all right ninja nerds in this video we are going to talk about the cerebral cortex focusing primarily on the parietal lobe let's go ahead and get started all right ninja so let's get started on the basic kind of anatomy of the parietal lobe so the first thing that we have to talk about is the boundaries right that's kind of our big thing so that we can kind of tell where the parietal lobe kind of starts and ends so i like to remember the boundaries based upon three ways we have an anterior boundary which is this central sulcus we have an inferior boundary which is your lateral sulcus or your sylvian fissure and then we have a posterior boundary which is formed by the parietal occipital sulcus now the central sulcus right which is the number one which does that separate right that separates the parietal lobe from the frontal lobe okay and again that forms kind of your anterior boundary two is your lateral sulcus in your lateral sulcus it separates the parietal lobe from the temporal lobe and that's going to form this inferior surface as we said and then the last one here is your parietal this one's a heck of a name parietal occipital sulcus and this one is going to form that posterior boundary right and that separates the occipital lobe from the parietal lobe all right so that covers our boundaries the next thing we have to do is cover some particular functional areas of the parietal lobe so you just see this blue chunk that's just here that we have shaded in just posterior to this central sulcus that blue area that we're going to talk about is called the primary somatosensory cortex okay primary somatosensory cortex and if you guys remember from our um a model on the brain anatomy this was a specific gyrus where that primary somatosensory cortex actually resides it's called the post central gyrus now the primary somatosensory cortex is kind of a one-line function it's involved in basically our conscious awareness so our conscious awareness of somatic sensations and we'll talk about this in more detail later but basically it's sensations like touch pain temperature vibrations pressure proprioception all of those things are consciously perceived in this area of the brain okay now the next one that we're going to talk about that we're going to come down here is this pink one it's just posterior to the primary somatosensory cortex this is called our somatosensory association cortex so again what is that area just posterior to the primary somatosensory cortex called it's called our somato sensory association cortex now this area is involved particularly with kind of analyzing sensations that come to the primary somatosensory cortex so it's involved in analyzing sensations it's involved in the recognition of those types of sensation and it's also involved within the memory storage of those somatic sensations okay so basically it provides meaning to the things that we feel and gives us a way to be able to identify basically where our arm is in a three-dimensional space being able to determine what kind of object is this this is an eraser this is a marker so it kind of gives us the ability to analyze those sensations and come up with a meaning and pattern kind of recognition to those sensations the last one that we're going to talk about is this red area up here okay so this we had the primary somatosensory you have the somatosensory association and then you have this red area here this one is very interesting because it's actually it takes up a decent chunk of the parietal lobe but it also overlaps here you see that kind of overlaps here after the parietal occipital sulcus it kind of overlaps a little bit with the occipital lobe and it even overlaps a little bit here into the temporal lobe so we call this area here as two names if you really want to be specific you call this the posterior association area or the parietal occipital temporal cortex we're just going to call it the posterior association area okay so what do we call that area there it's called the posterior association area now the posterior association area is very interesting it's called a multi-modal association area meaning that it receives sensations from multiple modalities visual sensations right so if you cap from the occipital lobe right remember we said it kind of takes up three spaces so it occupies a little bit of the parietal lobe that's where sensation somatic sensations are right then you have the a little bit of the occipital lobe that is where visual sensations are then you have a little bit of the temporal lobe and temporal lobe is where a little bit of the auditory sensations are what happens is you take all of these sensations somatic sensations visual sensations and auditory sensations and have all of them coalesce together into one area so all the somatic sensations all the visceral sensations all the auditory sensations coalesce with one another and they all kind of synapse on that one area which is this posterior association area and it basically helps with the main kind of thing here is spatial coordination so it's involved with spatial coordination okay and this area is very very important and very interesting and also something that we'll talk about in more detail a little bit later but this carries covers the basic anatomy and basic function of the parietal lobe now let's dig in a little bit all right so now let's go ahead and dig into the primary somatosensory cortex now if you guys really want to know sometimes we give a particular broadman number to this area of the primary somatosensory cortex it's referred to as broadman area number three one two so you guys can remember that sometimes they will ask that on your exams big thing that we talked about the primary somatosensory cortex is that it's involved with conscious awareness and perception of somatic sensations well what are those somatic sensations well remember we have two pathways that are going to pretty much kind of coalesce onto that primary somatosensory cortex one of them is called your dorsal column medial meniscus pathway right