The three-dimensional microanatomy of Meissner corpuscles in monkey palmar skin

The Meissner corpuscle is a rapidly-adapting mechanoreceptor in the dermal papillae of digital skin. For an analysis of how the sensory endings detect tissue deformations, an examination of their fine structure and relationships with dermal collagen was carried out in the Japanese monkey, Macaca fuscata, using a combination of three methods: SEM of cell architecture denuded by 6N sodium hydroxide maceration, SEM of collagen networks exposed by a mild alkaline corrosion, and TEM according to a conventional procedure. Observations showed the sensory corpuscles to be represented by a stack of discoid components consisting of flattened axon terminals sandwiched between Schwann cell lamellae, as reported previously. Each corpuscle was entirely covered by a connective tissue capsule, which was linked with the basal aspect of the epidermis by dermal collagen fibers. Margins of the discoid components of the corpuscles were serrated with numerous fine projections of lamellar Schwann cells, which tightly held collagen trabeculae on the inner aspect of the pericorpuscular capsule. Central portions of the discoids, on the other hand, displayed extremely smooth surfaces, which were covered by a thick layer of basal lamina-like matrix. The former portions of the discoids appear susceptible to mechanical deformations of surrounding tissues, while the latter may follow the tissue movements rather slowly because of their indirect linkage with the dermal collagen network. The resulting distortions of the axon endings during dynamic phases of the tissue deformations will be in favor of the generation of rapidly adapting receptor potentials in the sensory corpuscle.