Neurology | Cerebrum: Frontal Lobe Anatomy & Function

all right ninja nerds in this video today we are going to talk about the cerebral cortex but we're going to primarily focus on the frontal lobe all the basic functional anatomy of the frontal lobe so let's go ahead and get started all right ninja so what i want us to first do is cover the basic kind of like functional anatomy and then talk about the basic functions of these different kind of areas located within the frontal lobe well the first thing that we have to do when we talk about the frontal lobe is develop an understanding of the boundaries of the frontal lobe that's kind of like a really kind of an anatomical portion that we have to discuss so the way i like to remember the boundaries is what's separate how do we separate this lobe the frontal lobe this entire area here with all these colors how do we separate this lobe from this lobe here and this lobe here well we actually should come up with a name for these lobes right this lobe here this like kind of like thing here with this wing this is called your temporal lobe and we're going to talk about this separately in another video and then there's one back here which is bordered by this sole because we're not going to mention this now and this sulcus which we will discuss is called your parietal lobe right so these are two lobes how does my frontal lobe which is this one right here this whole one in color how do i separate this from the parietal lobe well separating it from the parietal lobe there's this black line this sulcus that separates frontal from parietal what is this guy here called we're gonna number it one this one this is called the central sulcus right so the central sulcus that basically performs a boundary that separates the frontal lobe from the parietal lobe the second one is this sulcus right here this sulcus here that runs in between separates the frontal lobe from the temporal lobe what is this sulcus here this is called your lateral sulcus or sometimes you might even see it written as the sylvian fissure but i like the simple ways the lateral sulcus so separate the frontal lobe from the parietal lobe by the central sulcus and frontal from temporal by the lateral sulcus okay okay beautiful now we got to talk about some of these functional areas located within the frontal lobe let's start just anterior to the central sulcus and work our way kind of forward through here so the first one is this red portion here now just anterior to the central sulcus we there's a gyrus here which is just like a big kind of like mountain and then there's little furrows in between the mountain which are called your sulci right this gyrus here is actually called your pre-central gyrus but that's the structural anatomical term the functional portion of this gyrus is actually referred to as the primary motor cortex so it's called the primary motor cortex and the basic function of this primary motor cortex is it is involved in voluntary movement particularly of skeletal muscles okay voluntary movement so if there's one way to describe it voluntary movement all right beautiful go just a little bit interior right so here we had our primary motor cortex go just a little bit anterior to this then you have this next functional lobe this next functional lobe in this navy blue color is called it's actually called your motor association cortex so it's actually called your motor association cortex but it's made up of two components it's actually made up of what's called the pre-motor cortex and another one which we're going to just abbreviate right now called the supplementary motor area or supplementary motor cortex these two areas make up this blue portion called the motor association cortex their job is relatively straightforward they're involved in movement but particularly the planning of movement the sequence of movement and also the execution and the execution of movement okay boom all right so we have the primary motor cortex and the motor association cortex which is made up of two areas the pre-motor cortex and the we're going to actually be more specific and put the supplementary motor area or cortex all right involved in planning sequencing and execution of movement all right so we hit the primary motor cortex we hit the motor association cortex which is made up of pre-motor and supplementary motor cortex move a little bit anterior this right here is another special structure called the frontal eye fields what is this structure here called it is called the frontal eye fields and these are really cool structure and they're involved with particularly voluntary rapid or sometimes referred to as cicada eye movements and we'll discuss this in a little bit more detail what i mean with this but for right now if you just had to come up with a really simple way of explaining the frontal eye fields it's involuntary involved involuntary rapid eye movements okay the next structure here we covered the primary motor we covered the pre-motor supplementary motor we covered the frontal eye fields now move a little bit more anterior you have this big portion here in this baby blue color what is this one this is called your prefrontal cortex what is it called your prefrontal cortex now sometimes it's actually more specifically referred to as your prefrontal association area but for right now we're going to stick with prefrontal cortex and i'll explain what i it actually more in detail what it does but for right now the basic function of the prefrontal cortex is it's involved with memory right so memory and learning that's one big thing so it's involved with memory and learning it's also involved very interestingly in motor planning so it does have some