we'll abbreviate that one there the other one is called your spinothalamic tracts now we've already covered these in great detail in a neurology playlist so we're not going to cover all this pathway but what i want you to remember is that this is where all the sensations are pretty much carried the somatic sensations that are going to be going to this area so what kind of sensations does the dorsal column actually carry and what kind of sensations does the spinothalamic tract carry and how is the somatosensory cortex actually going to receive those sensations it's relatively simple the types of sensations coming from the dorsal column is actually touch now if we're really being specific it's fine touch find touch or another way that we can describe it is also fine and discriminative touch so it involves fine touch and discriminative touch the other sensation here that it also carries is called proprioception so proprioception and some kinesthetic sensations as well so proprioception so it carries fine and discriminative touch proprioception and it also carries vibration sense so it also carries vibration sense all of these sensations are picked up and taken via the actual nerves spinal nerves that will come into the actual spinal cord right so it'll go through the dorsal root ganglion we're not going to go through the whole pathway here but it moves into the posterior gray horn into your dorsal column and then ascends upwards the big thing that i want you to remember here and we're not going to go through the pathway but what happens is eventually these sensations cross over in the medulla and eventually go where to the what side of the cerebral cortex the contralateral side from the sensations so all the sensations of fine discriminative proprioceptive and vibration sensations that are coming from the right side of the body will go to the left primary somatosensory cortex the same concept is that with your motor cortex all the motor function from the right side of the brain will supply the left side of the body that's one thing i want you to take away the other aspect here is the spinal thalamic tract what kind of sensations is this carrying this is carrying pain and temperature sensations right and it's also carrying crude or light touch and even pressure sensations all right and these sensations are carried from these receptors via the spinal nerves and they move into the again the spinal cord into the posterior gray horn and again don't worry about this pathway the basic concept i want you guys to remember here is that eventually where does it what does it do it goes to what side of the somatosensory cortex with respect to the sensation well here's the right primary somatosensory cortex and this is sensations coming from the left side of the body so again i want you to remember that this area what area again here's your central sulcus the primary somatosensory cortex it's responsible for conscious awareness of somatic sensations via these pathways from the contralateral side of the body here's one more thing that we have to mention besides the sensation aspect we didn't talk about it in detail really in the basic kind of overview but here's what else is really weird of the primary somatosensory cortex we know it has a mainly a sensory function but do you guys remember within the frontal lobe you had the primary motor cortex right in front of the central sulcus then in front of that you had the pre-motor and supplementary motor cortex and then in front of that you had your frontal eye fields and but all that stuff was basically going to eventually be involved in what and your motor pathways the corticospinal tracts in some way corticospinal cortical bulbar tracts right well guess what else contributes to your corticospinal tracts of your motor pathways your primary somatosensory cortex surprisingly this contributes up upwards of around 40 percent of the motor pathways your corticospinal and cortical bull bar tracks so it's also involved in your motor pathways so it's involved in motor function via what kind of things via the corticospinal tracts and cortical bulbar tracts how much percentage-wise does it actually contribute into this 40 percent isn't that weird so it has a sensory function but it's also involved in the motor function of the body so i just wanted to make sure that you guys knew that as well all right let's come down because now we have to talk about a very important type of somatotopic arrangement of this primary somatosensory cortex all right so the next thing we have to talk about here is the somatotopic arrangement of the primary somatosensory cortex right so when we looked at it above we were just seeing how sensations went up to this whole sensory cortex but sensations in the same way that the motor function came from different areas of the primary motor cortex sensations that are com are go to different areas of the primary somatosensory cortex so again you have this little type of thing here we put like a little man what's a little man called it's actually this is actually called a homunculus but we're really focusing on sensation here so this thing that we're going to talk about here is called your sensory homunculus and what's the purpose of this sensory homunculus well again it gives us our somatotopic arrangement so if you look here okay we have that coronal section we're going to say this is more of the medial portion of the primary somatosensory cortex this is going to be more of the lateral portion of the primary somatosensory cortex on the medial portion here you see more of the lower limb right so here you see the foot here you see the lower leg right so the low leg here you see your thigh then you see the trunk then you see the arms right then you see your hands then you kind of see the face and the the head and neck area right and neck and then you see the tongue the whole purpose of this is why sensations that are going to be coming from basically your lower limbs let's say this whole lower limb area are going to be going to the more medial