In this video I continue explaining parts of the brain and focus on the cerebral cortex. The cortex is the thin, wrinkled, outer covering of the brain and the wrinkles and folds create gyri, sulci, and fissures. The cortex is divided into two hemispheres, left and right, each with 4 lobes: frontal, temporal, parietal, and occipital.

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The Unfixed Brain
https://www.youtube.com/watch?v=jHxyP-nUhUY

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Video Transcript:

Hi, I’m Michael Corayer and this is Psych Exam Review. This will be our last video looking at parts of the brain and in this video we’re going to be looking at the forebrain and talking about the cerebral cortex.

So what is the cortex? The cortex is the wrinkled outer layer of the brain. So it’s about 2 to 4 mm thick and it covers the other surface of the brain. And it’s where a lot of the information processing of your brain takes place.

The first question you might have when you look at the cortex is, “why is it wrinkled?”

Well let’s say we had some distance here that we were going to have this layer of cortex on, now you can see if we had that same distance but we were allowed to wrinkled the cortex you can see that we’d be able to fit a lot more cortex into the same space.

And that is the answer to why the cortex is wrinkled. It lets us fit more cortex into the same space. So if we were to flatten out the cortex, we’d find that it covers a surface area about the size of an open sheet of newspaper but luckily we don’t have to have heads the size of an open sheet of newspaper. We can have much smaller skulls and we can fit all that cortex in by crumpling it up. So the wrinkles in the cortex allow us to fit more cortex into a smaller space.

Now when we talk about these wrinkles in the brain we can refer to either the smooth outside that we’d see, and that’s called a gyrus, or we can talk about the stuff that’s hidden inside a fold, so the cortex hidden there is in a sulcus. Gyrus is the outer part of a wrinkle and a sulcus is the inner part.

You might remember that by thinking maybe when you were a kid you were upset and you went to sulk in your room and you hid in the closet or something. Well you can imagine hiding in one of these folds here to go and sulk, and maybe that will remind you of sulcus.

Now it’s important to note there’s a myth, I don’t know how this got started, that each time you learn something you get a new wrinkle in your brain. That’s totally false. Don’t worry unlearning that isn’t going to get rid of a wrinkle in your brain either.

Ok, so that’s a gyrus and a sulcus. We also have larger folds in the brain and these are fissures. So a fissure is a larger fold in the brain. That’s really the only difference between a fissure and a sulcus is just that a fissure is larger. And fissures divide the brain into regions.

The largest division that we have, the largest fissure we have runs all the way across the top of the brain and this divides the brain or divides the cortex into these two hemispheres.

So this longitudinal fissure that we have separates the left hemisphere from the right hemisphere. An interesting thing about the hemispheres is that we have what’s called contralateral control.

So contralateral means “against side” or “opposite side” and this just means that the hemispheres control opposite sides of the body. So the left hemisphere controls the right side of the body and the right hemisphere controls the left side of the body. So when something is touching your right arm that information is actually being processed in your left hemisphere.

So that’s the two hemispheres divided by this longitudinal fissures. We also divide each hemisphere up into four lobes. So there’s four main regions of each half of the brain so in total you’d have 8 lobes, but they’re paired so you have two of each lobe, one on the left hemisphere and one on the right hemisphere.

Ok, so let’s take a look at some pictures of the brain to see what we’re talking about here. First we’re going to look at a cross-section. This is so you can see that the cortex is this thin outer layer, referred to as gray-matter. Underneath it is white matter that holds it into place and does some other processing as well but most of the really interesting stuff is happening, most of the information-processing is happening in the cortex, on the outer surface.

Looking at this cross-section you can already see; gyrus, sulcus, the folds here and how they let us fit more cortex into a smaller space. You also see the fissures. This would be that longitudinal fissure along the top of the head here and that separates the left hemisphere and the right hemisphere. Notice that also means we also have cortex all along the inside of that on each side of the hemisphere here.

You can also see another big fold here, this lateral fissure. And we have another big fissure underneath here that separates the cerebellum from the cortex, called the transverse fissure, you don’t really need to know that. Let’s look at a different view here.

