The larynx has two primary functions: biological functions like preventing substances from entering the lungs and non-biological functions like sound production. Sound production occurs when the vocal folds in the larynx vibrate from the air flow from the lungs. There are various theories about voice production, including the myoelastic-aerodynamic theory which states that the vocal folds vibrate due to air pressure from breathing, and the neurochronaxic theory which argues each vibration is initiated by a nerve impulse from the brain.

1. Function of the Larynx & Speech production
The two primary functions of the larynx are:
1. Biologic functions
2. Non-biologic functions

2. Function of the Larynx & Speech production
 The biologic functions of the larynx:
1. Prevent air from escaping the lungs
2. Prevent foreign substances from
entering the larynx.
3. Forcefully expel foreign substances
which threaten the larynx or trachea

3. Function of the Larynx & Speech production
The non-biologic function is
sound production.

4. Function of the Larynx & Speech production
 The vocal folds lay within the larynx and
their movement creates contributes to
sound production.
 They are muscle tissue which may be
lengthened or shortened, tensed or
relaxed, abducted or adducted.

5. Function of the Larynx & Speech production
The cycle of a vocal fold in glottal sound
production has three phases.
(ref. Zemlin pg 151) They are:
1. The opening phase (50% of the cycle).
2. The closing phase (37% of the cycle).
3. The closed phase (13% of the cycle).

6. Function of the Larynx & Speech production
During normal vowel production, such
vibration occurs at a rate of about 125
vibrations per second for men; and about
210 vibrations per second for women.

7. Function of the Larynx & Speech production
Adductor muscles can forcibly stop the
vocal folds from moving. This is referred
to as a glottal stop. The abrupt release by
the adductor muscles is known as a glottal
attack.

8. Function of the Larynx & Speech production
 The vocal fold contains five layers.
They are:
1. The epithelium (maintains the shape of the vocal fold).
2. The superficial layer (similar to a mass of soft gelatin).
3. The intermediate layer (similar to a bundle of soft
rubber bands).
4. The deep layer (somewhat like a bundle of cotton
thread).
5. The vocalis muscle (it’s the main body of the vocal fold
and is like a bundle of rather stiff rubber bands.

9. Function of the Larynx & Speech production
 The Glottis is the variable opening
between the vocal folds.
 Its dimensions are highly variable
depending upon the laryngeal activity and
the adjustments of the cartilages.
Note: Review Zemlin pages 120 and 121

10. Function of the Larynx & Speech production
 The onset of Phonation may be divided
into two phases. They are:
1. The prephonation phase.
2. The attack phase.

11. Function of the Larynx & Speech production
The Prephonation Phase
The vocal fold begins to obstruct air flow from
the lower respiratory tract.
The pressure beneath the folds begins to build.
The velocity of air flowing through the glottal
restriction is raised sharply.

12. Function of the Larynx & Speech production
The Attack Phase
There are three types of vocal attack.
They are:
1. Simultaneous attack (healthy balance between
laryngeal and respiratory mechanism)
2. Breathy attack (air stream is released before
vocal fold adduction is completed)
3. Glottal attack (the initiation of phonation with an
explosive nature)

13. Function of the Larynx & Speech production
The average rate of vocal fold vibration is
known as its fundamental frequency. It
determines to a large extent the pitch of
the voice

14. Function of the Larynx & Speech production
The average fundamental pitch for a male
voice is 130Hz.
Almost an octave higher, you will find the
fundamental pitch for a female voice at
220Hz.
Ref. Zemlin page 163

15. Function of the Larynx & Speech production
Not only does the vibration of the vocal
cords determine pitch but, also the
subglottal air supply to the larynx has
been recognized to also be a factor in the
influence of pitch.

16. Function of the Larynx & Speech production
When subglottal pressure increases, so
does the intensity of one’s voice.
A general rule is when the subglottal
pressure is doubled, the voice intensity
increases by about 8 to 10 decibels.

17. Function of the Larynx & Speech production
Intensities of low and high pitches
 Low pitched phonation is accomplished
when voice intensity was raised by an
increase in glottal resistance.
 High pitched intensity is accomplished by
the rate of air flow through the glottis—not
its resistance.

18. Function of the Larynx & Speech production
In the mid-frequency range, an expected
normal intensity level for speech
production will be about 50dbSPL.

19. Function of the Larynx & Speech production
There are age related pitch changes due to
vocal fold development.
 At birth the infant larynx does not
resemble an adult larynx. It differs in
shape, size, and the position in the neck.

20. Function of the Larynx & Speech production
 Prior to the onset of puberty, there is little
difference in the pitch range between
males and females. The fundamental
pitch frequency decreases upon the onset
of puberty.

21. Function of the Larynx & Speech production
 The aging larynx usually finds a decrease
in pitch range due to the deterioration of
the muscle tissue and an increase in
connective tissue within the vocal folds.

22. Function of the Larynx & Speech production
There are two theories formed regarding
voice production.
They are:
1. Myoelastic—aerodynamic theory
2. Neurochronaxic theory

23. Function of the Larynx & Speech production
Myoelastic—aerodynamic theory
It states that the vocal folds are subject to well
established aerodynamic and physical
properties. The compressible and elastic vocal
folds are set into vibration by the air stream from
the lungs and trachea.

24. Function of the Larynx & Speech production
The Neurochronaxic Theory
It states that each vibratory cycle of the vocal
fold muscle is initiated by a nerve impulse from
the brain.

25. Function of the Larynx & Speech production
Various models have been developed for
the study of the larynx and speech
production.
(Ref. Zemlin pages 183 thru 185)