The sources provide an overview of the types and causes of traumatic brain injury (TBI), which is a serious condition that can result from both closed and penetrating injuries. Closed head injuries occur when the skull remains intact, while penetrating injuries involve objects that pierce the skull and enter the brain tissue. Common causes of TBI include falls, motor vehicle crashes, sports injuries, and being struck by an object. The severity of symptoms can range from mild to severe depending on the extent and location of brain damage.