The vertebral column (spine) consists of 26 vertebrae bones (Table 1). It provides support for the head and trunk of the body, protection for the spinal cord, and connecting points for the ribs and muscles.
A typical vertebra has the following characteristics (see Figure 1):
- The body (centrum) is the disc‐shaped, anterior portion that gives strength to the bone.
- The vertebral arch is a bony ring behind the vertebral body. The opening in the ring is the vertebral foramen, the passageway for the spinal cord. The vertebral canal is the continuous passageway formed by the vertebral foramina of successive vertebrae.
- The pedicles and the laminae form the anterior and posterior sides, respectively, of the vertebral arch.
- Seven processes project from the vertebral arch:
- A spinous process projects posteriorly from the vertebral arch. Muscle and ligaments attach to the spinous process
- Two transverse processes project from the vertebral arch, one from each side, at each of the junctures of the pedicles and laminae. Muscles and ligaments attach to the transverse processes. Each transverse process of cervical vertebrae contains a transverse foramen through which blood vessels pass to the brain.
- Two superior articular processes project from the superior surface of the vertebral arch, one from each of the pediclelamina junctions. These processes articulate (form joints) with the preceding vertebrae.
- Two inferior articular processes project from the inferior surface of the vertebral arch, one from each of the pediclelamina junctions. These processes articulate (form joints) with the vertebra next in line.
- The intervertebral foramina are openings between the superior and inferior surfaces of each pedicle of the vertebral arch. Adjacent openings of successive vertebrae form a passage for nerves that leave the spinal cord and emerge outside the vertebral column.
- Intervertebral discs separate adjacent vertebrae. Each disc consists of an outer ring of fibrocartilage (annulus fibrosus) surrounding a semi‐fluid cushion (nucleus pulposus) that provides elasticity and compressibility.
Figure 1. The four regions of the vertebral column.
The vertebral column is divided into four regions, with each region contributing to the alternating concave and convex curves of the spine (see Figure 1). As the vertebrae progress down the column, their bodies get more massive, enabling them to bear more weight.
The sacrum is a triangular bone below the last lumbar vertebra (see Figure 1). It is formed by the fusion of five vertebrae (S 1–S 5).
The coccyx, formed by four fused vertebrae, is a small triangle‐shaped bone that attaches to the bottom of the sacrum (see Figure 1).