Anatomy of the Sciatic Nerve The sciatic nerve is the thickest and longest nerve in your body, running from your lower back all the way down the backs of your legs. Its main job is to help you move and feel things in your legs and feet, controlling muscles and sending sensory signals like touch and temperature. But when this nerve is compressed or impinged, it can cause discomfort - think pain, tingling, numbness, or even weakness in your legs. If you've ever had sciatica, you know exactly how i