Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Sciatica ?
    ### Response:
    Sciatica is a symptom of a problem with the sciatic nerve, the largest nerve in the body. It controls muscles in the back of your knee and lower leg and provides feeling to the back of your thigh, part of your lower leg, and the sole of your foot. When you have sciatica, you have pain, weakness, numbness, or tingling.
    