Nucleus pulposus is the jelly-like substance in the middle of the spinal disc. It is the remnant of the notochord. It functions to distribute hydraulic pressure in all directions within each disc under compressive loads. The nucleus pulposus consists of chondrocyte-like cells, collagen fibrils, and proteoglycan aggrecans that aggregate through hyaluronic chains. The glycosaminoglycan (GAG) chains of chondroitin sulfate and keratan sulfate are attached to each aggrecan molecule. Aggrecan is negatively charged and hydrophilic. This property allows it to draw water into the Nucleus Pulposus.