involvement in motor planning because it interacts with the basal ganglia and then the other thing is it's involved with our personality and our behavior very cool right okay so we have that function of prefrontal cortex being memory learning motor planning and even personality and behavior okay the last area that i want to talk about and point out here which is in the frontal lobe is this orange lobe right this orange portion here this orange portion in the frontal lobe is actually called broca's area okay so this this area is called broca's area now one thing i want to make sure that we point out is that this broca's area is actually found particularly in the dominant hemisphere of a patient so in other words if a person is right-handed broca's area will more likely be on the left side of that frontal lobe okay so broca's area broca's area again remember what do you need to know about broca's area it is usually in right-handed people is actually in the left frontal lobe okay now the next thing i want you to remember here is broca's area not only is it only located in the dominant hemisphere which is usually in right hand people left frontal lobe it's involved with muscles of speech so it's involved in the muscles that help us to produce speech all right so that covers the basic functional anatomy and the basic kind of just one sentence function of each one of these cortical areas now let's really dig into detail in each one of these and really discuss them in clinical correlations all right so now let's go ahead and talk about a little bit more detail the primary motor cortex right we said that it's involved in voluntary motor movement right now how is it involved in voluntary motor movement okay you guys got to remember again where is the primary motor cortex just anterior to the central sulcus and this portion here right and this is actually the anatomical term for this is called the pre-central gyrus now the primary motor cortex is very interesting because it descends down from the cortex to the brain stem and to the spinal cord the final motor plan so when it sends this motor information down it sends it down via what's called two tracks one track will go all the way down to the spinal cord and innervate the neurons of the anterior gray horn this will then activate the neurons of the anterior gray horn that will come out of the spinal cord and go to the muscles particularly of limbs trunk right limbs and trunk particularly your axial and kind of appendicular skeleton this tract going from your cortex all the way down to your spinal cord is called the cortico spinal tract and there's two types your ventral and your uh your lateral corticospinal tract regardless of that again the way that it actually causes voluntary movement is it sends a motor plane from your cortex down to your spinal cord out to the muscles okay the other thing is it not just is the muscles of the limbs in the trunk but also muscles of kind of the the head and neck area as well so on the way down sometimes it also gives innervation to some nuclei located within the brain stem like what nuclei well particularly motor nuclei of particular cranial nerves that supply skeletal muscles of the head and neck like which ones well the first one is your trigeminal nerve your trigeminal nerve is what cranial nerve five and cranial nerve five supplies what muscles of mastication your chewing muscles it also will innervate what else this red neuron here this is your facial nerve facial nerve is also known as cranial nerve seven and cranial nerve seven supplies the muscles of facial expression okay the blue one this is actually a combination of multiple neurons here actually uh cranial nerves 9 10 and the cranial part of 11 which is the accessory nerve so we're not going to write all that down i'm just going to put down here cranial nerve nine which is your glossopharyngeal cranial nerve 10 which is your vagus and cranial nerve 11 which is the accessory nerve these supply both the glossopharyngeal vagus the muscles of your pharynx your uvula your soft palate your larynx and then the accessory nerve it can also supply some of those muscles but it also supplies the sternocleidomastoid and your trapezius muscles okay the other thing is it can come down and stimulate this nucleus here which goes to your tongue do you guys know what nucleus this is this is the hypoglossal nucleus which will go via the hypo glossal nerve and the hypoglossal nerve is actually known as cranial nerve 12. so the motor cortex not only can communicate with the spinal cord but it can also communicate with these cranial nerve nuclei and this is a special tract the track going from the motor cortex to these cranial nerve nuclei is actually referred to as the cortico bulbar tract so when i say it's involved with voluntary control of motor movements this is how it is involved in it so again it's involved in voluntary motor movements and how the way we just described all of it isn't that cool all right there's one other thing that we have to talk about here and it's very important especially when it comes to clinical correlation this primary motor cortex it has a specific somatotopic arrangement that we have to discuss what does that mean let's come down and discuss what this means all right so now what i want you to imagine is we take that area of the cerebral cortex right so if i were to kind of just give you a mini diagram here imagine here i have that cerebrum here and i'm taking that i'm taking that central sulcus here and i'm taking a slice right here okay so here's my slice and i'm really zooming in on this portion in a coronal view so this is what we're seeing when you look at it here's all of your primary motor cortex all