Periosteum

Structure

The periosteum consists of an outer fibrous layer, and an inner cambium layer (or osteogenic layer). The fibrous layer is of dense irregular connective tissue, containing fibroblasts, while the cambium layer is highly cellular containing progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone (the length of a long bone is controlled by the epiphyseal plate) 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. The outer fibrous layer and the inner cambium layer are differentiated under electron micrography.

As opposed to osseous tissue, the periosteum has nociceptors, sensory neurons that make it very sensitive to manipulation. It also contains blood vessels, the periosteal arteries, which supply blood to the periosteum and to the cortical bone. The periosteum is attached to the bone by strong collagen fibres called "Sharpey's fibres", which extend to the outer circumferential and interstitial lamellae. It also provides an attachment for muscles and tendons.

The periosteum that covers the outer surface of the bones of the skull is known as the pericranium, except when in reference to the layers of the scalp.