TBI is caused by the application of an external force and transfer of energy from the environment to brain tissue above the amount that can be absorbed without structural damage and/or physiological disruption. Because of its large size, the human brain is particularly prone to an additional mechanism of injury from acceleration and deceleration forces. Such forces produce a combination of rotational and linear movements of the brain; Forces generated by a rotational movement can cause shearing of axons and neuronal cell bodies.