Direct trauma to the brain can occur when the skull strikes, for example, the floor in a fall accident or strikes a steering wheel in a car accident. Although the skull may not be penetrated or fractured in these types of accidents, the forces imparted to the brain can cause the brain to collide against the inside of the hard skull. When a moving head comes to a quick stop, the brain continues in its movement, striking the interior of the skull.
This can cause bruising of the brain (a contusion) and bleeding (hemorrhage). Injury in these types of accidents occurs in parts of the brain closest to the point of impact, quite often the tips of the frontal and temporal lobes. In cases of blunt head trauma the brain can also be injured directly opposite the site of trauma -- on the other side of the brain, an injury known as contrecoup.
This injury typically occurs when a moving head strikes a stationary object like the windshield. At impact the brain opposite the site of impact is pulled away from the skull, injuring the brain.
Traumatic Brain Injury (TBI), which can also be called "acquired brain injury” or simply “head injury” can occur when a sudden trauma causes damage to the brain. TBI can result when the head suddenly and violently hits an object, or when an object pierces the skull and enters brain tissue. Symptoms of a brain injury could be mild to moderate, or severe, depending on the extent of the damage to the brain.