First, let me say a few words about the spine! Composed of a series of bones called vertebrae stacked one upon another is the spineor also called the vertebral column or spinal column. There are four regions of the spine: cervical (neck); thoracic (chest/trunk); lumbar (low back) and sacral (pelvic). You should also know that made up of seven cervical vertebrae is the cervical spine. To support the weight of the head which is approximately 10-12 pounds is the main function of the cervical spine. Because of two specialized vertebrae that move with the skull the cervical spine has the greatest range of motion.
The smallest of the vertebrae are cervical vertebrae. The atlas is called the first cervical vertebra and is significantly different from the other vertebrae. It is ring-like in shape with two large protrusions on the sides to support the weight of the head. The axis is called the second cervical vertebra. The axis is also unique in that it has a bony peg-like protrusion, called the dens or odontoid on its upper surface that fits within the ring of the atlas. As a lordosis curve is described the curve of the neck, and looks like a “C” in reverse.
To protect the organs of the chest, especially the heart and lungs is the main function of the thoracic spine. To create a thoracic cage, which protects the internal organs of the chest there are 12 thoracic vertebrae with one rib attached on each side. The thoracic spine has a normal kyphosis, or “C” curve. Because of the thoracic cage the thoracic spine is less mobile than the cervical and lumbar spine. And finally – the lumbar spine has five lumbar vertebrae, which are the largest vertebrae. Creating a normal lumbar lordosis these vertebrae are also aligned in a reverse “C” like the cervical spine. The five lumbar vertebral bodies are the weight-bearing portion of the spine and are the largest in diameter compared to the thoracic and cervical vertebral bodies.