Vocal Fold Structure and Function

Vocal Fold Anatomy - Anatomy Unlayered

• Paired mucosal folds within the larynx, crucial for phonation (voice production).
• Extend from thyroid cartilage (anteriorly) to arytenoid cartilages (posteriorly).
• Length: Adult males 17-23 mm; adult females 12-17 mm.
• Layers (Hirano's Body-Cover Theory): 5 distinct histological layers, grouped into 3 functional sections.
  • Cover (Vibratory segment):
    • Epithelium: Stratified squamous, non-keratinized.
    • Superficial Lamina Propria (SLP) / Reinke's Space: Gelatinous, highly pliable. 📌 Site of Reinke's Edema.
  • Transition (Vocal Ligament - provides resilience):
    • Intermediate Lamina Propria (ILP): Elastic fibers.
    • Deep Lamina Propria (DLP): Collagenous fibers.
  • Body (Muscular core - provides bulk & tension):
    • Thyroarytenoid (Vocalis) Muscle.
• Glottis: Airway space between the true vocal folds.

⭐ Reinke's Space (SLP) is the primary vibrating layer; its condition critically impacts voice quality. Fluid accumulation (edema) here is common.

Phonation Physiology - Voice Mechanics

• Myoelastic-Aerodynamic Theory: Voice production via interplay of muscle (myoelastic) & airflow (aerodynamic) forces.
  • Vocal folds (VFs) adduct (LCA, IA muscles).
  • Subglottic pressure ($P_{sub}$) builds.
  • $P_{sub}$ overcomes glottic resistance → VFs open (inferiorly then superiorly).
  • Air puff released, $P_{sub}$ drops.
• Bernoulli Principle: ↑ airflow velocity in constricted glottis → ↓ pressure.
  • This negative pressure sucks VFs medially, aiding closure (inferiorly first).
• Mucosal Wave: Rippling of VF mucosa over the vocalis muscle.
  • Essential for clear, resonant voice; assessed by stroboscopy.
  • Reduced/absent in VF stiffness (e.g., scar, sulcus).

⭐ The myoelastic-aerodynamic theory is the most widely accepted model explaining voice production, highlighting the interplay of muscle tension, elasticity, and airflow.

Innervation & Blood Supply - Power & Pipes

• Innervation (Vagus Nerve - CN X):

  • Superior Laryngeal Nerve (SLN):
    • Internal br: Sensory to supraglottic mucosa (cough reflex).
    • External br: Motor to Cricothyroid m. (VF tensor, ↑pitch).
  • Recurrent Laryngeal Nerve (RLN):
    • Motor: All intrinsic laryngeal muscles (except Cricothyroid); controls VF abduction/adduction.
    • Sensory: Infraglottic mucosa & vocal folds.
    • 📌 L RLN longer (aortic arch); R RLN (subclavian a.).

    ⭐ Cricothyroid m. (pitch elevation) is the sole muscle innervated by External SLN.

• Blood Supply:

  • Arteries:
    • Sup. Laryngeal A. (from Sup. Thyroid A.): Supraglottis; with Int. SLN.
    • Inf. Laryngeal A. (from Inf. Thyroid A.): Infraglottis; with RLN.
  • Veins:
    • Veins parallel arteries: drain to Sup. Thyroid V. (→IJV), Inf. Thyroid V. (→Brachiocephalic V.).

High‑Yield Points - ⚡ Biggest Takeaways

• Vocal folds: 5 layers (Epithelium, Superficial LP/Reinke's space, Intermediate LP, Deep LP, Vocalis muscle).
• Reinke's space (Superficial LP): key for mucosal wave; site of Reinke's edema.
• Vocal ligament: formed by Intermediate and Deep Lamina Propria.
• RLN innervates most intrinsic muscles; SLN (External branch) innervates Cricothyroid.
• Cricothyroid tenses folds, ↑ pitch; Vocalis muscle forms the fold's body.
• Voice production relies on Myoelastic-Aerodynamic theory & Bernoulli effect.