Larynx: Anatomy and Function

• Objective: To describe the muscular wall, nerve and blood supply, plus venous and lymphatic drainage of the larynx

Laryngeal Inlet

• It is the opening of communication between the pharynx and larynx.
• Boundaries:
  • Upper border of epiglottis anteriorly
  • Aryepiglottic folds on both sides
  • Mucous membrane between the arytenoid cartilages posteriorly
• Aryepiglottic fold:
  • Mucosa fold extending between the apex of the arytenoid cartilage and the side of epiglottis
  • Encloses the aryepiglottic muscle, cuneiform and corniculate cartilages

Laryngeal Cavity

• Vocal fold:
  • Mucous membrane fold extending from the inner surface of thyroid cartilage to the vocal process of arytenoid cartilage
  • Folds enclose the vocal ligaments, which is the upper border of lateral cricothyroid ligaments
  • Fissure between the 2 vocal folds is called the rima glottidis
• Vestibular fold:
  • Mucous membrane fold extends from the inner surface of thyroid cartilage to the anterolateral surface of arytenoid cartilage
  • Encloses a fibrous band called the vestibular ligament
• Sinus of the larynx is a recess found between the vestibular and vocal folds
• Vestibule of the larynx is part of the cavity appearing between the inlet and the vestibular folds

Muscles of the Larynx

• Cricothyroid muscle:
  • Originates from the arch of the cricoid cartilage
  • Insertion is at the lamina and inferior cornua of the thyroid cartilage
  • Function: Increases tension on vocal ligaments
  • Innervated by the external laryngeal nerve
• Thyroarytenoid muscle:
  • Originates from the angle of the thyroid cartilage
  • Inserts at the arytenoid cartilage vocal process
  • Decreases tension on vocal ligaments
  • Innervated by the recurrent laryngeal nerve
• Vocalis muscle:
  • Inferior fibers of the thyroarytenoid
  • Decreases tension on the posterior part of the vocal ligaments
• Posterior cricoarytenoid:
  • Originates from the lamina of the cricoid cartilage
  • Inserts at the arytenoid muscular process
  • Opens the rima glottidis
• Lateral cricoarytenoid:
  • Originates from the arch of the cricoid cartilage lateral portion
  • Closes rima glottidis
• Transverse arytenoid:
  • Originates from the arytenoid muscular process
  • Inserts at the opposite arytenoid muscular process
  • Closes rima glottidis
• Oblique arytenoid:
  • Originates at the arytenoid
  • Inserts at the apex of the opposite arytenoid
• Aryepiglotticus:
  • Originates from the arytenoid apex
  • Inserts at the epiglottis
  • Function: To help close the laryngopharyngeal opening
• Thyroepiglotticus:
  • Originates from the thyroid lamina

Muscle actions and summary:

• Altering Rima Glottidis:
  • Posterior cricoarytenoid opens the rima glottidis
  • Transverse arytenoids, oblique arytenoids, and lateral cricoarytenoid close the rima glottidis
• Altering Tension on Vocal Cords:
  • Cricothyroid increases tension
  • Thyroarytenoid decreases tension

Nerve Supply

• Receives sensory supply from the vagus nerve
• Above the vocal folds, the mucous membrane is supplied by the internal laryngeal branch of the vagus nerve
• Below the level of the vocal folds, it is supplied by the recurrent laryngeal branch of the vagus

Blood Supply

• Superior laryngeal artery: branch off the superior thyroid artery, branching off the external carotid artery
• Inferior laryngeal artery: branch off the inferior thyroid artery from the thyrocervical trunk coming from the 1st part of the subclavian artery

Lymph Drainage

• Drains to the deep cervical lymph nodes

Applied Aspects

• Laryngitis:
  • Inflammation of the vocal cords in the larynx that typically doesn't persist longer than 7 days
    • Weak and hoarse voice
    • Sore throat
    • Cough
  • Most commonly caused by viral infection, or bacterial infection
  • Can also arise from excessive yelling or smoking