The larynx, commonly known as the voice box, is a complex organ situated in the neck at the top of the trachea (windpipe). This structure connects the throat to the lungs and separates the body’s air and food passages. Its location makes it central to survival and communication. The larynx manages the flow of air, protects the lower airway, and enables the production of sound.
Understanding the Basic Anatomy
The physical structure of the larynx is built upon a framework of nine cartilages that maintain its shape and flexibility. The largest is the thyroid cartilage, a shield-shaped plate forming the front and sides of the larynx. The anterior point of this cartilage is often felt under the skin and is called the Adam’s apple.
Directly below the thyroid cartilage is the cricoid cartilage, the only complete ring of cartilage in the airway. It resembles a signet ring with a wider section facing backward. These two large cartilages provide the main structural support for the organ. Anchored to the upper, posterior rim of the cricoid are the arytenoid cartilages, which are small, pyramid-shaped structures.
These arytenoid cartilages attach to the back ends of the true vocal folds. They pivot, slide, and rock, allowing them to precisely open and close the vocal folds. The true vocal folds are multi-layered, wedge-shaped structures composed of muscle tissue covered by a flexible mucosal membrane.
Just above the true vocal folds are the vestibular folds, or false vocal folds. These folds are thicker and do not typically vibrate to produce sound, but they assist in airway protection. The space between the two true vocal folds is called the glottis, which must be controlled to manage airflow and sound production. This cartilaginous and muscular arrangement is suspended by the hyoid bone, allowing the larynx to move up and down during swallowing.
Core Functions of the Larynx
The larynx performs three primary physiological roles, with its oldest function being airway protection. During a swallow, the entire larynx elevates toward the lower jaw. The epiglottis, a leaf-shaped cartilage, folds backward over the laryngeal opening. This movement, combined with the closure of the true and false vocal folds, creates a three-tiered seal, ensuring food and liquid are diverted into the esophagus and kept out of the lungs.
The second function, respiration, is managed by the constant movement of the vocal folds to regulate air flow. During quiet inhalation, the folds move apart (abduct) to create a triangular opening that allows air to pass freely into the lungs. This action ensures a sufficient volume of air can be taken in for breathing.
The third function is phonation, the production of voice, which relies on the aerodynamic-myoelastic theory. To begin sound production, the vocal folds must be brought close together by the intrinsic laryngeal muscles. Air pressure from the lungs, known as subglottal pressure, builds up beneath the closed folds until it forces them apart.
This burst of air creates a rapid, cyclical vibration that is an effect of physics and tissue elasticity, not muscular effort. As air rushes through the narrow gap, the fast-moving column causes a drop in pressure along the medial edges of the vocal folds (the Bernoulli effect). This vacuum-like effect pulls the flexible folds back toward the midline, initiating the closing phase of the cycle.
The vibration is a complex, wave-like motion of the mucosal covering, called the mucosal wave. This wave travels across the surface of the vocal fold, from the bottom edge to the top edge, maintaining the oscillation. The frequency of these vibrations determines the pitch of the voice, while the air pressure from the lungs dictates the intensity, or loudness.
What a Healthy Larynx Looks Like
A normal larynx, viewed during an examination like laryngoscopy, presents a distinct visual appearance. The true vocal folds should appear smooth and straight along their edges, with a pearly-white or pale pink coloration. This lighter hue contrasts with surrounding tissues, such as the ventricular folds, which typically show a slightly pinker, more vascular appearance.
When the larynx is observed in motion, health is measured by the symmetry and quality of movement. The two vocal folds must move together in a coordinated, mirror-like fashion during both abduction for breathing and adduction for voicing. During phonation, stroboscopy reveals the mucosal wave, which should travel across the folds with a regular, fluid, and symmetrical ripple.
Minor visual variations are commonly observed and are not necessarily signs of disease. Slight redness or swelling (erythema and edema) in the back part of the larynx can sometimes indicate acid reflux or general vocal strain. A healthy larynx is characterized by its pliable, moist appearance and the smooth, rhythmic quality of its vibratory cycle.