Why does a bullet instantly kill someone when through the brain? Why isn’t only part of their functioning impaired?


I know there are plenty of cases in which someone has survived a shot through the brain, or in which only part of their functioning is impaired, but for the most part, why does a bullet randomly aimed at someone’s head kill them nearly instantaneously? Rather than just losing eyesight or the ability to move an arm or leg. Thanks!

In: Biology

It depends on what parts of the brain are damaged. Many parts result in death, some slow and others fast. But there have been cases of someone being shot in the head and it only affecting specific functions, and a few cases of them being shot in a manner that results in little to no impairment.

It also depends on the caliber of the bullet and the speed at which it enters the skull. Low caliber and low speed rounds have the power to enter the skull but not exit, causing them to bounce around inside and turn the brain to soup. And when bullets have enough power to also exit the skull, the force of the exit causes extra trauma on its way out.

Because you are mostly incompressible liquid the bullet creates a shock wave that damages tissues well beyond the actual impacted areas.

As previously mentioned, it depends where the bullet transects. If the bullet can travel in a manner that doesn’t interfere with the motor cortex, movement could possibly be spared. The sheer impact alone may cause loss of consciousness.

Blood vessels being severed is major problem that can and does frequently. The brain receives anywhere from 15-25% of the blood supply. If a major artery is punctured, one can quickly bleed out.

Hopefully that answers your question a little bit.

Most bullets don’t make a perfect bullet size hole through the body, they shatter and along with bone they cause large portions of damage, if the inner part of your brain is damaged its near immediate death, the further the damage is from the main center the higher your chances of survival, but the brain has so many blood vessels even if you survive the initial wound you’d bleed out quickly. Gunshot wounds are still one of the worst wounds you can get and death rates for gunshot wounds to the head are at 90%.

Temporary cavitation, you mught survive with effects like you described from a fairly low power round but anything from a rifle or decent pistol calibre will essentially cause a pressure wake as it travels through turning everything in the surrounding area into mush, not just what’s in the path of the bullet. Think of the wake left beind by a boat as it goes through water except the boat is travelling at several hundred miles an hour and the water is your brain matter.

Beyond what the others already said about brain damage as such, also consider the blood loss. If there is catastrophic drop of blood pressure (which can be caused by damage anywhere in the victims body), then the whole sensitive tissue of brain remains without sufficient oxygen supply. If this lasts for longer than [about 6 minutes](https://en.wikipedia.org/wiki/Cardiopulmonary_resuscitation), then the brain is killed dead without direct mechanical damage.

Bullet often splits into fragments + the fragments of skull. They damage multiple parts of the brain. Yes there have been cases when people have survived headshots but those are very rare and lucky ones in which there were little to no fragments and the bullet/fragments miss the blood vessels of the brain and only damage non critical areas.

Tv and movies always show an instant death but in reality there’s body twitching, similar to beheadings. Your spinal cord can directly control motor functions. Respiration will continue if there is no damage to the part controlling it, the person will eventually die from blood loss and the respiratory center being compromised by the blood loss. The heart keeps beating, as long as there’s enough oxygen and blood, it keeps beating, the heart has a system of nerves independent of the brain.

Real death isn’t caused by the heart stopping, it’s brain death. The brain controls how you breathe, your heart rate, your temperature, sleeping, eating, conduction etc.
If the parts of the brain that control these functions is damaged (brainstem), you die.
When you’re shot elsewhere, you die from blood loss.
Those people who survive a bullet to the brain, will probably have an impairment of some sort (even if it is just a slight change of personality, preferences or facial expression)

It is amazing what people can survive.

Having part of your brain destroyed is not necessarily always fatal.

Up until a couple of decades ago, lobotomies were quite common procedures.

These weren’t always complicated medical procedures but in some cases amounted to little more than telling a patient to sit in a chair taking an icepick inserting into their skull through their eye-socket and then moving it around until a sufficient amount of brain was destroyed. Afterwards the patient could then simply be walked away under their own power.

The part of their brain that made them the person that they had been may have been gone or at least greatly altered and reduced, but more basic stuff remained.

Lots of people get brain injuries of some kind and lose stuff that in some cases they can at least partly relearn and in others is gone forever.

Of course there are some parts oft the brain that are more vital than others.

The thing about guns is that they don’t just destroy the stuff in their path, but also generate a shockwave that travels though the body and mushes parts that weren’t directly hit.

Also once you have a hole in your head, even if the brain isn’t totally destroyed you still have to deal with blood and other stuff leaking out oxygen no longer reaching the parts of the brain that weren’t destroyed outright and lots of other unpleasant things.

Death is rarely a clean on/off thing but if you do enough damage to soothing vital the transition from alive to dead may be quick enough to look that way.

It all comes down to what’s hit and by how much force. Some areas of the brain we can do without (it’s not recommended but it’s possible to function without some parts of the brain) however a lot of the brain we can’t do without and damage to those parts of the brain is usually fatal. The problem with ballistics is weird shit happens when a bullet going really fast hits a solid object. Most bullets upon impacting the skull or body will deform and tumble (called keyholing in the shooting world) this is an intentional as it increases tissue damage and helps ensure what/whoever you shot goes down. I’m sure you can imagine why this happening in your brain cage is a bad thing. There’s also something called hydrostatic shock. The human body is mostly water and water doesn’t compress well the pressure created by the projectile cause further tissue damage. The bigger and faster the round the more this effect comes into play. That said it is 100% possible to survive a head shot (like I said ballistics can get weird) when I was in nursing school one of my teachers told us about the time she saw a young man come into the ER with a gunshot wound to the forehead. Somehow the 9mm bullet didn’t penetrate the skull and instead rode the curve of his skull under the skin exiting out the back of his head and leaving a channel wound several inches long. The kid was still concussed (the force has to go somewhere) but all he needed was stitches and observation.

The brain controls important bodily functions and the bullet stops the brain from performing those functions. That said, I read about Rep. Gabrielle Giffords who was shot in the head and has survived. The doctor said that had both sides of her brain been impacted, she would have died. But the bullet only penetrated one hemisphere of her brain so the other hemisphere was able to maintain enough cognitive functions for her to live. In fact, after the shooting, she was at least semi-conscious within a short time–you can see her adjusting her skirt as the ambulance takes her to the hospital after the shooting. She’s lost a bunch of brain function even so–she’s lost 50% of her vision and she has aphasia (can’t string together more than a few words at a time) because the verbal area of her brain was damaged. Plus one half of her body is partially paralyzed. But she’s made enormous strides in the 10 years since the attack.

When a high speed projectile enters the skull several things happen. Bone fragments are forced into the brain. The projectile can fragment or and deform if a soft metal (lead), and there is a shock wave that traverses through the brain and rebounds off the inside of the skull

These produce trauma to multiple parts of the brain as well as damage to the blood vessels that provide the brain with oxygen and nutrients. Any of these factors can cause death. Some parts can cause death quicker than others. The blood loss, may not cause immediate death, but damaging the part of the brain that regulates the breathing would cause a slow death (2-3 minutes) if the part of the brain that controls the heart is damaged, death would be almost instantaneous if the person wasn’t put on life support immediately (CPR), if parts of the motor functions are damaged, a person could remain ‘brain alive’ but be in a vegetative state unable to respond to the outside world.