Biology: The Human Brain

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I want you to remember something about cephalization. Remember way back in the phylogenies that the first thing that happened was you went from just some simple neurons that were kind of--say, in the cnidarians that kind of shot all over the place to the eventual creation of a head area, and in that head area you had neurons collecting in what we called "ganglia." You get a bunch of ganglia together and we start to call it a brain. So what is a brain? A brain is just a bunch of neurons/ganglia centered in one region--your head. I want you to think about your brain with your brain right now. Are you thinking? Let's make a list together. No official list, but let's make a list together of all the different things you know from elementary school that your brain does. If you want to click and turn me off for a second and make a list, go ahead, but I'm going to keep going.
First of all, we all know that the brain is in charge of sense interpretation. Now, obviously the brain is not sensory in a sense that it's outside your body, but it is in charge of sense interpretation. When you feel, touch, smell, whatever, it's going to get interpreted by your brain. Your brain, and parts of your brain are in charge of reflex actions. Certainly we know that the spinal cord, which is part of your central nervous system, controls a lot of your reflexes by being a switch. Many other of your reflexes come literally out of your brain.
Thought--you know, we call that processing. But think of all the things that you think about. But you see, all of the complex neuronal activities that are going on during thought falls on your brain. Something as simple as coordination-- your brain coordinates. Walking and chewing gum at the same time is an incredible feat done by your brain.
Memory--memory always amazes me, especially when we think of it at the level of the nerve cell and biochemistry.
Emotion--yes, your brain does all of your emotions, too whether it's anger, pleasure, happiness. It's all those ganglia, those centers of your brain.
And it's got a link to other systems. It's a link. For example, you're walking down the street and you see a lion. Well, you know, when you see the lion, for those of you watching this where there are lions, or you see something that scares you, all of a sudden your heart starts beating and you say, "Oh, that's adrenaline. That's not my brain." But think about it. Your brain perceived the thing that scared you, through your vision, into your brain, your brain sent the message, glands said, "Oh-oh, better start producing this adrenaline."
Where do you start a discussion of the brain? Well, you start with what you know, and probably most of you know some generalizations about the brain and the central nervous system. Let's take a look at this thing right here and start with what you know. First of all, you know that the central nervous system consists of the brain and the spinal cord. You probably know--somewhere along the way you were told about the three major parts of the brain. You probably know that at the base of the brain we have a region called "the brain stem." It's literally going to consist of several different parts, and for now we're just going to say it's down at the base of the brain--the brain stem. You also probably know that you have the major part of your brain that gets the most publicity, anyway, is the cerebrum, and over here is the cerebellum. What I want to do with you today is get you a little bit smarter with those brains and teach you some of the parts and what they do. Now, I've got to warn you--you're not going to be a brain surgeon after this lecture, but you're going to know a whole lot more about the brain than you did before. Hopefully, you'll be all inspired to go out and learn more.
Let's start out with the brain stem. Now the brain stem is going to be this region I'm going to tell you about right now, and we're going to start out with a part called the "medulla oblongata." I remember being so amazed by that very cool term back when I was a kid--the medulla oblongata. It's literally at the top of the spinal cord, or in other words, the base of the stem, the stem of the brain. So I'll just call it the medulla. No, I'd better call it the medulla oblongata.
We're going to come back to this diagram in a second. The Medulla oblongata has several functions. We've got the brain stem, that's our number one thing we're talking about (well, after the spinal cord), and the brain stem is going to have the medulla oblongata, and the function of that, it's a relay. Pretty much at down at the bottom of the brain...
Look, most of your processing is going to take place up at the top, up at the cerebrum. That's where we're going eventually. But just like telephone lines and the Internet and everything else, there's an incredible communication link that has to take place, and so many of the things I'm going to tell you about right now are merely relay switches that have to relay hundreds of different impulses at once to that cerebrum for processing, and the medulla oblongata is one of those things.
Now, the medulla oblongata relays information to a part of the brain called a "thalamus." So it relays it to the thalamus, and I'm going to tell you where the thalamus is in a minute, so just be patient, and the thalamus is going to relay to the cerebrum and from the cerebrum. You remember what happens at the cerebrum. That's where all the processing is going to occur. So you can see now we have this really important switchboard right there. There's other things that happen, by the way, at the medulla oblongata, too. There are certain centers or nuclei or ganglia, if you will, collections of neurons, and other things that are controlled right there at the medulla oblongata are swallowing, some of what we call your autonomic responses or automatic responses--things like breathing, swallowing, vomiting, the kinds of things that you do without thinking about. Do you think you have control over breathing? Stop breathing for
10 minutes and see what happens. So these are the autonomic things that the medulla controls.
At the top of the medulla is a part called the "pons," which means bridge. The pons we have right here is this green structure, flattened for bridge, and you can see it must be bridging the medulla for this yellow thing up here--stay tuned for the yellow thing. What is the pons going to do? That's going to relate to the cerebellum. So A, brainstem, medulla oblongata; B, pons. Let's go back to that third, fourth, fifth grade lesson. Do you remember what the cerebellum does? We learned back in elementary school that the cerebellum, coordination and control. We'll come back to the cerebellum later, but the cerebellum--kind of movement coordination. So the pons is a relay--another relay--I said relays were going to be important. It's a relay to the cerebellum and, here we go again, the thalamus, and it also has some other involuntary or autonomic things. And literally the pons literally controls the medulla. So I'm going to also add breathing here, and even though I said breathing was part of the medulla oblongata responses, literally, the pons controls the medulla, so breathing here, too.
Between the pons and this yellow thing here is going to be something called the "midbrain," which is sort of in the middle. I'm going to write it as midbrain, but I'm going to give you its anatomical term in a second. The midbrain is known as the mesencephalon, which means middle of the brain, and what this is going to do is it's going to take in relay visual and auditory data. So anything that's coming into your eyes and ears, it's going to take care of those things, and it's going to literally send them to certain places. It also is going to take care of things like the visual reflexes. You know, if somebody goes like this to you and you blink your eyes, that's mesencephalonic. Somebody who has damage to his mesencephalon, it's kind of interesting. They're going to have problems with their visual reflexes. It's also going to maintain you conscious. So, in other words, if you ever get knocked unconscious, it's usually a mesencephalon phenomenon.
Now, to the yellow thing, the diencephalon. The diencephalon is above the mid-brain and it's going to consist of two parts. These are very important. They are going to be called the thalamus and the hypothalamus. Where are we?
We've done the spinal cord, we've done the brain stem, let's talk about the diencephalon. The diencephalon is above the midbrain. We've talked about the thalamus already. Think about that. It's that relay I told you about. But the hypothalamus, how important is this? This is an organ, a part of your brain that weighs a few grams, and yet, look at everything it does. Ready? It's your thermostat. You know that your brain controls heat sensing. Not only is it your thermostat, it controls hunger, thirst, mating behaviors, sexual response, pleasure. You know, they did experiments with rats and somehow they figured out that when they damaged the rat's hypothalamus they couldn't experience pleasure, and I'm really not sure how they measured pleasure in rats. I don't know if they wiggle their ears or wag their tails or squeak or whatever, but it's the link. Not only that, the hypothalamus is a link to the endocrine system, and on top of all of that, it controls those rhythms inside of your body called "circadian rhythms," those day/night cycles--25 hours pretty much. We've taken people in a room, darkened it, and said figure out your own schedule, and it's been about 25 hours, which we've seemed to have adjusted to about 24 just because of daylight.
And you know what? We haven't even got to the parts of the brain that do most of the work. We still have to talk about the cerebellum and the cerebrum and all the things they do, but we'll come back to those at another lecture.
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