Structure
The organ consists of a minute skin papilla with 0.1-0.2mm diameter. At the papilla's core, a geometric constellation of nerve fibres with free endings is embedded symmetrically in a column of epithelial cells. Eimer saw two to three single nerve fibres, rising strait in the middle of the column and ending in the fifth layer under the stratum corneum that forms the hard top of the epidermis. The fibres extend short protrusions perpendicularly into each epithelial layer they traverse, where the protrusions end in 'buttons'. They are ringed by a circle of roughly 19 evenly-spaced nerve fibres, known as satellite fibres, whose protrusions point inwards. In addition, Eimer distinguished a separate set of nerve fibres with free nerve endings. By contrast to the fibres in the papilla's core, these travel obliquely toward the surface at the papilla's perimeter.
With improved histological techniques, a second touch receptor type, Merkel cell-neurite complexes, was found in the stratum germinativum at the bottom of the epidermis, and a third, lamellated corpuscles of Vater and Pacini, was discovered in the stratum papillare of the dermis underneath the Merkel cells as published by Halata in 1975.
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