Anatomy, vocal fold histology and phonation

Question 1

What are the 5 layers of the VFs?

Answer 1

1. Epithelium (thin, pliable)
2. SLLP
3. ILLP
4. DLLP (progressively stiffer)
5. Vocalis muscle (most dense)
   SLLP+ILLP+DLLP = lamina propria

Question 2

Features of the epithelium of the VFs? (3)

Answer 2

• 6-8 layers of stratified squamous cells
• Covered in mucus to protect/lube
• Basement membrane secures epithelium to SLLP

Question 3

Features of the lamina propria of the VFs? (2)

Answer 3

• SLLP/ILLP/DLLP
• Each layer has diff concentrations of elastin and collagen - affect vibe properties

Question 4

Features of the lamina propria of the VFs (2)

Answer 4

• SLLP+ILLP+DLLP
• Different concentrations of elastin and collagen which affect vibratory properties

Question 5

Features of the SLLP of the VFs (6)

Answer 5

• AKA Reinke’s space
• Pliable and flexible
• Predominantly elastin, loose/fibrous
• Allows VFs to move liberally during voicing
• Slippery/gelatin like appearance
• Clear border between SLLP and ILLP

Question 6

Features of the ILLP and DLLP of VFs (4)

Answer 6

• ILLP predominantly elastin, vibrates during phonation
• DLLP predominantly collage, denser
• ILLP + DLLP = vocal ligament
• DLLP joins with vocalist muscle providing stability for vibrating lamina propria

Question 7

Features of vocalis muscle (2)

Answer 7

• Main body of VF
• Provides tonicity, stability and mass

Question 8

What is Hirano’s cover body theory? (3)

Answer 8

• Cover = epi + SLLP, compliant, fluid oscillation
• Body = vocali, stiffer underlying stability of VF
• ILLP and DLLP are transitional layers

Question 9

How vocal fold vibration works

Answer 9

1. Column of air moves up towards VF in closed position
2. Column of air pressure opens bottom vibrating layers of VFs, body stays in place
3. Column of air pressure continues up, towards top of VFs and opens the top
4. Low pressure created behind the fast-moving air column produces a Bernoulli effect, causing bottom to close again followed by top
5. Closure of VFs cuts of air column and releases a pulse of air

Question 10

Fundamental frequency and the VFs

Answer 10

• f0 = rate of VF vibration in Hz
• Perceptual = pitch
• Determined by VF length and tension
• High = cricothyroid musc contracts, VF lengthen and tense
• Low = thyroarytenoid musc contracts, VF shortens

Question 11

Intensity and the VFs

Answer 11

• Sound pressure level
• Perceptual = loudness
• Influenced by subglottal pressure, VF vibe phase closure, transglottal flow
• Increased subglottal pressure/pitch = increased intensity

Question 12

What is voice quality affected by? (4)

Answer 12

1. Integrity of VFs
2. Compliant/symmetric biomechanic properties of VFs
3. Adequate/consistent subglottic pressure and flow source
4. Appropriate vocal tract tuning characteristics

Question 13

Features of falsetto register (5)

Answer 13

• High f0 (thin, high quality)
• Strong cricothyroid contraction
• Vibration only at medial edges of VFs
• Little to no closed phase
• High flow and subglottic pressure

Question 14

Features of modal/chest register (3)

Answer 14

• Mid frequency ranges
• Thyroarytenoids contracted, shortening vocalist, relaxing passive cover layers to produce rounded VF edges
• Allows complete closure with large vibratory cycle and mucosal wave

Question 15

Features of glottal fry/pulse (5)

Answer 15

• Lowest end of frequency range
• Pulsed, irregular VF vibration
• Prolonged closed phase
• Low subglottal pressure
• Limited transglottal flow

Question 16

Key factors for effect VF vibration (4)

Answer 16

1. At the midline/closed - otherwise breathy, air escaping
2. Pliable - can change due to lesions/scarring
3. ‘Just right’ tension - able to adjust, if not might get breaks/not able to reach notes
4. ‘Just right’ mass - decreased or increased mass can lead to roughness, change in pitch, effortful phonation