 Hey everybody, Dr. O here. In this video, I'm going to introduce some of the different sensory receptors, but I really want to focus on receptive fields, but let's start here. So sensory receptors are going to be anything that can detect an arriving stimulus, and they translate it into an action potential, and they send that information on to your central nervous system so you can respond to it, either consciously or subconsciously. So detection depends on the different receptors, right? So certain, some receptors respond to very specific things, some much more broad. The simplest, most basic receptor we have there is the top one on the list, just the free nerve endings. These are going to be the ends of dendrites of sensory nerves. They can be stimulated by many different stimuli, as you can see here. So pain, temperature, mechanical deformation, all of those will send signals to the brain. Now that's good because they're useful because they can detect a lot of different stimulations or a lot of different things, but that also makes it hard for your brain to know exactly what's going on there, which is sometimes you might hear someone talk about burning pain or these types of things, so there's a little bit of overlap there. So the free nerve endings are going to be your most basic receptors, like compare that to your eye. Your eye is one of the most complex machines in the universe, and that's a sense of receptor as well. So you have really basic ones, just a couple more here. You see like muscle spindles they're going to, they respond or sense muscle contraction and stretching. You'll notice that several of them respond to different frequencies of vibration, so there's a lot more vibration sensation than you might think. We'll cover mechanical reception later on. So I'm not asking you to know this list of receptors, I just want you to know that there are. These would be your general sense receptors, and then we'll talk about your special sense organs later. But I really want to talk about this, the idea of a receptive field. So a receptive field is the area being monitored by a single receptor. That's called its receptive field, and you can have small receptive fields or large ones. So if I'm a free nerve ending, for example, and that means that if something in my receptive field triggers me, the free nerve ending, I'm going to send the information to the brain that says there's a stimulus coming to the brain from this area. Now with free nerve endings, it's going to be hard to tell, is it pain, is it temperature, is it mechanical deformation, whatever. But it's still, that's how your brain perceives what's going on, both inside and outside of your body. It knows where a certain type of stimulus is coming from because of these receptive fields. So you notice they're small and large ones. So basically the smaller a receptive field, the more fine, the more specific the information to the brain. So you see like the back, especially the smaller back is going to have real large receptive fields. Organs have huge receptive fields. So like if you have, I can't say exactly where my stomach hurts, I just know I have a stomach ache, these types of things. So if you want to figure out, if you want to learn about receptive fields, one thing I do is what's called the two point discrimination test. And that's where you use, I use a slide rule, two little pins on it, but you can use a paper clip and bring the points closer and closer together. So what you want to do is you want to bring these two points closer and closer together on someone's skin until all they feel is one stimulus. That means the two points of this, of this tool, whatever you're using, are in the same receptive field. So large receptive fields are very vague somewhere in this area. We're feeling this sensation. Small receptive fields are going to be very specific. So you see here like your fingers, your fingertips are going to have really small receptive fields, your lips, your genitalia, these kind of things. The skin on your back and those areas are going to be much larger. So these receptive fields, they can monitor all sorts of things. But that's the important thing here. So I just wanted to talk about the different types of receptors that are going to tell your brain what's going on. But these receptive fields are very important, small versus large. Next video, we'll talk about the different types of sensations they actually will send to your brain. I hope this helps. Have a wonderful day. Be blessed.