Context: Injuries to the central nervous system may damage tissues of the brain or spinal cord. If an injury is mild, a person may have a full recovery. If an injury is severe, it may cause permanent disability or even death. Brain and spinal cord injuries most commonly occur because of car crashes or sports accidents. The best way to deal with such injuries is to try to prevent them. Brain injuries can range from mild to extremely severe, but even mild injuries need medical attention. Brain injuries can result from falls, car accidents, violence, sports injuries, and war and combat. Falls are the most common cause of brain injuries, particularly in older adults and young children. The mildest and most common type of brain injury is a concussion. This is a bruise on the surface of the brain. It may cause temporary problems such as headache, drowsiness, and confusion. Most concussions in young people occur when they are playing sports, especially contact sports like football. Other sports, like soccer, boxing, baseball, lacrosse, skateboarding, and hockey can also result in concussions. A concussion normally heals on its own in a few days. A single concussion is unlikely to cause permanent damage. But repeated concussions may lead to lasting problems. People who have had two or more concussions may have life-long difficulties with memory, learning, speech, or balance. For this reason, concussions are treated very seriously among athletes and in professional sports. You can see an animation of how a concussion occurs by visiting A person with a serious brain injury usually suffers permanent brain damage. These brain injuries usually occur when an external mechanical force, such as a violent blow or jolt to the head or body, causes brain dysfunction. An object penetrating the skull, such as a bullet or a shattered piece of the skull, also can cause traumatic brain injury. As a result, the person may have trouble talking or controlling body movements. Symptoms depend on what part of the brain was injured. Serious brain injuries can also cause personality changes and problems with mental abilities such as memory. Medicines, counseling, and other treatments may help people with serious brain injuries recover from, or at least learn to cope with, their disabilities. Symptoms of severe brain injuries include the loss of consciousness from several minutes to hours, profound confusion, slurred speech, the inability to awaken from sleep, seizures, loss of coordination, persistent headache or headache that worsens. A spinal cord injury is damage to any part of the spinal cord or nerves at the end of the spinal canal. This injury often causes permanent changes in strength, sensation and other body functions below the site of the injury. Spinal cord injuries make it difficult for messages to travel between the brain and body. They may cause a person to lose the ability to feel or move parts of the body. This is called paralysis. Whether paralysis occursand what parts of the body are affected if it doesdepends on the location and seriousness of the injury. In addition to car crashes and sports injuries, diving accidents are a common cause of spinal cord injuries. Quadriplegia means your arms, hands, trunk, legs and pelvic organs are all affected by your spinal cord injury. Paraplegia means the paralysis affects all or part of the trunk, legs and pelvic organs. These people can still use their arms and hands. Some people recover from spinal cord injuries. But many people are paralyzed for life. Thanks to the work of Christopher Reeve ( Figure 1.1), more research is being done on spinal cord injuries now than ever before. For example, scientists are trying to discover ways to regrow damaged spinal cord neurons. If you suspect that someone has a back or neck injury: dont move the injured person as permanent paralysis and other serious complications may result, call 911 or your local emergency medical assistance number, keep the person very still, place heavy towels on both sides of the neck or hold the head and neck to prevent them from moving, until emergency care arrives, provide basic first aid, such as stopping any bleeding and making the person comfortable, without moving the head or neck. 
 Question: what is the most common cause of brain injuries?
Output: falls