The lumbar nerve roots originate in the spinal cord (not pictured) and travel in the spinal canal. The L5 and S1 nerve roots exit to form the sciatic nerve. In this diagram only one pair of nerve roots are shown (L5 and S1) but another pair would exist on the opposite side as well. The L5 and S1 nerve roots exit the spine and form the sciatic nerve. Different conditions can effect the L5 and S1 nerve roots and thus produce sciatica.

Problems outside the nerve fluid filled sac (extradural)		Problems inside the nerve fluid filled sac (intradural)
Herniated Disc Spinal Stenosis (Bone spur) Spondylolisthesis Synovial Cyst Tumors Infection		Tumors Infection Inflammatory (Arachnoiditis)

The different causes of sciatica (pain radiaitng down the back of the leg) should be consdered in patients with leg pain.