on the special census for the general census the receptor structure is simple it's very simple the first order neuron is the receptor and the special census is a very complex setup okay the we have a special receptor cell that communicates to the first order the neuron and that's just the way that it is okay I'm gonna abbreviate neuron as little anvil in that's my I have a bunch of shorthand that I use so when I was a student I could keep up with what the instructor was saying instead of writing out every word but that's my usual abbreviation for neurons so even though I mean I need this space I'm gonna write on it really quickly so that in the general census my first order neuron out in the periphery is the receptor so there might be some special modifications near the end of it as we'll see later but for the most part this cell is the receptor in the special senses let's say in the sense of smell I'm gonna have a receptor cell that's going to go synapse on the first order neuron which will then talk to the second order neuron and so on and so forth so we have an extra cell out in the periphery in the special senses so it's a more complex setup and the reason it's there is that allows for a more complex signaling pathway we won't have time to get in all of that detail and I'm a neurobiologist by training and we hit a ton of this stuff but not all of it is going to be super important for you guys okay at least at this level so that's one of the main differences between the general and special senses general sensors have simple receptors it's just the first order neuron special senses have a complex arrangement where there's an extra receptor cell that has to communicate released neurotransmitter onto the first order in Iran for receptor distribution this is very generalized on the surfaces of the body so if I have a touch receptor and the tip of my finger that does fine touch I have them all over the hand all over the arm all over my entire body I have some fine touch receptors I have thermal receptors that can detect heat on the tip of my nose the tip of my finger and the tip of my toes or the tip of the tongue and even on the internal surface this is very often like if you drink something hot and you can feel it in your stomach so these are all over the surfaces of the body all those modalities that we listed pain temperature touch vibration they're located all over the surface of the body the special senses are located in special sensory organs for example we only find photo receptors for vision in the retina of the eye the retina is considered an organ so to speak as the eyeball is or it's a layer of tissue in the eyeball and that is a special sensory organ only for vision for photoreceptors we don't find them anywhere else auditory receptors are found in a structure inside the inner ear called the cochlea we don't find them anywhere else so these always have a very special location where we find the specific receptors and they're not found anywhere else gustatory receptors on the tone olfactory receptors in the nose and so on central processing these are usually processed and what we call the primary that's our abbreviation for primary a one with a lot sensory cortex which would be the post central gyrus if you remember that from part one aap okay so almost every general sensation will go to the post central gyrus on either side of the main brain of course you should remember the right side of our body is monitored by the left side of the brain and vice versa the special senses are located or processed in specialized cortical regions cortical regions I should say there's special special areas I can't say the word special today there's special areas or regions of the cortex this ebrill cortex for example if we were to look at a brain and you should know this from Part one vision is done and the post and the occipital lobe at the back olfaction and gustation are done in the temporal lobe and our areas close to the temporal lobe and hearing is done different locations of the brain but every area of the brain has its own special cortical region that processes at least initially okay so these all go to the same location each one of these has a special area that it communicates to finally the receptive field these are usually relatively large not huge but larger and these are very small in very many instances the receptive field for the special senses is so small that you actually have to hit the neuron in order for it to fire we're in the general senses sometimes there's some specialized tissue some connective tissue or a modified Schwann cell wrapped around the end of the receptor so that if something bumps that it still messes with the receptor kind of like if I put a big sumo wrestling suit on you and I try to punch you even though I don't touch your skin because of that big wrapping around you something hits it you still feel it so these usually have a large receptive field with some specialized tissue although not always these have very small receptive fields we get and you have to do almost always hit the receptor cell for it to fire alright so listen um there's a lot of information on this page and we've covered quite a bit I'm gonna I'm gonna try to wrap this up I'm going to try to finish a little bit of page six and then we're gonna start another video where we're going to talk about the actual receptors themselves so I can tell you this for a fact as a neurobiologist at studying this stuff in great detail our understanding of sensory receptors some of them is pretty good some of them not so much we're still trying to figure them out it's very complex how our brain interprets information and how we process this information so if you look at the top of page six it talks about the interpretation of sense information now when we go from the periphery to the cerebral cortex and even if you look at the primary sensory cortex that the post central gyrus even that is mapped at so let me give you an example okay so if I'm looking at one side of the brain here and I have the central sulcus and I have the post central gyrus right behind it if I look along the post central gyrus almost every part of the bubble every