Spinal cord injuries occur when a person's spinal cord is harmed by an accidental or intentional trauma. Spinal cord injuries vary in intensity depending on the degree of harm done to the spinal cord and where on the spinal cord the injury occurs. Spinal cord injuries that occur to the sacral nerves on the lower back can affect bladder and bowel function and sexual function. Injuries that occur to the lumbar nerves on the lower to middle back affect the legs. If the thoracic nerves of the middle to upper back are affected then the chest and abdominal muscles may be paralyzed. Finally, if the cervical nerves in the neck are affected then the head, neck, diaphragm and arms may be paralyzed.