The organ commonly known as the voice box is scientifically termed the larynx. This complex, cartilaginous structure is a tube-shaped organ in the neck that plays a role in breathing, sound production, and airway protection. Although primarily associated with speech, the larynx is a protective valve that is part of the respiratory system. Understanding its anatomy and function reveals its importance to human life.
Defining the Larynx: Structure and Location
The larynx is situated in the front of the neck, located above the windpipe (trachea) and below the pharynx. In adult humans, it is positioned between the third and sixth cervical vertebrae. The framework of the larynx is a skeleton of nine cartilages, connected by membranes and muscles.
Three cartilages are unpaired, forming the major structural components. The largest is the thyroid cartilage, which wraps around the front and sides. It is more prominent in males, where it forms the laryngeal prominence, commonly called the Adam’s apple. Beneath the thyroid cartilage sits the cricoid cartilage, the only complete ring of cartilage in the airway, connecting the larynx to the trachea.
The third unpaired cartilage is the epiglottis, a flexible, leaf-shaped structure made of elastic cartilage. Three pairs of smaller cartilages—the arytenoid, corniculate, and cuneiform—also contribute to the framework. The paired arytenoid cartilages are important, as they sit atop the cricoid cartilage and serve as attachment points for the vocal folds. Extrinsic muscles and ligaments hold the structure in place, allowing movement during swallowing and pitch change.
The Mechanics of Voice Production
The primary function of the larynx is phonation, the physical process of creating vocal sound. This occurs when air expelled from the lungs is modulated by the two bands of muscle tissue housed within the larynx, known as the vocal folds (or vocal cords). When preparing to speak, intrinsic muscles pull the vocal folds together (adduct them), closing the space between them called the glottis.
Voice production follows the myoelastic-aerodynamic theory, which describes how the vocal folds vibrate passively in the exhaled airstream. Air pressure builds up below the closed vocal folds until it forces them apart in a quick puff of air. The elasticity of the tissue and the drop in pressure immediately snap the folds back together, repeating the cycle hundreds of times per second.
The frequency of this opening and closing cycle determines the pitch of the voice. Muscles like the cricothyroid and thyroarytenoid adjust the length and tension of the vocal folds to control this frequency. Contraction of the cricothyroid muscle lengthens and tightens the folds, causing them to vibrate faster and create a higher pitch. Volume is controlled by the force of the air pushed from the lungs, with stronger air pressure resulting in a louder sound.
Functions Beyond Sound
While sound production is the larynx’s most recognized role, its most important biological function is acting as a protective barrier for the lower airway. The larynx serves as a gatekeeper, ensuring that only air enters the trachea and lungs. This protective action is important during swallowing, a process known as deglutition.
During swallowing, the larynx moves upward, and the epiglottis folds downward like a lid to cover the airway entrance. Simultaneously, the vocal folds come together to form a tight seal, creating a twofold defense against aspiration into the lungs. This mechanism prevents choking and is considered the evolutionary basis for the organ.
The larynx also regulates airflow during breathing by controlling the opening of the glottis. For normal respiration, the vocal folds are pulled apart (abducted) to maximize the air entering and leaving the trachea. It is also involved in forceful expiration actions, such as coughing, where the vocal folds close rapidly to build up pressure before violently expelling air to clear irritants.