This exhibit shows the mechanism of a coup – contrecoup brain injury and the effects of a diffuse traumatic brain injury on a brain cell. The force of an impact causes the head to suddenly hyperextend backward, while the brain shifts forward and strikes the anterior skull (coup injury). The head then recoils forward and stops sharply, causing the brain to shift backward and strike the posterior skull (contrecoup injury). Diffuse axonal injuries also occur as a result of acceleration forces on the brain. Differing densities between the grey matter (neurons) and white matter (axons) causes them to shift at varying speeds, shearing the axons at the grey-white matter junction.