Vocal folds
 |
Laryngoscopic view of the vocal folds. |
The
vocal folds, also known popularly as
vocal cords, are composed of twin infoldings of
mucous membrane stretched horizontally across the
larynx. They
vibrate, modulating the flow of air being expelled from the lungs during
phonation.
Another name for the airway at the level of the vocal cords is the glottis, and the opening between the cords is called the glottic chink. The size of the glottic chink is important in respiration and phonation. Open during inhalation, closed when holding one's breath, and held apart just a tiny bit for speech or singing; the folds are controlled via the
vagus nerve. They are
white because of scant
blood circulation.
The folds vibrate when they are closed to obstruct the airflow through the
glottis, the space between the folds: they are forced open by increased
air pressure in the lungs, and closed again as the air rushes past the folds, lowering the pressure (
Bernoulli's principle). A person's voice
pitch is determined by the
resonant frequency of the vocal folds. In an adult male this frequency averages about 125
Hz, adult females around 210, in children the frequency is over 300 Hz.
The term
vocal cords is occasionally mis-spelled 'vocal chords', possibly due to the musical connotations or to confusion with the
geometrical definition of the word "chord".
The vocal folds discussed above are sometimes called 'true vocal folds' to distinguish them from the
false vocal folds (
false vocal cords). These are a pair of thick folds of mucous membrane that sit just above, and protect, the more delicate true folds. They have minimal role in normal
phonation, but are often used in screaming and the
death grunt singing style.
The false folds are also called
vestibular folds and
ventricular folds. They can be seen on the diagram above as
ventricular folds.
*
Adam's apple*
Falsetto*
Overtone singing*
Bogart-Bacall Syndrome 
