Human Anatomy - H. I. Koliadenko 2009

Musculoskeletal System
Skeleton of the Trunk
Ontogeny of the Vertebral Column

During ontogeny, skeletal development begins with the notochord, around which the mesoderm accumulates in a metameric pattern. Subsequently, the mesoderm forms somites, which in turn differentiate into dermatomes, myotomes, and sclerotomes. The latter are located closer to the notochord. Initially, they give rise to cartilaginous vertebrae that gradually ossify into Bone tissue. In the course of Human Development, the notochord disappears, leaving remnants only in the center of the intervertebral discs as The Nucleus pulposus.

Ossification of the vertebrae begins during the second month of intrauterine development. Initially, three ossification centers appear: one in the vertebral body and two in the vertebral arch. During the child's first year of life, the ossification centers of the arch fuse, and by the third year or later, the arch unites with the vertebral body. Because intervertebral discs in children are significantly thicker than in adults, their spine is more flexible and elastic, yet less rigid, and cannot support body weight for extended periods. Consequently, children's loads are primarily borne by Muscles that fatigue quickly, preventing them from maintaining a single posture for long. Therefore, children need frequent rest and changes in body position (such as periodic physical exercises during active breaks). With Aging, changes occur in the human Skeleton, becoming more pronounced the older the person gets. In elderly individuals, assimilation processes slow down, the number of trabeculae in the spongy bone decreases, the spaces between them enlarge, and vertebral Osteoporosis develops, leading to a reduction in vertebral body height. As a result, the spinal Column deforms, spinal curvatures increase, Scoliosis becomes more pronounced, and thoracic Kyphosis especially so. An elderly person's height may decrease by 7—15 cm, which is often accompanied by back pain and fatigue.

A person's occupation also leaves its mark on The Structure of their skeleton. Physical Exercise has a positive effect on its condition. For instance, gymnasts possess a significantly more elastic and flexible spinal column, enabling them to perform movements that an untrained person can hardly imagine. Conversely, sitting at a desk for prolonged periods with a persistently tilted HEAD can lead to The Development of slouching. Similarly, systematically working in a standing position while leaning on one leg can cause scoliosis. Thus, throughout a person's life, structural changes occur in the skeleton driven by both occupational factors and aging.