The vocal cords are white-colored structures located in the larynx. They allow people to communicate by producing sounds through breathing. This sound is created through vibration of the cords, which are shaped like folds lying over the trachea. The surrounding structures (like the epiglottis, which functions like a valve) prevent solid or liquid food from entering the trachea. There are two layered pairs of vocal cords, but only the lower (also called the true) vocal cords are able to produce sounds as they are attached to small bones, of which movement can be controlled by ligaments. This control over sounds is learned instinctively and empirically.
The contraction or relaxation of the vocal cords allows you to alter the flow of air through the throat. Controlled contractions produce different sounds, of which the pitch is mostly determined by the dimensions and tension of the cords. Young children and women have a different vocal cord structure compared to men, which explains the difference of pitch. The upper, also called false vocal cords, can be trained for adapting the sounds created by the lower or true vocal folds, which is mostly done unconsciously or by professional singers.
Voice strain, infections and tumors to the thyroid gland can lead to damage to the vocal cords, and result in formation of nodules, irritation and swelling. As other unconsciously developed body functions, a long period of damage can result in permanent consequences, which can mostly only be treated by a combination of surgery, medication and speech therapy.