Main content
MCAT
Course: MCAT > Unit 11
Lesson 1: Biological basis of behavior: Nervous system- Biological basis of behavior: endocrine system questions
- Structure of the nervous system
- Functions of the nervous system
- Motor unit
- Peripheral somatosensation
- Muscle stretch reflex
- Autonomic nervous system
- Gray and white matter
- Upper motor neurons
- Somatosensory tracts
- Overview of the functions of the cerebral cortex
- Hemispheric differences and hemispheric dominance
- The old brain
- Cerebellum
- Brainstem
- Subcortical cerebrum
- Cerebral cortex
- Neurotransmitter anatomy
- Early methods of studying the brain
- Lesion studies and experimental ablation
- Modern ways of studying the brain
- Endocrine system and influence on behavior - Part 1
- Endocrine system and influence on behavior - Part 2
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The old brain
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- 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)
- I reckon the brain overall is divided into the old brain, the midbrain, and the new brain. Therefore the midbrain is not included in the old brain; although an explicit clarification should be edited into this video.(13 votes)
- 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.(14 votes) - 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)
- 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)
- 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)
- Damage to the reticular formation causes coma.(4 votes)
- 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)
- Atyou 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. 1:11(2 votes)
- Are the hypothalamus, amygdala, and hippocampus part of the old brain too?(2 votes)
- 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)
- 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)
- 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 ? 3:15(1 vote)
- This was asked above by Residuum. There is no factual answer, but there are many cool theories, including the one regarding vision in the answer to that question. Quora also has a good discussion of this issue here: https://www.quora.com/Why-is-our-brain-contralateral(1 vote)
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.