NEUROMUSCULAR COMPARTMENTS OF LARYNGEAL MUSCLES

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In the report of the National Strategic Research Plan by the NIDCD, the first recommendation for research priorities in voice reads as follows: "Valuated the compartmentalization of laryngeal muscles with regard to histochemistry and motor unit organization..."(p.122). Using this recommendation as a basis, preliminary work was performed to define these compartments in the canine larynx. It was found that all muscles except the lateral cricoarytenoid. Muscle. This muscle has two lateral compartments, the vertical and oblique, which appear to cause the lateral sliding and backward rocking of the arytenoid cartilage which is seen during inspiration. The medial compartment is termed the horizontal and appears to swivel the arytenoid cartilage in order to precisely position the vocal process during phonation. It is hypothesized that most laryngeal muscles are composed of neuromuscular compartments. It is possible that these compartments are organized into two main systems: a midline phonatory system, composed of the transverse interarytenoid and the medial parts of the posterior cricoarytenoid, thyroarytenoid and cricothyroid muscles; a lateral articulatory system, composed of the oblique interarytenoid, lateral cricoarytenoid, and the lateral parts of hie posterior cricoarytenoid, thyroarytenoid and cricothyroid muscles. In the proposed study human laryngeal muscles will be examined for compartments. Neuromuscular compartments will be defined by muscle fiber orientation, fascial barriers, and patterns of their nerve supply. Specialization within compartments will be defined by the ATPase of their muscle fibers and the content and arrangement of motor and sensory axons. All muscles will be examined, however the emphasis will be placed on the thyroarytenoid, where there appears to be a large number of subcompartments which interact to control vocal cord vibration during phonation. This study is expected to have critical relevance for all aspects of neurolaryngology.