physiology of larynx& theories of voice production(dr.ravindra daggupati)

03/05/2023 Dr.Ravindra,DLO(ENT)

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PHYSIOLOGY OF LARYNX & VOICE PRODUCTION

MODERATOR:DR.S.N.MUKHARJEEPRESENTER:DR.RAVINDRA


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The larynx has a number of functions,

Larynx acts as sphincter to protect the lower airways during swallowing .

It also acts as a valve which can control air pressure and airflow, this function is useful in breathing, weight bearing and

Larynx acts As a vibrator for generating sound.


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4Laryngeal mechano receptors Free fibrils and terminal filaments enclosed in capsules constitute the

receptor end organs (the mechanoreceptors)

These are embedded in the laryngeal tissues at sites sensitive to muscle stretch and airflow pressures.

Some are involved in protecting the airway while others contribute to the control of phonation.

Reflex closure of the larynx is triggered by tactile receptors in the glottic and supraglottic mucosa, which evoke reflex contraction of the laryngeal muscles.

Similar receptors in the subglottic mucosa elicit laryngeal closure and cough.


5 Wyke postulated that mechanoreceptors are found in three sites:1. The mucosal lining of the larynx (subglottic mucosal

mechanoreceptors): The corpuscular nerve endings in the subglottic mucous membrane covering the surface of the vocal folds are particularly numerous and sensitive to the stimuli of muscle stretch, air pressure level, liquid and touch. They discharge impulses into the afferent fibres of the vagus.

2. The capsules of the articulatory joints (articular mechanoreceptors): The existence and function of this group remain controversial.

3. The extrinsic and laryngeal muscles (myotatic mechanoreceptors): The tone of the laryngeal muscles depends on the myotatic reflex, which is a function of the muscle spindles.

The laryngeal muscles contain a large number of muscle spindles.


6FUNCTIONS OF THE LARYNX1. Swallowing (deglutition):

During swallowing, the primary function of the larynx is to prevent food and liquid entering the airway.

This is achieved by means of the sphincteric action of the aryepiglottic folds and the true and false vocal folds which occurs simultaneously with elevation of the larynx.

The process of swallowing can be divided into the oral stage and the pharyngeal stage.

The oral stage is under voluntary control and consists of the oral preparatory stage and the oral transport stage.

The food bolus is manipulated by the tongue and broken down by the teeth before being propelled towards the oropharynx.


7 The pharyngeal stage of swallowing is a reflex

activity which is initiated as the bolus reaches the back of the tongue.

During this phase, the glottis is closed by adduction of the arytenoids and contraction of the lateral cricoarytenoid muscles, false vocal folds and true vocal folds.

Vocal fold adduction during swallowing is thought to average approximately 2.3 seconds.

The airway is also protected by the epiglottis which covers the laryngeal entrance and directs the bolus in two parts into the valleculae and the pyriform sinuses.

The two columns of the divided bolus meet at the upper border of the cricopharyngeus muscle which relaxes to allow the bolus to enter the oesophagus.


8 Rapid laryngeal elevation occurs during the pharyngeal phase of

the swallow and appears to be essential for normal swallowing.

This manoeuvre produces a drop in pressure and transient negative pressure in the cricopharyngeal sphincter as the bolus passes from the pharynx into the oesophagus.

It has been established that if laryngeal elevation is impaired, the pressure drop during deglutition is slower and the fleeting negative pressure does not occur, so contributing to swallowing problems.


92.Coughing

Cough ejects mucus and foreign matter from the lungs and helps maintain patency of the pulmonary alveoli. May be voluntary, but more often in response to stimulation of receptors in the larynx or lower respiratory tract.

Three phases: inspiratory- larynx opens wide to permit rapid and deep

inspiration; compressive- tight closure of the glottis and strong

activation of expiratory muscles; expulsive- larynx opens widely and a sudden outflow of

air in the range of 6-10 liters/sec


103.Effort closure Expiratory effort against a closed glottis is known as the

Valsalva manoeuvre.

During any form of exertion involving use of the arms, the vocal folds are firmly adducted preventing expulsion of air and collapse of the chest walls, thus providing a fixed origin for the arm and shoulder muscles.

The persons who have undergone laryngectomy or who have paralysis of one or both vocal folds, may have difficulty with weight bearing activities because of their inability to close the glottis effectively.


11The Neuroanatomy of Speech Phonation is dependent upon the integrated functioning of many

elements of the central nervous system (CNS) and peripheral nervous system (PNS).

There is some evidence that the periaqueductal grey matter (PAG), a region of the midbrain, is a crucial site for mammalian voice production.

The motor activity for vocalization appears to be integrated through a projection from the PAG to a column of neurones, known as the nucleus retroambigualis (NRA).

