Ultrastructure of the Eimer's organ of the star-nosed mole.

The nose of the star-nosed mole consists of 22 fleshy appendages that fan out from around the nostrils and are covered with specialized epidermal sensory receptors called Eimer's organs. The Eimer's organs of the star-nosed mole are domed epidermal papillae approximately 40 to 50 microns in diameter. The center of each papilla contains a column of stacked circular epidermal cells closely associated with five to ten neural processes that originate from three myelinated fibers in the underlying dermis. At middle and lower levels in the cell column, a single nerve fiber is located in the center of the column, enclosed by the epidermal cells which wrap around the fiber and form desmosomes between their own adjacent plasma membranes. An additional five to ten fibers travel up the sides of the column ensheathed in the margins of the epidermal cells. At the top of the cell column, the nerve fibers produce a repeated series of terminal swellings. These terminal swellings converge in the center of the column, where a single epidermal cell completely encapsulates each circular arrangement of nerve terminals. No synapses or other cellular junctions were observed between the nerve terminals where they converge within the cell column. There is a single Merkel-like ending at the base of the cell column, and a single encapsulated corpuscle beneath the cell column, in the connective tissue of the dermis. The structure of Eimer's organs is consistent with a mechanoreceptive function.