The three main functions of the spine are:
Protect the spinal cord, nerve roots and several of the body’s internal organs.
Provide structural support and balance to maintain an upright posture.
Enable flexible motion.
Typically, the spine is divided ito four main parts: Thoracic, lumbar and sacral. Each part has its own characteristics and functions.
The neck region of the spine is known as the Cervical Spine. This area consists of seven vertebrae, which are known as C1 through C7 (top to bottom). These vertebrae protect the brain stem and the spinal cord, support the skull, and allow for a wide range of head movement. The first cervical vertebra (C1) is called the atlas The Atlas is ring shaped and it supports the skull. C2 is called the Axis. It is circular in shape with a blunt peg-like structure (called the Odontoid Process or “dens”) that projects upward into the ring of the Atlas. Together, the Atlas and Axis enable the head to rotate and turn. The other cervical vertebrae (C3 through C7) are shaped like boxes with small spinous processes (finger like projections) that extend from the back of the vertebrae.
Beneath the last cervical vertebra are the 12 vertebrae of the Thoracic Spine. These are known as T1 through T12 (top to bottom). T1 is the smallest and T12 is the largest thoracic vertebra. The thoracic vertebrae are larger than the cervical bones and have longer spinous processes.
In addition to longer spinous processes, rib attachments add to the thoracic spine’s strength. These structures make the thoracic spine more stable than the cervical or lumbar regions. In addition, the rib cage and ligament systems limit the thoracic spine’s range of motion and protect many vital organs.
The Lumbar Spine has 5 vertebrae known as L1 through L5 (largest). The size and shape of each lumbar vertebra is designed to carry most of the body’s weight. Each structural element of a lumbar vertebra is bigger, wider and broader than similar components in the cervical and thoracic regions.
The lumbar spine has more range of motion than the thoracic spine, but less than the cervical spine. The lumbar facet joints allow for significant flexion and extension movement but limit rotation
The Sacrum is located behind the pelvis. Five bones (S1 through S5) fused into a triangular shape, form the sacrum. The sacrum fits between the two hipbones connecting the spine to the pelvis. The last lumbar vertebra (L5) moves with the sacrum.
Immediately below the sacrum are five additional bones, fused together to form the Coccyx (tailbone).
When viewed from the front the healthy spine is straight. (A sideways curve in the spine is known as scoliosis.) When viewed from the side the mature spine has four distinct curves. These curves are described as being either kyphotic or lordotic.
A kyphotic curve is a convex curve in the spine (i.e. convexity towards the back of the spine). The curves in the thoracic and sacral spine are kyphotic.
A lordotic curve is concave (i.e. concavity towards the back of the spine), and is found in the cervical and lumbar levels of the spine.
All vertebrae consist of the same basic elements, with the exception of the first two cervical vertebrae.
Between each vertebrae is a “cushion” called an intervertebral disc. Each disc absorbs the stress and shock the body incurs during movement and prevents the vertebrae from grinding against one another. Each disc is made up of two parts: the annulus fibrosis and the nucleus pulposus.
The annulus is a sturdy tire-like structure that encases a gel-like centre the nucleus pulposus. The annulus enhances the spine’s rotational stability and helps to resist compressive stress. The annulus consists of water and layers of sturdy elastic collagen fibres.
The centre portion of each intervertebral disc is a filled with a gel-like elastic substance. Together with the annulus fibrosus, the nucleus pulposus transmits stress and weight from vertebra to vertebra.
Like the annulus fibrosus, the nucleus pulposus consists of water, collagen and proteoglycans. However, the proportion of these substances in the nucleus pulposus is different. The nucleus contains more water than the annulus.