Let’s bring up a picture of the brain here. So in this we’re going to look at the different lobes of the brain. One thing you’ll notice, here’s that fissure that was on the side, the lateral fissure, sort of running through here. That’s going to help us to divide up the lobes here.

You’ll notice there’s also a big sulcus running right down the center here, this is called the central sulcus. Not to be confused with the precentral sulcus or the postcentral sulcus here, but this is the central sulcus running down the middle here. In the back we don’t really have a clear sulcus for dividing these but or fissure, but we’re going to divide this up so we have these 4 lobes here.

The first lobe is the easiest to remember because it’s at the front of the brain and it’s called the frontal lobe. So you have two frontal lobes, left and right, and the processing that happens in the frontal lobes, there’s a section of it that controls motor information called the motor cortex which we’ll talk about in a future video but the rest of the frontal lobes do all those things that make us human really.

The really unique things that we do that other animals don’t do because we have very large frontal lobes compared to other animals. So we can do things like make complex decisions, and we can plan for our future and think about what we’re going to do that’s going to influence us a year or 10 years from now. And that sort of stuff is mostly happening in the frontal lobes.

If we move to the sides here we get to the temporal lobes. The temporal lobes on each side and you can remember that’s where the temporal lobes are if you think of your temples on the side of your head here, just beyond those would be where you’d find the temporal lobes. You can also use that to remember what the temporal lobes do. The temporal lobes process auditory information, so they do hearing. And they are conveniently located near your ears so that can help you to remember that the temporal lobes are on the sides and they process hearing.

On the top here, near the back, starting in the center and moving back you have the parietal lobe, on either side, the parietal lobes. One of the things that the parietal lobes do is they process touch information. So they have a section called the somatosensory cortex that I’ll talk about in a future video and that’s one thing that the parietal lobes do. Parietal may be a little harder to remember than frontal or temporal, parietal comes from the Latin for wall, so maybe you can imagine bashing the top of your head against a wall, maybe that will help you to remember the parietal lobe.

At the very back here we have the occipital lobes. So the very back of your head is the occipital lobes and what the occipital lobes do is they process visual information. So I have a mnemonic for you to remember the occipital lobe. Think of the O for Occipital we’re going to take that O and turn it into an eyeball here. So you can think of the eyes in the back of your head. The O for occipital can make you think of the shape of an eyeball and you can remember that the occipital lobes process visual information and they’re located at the back of your head.

So those are the four lobes of the brain: frontal, parietal, occipital, and temporal. Let’s just take a look at a couple other angles to show you this so you can see this longitudinal fissure if we look at the top of the brain. A very clear division between the left hemisphere and the right hemisphere.

And also remember as I said before that there’s cortex on the inside of that fissure. You’ll notice that on that lateral fissure there’s also some cortex on the inside. This is kind of interesting, if we were to pull apart that lateral fissure, the temporal lobe here and the frontal and parietal lobes above it, if we were to pull apart on that fissure we’d actually find a strip of cortex inside here. This is called the insula, and this is Latin for “island”.

So it’s this little island of cortex that’s hidden away, you can’t see it from the outside unless you were to pull that apart. You can see that here. Here’s a view where they’ve taken away part of the frontal, parietal, and temporal lobe. You can see the insula here, this little hidden section, this island of cortex underneath.

OK so those are the hemispheres and the lobes of the cortex and I’m going to post a link to a video in the description of an unfixed brain. When we see pictures like this, this is a fixed brain, it’s been stabilized using chemicals that make it firmer, and this might give you the wrong impression that the brain is firmer than it actually is. So in this video of an unfixed brain you can see just how soft the cortex is, very very soft, just holding it, the weight of the brain will deform it. That will give you an idea of just how delicate your brain is. It’s suspended in fluid in your head so it won’t essentially crush itself under its own weight.

So the video is not for the squeamish, it is a real brain that’s just been removed from a person who died, so you don’t have to watch it, but I think it’s very interesting. I think you’ll enjoy seeing just how soft the brain is and you’ll also see some review of some other brain structures that are talked about in that video.

Ok, so I hope you found this helpful, if so please like the video and subscribe to the channel for more. Thanks for watching!