finishing up the nervous system they're gonna talk about the senses to do that we need discussed the difference between sensation and perception few fundamental things we look at two types of receptors some easy ones like touch and temperature but then also some complicated ones like vision sensors or smell sensors and then we look at adaptability for the nervous system and that goes together with receptive fields and from there we gotta move straight to the special senses and we talk about the sense of vision the sense of hearing and equilibrium and the sense of taste and smell but first let's talk about some phenomenal team sensation is the awareness that something happened either on the outside like you hear something outside or in the inside of the body you know like a pain for example perception is that a conscious interpretation of what we have felt or what we've heard so that's an interpretation that's not just the stimulus being registered in consciousness this is actually interesting this is where a lot of Buddhists or Buddhists only just a lot of modern psychology thinking goes into the suffering where we look at a twisted ankle is a pain but what do we do with the pain are we really struggling with it are we really worried about it or are we just dealing with it that difference is the perception difference and so we can have these two things also differentiated within the basic neurology discussion when we look at the sensory receptors we have some that lie up superficially in the skin or in mouth area mucous membrane areas we got some that are deep that's more muscle tendon joints we got some that are in the internal the visceral organs and then of course we got the special senses right down here we talked about smell we talk about vision we talk about hearing and equilibrium and we talk about taste we can classify a receptor by what type of stimulus doesn't transduces it's a mechanical that would be a pressure or touch is it thermal that would be heat is it a chemical for example or photo by chemical could be an order that we pick up and nociception right here that describes pain for us but it actually for my body's perspective it describes danger so no see meaning danger meaning we gotta pay attention to that is very very important because in our modern understanding of pain we still believe that pain just needs to be gone however the body views pain not as an unpleasant thing but as a danger language that it can tell something's going on so we gotta pay attention to the pain they're not just numb it especially not with opioids that don't help and then we can also classify receptors according to structural complexity the complex receptors serve our special senses and the simple receptors transduce generals right sensations either through free nerve endings or encapsulated ones and free nerve endings we can sort of visualize that that's down here you see a free nerving the nerve ending down here we can visualize pain with that like you caught yourself some of these get caught they get stimulated that's pain touch for example on pressure or more Dom is encapsulated nerve endings always get encapsulated once what we have here is an one that looks like an onion so a lot of them the nerve ending comes in and then around it we have cell membrane type material that goes a rounded like an onion and when you feel like you can press something down here you gonna press these onion rings and these layers together and that fires a nerve impulse off I like this many receptors thank the Lord they adapt to a continuous stimulus that means for example we could put a hand in a cold water we can put a hand in a hot water those two will adapt to the temper to drain and then and so we don't feel the cold anymore or you don't feel the warm or the heat anymore as much unless of course it's scalding hot and it's different story but then we then take those hands and put them in a lukewarm water we can feel that adaptation because the hot water hand will feel cold awesome and cold water hand will feel warm also so that's kind of a good way to figure that out but the application is important because like you put on a sock or a piece of clothing and you don't feel it anymore after a little bit if it would be always in your face feeling about it what else would you be thinking about it so we need to make brain space free for for the brain you think about other things and not just about the clothes that we're worried for example all the time some recept and of course this picture I have to put in because we come from an ape and we end up in the same position again appropriate sectors and pains receptors the harm receptors they do not adapt and that's because of protective reasons just think about you walking and you walking and all of a sudden the receptors in the foot they don't fire back anymore of the brain what's going on underneath the foot because we're all adapting and all of a sudden something you know we fall down because it's not protecting us anymore or the pain if we for example caught ourselves and to think just adapts and we don't pay attention to the Kotton our skin and we just put dirt in it because you don't remember it that wouldn't make any sense so every time we touch an area that we caught for example until the cops healed it's gonna hurt so we don't touch it we don't do anything with it and that makes a lot of sense I like this chart a lot this is a this is a thing that actually is not described over here this is the gait theory and the gait theory is a thing when we have pain when we create pain like we hit the thumb with a hammer a pain signal goes into the brain to doing pain pain pain pain however when we then take a finger or whatever kiss it whatever rub the area that we had we send a different signal to the brain we send the proprioceptive signal to the brain actually a mechanoreceptor form and that message will then shut the pain transmission to the brain and it doesn't happen or not as much so that's very very important to understand why when we do work with pain moving it's very very important so that's a very interesting concept that I just want to mention here because it's so valuable and for some reason we're not really you know talking about it as much as we sure they figured this stuff out in the fifties everybody should know that stuff because it's so difficult for patients to get better and they are in pain and they do not move because they're afraid they're gonna hurt themselves again so we got to bridge that gap a little bit obviously you don't want to move it or it's much much more and you do more damage but most the time or you do with movement you create this situation you don't make more damage to the tissues many receptor cells are responsible to monitor specific surface area they call that a receptive field so that is very well described here like this nerve here serves this part of the skin this nerve here serves this part of the skin so now what we can do is we can take to poke pokers and we can poke you know like two prongs we can poke them here and here the person thinks it's one poke to pause but if we now poke it here and ride it out and poke in here the person on some things oh that's two folks and so we can actually map out we can map out the size of a receptive field and the larger the size of receptive field is the lower the resolution is in the brain you can feel this you can like take your hand in a pocket and feel which coin is going to be the right one for parking like which one is the quarter but if you have to have a coin laying on your back I doubt that you could differentiate between a quarter and a dime and so that's a visual for the receptive field this is also the receptive fields also how the cent more the sensory cortex the primary sensory cortex is organized did you see how many how big the areas in there are that represent a body area it's the same thing like this it corresponds to this and so we can take this two-point discrimination test which is will be poking your in two different parts and figure out how big is a receptive field so we see the tactile receptor distribution that way that's kind of cool alright from there let's get to special stuff let's get to the eye and let's get to vision the organ of seeing includes the eyeball is the optic nerve and then we have accessory organs such as the eyelids eyelashes lacrimal apparatus and extra ocular eye muscles hmm so basically we got an eyeball that sees and we gonna have a whole bunch of stuff to help the eyeball one of the things are healthy eyeball are muscles they actually move the eyeball around up down sideways twisted you know the pupils coming together looking then we also have a lacrimal apparatus we have to make tears that's the place where we make tears and then the tears are made up here and they get sent into the eye and they flow out down into here and when we cry a lot we gotta have a tissue because we need to get rid of the tears to come out of the nose so that's the lacrimal apparatus and there we go a few more we got eyebrows right here did I actually put those down no I did not but we have eyebrows we have eyelashes we have eyelids and they all help protect and supports the eyeball the eyebrows for example make sure the sweat doesn't get into the eye because that stings and then we can't see because we have to close the eye things like that but let's first get a little bit to the eyeball the eyeball lies in the bony orbit and that is embedded in fatty tissue so that what that means is the eyeball lies in this bony place here and that we don't bang the ball around we're gonna have a little fatty tissue around it that's not the fat we often think of or in fact it's just you know protective tissue that way we better don't take rate of get rid of that fat that's for sure