Merkel cells

Merkel cells are oval receptor cells found in the skin of vertebrates. They are associated with the sense of light touch and are responsible for the highly malignant skin tumor known as Merkel cell carcinoma.

History
They were named after the 19th century German anatomist Friedrich Sigmund Merkel who was the first to fully describe them in 1872.

Location
Merkel cells are found in the skin and some parts of the mucosa (stratum germinativum) of all vertebrates. In mammalian skin, they are clear cells found in the stratum basale (at the bottom of sweat duct ridges)of the epidermis approximately 10 µm in diameter. Most often, they are associated with sensory nerve endings, when they are known as Merkel nerve endings. They are associated with Rapidly Adapting (RA) nerve fibers.

Function
The exact function of Merkel cells is unclear. F.S. Merkel referred to them as Tastzellen or "touch cells", although their function has been disputed ever since. Merkel cells are sometimes considered APUD cells because they contain dense core granules, and thus may have a neuroendocrine function.

Developmental origin
The origin of Merkel cells is still debated. Evidence from skin graft experiments in birds implies that they are neural crest derived, while experiments in mammals generally point to an epidermal origin.