"A good analogy is to think of the spinal cord is like a really thick noodle, surrounded by a sac. Better, think of a thick noodle in water, in a Ziplock bag. IF your disc pushes hard enough, it will deform the bag (THECAL SAC), which COULD affect the nervous system. If it pushes on the noodle (CORD), it WILL affect the nervous system at that level, and what that nerve influences in your body."