What is the spine?
The spine is the bony axial skeleton that supports the trunk and enables its movements. It is straight when viewed from the front. Viewed from the side, on the other hand, it has a double S-shape:
How many vertebrae does a human being have?
The human spine consists of 33 to 34 vertebrae. It is divided into five spinal segments, each consisting of several vertebrae:
Cervical spine (C-spine).
It is made up of the seven cervical vertebrae (cervical vertebrae, C1- C7). You can read more about this uppermost section of the spine in the article Cervical spine.
Thoracic spine (BWS)
Lumbar spine (LWS)
The third section of the spine is made up of five vertebrae (lumbar vertebrae, L1 – L5). You can read more about this in the article Lumbar spine.
Sacrum (Os sacrum)
During development, the five sacral vertebrae (sacral vertebrae, S1 – S5) grow together to form a single bone. Read more about this in the article Sacrum.
Coccyx (Os coccygis)
The 24 cervical, thoracic and lumbar vertebrae remain mobile throughout life – except in cases of illness or injury.
The vertebral structure varies
For this reason, the vertebrae of the cervical spine, which have to bear relatively little weight with the head but allow a large range of motion, are shaped differently and are smaller than the lumbar vertebrae. The latter must support a much greater weight and therefore be stronger, but allow only a smaller range of motion.
The vertebral body
The vertebral body is actually the load-bearing and supportive part of the spine. It has a thin compact outer layer and a strong cancellous bone inside, a spongy system of fine bone bellicles filled with red bone marrow. The central area of the upper and lower surfaces of the vertebral bodies is porous, and only the marginal ridges are built of solid bone.
The intervertebral discs
Between every two adjacent vertebral bodies lie pressure-elastic intervertebral discs made of cartilage tissue, the intervertebral discs. You can read more about this in the article Intervertebral disc.
The vertebral arch and the processes
The posterior part of each vertebra is the vertebral arch (arcus vertebrae), which is narrower and weaker than the vertebral body. Several processes extend from the vertebral arch:
Spinous process
Read more about this vertebral process in the article spinous process.
Ligaments for stabilization
Between the vertebral arches – from the second cervical vertebra down to the first sacral vertebra – there are ligaments of elastic connective tissue (ligamenta flava), which together with muscles stabilize the spine. Their thickness increases from top to bottom.
The vertebral canal
The hole in the bony ring of the vertebrae is the vertebral hole. All vertebral holes together form the vertebral canal (canalis vertebralis), in which the spinal cord (medulla spinalis) with the surrounding spinal meninges runs from the brain down to the sacral region. The spinal canal becomes narrower and narrower from top to bottom because the spinal cord inside also becomes narrower and narrower toward the bottom.
What is the function of the spinal column?
The necessary compensation, when the belly becomes too fat and heavy and thus the lumbar lordosis increases, can be observed in pregnant women, who shift the chest, neck and head area backwards to compensate.
The ligaments between the vertebral arches (ligamenta flava) are stretched when the spine is bent, and their predetermined tension helps the back muscles to straighten the spine again.
The mobility of the spine
Lateral inclination is possible to about the same extent in the cervical and lumbar spine. It is greatest in the thoracic spine and is limited only by the ligaments of the spine and the ribs.
Where is the spine located?
The spine is located at the back of the body when viewed in cross-section of the torso. The processes of the individual vertebrae lie close together under the skin of the back, where they can be seen and felt in slender people.
What problems can the spine cause?
If, for example, the first cervical vertebra is fused with the occipital bone, this is called atlas assimilation. If there is an additional (sixth) lumbar vertebra, this is called lumbarization. If the last (fifth) lumbar vertebra is fused with the sacrum, this is called sacralization.
Due to muscle tension or other causes, individual vertebrae may be blocked in their mobility.
A lateral curvature of the spine, which may additionally be twisted in itself, is called scoliosis.
Bekhterev’s disease (ankylosing spondylitis) is a chronic, progressive rheumatic disease in which the joints of the spine and the sacroiliac joints in particular are inflamed.
