The functions of human organs of speech are to produce sounds that are perceived as speech by pushing the air from the lungs up and, while modifying it by various means, out of the mouth. Organs of speech produce consonants and vowels and voiced and voiceless sounds.
The main three parts of the speech producing apparatus in humans are the lungs, the voice box and the vocal tract. The lungs produce the initial push of air that is necessary for every utterance. The larynx, or the voice box, contains the vocal folds, which are sometimes incorrectly called vocal cords, and the glottis. Nasal and oral cavities constitute the vocal tract.
The larynx sits on top of the division between the windpipe and esophagus, down which the food travels to the stomach. The glottis is the space between vocal folds. The latter create voiced (z, d) or voiceless sounds (s, t) by vibrating when closed and by being open, respectively.
In the oral cavity, the tongue, lips and teeth are used to articulate various consonant and vowel sounds of the speech. Some languages, such as the language of the Bush People in Africa, use click sounds, created entirely in the oral tract. The role of the nasal cavity is to control production of oral and nasal sounds. To make nasal sounds (m, n), the vellum at the back of the mouth is lowered, and the air passes out of the nose.