Laryngeal Inlet and Vestibule
The upper expanded compartment is called the laryngeal vestibule (vestibulum laryngis). It extends from the laryngeal inlet (aditus laryngis) down to the vestibular folds (plicae vestibulares).
Anatomical boundaries of the laryngeal inlet:
- Anteriorly: Posterior surface of the epiglottis.
- Posteriorly: Apices of the arytenoid cartilages.
- Laterally: Aryepiglottic folds (plicae aryepiglotticae).
The epiglottis plays a crucial role in airway protection. Its position is regulated by the contraction of the aryepiglottic (m. aryepiglotticus) and thyroepiglottic (m. thyroepiglotticus) muscles. During swallowing, it descends and hermetically seals the laryngeal inlet. A depression called the piriform fossa (recessus piriformis) forms between the lateral walls of the vestibule and the inner surface of the thyroid cartilage.
Mucous Membrane and Its Structures
The laryngeal mucosa (tunica mucosa laryngis) is anchored to the cartilaginous skeleton by the fibroelastic membrane of the larynx (membrana fibroelastica laryngis). The density of this attachment varies: the loosest connection is observed in the region of the aryepiglottic folds and at the free edges of the vocal cords.
The mucosa forms several important structures:
- Vestibular folds (plicae vestibulares) — cover the corresponding ligaments.
- Vocal folds (plicae vocales) — formed by mucosa covering the vocalis muscle, vocal ligament, and conus elasticus.
- Laryngeal ventricle (ventriculus laryngis) — a paired small recess on the lateral wall between the vestibular and vocal folds. Anteriorly, it leads into a blind pouch, the laryngeal saccule (sacculus laryngis).
Most of the surface is lined by pseudostratified ciliated epithelium. However, areas subjected to high mechanical stress (vocal folds, lingual surface of the epiglottis, and inner surface of the arytenoid cartilages) are covered by stratified squamous epithelium.
Numerous mucous glands (glandulae laryngeales) moisten the surface. They are particularly abundant in the laryngeal ventricles, on the posterior surface of the epiglottis, and near the interarytenoid fold. Glands are absent on the free edges of the vocal folds.
Vocal Apparatus and Infraglottic Cavity
The middle part of the laryngeal cavity is the vocal apparatus (glottis). This is the narrowest compartment, which visually appears as a sagittal cleft.
Two important slit-like spaces are distinguished here:
- Rima vestibuli — located between the vestibular folds.
- Rima glottidis (rima glottidis / vocalis) — the space between the vocal folds. This is the primary structure for phonation.
Topographically, the rima glottidis is divided into:
- Intermembranous part (pars intermembranacea) — the anterior portion between the margins of the vocal folds.
- Intercartilaginous (respiratory) part (pars intercartilaginea) — the posterior portion located directly between the arytenoid cartilages.
Posterior to the rima glottidis lies the interarytenoid notch (incisura interarytenoidea), which continues upward into the vestibule.
The lower compartment of the larynx, beginning just below the vocal folds, is called the infraglottic cavity (cavitas infraglottica). It has a conical shape, gradually expanding inferiorly and continuous with the tracheal lumen without a sharp boundary.
Blood Supply, Drainage, and Innervation
The blood supply and innervation of the larynx are strictly segmented and depend on the level relative to the glottis.
Arterial supply:
- Superior laryngeal artery (a. laryngea superior) — branch of the superior thyroid artery.
- Inferior laryngeal artery (a. laryngea inferior) — branch of the inferior thyroid artery.
Blood and lymph drainage: Venous blood drains via corresponding veins emptying into the superior and inferior thyroid veins. Lymph drains into the deep anterior cervical (nodi lymphoidei cervicales profundi anteriores) and lateral jugular lymph nodes.
Innervation: Provided by branches of the vagus nerve (n. vagus):
- Above the glottis, the mucosa is innervated by the superior laryngeal nerve (n. laryngeus superior).
- Below the glottis, by the inferior laryngeal nerve (n. laryngeus inferior), which is the terminal branch of the recurrent laryngeal nerve.