The first skull acceleration + inertia of the brain led to an impact on the front of the brain, then as the brain and skull move backward the second skull acceleration + brain inertia lead to a second...The first skull acceleration + inertia of the brain led to an impact on the front of the brain, then as the brain and skull move backward the second skull acceleration + brain inertia lead to a second impact on the back of the brain, as illustrated in the following image. The alternating accelerations of the skull and the inertia of the brain combine to cause impacts on opposing sides of the brain during a coup contrecoup injury.