part of the body really the neurons can go to a specific area of the post central gyrus so we would have the precentral gyrus here and when we look at the post central gyrus it's actually very highly mapped out for example deep inside the fold close to the longitudinal fissure we would have the genitals I'm just going to put male genitals because they're easier to draw okay and then we would have the big toe and the sole of the foot and then the ankle the lower leg the buttocks the torso the shoulder arm your hand thumb gets a huge area the face and the lips actually get a very large surface area there's a huge area that monitors the lips in our face all of this is mapped out along here okay so somewhere along the post central gyrus let me redraw this one but I'm not going to color it in okay all along this post central gyrus is this little person this little person by the way is called a homunculus the ulis are uncle s usually means little and hobo means man it's a little man or a little person mapped out all along the post central gyrus so somebody poked a finger then the neuron from that finger it's going to go from wherever we poked into the spinal cord the first order neuron will fire on the second order neuron that will go up to the thalamus and that's going to go up to somewhere here to this area that same would be right here along the postcentral gyrus so the pathway from the receptor cell in the periphery all the way up to the cerebral cortex is called a labelled line that labeled line is going to tell us the location and the type of stimulus somebody poked you with the needle so it's a no susceptor and you know that it happened all the way out here on this specific finger based upon where it fires in the brain if I were to go and tickle another part of the body let's say your foot is down here your big toe and someone tickles the bottom of your foot with a feather or something then these neurons are going to go into the spinal cord it's going to go up to your brain to your thalamus and then it's going to go to another area of the postcentral gyrus but it'll fire much deeper and it will fire maybe way up here where the foot is located so that enabled line is simply a connection between the receptor and the periphery and the part of the cerebral cortex the neurons in the cerebral cortex that interpret that information it's almost this way if you ever look behind your TV or DVD planners or whatever things are hooked up and you've got a million plugs and you can't figure out which one to unplug to get the TV to to move you got to unplug everything and check it it's a mess you don't know which plug is connected to which if you go and you tag them with a piece of tape and write TV DVD player I don't know Xbox 360 whatever games kids play I don't know what they're all called so now you know which plug goes to which location every line has been labeled so that we know this cable goes from here to there now our brain will only interpret the type of stimulus and the location of the stimulus based upon the labelled line if I cut a labelled line if you damage a nerve or cut it then I've cut communication on my brain and I can't detect that stimulus oddly enough though what's really unique is what if I could somehow take this blue neuron and rewire it to synapse on this neuron here literally changing where I communicate to and I have both this neuron and this neuron communicates the exact same neuron say up here in the thalamus well I would possibly interpret the interpretation even if I took my foot I would feel like you're also tickling my finger we can actually get some cross wiring here and sometimes that happens in what we call referred to pain we're going to talk about referred pain and a little bit but essentially referred pain as pain that's interpreted is coming from one part of the body but the stimulus is in another location the very most common one is when people are having a heart attack the pain in the heart is going to travel to the same nerve that has a branch that goes down part of your arm so a lot of times when people are having the heart attack they feel pain radiating down their left arm it's one of the symptoms and signs that you look for there's nothing wrong with the arm the pain is also being referred over there like when a doctor refers you to someone else to another location and in some very weird instances and amputations people can get some cross wiring and there's some some interesting cases where if you tickle a person's face they feel the hand that's been amputated because sometimes the neurons that were located here we'll cross wider to the neurons that are communicating here they're looking for connections and our body can sometimes cross wires so and so our body will interpret the location of the stimulus based upon the labeled line on that arrives if it arrives here my brain things that came from there even if I cross wired this neuron and actually tickled the foot anyway that's a interesting aside I'm starting to sidetracked but this stuck it's really interesting we just don't have time to go into all the different detail now what about the intensity what about the duration how long does it last so the intensity and the duration of the stimulus the labeled line tells us the location and the type of stimulus but what we call sensory coding tells us about the intensity the duration if there's any direction of movement of the students sensory coding is actually similar what they used to call Morse code I don't know how many of y'all know what this is anymore these days with cell phones kids don't even know what payphones are if they see one somewhere but in Morse code this guy's Samuel Morse figured out that if I take this device that's hooked up to a wire if I touch this thing and complete the circuit so that when I touch this metal to this metal the electricity will flow here at the end I can get a beep and they would sit there and tap things out Morse code is the series of dots and dashes that make out letters of the alphabet and you can send a signal DT DT T people would read the duct dashes they would be trained in Morse code this code of dots and dashes and be able to write out