Invertebral Discs

The invertabral Discs make up one fourth of the spinal column's length. There are no discs between the Atlast (C1), Axis(C2) and Coccyx. Discs are not vascular and therefour depend on the plates to diffuse needed nutrients. The cartilaginous layer of the end plates anchor the discs in place.

The invertabral Discs are fibrocartilaginous cushions serving as the spine's shock absorving system. which protect the vertebrate, brain, and other stuctures. The discs allow some vertebral motion : extensions and flexion. Individual discs movement is very limited.

Annulus Fibrosus and Nucleus Pulposus
Invertebral discs are composed of an annulus and a nucleus pulposus.

The annulus fibrosus is a strong radial tire - like structure made up of lamellae; concentric sheers of collagen fibers connected to the vertebral end plates. The sheets are oriented at various angles. The annulus fibrosus encloses the nucleus pulposus.

Although both the annulus fibrosus and nucleus pulposus are composed of water, collagen, and proteoglycans (PGs) is greatest in the nucleus pulposus. PG molecules are important because they attract and retain water. The nucleus pulposus contains a hydrated gel - like matter that resists compression. The amount of water in the nucleus  varies throughout the day depending on activity.