The supporting part of the spine is the vertebral column. This consists of blocks of bones and cartilaginous discs. The blocks of bones and discs are stacked one over the other like a tower. The blocks of bones are the vertebrae. The cartilaginous cushions are the inter-vertebral discs. The inter-vertebral discs function as a cushion between two vertebrae.
Behind each vertebra is a bony arch (neural arch) which forms a ring / hole. All the rings / holes combine to form a tunnel. This tunnel is the spinal canal.
The spinal cord which is the continuation of the brain runs through the spinal canal. The spinal nerves start from the spinal cord and go to different parts of the body. The spinal cord is like the motorway (Highway) from the brain. The spinal nerves are the “A Roads” (Smaller roads) from the spinal cord to different parts of the body.
There are thirty-one pairs of spinal nerves in the human body. Some of these nerves join together to form bigger nerves. Nerves from the lower part of the spine join to become the sciatic nerve that goes down the leg. Pain starting from the back and going down the leg is sciatica.
Curves of the spine
The natural spine curves to the front and back. These curves increase the stability of the spine. There is no natural side to side curve. When the spine curves to the front it is called lordosis. When the spine curves to the back it is called kyphosis. In the neck (cervical spine) and in the lower back (lumbar spine), the spine curves forward. This creates the natural lordosis in the neck and the lower back. In the mid back (thoracic spine), behind the chest wall, the spine curves to the back. This creates the natural kyphosis behind the chest cage.
The inter-vertebral disc is like a jam doughnut
The intervertebral discs are plump and keep the vertebral bodies apart. The cross section of a disc looks like a “jam doughnut”. The doughy part on the outside is the “annulus fibrosus”. The jammy part on the inside is the “nucleus pulposus”.
Lack of blood supply to the inter-vertebral disc
The inter vertebral disc does not have a direct blood supply. The blood vessels / channels only come up to the edge of the bone. Oxygen and fluid from here have to then diffuse into the disc. When we move we create pressure differences across the disc. These pressure differences helps the passage of fluid and oxygen into the disc space.
The back corner of each vertebra has small pegs. Two pegs point upwards and two point downwards. These pegs are the articular processes. The peg of the upper vertebrae hooks onto the peg of the lower vertebrae. There are small joints when the pegs meet each other. These joints are the facet joints. The facet joints add extra stability to the spine.
Sacrum and the sacro-iliac joints
At the very bottom of the vertebral column is the sacrum. In the sacrum the individual vertebrae are not separate. It fuses into a wedge shaped bone. The sacrum wedges into the pelvis. The joints formed when the wedge meets the pelvis on either side is the sacroiliac joint.
Created and designed by Dr. George Ampat, Consultant Orthopaedic Spinal Surgeon
Disclaimer: Dr. Ampat has a commercial interest in Feet and Spine which sells ergonomic office chairs, sit-stand tables, orthotics and comfort shoes.