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The old brain

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video.

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  • male robot donald style avatar for user MikeR8898
    The Brainstem video in this section noted that the brainstem includes the Midbrain, Pons and Medulla, not just the Pons and Medulla. Why was the Midbrain not included as one of the components of the brainstem in this video?
    (28 votes)
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  • leafers ultimate style avatar for user Mike Dacre
    I have to take exception to the statement that she makes that 'brains become more complex as animals become more evolved'. There is no such thing as one extant (currently living) animal being more evolved than any other. She says that human brains are more developed than sheep brains which are more developed than mouse brains. This is just completely wrong. During the course of recent human evolution, human brains have been selected for larger relative size and greater complexity of functions related to communication and reasoning/tool use, they did not just evolve more.

    Once you get outside of great apes, you cannot possibly ascribe an evolutionary ranking of brains. Sheep had different selective pressures, as did rodents. Rodents in fact, including mice, but particularly rats, tend to have more complex brains than sheep. This again is an example of a response to selective pressures (rats live in more complex environments and have more complex social structures than sheep). Also... sheep and rodents are the same evolutionary distance from us, we are not more closely related to sheep than to mice, and mice and sheep both have a cortex, so I am not sure why that is considered an example of recent human evolution.

    I know this isn't a question, but as an evolutionary biologist, this really irked me. Evolution has no direction, and humans are not 'more evolved' than sheep or mice.
    (11 votes)
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  • purple pi purple style avatar for user Residuum
    Why does the right side of the brain control the left side of the body, and vise versa? It doesn't seem to be the most effective way to process data. Any thoughts?
    (5 votes)
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    • male robot hal style avatar for user Collin Nadarajah
      From what I've learned (i believe it was first postulated by Ramon y Cajal who formulated the Neuron Doctrine) is that in vision, the the various inputs from one visual field have to be processed on the contralateral (opposite side). They do this in order to maintain proper orientation of the image (I think he used an example of an arrow).

      For example, something in the left visual field goes to the right side of the left eye as well as the right side of the right eye. If there was no crossing over, then where the left side of that object is relative to the rest of the object would be off. Thus, when the the neurons from the right side of the left eye cross over, the proper (flipped/mirror image) orientation is maintained

      Back to your original question, movement and sensation is flipped so that it can more easily mirror the flipped input from the visual system, thus streamlining the senses' integration
      (7 votes)
  • starky ultimate style avatar for user alina
    Is it possible to damage the reticular formation in such a way that you are ALWAYS on alert....so, instead of the coma, the reticular formation just doesn't know how to control itself?
    (4 votes)
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  • blobby green style avatar for user Mary Scinto
    you state that the cerebellum is involved in voluntary movement, but then end by saying all of these functions are happening outside of conscious awareness. Confused how something can be voluntarily moved unconsciously?
    (2 votes)
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  • blobby green style avatar for user wzkariampuzha
    At you said that some animals are more "evolved" than others which is false, all animals are (more or less) equally evolved to their own respective niches.
    (1 vote)
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  • duskpin ultimate style avatar for user Andrea🦔🤗
    why does our right brain controle the left part of the body and the left controlling our right side of the body instead of the other way around?
    (1 vote)
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  • blobby green style avatar for user brooke.m.briones
    As an example, the left cerebellum is in charge of moving the right foot and right cerebellum is in charge of moving the left foot?
    (1 vote)
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  • primosaur seed style avatar for user naheed khan
    At , it was said that the left part of the brain controls the right side of the body and vice versa. Why is that so ?
    (1 vote)
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  • blobby green style avatar for user fenitatan
    It was stated in a previous video that there are crossing over for nerves happen in the spinal cord. Are both of them crossing points?
    (1 vote)
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Video transcript