This nucleus appears to play a significant role in generating respiratory pressure and laryngeal adduction, which occurs in both vocalization and vegetative manoeuvres, such as coughing.


12 There is also evidence that the frontal lobes and other cerebral structures are important in the phonation.

The extrinsic and intrinsic muscles of the larynx are under voluntary cortical control.

They are responsible for the prephonatory tuning and also maintenance of length, tension, bulk and position of the vocal folds.

Stimulation of all categories of laryngeal mechanoreceptors initiates activity in the larynx which presumably ensures that the vocal folds are stabilized and return to their preset pattern following displacement by the expiratory air stream.


13The biomechanics of phonation

• When the larynx is at rest and respiration is quiet, the vocal folds abduct on inspiration and slightly adduct on expiration.

• They move up and down slightly in sympathy with the outflow and inflow of respiratory air, while the larynx descends on inspiration and ascends on expiration.

• The folds are drawn wide apart to a position of full abduction in forceful inspiration.


14 INITIATION OF VOICE Immediately before phonation, the vocal folds rapidly abduct to allow the intake of air.

This is termed as ‘prephonatory inspiratory phase’.

Then the vocal folds are adducted by the contraction of the lateral cricoarytenoid muscles.

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

The vocal folds working together, therefore, constitute a vibrator which is activated by the exciter, the exhaled air.


15 The production of the vocal note at this point is the result of the

repeated vibratory movement of the vocal folds, known as vocal fold oscillation.

The vocal folds, in common with all vibrators, have a degree of inertia which has to be overcome in order for phonation to occur.

The amount of air pressure required to begin voicing is known as the ‘phonation threshold pressure’.

The size and tension of the vocal folds in combination with the viscoelastic properties of the vocal fold cover will affect the phonation threshold pressure.


16THE VIBRATORY CYCLE Each vibratory cycle of the vocal folds

consists of three phases: adduction, aerodynamic separation and recoil

As the increased subglottic air pressure overcomes the resistance of the adducted vocal folds at the onset of phonation, the vocal folds peel apart from their inferior border.

When they finally separate at their superior margin, a puff of air is released. The resulting negative pressure in the glottis, caused by the Bernoulli effect, results in the vocal folds closing rapidly as they are sucked together, the inferior vocal fold margins closing first.


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The Bernouilli effect is a drop in pressure dependent on particle velocity.

In relation to the vocal tract, Maran describes it as follows, ‘When air passes from one large space to another (e.g. from lung to pharynx), through a constriction (the glottis), the velocity will be greatest and the pressure least at the site of the constriction.’

As a result of the drop in pressure at the glottis, the vocal fold mucosa is drawn into space between the vocal folds.


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

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

The process by which this undulating wave of movement of the mucous membrane occurs is dependent on what is known as the cover/body theory.


19COVER BODY THEORY OF VOICE PRODUCTION

The vocalis muscle provides the firm body of the vocal fold over which the mucous membrane cover of the vocal fold is blown by the expiratory air stream.

These undulations of the thin cover of the vocal folds and any abnormalities of the mucosal wave can only be observed using laryngostroboscopy or high speed photography.

The periods of vocal fold contact and lack of contact in one vibratory cycle can be divided broadly into closed and open phases, respectively, with associated closing and opening phases.

The closing phase of the vocal folds is more rapid than the opening phase.

The phases of the vibratory cycle can be classified, therefore, into four stages


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21 OTHER THEORIES OR VOICE PRODUCTION.

MYO ELASTIC AERO DYNAMIC THEORY ONE MASS MODEL THEORY THREE MASS MODEL THEORY NEUROCHRONAXIC THEORY.


22Myoelastic Aerodynamic Theory Of Vocal Fold Vibration (Van den Berg, 1950s)

1. Muscular activity rotates and rocks the arytenoid cartilages so that their vocal processes come together in the midline, thus positioning the vocal folds close together or in actual contact.

2. Air pressure increases below the glottis until folds forced apart

3. Air travels faster through the glottis when it is narrow. This causes a local drop in air pressure (Bernoulli effect) which causes the folds to be sucked towards each other.

4. The Bernoulli effect, together with the elastic recoil force exerted by the displaced vocal folds, causes complete glottal closure again.

