The primary or immediate injury disrupts the chemical responsible for brain functions, which in turn produces an altered state of consciousness and explains many of the symptoms associated with an initial injury.
Non-traumatic brain injuries (or internal injuries) include cerebral vascular accidents (when blood vessels become clogged), infections, brain tumors or oxygen depravation.
Traumatic brain injuries (or external injuries) are caused by a force outside of the body, such as a blow to the head or face, deceleration ( compression of the brain after an abrupt stop from a high-speed situation), head/neck rotation, cavitation (shock wave through brain matter), or diffuse axonal injury (tearing of brain nerve fibers).
Once the initial injury occurs, secondary injury evolves and can complicate the primary injury. When a primary brain injury is complete, a nonreversible event occurs, triggering a series of subsequent neuro-electro-chemical cascade events (secondary injury) that ultimately end in neuronal cell death. Cascade events include disrupted blood flow (emboli or hemorrhage), swelling (cellular edema), impairment of neuronal chemical messengers, and how the brain uses energy sources.