What is a Merkel Disc?
The Merkel Disc is a distinctive touch receptor called a Merkel cell-neurite complex in vertebrate skin. The Merkel Disc includes two different cell types: Merkel cells and Aβ-afferent nerve endings. These cells reside in the epidermis basal layer just above the basement membrane. At the same time, they reach their highest concentration in touch-sensitive areas like fingertips and palms in addition to soles and select mucosa regions [1, 2].
What Does a Merkel Disc Do?
Our tactile sensation depends significantly on Merkel Discs. These structures detect tactile stimuli and convert them into slowly adapting impulses necessary for tactile discrimination. Merkel Discs assist in perceiving and understanding different physical characteristics of objects, including their texture, shape, and edges [3, 4].
Piezo2 channels function as molecular transducers for mechanosensitive Merkel cells, which form the main structure of Merkel Discs. Serotonin release happens when these cells receive stimulation, activating the nearby Aβ-afferent nerve endings to send tactile signals [5, 6].
Merkel Discs serve sensory functions but also participate in complex sensory activities like social interaction and environmental exploration. These structures enable us to interact with our surroundings and comprehend the environment [5, 7].
Merkel cell carcinoma
The development of Merkel cell carcinoma, an aggressive skin cancer originating from Merkel cells, involves multiple risk factors.
One risk factor for developing merkel cell carcinoma is overexposure to natural and artificial light sources. Merkel cell carcinoma risk heightens due to ultraviolet radiation from sunlight and tanning beds. Skin surfaces with regular sun exposure show higher risk levels [8].
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Individuals with previous skin cancer diagnoses like basal cell carcinoma or squamous cell carcinoma show higher rates of developing Merkel cell carcinoma [8].
Age is another significant risk factor. Merkel cell carcinoma becomes more prevalent with advancing age yet remains possible at all ages, with the highest occurrence in individuals over 50 years old [8].
Light skin colour stands out as a risk factor. People with light-coloured skin often develop Merkel cell carcinoma—people who are white experience this skin cancer at higher rates than people who are black [8].
What is a Meissner Corpuscle?
A Meissner corpuscle, also called a Wagner-Meissner corpuscle or tactile corpuscle, represents a type of mechanoreceptor identified in 1852 [9]. These structures take on an ellipsoid form while their diameter spans roughly 20 to 40 micrometres, their length ranges from 80 to 150 micrometres, and they stand at a right angle to the skin surface [9].
Each Meissner corpuscle comprises three primary components:
- Elongated Schwann cells
- Connective tissue capsule
- Central axon
Within a structural matrix that contains collagen and microfilaments, Schwann cells arrange themselves in a stacked formation [9].
What does a Meissner Corpuscle Do?
Meissner corpuscles transmit information about gentle touch, delicate tactile perception, and vibration detection. Their highest vibration detection range is between 10 to 50 Hertz, while they can sense skin indentations below 10 micrometres in depth. The corpuscles detect when objects slip across the skin, aiding grip control [9].
The collagen fibres attached to the lamellae transform the applied external force on a Meissner corpuscle. Physical deformation of nerve axon terminals results in bending, which produces an action potential. Meissner corpuscles function as low-threshold phasic receptors because they rapidly adapt to stimuli, resulting in a quick decline of their response followed by cessation under continued stimulation [9].
Risk Factors of Meissner Corpuscles
The human sensory system depends on Meissner corpuscles for touch sensitivity and grip control. Multiple elements affect how Meissner corpuscles operate and their density, which may result in altered sensations or health issues.
Age stands out as the leading risk factor that affects Meissner corpuscles. The physical characteristics of these sensory receptors reduce dramatically as people grow older. The supply neurites of Meissner corpuscles develop into a coarser and more twisted state while developing varicosities, reducing touch sensitivity [9].
Multiple neurological disorders show changes in the density of Meissner corpuscles. Sensory neuropathy and Charcot-Marie-Tooth disease join Parkinson's disease and HIV neuropathy along with Friedreich’s ataxia as associated neurological disorders [9].
Diabetes is another significant risk factor. Research indicates that Meissner corpuscles experience hypertrophy and hyperplasia when diabetes first develops. The count of corpuscles exceeds that of non-diabetic individuals, but their structure and protein expression are abnormal. Long-term high blood sugar levels result in fewer neuronal axons in skin layers, affecting Meissner's corpuscles and indicating peripheral nerve damage seen in diabetic patients [9].
Nerve injury and denervation processes lead to changes in the functionality of Meissner corpuscles. Despite surviving for extended periods after injury or denervation, Meissner corpuscles display changes in protein expression. Following spinal cord injury, S100 expression, which marks lamellar cells in Meissner corpuscles, remains typical but reduces after nerve entrapment and ultimately disappears from denervated dermatomes [9].
Similarities and Differences Between Merkel Discs and Meissner Corpuscles
Mechanoreceptors Merkel Discs and Meissner Corpuscles are essential components of our tactile sensory system. These receptors process various touch and pressure signals, enabling us to engage with and perceive our surroundings.
The Merkel Discs, located mainly in the fingertips and whisker hair follicles and additional touch-sensitive areas, are vital for detecting light touch. Merkel Discs perform complex sensory roles, including social interaction processing, environmental investigation tasks and tactile discernment abilities [3, 5]. Meissner Corpuscles in glabrous skin's dermal papillae transmit sensations of light touch and vibrations at low frequencies directly to the central nervous system—their significance peaks in the skin of fingers and palms [4, 9].
The Merkel Disc structure includes Merkel cells together with Aβ-afferent nerve endings. Piezo2 channels are molecular transducers that transform tactile stimuli [3, 5]. Meissner Corpuscles form ellipsoid mechanoreceptors, including a mechanoreceptive sensory neuron encircled by Schwann-like cells that do not carry myelin sheaths. Meissner Corpuscles' structure includes spiral axons, lamellar cells, and a collagen capsule [10, 9].
Merkel Discs functionally convert touch signals into slowly adapting impulses, facilitating tactile discrimination [3, 4]. Meissner Corpuscles show maximum sensitivity to low-frequency vibrations within the 10 to 50 Hertz range and can detect skin indentations that measure beneath 10 micrometres. Their receptive field measures 3 to 5 mm in diameter while they function to transmit pain sensations [9].
These two mechanoreceptors, Merkel Discs and Meissner Corpuscles, both serve as essential components of the tactile sensory system yet have distinct locations, structures and functional roles.