The reticular activating system (RAS) is located in the middle of your brain and helps to regulate your sense of awareness and consciousness. Some signs of concussion may not appear for several hours after the injury and may persist for several days or weeks.
If the brain does bang against the skull — for example, due to a fall on a sidewalk or a whiplash-type of injury — it can be bruised, blood vessels can be torn, and the nerves inside the brain can be injured and these injuries can lead to a concussion. The best way to evaluate a person’s head injury is with a CT scan and when is used for a head injury, the doctor will look for evidence of bleeding under the skull or within the brain tissue itself.