of this that i'm kind of like kind of shading here in these lines this is all your motor cortex which motor cortex primary motor cortex well remember i told you that the motor cortex basically gives off its axons right that come down and do what supply the muscles of the corticospinal tract cst or corticobulbar tract which is the muscles of limb and the trunk and then the muscles of the head and the neck well if we really look at where the neurons that are controlling more of the limbs trunk head and neck is it's organized in this particular type of somatotopic arrangement that's very important i like to remember it very simply if you look at it here you see foot which is the most medial portion kind of going into the calf to knee to the thigh to the hip area working your way up towards the top and moving laterally you got the trunk you got the shoulder you got the arm you got the forearm you got the hand here then as we're continuously working laterally and down you have your head neck and then the tongue and some of the muscles involved with speech and swallowing down here at the bottom right most inferior and lateral that is very important right there's two reasons why okay one of the reasons there's two things that we need to take away from this one is that obviously based upon a particular area right of the cerebral cortex the neurons coming down is dependent upon which area you're at so more medial aspect is going to be where that's going to be lower extremity more of the lateral aspect is going to be upper extremity and as you go most lateral and inferior you're going to be talking about face and neck area right now what is this called there's a special name for this whole thing where we draw like a little man in this area what is this called this is referred to as a motor homunculus and this is one of the ways homunculus the ways that we describe somatotopic arrangement of the primary motor cortex there's a second thing i want you to take away not just kind of the way that this is arranged but also the size of particular body parts right the size of the body part there's a reason for that because you kind of look at the hands if you look at the face if you look at the tongue these are larger than some of the other actual organ body parts the reason why is the larger the body part the more motor units okay this means more motor units that means if there's more motor units that means that there's more fine control fine motor control involved so if you think about it there's more fine motor movement involved within your hands and within your tongue than there is within your toes and in your your thigh area okay so that's a big thing i want you to take away from this larger the body part that we see in this motor homunculus the more motor units are going to it because it needs more fine motor control the other aspect is that this is important because when people develop strokes you guys know that there is our an artery supply here right let's say that there's an artery that supplies this entire kind of area here okay this is actually referred to as the anterior cerebral artery so the anterior cerebral artery supplies most of the medial aspect of the primary motor cortex the other one which supplies most of the lateral portion of the cerebral cortex is which one this is actually via the metal cerebral artery so if someone develops an occlusion or an imbolus that blocks the middle cerebral artery where is the actual motor deficit going to be more if you look over here where upper extremity head neck area right so that's important if it's the anterior cerebral artery it's going to affect more of the medial portion what is this lower limbs bottom bottom part of the trunk so the easy way to remember it is if there is a basically an occlusion of the anterior cerebral artery which part and which motor deficit are you going to see well it's affecting more of the medial aspect which is where your lower limbs are so you're going to see more lower extremity what paralysis right all right beautiful but if it's the middle cerebral artery that's actually occluded and it's not delivering blood to that part of the motor cortex which area of the body is going to be actually having the paralysis well think about it this is more lateral so this is going to be more upper extremity head and neck region so we're just going to put upper extremity okay but do realize that it could the more lateral you go it obviously could affect even face head neck area okay all right so that covers the basic thing that i want you guys to know about the primary motor cortex it's basic function how those functions are actually carried out the motor homunculus the significance of it with respect to the size of that basic body part and motor unit and the clinical correlation behind all right the last thing i want to mention here with respect to the primary motor cortex is sometimes this can come up in exams where generally we apply a name right to this particular area of the cerebral cortex called the primary motor cortex but there was a guy named broadman who actually came up with particularly a way that he likes to describe the different areas of the cerebral cortex and he gave a number to that particular cortex and he liked to call this number oh well this cortex brodman area number four so sometimes you can't see these broadman areas come up on exams remember primary motor cortex is also known as broadband area number four all right let's move on all right so now let's talk about the again what is the name for the combined effect of these two it's called the motor association cortex right which is made up of the pre-motor cortex and the supplementary motor cortex now if we're really