It is schematic in which you see here between L3-4. This is a disc herniation and you can see this black blob which is impinging upon the 4^th lumbar nerve. This can occur at any level in the back, spinal column. Actually they say that theoretically you can tell which spinal nerve is involved by which particular part of the leg has the pain. This is one of these things that is theoretically true but I think in practice it is very hard to distinguish exactly where it is.