Encapsulated sensory corpuscle in the mucosa of human vocal cord: An electron microscope study.
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Abstract:
Encapsulated sensory corpuscles of the Krause type were found in the mucosa of surgically removed human vocal cords.The corpuscles were ellipsoidal structures of about 30 by 50μm and were located beneath the free edge in the mid-region along the intermembranous part. They contained a number of varicose nerve endings and lamellar cells. The lamellar cells had thin cytoplasmic lamellae which contained numerous cytoplasmic filaments and were interposed between the nerve endings. Attachment devices were frequently noted between the cytoplasmic lamellae and between the lamellae and nerve endings. Half-desmosomes were also noted along the plasma membrane of the lamellar cells. The intercellular space was filled with amorphous electron lucent material and contained a few collagen fibrils. Ladder-like filamentous structures were frequently encountered in the intercellular space.The location of the corpuscles at the free edge of the vocal cords suggests that the endings may receive the bilateral touch of the vibrating part of the cords in order to give sensory information for the control of the movement of the cords in phonation.Keywords:
Free nerve ending
Mechanoreceptor
Lamellar granule
Distributions of growth-associated protein-43 (GAP-43) in the periodontal ligament and dental pulp of adult rats were studied by light and electron microscopy. The mature periodontal ligament and dental pulp contained numerous GAP-43-positive neural elements, comprising periodontal Ruffini endings and thin nerve fibers, but expression patterns differed among the kinds of nerves. In the periodontal ligament of rat molars, immunoelectron microscopy revealed that GAP-43 like immunoreactivity in the Ruffini ending, an essential mechanoreceptor, was confined to the Schwann sheaths around the axon terminals and was not in the axon terminals themselves, unlike free endings that revealed axonal GAP-43. However, the lamellar Schwann cells associated with the cutaneous receptors did not exhibit any GAP-43 like immunoreactivity though they were intensely reactive for low affinity nerve growth factor receptor (p75-NGFR), a marker for lamellar Schwann cells in mechanoreceptors. The characteristically uniform expression of GAP-43 in the Schwann lamellae that surround the Ruffini mechanoreceptors of rat molar ligament suggests that Schwann cells are involved in the GAP-43 mediated plasticity of these receptors. On the other hand, the pulpal nerves were filled with the reaction products in their axonal spaces, suggesting the potential for neuronal plasticity during normal function and after tooth injury.
Mechanoreceptor
Periodontal fiber
Free nerve ending
Gap-43 protein
Periodontium
Immunoelectron microscopy
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Free nerve ending
Merkel cell
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The periodontal ligament receives a rich sensory nerve supply and contains many nociceptors and mechanoreceptors. Although its various kinds of mechanoreceptors have been reported in the past, only recently have studies revealed that the Ruffini endings-categorized as low-threshold, slowly adapting, type II mechanoreceptors-are the primary mechanoreceptors in the periodontal ligament. The periodontal Ruffini endings display dendritic ramifications with expanded terminal buttons and, furthermore, are ultrastructurally characterized by expanded axon terminals filled with many mitochondria and by an association with terminal or lamellar Schwann cells. The axon terminals of the periodontal Ruffini endings have finger-like projections called axonal spines or microspikes, which extend into the surrounding tissue to detect the deformation of collagen fibers. The functional basis of the periodontal Ruffini endings has been analyzed by histochemical techniques. Histochemically, the axon terminals are reactive for cytochrome oxidase activity, and the terminal Schwann cells have both non-specific cholinesterase and acid phosphatase activity. On the other hand, many investigations have suggested that the Ruffini endings have a high potential for neuroplasticity. For example, immunoreactivity for p75-NGFR (low-affinity nerve growth factor receptor) and GAP-43 (growth-associated protein-43), both of which play important roles in nerve regeneration/development processes, have been reported in the periodontal Ruffini endings, even in adult animals (though these proteins are usually repressed or down-regulated in mature neurons). Furthermore, in experimental studies on nerve injury to the inferior alveolar nerve, the degeneration of Ruffini endings takes place immediately after nerve injury, with regeneration beginning from 3 to 5 days later, and the distribution and terminal morphology returning to almost normal at around 14 days. During regeneration, some regenerating Ruffini endings expressed neuropeptide Y, which is rarely observed in normal animals. On the other hand, the periodontal Ruffini endings show stage-specific configurations which are closely related to tooth eruption and the addition of occlusal forces to the tooth during postnatal development, suggesting that mechanical stimuli due to tooth eruption and occlusion are a prerequisite for the differentiation and maturation of the periodontal Ruffini endings. Further investigations are needed to clarify the involvement of growth factors in the molecular mechanisms of the development and regeneration processes of the Ruffini endings.
