The skin is endowed with numerous sensory receptors of various types. These are the peripheral terminals of sensory nerves whose cell bodies are in the dorsal root ganglia. The receptors in the skin are described as free nerve endings and encapsulated nerve endings. Free nerve endings are the most numerous. They subserve fine touch, heat, and cold and are found in the basal layers of the epidermis and as a network around the root sheath of hair follicles. Encapsulated nerve endings include Pacinian corpuscles (deep pressure), Meissner’s corpuscles (touch, especially in the lips and thick skin of fingers and toes), and Ruffini endings (sustained mechanical stress on the dermis). Motor endings of the autonomic nervous system supply the blood vessels, the arrector pili muscles, and the apocrine and eccrine sweat glands.
Skin, fngertip, human, H&E ×20.
This specimen is a section of thick skin from the finger tip, showing the epidermis (Ep) and the dermis (De) and, under the skin, a portion of the hypodermis (Hy). The thickness of the epidermis is largely due to the thickness of the stratum corneum. This layer is more lightly stained than the deeper 522 portions of the epidermis. Note, even at this low magnification, the thick collagenous fibers in the reticular layer of the dermis. Sweat glands (SG) are present in the upper part of the hypodermis, and several sweat ducts (D) are seen passing through the epidermis. A feature of this specimen is that it depicts those sensory receptors that can be recognized in a routine low-power H&E–stained paraffin section.
Meissner's corpuscle, skin, human, H&E ×190.
This high-magnification micrograph shows portions of the upper left field of figure above in which two Meissner’s corpuscles (MC) are in direct proximity to the undersurface of the epidermis in adjacent dermal papillae. The section shows the long axis of the corpuscles. A Meissner’s corpuscle consists of an axon (sometimes two) taking a zigzag or flat spiral course
They are Meissner’s corpuscles and Pacinian corpuscles (PC). Several nerve bundles (N) are seen in proximity to the Pacinian corpuscles. Meissner’s corpuscles are in the upper part of the dermis, in the dermal papillae immediately under the epidermis. These corpuscles are small and difficult to identify at this low magnification; however, their location is characteristic. Knowing where they are located is a major step in finding Meissner’s corpuscles in a tissue section; they are shown at higher magnification in figure below.
Pacinian corpuscles are seen in the lower part of the hypodermis. These corpuscles are large, slightly oval structures, and even at low magnification, a layered or lamellated pattern can be discerned.
Pacinian corpuscle, skin, human, H&E ×320.
At this higher magnification, the concentric layers or lamellae of the Pacinian corpuscle can be seen to be due to flat cells. These are fibroblast-like cells, and although not evident within the tissue section, these cells are continuous with the perineurium of the nerve fiber. The space between the cellular lamellae contains mostly fluid. The neural portion of the Pacinian corpuscle travels longitudinally through the center of the corpuscle. In this specimen, the corpuscle has been cross-sectioned; an arrowhead points to the centrally located nerve fiber.
from one pole of the corpuscle to the other. The nerve fiber terminates at the superficial pole of the corpuscle. Consequently, as seen here, the nerve fibers and supporting cells are oriented approximately at right angles to the long axis of the corpuscle. Meissner’s corpuscles are particularly numerous near the tips of the fingers and toes.