Merkel cells are specialized sensory cells in the skin, playing a fundamental part in our sense of touch. They are essential for perceiving tactile sensations, allowing us to interact with our environment. Understanding their function provides insight into how our bodies process the sense of touch.
Where Merkel Cells Are Found
Merkel cells are primarily located in the epidermis, the outermost layer of the skin. They are found in the basal layer, the deepest part of the epidermis, approximately 0.1 mm from the skin’s surface. These oval-shaped cells are abundant in highly touch-sensitive areas, such as the fingertips, lips, and around hair follicles.
They have a neuroendocrine nature, meaning they possess features of both nerve cells and hormone-producing cells. Merkel cells are about 10 micrometers in diameter. They form close associations with nerve endings, creating Merkel cell-neurite complexes.
Recent research confirms the epidermal origin of Merkel cells, meaning they develop from the same precursor cells as other epidermal cells. Their connection with nerve fibers is key to their sensory function.
Their Role in Touch
Merkel cells function as mechanoreceptors, responding to mechanical pressure and distortion. They are sensitive to light touch, sustained pressure, and the discrimination of fine textures and shapes. As slowly adapting mechanoreceptors, they continue to signal as long as a stimulus is present.
Their sensitivity allows for precise tactile discrimination, which is why they are concentrated in areas like the fingertips. This precision is important for tasks such as reading Braille, where patterns of raised dots are distinguished through touch. Merkel cells help encode the fine details of an object’s surface, like its edges and curvature.
They enable the perception of continuous information about a touch stimulus, such as the consistent pressure of clothing or the shape of an object held in hand. Without functional Merkel cells, the skin’s ability to sense fine details and textures is reduced. Their small receptive fields allow for high resolution for detailed tactile perception.
How Merkel Cells Communicate
When mechanical force is applied to the skin, Merkel cells sense this pressure and convert it into a cellular signal. This process involves mechanically activated ion channels, specifically Piezo2 channels. Activation of these channels leads to an influx of calcium ions into the Merkel cell.
The increase in intracellular calcium triggers the release of neurotransmitters from the Merkel cell into the synaptic cleft. These neurotransmitters then act on the adjacent nerve fiber. This chemical communication transmits the touch signal.
Merkel cells form synaptic connections with specific afferent nerve fibers, primarily slowly adapting type 1 (SA-1) afferents. The released neurotransmitters excite these nerve fibers, generating electrical signals that travel along the nerve to the brain for interpretation. This process allows the brain to perceive the detailed tactile sensations initiated by Merkel cells.