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What is a Merkel Cell?
A Merkel cell is a touch receptor found in the skin. Merkel cells, or Merkel-Ranvier cells, are involved in the sensation of light touch, for example when feeling the texture of an object or determining its shape using the fingertips. High concentrations of Merkel cells are found in the fingertips and also in the lips, but they are also present in areas of hairy skin. Sometimes a type of cancer known as a Merkel cell carcinoma arises from Merkel cells. Merkel cells are named after Friedrich Sigmund Merkel, the German scientist who discovered them.
In the skin, Merkel receptor cells are typically situated near sensory nerve endings, with each Merkel cell and each nerve ending forming what is known as a Merkel cell-neurite complex. When the sensation of light touch is detected, the Merkel cell-neurite complex acts as what is called a mechanoreceptor. Mechanoreceptors respond to a particular stimulus, in this case touch, and react by producing electrical nerve impulses which travel along sensory nerves, eventually reaching the brain.
The type of mechanoreceptor formed by a Merkel cell is described as being slowly adapting, which means it can take a number of seconds to return to normal after electrical impulses have been produced by a stimulus. This can be useful in practice, for situations when an object, such as a cup, has to be gripped, because the brain will remain aware of the sensation for longer, decreasing the risk of dropping the cup. Some other types of mechanoreceptors adapt much more quickly — in a fraction of a second — with the result that the fingers would have to be moved over the surface of an object to keep causing new stimulus to maintain the sensation.
A rare type of skin cancer can form from Merkel cells, known as a Merkel cell carcinoma. The cancer is associated with exposure to sunlight, and generally appears on the limbs, head, or neck as a round, red lump, which is firm to the touch and can be mistaken for a harmless skin blemish such as a cyst. It is thought that cancerous changes inside the Merkel cell could be associated with a viral infection. If the tumor is diagnosed and surgically removed early in the disease, before the cancerous cells have had time to spread, the outlook is positive. In cases where the cancer has already spread, chemotherapy and radiotherapy are normally used in addition to surgery to improve symptoms and increase life expectancy.
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![Merkel cells register gentle touch.]()
By: Svetlana FedoseevaMerkel cells register gentle touch.
Discussion Comments
Does anyone know how Merkel cells interact with pain? I started thinking about playing the guitar. As a beginner, the strings can be very painful, and you can feel the strings under your fingers. After a while, you start to build calluses that lessen the sensation in your fingers.
I guess my question is: do the calluses damage the Merkel cells in some way, or are the calluses simply extra skin that dampen the signals to the Merkel cells?
Do all animals have Merkel cells? Surely they have some type of cells that send feelings to the brain, but do they work the same way, and are they called the same thing?
I would imagine that different animals have receptors in different parts of their bodies, too. For example, a lizard might have more Merkel cells on its feet so that it can tell whether it will be able to climb up a surface. I'm sure there are better examples that I can't think of.
I was also wondering about plants. Do climbing plants like vines have Merkel cells that let them know when they have come in contact with another object?
I loved the description of the mechanoreceptors. I don't know that I had every knowingly thought about the mechanisms behind it, but I have realized that after you touch something, the sensation goes away after a few seconds. I guess this would explain why.
The article mentions the two different types of receptors, though. Are these evenly spaced around our hands and other body parts, or do certain areas have more of one than the other?
How many people each year are diagnosed with Merkel cell carcinoma? I was not even aware that something like this existed, and I wouldn't have known what to look for.
I am still not quite certain what the symptoms would look like. Does anyone know a good place to find Merkel cell carcinoma pictures? How do you tell the difference between the carcinoma and a cyst?
I had no idea there were special cells that were responsible for us being able to feel and touch. I guess it makes sense, though, because all of our other senses have special cells.
One slight thing I'm confused on is: are the Merkel cells part of the skin or the nervous system? Since they cause electrical impulses, my guess would be that they are part of the nervous system. Someone please correct me if you know the answer.
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