Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) spina bifida ?
    ### Response:
    Spina bifida is a condition in which the neural tube, a layer of cells that ultimately develops into the brain and spinal cord, fails to close completely during the first few weeks of embryonic development. As a result, when the spine forms, the bones of the spinal column do not close completely around the developing nerves of the spinal cord.
    