| Summary: | Bone is a dynamic tissue, and its metabolism is regulated by bone cells that respond to various environmental signals, including chemical, mechanical, electrical and magnetic stimuli. Three cell types are found in bone: osteoblasts, osteoclasts and osteocytes. In general, specific responses are governed by cellular receptors found in the membrane of the cells or within the cell itself. The cell membrane receptors bind the exogeneous signals and transfer the information across the cell’s cytoplasm to the nucleus through a series of interactions that involve a complex set of transduction mechanisms. The periosteum lines the outer surface of bone. Periosteum covers the external surface of most bones to serve as a transitional region between the cortical bone and the overlying soft tissue or musculature. It is composed of two layers. The outer layer is in contact with muscle and other soft tissue elements and is populated by fibroblast-like cells. The inner layer is known as the cambium layer, and it is populated by fibroblast-appearing cells, many of which are committed progenitors of chondrocytes and osteoblasts. This layer contributes to appositional bone growth during bone development and is responsible for the expansion of the diameter of the long bones with aging. In this review of the basic elements of bone, bone cells, osteoclasts, osteoblasts and osteocytes and the periostium are discussed in detail in the light of the recent research. Turk Jem 2008; 12: 10-1
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