The larynx, commonly referred to as the voice box, contains a framework of cartilages that move relative to each other. Muscles produce movement by contracting between cartilages, and special joints restrict that movement to specific patterns that result in the proper positioning of the larynx for it’s various functions.
The vocal folds, also known as the vocal cords, are structures composed of muscle, connective and elastic tissue, a loose fluid filled layer, and a thin pliable covering. This layered structure allows for a rippling movement of the cover over the body of the vocal folds, known as mucosal wave, when they are positioned together and air passes between them. The basic sound wave of the voice begins with this, and is modified by other parts of the vocal tract to result in the voice we hear. Think of a brass instrument. The sound from the mouthpiece is thin and not very pleasant, as it passes through the rest of the instrument, the sound is enhanced to produce the distinct character of the instrument. Our throat, mouth and nose do similar modification to the raw sound coming from our vocal folds.
When the tissues of the vocal folds become injured or inflamed, hoarseness usually results from the breakdown in mucosal wave caused by the stiffening or swelling. More prolonged injury or inflammation can cause breakdown in the normal layered structure of the vocal folds from ingrowth of fibrous tissue or thickening of the cover. Nodules and polyps are examples of this sort of change. Illness can also affect the resonance of the other parts of the vocal tract. Think of how people can identify when you have a cold, just by the sound of your voice.
In addition to producing voice, the larynx also functions to protect the airway. It is situated at the top of the windpipe, or trachea in medical terms, and closes off the airway from the throat when we swallow. The vocal folds move together tightly. Along with some other movements, this closure causes food or liquid to bypass the airway and enter the esophagus, which opens right behind the larynx. When problems occur with the muscle activity of the larynx, both swallow and voice are often affected.