Structure and Function of Nails and Skin Innervation ➔ -The nail: The nail is a structure deriving from the epidermis, it is a plate of epithelial cells. keratinized which are located at the level of the dorsal surface of each distal phalanx and there are several parts to these nails:The root of the nail is the part that penetrates into the epidermis and there is a classic epithelium which covers this root with the stratum corneum etc. There's the tablet which rests on the epidermis which we call the nail bed and this tablet comes from the differentiation of an area which is called the matrix, ventral or dorsal, matrix which is in depth at the root level and it is these cells at the matrix level which will multiply, divide which will migrate and which will keratinized and this formation is important because we recognize that nail formation is rapid. The outermost part of the tablet separates from the bedgle, frees itself from him, and this tablet although very rigid and protecting the dorsal side of the last phalanx, this tablet is transparent and the epidermis of the nail bed is very thin which means that we can see the connective tissue through the nail.tif, the dermis and therefore we can see the vascularization, the oxygenation of the blood by observing the dermis, the connective tissue under the nail. The nail plays a role in tactile perception. ➔ -Innervation of the skin: It is important because the skin is very rich in nerve endings because the skin is the organ of touch, a sensory organ and it is a major function of the skin which is the collection of information coming from the outside. There was an important function which is the function of defense of which we spoke and there is this function of organ of tact. There are many different constituents that come together to form the innervation. There are book endings, encapsulated, there are vegetative, motor, cerebrospinal nerves etc. ➔ -Free nerve endings: There are myelinated fibers which will lose their myelin sheaths before branching or often which lose their myelin sheath before branching or often which lose their myelin sheath as it passes through the basal lamina of so they are myelinated in the dermis and which become unmyelinated in the epidermis and these endings can go up to the level of the stratum corneum and therefore completely cross the epithelium. There are unmyelinated fibers often of small diameters (1 micron in diameter) which have multiple branches and there often the Schwann sheath in which finds its unmyelinated fibers stops before the basal lamina so here again the envelope of the Schwann sheath exists in the dermis then it disappears when the fiber is passed through the basal lamina. These unmyelinated fibers are largely responsible for sensitivity to pain and temperature differences and then there are fibers related to hair which are numerous:80% of the fibers of a cutaneous nerve are intended for hairs so around each hair follicle of a hair, there are very many nerve endings. These fibers in relation to the hairs are also
myelinated fibers than unmyelinated fibers therefore at the level of the hair itself, of the follicle these are unmyelinated fibers so they have lost their myelin sheath prior. These fibers are sometimes so numerous that they form a kind of sleeve around the hair follicle. In fact, a single axon can make endings nervous for several dozen hairs. The activation of these fibers is directly linked to the mobilization of the hair. Alongside these simple, free nerve endings, there are encapsulated endings: we also call these associated fibers or tactile corpuscles and these tactile corpuscles are essentially the mechanoreceptors of the skin.