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A B M P m e m b e r s e a r n F R E E C E a t w w w. a b m p . c o m / c e b y r e a d i n g M a s s a g e & B o d y w o r k m a g a z i n e 47 FUNCTIONAL ANATOMY education Let's continue to examine structures that distribute forces and absorb impact in the human body. In previous issues, we explored the architecture and function of the pelvic girdle ("Pelvic Girdle Suspension System," November/ December 2017, page 41) and the foot ("Force Distribution in the Foot," January/February 2018, page 44). We continue here with the structure and function of the intervertebral disks. INTERVERTEBRAL DISK ANATOMY AND FUNCTION Intervertebral disks are the rounded layers of connective tissue that lie between each vertebra in the human vertebral column. Each disk is composed of three distinct segments: a fluid center called the nucleus pulposus; a tough, fibrous outer layer called the annulus fibrosus; and thin layers of cartilaginous end plates at the top and bottom. Each segment serves a particular role in fulfilling the overall function of maintaining space between adjacent vertebrae, while simultaneously distributing compressive forces through the vertebral column. Intervertebral Disks By Christy Cael The annulus fibrosus of the intervertebral disk absorbs force and enlarges the space between vertebral bodies The nucleus pulposus of the intervertebral disk is made up of fluid that is displaced as the spine moves. This distributes stresses between vertebrae. Anterior vertebral body Uncovertebral joint with intervertebral disk Annulus Fibrosus The annulus fibrosus is a tough, dense layer of fibrocartilage that contains much higher amounts of collagen than the nucleus pulposus. A complex network of collagen and other supportive fibers provides resistance to tensile forces, elasticity, and architectural "firmness" to the disk. Proper orientation of the fibers protects and properly distributes compressive forces placed on the nucleus pulposus. Though less prevalent than in the nucleus pulposus, proteoglycan production and associated water content is critical to the health and proper function of the annulus fibrosus. Cartilaginous End Plates The cartilaginous end plates are thin layers of hyaline cartilage at the superior and inferior margins of the intervertebral disk. They provide connection between Nucleus Pulposus The nucleus pulposus is a gelatinous segment that contains high levels of proteoglycans and water with lesser amounts of collagen. The water content is variable and chemically controlled by living cells. These cells produce proteoglycans, chemicals that attract and hold water. Healthy intervertebral disks are able to adjust hydrostatic pressure and water content in response to varying amounts of mechanical compression or loading, thus evenly and optimally distributing loads to surrounding structures. It is the high water content that gives the disk flexibility and "height," ensuring adequate space for nutrient diffusion within the disk and preventing compression or impingement of associated soft tissues like nerve roots located between vertebrae.