being specific right so again here's your central sulcus right here right that black line there just anterior to it is going to be your primary motor cortex now if i were to really be specific the pre-motor cortex and the supplementary motor cortex they actually technically are different defined areas if i were to draw the more lateral portion here in this blue color this navy blue color this is your pre-motor cortex to really differentiate it technically this little piece up here more medial superior portion that is technically your supplementary motor cortex but we're just going to consider this entire area here a part of what this entire area here is actually called your motor association cortex all right beautiful the pre-motor cortex and supplementary motor cortex they're very interesting one of the things that i think is really cool about these is that they also contribute to voluntary motor movement right so they're also involved in voluntary motor movement but here's what's very interesting they're more involved in fine motor movement okay and they contribute to the corticospinal tract now portion wise if we were to give an actual percentage it's somewhere around 15 percent contribution to the corticospinal tract right now if you guys remember from the corticospinal tract that was coming from one area that was coming from the primary motor cortex and it was coming down here and going all the way down to the anterior gray horn of the spinal cord and acting on these lower motor neurons here right well in the same way this pre-motor and supplementary motor area can also give their axons that can contribute into this entire thing here that is called the corticospinal tract but here's where we actually have to be a little bit more specific it does contribute to the corticospinal tract but we have a little man here right this is our little man here when it actually supplies these lower motor neurons these lower motor neurons only go to particular muscles and the particular muscles that it goes to is actually going to be more the proximal extremities so your hip and shoulders and it's also going to supply the muscles of the trunk so when we talk about muscles that this is contributing what's actually supplying being a contribution to the corticospinal tract it's really only supplying what kind of muscles here well your trunk what's your trunk muscles called it's called your axial musculature so it's applying the axial muscles and it's supplying the proximal muscle musculature right so it's supplying the proximal limbs which is the hip and shoulder joint so that's actually how it is contributing to the corticospinal tract but it's more particularly involved with fine motor movement of those muscle areas okay now that's one function of the pre-motor and supplementary motor cortex there's another involvement of them remember i told you that they're involved with planning sequencing and execution of the movement how let's talk about it all right so remember i told you that it's involved in three particular functions right what do we say it's involved with the planning of movement okay it's involved with the sequencing of movement okay and it's involved with the execution of movement this is actually a really cool thing so remember we said that we had the primary motor cortex right which is right here and then we're just going to draw all one area that entire motor association cortex which is an entire area made up of the pre-motor and the supplementary motor cortex here's what's really cool obviously the motor plan will go down to your skeletal muscles right so it has to go down to your skeletal muscles and stimulate lower motor neurons right that'll go out to your skeletal muscles we know that but you know what else is really interesting and also we know that the this cortex the pre-motor and supplementary is also contributing to this but regardless here's what's really cool the pre-motor and supplementary motor cortex have communications with two particular structures this is so cool one is your basal ganglia they love to communicate with the basal ganglia which are involved in kind of helping to initiate motor movements prevent unwanted motor movements and modify motor movements in a particular way so how does it does do this the pre-motor cortex can actually communicate so the pre-motor and supplementary motor area can actually communicate with one another and they communicate with one another to come up with actually some type of modified motor activity so basically helping to initiate movements that you want prevent movements that you don't want and modulate in a particular way here's the other great thing your cerebellum your cerebellum also interacts with this pre-motor and supplementary motor area now your cerebellum is getting information from your inner ear right so it's getting information from your inner ear about particularly like static and dynamic equilibrium it's also receiving sensations from the body what type of sensations maybe touch sensations proprioception which is the position of my muscles my tendons my joints and three-dimensional space it's receiving all that information going through it combing through it then it's also receiving information from my pre-motor and supplementary motor cortex about the pro the actual motor plan that they want to initiate it takes all the sensations it takes all the equilibrium information all the actual motor plan that we have kind of set out goes through it and then sends back upwards its modifications it sends back upwards to these motor cortical areas it's actual modifications so how does the pre-motor and supplementary motor cortex actually help to plan sequence and execute movements it