reaction. This is one of my favorite videos on YouTube. This is from youtube.com/RussiaToday.

So we got this person here walking down the street. All of a sudden they realize there's

a car coming and then they get out of the way. Now if I were to keep playing it the

guy jumps out of the car, comes running in this direction. But basically I want to talk

about what's going on. So once this guy sees the car, how does he number one get out of

the way? And then how does that affect his body? How does that affect the organs and

the chemistry and all of that inside his body. And so that whole thing is called the fight

or flight. And so when I ask students, you know, how does he get out of the way of the

car? The answer is always adrenaline. And the right answer is no, it's not adrenaline.

Adrenaline is not going to be able to get there that quickly. And so how does the guy

really get out of the way? Well, he's going to see the car coming. He's going to process

that in his brain. And then he's going to send a message down his nervous system. That

nervous system is going to be attached to muscles. And those muscles are going to have

ATP ready to go. And so the way he's able to jump out of the way and not get hit by

the car, doesn't have anything to do with the fight or flight response. It's simply

his nervous system, his muscles and just responding to that threat immediately. But if you've

ever been in a situation like that, where you just barely survive an accident or something

like that, all of the sudden you feel this rush of just your heart starts beating fast

or your breathing. You feel warm. Now that's part of the fight or flight response. Because

this guy right here, since he's living in a city, is able to just kind of walk back

on to the road and keep about his business. But back in the day if you were attacked by

a mountain lion or somebody else, you had to fight now. You had to flee. Or you had

to attack the attacker. And so all of that is part of what's called the sympathetic nervous

system. Or that system inside our body that allows us to fight or flight. And so let's

zoom inside this guy and talk a little bit more about how are the fight or flight works.

And so it's basically centered around his brain. And so in the center of his brain,

near the bottom we have something called the hypothalamus. So the hypothalamus, in that

area of the brain, is essentially going to send a signal. Now that signal, not only are

we getting signals that are going to the muscles that allow you to move, but it's going to

send a signal all the way down a nervous signal all the way down here. Because in the center

of our adrenal gland we have something called the adrenal medulla. It's connected nervously

to the brain. So the moment he sees that car and realizes he might die, there's a signal

being sent to the adrenal medulla or the center of the adrenal gland. It's going to give off

what's called adrenaline. And that adrenaline is epinephrine. Epinephrine is a chemical

signal that is going to be attached to the circulatory system. And so it's going to course

through the body. So as his heart beats faster and faster and faster epinephrine is going

to flow throughout the rest of the body. Now epinephrine is not going to go into the cells

of the body. It's simply going to, if we say this is a big liver cell, it's simply going

to bind to proteins on the surface of those cells. And so what's it going to do to the

liver? Well in the liver what it's going to do is it's going to trigger a signal transduction

pathway that's going to convert glycogen, glycogen that's found inside the cells of

the liver. And it's going to use that as glucose. Why is it doing that? Well glucose is our

energy supply and so now glucose is going to be coursing through our body along with

epinephrine. And so now we have a supply of energy so we can quickly breakdown that glucose.

Get ATP and we can do more out of it. But what's interesting is that epinephrine is

going to go other places in the body. And it's going to have different responses depending

on where it goes. And so what is epinephrine going to do to the cells that are in control

of the breathing? The cells of the lung. It's going to speed up that breathing rate. What's

epinephrine going to do when it goes to the cells of the heart? It's going to speed up

the rate of the heart beat. And so it's going to trigger a signal transduction pathway in

the heart that's very similar to the signal transduction pathway that we find in the liver

cells. However it's going to have a different response inside the cells. It's going to not

release glucose, but it's going to increase the rate of the beating of those cardiac cells.

What do you think would happen to the digestive system? Well epinephrine is going to go there

as well. But what it's going to do is it's going to vasoconstrict. So it's going to slow

down digestion. And so it's going to slow down those blood vessels that feed those areas

that allow us to breakdown and digest food. Because when you're getting out of the way

of a car or fighting an attacker, you don't really need to concentrate on breaking down

that bagel that you ate for breakfast. So it's going to shut that down. But it's going

to go to the muscles of your body. And it's going to vasodilate. And so it's going to

move more blood to those areas. And so our whole body is designed so we can have one

signal, that epinephrine, but it can have all these different responses throughout the

rest of the body. And so that's going to allow our body to respond to that threat. And that's

why your heart races. You breathe faster. Your pupils dilate. All that happens and you

can thank epinephrine for that. And it's that chemical response and the different either

gene expression or signal transduction pathways that we have as a result. And so I hope that's

helpful.