Anatomy of the Larynx

Laryngeal Cartilages & Framework - Skeleton Story

• Location & Key Functions:
  • Situated at C3-C6 vertebral levels.
  • Essential for: Airway protection (prevents aspiration), Respiration (maintains patent airway), Phonation (voice production).
• Unpaired Cartilages (Single):
  • Thyroid: Largest. Formed by two laminae fusing anteriorly (laryngeal prominence/Adam's apple). Superior & inferior horns project posterolaterally.
  • Cricoid: Signet ring shape. Only complete cartilaginous ring. Narrow anterior arch, broad posterior lamina.

    ⭐ Cricoid cartilage is the only complete cartilaginous ring in the airway.

  • Epiglottis: Leaf-shaped elastic cartilage. Stalk (petiole) attached to inner thyroid. Guards airway during swallowing.
• Paired Cartilages (Bilateral):
  • Arytenoid (2): Pyramidal. Base articulates with cricoid. Apex (superior), vocal process (anteriorly, for vocal fold attachment), muscular process (laterally, for muscle attachment).
  • Corniculate (of Santorini) (2): Small, conical. Sit atop arytenoid apices, within aryepiglottic folds.
  • Cuneiform (of Wrisberg) (2): Small, club-shaped. Located anterior to corniculates within aryepiglottic folds, providing support.

Laryngeal Membranes & Spaces - Inner Sanctum

• Extrinsic Membranes & Ligaments: Connect larynx to adjacent structures.

  • Thyrohyoid membrane: Connects thyroid cartilage to hyoid bone.
    • Median & Lateral thyrohyoid ligaments (thickenings).
  • Hyoepiglottic ligament: Connects hyoid bone to anterior epiglottis.
  • Cricotracheal ligament: Connects cricoid cartilage to first tracheal ring.

• Intrinsic Membranes & Ligaments: Form internal fibroelastic framework.

  • Quadrangular Membrane (Superiorly):
    • Free upper margin: Aryepiglottic fold (contains aryepiglottic muscle, cuneiform & corniculate cartilages).
    • Free lower margin: Vestibular ligament (forms core of false vocal cord).
  • Conus Elasticus / Cricovocal Membrane (Inferiorly):
    • Free upper margin: Vocal ligament (forms core of true vocal cord).
    • Attaches to cricoid cartilage inferiorly.

• Laryngeal Cavity Divisions:

  • Vestibule: Laryngeal inlet to vestibular folds.
  • Ventricle: Between vestibular folds (false cords) and vocal folds (true cords).
    • Laryngeal Saccule: Anterior extension of ventricle, contains mucous glands for vocal cord lubrication.
  • Infraglottic Cavity: Below vocal folds to inferior border of cricoid cartilage.

• Reinke's Space:

  • Subepithelial space (superficial layer of lamina propria) of the true vocal cord.
  • Loose, pliable connective tissue; crucial for vocal fold vibration and voice quality.

⭐ Reinke's space is the superficial layer of the lamina propria of the vocal fold, prone to edema (Reinke's edema), especially in smokers, leading to hoarseness.

Laryngeal Muscles & Function - Voice Box Dynamos

Intrinsic Muscles: (Voice production & protection; All supplied by Recurrent Laryngeal N. (RLN) except Cricothyroid)

• Abductor (Opens Cords):
  • Posterior Cricoarytenoid (PCA) - Only abductor, 'Safety muscle' for breathing.
• Adductors (Closes Cords):
  • Lateral Cricoarytenoid (LCA)
  • Transverse Arytenoid
  • Oblique Arytenoid
• Tensors (Tenses Cords):
  • Cricothyroid (CT) - External branch Superior Laryngeal N. (SLN). Main tensor. 📌 Cords Tense.
  • Vocalis (part of Thyroarytenoid) - Medial fibers, fine tunes tension.
• Relaxer (Relaxes Cords):
  • Thyroarytenoid (main bulk) - Main relaxer, shortens/relaxes vocal cords.

Extrinsic Muscles: (Laryngeal movement/support)

• Elevators: E.g., Stylohyoid, Mylohyoid, Digastric, Geniohyoid.
• Depressors: E.g., Sternohyoid, Sternothyroid, Omohyoid, Thyrohyoid.

⭐ The Posterior Cricoarytenoid (PCA) is the sole abductor of the vocal cords.

Laryngeal Nerves & Vessels - Vital Connections

• Nerve Supply (Branches of Vagus Nerve - CN X):
  • Superior Laryngeal Nerve (SLN): 📌 'SLN-In is In, Ex is Out' for branches.
    • Internal branch: Sensory to supraglottis; pierces thyrohyoid membrane.
    • External branch: Motor to Cricothyroid muscle.
  • Recurrent Laryngeal Nerve (RLN):
    • Motor: All intrinsic laryngeal muscles except Cricothyroid.
    • Sensory: Glottis & subglottis.
    • Left RLN longer (around aorta); Right RLN (around subclavian artery).
• Blood Supply:
  • Arteries: Superior Laryngeal Artery (from Superior Thyroid Artery), Inferior Laryngeal Artery (from Inferior Thyroid Artery).
  • Veins: Parallel arteries; drain to Superior & Inferior Thyroid Veins.
• Lymphatic Drainage:
  • Supraglottic: Superior deep cervical nodes.
  • Glottic: Sparse drainage.
  • Subglottic: Pretracheal, paratracheal, & inferior deep cervical nodes.

⭐ The left Recurrent Laryngeal Nerve has a longer course and is more vulnerable to injury in thoracic procedures.

High‑Yield Points - ⚡ Biggest Takeaways

• Larynx: 9 cartilages (3 unpaired: Thyroid, Cricoid, Epiglottis; 3 paired: Arytenoid, Corniculate, Cuneiform).
• Cricoid cartilage: the only complete airway ring. Arytenoids: key for vocal cord movement.
• Posterior Cricoarytenoid (PCA): the sole vocal cord abductor (safety muscle).
• Recurrent Laryngeal Nerve (RLN) supplies all intrinsic muscles except Cricothyroid (by ESLN).
• Cricothyroid tenses vocal cords (↑ pitch); RLN injury causes hoarseness.
• Sensory: Internal SLN (supraglottis), RLN (infraglottis).