Neural-epithelial interactions in sensory receptors.

The specific types of relationships that exist between sensory nerve fibers and the associated epithelial cells have been reviewed in a variety of sensory systems. In many sensory systems, perhaps most, specificity of terminal epithelial element provides a degree of specificity to the cytologic pattern of the terminal receptor. We can see examples of such interaction, not only in the case of intraepithelial nerve fibers where nerves tend to be associated with Merkel cells, but also in the case of corpuscular receptors, both of these being examples of mechanosensory systems. Equivalent types of specificity are present within the special senses, where a specific receptor cell can be described. These findings strongly suggest that specificity in the peripheral nervous system is the rule rather than the exception, a thesis proposed over a hundred years ago by F. Merkel.