 Hey everybody, Dr. O here. In the last video we talked about the structure of a typical neuron. Now we're going to look at the different types of neurons we're going to see in this class. You can see here on the screen we have three types structurally. We have unipolar neurons, bipolar neurons and multipolar neurons. So we'll talk about these but then I'm going to add another classification in as well. So it started with the unipolar neuron. It's called that because it just has that one long, like the dendrite and axon or just this one long structure. So unipolar. Notice that the cell body is off to the side. This is significant because unipolar neurons are going to be some of your sensory neurons. And this is why the sensory half of your spinal nerves are going to have their cell bodies outside of the spinal cords in what's called the dorsal root ganglion, whereas your motor neurons that are multipolar, the cell bodies of motor neurons are actually in the spinal cord. I'll review this when we get to the spinal cord, but the structure of individual nerves or neurons actually determines the structure of these two areas in the spinal cord. So that's a unipolar neuron. Notice the bipolar neuron that cell body is right in the middle and then you have the two poles, one on each side. Then a multipolar neuron will come to back in just a second. So unipolar neurons are going to be your basic sensory neurons. We have about, you know, give or take 10 million sensory neurons and the huge majority of them are these unipolar neurons. So they're going to be used by the sensory or afferent divisions of your peripheral nervous system. Bipolar neurons are going to be for some of your special sense neurons. So let me show you an example. Here we have the bipolar cells there. Those are the bipolar neurons. This would be in your eyes. So some of your special senses use bipolar neurons, but the most important sensory neurons are unipolar. And then remember that number. We have about 10 million sensory neurons. So back to the multipolar neuron. So the multipolar neurons, these are going to be your motor nerves, your motor neurons. We have around 500,000 of those. So unipolar and bipolar neurons are both sensory. Multipolar neurons are going to be motor. The last one that I wanted to talk about, so just, and then we talked about how there's 10 million sensory neurons and 500,000 motor neurons. We have another really important type of neuron called an interneuron. Its other name is an association neuron. These can be in the brain, in the spinal cord. They can be in even some of your sensory and motor neurons. But the key with these interneurons is they distribute sensory information and they coordinate motor activities and they're also really important in higher order functions like memory and learning. So there are a key number here. There are 20 billion of those. So there's 10 million sensory neurons, 500,000 motor neurons, 20 billion interneurons or association neurons. I want you to know those numbers. They look a lot. Usually they look like a bipolar neuron, but here you see that little white interneurons. So see how it's actually coordinating activity. So it's receiving information from a sensory nerve and it's going to coordinate activity to distribute these motor commands so that in this case you can actually be involved in this reflex. So we'll cover the reflex later. Right now we're just talking about the nerve types. So motor nerves, sensory nerves and interneurons are the main three types and then structurally, let me go ahead and bounce back, unipolar neurons think sensory, bipolar neurons think special senses, multipolar neurons think motor. Okay. I hope this helps. Have a wonderful day. Be blessed.