Brain damage splits into the hit and the aftermath
Brain injury destroys or degrades neural cells through blows, falls, stroke, infection, or lack of oxygen. Traumatic injury from outside force is the most common form. Doctors separate the primary mechanical insult from secondary cascades that unfold afterward.
Clinicians sort brain damage along several axes at once. Acquired injuries happen after birth, unlike congenital ones a person is born with, and trauma to the head is the most frequent route. Timing matters: the primary injury is the mechanical deformation at the instant of impact, while secondary injury follows from the body's own reactions, such as oxygen starvation, swelling, fluid build-up in the ventricles and rising pressure inside the skull.
Location is the other big divide. Focal damage is confined to one region and shows up as bleeds, bruises of brain tissue and haematomas above or below the dura. Diffuse damage spreads across many regions through torn axons, lack of oxygen or blocked blood supply. When both are severe, the focal kind kills more often, with mortality near 40 percent against about 25 percent for diffuse injury, yet diffuse injury is the more likely to leave lasting cognitive and neurological deficits.
What a person loses depends heavily on where the lesion sits. Damage to Wernicke's area can leave someone fluently producing invented words while struggling to understand speech; injury to Broca's area strips out small grammatical words and disrupts reading and writing. A lesion in the fusiform gyrus can erase the ability to tell faces apart, harm to region V4 can remove colour vision, and bilateral damage to MT/V5 can make motion invisible. A mild blow, a concussion, may bring only headache, ringing ears, fatigue and poor concentration, which patients often fail to link to the knock.
Recovery is possible because the brain rewires itself, building new connections that take over from damaged tissue, and therapy plus practice helps people relearn movement and speech. Longer-term risks include seizures, Parkinson's disease, dementia, depression and personality shifts toward higher neuroticism. At the far end, brain death is declared only when there is no brain activity 24 hours after resuscitation, no brainstem reflexes and no attempt to breathe despite high carbon dioxide.
Source: Brain injury
