Anatomy & Physiology: Vertebral Column

Vertebral Column

The vertebral column (spine) consists of 26 vertebrae bones (See 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.

TABLE 1

Bones of the Vertebral Column

Vertebra	Body	Spinous Process	Transverse Process	Vertebral Process
Cervical
C₁ (atlas)	none, bony ring	none	with transverse foramen	large; lightbulb-shaped
C₂ (axis)	relatively small; with dens (odontoid process)	bifid	with transverse foramen	large; heart-shaped
C₃-C₆	relatively small; oval	bifid	with transverse foramen	large; triangular
C₇ (vertebra prominens)	relatively small; oval	prominently long; not bifid	with transverse foramen	large; triangular
Thoracic
T₁-T₁₀	C₂-C₇, heart-shaped; 2 facets or demifacets for articulating with rib head	long; points down	with facets for articulating with rib tubercle	circular
T₁₁-T₁₂	larger than C₂-C₇, heart-shaped; 1 demifacets for articulating with rib head	long; points down	no facets for rib joints	circular
Lumbar
L₁–L₅	largest of all vertebrae; kidney- shaped	short, thick; points horizontally
Sacrum
5 fused S₁-S₅	fusion of 5 vertebrae forms a triangular bone	fuse to become the median sacral crest	becomes the lateral sacral crest	becomes sacral canal
Coccyx
4 fused

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.

Figure 1

The four regions of the vertebral column.

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 here.
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 here. 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 following vertebra.

The intervertebral foramina are notches in the superior and inferior surfaces of each pedicle of the vertebral arch. Adjacent notches 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 semifluid cushion (nucleus pulposus) that provides elasticity and compressibility.

The vertebral column is divided into four regions, 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 (S₁-S₅).

The coccyx, formed by four fused vertebrae, is a small triangle-shaped bone that attaches to the bottom of the sacrum (see Figure 1 ).