Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Muscle Cramps ?
    ### Response:
    Muscle cramps are sudden, involuntary contractions or spasms in one or more of your muscles. They often occur after exercise or at night, lasting a few seconds to several minutes. It is a very common muscle problem.     Muscle cramps can be caused by nerves that malfunction.
    