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Current time:0:00Total duration:7:44

Video transcript

so here's a brain I sketched out ahead of time and I wanted to label a couple of parts of this brain now we're going to talk about right now so the first is the pons and the second is what we sometimes call the medulla or you might even hear the term medulla oblongata and it's right right next to the pons kind of right there and people have actually studied these parts of the brains the pons the medulla oblongata they found that there are actually little little respiratory centers and I'm actually shading them on green and sometimes you might even see these areas subdivided but the idea is that there are a couple of spots here where the neurons in these green locations are very very important to our breathing and so they call them respiratory centers and even though I'm drawing it as kind of a green blob these are story centers are really just a bunch of neurons packed together right so many many neurons I'm going to draw a couple of them for us just to kind of illustrate the point and these neurons are going to put out their little feelers and they're going to try to collect information that's basically what they're doing they're going to collect information but all sorts of things like pain you know are youing anxious or you're running late for an exam you know what is the situation going on right now and they're going to make a decision about how fast we should be breathing how often we should be breathing all that kind of stuff so where do they get the information from exactly the information they need I'm actually going to draw in a couple of important neurons right here in the medulla and they're actually going to be these neurons that we're going to be talking about right now so these neurons are called the central chemoreceptors and that's the focus of our video today so central chemoreceptors are what we're going to be discussing and these guys let me just draw a little bit bigger they're basically neurons right so I'll draw a couple of them these neurons are going to be projecting their little axons all the way over to the restroom center and they're going to communicate their message through neurotransmitters which are basically these are kind of the language of neurons right neurotransmitters allow neurons to talk to one another so what we're going to see is that these central chemoreceptors are going to collect information about a chemical and that's why they're called chemoreceptors and just to back up a second they're called central because they're part of the central nervous system right there in the medulla oblongata itself they're there physically right there in the brain so that's why we call them central chemoreceptors and the first chemical that they're going to recept or receive information about is going to be carbon dioxide so like any cell these neurons are making carbon dioxide and where does it usually go where where would you assume that this waste product would go well of course there's a blood vessel right this blood vessel is going to have less carbon dioxide we presume maybe just a couple molecules of it and so you'd have this nice little gradient where the co2 is going to go into the blood and get swept away and of course eventually I'm going to make its way to the lungs and you might breathe it out but let's assume for a second that the levels of co2 in the blood are very high let's assume that the partial pressure of carbon dioxide in the blood is really really high what would that mean well let me draw you know a bunch of carbon dioxide molecules in this blood and what that means is that of course is gradient this wonderful little gradient that we had is going to not be so strong anymore right now there's no strong diffusion gradient because the the differences in pressure are negligible right there's a lot of co2 in the blood a lot of co2 you know around the neurons in the interstitial space that's this space right here interstitial space so because that gradient is not as impressive we let me write fluid instead of space because the gradient is not as impressive you're going to have more carbon oxide kind of building up around these central chemoreceptors in fact you might even have some molecules of carbon dioxide that are building up within the neurons the central chemoreceptors neurons so these chemoreceptors are going to notice the extra carbon dioxide and they're not going to like it one bit so you know what they're going to do they're going to start firing action potentials let's say usually they fire two action potentials let's say one second I'm just assuming that number that that's not the true number but let's just assume that now that the carbon dioxide levels are high they're going to fire off maybe six action potentials in that same time frame so all of a sudden they're firing more action potentials because they don't like the high co2 levels that they're facing so these respiratory centers are going to get this message loud and clear and they're going to say wow we need to do something maybe we need to do something in the way of making this person breathe faster for example so this is one of the many things that you might see happen is breathing faster so you can see how this signal might work now you remember we talked about the relationship between co2 and water we said that co2 binds to water in that they form carbonic anhydrase h2 co3 and that is actually in turn going to form bicarbonate right so it's going to form this so if you have high levels of co2 now if you have high levels over here you can also assume high levels of protons and that's just another way of saying a low pH so the two things that are central chemoreceptors respond to then are one high levels of co2 and the other thing they respond to would be high levels of protons or a low pH now what they don't respond to and this is actually very important what they don't respond to is oxygen levels so they don't respond to low oxygen levels and this is actually a difference between the central chemoreceptors and the peripheral chemoreceptors so this is something to keep in mind now a final point I want to make is that you want to show you a three-dimensional view of the same thing we just talked about so let's let's take this picture and kind of absorb it this is a picture I drew out a little bit earlier some of the important features are going to be let's orient ourselves first to the central chemoreceptors that's this guy right here actually I think there are two of them here so central chemoreceptors and they have of course a starring role in this picture that's this guy right here and of course there's a second fellow right there we also have our astrocytes these are kind of important cells for structural support and they are also important in setting up what we know is the blood-brain barrier so that's right here right I'm going to focus in on this right here and the blood-brain barrier of course allows us to keep what's going on in the blood separate in many ways from what's going on in the interstitial fluid around the brain so then to quickly recap if there's a lot of co2 in here if in this blood vessel you see high levels of co2 you're not going to get much diffusion into that into that blood vessel so co2 levels start going up all around our two central chemoreceptors they're not going to be too happy and so they're going to start firing more action potentials towards our respiratory centers down these two axons I hope you enjoyed that