Merkel Cells: What Are They? What Do They Do?

Cell Biology has always been a fascination of mine and I love researching all the cells that have to do with the skin. In this article I am going give a little information on our beautiful Merkel Cells.

So, what are they? Merkel cells are tactile epithelial cells they also are known as Merkel Ranvier cells. They are named after a German anatomist – Friedrich Merkel, this amazing scientist discovered these cells way back in 1875.

They are very specialized cells that are involved in light tough sensation.

You will find these cells in the basal or germativum layer of the epidermis, this is the bottom layer of the epidermis.

Being situated in the Basal layer allows the cells to have contact with sensory nerve endings, this is a crucial part of their function.

These cells are distributed throughout the skin, but they are most densely concentrated in areas that are particularly sensitive to touch, like the fingertips, the lips, and the bases of hair follicles.

Merkel cells are a type of mechanoreceptor, they are essential for detecting mechanical pressure and textile and, work in conjunction with nerve endings. Specifically, the terminal branches of afferent somatosensory neurons, this forms Merkel cell-neurite complexes.

Let's talk about the origin of the Merkel Cell

Merkel cells are believed to originate from the epidermal lineage. This means they arise from the same progenitor cells that give rise to other epidermal cells, like keratinocytes.

There is some debate and evidence suggesting that, at least in certain parts of the body, Merkel cells might arise from the neural crest lineage, a group of cells in the developing embryo that can give rise to a variety of cell types, including some nerve cells.

Differentiation: As the developing skin progresses, certain precursor cells receive molecular signals that induce them to differentiate into Merkel cells. The key transcription factors involved in this differentiation include a basic helix-loop-helix transcription factors. This is critical for Merkel cell specification.

Once the differentiated, Merkel cells associate with somatosensory neurons to form the Merkel cell-neurite complex, essential for their mechanosensory function. This interaction is likely facilitated by the release of specific growth factors and other molecular signals attract nerve endings.

Maturation: As Merkel cells mature, they begin to produce and store neurotransmitters, especially those like serotonin and metenkephalin. These neurotransmitters are crucial to Merkel cell function, as they are released upon mechanical stimulation to activate associated nerve endings.

Mechanosensitve Ion Channels: Mature Merkel cells express various ion channels that render them sensitive to mechanical stimulation, including Piezo2 channels. These channels play a pivotal role in translating mechanical force into cellular response.

Postnatal Development: Merkel cells can be detected as early as the second trimester of gestation. After birth, the number of Merkel cells in the skin gradually increases, reaching an adult pattern around adolescence. The development of Merkel cells involves a complex interplay of genetic, molecular, and environmental factors. Despite substantial progress in understanding their development , many details about the origins, differentiation, and maturation of Merkel cells continue to be subjects of ongoing research.

How do the cells function?

Because Merkel cells are mechanosensory cells, when pressure is applied to the skin, it deforms the Merkel cell. This action then causes the release of neurotransmitters. The cascade is stimulating the sensory neuron, and a nerve impulse is then sent to the brain. The response is a perception of a sensation of light touch or pressure.

This means they respond continuously to sustained pressure, which allows persons to sense prolonged touch and pressure. This is in contrast to other mechanoreceptors in the skin, like Pacinian corpuscles, which are fast-adapting and respond primarily to changes in stimulus.

Let me break down their importance for you!

Fine touch Sensation: Merkel cells are essential for detecting and processing tactile stimuli that inform us about the detailed textures of objects. When you can discern the difference between the feel of silk and sandpaper or differentiate between various fabric textures, you can thank the Merkel cell-neurite complexes. 

Shape and Edge Detection: Along with texture, Merkel cells are especially sensitive to points, corners, and edges. This ability is vital for tasks that require precision, like reading Braille. Steady-State Touch: Merkel cells are slow adapting type I mechanoreceptors, meaning they continue to send signals as long as a touch stimulus is present. This allows us to maintain a steady grip on objects or to be constantly aware of a light touch.

Contribution to Skin Health: While their primary role is sensory, the presence of Merkel cells in the skin suggests they might play other roles in maintaining skin health, although these functions are not as well-understood.

So, what can go wrong with our Merkel cells?

Abnormalities in Merkel cells can lead to Merkel cell carcinoma, a rare but aggressive form of skin cancer. Understanding Merkel cells is crucial for diagnosing and treating this condition.

Trauma: Physical damage to the skin might damage Merkel cells and their associated nerve endings, impairing tactile sensation.

Neurological Diseases: Conditions that affect nerve endings or nerve function can indirectly impact Merkel cell function since these cells rely on their interaction with nerve endings to transmit sensory information.

Skin Diseases: Some skin conditions might influence the health and function of the epidermis, potentially affecting Merkel cells.

Ageing: Like other cells in the body, Merkel cells might decline in function with age, contributing to decreased tactile sensitivity in the elderly.

Keeping Merkel happy and healthy!

Sun protection: Since sun exposure is a risk factor for Merkel cell carcinoma, using sunscreens, wearing protective clothing, and avoiding excessive sun exposure can help protect Merkel cells and the skin in general.

Maintain skin health: Hydrate, avoid using excessive drying agents, protect the barrier of the skin.

Avoid chemical exposure: Minimizing contact with harmful chemicals or potential irritants can help preserve skin cell function.

Avoid pollution as much as possible.

In conclusion, while the skin has various components and cell types that contribute to its multifaceted functions, Merkel cells are pivotal for the fine touch sensations that allow us to interact with our environment with precision and awareness. The absence or dysfunction of Merkel cells would significantly impair our ability to detect detailed tactile information.