A closed head injury is an injury to the brain without a breach of the skull or the brain’s surrounding tissues by a penetrating object. Often people in rear end collisions suffer this kind of injury without knowing it.
The biomechanics of a closed head injury can be understood by looking at the inner dynamics of the skull and brain when they are influenced by the forces of acceleration, deceleration and rotation. When the head is suddenly accelerated and then suddenly stopped, like happens in a rear end collision, the resulting motion in not only forward and backward, but also chin down and chin up rotation as the head pivots on the cervical spine. More than 570,000 people receive this type of injury annually.
Two laws of physics play a role in this action. Inertia: the tendency of matter to remain at rest if at rest, and to remain in motion if already in motion. Centrifugal Force: Rotating bodies will move outward, away from the center of rotation.
A magnified view of the brain’s tissues reveals the differences in density between the gray matter layers and the white matter layers. These differences, when combined with the actions of centrifugal force and inertia, cause one layer to slide over the other.
The stretching forces created by these shifting layers can affect axons along the line of varied structural densities. When subjected to the stretching, twisting trauma, the neurofilament system is disrupted at a specific point. Once damaged, it is thought these connections heal with scar tissue and certain brain functions are lost.