Quick Facts
The periosteum is a specialized connective tissue covering all bones of the body; in adults, it consists of two layers that are not sharply defined, the external layer being a network of dense connective tissue containing blood vessels, and the internal layer composed of more loosely arranged collagenous bundles with spindle-shaped connective tissue cells, osteogenic precursor cells, and a network of thin elastic fibers (Dorland, 2011).
Structure and/or Key Feature(s)
The periosteum is a thick layer of well vascularized connective tissue and can be found lining the surfaces of bones, including the delicate bony structures of the inner ear. Its outer fibrous layer is fibrous and becomes more fibroelastic internally due to the abundance of collagen and elastic fibers. The innermost osteogenic layer of the periosteum is believed to be associated with bone growth.
In the cochlea, the periosteum lines many of the surfaces. It lines the cavities of the cochlea, with the membranous labyrinth separated from the periosteum via the perilymphatic cells which line the periosteum in the scala tympani and scala vestibuli.
The periosteum is also modified where it makes up the body of some structures within the cochlea. For example, the spiral ligament is found on the outer aspect of the cochlear duct, forming part of the lateral wall. This is comprised of a denser and well vascularized periosteum. In contrast, the spiral limbus is found on the inner aspect of the cochlea duct. It is the upper plate of the osseous spiral lamina and is composed of thickened periosteum.
Anatomical Relations
The periosteum is found lining the inner surfaces of the cochlear canals. It is interjacent between the bony walls of these canals and the perilymphatic cells which line its surface.
Function
The fibrous layer of periosteum provides mechanical strength to the periosteum, which in turn provides considerable support to the bone. The osteogenic periosteal layer provides the necessary cells for bone growth, modeling, and remodeling. In the cochlea, it can support the overlying epithelial and perilymphatic cells across its surface.
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
