Paraplegia is loss of feeling and inability to move the lower part of the body. Tetraplegia, formerly called quadriplegia is loss of movement and feeling in both the upper and lower parts of the body.
Sometimes the spinal cord is only bruised or swollen after the initial injury and as the swelling goes down, the nerves begin to work again. Unfortunately, there are no tests to determine how may nerves, if any will work again. Generally, however, the longer there is no improvement, the less improvement will occur. In addition to movement and feeling, SCI affects other bodily functions, such as breathing, bowel and bladder control. It may also affect sexual function. The damage that occurs to spinal cord axons within the first few hours after injury is complex and occurs in stages. Normal blood flow is disrupted, which causes oxygen deprivation to some of the tissues of the spinal cord. Bleeding into the injured area leads to swelling, which can further compress and damage the axons. The chemical environment becomes destructive, due primarily to the release of highly reactive molecules known as free radicals. These negatively charged ions can break up cell membranes, thus killing cells that were not injured initially. Blood cells called macrophages that invade the site of injury to clean up debris may also damage uninjured tissue. Non-neuronal cells including astrocytes may divide too often, forming a scar that impedes the regrowth of injured nerve cell axons. Within weeks or months following injury, cysts often form at the site of injury and fill with cerebrospinal fluid, the clear, watery fluid that surrounds the brain and spinal cord.
Typically, scar tissue develops around the cysts, creating permanent cavities that can elongate and further damage nerve cells. In addition, nerve cell axons that were not damaged initially often lose their myelin, a white, fatty sheath that surrounds groups of axons to enhance the speed of nerve impulses. Scientists are trying to understand how this complex series of disruptive events occurs so they can find ways to prevent and treat it. They are also trying to identify treatments that will enhance some of the normal, but often limited kinds of recovery that can occur after a spinal cord injury. Another complication in spinal cord injury stems from the variety of nerve fibers and cell types that make up the tissue. The downward or descending pathways from the brain in the spinal cord carry nerve signals that control voluntary movements. The upward or ascending pathways carry sensory information–about touch, temperature, pain and body position–from the entire body to the brain. Researchers believe that the ascending and descending pathways, as well as different groups of nerve cells, called neurons in the spinal cord, may require individualized treatments to regenerate and regain their functions.