portion of the primary somatosensory cortex and then sensations coming from the upper limbs and even the head and neck region are going to be going to the more lateral portions of the primary somatosensory cortex you're probably like wondering why in the heck is that even important here's why when people develop strokes right cerebral vascular accidents it's due to an occlusion of some vessel well here we have this vessel here this little this hole here called the internal carotid artery the internal carotid artery is going to give off two vessels that we care about in this sense this one here going this way is called your anterior cerebral artery now the anterior cerebral artery is going to be supplying which portion here did you guys see which portion we're kind of talking about here well here would be the foot here would be the lower leg here would be the thigh here would be kind of the hip and trunk area this is pretty much all going to be the lower extremities right so again this is going to that whole anterior cerebral artery supplies the medial portion of the primary semicentric cortex and particularly if you damage this area you're going to lose sensations to which area of the body the lower extremity and again it's going to be on the contralateral side the other vessel here coming off the internal carotid is going to be called the middle cerebral artery so what is this one here called the middle cerebral artery now the middle cerebral artery is going to supply more of the which portions here the lateral portions of the primary somatosensory cortex and again what do we say would be here well here we said would kind of be like your shoulder here would be your arms here would be your hand and fingers here would be your head neck tongue area right so if you think about it this whole area here is going to be that we're going to be kind of supplying here is upper extremity and the head and neck so if for some reason you have occlusion of the middle cerebral artery you're going to lose sensations from the upper extremity and head and neck areas from the contralateral side right so again to really kind of recap this part here if you have an anterior cerebral artery lesion you develop what contralateral because again it's contralateral sensory loss but from which part of the body lower extremity sensory loss right and the same concept if you have a lesion or occlusion of the middle cerebral artery this will lead to contralateral upper extremity and head and neck we're just going to put hn sensory loss okay so that's why this is important for us to know the homunculi one other point for the homunculus to drive this home is the size of the body part in the homunculus there's a reason that's why sometimes it's so distorted if you look at it in a textbook usually you'll see areas like the hands you'll see areas like the face and kind of the neck region they're a lot larger well the larger that body part is right so the larger the body part what that means is that there's more sensation more sensor more sensory nerves coming from that area so in other words there's an increased sensitivity to that area so there's an increased sensitivity to that area okay that is large or distorted on the sensory homunculus all right so that covers the primary somatosensory cortex let's move on to the association cortex all right so the somatosensory association cortex is actually a really really cool area of the parietal lobe it's actually i think more interesting than the somatosensory cortex the reason why is every sensation that we experience particularly somatic sensation it analyzes it and tries to recognize that sensation and provide meaning and basically recognition to that actual sensation so let me kind of go through what i'm talking about here remember we said that we had the sensations we'll draw here green just so that we remember clearly here here was going to be our pain and temperature sensations crew touch pressure sensations and that was coming up via the spinothalamic tract the other thing that we had here in the red was all of the sensations being carried through the dorsal column right and so we said dorsal column medial meniscus pathway which was your fine touch your discriminative touch your proprioception your vibration all that stuff was being carried upwards and we said that it eventually goes where to your primary somatosensory cortex which is in the parietal lobe same thing with these dorsal column sensations right they also go here so now let's draw here in blue this is our somatosensory associate i'm sorry somatosensory cortex primary somatosensory cortex just posterior to that which we drew here in pink is your somatosensory association cortex guess what happens here all the sensations that we picked up via these pathways the primary somatosensory cortex sends these sensory signals to your somatosensory association cortex so that it can analyze all of these sensations the best way i can explain this is by using some examples here okay so here we have a marker right what i'm going to do is is i'm going to have you guys imagine that you close your eyes and grab the marker now obviously when you grab the marker there's going to be some type of sensations that are being carried via all these pathways mainly the dorsal column in this sense which is that fine discriminative touch all of that stuff proprioception and what it helps me to do is if i'm closing my eye so i can't see the object and i'm going to feel the object right i'm using all these sensory pathways i'm feeling the size of the object i'm feeling kind of the edges i'm feeling how heavy it is right i'm feeling any kind of edges or corners or anything around that object and to give me kind of an idea of what this object is and then basically i can say oh this kind of feels like a marker that is what this somatosensory association cortex does and the same way let's take example i close my eyes and i listen let's pretend i don't know what i'm being given but if i feel it i'm feeling again i'm feeling the texture of it