Final answer:
The adult human vertebral column is composed of 26 bones, including 24 individual vertebrae plus the sacrum and coccyx, with the sacrum being five fused vertebrae and the coccyx usually four fused vertebrae.
Step-by-step explanation:
Human Vertebral Column and Vertebrae
The human vertebral column, also known as the spine or backbone, is a crucial part of the skeletal system. In adults, it is comprised of 26 bones which include 24 individual vertebrae, the sacrum, and the coccyx. The sacrum is a single bone derived from the fusion of five vertebrae, and the coccyx, also known as the tailbone, is formed by the fusion of usually four vertebrae. During early development, the vertebral column consists of approximately 33 discrete vertebrae. As individuals mature, some of these vertebrae fuse together to form the sacrum and the coccyx. The adult spine is further organized into distinct regions—the cervical region with 7 vertebrae (C1-C7), the thoracic region with 12 vertebrae (T1-T12), and the lumbar region with 5 vertebrae (L1-L5).
The vertebral column plays a vital role in protecting the spinal cord, supporting the head, providing attachment points for ribs, and enabling a range of movements thanks to its S-shaped curve and flexibility. The fusion of the sacrum and coccyx vertebrae does not start until around age 20 and is usually completed by middle age. By the age of 70, it is common for the sacrum and the coccyx to fuse entirely.