5. The process begins again at step 2.


23THE ONE MASS MODEL THEORY Myoelastic-aerodynamic theory was improved by adding the contribution of the

vocal tract & its impact on airflow. In the physical world objects experience inertia which is resistance to starting &

stopping movement Vocal folds and the air moving through the vocal tract are subject to this natural law

In A-M theory glottis initially closed by muscles in larynx. Subglottal air pressure Increases till it overcomes muscular & tissue resistance &

opens glottis. decreased air pressure Through glottis (bernoulli)& elasticity / inertia of vocal folds

brings glottis back together


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Decreased flow of air because of inertia, air above glottis continues its forward motion through the glottis producing area of low air pressure immediately above glottis

Combined forces of elastic recoil of the folds + pressure drop through the glottis + low pressure region above the glottis completes cycle ,closing the glottis

Asymmetry of air pressure below & above glottis vocal fold oscillation to continue for as many times per second depending on the pitch that is spoken.


25THREE MASS MODEL THEORYVocal folds consider as 3 interconnected massesFirst & largest mass - body of the vocal fold ( thyroarytenoid muscle)

Two smaller masses - upper and lower portions of the cover (lamina propria and epithelium) Glottis opens and closes asymmetrically with vertical phase difference from bottom to top. Air pressure also is asymmetrical When glottis is

convergent Divergent (Bottoms of 2 folds r farther apart) (tops of 2 folds r farther apart) pressure is Increasing pressure is decreasingAsymmetry of air pressure + impact of pr. changes above glottis caused by Inertia is sufficient to sustain vocal fold

oscillation


26NEUROCHRONAXIC THEORY(Raoul Husson)

This theory incorrectly advanced the notion that the central generation of recurrent laryngeal nerve impulses produced cord vibrations by active contraction of the thyroarytenoid muscles.

Each vibration, therefore, represented the result of beat-by-beat impulses through the recurrent laryngeal nerve.


28VOCAL REGISTERS

HOLLIEN’S classification of vocal registers. Suggested that registers should be defined in terms of laryngeal

behaviour, rather than in acoustic terms as registers are governed by degree of contraction of vocalis muscle.

:Loft register{falsetto} :Modal register :Pulse register{glottal fry,vocal fry or creaky voice}


29 Loft register (or falsetto) covers the highest frequencies of the voice. The vocal

folds are lengthened, extremely tense and thinned so that there is minimal vibration. The knife-thin free edges are almost adducted and subglottic air pressure is high.

During the production of these high frequencies, the larynx is raised by the suprahyoid muscles and the pharynx is shortened.

Modal register encompasses the range of frequencies usually employed in speech and singing. The membranous portions of the vocal folds are adducted and make complete closure in the closed phase of each vibratory cycle. In cross-section, the vocal folds are triangular in shape. In low notes the intrinsic muscles relax, the folds increase in bulk, and their opposing surfaces deepen from 3 to 5 mm.

Pulse register (or glottal fry, vocal fry or creaky voice) occurs during the lowest vocal frequencies and is a feature of normal speech.


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VOICE PRODUCTION

•GENERATOR•PHONATOR•RESONATOR•ARTICULATOR

3103/05/2023Dr.Ravindra,DLO(ENT)


32VOICE AND SPEECH PRODUCTION.

The vibration of vocal folds(phonation)constitutes the raw glottal sound source.

This fundamental vibratory sound is modified and resonated by the rest of vocal tract to produce a recognizable voice quality.

The articulatory structures of vocal tract( lips, tongue ,soft palate) shape the sound source in an infinite number of combinations to make speech.


33Characteristics of sound source /Glottal signal.

The quality of sound source is dependent upon the vibratory characteristics of laryngeal structures.

It is dependent on the nature of vocal fold adduction during phonation and the regularity of mucosal waves of lamina propria.


34 For examples : Incomplete adduction of vocal folds during phonation will result in

audible air leakage and breathy voice quality.

Whisper occurs when there is insufficient vocal fold adduction to achieve vibration, but sufficient adduction to produce audible turbulent air.

An irregular mucosal wave form vibration will result in an aperiodic sound that will be perceived as hoarse.

A pressed or strained voice quality occurs when the vocal folds are strongly adducted (often with supraglottic muscular involvement) and there is raised subglottal air pressure .


35SINE WAVE:

In a hypothetically perfectly functioning larynx, adduction of vocal folds would be complete during closed phase of phonation.

Vibration of mucosal wave form would produce a perfectly periodic sound signal.

Sound would contain a fundamental frequency and its harmonics. Human voices are a combination of periodic and aperiodic sound.

Aperiodic sound or noise is one that is not harmonic of glottal signal.

Main sources of noise are air escape and irregular vibration.


36Hoarse voice.

the perceived breathiness quality of the voice (Bailey) The more severe the noise component of sound (in relation to

periodic component), the more hoarse voice will sound. Degree of Hoarseness:Ratio of periodic sound compared to

aperiodic sound. This is called Harmonics to noise ratio(HNR). This is Indicator of degree of hoarseness not the source. This is Popular measure of dysphonia severity and change in

voice quality during treatment.