i'm feeling the weight of it i'm feeling the corners i'm feeling the again all the different edges how much it weighs the size all of that stuff and i might be able to tell you oh man this this is an eraser because i'm not looking at it i'm depending on my sensations all of that stuff is carried out through your sensory association cortex so again what i want you to remember that it's involved in is it takes a sensation right so here we have a sensation and what does it do with that sensation it analyzes it in some way right it does two things actually it analyzes the sensation and it takes that sensation and stores it in our memory so that if we ever feel that object again we might have some type of thing to compare the sensation in the future to when we experience it but it analyzes it right how does it analyze it it looks at it basically helps us to determine how the size of it the texture of it right the weight of it the position of it of object in three-dimensional space right all of these things and then after it does that it use it utilizes all of these things that we've analyzed from it and maybe that sensations that we've experienced in the past to undergo an ability to recognize some patterns of this object that works that we're actually sensing and then basically helps us to identify what that object is so that's why this is such a cool thing but the another thing that you also have to remember is whenever there's damage of this somatosensory association cortex it's going to alter our ability to identify particular objects and not just objects but also helps it also can alter our ability to identify where our body parts are in a three-dimensional space because again proprioception has to come to that area as well so whenever there's lesions of this cortex let's talk about a couple things that can actually come you can test for in your neurophysical exam so the reason why i want you guys to know this is whenever we do our neurophysical exam we we hope this this area helps us to kind of really help us to test particularly like if there's a lesion maybe in the sensory pathways or in the somatosensory cortex somatosensory association cortex so what are the ways that we do this well one of the ways is that we basically take like let's say we take an object right so some type of object and again let's use the example of the marker right and we put that marker in someone's hands have them close their eyes right and then they have to identify that object right so again they have to identify the object with their eyes closed focusing and only depending on sensations if they can't identify the object that means that this pathway is not working this is actually a specific type of condition whenever you can't identify the object this is called a steri agnosis a stereognosis and this is something that we actually do test for in kind of a neurophysical exam give a patient an object have them feel it close their eyes and tell me what this object is if they can't that could be a sign of a stereognosis something's wrong with the sensory pathway or the cortexes here that are receiving those sensations the other thing here is we can take let's say for example i take a patient's hand right and then i draw i draw a particular like number let's say i draw a number on their hand right with my finger i draw the number eight okay and they have to identify the number i drew if they have difficulty now generally all these sensations are working to help us to basically tell us all that fine and discriminative touch sensations help us to tell us where and what that number is if you can't identify that number or whatever symbol is being drawn on the finger this is a particular condition this is called a graphistisia and again this is something that we can test for as well the next thing that you can do is you can tell the position so another thing that you can do is let's see that you take a patient's finger right you have them close their eyes so you have them close their eyes on all this so you're depending on sensation and what you do is you move their finger up and down up and down up and down right and let's say that you tell them this is up this is down then you start moving okay and you do this you ask them where is your finger pointing up or down so we go like this up up down if they can't tell you the direction that that body part is pointing that is called a statognosis so another thing is the inability to identify body part position right through that example we just talked about is referred to as a stat agnosis and then the last one it actually can tell us the the difference in weight right between objects again depending on sensations so if you take for example you close your eyes and someone puts two objects in your hand right so here i have a three pound dumbbell in here i've got a marker but let's pretend i don't know that they put this in my hand and the purse the the individual asked me which one is heavier and is your left hand object heavier or is the object in your right hand heavier i'm obviously going to be able to tell that the object in my left hand is heavier than the object in my right hand how is that done it's done through all the sensory processes being analyzed and so whenever there is an inability right to distinguish right the basic difference right weight difference okay this is referred to as a bear agnosis a bar ognosis okay so this is why i really want you guys to know this area of the cerebral cortex because look at all the clinical cues you can pick up if there's a lesion within the sensory pathway or these primary somatosensory cortex or maybe even more particularly the matter the somatosensory association cortex all right so that covers this area let's move on to the last area alright so the last area that i want to talk about is this posterior association area now remember what i told you guys this is technically not just in the parietal lobe it occupies a little bit of a couple lobes right so if you guys remember so far we've talked about the primary