[MUSIC] So, let's talk about what makes neurons unique. And here, I, I really apologize in advance. I'm going to show you pictures. Of neurons that, that I filled and stained. And these neurons are actually, they're sort of like members of my family. For instance, this neuron right here, I have incredibly deep, fond feelings for. So, yeah I understand that not maybe everyone feels that way but, indulge me for a moment, we're going to look at a few pictures. so, here is a neuron and this piece right here is the cell body, these are the dendrites They you can see that they divide, they divide a few times. We not the whole, the whole thing's not in focus, we're going to see later a reconstruction of this lovely cell. Okay so that's the dendrites and then here, this is the axon and you can see that the, now I'm going to take away these lines, you can see that the axon has a different appearance from the dendrites. The dendrites have their own appearance. Now I'm going to show you another cell. My feelings are not quite as deep for this cell, but it's a nice cell. So here's a cell and here is the cell body. These are dendrites, you can see and they're dividing, like this. Here's a dendrite, dendrites, etc. And you can see that the, the appearance of this cell is very different from the appearance of the last cell. Now we're going to see a, a reconstruction. What I did was I actually drew out the entire cell. And we're going to look at a few reconstructions and we're going to see, once again, that there's great variety in how these neurons look. And all of these neurons, that I'm showing you, are all in the same nucleus. They're in the same location. They got the same address, but they look really different. If you have the same address and you're in the lung, you are not looking different. So, this is really what's really, really different about neurons. Neurons are very unique. Very, very unique is a little bit of a of a toxism but they are, they are unique. and, and unlike cells of other organs. Ok, so here's a, a reconstruction. And this line here, that's got the arrows on it. That's the axon. The rest of this is the dendritic arbor. And you can see that the dendritic arbor gives you an area. This is where the neuron is collecting information from. Okay? So, the dendrites are taking information in and this entire arbor, describes a volume from which the neuron will listen to information. Here's a different looking cell. This is, in fact, my, my deeply fond cell, 451. Hm. Okay, so here's the cell, and it's a beautiful cell. It's got this, it's got a very large, dendritic arbor. It's listening to a lot of cells. And, and then it also has an axon which is not shown on this, reconstruction. And finally there's, here's a, a very simple cell. This is a cell, actually, that contains the neurotransmitter serotonin. And these other, the other calls did not contain serotonin, they contained other neurotransmitters. And you can see in this reconstruction, it's a pretty simple cell. There are only two primary dendrites, and they only divide a, a few times. So the, there's not that huge arbor. There's not that very delicate or elaborated arbor. I've spent my scientific life, staining cells in one place, in one nucleus and that nucleus tends to have, or has, cells that are fairly simple. In contrast, we know that there are other cells that are very complex, and this is one that I, I thank Giorgio Grasselli for. This is a purkinje cell in the cerebellum, and you can see that it has elaborate, it has a very elaborate dendritic arbor. Each one of these dendrites has actually little, protuberances called spines and that's what makes it look really hairy. The cells that I filled don't have spines and here's the axon for the cell, it's going to go down like this. So it's collecting information up here in the arbor and it's sending information down like that. In addition to variety in the size and the shape of the soma, the cell body, as well as the dendrites, there's variety in the axon. And so, I'm just going to show you these pictures. If they speak to you, fabulous. If they don't, that, that's okay too. So here's the, you can see the out of focus, this is the axon, it's the parent axon. And it gives off branches or collaterals and on these collaterals are little, little swellings and these are all synaptic terminals. So that's what this, that's what the words that I have used, that's what it really looks like. Here is another, this is a different appearance. So here is the axon. This is the axon and you can see that it gives off these little, terminals and it also has places where there's just simply a swelling, on root. So these are all synaptic, this a synaptic terminal, this is a synaptic terminal, this is an axon. So what we've just looked at is a wide variety of ways in which the anatomy of different neurons can, can make them different from each other. And the anatomy is different in appearance, but it's also different in the sense of, what is a neuron connected to? What neurons are talking to it and what neurons is it talking to? So the inputs and the outputs of each neuron are going to be different. They're either going to be very, very different or slightly different. In addition to the anatomy, it's, the other differences include the, what we call excitability. And this is essentially, how talkative is the neuron? How much do you have to goad it to get it to say something? And some neurons are, you know, they're talking all the time. And some neurons are very laconic, very unlikely to speak. And so, whether a neuron is, is, is very, very likely or very unlikely to fire action potentials, this is a, another way in which different neurons, are different from each other. And finally there's, how do they speak? And what we're talking about is the neurotransmitter. What is the neurotransmitter or what's the chemical, the substance that the neuron uses? And we saw one neuron there that was using serotonin. But other neurons use other neurotransmitters. And we can think about this rather than go through the different neurotransmitters, we can think about this as what, what can you say? Well some neurons can say yes, yes, yes, yes. Some neurons say no, no, no, no. Some neurons kind of hem and haw before they say maybe, probably, or questionable. So there is a difference in both speed, whether is something's fast or slow, or also whether it's affirmative or or negative. So yes or no and how, how fast does it take you to get to yes or no, versus negative? Neurons differ in all these various ways and that's why neurons, to me, they're as different as all the stars in the sky. Everyone's its own, its own self. In the next segment, we're going to look at the support staff. What enables neurons to, to shine like the stars in the sky? And, and they need a lot of support and we'll meet that support staff in the next segment.
