痛觉与温觉

so two senses that are extremely important for our survival our sense of pain and our sense of temperature and of course we have more scientific terms for pain and temperature so pain is known as nociception nociception and temperature as our ability to sense temperature is known as thermo ception thermo ception alright so how is it that we're able to sense pain and temperature well just like all of our other senses we rely on a very specialized type of receptor found in various cells throughout our body and in this case in order for us to sense temperature we rely on a receptor known as the trip v1 receptor and interestingly enough this trip v1 receptor is also sensitive to pain and we're gonna go into how this receptor is able to recognize when there's some kind of painful stimulus in the environment so over here I have a little representation of what the trip v1 receptor looks like and this is not you don't need to know this you don't need to memorize this this just to give you an idea what it looks like it's a very complex structure and it's actually located within the cell membrane so you have cells that are sensitive to temperature and pain throughout located throughout your entire body and within the membrane of each one of these cells are thousands of these photoreceptors and how this receptor works is whenever there's a change in temperature so let's imagine that you place your hand on a stove so there's a little fire or you can't see that so let's imagine that there's a little fire under here that he actually causes a conformational change in this protein and basically what a conformational change is is just a change in the physical structure of the protein so you can imagine that we the protein was a little box and you apply heat to it maybe we'll make it look like a rectangle so this is the general idea behind a conformational change so when he is applied and also when is applied via a particular molecule you have a conformational change in this trip you want protein so let's look at a diagram of a hand and go into this in a little bit more detail ok so here we have a hand is that and as I mentioned before we have cells located throughout the hand and these cells are sensitive to temperature and to pain and within these cells there are trip v1 receptors so let's imagine that each one of these cells cells sends a little projection to a nerve that eventually reaches the brain so these cells whenever they are stimulated by either a changing temperature or the presence of some sort of painful stimulus so we keep saying a painful stimulus so what can that be so let's imagine that something pokes your hand so let's imagine that we have a sharp object and it pokes your hand what happens is the cell when it gets poked thousands of cells get broken up so the cell gets broken up and when it gets broken up it releases all kinds of different molecules and these molecules will travel around so let's imagine it releases this little green molecule it'll travel around and it will bind to one of the little trip v1 receptors and when it binds to a trip v1 receptors it causes the same conformational change that a change in temperature causes and so that conformational change actually activates the cell and the cell will send a signal to the brain so this nerve over here actually contains three different types of fibers so there are fast medium and slow fibers and let's go into why we have three different fibers so fast fibers are really really fat in diameter so we have these really big fat fibers and they have a lot of myelin so they are covered in myelin and what myelin is is is it's an insulator that basically allows the cell to conduct and actually potential very quickly so as an action potential or as a signal travels down the cell if we have a lot of myelin surrounding the cell as if the signal was able to travel really quickly and another way that a signal is able to travel quickly is if the cell has a really big diameter so a big diameter lowers the resistance so we have less resistance and you have greater conductance because of the myelin and these two things produce a very fast a cell that is able to produce send a signal pretty quickly so these types of fibers are known as a beta fibers and these fibers are able to send a signal really quickly to your brain saying hey there's there some sort of change in temperature it's really hot or there's something that's painful and allows you to withdraw your hand from that painful or really hot stimulus we also have medium fibers and basically these medium fibers are a little bit smaller in diameter so they might be about this big and they have a little bit less myelin and since they have a little bit smaller diameter and a little bit less myelin they don't conduct a signal as quickly as these fast fibers so these medium diameter fibers are known as a delta fibers so these a delta fibers are also found in this big nerve that goes to your brain and there is one more type of fiber so there's a slow fiber and this low fiber I'll draw it over here is really small in diameter and it's unmyelinated and so this sends a signal very very slowly it does get to your brain but it takes a lot longer for the signal to get to your brain so one way that we could conceptualize these three different fibers is if you think about touching a hot stove your hand quickly moves away from the hot stove so this is this really big a beta fiber activating to get your hand off the hot stove then you feel this really quick sensation of pain immediately after you touch the hot stove so that's this a delta fiber sending a painful stimulus to your brain and four minutes to maybe even hours after you've removed your hand from the hot stove you feel this lingering sense of pain you feel this burning sensation and so that's those are these C fibers that are really small in diameter and unmyelinated so we went into how temperature can induce a conformational change in this trip v1 receptor and how that conformational change can cause a cell to send a signal to the brain so let's go into how pain can do the same thing so whenever you eat a jalapeno you might have noticed that you get this you start sweating everything feels like it's burning and you basically have the same physiological response that you would if it was really hot outside and that again is because these this temperature receptor is the same receptor as a pain receptor so when you eat a jalapeno drawn a little jalapeno when you bite into the jalapeno you again you break the cells apart and the cells contain a molecule known as capsaicin so I'll write that down over here cap season and this capsaicin molecule exits the jalapeno cell and travels around until it binds to a trip v1 receptor in your tongue so this is a trippy one in receptor in the hand but let's imagine that it's in the tongue and it triggers the same response that a change in temperature would and so your body reacts to this capsaicin molecule in the same way that it would react to a change in temperature so if it was really hot outside you would start sweating Magill this burning sensation and so that is why when you eat a really hot chili pepper you have that type of response so in summary we have our ability to sense pain which is known as nociception and our ability to sense temperature known as thermo section and these two senses rely on this trip v1 receptor that is found within various sensory cells located throughout and the trippy one receptor is activated by changes in temperature and by molecules such as capsaicin or by molecules found within dying cells and it can activate this turbulent receptor and send a signal to your brain letting your brain know that hey there's either painful stimulus or if there's a change in temperature and allows you to react to that stimulus