Hi, I'm Michael Corayer and this is Psych Exam Review. In this video, we're going to continue looking at parts of the brain.
So in the last two videos we looked at the hindbrain and then the midbrain and now we're looking at the forebrain.
So the forebrain can be divided up into two main areas. We have the cortex, which is the outer wrinkled surface of the brain and then we
have all the stuff underneath that, which are called the subcortical structures. So in this video we're just going to be
looking at the subcortical structures and we'll talk about the cortex next time, in the next video.
OK so if you remember from the last video, we were moving up the midbrain,
and we got to this area where it starts to branch off in these two directions and I mentioned this area called the thalamus
the first structure of the forebrain that we're going to look at. So this is coming off of the midbrain we get these two egg-shaped
structures on either side. This is the thalamus. The thalamus helps to direct the information to the appropriate area of the cortex.
So
information comes up the brain stem, gets to the midbrain, then gets to the thalamus and the thalamus is going to direct it to the appropriate
area of the cortex. So you can think of this like an old switchboard operator for an old telephone system, where they had to actually
connect a wire. A call comes in, they say this call needs to go over to here, this call needs to go here. That's essentially what the thalamus is
doing. Information comes up the brain stem then says OK this needs to go to this part of the cortex and this needs to go to this part of the
cortex. So that's the thalamus.
Now under the thalamus we have a region called the hypothalamus.
And this literally means "under thalamus".
So the hypothalamus is under the thalamus and it's involved in a number of different processes. It's involved in hunger
it's involved in the fight or flight response so when you're threatened this activation of the fight or flight response
partially happens because of activity of the hypothalamus. It's also where you find the reward area of the brain, called the
nucleus accumbens. So it's involved in motivation, for certain behaviors that are pleasurable.
That's partially going to be controlled by the hypothalamus. So for this reason, you can remember the four main
activities of the hypothalamus with a bad joke which refers to them as the four Fs.
This is for Feeding, Fighting, Fleeing, and
mating.
So that's the hypothalamus.
And underneath the hypothalamus
we have a gland called the pituitary gland.
The pituitary gland is sometimes called the master gland. So a gland is a structure that releases hormones,
and the pituitary gland releases hormones that tell other glands to release their hormones. That's why it's sometimes called the master
gland. It tells the other glands what to do.
The truth is it's not really the master. So you might see this, but really the hypothalamus is the master because the hypothalamus tells the
pituitary gland when to release its hormones. So you might think of the pituitary gland as more of a middle-manager
with the hypothalamus really being in charge. But you might still see it called the master gland, that's because the hormones that it
releases tell the other glands to release their hormones. So that's the pituitary gland.
often called the
master gland.
OK so
the next part we're going to talk about it a group of structures.
This is
a collectively known as the limbic system.
The limbic system is responsible for
emotion and memory.
The hypothalamus is actually part of the limbic system, so we're going to include that here as
being part of the limbic system. And there's two other structures that we should be familiar with in the limbic system.
The first of these is
the hippocampus.
This is Greek for "seahorse"
and we'll see why in a minute. The hippocampus is responsible for the formation of memories. So whenever you're forming a new
memory that's going to involve activity of the hippocampus.
That's involved in memory formation.
Next to the hippocampus we find the amygdala.
The amygdala, this is Latin for "almond", and the amygdala is responsible for emotion.
So when you experience intense fear or some strong emotion you're going to have activation of the amygdala.
So together these three structures, the hypothalamus, the hippocampus, and the amygdala all work together to
do things like store memories of emotional events.
So that's the limbic system.
Another system that we'll look at briefly is the basal ganglia.
This is a system that's involved in voluntary movement.
It's also involved in reward and motivation but one of its main functions is initiating movement and helping to control those movements.
So that's the basal ganglia, we'll see there's a number of structures that make up the basal ganglia and they're
connected to an area of the midbrain that I mentioned last time, the substantia nigra,
which is, as I said, involved in voluntary movement. So you don't need to know all these individual parts of the basal ganglia but we'll
take a look at where it is in the brain. And the last thing that we'll look at
is the corpus callosum.
The corpus callosum is a big band of nerve fibers and what it does is it connects the two halves of the brain, the two hemispheres.
So the forebrain is divided up into two hemispheres and these are connected through
this group of nerves called the corpus callosum. So this connects
the hemispheres.
That's actually a good reminder. What I should have said when I talked about the limbic system is to remember that this has two halves.
