Lamellar Corpuscles Respond To __________.

Introduction

Meissner corpuscles, besides known as Wagner-Meissner corpuscles or tactile corpuscles, are a subset of mechanoreceptors first described past Professor Georg Meissner and Professor Rudolf Wagner in 1852. Located in the dermal papillae of glabrous pare, these specialized encapsulated nerve endings relay fine touch and depression-frequency vibration sensations to the central nervous system (CNS). Meissner corpuscles play an essential office in somatosensory vigil, specially in the digital extremities and palmar skin, meriting clinical significance for peripheral and diabetic neuropathy as well as historic period-related degeneration of dermatological tactile sensation.

Structure

Meissner corpuscles are ellipsoid mechanoreceptors located superficially inside the dermal papillae at a depth of approximately 150 micrometers. The corpuscles are approximately 20 to forty micrometers in diameter and lxxx to 150 micrometers in length, with their long centrality oriented perpendicularly to the skin surface.[1] Ane corpuscle may be establish within every two to four dermal papillae, with less than three corpuscles per papilla. Both the size and density of the receptors depend on the site of origin.

Each corpuscle is comprised of three primary components: elongated Schwann cells, a connective tissue capsule, and a cardinal axon.[2][3] The flattened Schwann cells are organized in a stacked conformation in a background of an interlamellar matrix composed largely of collagen and microfilaments.[iv] The capsule of Meissner corpuscles is derived from the endoneurial-perineural fibroblastic connective tissue. The deeper attribute of the corpuscle is lined past two to 4 layers of fibroblasts and fibrillary matrix. The apex of the capsule is incomplete. In this region, collagen fibrils from the interlamellar matrix extend into the dermis and anchor the receptor to the basal attribute of the epidermis.

Each corpuscle is supplied by a nerve ending derived from an intermediate-large amyloid-beta myelinated afferent fiber.[one][5] Innervation by additional unmyelinated C fibers has likewise been reported, although these fibers may simply pass through the corpuscle to reach the epidermis.[3] Typically, corpuscles are supplied by a single axon, but corpuscles with two to 7 accessory branches from the primary axon have been documented. The nerve fiber retains its myelin sheath as it enters the corpuscle merely becomes amyelinic afterward a brusque distance.[4] The nerve fiber branches multiple times, forming bulbous expansions equally it meanders tortuously throughout the lamellae. The cell trunk of the supplying neuron resides within a dorsal root ganglion or cranial nerve sensory ganglion. A single neuron from the sensory ganglion is capable of supplying multiple corpuscles.[half-dozen]

The development of Meissner corpuscles is dependent on brain-derived neurotrophic receptor (BDNF) signaling via tropomyosin receptor kinase B (TrkB). TrkB is an enzyme-linked transmembrane receptor encoded by the NTRK2 cistron. Animal studies involving knockout of BDNF or TrkB in mice resulted in a lack of Meissner corpuscles, highlighting the importance of this signaling system in corpuscular development.[7][eight][9]

Function

Meissner corpuscles consist of a cutaneous nerve catastrophe responsible for transmitting the sensations of fine, discriminative bear upon and vibration.[1] Meissner corpuscles are most sensitive to low-frequency vibrations between 10 to fifty Hertz and can respond to skin indentations of less than 10 micrometers. Additionally, these corpuscles may detect the awareness of slip between an object and the skin, allowing for grip control. Meissner corpuscles have been hypothesized to role in the relay of hurting sensations, as some axons may limited substance P and other nociceptive peptides.[10] Further investigation into the role of these corpuscles in human nociception is warranted. The receptive field of Meissner corpuscles is 3 to 5 mm in diameter. The corpuscles respond to any stimuli within this receptive field with approximate uniformity, resulting in relatively limited spatial resolution.

The external force applied to a Meissner corpuscle is transduced by the collagen fibers connected to the lamellae. The resulting physical deformation induces bending of the nerve axon terminals to generate an activeness potential.[11][7] Removal of the stimulus causes normalization of the corpuscle's shape, producing a second set of activity potentials. Meissner corpuscles are considered low-threshold phasic receptors in that they arrange quickly to a stimulus. With sustained stimulation, the response of Meissner corpuscles decreases rapidly earlier ceasing. Such receptors are unable to convey data regarding the duration of the stimulus.

