A joint is made where the two vertebrae meet. The bony nature of the spine protects the delicate spinal central nerve cord. It encases it along its length. The skeleton is made of bone. Calcium and other salts make the bone strong but slightly flexible.
Bone is a living tissue with a blood supply.
It is a mixture of soft living material and hard salts. Look at the microscopic view shown to see how bone is deposited in rings around blood vessels. Bone is constantly being dissolved and laid down. Bone is a dynamic tissue in constant change. It has very few nerve connections.