Vertebral Column
Composed of 33 separate vertebrae, the vertebral column, commonly called the spine, forms the rigid backbone of the body and is the major structural support and weight-bearing element in the skeletal system. The vertebral column is the axis of the spine, and in anatomical nomenclature is the axis dividing the body into bilaterally symmetrical halves.
The vertebral column is subdivided into five principal regions, each with their own characteristic vertebrae. Articulations between 24 of the vertebrae allow the spine to remain flexible and this flexibility provides allows a wide range of motion (e.g., flexion and extension) that would not be possible in a fused vertebral column. Nine of the vertebrae are fused and the fusions are important to spinal strength in intensely weight bearing areas.
The most superior region of the spine is the cervical region. Composed of seven cervical vertebrae, this region supports the skull on the first cervical vertebrae (the atlas). A unique articulation between the atlas and the second cervical vertebra (the axis) allows the head and neck to pivot (i.e., a limited degree of rotation about the axis).
Below or inferior to the cervical region is the thoracic region of the spine. Composed of 12 thoracic vertebrae, the thoracic region is the site of attachment for costal cartilages (ribs) and muscles of the thorax. The size of the thoracic vertebra increase in size from the uppermost first thoracic vertebrae to the lowest (most inferior) twelfth thoracic vertebrae.
Below the thoracic region are five larger lumbar vertebrae that compose the lumbar region. As with the thoracic region, the lumbar vertebrae increase in size as one moves inferiorly down the spine. Although large and important in weight baring the lumbar vertebrae retain independent articulations and a degree of flexibility.
Below (inferior) to the lumbar region of the spine lie the fused vertebrae of the sacrum and, most inferiorly, the coccyx. Five vertebral structures fuse to form the sacrum and four fuse to form the coccyx.
Viewed laterally the spine takes on a subtle double "S" like shape with the cervical and lumbar regions curved inward (anteriorly) while the thoracic region, sacrum, and coccyx are curved outward from the body (posteriorly).
Because the spinal cord runs continuously through the vertebral canal that is bounded by the vertebral foramen of each vertebra, any fracture of the vertebral column or other form of spinal injury may cause death or severe neurological injury or impairment (loss) of function at the level and below the level of injury. Spinal disorders may also cause a loss of neurological function. Mechanical slippage of the cartilage disks that help separate and cushion the individual vertebrae of the vertebral column impairs flexibility and mobility and may be painful if the slippage applies pressure to the spinal cord or causes inflammation of surrounding tissue.
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