somatosensory cortex right then we talked about the somatosensory association cortex well this last one that we have to talk about which we did in red is going to be what the posterior association area now remember what i told you there this is this is actually a multi-modal association area let's actually explain what that means that's important for us to understand what that means so [Music] multi-modal association area so what this means is let's take for example you have a sensation right so you have a sensation whatever that sensation may be whether it be a visual sensation an auditory sensation or a somatic sensation that's taken to a particular area of the primary cortex so primary auditory primary somatosensory primary visual cortex so the primary sensory cortex in this case let's say sensory cortex then from that primary sensory cortex it's then taken to another area which is called an association cortex in this case it could be an auditory association cortex a visual association cortex or a somatosensory association cortex so now the association cortex from these areas right so let's say that we have the the three types that we're discussing here you have the visual association cortex the auditory auditory association cortex and the somatic sensory somatic sensory cortex and again this is all the association all of these will coalesce with one another and make a multi-modal association area so that's what this is it's where multiple sensations coalesce so in other words ability for you to analyze recognize and provide meaning to whatever visual stimulus analyze recognize and provide meaning to auditory stimulus analyze recognize and provide meaning to somatic sensory stimulus and put all of those sensations into one area to help you have multiple functions working with one another to provide spatial coordination the one of the big things here that i want you guys to know is that this posterior association area right so where is it receiving sensations from visual auditory and somatic sensory from here this posterior association area it can communicate with a ton of different structures one that is important for us to know that it actually loves to communicate with is the prefrontal cortex it loves to communicate with the pre-frontal cortex because that's where elaboration of thought executive function memory is all involved in but you know what else it actually loves to communicate with part of your motor cortex to help with the elaboration of movement as well so this posterior association area is receiving all kinds of sensory information and then communicating that to the areas which help with elaboration of thought executive function memory and motor activity the best way i can explain this is through an example that i was taught so let's pretend here we're going to go drastic you got a beaker of some nasty hydrochloric acid right and then what happens is you're not being careful and you drop the beaker of hydrochloric acid whenever you drop the beaker of hydrochloric acid three things happen what are those three things well the first thing here is that some of that hydrochloric acid spills off onto your foot right spills off into your foot and so that is the somatic sensation of the acid right the other aspect here is that whenever this glass this uh this flask drops on the ground it makes a loud sound when it shatters into pieces so there's also going to be a auditory sensation okay some auditory sensation and again that auditory sensation is from the loud sound that it makes when it crashes onto the ground and the last thing that's going to happen here is that you're going to have you're going to see the actual bottle of acid hit the ground smash into pieces and some of the acids spill onto your leg so you're also going to have the visual sensation of that that will then the visual sensation auditory sensation somatic sensations have to go where to their associated primary cortex then from all of these primary cortex they have to get analyzed recognized undergo the particular recognition compare with past memories and then what all coalescent to what a multi-modal association area what is that multimodal association area that posterior association area what is that posterior association area going to do well then it's going to send that information where it's going to send some of that information to your prefrontal cortex why is it going to send it there because that's going to help with your executive function your memory your elaboration of thought with respect to this what am i going to do and then store this in memory so you never let it happen again the other aspect of this is that it's also going to send that information to what other area to your motor cortex why would it send it to your motor cortex particularly if we're really being specific it's the pre-motor but for right now just motor cortex why is it going to send it to the motor cortex well if a bottle of acid hits the ground smashes glass is flying everywhere acids flying everywhere what are you going to do you're going to move out the way so you need movement to help you to move out of the way so this is going to help with the movement or the motor active function and this is going to help with the elaboration of thought executive function and memory activity this is what the posterior association area does i hope that makes sense all right so in this video today we talk about the cerebral cortex primarily the parietal lobe the functional anatomy and the basic understandings involved with it and along with some clinical correlation i hope it made sense i hope you guys did enjoy it i hope you liked it if you did hit that like button comment down the comment section and please subscribe also down in the description box we have links to our facebook instagram go check that out follow us also we'll have links to our patreon you guys want to go check that out go there if you guys want to donate we would truly appreciate it all right ninja nerds as always we thank you love you and until next time [Music] you