The human voice originates from two small bands of tissue located in the neck, known as the vocal folds (or vocal cords). These structures reside within the larynx, often called the voice box, situated atop the trachea or windpipe. Their primary function is to modulate the air stream expelled from the lungs, transforming breath into the complex acoustic patterns of speech and song.
The Anatomy of Vocal Folds at Rest
When a person is breathing quietly, the vocal folds are in an open, relaxed position. In this resting state, they appear as two flat, triangular bands of tissue stretching horizontally across the airway. The space between the folds is called the glottis, and when open, it forms a characteristic V-shape that allows air to pass freely.
Healthy vocal folds present a smooth, almost pearly white or pale appearance due to the lack of superficial blood vessels in the outer layers. The structure is layered, composed of a deep vocalis muscle covered by a pliable, multi-layered mucous membrane. The length of these folds varies between individuals, with adult male folds typically measuring between 1.75 and 2.5 centimeters, and female folds measuring between 1.25 and 1.75 centimeters.
Appearance Changes During Speaking and Singing
When a person begins to speak or sing, the static, V-shaped appearance transforms. To produce sound, the folds move from their open, resting position to a closed, approximated one, creating a tight slit across the airway. This closure is achieved through the coordinated movement of surrounding laryngeal muscles and cartilages.
Once closed, the folds are held in tension, and controlled air pressure from the lungs forces them to vibrate rapidly in a wave-like pattern known as the mucosal wave. The speed of this vibration is extremely fast, ranging from 100 to 300 times per second during normal speech.
The appearance of the folds changes significantly based on the pitch being produced. Higher pitches are generated when the folds are pulled longer, thinner, and more taut, similar to tightening a guitar string.
Conversely, a lower pitch results when the folds are shortened, making them appear thicker and slightly more relaxed. The loudness of the voice influences the extent of the closure and the force with which the folds are blown apart by air pressure. This rapid action creates a blurred or oscillating appearance when viewed without specialized equipment.
How Doctors Visualize the Vocal Folds
Because the vocal folds vibrate so quickly, special medical techniques are necessary to visualize their movement clearly. The general examination of the larynx and vocal folds is called laryngoscopy, which can be performed using various tools. One method involves using a rigid telescope inserted through the mouth, which provides a highly magnified and bright image.
An alternative technique uses a flexible endoscope, a thin tube passed through the nasal passage, allowing the patient to speak and swallow naturally during the examination. Neither of these methods, however, can capture the actual speed of the vibration under continuous light.
To overcome this challenge, doctors use a technique called stroboscopy, which combines either a rigid or flexible scope with a synchronized, flashing light source. A microphone detects the frequency of the patient’s voice, and the strobe light flashes at a rate slightly out of sync with the vocal fold vibration.
This creates an optical illusion, allowing the observer to perceive the rapid, wave-like motion in what appears to be slow motion. This technique enables health professionals to assess the function and health of the vocal fold tissue during phonation.