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Frequency of glottal signal: Number of vibratory cycles per second.(Hz)

Rate of vibration of vocal folds is function of: vocal fold length elasticity tension mass resistance to subglottal air pressure.


38Pitch

The perceptual correlate of frequency is pitch, though relationship between two is complex one.

Frequency, intensity, and spectral properties of sound interact in very complex way to give pitch perception.

3 pitch registers :loft modal pulse .distinguish between different vibratory patterns of vocal folds

determined by degree of contraction of vocalis muscles.


39Jitter or pitch pertubation.

It is the short term cycle to cycle variance in frequency of vocal fold vibration.

It may indicate instability in phonatory mechanism and may be further useful index of dysphonia.


40Vocal loudness

Perceptual correlate of amplitude is determined by the size of oscillation of vocal folds .

Determined by force of trans glottal air flow. Shimmer: short term variance in intensity of vocal signal is called

shimmer or amplitude pertubation. It indicates characteristics of dysphonic speaker


41Modifying the glottal signal.

Sound source produced by vibrating vocal folds is modified by rest of vocal tract to produce the voice quality that radiates from speakers mouth to listeners ear.

Complex acoustic signal is filtered by supralaryngeal tract with some anatomical structures resonating different harmonics of the source signal.

Changes in dimension of vocal tract will alter the sound of resultant voice .


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The fact that voice is more than its vibratory source is a fundamental principle of auditory evaluation of voice quality.

Vocal resonance : The specific geometry and dimensions of an individual speakers vocal tract will determine the timbre or resonating properties of voice.

Skilled speakers and singers learn to manipulate these oral , nasal, and pharyngeal structures to maximize there resonant properties.


43Speech/Articulation.

Orchestrated movements of organs of articulation change the vocal sound into recognizable speech.

This is called “source filter "model of voice production. Articulatory movements classified into: vowels consonants


44VOWELS

Vowels are sounds in which there is no obstruction to flow of air as it passes from larynx to lips.

Vowel articulations are made by varying the resonating shape of oral and pharyngeal cavities.

Resonance peaks of vocal tract are called formants . Formant structures vary for each vowel and are easily identifiable

on sound spectograph.


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It is possible to distinguish between vowels by; 1)changing the height of tongue raising in mouth. 2)part of tongue raised( front, middle, back) 3)positionof lips spread or rounded. Example: i as in see front of tongue raised and lips spread.,u as

in sue is made with posterior tongue raising and rounded lips. Diphthongs i.e. beer, air :start with one oral tract articulatory

shaping and glide into another.


46CONSONANTS

Speech consonants are defined by their much clearer articulation(and often obstruction of airflow)within the oral tract.

Distinction is made using three main elements: Place of articulation:ie lips, alveolar Manner of articulation :(ie plosive , fricative) State of larynx (voiced or voiceless)


47Consonants based on place of articulation. Bilabial consonants :articulation between upper and lower lips (p,

b,m.w). Labiodental :top teeth and lower lip articulation (f,v). Dental articulation: tongue tip and top teeth occlusion(th). Alveolar consonants :tongue tip touching the ridge behind the teeth

(t,d,n,s,z,r,ch,dj).


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Velar consonants :posterior tongue and soft palate articulation (k,g,ng).

Articulation of middle tongue with hard palate produces ,y.


49MANNER OF ARTICULATION.

Based on how airflow is obstructed in oral tract. Plosives:p, b, t, d, k,g/:They have different places of

articulation,one is moved against another in order to interrupt completely the air flow through the vocal tract. Air is compressed behind point of articulation and then released with audible noise called plosion.


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Fricatives:continuant consonants,they continue for a long time .Air turbulent sound that is made by air hissing through close (but not complete )approximation of articulators .eg f, z,s.

Affricates :combination of plosion and fricative articulation.ch, in church, and dj.


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Nasal consonants:eg m, n, ng :Air escapes through the nose .Air is prevented from passing through the mouth by obstuctive lip or tongue articulation and soft palate is lowered to allow nasal air escape.

Velopharyngeal incompetence :Inappropriate nasalization of non nasal consonants and vowels.

Obstruction in nasopharynx will result in denasalization of nasal consonants.


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Approximant consonants :when articulators are not sufficiently close to produce complete consonants .

Articulated similar to vowels and are called semivowels.eg w, y.


53BIBLIOGRAPHY

Scott browns 7th edition chapter 164,165,166 Cummings 3rd edition chapter97,98 Bailey chapter 644 Otolaryngologic clinics of north america vol39,40(2007). Journal of laryngology and otology feb 1997, vol 3. Journal of phonetics , hollien h ,1974


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physiology of larynx& theories of voice production(dr.ravindra daggupati)

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