The periosteum covers the outside of bones.
Periosteum consists of dense irregular connective tissue. Periosteum is divided into an outer "fibrous layer" and inner "cambium layer" (or "osteogenic layer"). The fibrous layer contains fibroblasts, while the cambium layer contains progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone[nb 2] and the overall size of the other bone types. After a bone fracture the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process.
As opposed to osseous tissue, periosteum has nociceptive nerve endings, making it very sensitive to manipulation. It also provides nourishment by providing the blood supply. Periosteum is attached to bone by strong collagenous fibers called Sharpey's fibres, which extend to the outer circumferential and interstitial lamellae. It also provides an attachment for muscles and tendons.
Periosteum that covers the outer surface of the bones of the skull is known as "pericranium" except when in reference to the layers of the scalp.
The word Periosteum is derived from the Greek Peri- meaning "surrounding" and -osteon, meaning "bone". The Peri refers to the fact that the Periosteum is the outermost layer of long bones, surrounding other inner layers.
- Brighton, Carl T. and Robert M. Hunt (1997), "Early histologic and ultrastructural changes in microvessels of periosteal callus", Journal of Orthopaedic Trauma, 11 (4): 244-253