Cutaneous Meissner corpuscles are establish in glabrous skin, particularly the fingertips, palms, and soles, enhancing the sensitivity of these tissues to light touch. Additional Meissner corpuscles may exist found on the lips, palate, natural language, and genitalia. The density of Meissner corpuscles varies widely betwixt studies, with a consensus on their quantity yet to be reached. One study reported corpuscular densities of 12 and v.ane corpuscles per millimeter in digit five and the thenar eminence, respectively.[12]

Tissue Preparation

Meissner corpuscles can be identified on skin biopsy specimens under traditional light microscopy. Immediately after excision, the biopsied specimen is placed into a fixative solution of neutral buffered formalin that forms crosslinks between lysine residues to preserve tissue structure. The specimen is and then placed into a pocket-sized cassette before existence infiltrated by paraffin. Afterward the wax cools and hardens, the tissue-containing paraffin cake is sliced into thin sections by a microtome. The sections may then be stained according to previously-described protocols for hematoxylin and eosin staining, immunohistochemistry, or immunofluorescence.

Historically, the silverish impregnation technique was recommended for staining of peripheral nerve endings, including Meissner corpuscles.[13] The silvery impregnation method tin can selectively highlight both myelinated and unmyelinated neurites and preserve the fine item of nerves. Tissue samples are fixed in neutral or elementary formalin or Bouin solution. Frozen sections are cut into sparse sections and placed into the impregnating solution composed of urea, 1% argent nitrate, 95% ethyl alcohol, pyridine, i% mercuric cyanide, and 1% picric acrid in distilled water. Subsequently incubation for 5.5 hours, the specimens are submerged in a solution of one% hydroquinone, 5% anhydrous sodium sulfate, and urea, followed by a mixture of 0.2% gold chloride and glacial acerb acrid, and then 5% sodium hyposulfite. Subsequently immunofluorescent staining, specimens are viewed using confocal scanning laser microscopy.

Two-photon excitation microscopy is a novel fluorescence imaging technique enabling loftier-resolution visualization of living tissue virtually the pare surface, including Meissner corpuscles.[14] Ii-photon microscopy utilizes the long-lasting lipophilic fluorescent dye carbocyanine DiOC(3) and 484 nm laser for alive imaging of the axonal components of the corpuscles. The persistence of the dye for several weeks allows for the ability to prototype the corpuscular neurites in vivo over a prolonged period to evaluate the mechanical response and structural changes of the corpuscles. A limitation of this visualization method is the inability to highlight other components of the receptors, such as the collagenous sheathing or Schwann cells.

Histochemistry and Cytochemistry

Immunohistochemical staining targeting differential antigenic expression tin distinguish between the neural and supportive components of Meissner corpuscles. Vega et al. reported that double immunolabelling with monoclonal antibodies against human neurofilament proteins (NFP) and S100 could reliably stain the central axon and Schwann cells, respectively.[15] Other immunohistochemical stains for the cardinal axon include neuron-specific enolase, protein gene product 9.5, neurocalcin, and neurofilament subunits. Substance P, calcitonin gene-related peptide, and gamma-melanocyte stimulating hormone have also been utilized to stain the neuronal components of Meissner corpuscles. Lamellar cells are identifiable past using stains targeting the receptor for the vimentin and growth factor receptor TrkB.

Microscopy Light

Under low-cal microscopy, Meissner corpuscles appear as coiled, leap-similar structures composed of stacked, disk-like lamellar cells. The orientation of the lamellae is variable, just they are typically parallel to the skin surface. The Schwann cell-derived lamellar cells accept peripherally displaced nuclei and are contained within a fibroblastic capsule that is incomplete at its apex. The neurites that class through the lamellae are not visible by traditional hematoxylin and eosin staining techniques.

Microscopy Electron

Much greater detail of Meissner corpuscles may be appreciated on manual and scanning electron microscopy.[2] The lamellar cells can be visualized as peripheral nuclei and 2 to iii micrometer-thick cytoplasmic extensions into the interior of the corpuscle. These projections are connected by desmosome-like junctions within a basal lamina and surrounded by an interlaminar substance composed of collagen and microfilaments. The internal portion of lamellar cells is shine, although their external aspect is covered by fine 0.one to 0.3 micrometer-thick projections, lending them a serrated appearance.[16] These projections mediate adherence to the interior portion of the collagenous capsule. Neuronal axons may exist recognized on electron microscopy, as they branch and grade helically throughout the lamellae. The neurites comprise varicose regions rich in mitochondria and terminate in wide, bulbous endings. The apex of the corpuscle is in straight contact with the basal cells of the epidermis, with axon terminals and lamellar cells interdigitating with the stratum basale.[3]

Pathophysiology

As currently understood, Meissner corpuscles play a relatively small-scale role in human being disease. Meissner corpuscles are often noted as a benign accessory component in some cellular nevi, schwannomas, and neurofibromas. A single case written report describes the presence of Meissner-like corpuscles within a mature ovarian cystic teratoma.[17]

