Meissner’s corpuscles (see Figs. 15.11 and 15.12b) are touch receptors that are particularly responsive to low-frequency stimuli in the papillary layer of hairless skin (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 m along their long axis and are oriented perpendicular to the skin surface. Meissner’s corpuscles are present in the dermal papillae just beneath the epidermal basal lamina (Plate 46, page 523). 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.
Ruffni’s corpuscles are the simplest encapsulated mechanoreceptors. They have an elongated fusiform shape and
FIGURE 15.12 • 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, fibroblastlike 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 (arrow). Several nerves (N) are present adjacent to the corpuscle. 85. b. Three Meissner’s corpuscles (MC) are shown residing within the dermal papillae. Note the direct proximity of the corpuscle to the undersurface of the epidermis. 150. 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. 320.
measure 1 to 2 m in length (see Fig. 15.11f ). 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 knoblike 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, thus they respond to stretch and torque. Ruffini’s corpuscles functionally belong to the family of rapidly adapting receptors (phasic receptors) that generate short action potentials at the beginning and end of a stimulus.
Skin appendages are derived from downgrowths of epidermal epithelium during development. They include the following:  Hair follicles and their product, hair  Sebaceous glands and their product, sebum  Eccrine sweat glands and their product, sweat taining a form of sweat with a high concentration of carbo hydrates, lipids, and proteins
Both hairs and sweat glands play specific roles in the regulation of body temperature. Sebaceous glands secrete an oily substance that may have protective functions. Apocrine glands produce a serous secretion containing pheromones that act as a sex attractant in other animals and possibly in humans. The epithelium of the skin appendages (especially hair follicles) can serve as a source of new epithelial stem cells for skin wound repair.