Figure 1413

Pacinian and Meissner's corpuscles in H&E preparations, a. In this photomicrograph, the concentric cellular lamellae of the Pacinian corpuscle are visible because of flat, fibroblast-like supportive cells. Although not evident within the tissue section, these cells are continuous with the endoneurium of the nerve fiber. The spaces between lamellae contain mostly fluid. The neural portion of the Pacinian corpuscle travels longitudinally through the center of the structure (ar row). Several nerves (N) are present adjacent to the corpuscle. x85. b. Three Meissner's corpuscles (MC) are shown residing within the dermal papillae. Note the direct proximity of the corpuscle to the under-surface of the epidermis. x150. Inset. A higher magnification of a Meissner's corpuscle. The nerve fiber terminates at the superficial pole of the corpuscle. Note that supporting cells are oriented approximately at right angles to the long axis of the corpuscle. x320.

spiral terminals of afferent axons

capsule tortuous

Schwann cells capsule spiral terminals of afferent axons dermal papilla tortuous

Schwann cells e.g., the lips and the palmar and volar surfaces, particularly those of the fingers and toes. Generally, they are tapered cylinders that measure about 150 /Am along their long axis and are oriented perpendicular to the skin surface. Meiss-ner's corpuscles are present in the dermal papillae just beneath the epidermal basal lamina. Within these receptors, one or two unmyelinated endings of myelinated nerve fibers follow spiral paths in the corpuscle. The cellular component consists of flattened Schwann cells that form several irregular lamellae through which the axons course to the pole of the corpuscle. In H&E-stained slides of sagittal sections, this structure resembles a loose, twisted skein of wool. It is the Schwann cells that give this impression.

Ruffini's corpuscles respond to mechanical displacement of adjacent collagen fibers

Ruffini's corpuscles are the simplest encapsulated mechanoreceptors. They have an elongated fusiform shape and measure 1 to 2 ¡jlm in length (see Fig. 14.12f). Structurally, they consist of a thin connective tissue capsule that encloses a fluid-filled space. Collagen fibers from the surrounding connective tissue pass through the capsule. The neural element consists of a single myelinated fiber that enters the capsule, where it loses its myelin sheath and branches to form a dense arborization of fine axonal endings, each terminating in a small knob-like bulb. The axonal endings are dispersed and intertwined inside the capsule. The axonal endings respond to displacement of the collagen fibers induced by sustained or continuous mechanical stress.

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