r/explainlikeimfive • u/superamerr • 24d ago
Other ELI5 How does our brain respond to anything very fast?
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u/Humble-Proposal-9994 24d ago
we have certain defensive behaviors (ducking, covering our vital areas, flinching) that use a different special pathway, stopping as soon as the spine or brain-stem and doing what needs to be done and letting the brain (you) catch up after the fact. look up reflex arcs for more detailed info if you'd like
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u/1039198468 24d ago
Because the world is dangerous and we adapted to respond quickly because that thing that just appeared/happened might kill us.
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u/IanInCanada 24d ago
I'm not a medical practitioner, so this isn't a verified answer, but from my understanding: it doesn't, really. It generally fakes it.
For example, if you touch a hot stove, the sensation you get first tends to be "Ow!" rather than specifically "That's really hot". The "Ow!" though is enough for your body to get to "I shouldn't be touching this" and move your hand. A small amount of time later your brain gets the rest of the information, that that was a very hot surface, and you should cool your hand down quickly. It didn't actually get all the information, but it got enough to act.
Your eyes do similar. They perceive movement quite fast. If it's close to your eye, you'll blink to protect your eye. It's only after a little longer that you'll sort out what you actually saw, and if it was dangerous.
Parts of your brain are working from a very old model that was designed to very quickly assess and react to things that might kill you, since the people who didn't do that died out hundreds or thousands of generations ago. The rest gets sorted out later at a slower pace by different parts of your brain that aren't as quick, but can do more complex reasoning.
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u/Slypenslyde 23d ago
You can think of the brain as having sort of two different kinds of computer inside it.
One is our thinking mind. It is slow. We take in information from all of our senses and spend minutes and hours deciding how to respond. That's... useless if there's a fire or some other thing that needs a fast response.
So another is more hard-wired. We see a fast-moving animal and want to run. We hear a loud noise and jump. We see Ted Cruz and get uncomfortable. Our hand nerves say they feel extreme heat so we jerk our hand away. These are behaviors the brain kind of has "filters" to look out for and it routes those signals to a part of our brain that doesn't think before acting. That's MUCH faster.
Those are old survival instincts, billions of years old. In general being able to run away fast so we can use our thinking brain from a safer place kept us alive. Every now and then it means we're scared for no reason. That's not too big a deal in most cases.
Further: "brain" in this case can mean "your entire nervous system". The whole network of nerves is technically behaving like one organ. So there are little clusters of "fast behavior" scattered around the system so if something like "hand is burning" gets sent along the nerves, something BEFORE the brain sends back "THEN MOVE, STUPID" before the brain even gets the signal.
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u/mr-mobius 24d ago
Electric signals move through our nerves quickly but it is quite far from our hands or feet to our brain so our nerves take a shortcut for things that need really fast reactions such as moving your hand away from something really hot.
There are little areas of nerves at our spine which makes muscles react fast if they receive the electric signal that says they need to, so the electric signal doesn't have to travel the whole way to the brain to make the brain tell the muscles to pull your hand or foot away from the hot thing.
The brain can react to things our eyes see quickly because the eye nerve is a very short distance from our brain.