The human
larynx contains two pairs of folds made of elastic tissue covered by mucous membrane. One of them, the
false vocal folds, narrows the
glottis during swallowing, preventing pieces of food from getting into the
trachea. Below them, there are are the
true vocal folds, which, when appropriately adjusted, can be made to vibrate as air from the lungs passes out between them (see:
phonation). The vibration produces
voice, which is the essential component of voiced
consonants as well as
vowels. If the vocal folds are drawn apart, air flows between them causing no vibration, as in the production of voiceless consonants. The vocal folds are also called
vocal cords.