Annulus fibrosus
- Attaches to the cartilaginous endplates via collagen fibers, which run obliquely at a 30° angle to the surface of the vertebral body and in a direction opposite to the annular fibers of the adjacent layer.
Nucleus pulposus
- Glycosaminoglycans and type II collagen
- can bind large amounts of water.
- In a normal healthy disc, loads acting on the disc are transferred to the annulus by intradiscal pressure generated by the nucleus.
- With aging, then nucleus binds less water and becomes dehydrated resulting in increased loading of the annulus.
- Fissuring and disruption of the annulus predisposes to herniation of nuclear material through it.
- The nucleus pulposus is an immunologically privileged site
- is isolated from the vascular and immune systems by the annulus fibrosus and cartilaginous endplates
Blood Supply of the Intervertebral Disc
- Nucleus Pulposus and Inner Annulus:
- These regions are avascular
- Nutrients and oxygen are supplied mainly by diffusion from adjacent vertebral endplates.
- Outer Annulus Fibrosus:
- Receives a limited blood supply from small capillaries that penetrate the outermost layers.
- These originate from branches of adjacent vertebral bodies and surrounding soft tissues (such as the anterior and posterior longitudinal ligaments).
Nerve Supply of the Intervertebral Disc
- Outer Annulus Fibrosus:
- Innervated by sensory nerve fibers, mainly from the sinuvertebral nerves (recurrent meningeal branch of the spinal nerve).
- Additional Nerves:
- Some nerve fibers come from branches of the gray rami communicantes and sympathetic trunk.
- These nerves are responsible for pain sensation, especially in pathological conditions.
- Nucleus Pulposus and Inner Annulus:
- Essentially devoid of nerve supply under normal conditions; only the outer third-to-half of the annulus is innervated.
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