The spine is the primary support of the body. It helps to connect other bony structures. The spine is made up of individual bone segments (vertebra), ligaments, and discs. There usually are 33 vertebrae in the spine, seven cervical, 12 thoracics, five lumbar, five fused sacral, and four fused coccygeal. In between these vertebrae are the intervertebral discs. T
here are normally 25 discs in the spine: 7 in the cervical region, 12 thoracics, five lumbar, and one sacral. Each disc is made up of 3 main components. These components include the nucleus pulposus (NP), the annulus fibrosis (AF) and the cartilaginous endplates (CEP) The annulus fibrosis is a structure that wraps around the nucleus pulposus and is made up of collagen-rich tissue. The cartilaginous endplates are composed of a small amount of hyaline cartilage that is located between the vertebral endplate and the NP. These cartilaginous endplates play multiple roles such as acting as a mechanical barrier and supporting nutrient transport for the intervertebral disc.
The NP is the inner gel-like portion of the intervertebral disc. It is essential in giving the spine its mechanical flexibility and strength. It is mainly composed of water (66%-86%) and type II collagen. Also, it has proteoglycans as well as small cartilage-like cells interspersed throughout. These proteoglycans are helpful in retaining water in the NP which helps create its gel-like consistency.