periosteum n : a dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles; contains nerves and blood vessels that nourish the enclosed bone [also: periostea (pl)]

English

Noun

1. A membrane surrounding a bone.

Periosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of all bones.

Periosteum consists of the irregular type of dense connective tissue. Periosteum is divided into an outer "fibrous layer" and inner "cambium layer". The fibrous layer contains fibroblasts while the cambium layer contains progenitor cells which develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone 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 nociceptors 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 skull is known as "fulacranium".

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References

• 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
• Netter, Frank H. (1987), Musculoskeletal system: anatomy, physiology, and metabolic disorders, Summit, New Jersey: Ciba-Geigy Corporation