The vertebral column or spine is a flexible column that supports the head, neck, and body and allows for their movements. It also protects the spinal cord.

Regions of the Vertebral Column

In an adult, the spine is subdivided into five regions: the cervical, the thoracic, the lumbar, the sacral, and the coccygeal region. The spine initially develops as a series of 33 vertebrae; after 20 years of age, the nine bones in the sacral region, five sacral, and four coccygeal bones fuse to form the sacrum and coccyx respectively, thus, reducing the number of vertebrae to 26. Out of the 26 vertebrae in adults, seven are cervical, twelve are thoracic, five are lumbar, and one each form the sacrum and coccyx.

Curvatures of the Vertebral Column

The adult vertebral column is not straight but has four curvatures along its length. These curves increase the spine's strength, flexibility, and ability to absorb shock. The spine can spring back when the weight applied to it is removed. The four adult curvatures are classified as either primary or secondary. Primary curves are retained from the original fetal curvature, while secondary curvatures develop post-birth.

During fetal development, the body is flexed anteriorly into the fetal position, giving the entire vertebral column a single curvature that is concave anteriorly. In the adult, this fetal curvature is retained in two regions of the vertebral column: the thoracic curve, which involves the thoracic vertebrae, and the sacrococcygeal curve, formed by the sacrum and coccyx. Each of these is thus called a primary curve. A secondary curve develops gradually after birth as the child learns to sit upright, stand, and walk. Secondary curves are concave posteriorly and present in the cervical and lumbar regions.

Disorders associated with the curvature of the spine include kyphosis — excessive anterior concavity of the thoracic region; lordosis — excessive posterior concavity of the lumbar region; and scoliosis — an abnormal lateral curvature accompanied by twisting of the spine.

This text is adapted from Openstax, Anatomy and Physiology 2e, Section 7.3: The vertebral column