Spine, vertebrae, and disks.

The spinal column undergoes developmental changes from infancy to the adult state and then degenerative changes with aging. The alignment of the spinal column at birth is in the shape of a C curve, the fetus having been curled up. This forward-tilted curve is retained except in the neck and lower back. As the infant raises its head and attempts to see things, head control and vision gradually require the head to tilt back, resulting in a posterior curve at the neck. As children progress to standing and walking, the lower spine also develops a posterior curve (a normal lumbar lordosis). As individuals increasingly use the predominant upper extremities, these muscles become stronger and increase the pull on that side of the spine, resulting in a lateral curve (a normal scoliosis).