The paired vocal folds (also called vocal cords) abduct – i.e., spread apart or separate – when we breathe in to allow air to pass into the lungs. The opposite of abduction is adduction. Humans adduct, or bring together, the vocal folds upon expiration to produce voiced sound. (An easy way to remember the difference between abduction and adduction is this: The first syllable of adduction is "add," or putting two things together.)

Abduction and adduction of the vocal folds is brought about by small muscles in the larynx. When the intrinsic muscles of the larynx contract, they pull on the arytenoid cartilages, which causes them to pivot. Contraction of the posterior cricoarytenoid muscle, for example, moves the vocal folds apart, thereby opening the rima glottidis. By contrast, contraction of the lateral cricoarytenoid muscles moves the vocal folds together, thereby closing the rima glottidis.