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The sensory quality of skin. The skin consists of two main layers, the epidermis and the dermis. Sensory receptors in or beneath the skin are peripheral nerve-fiber endings that are differentially sensitive to one or more forms of energy. The sensory endings can be loosely categorized into three morphological groups: endings with expanded tips, such as Merkel's disks found at the base of the epidermis; encapsulated endings, such as Meissner's corpuscles (particularly plentiful in the dermal papillae), and other organs located in the dermis or subcutaneous tissue, such as Ruffini endings, Pacinian corpuscles, Golgi-Mazzoni corpuscles, and Krause's end bulb; and bare nerve endings that are found in all layers of the skin (some of these nerve endings are found near or around the base of hair follicles).
There is a remarkable relationship between the response specificities of cutaneous receptors and five primary qualities of cutaneous sensation, the latter commonly described as touch-pressure (mechanoreceptors), cold and warmth (thermoreceptors), pain, and itch. Each quality is served by a specific set of cutaneous peripheral nerve fibers. More complex sensations must result from an integration within the central nervous system of information from these sets of nerve fibers. Exploration of the skin surface with a rounded metal point reveals that there exist local sensory spots on the skin, stimulation of which evokes only one of the five qualities of sensation. Thus, there may be plotted maps of pressure, warm, cold, pain, or itch spots. See Mechanoreceptors