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Spinal Column

Spinal Column, common name applied to the structure of bone or cartilage surrounding and protecting the spinal cord in vertebrate animals. It is also called a vertebral column, spine, or backbone,

Full information of the Spine

Anatomy and Physiology
The spinal column forms the major part of the skeleton. To it are attached the skull, shoulder bones, ribs, and pelvis. In very primitive animals having a vertebral column, the spine consists of a solid cartilaginous rod known as the notochord. Although remnants of the notochord persist in the cartilage's that form part of the apparatus connecting adjoining vertebrae, in higher animals the notochord is replaced by a series of separate bones called vertebrae.
The shape and number of vertebrae in general, the vertebrae are stacked like a column of poker chips and are held together by ligaments, the connective tissue that holds bones together at a joint. In humans the spinal column contains 33 vertebrae: 7 cervical vertebrae in the neck; 12 thoracic, or dorsal, vertebrae in the region of the chest, or thorax, providing attachment for 12 pairs of ribs; 5 lumbar vertebrae in the small of the back; 5 fused sacral vertebrae forming a solid bone, the sacrum (See Sacroiliac Joint), which fits like a wedge between the bones of the hip; and a variable number of vertebrae fused together to form the coccyx at the bottom of the sacrum.

Before birth, the human spinal column forms a single curve with the convex surface towards the back; at birth, two primary curvatures are present, both of which are concave forward. The upper one is located in the thoracic and the lower one in the sacral region. If the child develops normally, two compensatory forward curvatures develop in the cervical and lumbar regions, just above the primary curvatures. These normal curvatures provide a degree of resilience that would not be possible in a series of rigid, straightly stacked bones.

Most of the individual vertebrae are shaped somewhat like rings; the body, or thick portion of the ring, is located towards the front portion of the body. Between each of the separate vertebrae is a thick, fibrous disc of cartilage-called an intervertebral disc-that forms the principal joint between the bodies of adjoining vertebrae; however, the vertebrae also move with each other at several other joints.

Most vertebrae consist of a body-a large mass of solid bone that is the weight-bearing part of the vertebra. Extending backwards on each side of the body is a thick pillar of bone, or pedicle. The pedicles and back of the body help to form a circular opening, the vertebral foramen, through which the spinal cord passes. Two plates of bone, known as the laminae, meet the pedicles and join with each other in an angle at the back of the vertebra to complete the circular opening. The canal formed by the juxtaposition of the intervertebral foramens of all the vertebrae is called the neural canal. On each side, at the junction of the pedicle and lamina, is a projection known as the transverse process. At the angle formed by the junction of the two laminae is another projection, the spinous process. At the base of each transverse process is a smooth, movable structure that forms joints with the adjacent vertebrae. In erect animals, one pair of these processes is located on the top surface and another pair on the bottom surface of each vertebra.

The vertebrae of each region of the mammalian spinal cord have definite characteristics. In the upper cervical vertebrae, each transverse process is pierced by a hole through which the vertebral artery passes. The spinous processes of these vertebrae are very short. The first two cervical vertebrae are unlike any of the others. The first cervical vertebra, known as the atlas, has no body; the body is replaced by an arch of bone enclosing a depression. The superior articular processes of the axis are jointed to the occipital condyles, or rounded projection of bone, of the skull. The second cervical vertebra, known as the axis or epistropheus, has a projection on the top of its body that fits like a pivot into the special depression in the atlas. On the transverse processes of the thoracic vertebrae are special articulating surfaces for the ribs; the spinous processes, which are long, project downwards and overlap each other. The lumbar vertebrae have large, heavy bodies and reduced transverse and spinous processes. The fused sacrum and coccyx are described above.