The fine structure of intraepithelial free nerve endings in the canine vocal cord mucosa.

Innervation of the epithelium on the undersurface of the canine vocal cords was investigated by transmission electron microscopy. In the subepithelial lamina propria, nerve bundles containing unmyelinated fibers were observed. The nerve bundles, encircled by basal lamina, were enclosed by a thin connective tissue layer and by flattened fibroblast-like cells. With nerve bundles approaching the epithelium, the axons divided repeatedly and entered the epithelial layer. In the epithelial cells, nerve axons formed knob-like swellings that contained a small number of large granular vesicles and a large number of small agranular vesicles. A sensory function responsive to irritant chemical stimuli and to mechanical stimuli is presumed for these vesicle-containing nerve processes.