In this video I continue covering parts of the brain, explaining regions of the midbrain including the tegmentum, the substantia nigra, and the tectum. I also discuss the limitations of using 2D images when learning about brain structures, the use of “flowery” language for describing brain structures, and problems with somewhat arbitrary borders for brain regions (such as determining whether the reticular formation is part of the hindbrain or the midbrain).
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Video Transcript:
Hi, I’m Michael Corayer and this is Psych Exam Review. In this video we’re going to continue looking at structures of the brain. So in the last video we looked in parts of the hindbrain and now we’re going to be moving up and talking about the parts of the midbrain.
We’re mostly going to be looking at two areas of the midbrain. The first of these is the tegmentum and this comes from the Latin for covering and one of the roles of the tegmentum is that it’s involved in voluntary movement.
And one area of the tegmentum that’s involved in controlling movement is the substantia nigra and this is something that I talked about in a previous video because this area uses dopamine and one of the problems that we see in Parkinson’s disease is deterioration of these dopamine producing neurons in the substantia nigra and this results in the symptoms of shakes and tremors that we see in Parkinson’s patients. So that’s happening in this region of the tegmentum in the midbrain.
The other area of the midbrain that we’ll look at is the tectum and this comes from the Latin for roof and we’re really at the roof of the brainstem, the very top before we get into the forebrain and many of these other structures that we’ll be looking at in the next video. So this is the tectum, it’s the roof of the brainstem, and it’s involved in orientation, orienting ourselves to our environment.
So let’s take a look at a diagram of the brain and see where these areas are. OK so here’s a brain here and so the midbrain is quite small, it’s just this region here.
So just above the pons we get to this section here. This is the tegmentum and then here at the back of the brain on this end, the back end of the brain stem here, this is the tectum. The tectum refers to this group of structures here, you see these little protuberances here, these are called colliculi and the tectum refers to all of these together and they have individual names that we don’t need to worry about at this point.
An important thing to notice is that it looks like the tectum and the tegmentum are completely separate because we have this channel running through. In fact, that’s just the nature of this cutaway view. We’re looking at a column and that channel there is a hole running through the column. So this is called the cerebral aqueduct. I bring this up just to remind you that these areas aren’t separated. They’re actually part of the same column. It’s just hard to see that from this view. So we should think about some other views of the brainstem and actually if I make a little space here let’s imagine that we were looking at the brain stem from the front instead of this side angle that you usually see. So if we had the brainstem coming up here, then we’d have the pons, this sort of bulging out part of it, and then the midbrain is just this little section here.
Just this section here leading up and it’s leading to parts of the forebrain that we’re going to get to in the next video. So here at the top of this section is going to be a thalamus right here and actually you have another thalamus just next to it on the other side. So the midbrain is really the point where we start having this splitting off into the two hemispheres of the forebrain we’re going to talk about next time and it’s easy to forget that when you look at these side views. It’s easy to forget that there’s two of many of the structures that we’re going to talk about. When I talk about the thalamus in the next video, there’s two of them there’s two of the hippocampus, there’s two of the amygdala. And when you only look at the brain from this angle, it’s easy to forget that.
As a side note, this section leading up to the thalamus here is called the cerebral peduncle. I bring this up for two reasons. And the first is that I like saying peduncle. It’s a fun word.
The second is that peduncle means stalk and I like this analogy to think about this. It’s like the stalk of a flower. You could call the stalk of a flower a peduncle. So the cerebral peduncle is leading up to the thalamus. And it’s sort of the point where the brain begins to flower.
Where we have all this complexity emerging from the sort of simple brainstem that was leading up to it. I like this analogy, I think it’s one that you see in lots of structures. Obviously you see it in flowers, simple stalk leading up to this flowering part. You see it in trees, you see it in the structure of neurons with all of the dendrites coming off a single cell body and we see in the brain itself. All of these complex structures coming off of this single brainstem. In case you were wondering, this is the reason why the cover of my textbook “Master Introductory Psychology” features a picture of a flower. So now you know the reason for that.
OK, one last point about the midbrain. You might see in some places the reticular formation listed as being part of the midbrain. You might be a bit confused by this because I just said in the last video that it’s part of the hindbrain. So why is this? It turns out the reticular formation isn’t easily confined to eithe the hindbrain or the midbrain. Remember it’s a system, it’s a group of structures, so actually the reticular formation starts somewhere down in the brainstem beneath the pons and it’s continuing up here into what would technically be part of the midbrain.
And this brings up the larger point that we shouldn’t think too simplistically about these divisions of brain areas. It’s not the case that we say this is clearly the midbrain and this is definitely not the midbrain. Those are labels that we’ve given parts of the brain in order to make it easier to talk about them, but of course things are connected and they’re overlapping and so things aren’t always going to neatly fall into a single category and that is true of the reticular formation. So if you see it somewhere listed as part of the midbrain, it’s ok, it doesn’t mean you’ve got something wrong. It’s technically part of the midbrain and the hindbrain. Maybe more of it’s in the hindbrain, that’s not really too important to worry about.
Okay, so those are the structures of the midbrain and in the next video we’ll be talking about the many structures that are part of the forebrain. I hope you found this helpful, if so please like the video and subscribe to the channel for more.
Thanks for watching!
