Introduction

• The letter reflects the spinal region where the vertebra is located: C=cervical (neck region), T=thoracic (chest, or middle back, region), and L=lumbar (lower back).
• The number signifies the vertebra's place within that spinal region. The numbers start with 1 at the top of a region and count up as the vertebrae descend within the region. For example, C4 is the fourth bone down in the cervical region and T8 is the eighth thoracic vertebrae.

The Disks. Vertebrae in the spinal column are separated from each other by small cushions of cartilage known as intervertebral disks. Each disk is 80% water and contains two structures.

• Inside each disk is a jelly-like substance called the nucleus pulposus.
• The nucleus pulposus is surrounded by a tough, fibrous ring called the annulus.

This structure plus its heavily fluid-content makes the disk both elastic and strong. The disks have no blood supply of their own, however, but need to rely on nearby blood vessels to keep them nourished.

Click the icon to see an image of an intervertebral disk.

Processes. Each vertebra in the spine has a number of bony projections called processes. The spinal and transverse processes attach to the muscles in the back and act like little levers, allowing the spine to twist or bend. The particular processes form the joints between the vertebrae themselves, meeting together and interlocking at the zygapophysial joints (more commonly known as facet or z joints).

Spinal Canal. Each vertebra and its processes surround and protect an arch-shaped central opening. These arches, aligned to run down the spine, form the spinal canal, which encloses the spinal cord.

Click the icon to see an image of the vertebrae and spinal cord.

Spinal Cord. The spinal cord is the central trunk of nerves that connects the brain with the rest of the body. Each nerve root passes from the spinal column to other parts of the body through small openings bounded on one side by the disk and the other by the facets. When the spinal cord reaches the lumbar region, it splits into four bundled strands of nerve roots called the cauda equina (meaning horsetail in Latin).