Tactile cells, Merkel cells, or Merkel-Ranvier cells are oval receptor cells found in the skin of vertebrates that have synaptic contacts with somatosensoryafferents. They are associated with the sense of light touch discrimination of shapes and textures. They can turn malignant and form the skin tumor known as Merkel cell carcinoma.
It has been reported that they are derived from neural crest cells, but more recent experiments in mammals have indicated that they are in fact epithelial in origin.
Merkel cells are found in the skin and some parts of the mucosa 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. They also occur in epidermal invaginations of the plantar foot surface called rete ridges. Most often, they are associated with sensory nerve endings, when they are known as Merkel nerve endings (also called a Merkel cell-neurite complex). They are associated with slowly adapting (SA1) somatosensory nerve fibers.
Friedrich Sigmund Merkel referred to these cells as Tastzellen or "touch cells" but this proposed function has been controversial as it has been hard to prove. However, genetic knockout mice have recently shown that Merkel cells are essential for the specialized coding by which afferent nerves resolve fine spatial details. Merkel cells are sometimes considered APUD cells (an older definition. More commonly classified as a part of dispersed neuroendocrine system) because they contain dense core granules, and thus may also have a neuroendocrine function.
The origin of Merkel cells has been debated for over 20 years. Evidence from skin graft experiments in birds implies that they are neural crest derived, but experiments in mammals now demonstrate an epidermal origin.