What do cortical bone spaces contain?

Cortical bone, which is the dense outer surface of bone, primarily contains osteocytes within its spaces. Osteocytes are mature bone cells that originate from osteoblasts and are critical to bone maintenance. They reside in small cavities called lacunae and extend their processes through tiny channels known as canaliculi. These extensions enable communication between osteocytes and the surrounding bone matrix, allowing them to monitor stress on bones and regulate bone remodeling.

While bone marrow is found in the medullary cavity of long bones and is not a component of cortical bone spaces, osteoblasts are responsible for new bone formation but do not reside within the spaces of cortical bone. Instead, these cells are found on the surface of the bone matrix. Collagen fibers are a significant component of the bone matrix itself, providing structural support and tensile strength, but they are not contained within the spaces. Thus, osteocytes are the primary cell type that occupies the spaces within cortical bone, making them essential for the health and function of the skeletal system.