Physiology of Larynx
Dr. T. Balasubramanian
Functions of larynx:
1. Airway protection
Airway protection: is the most important function
of human larynx. Larynx in fact acts as a sphincter
protecting the lower airway from secretions of the oropharynx. It
also protects the airway from spillage of food during deglutition.
Larynx acts as a three tier protective mechanism. These are from
above downwards: Aryepiglottic fold, ventricular band and vocal
cords. These three structures when contracted can effectively seal
the lower airway from the contents of the oropharynx.
Contraction occurs from below
upwards, first the vocal cord adducts, followed by
ventricular bands. Finally the aryepiglottic fold adducts sealing
the lower airway completely.
Respiration: Another important function of larynx
is to keep the airway open during respiration. This is done by
gentle abduction of the vocal cords while the ventricular bands and
aryepiglottic folds are fully abducted.
swallowing the sphincters of larynx stay contracted
preventing aspiration of food into the air passage. During the
pharyngeal stage of swallowing the larynx is elevated towards the
lower jaw, this elevation opens up the cricopharyngeal sphincter
thus facilitating swallowing. The hyoid bone rotates in such a way
that the greater cornua becomes horizontal, producing a backward
tilting of the epiglottis towards the posterior pharyngeal wall.
This movement of hyoid bone effectively closes the laryngeal inlet.
Phonation: 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 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.
The requirements of normal phonation are as
1. Active respiratory support
2. Adequate glottic closure
3. Normal mucosal covering of the vocal
4. Adequate control of vocal fold length and
The vibrations of the vocal folds are complex in
nature and are known as the glottic cycle. This cycle involves
glottic opening and closing at set frequencies determined by the
subglottic air pressure. Normal vocal folds produce three typical
2. Modal voice
3. Glottal fry
In falsetto or (light voice) the glottic closure
is not complete, and only the upper edge of the vocal fold
In Modal voice complete glottic closure occurs.
This occurs in a majority of mid frequency range voice. During this
modal voice production the vocal fold mucosa vibrates independently
from the underlying vocalis muscle. This is the
basic frequency at which a person phonates. The modal frequency in
adult males is 120 Hz while in adult females it is 200 Hz.
Glottal fry is also known as low frequency
phonation is characterised by closed phase. This closed phase is
long when compared to the open phase. The vocal cord mucosa and
vocalis muscle vibrate in unison.
During phonation two vibratory phases occur i.e.
open and closed phases. The open phase denotes the
phase during which the glottis is atleast partially open, while the
closed phase denotes the phase when the vocal folds completely
occlude the glottic chink.
The open phase can be further divided into
opening and closing phases. The opening phase is defined as the
phase during which the vocal folds move away from one another, while
during the closing phase the vocal folds move together in unison.
One important physiologic parameter which must be
noted during phonation is the mucosal wave. The mucosal wave is an
undulation which occur over the vocal fold mucosa. This wave travels
in an infero superior direction. The speed of
mucosal wave ranges from 0.5 - 1 m/sec. The symmetry of these
mocosal waves must also be taken into consideration while studying
the physiology of voice production. Any mild assymetry between the
two vocal folds must be considered as pathological.
The function of vocal folds is to produce sound
varying in intensity and pitch. This sound is then
modified by various resonating chambers present above and below the
larynx and are converted into words by the articulating action of
the pharynx, tongue, palate, teeth and lips.
The consonants of speech can be associated with
particular anatomical sites responsible for their generation i.e.
'p' and 'b' are labials, 't' and 'd' are dentals and 'm' and 'n' are
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