The function of the glottis is to make several voicing sounds between the vocal folds when they vibrate. Voiceless consonants include the English h, f, s, p, t and k sounds. The glottis functions when vocal folds are narrowed yet apart, according to Healthline.
Voiceless consonants form because the glottis moves without other parts of the larynx. Voiceless consonants occur when the glottal elements are slightly apart from each other instead of vibrating together to make a full voice, notes Healthline. Glottal sounds are how Australian didgeridoo players create a wide range of sounds with their instruments by limiting the size of the glottal opening to make voiceless consonance.
Muscles in the larynx adjust the size of the glottal opening, explains Scott Sheffield from GetBodySmart. The glottis expands when humans breathe, and the opening forms a triangular shape to let air in and out of the lungs. To make glottal sounds, muscles in the throat constrict the size of the glottal opening to a very narrow slit.
The glottis is below the epiglottis in the throat, according to class notes from Austin Peay State University. Folds of skin protect the vocal cords when humans swallow, thereby protecting the glottis and the surrounding tissue from damage. The glottis opens when the vocal cords separate in the larynx for speaking.