Topography and Anatomical Regions
Superiorly, the larynx communicates with the pharynx, and inferiorly it transitions into the trachea. The internal cavity of the organ is narrowed in the center (resembling an hourglass), which divides the larynx topographically and functionally into three regions:
- Vestibule of the larynx (Supraglottic region). An expanded upper part leading from the laryngeal inlet to the constriction.
- Middle region (Glottis). A narrowed area where the vocal apparatus is located.
- Infraglottic cavity (Subglottic region). The expanded lower part of the organ that smoothly transitions into the trachea.
General Plan of the Wall Structure
Similar to the nasal cavity, the wall of the larynx lacks a submucosa. The wall is formed by three layers:
- Mucosa (Tunica mucosa). Characterized by heterogeneous structure across different areas. This heterogeneity is directly related to the varying functional demands on different parts of the larynx.
- Fibro-muscular-cartilaginous layer. The middle layer, whose thickness and histological composition vary depending on the specific region.
- Adventitia (Tunica adventitia). The outer layer formed by loose connective tissue. A distinctive feature is that it contains more collagen fibers than the lamina propria of the mucosa. Vascular and nerve plexuses run through this layer.
Fibro-Muscular-Cartilaginous Layer: The Framework of the Organ
This layer determines the shape and rigidity of the larynx. It consists of three interrelated tissue components:
- Cartilaginous component. Represented by two types of cartilage tissue. Hyaline cartilage forms the large cartilages (thyroid and cricoid). Elastic cartilage forms the epiglottis and smaller cartilages (cuneiform, corniculate).
- Fibrous component. The cartilages are united into a single framework by ligaments and membranes composed of dense regular connective tissue.
- Muscular component. Represented by both smooth and skeletal muscle tissue. Smooth myocytes are located within the false vocal folds. Skeletal muscle forms the vocalis muscle (within the true folds) and seven extrinsic muscles of the larynx responsible for swallowing and phonation.
Vocal Apparatus
The vocal apparatus is located in the narrowed middle region of the larynx. Its basis consists of two pairs of folds and the recesses between them:
- Vestibular folds (False vocal cords). The superior pair of folds. They are called "false" because their core lacks skeletal muscle tissue (containing only smooth myocytes). Consequently, they cannot alter the width of the rima glottidis and do not participate in phonation.
- Vocal folds (True vocal cords). The inferior pair of folds. Their core contains vocal ligaments and the vocalis muscle, formed by striated skeletal muscle. They actively participate in sound production.
- Laryngeal ventricles. Recesses located between the vestibular and vocal folds. Sometimes they extend superiorly to form blind appendices of varying lengths.