| Merkel cell | |
|---|---|
 Merkel cells (shown in blue) are located in the basal epidermal layer of the skin. | |
| Details | |
| Location | Skin ofvertebrates |
| Function | Light touch sensation |
| Identifiers | |
| MeSH | D018862 |
| NeuroLex ID | nifext_87 |
| Anatomical terms of neuroanatomy | |
Merkel cells, also known asMerkel–Ranvier cells ortactile epithelial cells, are oval-shapedmechanoreceptors essential for lighttouch sensation and found in theskin ofvertebrates. They are abundant in highly sensitive skin like that of the fingertips inhumans, and make synaptic contacts withsomatosensoryafferent nerve fibers. It has been reported that Merkel cells are derived fromneural crest cells, though more recent experiments inmammals have indicated that they areepithelial in origin.
Merkel cells functionally resemble theenterochromaffin cell, the mechanosensory cell of the gastrointestinal epithelium.[1]
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 thestratum basale[2][3] (at the bottom of sweat duct ridges) of theepidermis approximately 10 μm in diameter. They are oval-shaped mechanoreceptors essential for light touch sensation and found in the skin of vertebrates. They are abundant in highly sensitive skin like that of the fingertips in humans, and make synaptic contacts withsomatosensoryafferent nerve fibers.[4] They also occur in epidermal invaginations of the plantar foot surface calledrete ridges.[5]
Most often, they are associated with sensory nerve endings, when they are known asMerkel nerve endings (also called a Merkel cell-neurite complex). They are associated with slowly adapting (SA1) somatosensory nerve fibers. They react to low vibrations (5–15 Hz) and deep static touch such as shapes and edges. Due to a small receptive field (extremely detailed info) they are densely present in areas like fingertips; they are not covered (shelled) and thus respond to pressures over long periods.
The origin of Merkel cells has been debated for over 20 years. Evidence from skin graft experiments in birds implies that they areneural crest derived,[6] but experiments in mammals now demonstrate an epidermal origin.[7][8]
The German anatomistFriedrich Sigmund Merkel referred to Merkel cells asTastzellen or "touch cells". Until recently this proposed function was controversial and hard to prove, due to the close physical association of Merkel cells with sensory nerve endings. However, recent work in mice and other model organisms demonstrates that Merkel cells intrinsically transform touch into electrical signals that are transmitted to the nervous system.[9] Merkel cells expressPIEZO2, a mechanosensitive ion channel that responds to mechanical forces. Mice in which Piezo2 is knocked-out specifically in skin cells, but not sensory neurons, show decreased behavioral responses to gentle touch.[10]
Merkel cells are sometimes consideredAPUD 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 aneuroendocrine function.[11]
Although uncommon, thesecells may become malignant and form aMerkel cell carcinoma—an aggressive and difficult to treatskin cancer.[12][13]
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