Laryngeal Physiology

Valving for Life: NonSpeech

1. Breathing:– Airway open

– Three laryngeal valves open (supraglottal cavity, the false vocal folds & true vocal folds)

– Quiet respiration= true folds open to intermediate position

– Forced respiration= Abducted to lateral position

Valving for Life: NonSpeech2. Swallowing:• Guards against entrance of any

substance into the airway

• Swallowing reflex: – larynx elevates,

– epiglottis drops to to cover larynx,

– aryepiglottic folds tense,

– vocal folds adduct

Valving for Life: NonSpeech

3. Pressure Activities (sneezing, coughing, lifting)

– Require alveolar pressure

– Compression of air by respiratory pump

– Dependent on how tightly the laryngeal valve can be closed

– Without airway resistance, thoracic compression produces only expulsion of air

– Cough- deep inhalation, abducted vocal folds, elevation of larynx, significant subglottal pressure (tissue recoil and expiratory muscles)

Valving for Speech

• Modified use of laryngeal valve

• Breathing adjustments of the larynx are modified least

• Swallowing reflex prevents speech

• Pressure reflex evolved solely for speech

• Start phonation: adduct vocal folds, moving them into airstream, hold this position as aerodynamics of phonation control vibration

Valving for Speech1. Mechanics of voiceless sounds :

– Voiceless consonants (first sounds of: pad, tad, cad)• Laryngeal valve open• Airflows unobstructed• Restricted partially by tongue or lips

– Whispering• No voicing occurs• V.F’s offer resistance to airstream, partially adducting V.F’s• Vibrating glottal edges bordering vocalis muscle are stiffened

and positioned far apart to prevent vibration but vocal processes are towed in ( by LCA), the cartilaginous portion is separated to form the posterior glottal chink (permits air through glottis without fold vibration)

The Glottis- Whispering

Whispering Triangle

Muscular Glottis

CartilaginousGlottis

Valving for Speech2. Mechanics of glottal vibration:

vibratory cycle- single vibration of the vocal folds (or glottal cycle)

“Begins when subglottal pressure (Ps ) overpowers fold resistance just enough for the v.f.’s to first blow open.”

*opening phase: v.f. continue to blow apart

* closing phase: escape of air reduces Ps

enough for fold resistance to overpower airflow, then close.

Glottal Cycle

• Arrows represent driving air pressure changes • Notice that the vocal folds are always in transition

opening phase closing phase closed phase

open phase

Valving for Speech• Mechanics of glottal vibration cont.

1. Two ratios to describe the features of vibration:

* speed quotient (SQ)- the ratio of the durations of the opening phase to the closing phase (opening/closing).

* open quotient (OQ)- the ratio of the duration of openness to the duration of the entire cycle (open/entire cycle)

Valving for Speech• Mechanics of glottal cycle cont.

1. V.F.’s vary in compliance: How absorptive of force & vary in complexity of vibratory movement.

*Compliance: Closed phase is period of v.f. absorption (time of closed phase= force of collision). More compliant = more absorption

.

Effects of Compliance on Glottal CycleSteel Balls Rubber Balls

Point ofImpact

CompliantAbsorption of

ImpactOpen Phase

Opening Phase

Closing Phase

Closed Phase

Valving for Speech• Mechanics of glottal cycle cont.

– Complexity in Vibratory Motion:*Vertical Phase Difference:

-V.F.’s open and close from bottom to top

-They also open from back to front and close from front to back

* Also, another vibratory complexity is the motion of the mucous membrane

covering the true vocal folds

Movement of vocal folds

• Note how the vocal folds open from bottom to top & back to front.

Spread of glottal opening

Vertical Phase difference

Valving for Speech3. Vibratory Forces:• Aerodynamic-myoelastic theory of phonation-

“Glottal vibration is a result of the interaction between aerodynamic forces & vocal fold muscular forces.”

*Aerodynamic forces-

-Bernoulli Effect: as velocity of a gas or liquid increases, pressure decreases.

Bernoulli Effect• Trachea & laryngeal airway

as a freeway

• molecules of air= cars

• closer the molecules (cars), slower they move

• faster they move the farther apart they are spaced (lower pressure)

• faster air moves through glottis, farther molecules are apart & exert less force on v.f.’s

Molecules(Cars

accelerate)

Compressedmolecular traffic

Valving for Speech

• Vibratory Forces cont.

* Myoelastic Forces-

The opposing myoelastic (muscular & elastic

tissue) forces provides the vertical phase difference essential for phonation.

* Myoelastic component cont.-1) The glottal edge, particularly the loose mucosal

covering functions as two separate but interconnected masses, one below the other,

2) These two masses are actually the upper & lower portions of the mucous membrane & the underlying vocalis muscle,

3) When lower portion is pushed aside by air pressure, the upper portion is dragged along,

4) The strength of the connection between these two masses is the mechanical coupling stiffness

Mechanical Coupling Stiffness• Upper & lower

portions work together (coupled),

• Remember: The masses are the vocal folds,

• One of several muscular forces involved with phonation.

UpperMass

LowerMass

Upper Mass

Lower Mass

Other Muscular Forces• All provide resistance to airflow-

1) Stiffness or “longitudinal tension”- inc. in muscle stiffness increases resistance; elongation merely thins the vocalis muscle,

2) Mass resistance- thickness in the vocalis muscle, more mass in the cords the more force required to blow them apart,

3) Viscous forces- more viscous the vocal folds, the more they decrease the velocity of movement they are forced to make, inc.. resistance to aerodynamic forces

Summary of Aerodynamic-Myoelastic Theory

• “v.f. vibrations are dynamic interchanges of intraglottal pressure between the folds that force them apart and their mechanical resistance to this pressure.”

Summary Cont...• Beginning of glottal cycle:

1) Intraglottal pressure exceeds atmospheric pressure above the folds & forces

open a small glottal chink,

2) Air flows through the chink; molecules are slow in the trachea than increase velocity

traveling through the glottis (i.e. Bernoulli slide),

3) Air molecules accelerate and start to move farther apart,

4) Pressure against upper portion of the folds decreases, but remains high against the

lower portion (where molecules are still compressed in a “traffic jam”),

5) Therefore, the upper glottis is not blown open by pressure but “dragged” along by

the stiffness of mechanical coupling,6) Lower potion is where the intraglottal pressure

forces the folds apart,7) Aerodynamic force continues to open the

glottis,8) Closure when resistance exceeds intraglottal

pressure.

Reading/Assignments

• Seikel: Pgs.157-164

• Dickson: Pgs. 134-139