Cutaneous Sensory System
The integumentary surfaces are derived from ectoderm and consist of a variety of general and specialized regions of stratified epithelium with a superficial keratinized layer of varying thickness. The sensory function of the skin and its appendages (e.g., hairs and claws, which serve as mechanical levers) is achieved by means of a wide diversity of sense organs specialized for several distinct sensory modalities. Mechanical sensibility appears to be dominant, and sensations of touch, pressure, vibration, tickle, itch, with perhaps a contribution from position and movement (kinesthetic) sense, can be correlated with the properties of a variety of sensitive mechanoreceptors. Thermal sensations are conveyed by distinct populations sensitive to either warming or cooling. In many regions, the most numerous innervation consists of the thinnest fibers subserving sensory reports of pain or related noxious and aversive qualities.