (SIL): Glossopharyngeal nerve (CN IX) - contains slow-tonic and alpha-cardiac muscle fibers specialized for sustained contraction during speech and respiration 3
- Fast outer layer (FOL): Pharyngeal plexus (vagus nerve CN X and accessory nerve CN XI) via dorsal surface - adapted for rapid movement during swallowing 1, 3
Anatomical subdivisions:
- Pterygopharyngeal part (from pterygoid hamulus)
- Buccopharyngeal part (transitionally originates from buccinator muscle) 2
- Mylopharyngeal part (from mylohyoid line of mandible) 2
- Glossopharyngeal part (from tongue root) - innervated by CN IX 1
Middle Pharyngeal Constrictor
Actions:
- Constricts the middle pharynx during pharyngeal phase of swallowing 4
Innervation:
- Pharyngeal plexus (vagus and accessory nerves) from both ventral and dorsal surfaces 1
- The plexus sends branches between the constrictors to reach the muscle 1
Inferior Pharyngeal Constrictor
Actions:
- Constricts the lower pharynx and coordinates with upper esophageal sphincter opening 4
Innervation:
- Pharyngeal plexus (vagus and accessory nerves) from ventral and dorsal surfaces 1
- Additional innervation: Superior and recurrent laryngeal nerves 1
Longitudinal Muscles (Vertical Layer)
Stylopharyngeus
Actions:
Innervation:
- Glossopharyngeal nerve (CN IX) - the nerve occasionally penetrates through the muscle 1
Palatopharyngeus
Actions:
- Elevates the pharynx and larynx during swallowing 5
- Assists in soft palate elevation by holding the levator veli palatini muscle 5
- Functions in respiration and phonation via attachments to laryngeal cartilages (arytenoid, thyroid) 5
- Transverse part acts as a sphincter to help maintain upper airway patency 5, 6
Innervation:
- Pharyngeal plexus (vagus and accessory nerves) entering mainly through the lateral border 6
- Additional fibers from lesser palatine nerves 6
Anatomical organization:
- Originates from palatine aponeurosis and median soft palate 5
- Divides into medial and lateral bundles around levator veli palatini 5
- Lateral bundle further divides into longitudinal and transverse parts 5
- Inserts into palatine tonsil, epiglottis, arytenoid cartilage, piriform recess, thyroid cartilage, and pharyngeal wall 5
Salpingopharyngeus
Actions:
- Elevates the pharynx during swallowing 4
Innervation:
- Pharyngeal plexus (vagus and accessory nerves) from dorsal surface 1
Clinical Pitfalls
The slow inner layer of the superior constrictor is unique to adult humans (not present in newborns or nonhuman primates) and is specialized for speech and sustained respiratory tone - this layer becomes obscured in elderly patients and those with Parkinson's disease, contributing to dysphagia susceptibility 3
Anomalous muscle bundles frequently occur between the superior and middle constrictors and the stylopharyngeus, likely caused by the stylopharyngeus penetrating between constrictor groups during development 1
The pharyngeal plexus spreads not only on the dorsolateral pharyngeal surface but also sends branches between the constrictors, making surgical dissection complex 1
Surgical procedures involving the palatopharyngeus muscle should preserve innervation entering through the lateral border to maintain swallowing and speech function 6