Free nerve ending
Mechanoreceptor
Periodontal fiber
Inferior alveolar nerve
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In Brief Study Design. Immunohistochemical study on fresh cadaver specimens. Objective. Assessment of mechanoreceptor and nociceptor levels and distribution in iliolumbar ligament. Summary and Background Data. The function of iliolumbar ligament and its role in low back pain has not been yet fully clarified. Understanding the innervation of this ligament should provide a ground which enables formation of stronger hypotheses. Methods. Bilateral 30 iliolumbar ligaments of 15 fresh cadavers were included in the study. Morphologic properties were recorded and the ligaments were examined by focusing on 3 main parts: ligament, bone insertions, and tendon body. Assessment of mechanoreceptor and nociceptor levels and their distribution in iliolumbar ligament were performed on the basis of immunohistochemistry using the S-100 antibody specific for nerve tissue. Results. Iliac wing insertion was found to be the richest region of the ligament in terms of mechanoreceptors and nociceptors. Pacinian (type II) mechanoreceptor was determined to be the most common (66.67%) receptor followed by Ruffini (type I) (19.67%) mechanoreceptor, whereas free nerve endings (type IV) and Golgi tendon organs (type III) were found to be less common, 10.83% and 2.83%, respectively. Conclusion. Immunohistochemical staining has shown that iliolumbar ligamen had a rich nerve tissue. Those results indicate that ILL plays an important role in proprioceptive coordination of lumbosacral region alongside its known biomechanic support function. Moreover, the presence of type IV nerve endings suggest that the injury of this ligament might contribute to the low back pain. Assessment of mechanoreceptor and nociceptor levels and distribution in iliolumbar ligament is the main purpose of the study. Immunohistochemical study on fresh cadaver specimens was performed. Results indicate that iliolumbar ligament plays an important role in proprioceptive coordination of lumbosacral region alongside its known biomechanic support function.
Mechanoreceptor
Nociceptor
Free nerve ending
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Abstract Lamellar body ultrastructure was examined in cultured type II alveolar epithelial cells processed by a method of rapid freezing and freeze drying in the absence of both chemical fixation and solvent dehydration. This method of specimen preparation was chosen to optimize the retention of soluble substances within the type II cell. The use of cultured cell aggregates in which type II cells line the free surface facilitated the effectiveness of rapid freezing for the preservation of lamellar body fine structure. Lamellar bodies preserved by rapid freezing/freeze drying to optimize the in situ retention of intracellular components possess closely adherent concentric membranous lamellae. This supports the contention that the widely appreciated lamellar pattern of the pulmonary lamellar body represents the in vivo molecular organization of intracellular surfactant phospholipids. Lamellar bodies of frozen/frozen dried type II cells showed none of the often profound lipid extraction artifact produced by conventional processing. Instead they exhibited a substructure with noteworthy characteristics in common with lamellar bodies processed by resin dehydration lipid retention methods (Stratton, 1976). Importantly, the lamellae of frozen/frozen dried lamellar bodies were contiguous, with no interlamellar space, as is commonly observed in solvent‐processed (extracted) specimens. The dimensions of lamellar components in frozen/frozen dried lamellar bodies were, however, different from published values for resin‐dehydrated lipid‐retained specimens. Lamellar width and the widths of component phospholipid head and fatty acid tail regions in frozen/frozen dried lamellar bodies were approximately 35% smaller than values reported for resin‐dehydrated lamellar bodies. This difference was attributed to shrinkage of lamellar components as water was removed from the unfixed tissue during the freeze‐drying process.
