The nerves originate in the spinal cord (not shown) and exit the spine at different intervals. The specific nerves control specific sensation, muscle function, pain territories and reflexes. The nerves shown in red form the Femoral Nerve. The femoral nerve produces pain in the front of the thigh or groin or knee. The nerves shown in green form the Sciatic Nerve. The sciatic nerve produces pain in the buttock, back of the thigh, back of the knee and calf. The blue rings are the pedicles, the single numbers are the named level of a vertebra, (e.g. L1 is the L1 vertebra) and the numbers with dashes are the corresponding disc spaces. (e.g. L1-L2 is the disc space between the L1 vertebra and the L2 vertebra. Spinal Stenosis is named based on its motion segment. (e.g. an L4-L5 spinal stenosis is derived from the L4-L5 motion segment). Depending on the level of the spinal stenosis in the spine, and the exact location of spinal stenosis (central,lateral recess, foraminal, extra-foraminal), a single nerve or multiple nerves may be affected.. The spinal nerve anatomy is essentially and electrical wiring diagram. By examining a patient with spinal stenosis, an assessement of the symptoms, physical exam, and diagnostic studies can lead to an understanding of the location of interruption in the wiring diagram. The drawing above demonstrates the nerves on the right side of the spine. The same color coded nerve organization would exist on the left side of the diagram but is not shown to avoid confusion.