The spine is made of 33 individual bones stacked one on top of the other. This spinal column provides the main support for your body, allowing you to stand upright, bend, and twist, while protecting the spinal cord from injury. Strong muscles and bones, flexible tendons and ligaments, and sensitive nerves contribute to a healthy spine. Yet, any of these structures affected by strain, injury, or disease can cause pain.
- Regions of the Vertebral Column
The vertebral column originally develops as a series of 33 vertebrae, but this number is eventually reduced to 24 vertebrae, plus the sacrum and coccyx. The vertebral column is subdivided into five regions, with the vertebrae in each area named for that region and numbered in descending order. In the neck, there are seven cervical vertebrae, each designated with the letter “C” followed by its number. Superiorly, the C1 vertebra articulates (forms a joint) with the occipital condyles of the skull. Inferiorly, C1 articulates with the C2 vertebra, and so on. Below these are the 12 thoracic vertebrae, designated T1-T12. The lower back contains the L1-L5 lumbar vertebrae. The single sacrum, which is also part of the pelvis, is formed by the fusion of five sacral vertebrae. Similarly, the coccyx, or tailbone, results from the fusion of four small coccygeal vertebrae. An interesting anatomical fact is that almost all mammals have seven cervical vertebrae, regardless of body size. This means that there are large variations in the size of cervical vertebrae, ranging from the very small cervical vertebrae of a shrew to the greatly elongated vertebrae in the neck of a giraffe. In a full-grown giraffe, each cervical vertebra is inches tall.
- Vertebral Column
Developmental anomalies, pathological changes, or obesity can enhance the normal vertebral column curves, resulting in the development of abnormal or excessive curvatures Kyphosis, also referred to as humpback or hunchback, is an excessive posterior curvature of the thoracic region. This can develop when osteoporosis causes weakening and erosion of the anterior portions of the upper thoracic vertebrae, resulting in their gradual collapse. Scoliosis is an abnormal, lateral curvature, accompanied by twisting of the vertebral column. Compensatory curves may also develop in other areas of the vertebral column to help maintain the head positioned over the feet. Scoliosis is the most common vertebral abnormality among girls. The cause is usually unknown, but it may result from weakness of the back muscles, defects such as differential growth rates in the right and left sides of the vertebral column, or differences in the length of the lower limbs. When present, scoliosis tends to get worse during adolescent growth spurts. Although most individuals do not require treatment, a back brace may be recommended for growing children. In extreme cases, surgery may be required.
- Spinal Discs are in Between Each Vertebra
Spinal discs are located in between each of the vertebral bodies along the back bone and may also be referred to as an intervertebral disc, spinal disc, or disk. Each disc is named according to which two vertebral bodies it lies between. For instance:1. The L4-L5 disc in the low back is between the L4 vertebrae and L5 vertebrae which make up the L4-L5 spinal segment.2. The L5-S1 disc at the bottom of the spine lies between the L5 vertebra and the first bony segment at the top of the sacrum, which is sacral segment 1 (or S1).
The disc and vertebra above and below the disc comprise one segment of the spine – usually called a spinal level or spinal segment. The L4 vertebra and L5 vertebra, along with the disc in between them, make up the L4-L5 segment Discs are always labeled for the vertebrae that they lie between, and this is consistent throughout the length of the spine – for the cervical, thoracic and lumbar spine. For example, the C1-C2 disc in the neck lies between the first and second vertebrae in the cervical spine, and the T1-T2 disc lies between the first and second vertebrae in the thoracic spine.