system
Given the following post, respond as if you're commenting on Reddit:
human
This may sound dumb, but why when a human gets shot in the brain its an instantaneous death?

I understand a bullet to the brain would kill u very fast but why is it immediate and why can't surgeons retract the bullet and cauterize the vessels as any other part of the body? I'm not looking for answers like "because it's the control center". I would appreciate a detailed answer. Thank you.
gpt
It's not necessarily instantaneous death, but it can very well be. The difference is in the degree of disruption.

A bullet passing through the skull imparts a great deal of its kinetic energy on the substance of the head. Depending on the closeness of the gun, expanding vapors may also accompany the bullet. The brain itself is very gelatinous and not all that sturdy. A bullet dumping a great deal of its kinetic energy into the brain, and into skull fragments that get dragged through the brain, will disrupt the structure of the brain pretty badly. Even apart from the actual bullet track, pressure waves traveling outward from the path will disrupt white matter tracts in the brain. Excess pressure will also have an overall negative effect because the skull presents an essentially rigid structure. What's more, the brain is very metabolically active and the lack of blood from damaged vessels can lead to irreversible injury in a matter of minutes.

In the end, what constitutes death is a fraught question. In places where brain death criteria are recognized, it's irreversible death of the whole brain. Getting shot in the head, unless with a projectile that essentially obliterates the entire brain, is unlikely to cause instantaneous death of the whole brain. Brain stem cells, for instance, would likely survive for some time. But consciousness is typically lost because the wide-scale projections of the ARAS (ascending reticular activating system) are disrupted, and the injury itself may lead to rapid death of most of the brain, herniation of the brain stem, and other effects, leading to an irreversible loss of function.

Some people do survive the initial gunshot. I've seen them in the neurosciences ICU. They do surgery, remove dead tissue, possibly leave the skull open in the event of swelling, and do aggressive intracranial pressure monitoring in the unit. The people who survive are often fairly devastated because of the brain that they lose.