Short answers, pulled from the story.
The human voice is the only instrument that grows from within the body and transforms air into meaning, emotion, and music through a three-part mechanism. The lungs force air upward to strike the vocal folds, which vibrate to generate raw sound pulses that articulators shape into language.
Adult male vocal folds typically measure between 17 millimeters and 25 millimeters in length, while female vocal folds range from 12.5 millimeters to 17.5 millimeters. This size difference results in a lower pitch for men, and men generally possess a larger vocal tract that gives the voice a lower-sounding timbre.
Children learn to use the action of vocal fold separation consistently during speech at an early age, often before the age of two. They master this by listening to the voices of adults around them and distinguishing between utterances that require abductory-adductory gestures.
The seven areas that may be listed as possible vocal resonators include the chest, the tracheal tree, the larynx itself, the pharynx, the oral cavity, the nasal cavity, and the sinuses. Singers enhance the basic product of phonation in timbre and intensity by using these air-filled cavities to resonate sound.
Speech pathologists identify four vocal registers based on the physiology of laryngeal function: the vocal fry register, the modal register, the falsetto register, and the whistle register. Each register produces a particular series of tones in the same vibratory pattern of the vocal folds.
Vocal nodules are caused over time by repeated abuse of the vocal cords which results in soft, swollen spots that develop into harder, callous-like growths. Voice therapy is generally delivered by a speech-language pathologist to teach the patient how to eliminate the irritations permanently through habit changes and vocal hygiene.