Current understanding of Merkel cells, touch reception and the skin

Abstract

Merkel nerve endings are found in human skin, as well as the skin of all vertebrates functioning as mechanoreceptors. Merkel cells are located in the basal layer of the epidermis both in hairy and in glabrous skin, and are often arranged in clusters. In hairy skin, Merkel cells are typically associated with large guard hairs and specialized sensory complexes known as touch domes. Merkel cells have lobulated nuclei and dense-core granules in the cytoplasm facing the associated afferent nerve terminal. Developmental studies have shown that avian Merkel cells are derived from the neural crest. In mammals, studies on transgenic mice have resulted in contradictory findings. Thus, the question of the developmental origin of mammalian Merkel cells remains to be resolved. Functionally, mammalian Merkel cell nerve endings are slowly adapting mechanoreceptors. In response to maintained mechanical stimulation they keep firing action potentials with characteristic irregular patterns. New experimental evidence strongl...