Support and Motion Functions
The upright position permits our spine to engage in more complicated tasks than quadrupeds can. It must carry the entire weight of the body, cushion the impact of walking and jumping, enable sitting and working positions, lifting and carrying of weight and movement of the head and trunk. The 23 to 25 motion segments of the spine, especially between the vertebrae, also known as the intervertebral disc, support the movement functions of spine. The motion segments are simultaneously half of a joint and an elastic cushion.
Each motion segment intercepts and distributes pressure over the discs of the adjacent vertebral bodies. Additionally, they will exert a dampening affect through its double S shape, in that it arches towards the shoulder blades and then back toward the stomach. Without this cushioning and dampening the spine would wear down in a short time.
The tendons and muscles of the spinal column guarantee interconnection of every vertebrae with the next, thus completing the spinal column. The main tendons run outside and inside and along the spinal column. The muscles consist of bundles of fibers that work in pairs, i.e. if a muscle contracts by order the brain for example, when arching, stretching or sitting, the opposite muscle must relax. Every movement always involves multiple motion segment.