Vocal apparatus

The human vocal apparatus is like two kinds of musical instruments at once: a wind instrument and a string instrument. This apparatus includes a source of wind (the lungs), components that vibrate (the vocal cords in the larynx), and a series of resonant chambers (the pharynx, the mouth, and the nasal cavities). 

The first component of this apparatus is the lungs that provide the necessary air and that can thus be described as the “generator”. When you are speaking, your inhalations become faster and shorter and you breathe more with your mouth, whereas otherwise you inhale only with your nose. When you exhale while speaking, you increase the volume and pressure of your airstream to vibrate the vocal cords in your larynx.

The larynx consists of a set of muscles and pieces of cartilage, with varying degrees of mobility, that can be raised or lowered like a gate to protect your bronchi and lungs from food and other foreign bodies. When you swallow food, your larynx rises, while the epiglottis, a flap of cartilage at the entry to the larynx, closes down over it to block the upper airways and let the food move down your esophagus safely into your stomach.

When you speak, the air expelled from your lungs moves up through the trachea to the larynx, where it passes over the vocal cords. These cords are a matched pair of muscles and ligaments, pearly white in colour, 20 to 25 millimetres long, and coated with mucus. They constitute the second component of your vocal apparatus: the “vibrator”.

The vocal cords are attached horizontally from the thyroid cartilage (the “Adam’s apple” in men) at the front to the arytenoid cartilages at the rear. By moving these cartilages as you speak, you alter the length and position of your vocal cords. When you start to say something, the arytenoid cartilages press the vocal cords against each other, thus closing the opening between them (known as the glottis).

Under the pressure of the air being exhaled, the vocal cords separate, then close again immediately, causing the air pressure beneath the glottis to increase again. By opening and closing the glottis rapidly during phonation, the vocal cords thus release the air from the lungs in a vibrating stream. When you speak a sentence, you modify the vibration frequency of your vocal cords many times to produce the acoustic vibrations (sounds) that are the raw materials for the words themselves.

For these sounds to be transformed into words, they must then be shaped by the rest of the vocal apparatus. The first step in this process occurs in the pharyngeal cavity, where the respiratory and digestive systems meet. The pharynx and the other cavities with which it communicates (the nasal cavities, mouth, and larynx) act as a “resonator” that alters the sounds issuing from your vocal cords, amplifying some frequencies while attenuating others.

The transformation of the sounds from the larynx is then completed by the position of the soft palate, tongue, teeth, lips, and other parts of the mouth, which act as “modulators” for this sound. While the larynx produces the vibrations without which you would have no voice, it is these other parts of your vocal apparatus that make your voice so flexible and versatile. They do so in different ways. Your he soft palate either blocks the passage to the upper nasal cavities or leaves it open so that the vibrating airstream can enter them. Your jaws open or close to change the size of the oral cavity. Your tongue changes shape and position to alter this cavity further. Your tongue and the lips obstruct the airflow through the teeth to varying extents. The lips also alter their shape—open, closed, pursed, stretched, and so on—to shape the sound further.