Functions of Larynx

Fuad Ridha Mahabot

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Introduction

Functions of larynx:• to protect the airway (sphincteric action) during swallowing and by its

sensitivity• as a valve – control air pressure and air flow• as a vibrator – generating sound

* both functions are of fundamental importance during breathing, weight bearing and phonation

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Swallowing (Deglutition)• Primary function – prevent food and liquid entering the airway• Sphincteric action of aryepiglottic fold, true and false cold – occurs

simultaneously with elevation of larynx• Swallowing: Oral stage, pharyngeal stage• Oral stage (voluntary control): Oral preparatory, Oral transport

Food bolus manipulated by tongue broken down by teeth propelled towards oropharynx

• Pharyngeal stage: Initiated as the bolus reaches the back of the tongue Glottis closed by adduction of arytenoids dan contraction of lateral

cricoarytenoids, false vocal cords and true vocal cords Vocal fold adduction: ~2.3 seconds

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Epiglottis: covers laryngeal entrance and directs bolus in two parts into valleculae and pyriform sinuses

The two columns of the divided bolus meet at the upper border of the relaxed cricopharyngeus muscle allow food to enter oesophagus

Rapid laryngeal elevation produces a drop in pressure and transient negative pressure in the cricopharyngeal sphincter as the bolus passes from the pharynx into the oesophagus

If laryngeal elevation impaired pressure drop is slower negative pressure does not occur swallowing problems

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Coughing• Process by which material is expelled from the airway• Preceded by rapid inspiration forceful closure of both vocal and

vestibular folds• Diaphragm ascends spasmodically Air pressure built up below the

adducted folds Folds separate explosively mucous / foreign material expelled

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Effort Closure• Laryngeal structure has evolved in order to contain intrathoracic

pressure - provide stable fulcrum for the upper limbs• During any form of exertion involving use of arms, vocal folds are

firmly adducted preventing expulsion of air and collapse of chest wall providing a fixed origin for the arm and the shoulder musclesPost laryngectomy patient / laryngeal paralysis – may have

difficulty with weight-bearing activities • Effort closure also occurs during childbirth and defaecation

abdominal contents are compressed by abdominal muscles in order to achieve expulsion

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Biomechanics of Phonation• At rest (quiet respiration): vocal folds abduct on inspiration and

slightly adduct on expiration• Vocal folds move up and down slightly with the outflow and inflow of

respiratory air• They are drawn wide apart (full abduction) in forceful inspiration

INITIATION OF VOICE

• Prephonatory inspiratory phase: vocal folds rapidly abduct to allow the intake of air.

• Subsequently, vocal folds are adducted by the contraction of lateral cricoarytenoid muscles

Wyke B. Neuromuscular control systems in voice production. In: Bless DM, Abbs JH (eds). Vocal fold physiology. San Diego: College Hill Press, 1983: 71-6.

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• The vocal note is generated by pulmonic air (air from the lungs) as it is exhaled between the adducted vocal folds

• Vocal folds – working together – constitute a vibrator – activated by the excitor (exhaled air)

• Subglottic air pressure increases below the adducted vocal folds until it reaches a level which overcomes their resistance and blows them apart vibratory cycles phonation

• Repeated vibratory movement of vocal folds production of vocal note (vocal fold oscillation)

• The amount of air pressure required to begin voicing – “phonation threshold pressure”

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THE VIBRATORY CYCLE

• 3 phases: adduction, aerodynamic separation and recoil• Increased subglottic pressure overcomes resistance of adducted

vocal folds vocal fold peel apart from their inferior border separation of superior margin release puff of air

• Bernoulli effect negative pressure in the glottis vocal folds closing rapidly as they are sucked together (inferior margin closing first)

• Contact between the vocal fold increases until subglottic air pressure is high enough to blow the vocal folds apart again and the cycle recommences

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• Body-Cover Theory: helps to explain mucosal wave cover - stratified squamous epithelium and the superficial layer of the lamina

propria (Reinke’s space)• pliable, elastic, and nonmuscular

body - intermediate and deep layers of the lamina propria (vocal ligament) - more fibrous than the superficial layer

• stiffer and has active contractile properties - allow adjustment of stiffness and concentration of the mass

mucosal wave occurs in loose cover changes in stiffness or tension in the fold alters the mucosal wave

stiffness in the fold with contraction of the cricothyroid muscle velocity of the wave pitch

Each cycle of adduction, separation and recoil is the manifestation of a mucosal wave travelling from the inferior to the superior surface of vocal

folds

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• The period of vocal fold contact and lack of contact in one vibratory cycle

Phase Description

Closing The vocal folds begin to close rapidly from their lower margin

Closed The medial edges of the vocal folds are in full contact

Opening The vocal folds begin to separate from their lower margin and gradually peel apartThe superior margin remains in contact until the end of this phase

Opened The vocal folds are separated, the longest part of normal vibratory cycle

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• Vocal fold have to be structurally and functionally symmetrical• Insufficient approximation (glottal insufficiency) air wastage

breathy voice

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Thank You

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