Lamellar granule
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Twenty-one cervical facet capsules, taken from three normal human subjects, were examined to determine the type, density, and distribution of mechanoreceptive nerve endings in these tissues. Clearly identifiable mechanoreceptors were found in 17 of 21 specimens and were classified according to the scheme for encapsulated nerve endings established by Freeman and Wyke. Eleven Type I, 20 Type II, and 5 Type III receptors were identified, as well as a number of small, unencapsulated nerve endings. Type I receptors were small globular structures measuring 25–50 μm in diameter. Type II receptors varied in size and contour, but were characterized by their oblong shape and broad, lamellated capsule. Type III receptors were relatively large oblong structures with an amorphous capsule, within which a reticular meshwork of fine neurites was embedded. Free (nociceptive) nerve endings were found in subsynovial loose areolar and dense capsular tissues. The presence of mechanoreceptive and nociceptive nerve endings in cervical facet capsules proves that these tissues are monitored by the central nervous system and implies that neural input from the facets is important to proprioception and pain sensation in the cervical spine. Previous studies have suggested that protective muscular reflexes modulated by these types of mechanoreceptors are important in preventing joint instability and degeneration. It is suggested that the surgeon take steps to avoid inadvertently damaging these tissues when exposing the cervical spine.
Mechanoreceptor
Free nerve ending
Proprioception
Joint capsule
Facet (psychology)
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Mechanoreceptor
Free nerve ending
Periodontal fiber
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Lamellar granule
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Study Design. Histologic analysis of normal human facet capsules to determine the density and distribution of encapsulated nerve endings in the thoracic and lumbar spine. Objectives. To quantify the extent of mechanoreceptor innervation in normal facet tissues and determine the relative distribution of three specific receptor types with respect to thoracic and lumbar segments. Summary of Background Data. Ongoing studies of spinal innervation have shown that human facet tissues contain mechanoreceptive endings capable of detecting motion and tissue distortion. The hypothesis has been advanced that spinal proprioception may play a role in modulating protective muscular reflexes that prevent injury or facilitate healing. Methods. Whole facet capsules harvested from seven healthy adult patients were processed using a gold chloride staining method and cut into 35-micron sections for histologic analysis. No sampling was performed; all sections were analyzed. Receptor endings were classified by the method of Freeman and Wyke if they met the following three criteria: 1) encapsulation, 2) identifiable morphometry, and 3) consistent morphometry on serial sections. Results. One Type 1 and four Type 2 endings were identified among 10 thoracic facet capsules. Five Type 1, six Type 2, and one Type 3 ending were identified among 13 lumbar facet capsules. Occasional atypical receptive endings were noted that did not fit the established classification. Unencapsulated free nerve endings were seen in every specimen, but were not quantified. Conclusions. Encapsulated nerve endings are believed to be primarily mechanosensitive and may provide proprioceptive and protective information to the central nervous system regarding joint function and position. A consistent, but small population of receptors has been found previously in cervical facets, but innervation of the thoracic and lumbar levels is less consistent. This suggests that proprioceptive function in the thoracic and lumbar spine is less refined and, perhaps, less critical than in the cervical spine.
Mechanoreceptor
Free nerve ending
Facet (psychology)
Proprioception
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Location and structure of sensory nerve endings in the periodontium of the third premolar in <i>Monodelphis domestica</i> have been investigated by means of light and electron microscopy. The periodontal cleft of the tooth is apically enlarged. The number of nerve endings increases towards apex. Three types of sensory nerve endings have been observed: free nerve endings, Ruffini nerve endings and lamellated corpuscles. Free nerve endings could only be identified by electron microscopy. Ruffini nerve endings are only incompletely surrounded by lamellae of the terminal Schwann cell. Protrusions of nerve terminals of the Ruffini corpuscles are anchored between bundles of collagen fibers. Small lamellated corpuscles occur exclusively in the apical portion of the periodontium. Ruffini and lamellated corpuscles are considered as part of a masticatory reflex feedback control system. Ruffini corpuscles detect tension, rapidly adapting lamellated corpuscles detect pressure and vibration in the periodontium. Free nerve endings may function as thermoreceptor or nociceptor.
Free nerve ending
Mechanoreceptor
Periodontium
Inferior alveolar nerve
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