Back structure and how the back functions
Basically, the back serves to:
- Support the body. Therefore, it must be solid.
- Allow movement. Therefore, it should be flexible.
- Contribute to maintaining a stable center of gravity at rest
and, especially, when in motion.
- Protect the spinal cord with a bony encasement.
The back must be solid in orden to support the body. It is composed
of very sturdy bones and powerful muscles.
The spine must be flexible to allow for movement. This is why
it is not composed of one solid bone, but 33 separate vertebrae,
which are set one on top of the other and connected by a system
of muscles and ligaments.
In order to maintain a stable center of gravity, back muscles
should be strong so they may act as a counterweight and able to
contract in order to compensate for body movements.
To protect the spinal cord, vertebrae have a special shape, with
a foramen or canal to house the cord.
The spine
Thirty three vertebrae form the human spine. The 7 cervical 12
thoracic, and 5 lumbar vertebrae are separated by 23 intervertebral
discs. The 5 sacrum vertebrae are fused just like the 4 coccyx pieces,
forming the sacrum and coccyx bones.
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Taking a front view of the vertebrae, they are perfectly
aligned in vertical form. However, from a side view the alignment
is curved. The upper (cervical) are and the lower (lumbar)
areas are curved backward. This is referred to as lordosis
-cervical or lumbar lordosis-. The middle area is curved forward,
referred to as dorsal kyphosis.
This positioning permits the spine to be very resistant
to vertical weight, since its curves allow flexibility. If
weight is considerable, the spinal curve may increase temporarily,
cushioning the pressure exerted on the vertebrae. This is
why transporting weight on the head was a traditional practice
in certain countries. By carrying weight this way, the center
of gravity was kept at the spinal axis, and back muscles were
relieved from much of the strain. |
Side view of the spine
1. Cervical
2. Thoracic
3. Lumbar
4. Sacrum
5. Coccyx |
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