physiology of phonation

aditus

“doorframe” to the laryngeal vestibule

vestibule

first cavity of the larynx

false vocal folds

ventricular folds

laryngeal ventricle

space between the false and the true VFs

outermost layer

Squamous epithelium: white in color, protects the inner layers

Lamina propria (Vocal ligament)

• Superficial lamina propria

• Intermediate lamina propria

• Deep lamina propria

Muscular layer (thyroarytenoid muscle: TA)

• Make up the bulk of the vocal folds; consists of 2 different muscles

• Muscle course: thyroid (origin) and arytenoid (insertion)

Protection/clearing of the airway

the most important function of the larynx

• Coughing: forceful evacuation of the respiratory passageway in response to irritants or foreign matter

• Throat clearing: clears the respiratory tract of mucus

Abdominal fixation

the process of capturing air within the thorax to stabilize the torso

• Lifting or pushing heavy objects

• Giving birth

• Defecation

Laryngeal function for speech

Phonation, or voicing – the product of vibrating vocal folds

• Source of voice for speech

• Vocal folds vibrate as air passes through them (as they are approximated/adducted)

• Phonation is maintained by the Bernoulli effect and tissue elasticity - myoelastic aerodynamic theory

Myoelastic aerodynamic theory

• Glottal vibration is the result of interaction between aerodynamic forces and vocal folds’ tissue property

(i.e., elastic).

• Air stream passes between folds

• Vibrate as result of elastic quality of tissue interacting with aerodynamic principles embodied in Bernoulli Effect

• Power source of the opening phase: subglottal pressure

• increased subglottal air pressure from the lungs initiates the opening phase of the VFs.

• Two driving forces of the closing phase

• Aerodynamics: Bernoulli Effect

• Myoelasticity: VFs are made up of elastic tissue

• During sustained phonation, muscle contraction is tonic (sustained); muscles do not contract and relax for each cycle of VF oscillation, instead aerodynamics and tissue elasticity result in vibration (oscillation) of the vocal folds.

Bernoulli Effect

• When the vocal folds are open (abducted) there is no constriction

• Adducting folds produces constriction

• Given a constant volume flow, there will be a decrease in pressure perpendicular to the flow (on the wall) and increase in velocity at a point of constriction in the flow

• Inverse relationship between the velocity and the pressure

• increase in the velocity will result in a decrease in the pressure.

Stage 1

VFs are closed (completely adducted) (contraction of muscles of

adduction) → Subglottic pressure increases

stage 2

VFs gradually separates at the BOTTOM (opening phase starts here)

stage 3

Upper part of the glottis opens next.

stage 4

Opening continues (*This is NOT abduction! Called the opening phase.)

stage 5

Opening is completed! (The VFs are blown apart!) →

Simultaneously, air molecules will be rushing upward FAST!

• Air flow velocity between the vocal folds very quick→

• The air pressure in the glottis becomes negative

• This is the aerodynamic component of the theory.

Stage 6

Pressure in the glottis is now negative.

Myoelasticity

VFs are very elastic, highly flexible, and mobile → VF tissue wants to return to resting shape and negative pressure sucks the VFs to the midline (just like two pieces of paper).

Stage 7

VFs continue to move to the midline

Stages 8-9

closing continues (lower portion first)

Stage 10

closing is completed.

Attack stage (Vocal attack)

Begins at adduction

Process of brining vocal folds together (adduction)

Sustained phonation

hold the VFs in fixed position in the airstream as the aerodynamics of phonation control the actual vibration (Myoelastic aerodynamic theory*)

Phonation is maintained by the interaction of two systems: Aerodynamic & Myoelastic forces

Offset stage

Ends at abduction

• Vocal folds abduct (move apart) to stop vibration

• As the glottis widens, airflow velocity decreases, and pressure differences are reduced

• Vocal fold vibration stops – phonation ends

Simultaneous vocal attack

adduction and onset of respiration at the same time

Breathy vocal attack

start significant airflow before adducting the vocal folds

Glottal (hard) attack

adduction of the vocal folds prior to the airflow

Aerodynamic forces

• Subglottal pressure (drives vocal fold opening)

• Glottal airflow (creates pressure changes via Bernoulli effect)

Myoelastic forces

• Vocal fold adduction

• Elasticity of vocal fold tissue (restores shape)

Membranous portion

Portion including free margin of vocal folds

• 15 mm in males

• 12 mm in female

• About 2/3 of glottis

Cartilaginous portion

• Portion bounded by cartilage of arytenoids

• 7-9 mm (about 1/3 of glottis) long