A functional voice disorder is one that results from improper or inefficient use of the vocal mechanism when the physical structure is normal. For example, vocal fatigue; muscle tension dysphonia or aphonia; vocal abuse or overuse; diplophonia (sounds like two voices are being produced); ventricular phonation (engaging the false vocal cords in voice production); psychogenic (related to a trauma or a severe emotional distress).
However is it important to keep in mind that voice disorders are not mutually exclusive and overlap can occur. For example, nodules on the cords are produced from a functional voice disorder, as they result from behavioral voice misuse. The voice misuse results in repeated trauma to the vocal folds, which may then lead to structural (organic) change to the vocal cord tissue.