The vertebral column (also known as backbone, spine, spinal column, latin: columna vertebralis) is a sequence of bones called the vertebrae separated from each other by intervertebral discs. The vertebral column forms the main axis of the human body.
The human spine is flexible and it supports the head, neck and body, allowing their movements. The vertebral column also provides protection for the spinal cord, which is located within the spinal canal that is formed by a central hole in each vertebra.
Normally, there are 32 to 34 vertebrae (singular: vertebra) forming the human spine. There are 24 free vertebrae and 8 to 10 fused vertebrae.
The vertebral column has the following parts:
- cervical part - consists of 7 cervical vertebrae (C1 - C7);
- thoracic part - consists of 12 thoracic vertebrae (T1 - T12);
- lumbar part - consists of 5 lumbar vertebrae (L1 - L5);
- sacral part - consists of 5 sacral vertebrae fused together, forming a single bone - the sacrum;
- coccygeal part - consists of 3 to 5 fused coccygeal vertebrae, forming a single bone - the coccyx (tailbone).
The adult human vertebral column does not form a straight line, but it has four curves along its way corresponding to parts of the spine (cervical, thoracic, lumbar and sacral). The cervical and lumbar parts of the vertebral column are curved anteriorly, while the thoracic and sacral parts curve posteriorly. The curves increase stability, flexibility of the vertebral column and its ability to absorb shock..
The Intervertebral discs are important structues in shock absorption. Intervertebral discs have two primary parts:
- The outer portion or the anulus fibrosus which consists of many tough laminae of fibrocartilage oriented perpendicular to each other.
- The inner portion or the nucleus pulpsos which has a gel like consistency.
The orientation of fibrocartilage of the outter portion allows for multi- directional support for the nucleus pulposus which has a gel-like consistency.
A herniated disc is when the nucleus pulposus has breached the annulus fibrosis and may impinge upon a spinal nerve. This, in turn, can result in back pain, pain or sensation in different parts of the body.
The spine has four curvatures, two of which are primary and two - secondary.
In the adult, the thoracic and sacral curvatures are in the same direction as in the fetus and so are called primary curvatures.
The secondary curvatures of the adult (cervical and lumbar) spine bend in the opposite direction (concave posteriorly). The secondary curvatures begin to develop after birth as the infant learns to hold up the head (cervical curvature) and to walk upright (lumbar curvature).
Disorders affecting the curvatures of the vertebral column are classified as spinal disease (dorsopathy)
The three abnormal curvatures are:
- Kyphosis: exaggerated curvature of the thoracic spine hunched-back.
- Lordosis: exaggerated lumbar curvature.
- Scoliosis: a complex abnormality which presents as an S shaped spine when viewed from posterior and has a rotational component as well.