The larynx, commonly known as the voice box, is a structure situated in the anterior neck, connecting the lower part of the throat (the pharynx) to the windpipe (the trachea). It functions in several biological processes, including breathing, airway protection, and sound production. The organ is built from a skeleton of nine cartilages, including the large thyroid cartilage, which forms the prominent laryngeal prominence often called the Adam’s apple. It is suspended by muscles and ligaments and contains the vocal folds.
Facilitating Air Passage
The larynx serves as a rigid conduit that maintains an open, unobstructed pathway for air between the upper and lower respiratory tracts. During quiet breathing, the intrinsic laryngeal muscles actively pull the paired vocal folds apart, a process known as abduction. This action widens the opening between the folds, the glottis, minimizing resistance and allowing for the efficient exchange of air.
The posterior cricoarytenoid muscles are responsible for this lateral movement, ensuring the airway remains sufficiently dilated during inhalation and exhalation. The laryngeal muscles can also adjust the size of the glottis to regulate airflow, adapting to the body’s changing oxygen demands.
Protecting the Lower Airway
A primary function of the larynx is to prevent food, liquids, and foreign materials from entering the trachea and lungs, a process called aspiration. This protective action is triggered during swallowing. As a person swallows, the entire larynx structure moves upward and forward beneath the tongue base.
Simultaneously, the leaf-shaped epiglottis, a cartilage attached at the top of the larynx, folds downward like a lid over the laryngeal inlet, diverting the swallowed material toward the esophagus. At the same moment, the true and false vocal folds within the larynx tightly squeeze together (adduct), creating a sealed barrier against the lower airway. The larynx also houses sensory receptors that initiate the cough reflex if irritants or particles manage to reach the airway.
Generating Sound and Voice
The larynx’s most recognized function is phonation, the generation of sound that forms the basis of human speech. This process begins when air pressure built up in the lungs is forcefully expelled upward against the closed or nearly closed vocal folds. This subglottic pressure causes the folds to separate and vibrate rapidly, which creates audible pulses of air.
The rapid closing of the vocal folds is assisted by the Bernoulli effect, where the fast-moving air passing through the narrow glottis creates a drop in pressure, sucking the folds back together. The rate at which the vocal folds vibrate determines the pitch of the sound produced. Intrinsic laryngeal muscles, such as the cricothyroid muscle, precisely control this frequency by adjusting the length and tension of the vocal folds; stretching the folds increases the frequency, resulting in a higher pitch.
The force of the air expelled from the lungs controls the amplitude of the vibration, which correlates directly to the volume or loudness of the sound. The sound initially produced by the larynx is a raw, buzzing tone before it is modified. This raw sound travels upward into the vocal tract, where it is shaped into intelligible speech by articulators like the tongue, palate, and lips.