The human spine has natural curvatures. When you look at a back from behind, the spine should be straight and centered over the pelvis. However, when you look at the spine from the side, the curves are designed to maintain balance as the spine is behind organs in the chest and abdomen. The spine has two alternating curves to create an “S” like shape. In the neck and low back there is normally an inward curvature or sway back known as lordosis. In the thoracic spine and sacrum there is an outward curvature known has kyphosis or hunchback. These curves normally balance out each other so that when we stand we are well balanced with the head straight above the hips when viewed from the side. Standing in this position minimizes the effect of gravity and allows us to stand with the best posture and use the least energy when moving or walking.
On our spine we can find 7 cervical vertebrae that will be connect with the skull on the first vertebra, 12 thoracic vertebrae connecting with the cervical and play a role to connect the ribs on the rib cage and specialized for stability aids in keeping the body upright and protecting the vital organs inside the rib cage. Connecting on the thoracic is lumbar spine with 5 vertebrae and does not have the ability to twist side to side as the same as we find in cervical and thoracic spine. Also it is in the lumbar that the muscles that moves the legs are connected, for example Psoas muscles connected on the L1 to the femur bone. And finally in the lower part of the spine we find sacrum and coccyx. Sacrum is a fusion of 5 vertebrae that forms a single bone and acts as a wedge between the two iliac pelvis bones. The coccyx is also formed by the fusion of 4 to 5 vertebrae and is known as the tailbone.
In between nearly every vertebrae we have a intervertebral disc to connect and protect the bone part of the vertebrae just like a cushion. There is one disc between each pair of vertebrae, except for the first cervical.