Sciatica refers to the nerve pain resulting from an injury or irritation to your sciatic nerve. Sciatica is not a condition, but rather a symptom of another problem involving the sciatic nerve. 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 legs, ending just below the knee. The sciatic nerve controls several muscles in the lower legs and supplies sensation to the skin of the foot and the majority of the lower leg.