Periosteum is a membrane that lines the outer surface of all bone

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

s, except at the joints of long bones. Endosteum

Endosteum

In anatomy the endosteum is a thin layer of connective tissue that lines the surface of the bony tissue that forms the medullary cavity of long bones. This endosteal surface is usually resorbed during long periods of malnutrition, resulting in less cortical thickness...

 lines the inner surface of all bones.

Periosteum consists of dense irregular connective tissue

Dense irregular connective tissue

Dense irregular connective tissue has fibers that are not arranged in parallel bundles as in dense regular connective tissue.-Substances formed:...

. 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 osteoblast

Osteoblast

Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...

s. 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

Bone healing

Bone healing, or fracture healing, is a proliferative physiological process in which the body facilitates the repair of a bone fracture....

 the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process.

As opposed to osseous tissue

Osseous tissue

Osseous tissue, or bone tissue, is the major structural and supportive connective tissue of the body. Osseous tissue forms the rigid part of the bone organs that make up the skeletal system.-Formation:Bone tissue is a mineralized connective tissue...

, periosteum has nociceptor

Nociceptor

A nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...

s 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

Sharpey's fibres

Sharpey's fibres are a matrix of connective tissue consisting of bundles of strong collagenous fibres connecting periosteum to bone...

, which extend to the outer circumferential and interstitial lamellae

Lamellae (zoology)

thumb|Lamellae on a gecko's foot.A lamella is a thin plate-like structure, often one amongst many lamellae very close to one another, with open space between...

. It also provides an attachment for muscles and tendons.

Periosteum that covers the outer surface of the bones of the skull

Skull

The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

is known as "pericranium" except when in reference to the layers of the scalp.

Etymology

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.