 Hey everybody Dr. O here. So in earlier video we talked about general senses versus special senses. Now we're going to look at the general senses and we're going to classify them based on the type of stimulus that excites them and sends information to your central nervous system. So here we're going to look at nociceptors which are pain receptors, thermoreceptors which respond to changes in temperature, chemoreceptors which respond to chemical concentration and mechanoreceptors which respond to physical distortion of their cell membranes. So let's go ahead and jump in before we actually talk about nociceptors our first group. I do want to talk about the nature of these receptors in a term called adaptation. So adaptation is how your nervous system will respond to or the presence of a constant stimulus. So something is painless and constant your nervous system will basically get used to it and will stop wasting all its energy reminding your brain about these things. So there's two different types peripheral adaptation is when a receptor changes and that's what we're going to talk about here and then central adaptation actually changes in the brain. This is why when you smell a new smell you get used to it pretty quickly. Physical sensation I always talk about like a ring when you first get married you're wearing a wedding ring you're constantly reminded of it but it's painless it's constant so sooner or later your brain just quit sending that information to the conscious parts of your brain that's adaptation. So getting used to a smell, getting used to a touch, getting used to the feeling of your clothing these would all be examples of adaptation. But here we're talking about peripheral adaptation with receptors. So whether or not you stop sensing something depends on the type of the receptor. So there are two types there are phasic receptors which are also known as fast adapting receptors. These are ones that respond to change so they're usually off they're triggered when there's a change and then they turn back off. So the textbook example would be thermoreceptors. So you respond to changes in temperature not just constant response to temperature unless it's extreme enough to cause pain I guess. So those phasic receptors are your fast adapting receptors. Excuse me tonic receptors are going to be slow adapting they're always on so as long as there's a stimulus you're going to know it and this is going to be your nociceptors or your pain receptors will be an example here. Speaking of that let's go ahead and dive in to our first type so excuse me nociceptors are going to be your pain receptors. So where do we have a lot of pain receptors your skin around your joint capsules around the periosteum the skin around your bones and around the walls of blood vessels so that any anytime there's pain so what is pain pain receptors are triggered by tissue damage whether that's chemical whether it's caused by extremes of temperature whether it's mechanical doesn't matter. So pain receptors are free nerve endings and if they sense tissue damage from one of those three things extremes of temperature chemical changes like from dying cells or mechanical damage they will send pain information to your brain and the reason it's important to note that they're sensitive to all these different things is it's why it's hard to classify pain so you whether you've been burned by acid whether you've been burned by heat or whether you have a deep cut you might feel burning pain and that's because of this overlap overlap and extremes of temperature is pretty important so if it gets so hot or so cold it's uncomfortable it is actually painful. So those are your nociceptors the pain receptors are tonic or slow adapting receptors which means that you don't so if you hurt your knee like this person here you know oh I hurt my knee it hurts really bad no the pain's gone no that knee is going to hurt as long as the tissue damage is still there so the sensation is going to stick with you and you can manage pain you can try to think about it you can use ice and Advil and these kind of things but the receptors are going to continue to tell your brain that knee hurts until the source of the damage is gone and that's good because pain is a reminder to not do further injury to this joint we don't want to feel pain but a life without pain would lead to lots of damage and lots of extra destruction in our body so we need to feel it as a reminder to be careful all right so that's nociceptors or pain receptors next we have your thermoreceptors so these are going to be your temperature receptors also free nerve endings you're going to find a lot of them in the dermis of the skin your muscles have thermoreceptors as well as your liver and your hypothalamus so there so there are both cold and hot receptors there are three to four times as many cold receptors as warm or hot receptors now there's actually no structural difference but we do know that they that they are different so why would you have so many more cold receptors than warm receptors well it's because cold can kill you so much more quickly right you're outside in the bitter cold or you fall in cold water i mean you can be dead in minutes heat isn't going to be isn't going to kill you that quickly so you don't need as much information about it so there are so make sure you know that there are three to four times as many cold receptors as warm receptors these are phasic receptors which means that they're usually off they're triggered by changes in temperature but then that the initial stimulus goes away because of adaptation so think about you go outside and it's five degrees colder than you'd like it to be you're going to be very aware of that because your brain's trying to tell you to warm up put some clothes on go back inside but you will quickly adapt to that temperature unless it's bitter cold or really hot unless it's actually painful if you go outside it's just a little bit colder than you'd like we'll just wait a few