Which of the following best describes the periosteum?

The periosteum is best described as a fibrous membrane that surrounds the diaphysis, which is the central shaft of long bones. This dense layer of connective tissue serves several essential functions. It provides a protective covering for the bone, serves as an attachment point for tendons and ligaments, and contains blood vessels and nerves that nourish the bone. The periosteum plays a crucial role in the growth and repair of bone, and it is vital for the overall health and maintenance of skeletal structure.

The other options do not accurately describe the periosteum. The fibrous membrane surrounding articular surfaces refers to a different type of connective tissue, which helps in cushioning the joints. A soft tissue layer inside the bone describes the bone marrow or other internal structures rather than the periosteum. The protective cover for the brain refers to the meninges, which are entirely separate structures from the periosteum associated with bone. Understanding these distinctions reinforces the importance of accurately identifying the periosteum's role and location within the skeletal system.