How The Back Works?
Basically, the back serves to:
1. Keep up the body and allow movement.
2. Contributing to maintain a stable center of gravity, both at rest and, above all in motion.
3. Protect the spinal cord in a wrapped stone.
In order to sustain the weight of the body, the back has to be solid. It is composed of very strong bones and muscles strong.
To allow movement, the spine has to be flexible. It is therefore not composed of a large bone but by 33 separate vertebrae, arranged one above the other and supported by a system of muscles and ligaments.
To help maintain a stable center of gravity, the contraction of muscles of the back acts as a counterweight compensates for the rest of the body. To do so, the muscles must be strong.
To protect the spinal cord, vertebrae have a special shape, a hole in its center through which runs the spinal cord.
The vertebral column
The human spine is made up of 33 vertebrae. The 7 cervical, 12 thoracic and 5 lumbar vertebrae are separated by intervertebral discs 23. The 5 sacral vertebrae are fused, as are the four coccygeal, forming the sacrum and coccyx bones.
Looking ahead, the vertebrae are perfectly aligned and form a vertical. However, in profile, forming curves. The upper cervical area-in-and lower-back-in concave back and are called cervical and lumbar lordosis, respectively. The mean curve is concave forward and is called kyphosis.
This provision allows the column to be resistant to the applied load in the vertical direction, as its curves give you flexibility. If the load is very important, the curvatures can transiently increase, lessening the pressure on the vertebrae. Therefore, it was traditional in some countries carry the load on the head. Moreover, in doing so kept the center of gravity in the axis of the column, so that the muscles of the back just had to work.
Source: www.espalda.org/divulgativa/como_es_funciona/comoes.asp
image source: www.bodystressrelease.co.uk/images/body.jpg