For most of his long history, the backbone evolved in quadrupeds as a horizontal structure, a bridge between two limb girdles. A brief journey to understand their relationship
The backbone, according to fossil record, made its appearance 550 million years ago as a simple rod of cartilage among the most primitive forms of water organisms. Later as Amphibians emerged from the sea, it diversified and ossified in order to offer support for vital organs, protection for the main nerve trunk and free mobility for predation and survival of the species.
For most of his long history, the backbone evolved in quadrupeds as a horizontal structure, a bridge between two limb girdles. Quite recently (5 -8 million years ago) it had to adapt to a radical change of orientation as the early hominids adopted bipedal posture. As a vertical column the mechanics are more like a pylon with gravity acting down its length as a compressive force and requiring broad based tensile tissues to keep it upright.
Nearly a quarter of the length of the column is cartilage, an ideal tissue for combining mobility with shock-absorbing. The maintenance of the hydric content in the disks depends on the vertebral bodies´s mechanics. So when the vertebral column compresses the disks fluids flow outwards and when the discal column decompresses, fluids flow inwards.