Head injuries range from minor trauma to concussions, unconsciousness and death. Traumatic injury to the brain can cause bleeding on the surface of the brain or within the brain. The brain can be permanently damaged by this trauma. Coma occurs when the central portion of the brain is unable to activate or stimulate the rest of the brain to wakefulness or when there is extensive injury to the brain. Head injuries can also produce fractures of the skull. Depressed skull fractures can cause a piece of bone to penetrate or deform the brain. Basilar skull fractures involve the base of the skull. They can injure the nerves that pass through these regions and produce cerebrospinal fluid leaks.