The spine’s remarkable and complex anatomy is explained below. From a patient's point of view, it is important to have a basic understanding of its anatomy and functions so you can better understand your care and become a partner in your healthcare.
WHAT ARE THE FUNCTIONS OF THE SPINE?
- There are four (4) main functions of the spine;
WHAT ARE THE REGIONS OF THE SPINE?
- There are four (4) regions of the spine;
Let's take a slightly closer look at your spine and its four (4) regions: cervical, thoracic, lumbar and sacral.
While reading, it is a good idea to know what a vertebrae is.
Vertebrae are bones (approx. 33) which are separated by intervertebral discs.
-More on vertebrae & intervertebral discs below.
The neck region is the Cervical Spine. This region consists of seven vertebrae, which are abbreviated 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 supports the skull. C2 is called the Axis. It is circular in shape with a blunt tooth-like structure (called the Odontoid Process or dens) that projects upward into the Atlas. Together, the Atlas and Axis enable the head to rotate and turn. The other cervical vertebrae (C3-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 12 Thoracic vertebrae abbreviated T1-T12 (top to bottom). T1 is the smallest and T12 is the largest thoracic. The thoracic vertebrae are larger than the cervical bones and have longer spinous processes.
Rib attachments add to strength and stability of the thoracic spine. The rib cage and ligaments limit range of motion and protect many vital organs.
The Lumbar Spine consists of 5 vertebrae abbreviated L1-L5. The lumbar vertebrae are the largest and carry most of the body’s weight. This region allows more range of motion than the thoracic spine, but less than the cervical. Lumbar facet joints enable significant flexion and extension movement, but limits rotation.
The Sacrum is located behind the pelvis. Five bones, abbreviated S1-S5, fused into a triangular shape, form the sacrum. The sacrum fits between the two hip bones connecting the spine to the pelvis. The last lumbar vertebra (L5) articulates (moves) with the sacrum. Immediately below the sacrum are five additional bones, fused together to form the Coccyx (tailbone).
As briefly stated above, vertebrae are the approx. 33 bones separated by intervertebral discs which make up the spine (vertebral column). All vertebrae share a basic common structure. They each consist of an anterior (closest to front) vertebral body, and a posterior (further back) vertebral arch.
Vertebrae are the weight-bearing components of the spine, and vertebrae in the lower portion of the column have larger bodies than those in the upper portion (to better support the increased weight).
Adjacent vertebral bodies (see chart) are separated by an intervertebral disc.- More on intervertebral disc below.
The vertebral arch forms the lateral (side) and posterior (back) aspect of each vertebrae.
In combination with the vertebral body, the vertebral arch forms an enclosed hole – the vertebral foramen. The foramina of all the vertebrae line up to form the vertebral canal, which encloses the spinal cord.
The vertebral arches have several bony prominences, which act as attachment sites for muscles and ligaments.
Between each vertebral body 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. The intervertebral discs are the largest structures in the body without a vascular supply. By means of osmosis, each disc absorbs needed nutrients.
Each disc is comprised of two (2) parts: The annulus fibrosus and the nucleus pulposus.
The annulus is a sturdy tire-like structure that encases a gel-like center, the nucleus pulposus. The annulus enhances the spine’s rotational stability and helps to resist compressive stress.
The annulus is a layered structure consisting of water and sturdy elastic collagen fibers. The fibers are oriented at different angles horizontally similar to the construction of a radial tire. Collagen consists of fibrous bundles made of protein bound together by proteoglycan gel.
The intervertebral discs are the largest structures in the body without a vascular supply. Through osmosis, each disc absorbs needed nutrients.
The center portion of each intervertebral disc is a filled with a gel-like elastic substance. Together with the annulus fibrosis, the nucleus pulposus transmits stress and weight from vertebra to vertebra.
The structural components of the nucleus pulposus is similar to the annulus fibrosus; water, collagen and proteoglycans. The difference is the concentration of these substances. The nucleus contains more water than the annulus.
The top (superior) and bottom (inferior) of each vertebral body is coated with an endplate. Endplates are complex structures that blend into the intervertebral disc and help hold the disc in place.
The intervertebral disc is a fibrocartilaginous cylinder that lies between the vertebrae, joining them together. They permit the flexibility of the spine, and act as shock absorbers. In the lumbar and thoracic regions, they are wedge-shaped and support the curvature of the spine.
Each vertebral disc has two parts: the nucleus pulposus and annulus fibrosus. The annulus fibrosus is tough and collagenous, and it surrounds the jelly-like nucleus pulposus.
Herniation of an intervertebral disc occurs when the nucleus pulposus ruptures, breaking through the annulus fibrosus. The rupture usually occurs in a posterior-lateral direction, after which the nucleus pulposus can irritate nearby spinal nerves – resulting in a variety of neurological and muscular symptoms.
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