National Center for Voluntary Action

Transcription

So in this video what I wanted to focus on is one particular area of the brain-- actually, two areas I'm going to sketch out, not just one. I'm going to show you how I think that these two areas can be kind of united in a way. So, these two areas, where I'm sketching out these little green circles, are going to be responsible for breathing-- how fast you breathe, how deep you breathe. And there are lots of little neurons in these two areas. And these neurons are going to be communicating. Let's say this neuron sends a little axon on down here, maybe this guy sends an axon up here. They're going to be communicating information among themselves and between themselves to kind of make sure they're working in a coordinated way so that the breathing that you do is the way that it should be, you know, how fast it should be, given a particular situation. So the way I think of it is kind of uniting these two areas. In fact, sometimes it's subdivided even further. I just put it all together and say this part of the brain that I'm just sketching out in green, this area then, is our respiratory center. This is going to be responsible for all of the important activities of breathing. So let me just write that out here. Respiratory center. So our respiratory center is going to gather information from different places. And then it's going to have to make a decision and execute based on all the information it receives. So one key piece of information is going to come from cells right here, neighborhood cells. And these cells are called the central chemoreceptors. The reason I'm calling them central is because they're also part of the brain, right? They're right in the same neighborhood, and so these central chemoreceptors don't have to go too far to communicate their information. And specifically they're going to gather information on things like carbon dioxide levels and pH levels. One thing they don't do is oxygen levels. So that's these guys right here. So if you have central chemoreceptors you also probably can expect that there would be some peripheral chemoreceptors, and these ones are also very important. And they exist outside of the brain, so they're going to be actually sending their information along through neurons that are going to extend all the way into the brain. So for example, you might have two key groups. One is called the aortic body and the other is called the carotid body. Aortic body and the carotid body. They're coming from different locations and are actually going to use different nerves to get into the brain. So the carotid body, for example, is going to extend out this way through a neuron. And that's going to be through a nerve called the-- right here-- called the glossopharyngeal nerve. This is cranial nerve number nine, also called the glossopharyngeal nerve. So this is one of the key peripheral chemoreceptors. You've also got some nerves or neurons projecting from the aortic body going through the vagus nerve. So this is our vagus nerve, or cranial nerve number 10. It goes by two different names. These peripheral chemoreceptors are going to detect things like oxygen-- in fact, that's probably one of the most important things they detect-- as well as carbon dioxide and pH. So that's information coming to the respiratory center from our peripheral and central chemoreceptors then is mostly about chemicals. In addition, there's another whole group of receptors called mechanoreceptors. And these ones are actually going to be sending information about pressure. Now you may be thinking, well, wait a second. I thought baroreceptors told us about pressure. And it turns out, baroreceptors are one type of mechanoreceptor that's found inside of the blood vessels. So there are many other types and many other locations. And so the bigger, more general term would be mechanoreceptor. You can find them in places like the nose, you can find them in the lungs, in the GI tract, so lots of different locations for these mechanoreceptors. And they're all sending their own projection over to the respirator center. And in fact, the lungs and the GI tract are going to hitch a ride in this vagus nerve and the nose mechanoreceptors they're going to travel through another nerve that's called the trigeminal nerve or cranial nerve number five. So these are the routes that these receptors are going to take to get to that respiratory center. But how do these work exactly, these mechanoreceptors? Let's take an example. Let's say you're walking and you inhale some pollen. Well, that's going to trigger one of these mechanoreceptors in your nose and it's going to want to relay that information over to your respiratory center so you're going to get a little nerve impulse through that cranial nerve number five. Similarly in your lungs, let's say you actually inhale some cigarette smoke. And let's say the lungs don't like that. And then the mechanoreceptor feels that little particle. It's going to trigger cranial nerve number 10, the vagus nerve. Similarly, you have these stretch receptors that are in the lungs. And these are actually kind of interesting because what they're doing is they're saying, hey, you know these lungs are starting to get really, really full, really distended, and so they want to let the respiratory center know that maybe it's time to exhale. And similarly, in the GI tract you can imagine, let's say a baby is taking milk and the stomach is getting really distended, you might also imagine that that information would go back to the respiratory center as well, in this case through cranial nerve number 10. So we have information about pressure or stretch, we also have information about chemicals coming in. But what about information on things like, I don't know, things like anxiety for instance, or fear. Let's say someone is having these emotions. Their breathing pattern may change. Maybe they're in pain. So these kinds of things are actually coming from the hypothalamus. So this is another region of the brain that's sending information down to the respiratory center and helping to affect how we breathe. And finally, this is probably the largest part of our picture, this is our cerebrum. And the cerebrum is responsible for all the voluntary stuff that we do, things like singing, where you've got to control your breath. Or maybe you're playing a musical instrument, or maybe you're yelling or screaming. Let's put yelling down here. Anything like that, you're going to want to control your breath. And so that's all voluntary control. So this is our voluntary control. And it's good that actually we have this mechanism so we can-- if we want to-- we can change our breathing pattern. But it's also great that our respiratory center can work on its own. Can you imagine if you had to always think about taking a breath? You couldn't do anything else, right? You couldn't sleep, you couldn't eat. You would always just be thinking about taking a breath so that you wouldn't miss the next breath and subsequently run out of air. So this is all the information coming into our respiratory center. Let me just scoot this over and actually show you now what our brain can do with that information to actually make sure that we're breathing comfortably. This is our spinal column. And I'm actually just going to label out the motor nerves and some of the muscle groups. So we've got motor nerves and muscle groups. And there are four key muscle groups that are going to be controlled by our respiratory center. And we're going to go through them one by one. So the first one, and the one that people usually always talk about or think about, is this one right here. This is going to be C3, C4, and C5. So C3 through C5, and the muscle is the diaphragm. This is the giant muscle that kind of sits right below our lungs and when it contracts you take in a nice deep breath. But it doesn't work alone. We've got other muscles involved as well. So I'm actually going to sketch out what these other muscle groups are. The first one is T1 through T11. All these levels are going to send off a little nerve. And each nerve will go through a different intercostal muscle. So intercostal muscles are-- these are the muscles that kind of go between the ribs-- these are going to help expand or pull out your ribs, right? So these are important for breathing as well. A little bit lower then, you also have these abdominal muscles. Abdominal muscles here are going to be T6 through L1. These are the levels where the little nerve fibers come out and are going to help innervate or help these muscles, abdominal muscles, contract. So this is a third group of muscles and they're controlled by these spinal levels. And the final group would be this group up here. So this is actually C1 through C3. And these would be the accessory muscles. Accessory muscles are the ones-- usually I think of them as the ones around your neck area. And they're going to also kind of help pull out the rib cage and expand the lungs. So there you have it. You have information coming in, that's the stuff that we started talking about, from all the different locations, around chemicals, information about pressure, and your emotional status, and what you're thinking about doing involuntarily. All that information is going to come in and then the respiratory center has to decide how to kind of balance all that information. And on the way out it's going to be able to execute by controlling all these different muscle groups and sending information down the motor nerves that we just listed to these four big groups of muscles.