Vocal folds
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The vocal folds, also known popularly as vocal cords, are composed of twin infoldings of mucous membrane stretched horizontally across the human larynx. They vibrate, modulating the flow of air being expelled from the lungs during phonation.
Open during breathing, the folds are controlled via the arytenoid cartilages for speech or singing. They are white because of poor 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".
False vocal folds
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.
The false folds are also called vestibular folds and ventricular folds. They can be seen on the diagram above as ventricular folds.
See also
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