What is Periosteum?

N. Madison
N. Madison

The bones do not lay bare within the human body. Instead, there is a membrane that covers, or lines, most of the bones of the human body, called the periosteum. It lines every bone's outer portion, with one exception: it is absent at the joints of long bones of the body. These bones include the femur, tibula, humeri, and radii; the ulna, metacarpals, metatarsals, and phalanges are also considered long bones. The bones also have a lining inside, which is called the endosteum; the periosteum that covers the bones of the skull is called the pericranium.

A diagram of the anatomy of a bone, showing the periosteum.
A diagram of the anatomy of a bone, showing the periosteum.

This bone membrane is fibrous, dense, and composed of connective tissue. It is divided into two separate layers. The outer layer is called the fibrous layer. It contains cells that synthesize collagen and the extracellular part of body tissue. These cells are also important in the healing of wounds.

Periosteum, the equivalent to endosteum on the outside of the bone, plays a vital role in the healing of fractures.
Periosteum, the equivalent to endosteum on the outside of the bone, plays a vital role in the healing of fractures.

The inner layer of the periosteum is called the cambium layer. This layer contains cells, called progenitor cells, that can change into osteoblasts, which are cells responsible for the growth and formation of the bone. These cells can also be important in healing. For example, when a bone breaks, these cells change into osteoblasts and another type of cell called chondroblasts, which form cartilage cells. This cell differentiation is an important part of the healing process.

The periosteum has blood vessels and nerves. The blood vessels provide vital nourishment to the bone. The nerves give the bones sensation or feeling. For example, there are nociceptors in the periosteum. Nociceptors are sensory receptors that send signals to both the brain and the spine when there is a dangerous form of stimulation. Often, the transmission of these nerve signals leads to the perception of pain.

When picturing the periosteum, it may seem probable that this membrane just rests on the bone. However, this is not the case. It is actually attached to the bone by fibers that are referred to as Sharpey’s fibres. These fibers are actually a configuration of connective tissues that contain bundled up fibers of collagen.

N. Madison
N. Madison

Nicole’s thirst for knowledge inspired her to become a wiseGEEK writer, and she focuses primarily on topics such as homeschooling, parenting, health, science, and business. When not writing or spending time with her four children, Nicole enjoys reading, camping, and going to the beach.

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Discussion Comments


Wow, I really love how you summarized the importance of the periosteum. I'm having a really hard time imagining all the different components of A&P, and your perspective helped me to see things a bit clearer. Thanks -- TurtleeyMC!


It's hard to wrap your head around the fact that a bone is really a living thing. They may look like a type of spongy stick, but they are able to grow, heal and can give a little without breaking. You have to have this membrane to keep the bone alive. This membrane is the delivery mechanism that keeps the bones healthy.

Just like any other part of the body the bone is susceptible to infection and blood is a major barrier against that. Without blood the bone could just die, just like any other organ in the body.

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