When most people mention their back, what they are actually referring to is their spine. The spine runs from the base of your skull down the length of your back, going all the way down to your pelvis. It is composed of 33 spool-shaped bones called vertebrae, each about an inch thick and stacked one upon another.

Each vertebra consists of the following parts:

The body is the largest part of the vertebrae and the part that bears the most weight.

The lamina is the lining of the hole (spinal canal) through which the spinal cord runs.

The spinous process is the bony protrusions you feel when you run your hand down your back.

The transverse processes are the pairs of protrusions on either side the vertebrae to which the back muscles attach.

The facets are two pairs of protrusions where the vertebrae connect to one another, including:

• The superior articular facets, which face upward
• The inferior articular facets,
which face downward.

The connection points between the vertebrae are referred to as the facet joints, which keep the spine aligned as it moves. Similar to other joints in the body, the facet joints are lined with a smooth membrane called the synovium, which produces a viscous fluid to lubricate the joints.

Located between the individual vertebrae, discs serve as cushions or shock absorbers between the bones. Each disc is about the size and shape of a flattened doughnut hole and consists of two parts:

• The annulus fibrosis – a strong outer cover
• The nucleus pulposis – a "jelly-like" filling.

Running through the center of the spinal column is the spinal cord, a bundle of nerve cells and fibers that transmit electrical signals back and forth between the brain and the rest of the body via 31 pairs of nerve bundles that branch off the spinal cord and exit the column between the vertebrae.