Functions Of Larynx

The larynx performs the following important functions:
1. Protection of lower airways
2. Phonation
3. Respiration
4. Fixation of the chest.
1. Protection of Lower Airways
Phylogenetically, this is the earliest function to develop;
voice production is secondary. The larynx protects the
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 (i) laryngeal inlet (aryepiglottic folds, tubercle of
epiglottis and arytenoids, approximately closing the laryngeal
inlet completely), (ij) false cords, (iii) true cords,
which close the glottis. Thus, no foreign matter meant to
be swallowed or accidentally vomited can enter the larynx.
Respiration temporarily ceases through a reflex generated
by 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.
2. Phonation
Larynx is like a wind instrument. Voice is produced by the
following mechanism (Aerodynamic myoelastic theory of
voice production):
(a) Vocal cords are kept adducted.
(b) Infra glottic air pressure is generated by the exhaled
air from the lungs due to contraction of thoracic and
abdominal muscles.
(c) The air force open the cords and is released as small
puffs which vibrate the vocal cords and produce
sound which is amplified by mouth, pharynx, nose
and chest.
This sound is converted into speech by the modulatory
action of lips, tongue, palate, pharynx, and teeth.
Intensity of sound depends on the air pressure produced
by the lungs while pitch depends on the frequency
with which the vocal cords vibrate.
3. Respiration
Larynx regulates flow of air into the lungs. Vocal cords
abduct during inspiration and adduct during expiration.
4. Fixation of Chest
When larynx is closed, chest wall gets fixed and various
thoracic and abdominal muscles can then act best.
This function is important in digging, pulling and climbing.
Coughing, vomiting, defaecation, micturition and
childbirth also require a fixed thoracic cage against a
closed glottis.