Role of the thyroid cartilage in phonation.

Larynx is a part of the respiratory system and is supposed to be a complex apparatus responsible for the phonation-creation of voice. However, the extensive anatomical knowledge about the larynx does not correspond to an obscure speculation about creation of voice. Therefore the function of the larynx can be compared with the function of electro-acoustic transducers and on this basis certain roles can be ascribed hypothetically to the functional details of phonation system. The thyroidal cartilage seems to be ideal for such a comparison. Diffusion of acoustic signal by densing and diluting of an elastic milieu is due to the initial stimulus mediated by a solid and elastic sound. In case of vocal system, the initial stimuli occur stimultaneously at two sounds that behave as membranes of coaxial mechanic-acoustic resonators in the function of a radiator. Vocal cords represent a membrane of more subtile system, and the thyroid cartilage is a membrane of more robust system. The mechanism of oscillation is the subject of the present communication. It was concluded that the thyroid cartilage is not only a passive shield protecting the fine glottic structures, but on the contrary an active element of this mechanic-acoustic radiator. The recorded movements of the thyroid cartilage enabled to subtract the presence of neuroreflexive activity accompanying the vocal cycle. The anatomical structures in the vicinity of the thyroid cartilage indicate possible modifications of its motion so that the laryngeal articulation can be supposed.