The trachealis muscle is a band of smooth muscle that constitutes the posterior (membranous) wall of the trachea. It extends longitudinally between the cartilaginous rings, completing the cylindrical tube by bridging the gap left by the incomplete cartilaginous support on the dorsal aspect.
Anatomical location and structure
- Situated at the back of the trachea, posterior to the tracheal lumen.
- Composed of longitudinally oriented smooth muscle fibers that interdigitate with the adventitial connective tissue.
- The muscle is continuous with the smooth muscle of the adjacent bronchi (the bronchial smooth muscle) and with the muscularis of the esophagus at the level of the tracheoesophageal groove.
Innervation and vascular supply
- Receives parasympathetic innervation primarily via the vagus nerve (via the recurrent laryngeal and other branches of the pulmonary plexus).
- Sympathetic fibers may influence tone indirectly through the thoracic sympathetic chain.
- Vascularized by branches of the inferior thyroid artery superiorly and the bronchial arteries inferiorly.
Physiological function
- Modulates the diameter of the tracheal lumen. Contraction of the trachealis muscle narrows the tracheal lumen, especially during forced expiration, coughing, or Valsalva maneuvers, aiding in expulsion of secretions and protective airway closure.
- Relaxation of the muscle permits maximal airway patency during inspiration.
- Works in concert with the cartilaginous rings, which provide rigid lateral support, to allow dynamic changes in airway caliber.
Developmental origin
- Derives from the mesodermal mesenchyme of the foregut during embryogenesis, differentiating alongside the surrounding tracheal cartilage and the smooth muscle of the bronchial tree.
Clinical relevance
- Hypertonicity of the trachealis muscle may contribute to airway obstruction in conditions such as asthma or chronic obstructive pulmonary disease (COPD).
- Pharmacological agents that affect smooth muscle tone (e.g., anticholinergics, beta‑adrenergic agonists) can alter tracheal caliber by acting on the trachealis muscle.
- In surgical procedures involving the trachea (e.g., tracheostomy, tracheal resection), awareness of the trachealis muscle is important for preserving airway dynamics and preventing postoperative stenosis.
Comparative anatomy
- The presence of a posterior membranous wall formed by smooth muscle is a characteristic shared by many mammals, though the proportion of muscle to cartilage varies among species.
References
(Encyclopedic sources such as standard anatomical textbooks and peer‑reviewed articles on airway physiology describe the trachealis muscle and its role in respiratory mechanics.)