Functions of LarynxCristi Francis

3 Important functions

The Larynx serves 3 important functions in order of functional priority ,they are:1.Protection of lower airways2.Respiration3.Phonation

Evolution of functionsThe primitive larynx basically functioned as a simple sphincter its Primary function was to protect the lower airway from the intrusion of foreign matter.

NASOLARYNGEAL RELATIONSHIP :

The larynx of humans and great apes in infancy is higher in the neck so that they

can breathe and suckle at the same time. In humans it descends before the age of

two.

Its Secondary function,supported by the sequential phylogenetic acquisition of the cricoarytenoid complex, centers about its role in respiration governed by active muscular dilatation of the laryngeal aperture.

The third function of the larynx,phonation (best observed in mammals),appears to be a late phylogenetic acquisition.

Modulation in phonation results in speech

1.Protection of lower airways

This is the primary function of the Larynx.Protection of lower passages in three different ways:(a) Sphincteric closure of laryngeal opening.(b) Cessation of respiration.(c) Cough reflex .

➔ When food is swallowed, its entry into air passage is prevented by closure of three successive sphincters consisting of :

★ Laryngeal inletAryepiglottic folds Tubercle of epiglottis Arytenoids★ False cords★ True cords which close the glottis.

➔ Thus,no foreign matter meant to be swallowed or accidentally vomited can enter the larynx .

Protective ReflexsRespiration temporarily ceases through degluttition reflex generally afferent fibres of ninth nerve, when food comes in contact with posterior pharyngeal wall or the base of tongue.

Cough is an important and powerful mechanism to dislodge and expel a foreign particle when it comes into contact with respiratory mucosa.

Larynx is aptly called the watch-dog of lungs as it immediately 'barks' at the entry of any foreign intruder .

Role of degluttition reflex

The characteristic flat,shield-like configuration of the epiglottis serves to direct swallowed food laterally into the pyriform fossae, away from the midline laryngeal aperture.Co-ordination of degluttition & respiration prevents choking or pulmonary aspiration.Elevation of the larynx toward the nasal cavity during the height of deglutition exaggerates this protective function.

Cough Reflex

Cough ejects mucus and foreign matter from the lungs and helps maintain patency of the pulmonary alveoli. May bevoluntary, but more of ten 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

2.RespirationThe Larynx acts as a conduction pathway.Larynx regulates flow of air into the lungs.

Vocal cordsabduct - during inspiration and adduct - during expiration.

3.PhonationLarynx is like a wind instrument . Phonation is the laryngeal generation of voice.The larynx acts as a transducer during phonation converting the aerodynamic forces generated by the lungs, diaphragm, chest and abdominal muscles into acoustic energy.This energy transduction occurs precisely at the space between the two vocal folds. However subglottic and supra glottic pressures also play a role in this transformation of aerodynamic energy into sound energy.

Glottal vibration is the result or refers to interaction between aero-dynamic forces and vocal fold muscular action.

★ Sub-Glottal Pressure★ Bernoulli Effect

An increase in velocity results in a drop in the pressure exerted by the molecules of moving gas or liquid, the pressure drops

being perpendicular the direction of the flow

Set vocal folds into vibration due to the elasticity of the folds (elastic recoil the force which restores any elastic body back to its resting place)

★ Muscular ForceMuscles act to bring the folds together so they can vibrate, and muscles regulate their thickness and tension to alter fundamental frequency. Folds are FULLY or PARTIALLY ADDUCTED for phonation

Glottal vibration is the result or refers to interaction between aero-dynamic forces and vocal fold muscular action.

In the human larynx the ability to perform as an effective

valve depends on the unique shelf-like configuration of

its superior and inferior folds bilaterally represented.

The false cords, which are located superiorly, act as exit

valves, preventing the escape of air from the lower

respiratory tract .

When positioned by muscular contraction, they seal

even more tightly as tracheal pressure is increased from

below.

On the other hand, the true cords behave as a one- way

valve

The Glottal Cycle

★ Vertical Phase

Difference

Vocal folds open at the bottom

first. As top part opens bottom

part closes. Wave like motion

★ Longitudinal phase difference

The time lag between the opening and closing of the vocal cords from back to front

SpeechModulation of phonatory sounds produces speechVoice is produced by the following mechanism (Aerodynamic myoelastic theory of voice production)(a) Vocal cords are kept adducted.(b) Infraglottic air pressure is generated by the exhaledair from the lungs due to contraction of thoracic andabdominal muscles.(c ) The air force open the cords and is released as smallpuffs which vibrate the vocal cords and producesound which is amplified by mouth, pharynx , noseand chest.

4.Fixation of Chest

Fixed thoracic cage against a closed glottis.When larynx is closed, chest wall gets fixed and variousthoracic and abdominal muscles can then act best.This function is important in CoughingVomiting, Defecation Micturition