Encapsulated nerve structures in the human vocal cord. An electronmicroscopic study.

Encapsulated nerve structures which contain abundant axon terminals between dense collagen fibres are found in the intermuscular connective tissue of m. vocalis and the subepithelium of the cartilaginous part of the human vocal cord. Axon terminals are either partly surrounded by or lack the Schwann sheath. They directly face to the basal lamina and collagen fibres and together represent the receptors of mechanical stimuli. The location of these nerve structures in the vocal cord may indicate that they serve to detect its degree of rigidity. Encapsulated nerve structures in m. vocalis contain a striated muscle fibre. The termination of this fibre within the capsule resembles that of the Golgi tendon organ. Since the encapsulated nerve structures are located near the termination of muscle fibres in the vocal ligament, they may serve to detect the tension of muscle fibres which pull on the vocal cord during vibration of the vocal mucosa. Encapsulated nerve structures in the cartilaginous part of vocal cord are located in the submucosa where they are covered by thick stratified squamous epithelium with papilla. These regions often contact each other in the state of full adduction of the arytenoid cartilages. Therefore the encapsulated nerve structures may detect the bilateral contact of the vocal cord when the glottis is closed.