When a person with a head injury arrives at the hospital, doctors and nurses first check life signs: cardiac work, blood pressure and breathing. For those who do not breathe satisfactorily, a extractor fan may be required. Doctors immediately assess the patient's state of mind and memory. They also test the brain's basic functions by checking the size of the pupils and their response to light, assessing reactions to sensations such as heat and stab of the needle, and testing the ability to move their arms or legs. Computed tomography or magnetic resonance imaging is required to evaluate possible brain injury. Traumatic brain injury occurs when an external mechanical force causes brain dysfunction. Brain trauma is usually the result of a violent hit to the head. An object that pierces the skull, such as a bullet, can also cause brain trauma. Mild trauma can be caused by temporary brain cell dysfunction. More serious brain trauma can lead to bruising, torn tissue, bleeding and other physical injuries to the brain, which can result in long-term complications or even death. Head injuries are the cause of disability and death of people under the age of 50, more than any other type of neurological impairment. Nearly half of people with severe head injuries die. The brain can be damaged even when the skull is not pierced.