A nerve is a cordlike structure composed of fibers that conduct sensory and motor impulses between the brain and spinal cord and other areas of the body. Nerve fibers can convey sensory signals to the brain from the skin or organs (afferent nerves) or conduct stimulatory signals from the brain to the muscles (efferent nerves).
Back pain commonly arises when the nerves are pinched. The two nerves in the spine most commonly pinched are L5 (lumbar 5) and S1 (sacral 1), which cause weakness in the muscles responsible for foot push off. Nerves need both inflammation and pressure to be painful, so either relieving the inflammation or the pressure can relieve the pain.