The axial skeleton is divided into three sections: the skull, the vertebral_column (spinal_column), and the thorax.
The vertebral column extends from the skull to the pelvis, and creates a central support system for the body. The bones of the vertebral column are called the vertebrae (sing: vertebra). There are 24 single vertebral bones (7 cervical, 12 thoracic, and 5 lumbar) and 9 fused bones (the sacrum has 5; the coccyx has 4).
The vertebral column is flexible because of pads of fibrocartilage that lie between each bone. These pads are called intervertebral_discs. Each disc has a fluid center called the nucleus_pulposus and an outer ring of fibrous tissue called the annulus_fibrosus.
The basic structure of a vertebra consists of:
superior and inferior_articular_processes, and the
The different categories of vertebrae (cervical, thoracic and lumbar) each have their own unique specializations.The first two cervical vertebrae (C-1 and C-2) have the most specialized shapes.
The sacrum consists of five fused vertebrae. The coccyx consists of four fused bones, and lies below the sacrum. It is attached to the sacrum by ligaments and is called the tailbone (nowadays its called the "movie bone" - it's what hurts when you sit down too long!).