[Music] we have the thalamus vpn vpl projecting up to uh rhodemont areas one two and three are generally going to be considered primary somatosensory cortex and these are so depicted in the far right diagram so if you have input coming in touch to your finger you have a sense of touch coming up in the green it's going to cross at some point go up to thalamus and under cortex and then likewise your sensation of pain is going to cross right away at the white anterior commissure go up a separate pathway and go up to cortex and in primary somatosensory cortex whether you feel pain or light touch deep pressure that primary sensory cortex is saying oh here's where i'm feeling it's going to localize where that sensation is on your body type and so the neurons up in here going to have sensitivity to light touch and as you get to areas one and two then you get a little bit more association going on and you have more complex receptive fields such as the limbs position and the shape of an object when you're touching us with your skin you can determine some shape features and so forth as you go from three to one to two then secondary somatosensory cor sorry primary somatosensory cortex if you stimulate that with an electrode i tend to get a tingling or numbness numbness in that contralateral part of the body so we stimulate on the right side medicines or cortex i'll feel like a tingling sensation over here in my left hand somewhere rarely feel pain uh and sometimes you can elicit a little bit of movements if you have a lesion here larger lesions you can compare finer aspects of sensory uh sensation it's hard to tell exactly where in what space you're being stimulated deficit in your sense of position and movement of affected parts uh but does not abolish your tactile sensation of pain or for pain so in general s1 good for localizing pain or touch but if you want to see the unpleasantness quality of pain that tends to be other cortical areas uh is more uh just widely distributed throughout the brain pain's more difficult to deal with okay oh and with regard to s2 and our second slide here so our secondary somatosensory cortices mostly located up here along the parietal operculum the perchium just means lid here's the parietal cortex and here's the lid overlying that sylvian fissure parietal perculum and it too has a somatotopic map so in the lower right diagram again we have with s1 we had the lower limb on the mesial surface and thorax neck shoulder hand here we have fingers and then we go to tongue and face is out here and then with s2 it goes the other direction face to arm to leg as you go back lateral to medial up into that parietal perfume so it too has a somatotopic map and the receptive fields in here if you go with an electrode and try to map that out on a person it's going to be more bilateral touch to symmetrical places slights to activate them say on both of your index fingers and with this fun demo for those of you who happen to have some coins in your pockets i have here various coins and you can try this with a friend at home or if you're with someone in the room there is to put a coin in your hand i'm going to put uh i'm going to put this one right here in my hand and without looking tactile feel what is that coin is that a nickel no is that a silver dollar no i don't think so quarter i can figure out what that is and that's using stereognosis where you are grasping the coin tactile palpating it putting together what is that three-dimensional object and with lesions that take out s2 you can then lead to a sterignosis or that inability to identify what is this object based on sense of touch all right so a question comes up as to why on earth does this here we have the homunculi milton and freddy here the somatosensory cortex of the motor cortex models a question often comes up why does it go leg to foot to hand and right next to face because i mean your face and your hand are pretty darn far apart anatomically [Music] hey everyone ryan rad here from neurosurgery training.org if you like that video subscribe and donate to keep our content available for medical students across the world