0.8 Skeletal system module 9: the vertebral column

The vertebral column is also known as the spinal column or spine ( [link] ). It consists of a sequence of vertebrae (singular = vertebra) , each of which is separated and united by an intervertebral disc    . Together, the vertebrae and intervertebral discs form the vertebral column. It is a flexible column that supports the head, neck, and body and allows for their movements. It also protects the spinal cord, which passes down the back through openings in the vertebrae.

Vertebral column

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 7 cervical vertebrae . The first vertebra articulates (forms a joint) with the skull. It is called the atlas    . The second vertebra is called the axis    . Below these are the 12 thoracic vertebrae , each of these vertebrae form a joint with a pair of ribs. The lower back contains the 5 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. However, the sacral and coccygeal fusions do not start until age 20 and are not completed until middle age.

Curvatures of the vertebral column

Disorders associated with the curvature of the spine include kyphosis    (an excessive posterior curvature of the thoracic region), lordosis    (an excessive anterior curvature of the lumbar region), and scoliosis    (an abnormal, lateral curvature, accompanied by twisting of the vertebral column).

General structure of a vertebra

Within the different regions of the vertebral column, vertebrae vary in size and shape, but they all follow a similar structural pattern. A typical vertebra will consist of a body , a vertebral foramen    , along with other processes. The body is the anterior portion of each vertebra and is the part that supports the body weight. Because of this, the vertebral bodies progressively increase in size and thickness going down the vertebral column. The bodies of adjacent vertebrae are separated and strongly united by an intervertebral disc    . ( [link] ). The large opening between the vertebral arch and body is the vertebral foramen, which contains the spinal cord. The vertebral foramina of all of the vertebrae align to form the vertebral (spinal) canal    , which serves as the bony protection and passageway for the spinal cord down the back.

Parts of a typical vertebra

Regional modifications of vertebrae

In addition to the general characteristics of a typical vertebra described above, vertebrae also display characteristic size and structural features that vary between the different vertebral column regions. Thus, cervical vertebrae are smaller than lumbar vertebrae due to differences in the proportion of body weight that each supports. Thoracic vertebrae have sites for rib attachment, and the vertebrae that give rise to the sacrum and coccyx have fused together into single bones.

Chapter review

The vertebral column forms the neck and back. The vertebral column originally develops as 33 vertebrae, but is eventually reduced to 24 vertebrae, plus the sacrum and coccyx. The vertebrae are divided into the cervical region (C1–C7 vertebrae), the thoracic region (T1–T12 vertebrae), and the lumbar region (L1–L5 vertebrae). The sacrum arises from the fusion of five sacral vertebrae and the coccyx from the fusion of four small coccygeal vertebrae. The vertebral column has four curvatures, the cervical, thoracic, lumbar, and sacrococcygeal curves. The thoracic and sacrococcygeal curves are primary curves retained from the original fetal curvature. The cervical and lumbar curves develop after birth and thus are secondary curves. The cervical curve develops as the infant begins to hold up the head, and the lumbar curve appears with standing and walking.