Closed head injury is almost always the consequence of an impact to the head, hospitals in The Bronx and Brooklyn have noted. There are experiments and references, however, that relate to brain injuryin non-impact situations, such as when the body is accelerated in such a manner as to cause injury. For now, the basic distinction to be focused upon is the difference between an impact to the head and an impulse transmitted to the head from the neck.
An impact or an impulse can accelerate or decelerate the head to the point of injury, but the effects of an impact are usually very clear. A deformation of the skull or a fracture can occur, with the attendant injury to the brain. Doctors have seen that brain injuries are almost always the result of an impact to the head or to a helmet protecting the head, rather than an impulse transmitted through the neck.
Some research has indicated to experts that brain injuries may different depending upon whether the head is stationary and struck by a moving object, or is moving and strikes a stationary object. This matter is important for legal concerns when it must be determined if an injury was caused by a blow to the head or by striking the head in the resulting fall. Physicians have noted, however, that when the head is moving, it generally strikes and object much more massive than itself, whereas a moving object that strikes that head is generally of a similar or lesser mass to the head itself, such as a club, a brick, or a baseball.