The spine, or spinal column, is the body’s main support structure. Its 33 bones, called vertebrae, are divided into five regions – cervical, thoracic, lumbar, sacral, and coccygeal.
Regions of the Spine
The cervical region consists of seven vertebrae, labeled C1 to C7, that get smaller as they get closer to the base of the skull. The first cervical vertebra is called the atlas. The second is called the axis. Together, the atlas and the axis form the joint that connects the spine to the skull, and allows the head to swivel and nod.
The thoracic region, located mid-back, consists of twelve vertebrae, labeled T1 to T12. These vertebrae serve as attachment points for the rib cage. The firm attachment of the rib cage at each level of the thoracic spine provides stability and structural support to the upper back and provides very little motion. The thoracic spine & ribs are basically a strong, protective cage for the heart and lungs.
Since the upper back is not designed for motion, there is not much wear or injury in this region of the spine. However, while uncommon, herniation of a thoracic disc is possible.
The lumbar region, commonly called the lower back, consists of five vertebrae, labeled L1 to L5. The lumbar region is the primary weight-bearing section of the lower back, which makes this section of the spine prone to injury and degenerative disc disease. The two lowest discs (L4-L5 and L5-S1) experience the most strain and are the most likely to herniate. A herniated disc in this region of the spine can cause lower back pain, tingling and numbness that radiates down the leg. This condition is referred to as sciatica.
The sacral region consists of five fused vertebrae, labeled S1 to S5. These vertebrae form a solid mass of bone called the sacrum, which provides the attachment point for the pelvis. Pain in the sacrum is often called sacroiliac joint dysfunction, and is more common in women.
The coccygeal region, called the tailbone, consists of four small vertebrae. These tiny bones may be fused or separate. Together, they form the coccyx, an attachment point for various tendons and ligaments. The coccyx also helps support the body when a person is in a seated position.
Altogether, the vertebrae of the spine’s five regions support the weight of the body, and protect the spinal cord and nerve roots. Each individual vertebra has a complex set of structures necessary to the overall functioning of the spine.
Parts of the Vertebrae
The main structure of the vertebra is the vertebral body, a cylinder-shaped bone at the front of the vertebra. It is the primary weight-bearing section of the vertebra.
Behind the vertebral body is the vertebral canal. The spinal cord travels through this channel.
The spinal cord is the main bundle of nerve fibers connecting the brain to the rest of the body. The spinal cord ends near the L1 and L2 vertebrae, where it divides into bundles of nerve roots, called the cauda equina.
Exiting the side of the spine are nerve roots – thick nerve branches that transmit signals between the spinal cord and the other parts of the body.
On either side of the vertebral canal are pedicle bones, which connect the vertebral body to the lamina.
The lamina create the outer wall of the vertebral canal, covering and protecting the spinal cord.
Protruding from the back of the lamina is the spinus process. It provides and attachment point for muscles and ligaments that move and stabilize the vertebrae.
Transverse processes protrude from the sides of each vertebra. Muscles and ligaments that move and stabilize the vertebrae attach to the transverse processes.
The articular facets form the joints where each vertebra connects with the vertebrae above and below it. Each vertebra has four facets – two superior facets and two inferior facets. The facet joints have a covering of cartilage that allows movement.
Between the vertebral bodies are the tough elastic spinal discs. They provide a flexible cushion, allowing the vertebrae to bend and twist. Each disc has a tough outer wall called the annulus fibrosus and a soft interior called the nucleus pulposus.
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