letters this is back in the 1800s okay well that sounds sensory coding kind of works the series of dots and dashes so the stimulus when I get a when I interpret something at the end I can tell if the signal is coming say from San Francisco through the Weider's of across the nation or if it was coming from let's say I don't know Colorado so if I have another line firing and they're all going to the same location this guy at the end can you tell me did it arrive on this label - this message coming from San Francisco ORS are coming from Colorado now if this guy is firing a certain firing pattern then someone at this end over here it's going to take that series of dots and dashes and interpret it like SOS as the famous signals dot dot dash dash dash is the letter O and dot dot thought is the letter S if someone else did this oops my bad let me change it then someone who took that as OSS the Office of Special Services or you know the British British special agents or something I figure that was called in World War two but nonetheless the label line tells us where the stimulus is coming from the firing pattern called sensory coding at the neuron in the cortex tells us more information how intense is it is it just a very light tickle is it a long tickle someone's really tickling you really hard yes sorry I dropped the markers sorry about that um so the sensory coding is the firing pattern in the cerebral cortex that tells us information about the intensity and the duration and sort of the length of the stimulus very often okay so you need to read the stuff that's in bold in the note set on this page you need to understand the difference between the labelled line now what sensory coding is telling us all right so now the last three things I want to cover before I move on sorry this is starting to dry down a little bit and I realize that but hey we got to do what we got to do we are going to talk about the different types of receptors as far as how the receptors are gonna fire there are two different types of receptors one receptor is called a tonic receptor and another type is called aphasic or scepter so when it comes to all the different modalities that we were talking about some of those the types of receptors are going to be phasic or they're going to be tonic I'm gonna talk about phasic receptors first when we talk about phasic receptors we usually say that they have an on face and by that what we mean is they are releasing neurotransmitter they're firing action potentials see is gonna be my abbreviation for the word neurotransmitter the chemical released by neuron under another cell or they have what's called the off phase they are not releasing neurotransmitter okay so this is how we learn how most neurons work I have a neuron a receptor here that's going to go and eventually fire the spinal cord on another neuron if there's nothing messing with this first-order neuron very often it's silent it's not releasing neurotransmitter it's in the off phase if something stimulates it and it starts releasing neurotransmitter here it's switched on when the stimulus goes away it switches off so there's a non phase or not face phasic receptors are like an old-school light switch the light is either on or it's off and there's no in-between okay now I'm gonna erase this and I'm going to talk about photonic receptors tonic receptors are a little bit more interesting and I'm not gonna make you memorize which ones are facing or which ones are tonic you guys can read and understand that stuff at some point in your near future on your own so when you're reading the chapter if you come across something that says this type of pain receptor is a faceook receptor you know it's usually off unless something stimulates it when you read about I don't know let's say a photoreceptor is the tonic receptor then you're gonna know what that means okay so for tonic receptors we say that these are always said to be on or releasing neurotransmitter there's a constant flow of communication in this set up a receptor cell will always be releasing a certain quanta or volume of neurotransmitter on the next neuron communicating it to mitigate it to it they can increase or decrease the neurotransmitter release okay so it allows for more complex signaling pathway in physics centers if nothing happens we're completely unaware but if something happens we know only one thing happened if I poke you you feel pain and that's it now for atomic receptors they allow us to respond to different stimuli in different ways so for example if in the sense of smell or the about taste taste is a better example on your tongue certain molecules binding to your tongue can cause certain receptors to increase neurotransmitter release start firing like crazy which will tell this neuron some ones its message and it will continue to fire even more than before and in some instances a different molecule that you taste on the same receptor cell can cause this receptor cell to start to decrease its neurotransmitter release and sometimes completely shut off and then this neuron gets a totally different signal so tonic receptors allow us to tell our allow us to communicate different types of information from the same receptor cell very often they can respond to two different chemicals one will cause it to depolarize and fire more action potentials release more neurotransmitter a different stimulus will cause it to fire less neurotransmitter and therefore we have different types of stimuli that one receptor can respond to or in phasic receptors it's one stimulus it either fires or it doesn't there's no variation in communication okay now a couple more definitions and then we'll wrap this video up I know it's getting long but hey I have that problem so get used to it I could do this stuff in five minutes with a bunch of powerpoints but I don't believe that lends to your real understanding so I take my time and try to explain things I hope that helps you if you don't like it drop my class and take some of those adaptation well when we adapt to things that means we get used to it we kind of accommodate to whatever the changes in that area are so an adaptation is in the world of sensory physiology is