Occasional case reports describe beneficial tumors composed largely or entirely of Meissner corpuscles known every bit Wagner-Meissner neurilemmomas (WMNs).[18] WMNs present equally slow-growing soft tissue masses involving the deep dermis and subcutaneous tissues. WMNs accept not been limited to the typical distribution of Meissner corpuscles, having been reported on the cheek, lower extremity, and vulva.[19][twenty] These tumors are typically well-demarcated, residing inside a gristly collagen capsule, although a single example report documents an infiltrative growth pattern. On histological examination, WMNs brandish lamellated complexes composed of upwards to 20 laminar cells, resembling Meissner corpuscles. These tumors stain positively for neuron-specific enolase, vimentin, and S100 but lack the nerve fibers that supply the receptors, differentiating these abnormal structures from the functional corpuscles in the dermis.[eighteen]

Structures morphologically identical to Meissner corpuscles are identified in aberrant locations take been termed tactile corpuscle-like bodies, Wagner-Meissner bodies, pseudo-Meissner corpuscles, and Meissner-oid corpuscles. Several cases have been published detailing the identification of proliferation of these Meissner corpuscle-like structures inside the lamina propria, the gastrointestinal mucosa, including the esophagus, breadbasket, and colorectum.[21][22][23]

The origin of these lesions is unclear only may represent hamartomas, neural neoplasms, or a reactive process. Typically discovered incidentally during colonoscopy, these proliferations often resemble colonic polyps, leading to their biopsy and identification. Pathological examination of these lesions reveals discrete clusters of eosinophilic aggregates within the lamina propria. These structures are comprised of spindle-shaped cells, each with a single eccentric, oblong nucleus and lamellated, eosinophilic cytoplasm. Staining for S100 is positive while the histiocytic marking CD68 is negative, indicating the Schwannian or neural origin of the lesions. The differential diagnosis of these proliferations includes mucosal amyloid degradation and mucosal granulomas, although negative staining for Congo red and CD68, respectively, can exist reliably used to differentiate these disorders. The presence of bodies within the alimentary canal is benign.

Clinical Significance

Meissner corpuscles are an integral attribute of the homo sensory organization, required for discriminatory touch and grip control. The loftier sensitivity of these receptors also allows for the reading of Braille using the fingertips. Males and females have a similar number of corpuscles in each digit, although, given the larger average surface area of male hands and fingers, men have a lower density of receptors which may contribute to a small difference in touch receptivity.[24] The size, density, and complication of Meissner corpuscles too pass up significantly with increasing age.[25] Animal studies have revealed that with increasing historic period, the neurites supplying Meissner corpuscles become progressively more coarse, tortuous, and varicose with the disintegration of lamellar processes.[26] Older neurites demonstrated less parallel orientation and an increased number of axonal bifurcations per corpuscle.[27] These findings may underlie the age-related decrease in bear upon sensitivity.

Differences in corpuscular density have been associated with a number of neurologic disorders, including sensory neuropathy, Charcot-Marie-Tooth illness, Parkinson's disease, HIV neuropathy, and Friedreich'southward ataxia.[28][29][30] Hypertrophy and hyperplasia of Meissner corpuscles take been described during the initial stages of diabetes in primate studies.[17] Post-obit chronic hyperglycemia, hypertrophy of the corpuscles decreased; although the number of corpuscles remained greater than those of non-diabetic control animals, the receptors continued to display abnormal structure and poly peptide expression. Additionally, the reduction of neuronal axons in the dermis, including those innervating Meissner's corpuscles, has been observed in patients with diabetes.[31] Axonal degeneration to Meissner'south corpuscles and the dermis thus suggests the peripheral neuropathy experienced by people with diabetes.

Meissner corpuscles can survive for long-periods following nerve injury or denervation just tin sustain alterations in protein expression. Expression of S100, a marking of lamellar cells within Meissner corpuscles, has been shown to be normal following spinal string injury, diminished in nerve entrapment, and absent in denervated dermatomes.[32] These findings suggest that the functional integrity of axonal innervation is required for S100 protein expression past corpuscular lamellar cells.[33]

Review Questions

Figure

Papilla of the paw, treated with acerb acid. Magnified 350 times. A. Side view of a papilla of the hand. a. Cortical layer. b. Tactile corpuscle. c. Small nervus of the papilla, with neurolemma. d. Its two nervous fibers running with spiral coils around (more...)

Effigy

Tactile Corpuscle. Contributed from Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine i (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. (CC Past iii.0 https://creativecommons.org/licenses/by/three.0/deed.en)

Effigy

100x light micrograph of Meissner'southward corpuscle (or tactile corpuscle) at the tip of a dermal papillus. Equally a type of mechanoreceptor it is responsible for sensitivity to light touch. Contributed from Webnsmith Wikimedia User (CC BY iii.0 https://creativecommons.org/licenses/by/3.0/human action.en) (more...)

References

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