Ultrastructure of the lamina propria of the human vocal fold.

We studied three-dimensional arrangement of collagen fibers and elastic fibers in the human vocal fold by scanning electron microscopy after digesting cellular elements and collagen fibers with formic acid treatment and cellular elements and elastic fibers with 10% sodium hydroxide. The superficial layer consisted of clusters of collagen fibers and fine elastic fibers running straight or coiled. The intermediate layer consisted of thick bundles of collagen and elastic fibers running longitudinally and fine coiled elastic fibers. The deep layer consisted of coil elastic fibers and dense collagen bundles. Collagen fibers may have a role of maintaining the organization of vocal folds even during vibration, and elastic fibers act to rapidly restore the vocal folds to their original form. We also studied the distribution of oxytalan fibers in vocal folds by aldehyde-fucusin staining. Oxytalan fibers were distributed throughout the connective tissue of the vocal folds, and a large number of fibers was present just under the epithelial basement membrane and around the muscle fibers. If these fibers are damaged and lose their functions, vibration of the vocal folds will be impaired.