Cancellous bone is also known as a spongy bone because it has many open spaces joined by flat planes of bone known as trabeculae, much like a sponge or honeycomb. There are three types of bone cells inside the trabeculae: osteoblasts, osteocytes, and osteoclasts. Osteoblasts are the cells responsible for the formation of new bones. They develop layers of hard tissue mostly composed of calcium and phosphate until they are completely surrounded, at which point they are classified as osteocytes. Finally, osteoclasts are bigger cells that break down and destroy old or damaged bone in order for osteoblasts to repair and replace it. This cycle of repair and rebuilding is continuing in order to keep bones strong and healthy.