The spinal column consists of 33 individual bones termed vertebrae. These vertebrae are stacked upon each other and form the four regions of the spine.
The cervical spine is divided into two sections. The upper cervical region consists of the C1 and C2 specialized vertebrae that are responsible for turning the head. The lower cervical region consists of C3 through C7 and allows for bending of the neck.
The thoracic region consists of T1 through T12. This area forms the trunk of the body and provides a site of attachment for the rib cage. The thoracic spine and rib cage offer protection for the vital organs of the body.
The lumbar region consists of L1 through L5 this area forms the low back which is responsible for supporting the weight of the upper body and movement of the trunk.
The sacral region consist of the S1 through S5 segments which are fused together and the tail bone called the coccyx.
|Region||Number of Bones||Body Area||Abbreviation|
|Cervical||7||Neck||C1 – C7|
|Thoracic||12||Chest||T1 – T12|
|Lumbar||5||Low Back||L1 – L5|
|Sacrum||5||Pelvis||S1 – S5
(Large Fused Bones)
|Coccyx||4||Tail Bone||A small fused bone.|
The vertebral bodies are the weight bearing structures of the spinal column. The vertebrae range in size in accordance with the distribution of weight in the body. Near the head the cervical vertebrae are smaller and the larger lumbar vertebrae are located near the waist.
The spine is arranged in a series of curves which act as a spring absorbing and distributing biomechanical stress. In the cervical and lumbar regions there are C-shaped curves with the opening towards the back of the body. These are called the lordotic curves. The curve in the thoracic and sacral regions open towards the front of the body. These are termed kyphotic curves.
The vertebral segments that are stacked on each other form a vertical tunnel which protects the spinal cord and nerves. This tunnel is referred to as the spinal canal. The spinal cord is a large collection of nerve fibers that extend from the brain through the spinal canal. The cord conducts nerve impulses, acting as a highway between the brain and the body.
As nerves branch off the spinal cord, they exit the spinal column and form the peripheral nerves.
Together, the peripheral nerves and cord are responsible for processing all movements, sensations and other body functions. Damage or pressure on the spinal cord or nerves can cause symptoms of numbness, tingling, burning, pain, pressure, weakness or in severe cases, a loss of function below the site of injury.
The basic component of the vertebral column is called the functional spinal unit. The functional spinal unit is composed of two vertebral segments and the disc between them. This basic structure allows for movement, stabilization, and redistribution of weight through the body using a three joint system. In the front of the functional spinal unit there is one large joint that looks like a sandwich with two vertebral bodies on either side and a large cartilaginous disc in the middle. The intervertebral disc acts as a cushion or shock absorber between the vertebrae. The disc has numerous layers of tough fibrous tissue called the annulus fibrosis. In the center there is a gel-like substance called the nucleus pulposus. A healthy disc will have its fluid rich gelatin fully contained within the walls of its fibrous tissue. This supports the bodies weight during seated positions. In the back of the functional spinal unit there are two specialized joints on either side that prevent movements that could damage the spinal cord and nerves and support the weight of the body during standing postures. The joints of the back are held together by fibrous ligaments and other connective tissues that support and help stabilize the spine.
The muscles are the engines that power the back during movements and help stabilize the trunk on the pelvis. Tendons are a specialized type of connective tissue that attaches muscle to bone.
The back is a dynamic structure with dedicated and specialized tissues designed to support, protect, and allow for movement of the body.