Confirmation of encapsulated nerve structures in the human vocal cord.

The overall morphology of the encapsulated nerve structure in the human vocal cord was studied. The nerve consists of a straight portion containing a striated muscle fiber and several side branches. The side branches consist of non-myelinated fibers and dense collagen bundles. Their ultrastructure resembles that of the Golgi tendon organ, suggestive of a pressure receptor. Since the side branches extend between muscle fibers of the vocal muscle, their purpose may be to detect the stiffness of the vocal cord. One end of the intracapsular muscle fiber terminates in the capsule and the other, tapered end terminates in dense collagen bundles within the capsular space. Contraction of muscle fiber alters the stiffness of the intracapsular space and may control the sensory threshold of the nerve ending.