defined as a decrease in sensitivity to a stimulus due to a constant stimulus so let's say you sit down next to someone at lunch and they say hey hi how are you doing you start listening oh I'm fine and you you start having a conversation if this person can talk for 10 minutes straight without taking a breath about nothing that's important you start to tune them out you quit listening then they ask you a question did you hear what I said hum what so that's adaptation we sort of can filter out information those sensory receptors if constantly exposed to a stimulus and that stimulus is not going to alter our ability to survive or reproduce which are the two primary goals of all animals to survive as an individual that means find food and avoid becoming food or survive as a species which means find a mate and mate as often as possible so if you receive some information you detect a smell you might look for what's causing that smell if the smell sticks around for long enough eventually you quit smelling that aroma like when you put cologne on you smell it at first but then after a while you can't smell it everyone else can so don't put any more on but some people keep putting it on every 10 minutes and flies can't even survive around them but anyway so that's adaptation our decreased sensitivity to a stimulus if the stimulus is constantly around there's two types of that app tation that we can talk about one is called peripheral adaptation in peripheral adaptation what occurs is the decrease in sensitivity oops a curse at the receptor cell which is out of the periphery so think about this again here's your CNS here's your spinal cord right your brain the spinal cord here's the thalamus the receptor and the general census would be this first order neuron if I stimulate it and I keep getting the information going up to the brain I haven't adapted yet but if you keep tickling the same spot like when you put your jeans on in the morning you feel them but then after a while you become unaware of your clothes their touch receptors adapt to that constant stimulus so that would be peripheral adaptation if the sensory receptor cell out of the periphery gets used to it the same thing can happen in the sense of smell our receptors if you're smelling I don't know verbena on lime coconut Luca or whatever that's been sent a signal into your brain through a series of neurons if you continue to smell that this neuron or will stop smelling that particular sensation but in the olfactory pathway the receptor cell doesn't stop responding it's one of the nuclei along the pathway out into our brain one of the centrally located nuclei is where these cells say oK we've been getting that message we're going to quit responding to it and in that case we call that central adaptation in central adaptation I'm sorry I'm not writing very well right now I realize this video is getting kind of long I'm trying to be conscious of that but we have a lot of material to cover so I start rushing a little bit in central adaptation the decrease in sensitivity occurs at a sensory nucleus along the pathway or a nucleus along the sensory pathway some books will say that one way when someone's in the other so essentially the name tells you where the adaptation is occurring is it occurring at the receptor and the periphery or is it occurring at a centrally located nucleus so long the sensory pathway the receptor is still firing but one of the cells receiving the information halfway through the pathway says that not that smell anymore what that allows is though if I continue this to me this this neuron will shut down and peripheral adaptation we can shut down the sensation for a while for extended periods one of the examples for those of you that do physical therapy assistant an occupational therapy assistant if someone has surgery you'll see this a lot with people that have carpal tunnel releases the the scar on the hand can be very sensitive if you cut some of the sensory neurons and they'll have what's called hyperalgesia super sensitivity to pain if they touch that scar man they just can't stand it other carpal tunnel patients no problems but some people just become super sensitive well one of the things that gets prescribed for OTAs and PTAs is called desensitization therapy well those have you constantly rub it as long as you can stand and the more that you do that eventually the receptor cells will get used to the stimulus and then they no longer respond to that pain the sensitivity goes away problem is if you stick a needle in that receptor now it's not going to respond it's shut off at least for a period of time we're in central adaptation I can filter out one aroma but if a new aroma comes along let's say you go to bath and Bodyworks and you're smelling coconut Glen verbena mocha melon or something and then all of a sudden you smell pair bear your vanilla mist Sierra sometimes this sensation what it arrives because of also the the metonic receptors one receptor cell can respond to as different stimulation a different sensation or a different stimulus I should say an alter inspiring pattern and then at this nucleus we let the new sensation through so you can filter out old smells but that new ones through because of the way that central adaptation works the receptor is not shut up it's responding to different stimuli the old stimuli can be filtered out at the sensory nucleus but the new one will be allowed through because of the change in firing pattern so anyway finally well listen that's going to cover everything that I wanted to talk to up to this point we're going to pick up with the general sensory receptors the different mode we're going to talk about each one and some detail in the next video so this was the first video in the series we're going to move on to video 2 on the general census and these will all be listed on my page on canvas so hopefully you guys can just follow along and do the lectures in the correct order all right that's a fear of my class if you're not in my class I hope this made some sense to you I hope you learned something I hope you had as much fun as I did I'll see you on the flip side the next video alright thanks for watching