A concussion is a brain injury, caused by either a direct blow to the head or a hit to some other part of the body that causes a whiplash type motion of the neck & head. Imagine the brain as the yolk of an egg, nestled comfortably in its shell and protected by the egg white. When the yolk is moved quickly and violently, it smashes into the rigid shell – the same with your brain inside the skull.
A concussion is not a structural injury to the brain, but rather, it is a functional injury. That is why concussions do not show up on MRI or CT scans. The brain has to be in perfect balance or equilibrium in order to function at its fullest potential. A concussion results in a disequilibrium or shift in metabolic need which then results in impaired brain function, and causes symptoms.