Coup and Contrecoup: Mechanisms for Injury

Newton's three laws of motion are inescapable drivers of traumatic brain injuries. When the head is in motion for any reason, so is the brain. When a force changes the motion of the head, the brain will continue the original motion until it is stopped (by limitations of movement with spinal cord, cerebrospinal fluid, skull, etc.) and equilibrium is achieved. If the force is small, so is the effect on the brain and equilibrium is achieved quickly. If the force change is strong enough, the brain may continue its movement and be damaged when it slams into the inner layer of the skull (called a coup injury). That slamming force may be strong enough to cause the brain to repel in the opposite direction, causing injury on the opposite side (called a contrecoup injury). Image by Scientific Animations.

Have you ever been bruised by accidentially bumping into a door, getting hit by an object or falling? Now, imagine two fighters in the ring, each taking numerous blows to the head. Our eyes see the results on the face (e.g., blood, bruises, cuts, swelling, damaged cartilage, broken bones), but what is happening to the brain?