minutes you're going to actually you're going to get used to it and you forget about it because these are quick adapting or phasic receptors okay chemo receptors they're going to monitor chemical composition the first key thing to note here is chemo receptors only respond when a lipid soluble or water soluble substance has been dissolved in the surrounding fluid so two examples we'll cover with special senses will be smell and taste you can't smell or taste anything until it's been dissolved in fluid we'll come back to that here since we're talking about your general senses these chemo receptors are monitoring primarily the chemical composition of your respiratory and cardiovascular systems so why is that your respiratory system these centers are monitoring pH and carbon dioxide levels because if you get if your pH of your blood drops too low or you get too much carbon dioxide in your blood you're going to die if the pH climbs too high or you don't have enough carbon dioxide in your blood you're going to die so we cover that name we cover that name b2 but for now just note that your your brain is constantly monitoring carbon dioxide levels and it and it responds by changing how you breathe so if your pH is if your if your blood's getting too acidic then you're going to breathe faster to get rid of that carbon dioxide which is an acid and vice versa but we'll come back to all that later the chemo receptors that are monitoring your cardiovascular system are looking for the same things they're monitoring the pH of blood carbon dioxide levels and oxygen levels but i do want you to note that and we cover that more in a and b2 your body cares way more about carbon dioxide levels than oxygen levels and that's because we have plenty of oxygen that's why people can go to higher altitudes and survive carbon dioxide becomes an acid so if we can't control carbon dioxide levels we can't control pH and we can no longer maintain homeostasis so these uh so the the cardiovascular centers we have what are called the carotid bodies that are near the origin of the internal carotid arteries and the aortic bodies where the aortic branches or the aorta branches off but so these are basically we basically have pH meters in our blood and in our brain that are monitoring all your body fluids to make sure that you have the right amount of carbon dioxide and the right pH those are chemo receptors all right and the last group here is the mechanical receptors but we have some further grouping here so these are going to be the ones that respond to physical distortion of their cell membranes so stretching compression twisting these types of things there are three types of mechanical receptors we have tactile receptors those are going to be the real physical sense ones so like touch pressure and vibration but we don't talk about them as much the last two groups are baro receptors and proprioceptors so baro receptors they're going to monitor pressure changes in hollow organs like the walls of your blood vessels your your stomach your your lungs etc so they they sense changes in pressure so we actually so like i said earlier we have a pH meter built into our our body we also have blood pressure cuffs inside our body so the carotid artery and the aorta both have baro receptors that monitor pressure that's how your brain knows if your blood pressure is getting too high or too low and it tries to respond baro receptors also monitor the degree of lung expansion so if you're overexpanding your lungs that will that will trigger these baro receptors and then all over in your digestive and urinary tracts we know that if your stomach gets full you're actually going to trigger these baro receptors or stretch receptors same thing in the urinary tract if your bladder gets full so those are baro receptors which monitor changes in pressure last group here is the proprioceptors i like to say these are called your joint position awareness receptors so you're going to find them in your joints and your muscles they're constantly active they're constantly telling your brain where your body is in space so they monitor the position of your joints the tension in your muscles and your ligaments and they monitor how whether or not your muscles are contracting so all that information gets sent to your brain so your body knows where you are in space so they don't adapt at all most of this is subconscious but think about it close your eyes where's your right elbow you know where it is because constant information being sent to your brain about where you are in space why is that but without this information you couldn't move properly if i don't know where my arm is now that i don't know how to reach for my coffee right if i don't know where my my legs are now then how do i take the next step how do i navigate obstacles things like that so proprioceptors think joint position awareness receptors i love proprioception it's something i did a lot of research in when i was in college on the last thing to note here proprioception is a purely somatic sensation so i said close your eyes where's your right elbow you know close your eyes where's your spleen you have no idea right this kind of that in your organs don't tell your brain where they are in space if you know where the spleen is it's because you've seen it in an image or in using a you know a cadaver a donor and you know you just know where it is because of memory you can't sense where the spleen is all right there's organs in general they do have receptors but they don't have proprioceptors they have pain receptors temperature receptors these types of things but they usually have huge receptive fields that's why like i mentioned in an earlier video if you have a stomach ache or let's say you have an ulcer right you don't know you you're just going to get pain from that general area you can't say exactly where it is okay so those are that's that's the the four main ways we classify your general senses i hope this helps have a wonderful day be blessed