Human Anatomy - Kotsan I. Ya. 2009

Anatomy of the Trunk Skeleton
The Vertebral Column as a Whole

The human spine is a long, curved Column that thickens downwards and then tapers again starting from the sacral region. It features several curves that evolved as an adaptation to bipedalism. Curves directed convexly forward are called lordosis, and those directed backward are called Kyphosis. There are two types of lordosis—cervical and lumbar—and Two Types of kyphosis—thoracic and sacral. In a newborn, the spine is nearly straight, with curves barely noticeable. As the baby begins to hold its HEAD up, the cervical lordosis develops; when it starts sitting, the thoracic kyphosis increases; and once the child learns to stand and walk, the primary curvature—the lumbar lordosis—is formed. By the age of 5–6, the spinal curves are already distinct, though they only fully mature between 15 and 20 years of age. These curves enhance the spine's stability and Shock-absorbing properties; together with the intervertebral discs, they provide resilience and elasticity, while also increasing the capacity of the thoracic and abdominal cavities.

In old age, the spinal curves smooth out somewhat. Due to a decrease in the thickness of both the intervertebral discs and the vertebrae themselves, along with a loss of elasticity, the spinal column flexes forward to form a single large thoracic curve (senile hunch), significantly reducing the overall length of the spine.

In addition to normal physiological curves (lordosis and kyphosis), lateral curvatures of the spine also occur, known as Scoliosis. Scoliosis most commonly develops during early school age due to asymmetrical body positioning and uneven Muscle Development on the right and left sides. Its development is facilitated by poor sitting posture at a desk or table when the furniture size does not match the child's height, as well as incorrect posture during work or rest. Besides Muscle Function Asymmetry and postural imbalance during work or leisure, lateral spinal curves can also be triggered by a slight discrepancy in leg length. If one leg is longer than the other, the pelvis does not sit completely level when standing, but tilts to one side. This induces a compensatory lateral curvature of the spine in the opposite direction. Pronounced forward or backward spinal curves are also considered pathological.