The sciatic nerve is the longest and widest nerve in the human body. It runs from the lower back, through the buttocks, and down the back of each leg. It is responsible for controlling the muscles of the lower legs and providing sensation to the thighs, legs, and feet. When this nerve is compressed or irritated, it can cause pain, numbness, and weakness in the legs, as well as a tingling sensation in the feet. Sciatica is a term used to describe the symptoms of sciatic nerve compression or irritation.