There's a hippocampus on the left side, there's a hippocampus on the right side. There's an amygdala on the left side, there's an amygdala
on the right side. And we'll see this when we look at some diagrams. But the corpus callosum is this connection between the two
hemispheres. OK so let's take a look at some diagrams and see where each of these parts of the brain is located. First we'll bring up the
picture we looked at last time when we talked about the midbrain. Ok, so we came up, we had the brainstem, the medulla, the reticular
formation running up here, the pons, we got to the midbrain, the tectum and the tegmentum
and we left off just where that meets the thalamus. So that round sort-of egg-shaped structure is going to be the thalamus here.
Label that with a T for thalamus. And under the thalamus, of course, is the hypothalamus. That's this region here.
That's going to be the hypothalamus.
Just here, this is the pituitary gland connected to the hypothalamus here.
It looks like it's just dangling there, there is actually some bone that's not in this diagram supporting it because it's a very important gland
so we have it sort of protected by this little cradle of bone in here. So that's the pituitary gland right there.
Now the limbic system and the basal ganglia these are systems here that
aren't very easy to see in this side view, this sagittal view of the brain. We've got this cross-section right through the middle and those
structures are going to be toward and away from us on either hemisphere, so we can't really them in this view. We'll have to change
views to see those but we can see this big connection here, this big
group of fibers here and this is the corpus callosum, or the very center of the corpus callosum. This is what's connecting the two
hemispheres. So we're going to have to look at another view in order to see some of these other structures.
I highly recommend you check out this site, Genes to Cognition, I'll put a link in the video description
because they have a feature called 3D Brain where you can go in and see these different areas of the brain. So we start with this sagittal
view here that we were just looking at and we're going to look at the limbic system. And you'll see, as we rotate this,
now you can actually see these parts that sort of extend into each hemisphere that we can't see from that cut, cross-section view.
So there's the hypothalamus there right in the middle and then we have this structure that leads off of it and this brings us out to the
hippocampus right here. So here's the hippocampus, again you have one on each side, each hemisphere,
and then right next to the hippocampus is the amygdala. The amygdala is responsible for emotion, hippocampus helps to form memories.
You might look at this and say OK I can see why the amygdala is called the almond because it looks just like an almond,
I'm not really seeing the seahorse there, it doesn't really look like a seahorse to me. But if we look at a dissected hippocampus and include
some of this structure leading off to it called the fornix, then maybe you can see the seahorse comparison a little more clearly.
So this is the hippocampus this would be part of the fornix leading off to it and here's a seahorse. You can see a little more clearly why
it is called the hippocampus. OK let's look at the basal ganglia using this 3D Brain structure so you can go
on this site and use this drop-down menu here, you can select a certain
structure that you want to see. You can rotate it, you can also rotate it top-to-bottom. So here we can see these different parts of the basal
ganglia. You probably don't need to be responsible for these names at this point. You can also see the substantia nigra in the
midbrain that I talked about in the last video. And you can see why we couldn't see this in the first diagram. We're just seeing the cross-
section here and none of the basal ganglia is there. It's further out on these edges here so we couldn't see it in that view.
But using this 3D brain we can get a pretty clear picture
of where these structures are located.
And I just realized I should probably have moved this here so you could see it a little better.
OK so that's the parts of the basal ganglia and the last thing I'll show you is the corpus callosum.
Even though we could see this in the sagittal view that we started with.
We could see this band here but it's important to remember that it extends into the hemispheres. It's easy to forget that because
we often just see it from this angle. Ok it's just this little connection in the middle. But when we rotate it we see the corpus callosum is very
large, it extends very far into either hemisphere, it's a very big structure.
It's a lot of nerve fibers. We can rotate and see from the top or from underneath we can see just how
just how large this really is. And in a future video we'll see what happens when we cut the corpus callosum.
It's a rare procedure but occasionally this is severed to disconnect these two hemispheres
and we'll see what happens to patients who have undergone that procedure.
OK so those are all the subcortical structures that you should know for now.
Don't try to learn them all at once, I know it can be overwhelming, but if you focus on just learning some of the functions associated with
each so you get comfortable with the names of the structures, and then with the functions,
and then you can worry about where they're located in the brain. Don't try to do it all at once, learn the position and the function and
the name all at once. That's going to be a little overwhelming. But break it into pieces, learn it one part at a time. Ok, the function of the
hippocampus is memory formation, then worry about where is it in the brain,
how does it relate to the other structures of the limbic system, something like that.
So break it up, I think you'll find it easier to learn that way.
OK I hope you found this helpful, if so, please like the video and subscribe to the channel for more.
Thanks for watching!