68 Chapter 4
The Human Sound Source–Resonating System
One way of looking at the speech mechanism is to compare it to a musical instrument. In a
trombone, for example, the player places the mouthpiece— the sound source— against the lips and
makes a buzzing sound. The air and the trombone are set into vibration corresponding to the
frequency and intensity of the sound. Certain frequencies of the buzzing sound are either ampli-
fied or damped by the trombone, and the player changes the pitch by altering the frequency of the
buzzing and by adjusting the length of the resonating chamber with the slide; the pitch decreases
when the slide is extended. The trombone sounds like a trombone because of its shape, its texture,
and the adjustable length of the resonating chamber. All musical instruments work in a similar
sound source– resonating manner. They operate on the same princi ple whether the sound source
is the buzzing of a reed, the vibration of a violin string, air turbulence over the mouth opening of
a f lute, or the hammering of a piano string. Some instruments have valves that open and close,
changing the length of the resonating tube.
The voice production mechanism works in the same way as a musical instrument. The main
sound source is the vibration of the vocal cords. Air pressure builds up below the vocal cords,
and when it is great enough to overcome the muscular re sis tance and static air in the vocal tract,
the cords are blown apart. They would stay apart were it not for aerodynamic force and muscu-
lar elasticity. The aerodynamic force is Bernoulli’s princi ple, which accounts for a suction effect
bringing the vocal cords together. Elasticity is the tendency of tissue to regain its original shape
when stretched and distended. The suction effect of Bernoulli’s princi ple and the tendency of the
muscles and tissues in the larynx to regain their original shape after being stretched and distended
allow the vocal folds to vibrate very rapidly. This myoelastic- aerodynamic princi ple of vocal fold
vibration accounts for the ability of the vocal cords to vibrate extremely rapidly and not to fatigue
over time.
The rate of vocal cord vibration is called the fundamental frequency and is the prime deter-
minant of a person’s pitch, the psychological perception of frequency of vibration. Although
frequency and pitch are related, there is no one- to- one relationship between them; a unit increase
or decrease in frequency does not necessarily correspond to the same subjective change in pitch.
Anatomy and Physiology of the Larynx
The larynx can be viewed as a valve that opens for breathing and closes when foods and liquids
enter the throat. The larynx consists of nine cartilages, three of which are paired. (See Figure 4-1
for anterior and posterior views of the larynx.) The epiglottis, cricoid, and thyroid are the unpaired
cartilages. The epiglottis closes over the larynx during swallowing to provide protection. It is help-
ful but not essential to a safe swallow. The cricoid cartilage resembles a signet ring and is located
below the thyroid cartilage. The thyroid cartilage is the largest, and the “Adam’s apple” is its ante-
rior prominence (Culbertson & Tanner, 2011).
The arytenoid, corniculate, and cuneiform are paired cartilages. The arytenoids are shaped
like a pyramid and are impor tant to pitch change. They slide, rock, and rotate and are primary
structures in abduction (opening) or adduction (closing) of the vocal folds. The cuneiforms are
wedge shaped, and the corniculates are small cartilages attached to the apex (upper part) of the
arytenoids. Cranial nerve X, also known as the vagus nerve, innervates, abducts, and adducts the
vocal folds (Culbertson, Christensen, & Tanner, 2013).
There are two types of laryngeal muscles: extrinsic and intrinsic. Extrinsic laryngeal muscles
have their origin outside of the larynx and are sometimes called neck strap muscles. Extrinsic
muscles may also be classified by their location: superior (suprahyoid) or inferior (infrahyoid) to
the hyoid bone. The extrinsic laryngeal muscles are generally responsible for support of the lar-
ynx because it does not rest on a bone. They also move the larynx up or down during speech and
swallowing. The intrinsic laryngeal muscles have both their origin and their attachment within