The larynx forms the uppermost unit of the trachea or windpipe
The primary purpose of the larynx is to serve as a valve which keeps food, drink, and other foreign matter out of the lungs.
The larynx's use in the act of phonation is a secondary function.
Speakers and singers often unconsciously introduce unnecessary strain and tension into the larynx by using too much of its valving action while phonating.
Skeletal Framework of the Larynx
Thyroid cartilage: serves as a protective housing for the vocal folds and forms the visible projection in the front of the throat known as the Adam's apple.
Cricoid cartilage: serves as a foundation for the laryngeal framework. It sits atop the highest cartilage of the trachea proper and is joined to it by ligament.
Arytenoid cartilages: irregular in shape. Each arytenoid has three prongs; one projects forward into each vocal cord and is called the vocal process; one projects sideways and is called the muscle process; the third projects upward and is called the apex.
Epiglottis: a leaf-shaped cartilage which assists in the valving function of the larynx and is also active in the production of certain speech sounds. When swallowing, the epiglottis is pulled toward the back of the throat and down over the opening of the larynx; together with the laryngeal collar it keeps food or drink from entering the trachea.
Hyoid bone: a U-shaped bone which is attached to the base of the tongue and opens toward the back of the throat.
Musculature of the Larynx: Intrinsic Muscles
Intrinsic: muscles which have both ends--the origin and the insertion--in the larynx.
Thyroarytenoid muscle: connects the thread and arytenoid cartilages. The lower set form the true vocal cords (vocal folds), which are called the vocals muscle or the internal thyroarytenoids. The upper set are called the false cords or ventricular bands.
Cricothyroid muscle: originates at the front of the cricoid cartilage and fans out upward and backward to the lower surfaces of the thyroid cartilage. When it contracts, it tends to pull the thyroid forward and down, bringing the two cartilages closer together and stretching the thyroarytenoid muscles.
Cricoarytenoid muscles: divided into the posterior cricoarytenoids and the lateral cricoarytenoids. The posterior resist the forward pull on the arytenoid by the vocals muscle and open the vocal cords by pulling the arytenoids out to each side. The lateral help bring together the vocal cords by pulling forward on the muscle processes, thus rotating the vocal processes toward each other and closing the glottis.
Arytenoid muscles: connect the arytenoid cartilages and are the primary factor in bringing the back end of the vocal cords together. These muscles consist of the transverse arytenoid and a pair of oblique arytenoids.
Musculature of the Larynx: Extrinsic Muscles
Extrinsic: those that originate above the larynx--supralaryngeal muscles; and those that originate below the larynx--the infra laryngeal muscles.
Supralaryngeal muscles: active in swallowing, chewing, and the tongue movements associated with articulation (frequently referred to as the "swallowing muscles").
Infralaryngeal muscles: active in yawning and inhaling.