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Vertebral column

The meaning of «vertebral column»

The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs.[1] The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

There are about 50,000 species of animals that have a vertebral column.[2] The human vertebral column is one of the most-studied examples.

The number of vertebrae in a region can vary but overall the number remains the same. In a human's vertebral column, there are normally thirty-three vertebrae.[3] The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone. The articulating vertebrae are named according to their region of the spine. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of those in the cervical region, however, is only rarely changed,[4] while that in the coccygeal region varies most.[5] One study of 908 human adults found 43 individuals with 23 pre-sacral vertebrae (4.7%), 826 individuals with 24 pre-sacral vertebrae (91%), and 39 with 25 pre-sacral vertebrae (4.3%).[6]

There are ligaments extending the length of the column at the front and the back, and in between the vertebrae joining the spinous processes, the transverse processes and the vertebral laminae.

The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are essentially alike, with minor variation. These regions are called the cervical spine, thoracic spine, lumbar spine, sacrum, and coccyx. There are seven cervical vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae.

The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region, however, is only rarely changed.[4] The vertebrae of the cervical, thoracic, and lumbar spines are independent bones and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis, on which the head rests.

A typical vertebra consists of two parts: the vertebral body and the vertebral arch. The vertebral arch is posterior, meaning it faces the back of a person. Together, these enclose the vertebral foramen, which contains the spinal cord. Because the spinal cord ends in the lumbar spine, and the sacrum and coccyx are fused, they do not contain a central foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous, the latter also being known as the neural spine. Two transverse processes and one spinous process are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out the left, and one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin.

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