Vocal Fold Histology and Theories of Voice Production

Question 1

Layers of of Vocal Folds

Answer 1

Epithelium

• Stratified squamous cells
• Separated between basement membrane
• Protects from mechnical stress of vibration

Lamina Propria (3 layers)

• Consists of 2 types of protein
• Elastin
  
  • Allows the vocal folds to recoil after being stretched
• Collagen
  
  • Provides strength and structural integrity to the vocal folds

1. Superficial Layer
   
   • Loosely organized elastin
   • Also called Reinke’s space
2. Intermediate Layer
   
   • Mostly elastin with some collagen
3. Deep Layer
   
   • Collagen

Muscle

• Bulk of the vocal folds made up of the thyroarytenoid muscles

Question 2

Basement Membrane

Answer 2

• Between epithelium and superficial layer of lamina propria
• Secures epithelium to lamina propria
• Very susceptible to injury from shearing forces

Question 3

3-Layer Vocal Fold Schematic

Answer 3

• Mucosa
  
  • Epithelium
  • Superficial layer of LP
• Vocal Ligament
  
  • Intermediate layer of LP
  • Deep layer of LP
• Muscle

Question 4

2-Layer Vocal Fold Schematic

Answer 4

• Cover
  
  • Epithelium
  • Superficial layer of LP
  • Intermediate layer of LP
• Body
  
  • Deep layer of LP
  • Muscle

Question 5

How do the vocal folds vibrate?

Answer 5

Airstream >> sound

Neurochronaxic Theory (Husson, 1950)

Myoelastic – Aerodynamic Theory (Van Den Berg, 1958)

• Vocal fold vibration results from the interaction of muscular contraction, elastic properties of the vocal folds, and the air from the respiratory system
  
  • Myo: muscle
  • Elastic: recoil
  • Aerodynamic: air

1. The vocal folds are brought together at the start of vibration by muscles
2. The muscles contract one time at the start of vocal fold vibration to adduct the arytenoid cartilages and vocal processes
3. After that, the muscles remain contracted, holding the arytenoids and vocal processes closed
4. The vocal folds vibrate (open and close) due to aerodynamic and elastic forces.

Muscles contract to adduct the arytenoid cartilages (and the vocal folds)

• Thyroarytenoid muscles
• Lateral cricoarytenoid muscles
• Oblique interarytenoid muscles
• Transverse interarytenoid muscles

1. Pressure builds up under the closed vocal folds
2. Subglottal pressure
3. When subglottal pressure is greater than atmospheric pressure AND the resistance at the level of the vocal folds
4. The vocal folds are “pushed” away from each other
5. Vocal folds open from bottom to top
6. As the vocal folds are being “pushed” apart the pressure between the vocal folds (intraglottal pressure) increases

• Airflow is proportional to pressure
• Increasing intraglottal airflow
• Vocal folds begin to recoil back to midline due to elastic properties
• Close from bottom to top
• As vocal folds begin to close, intraglottal pressure and airflow start decreasing
• Facilitates vocal fold closure
• The vibration of the vocal folds can be sustained indefinitely assuming that energy is available to keep them going
• Considered a “self-oscillating system”

Question 6

What is the Neurochronaxic Theory and why is it wrong?

Answer 6

• Each vibratory cycle is triggered by a nerve impulse from the brain to the Thyroarytenoid muscles via the Recurrent Laryngeal Nerve (RLN)
• Frequency of vocal fold vibration dependent on rate of neural impulses
• Theory is INVALID
  
  • Recurrent laryngeal nerve longer on left than right
  • Nerve impulses cannot be transmitted quickly enough

Question 7

What happens when intraglottal pressure and airflow during vocal fold opening and closing?

Answer 7

• Vocal folds are “pushed” open when subglottal pressure is higher than atmospheric pressure and the tension of the vocal folds
• Intraglottal pressure increases and airflow increases
• Vocal folds begin to close due to elastic properties ◦ Intraglottal pressure decreases and airflow decreases
• Change in pressure facilitates return to midline

Question 8

Mucosal Wave

Answer 8

• Ripple on the surface of the vocal folds
• Caused by rotation of the vocal fold cover around the body
• Travels from medial to lateral edge
• Velocity increases with increasing subglottal pressure and airflow

Question 9

Vocal Fold Paralysis

Answer 9

• One: breathy
• Closed: yes
• Open: no
• Midline: yes