The Spinal Cord
The spinal column is the body’s main support structure. It has thirty-three bones, called vertebrae, which are divided into five regions: cervical, thoracic, lumbar, sacral and coccygeal. It surrounds and protects your spinal cord much like a conduit around an electrical cord. The spinal cord is a bundle of nerves that run from your brain through your spinal column and branch out to the rest of the body. The spinal cord connects the brain to the rest of the body.
Anatomy of the Spine: Vertebral Bones
Each vertebra has a large, cylinder-shaped body and a vertebral arch, known as the vertebral body. The arch can be further subdivided into the spinous process (the bone that you can feel sticking out) and facet joints that wing out to the sides. Seen from above, a vertebra looks like a giant head with three pieces sticking out and a hole in the middle. Muscles, ligaments, and discs attach to various parts of the vertebra.
The space between the vertebral body and the arch is the spinal canal, for your spinal cord. If this canal narrows, due to disease, for example, it can squeeze the spinal cord and cause pain. There are other openings among the stacked vertebrae, too. Spaces called intervertebral foramina are where nerve roots branch out of the spinal cord.
Five Main Areas of the Spine
When healthcare professionals refer to the different parts of the spine, they reference them by the five main areas (cervical, thoracic, lumbar, sacral and coccygeal). Each bone within an area has its own number.
- The cervical region consists of seven vertebrae labeled C1 to C7. The first two cervical vertebrae form the joint that connects the spine to the skull and allows the head to swivel and nod.
- The thoracic region, located in the mid-back, consists of twelve vertebrae labeled T1 to T12. These vertebrae serve as attachment points for the ribcage.
- The lumbar region, commonly called the lower back, consists of five vertebrae labeled L1 to L5. This is the main weight-bearing section of the spinal column.
- 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.
- The coccygeal region, commonly 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 muscles, tendons and ligaments. The coccyx also helps support the body when a person is sitting.
All together, the vertebrae of the spine’s five regions support the weight of the body and protect the spinal cord and nerve roots.
Anatomy of the Vertebra
Each individual vertebra has a complex set of structures necessary to the overall function of the spine. The main structure of a vertebra is the vertebral body — a cylinder-shaped section of bone at the front of the vertebra. It is the main weight-bearing section of the vertebra.
Behind the vertebral body is the vertebral canal. The spinal cord travels through this channel. The spinal cord ends near the L1 and L2 vertebrae, where it divides into bundles of nerve roots called the cauda equina. Exiting the sides 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 spinous process. It provides an 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. The facet joints have a covering of cartilage, which 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 and a soft interior.
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