- Here I have two pictures of the brain. This one is a whole brain, this is what you would see if you could take the brain out of a person's skull. And this side is the front of the brain, this side is the back, here's the top, here's the bottom. And so, if you can imagine someone's eye being down here and their nose, this is what you would see if someone was standing in profile. On this side I have what you would see if you were going to take this brain and cut it in half down the middle. So, let's say I have a face, and here's their eyes and their mouth, this is what we would see if we could slice directly down the midline of a person's head. And, we refer to this type of slicing of the brain as a sagittal slice, specifically this one is a midsagittal slice because it goes directly through the middle of the brain. And, these two images are human brains. Although, other animals do have brains that look somewhat like ours, other animals have brains that are not nearly as complex. For some really simple animals their brains take care of the basic survival functions, things like breathing, and resting, and eating. And, this changes as we move to different sections of the evolutionary tree. And, even though I don't really like to think of evolution having directionality I think it's pretty fair to say that brains get more complex as animals become more evolved. So, mouse brains are more developed that fish brains, and sheep brains are more developed than mouse brains, and human brains are more developed than sheep brains. But, just because a brain is more developed doesn't mean that it doesn't have those earlier structures. In fact, as the brain increases in complexity it builds on itself. So, brain systems are constantly being built on top of old ones. And so, as one moves further inside of the brain one is getting to older and older structures. And, this has a couple of consequences. It means that the things in the middle of our brain, the oldest structures, are also the simplest. Because they're the ones we would also share with really early animals. So, deep inside the brain is where things like breathing and sleeping are controlled. However, as we move further out, so as we get to newer, more evolved structures the tasks that these brain areas perform become more and more complex, ending with the Cerebral Cortex, which is the outer covering of the brain that you can see right here. And, we'll talk about all of the different levels of the brain, but right now I wanna talk about that old brain, the brain that's in the middle, the brain that we share with much simpler animals. And, this area of the brain has a couple of different parts. One area is referred to as the Brainstem. And, if we're looking at the brain from the side that would include this section. And here, with the brain split in half this is where the brainstem is located. So, you can see its mostly covered by the brain when we haven't split our brain in two. And, the brain stem is split into two parts, one is called the Medulla, and the other is referred to as the Pons. The medulla is this area that's right here. And, this area right here is called the Pons. The brainstem controls really basic fuctions, things like heart beat, and breathing. But, it also serves as a crossover point for our body's nerves. And, to talk about this I need to reference the fact that the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body. And so, in the brain stem nerves that are coming in from the left side of our body crossover and move to the right side of our brain. And similarly, information coming in through nerves from the left side of our body crossover and move to the right side of the brain. And, that occurs in the brainstem. Inside of the brainstem, and you can't really see 'cause it's covered but I'll draw this here anyway to let you know where it is is a structure referred to as the Reticular Formation. And, this actually extends up from the brainstem into other brain areas. And, the reticular formation does a couple of really important things. First of all, it acts as a filter. So, as information is coming in through the spinal cord part of it is filtered by the reticular formation which can then send important information to other brain areas. Specifically, the reticular formation extends into an area of the brain known as the Thalamus which we'll be discussing in a moment. And, the thalamus acts a relay station for the brain sending information to different areas. The reticular formation is also really important for our sleep awake cycles, or for arousal more generally. Stimulating this area of the brain when an animal is sleeping can cause the animal to immediately awaken. And, not just awaken, but be alert. At the same time, if this area of the brain is damaged it typically results in the person lapsing into a coma. So, not only does it act as a filter, but it also plays a role in our ability to be alert and aware of our surroundings. So, I just mentioned the thalamus, so I might as well talk a little bit more about that now. So, the thalamus is located here, above the brainstem. And, even though we speak of it as if it's one structure, like most things in the brain, there are actually two of them, so they're two egg shaped structures that sit side by side in your brain. And, as I mentioned before when talking about the reticular formation the thalamus acts as relay station. So, when information from our senses, from our eyes, or our ears comes in, it gets relayed through the thalamus before eventually moving on to the areas of the brain where they're actually processed. So, all of the sensory information goes through the thalamus before being routed to other areas of the brain. The one exception to this is the sense of smell. But, everything else seeing, hearing, tasting, touching all of those senses go through the thalamus. The thalamus is also responsible for relaying information from the higher brain areas. The information is routed down through the thalamus, down through our brainstem and our spinal cord. The last old brain structure that I wanna talk about today is the Cerebellum. And, that's the sort of squishy area that you see down here. And, it's over here in the midsagittal slice of the brain. And, the cerebellum is about the size of a baseball and it extends around our brainstem. And, it's involved in a number of very important tasks. Specifically, it helps us coordinate voluntary movement. So, the cerebellum allows us to do things like run and kick a soccerball at the same time. When this area of the brain is damaged people's movements can be pretty jerky and awkward. And, before I go on I should note that you might have had some issues with cerebellum coordination at some point in your life as well, because this is at least one of the areas of the brain that's affected when you drink alcohol. And, as you may know when people drink a lot of alcohol their coordinated movements tend to suffer. They stumble around, they have trouble putting their keys in their front door. And, so these are all the kinds of coordinated movements that the cerebellum is associated with. I want you to take a moment to think about the tasks that are performed by these older brain structures and one thing that you might notice is that all of these things happen without our conscious awareness of them. So, all of these things, our heart beat, and alertness, and stringing all our movements together, all of these things happen outside of our awareness.