does that by interacting with two primary structures one is the basal ganglia and the second one is the cerebellum oh that's so cool man all right so that's what i want you guys to know with respect to how the pre-motor and supplementary motor cortex perform their activities all right and the same thing remember i told you that they can be asked broad you can be asked broadband areas on your exam so pre-motor and supplementary motor cortex or your motor association cortex is actually given a particular broadband area and this broadband area is referred to as broadman area number six okay so that covers the pre-motor and supplementary motor cortex let's move on to the prefrontal so now prefrontal cortex prefrontal cortex is also known as the prefrontal association area this area is super interesting because it carries out so many functions it can really be quite complicated when you really dig into the nitty-gritty of this prefrontal cortex we're going to kind of keep it for the most part to the most important things that you guys should take away from the prefrontal cortex related to clinical conditions so prefrontal cortex is really your thinking area of the brain but again let's outline where it is so just to recap again what's this cortex here primary motor cortex what's this cortex just anterior to it this is your pre-motor and supplementary motor cortex which is called your motor association cortex we're going to come back to this next one here which is just anterior too we're going to talk about that next this is called your frontal eye fields and this next one the one that we're focusing on primarily is going to be this entire area here what is this one called this is called your prefrontal cortex now the prefrontal cortex is very important because it has a lot of different functions one of the big ones that i think is really important to remember is it's involved with your personality okay so it's involved with personality and it's involved in your behaviors right so it has some type of emotional type of involvement here the other aspect here is that it's involved in your memory okay so it's involved in your what's called particularly your working memory so taking short-term memory plus rehearsal and helping to commit that into your working memory okay so it's involved with your working memory the third thing that it's also involved for besides personality behaviors working memory is it's also involved in your cognition okay so it's also involved in your cognition so your ability to learn new things so it's involved in cognition or your ability to learn new things the next thing that it's involved with is your actual your reasoning and judgment okay so it's involved in your decision making so decision making okay so particularly you know your reasoning behind making a decision in the judgment involved in that decision so again it's involved in reasoning and judgment all right beautiful and the last thing that i want you to remember of this is that it's involved in motor planning so it's also can be involved in motor planning okay so let's kind of talk about how the prefrontal cortex or prefrontal association area does this the way that i want to explain a lot of this is that the prefrontal cortex has communication with so many other structures of the brain like tons some of the areas to highlight here that it is communicating with that are important is one is called your one of the areas where you store memory you know deep within the temporal lobe you have this structure here called the hippocampus so you have this structure here called the hippocampus the hippocampus is really important for the memory aspect of your brain so memory is obviously important because that isn't going to be one of the functions of the prefrontal cortex so the hippocampus has to communicate with the prefrontal cortex the other thing is with respect to your personality your behaviors this has to connect with your limbic system and there's a lot of limbic structures that communicate with the prefrontal cortex what are some of these areas one of the areas is actually kind of deep in here we're just going to kind of show it like this it's going to be deep you can't see it here it would be deep in the cerebrum but it also communicates what's this structure this structure is called the hypothalamus so the hypothalamus will also interact with the prefrontal cortex because that's a limbic nuclei another limbic nuclei is called the amygdala so there's another structure here deep within the temporal lobe and this also communicates with the prefrontal cortex again what is this structure here called this is called the amygdala so the amygdala is another important limbic system structure that influences our kind of personality and behavior the other aspect behind so that kind of explains the working memory that kind of explains the cognition that kind of explains the personality and behaviors there's another area deep within our actual midbrain actually called the ventral tegmental area so we'll draw it like this there's another area here called the ventral tegmental area and what happens is the ventral tegmental area which is in your midbrain it also can communicate with your prefrontal cortex and this is actually involved in a lot of your reward systems your addiction kind of systems which can also involve some of your decision making skills the last thing is your motor planning here's what's really interesting the prefrontal cortex can also communicate with this multi multimodal area back and deep into your parietal temporal kind of occipital lobe area there's this area here called the posterior association area and what happens is a lot of stimuli kind of end on this area so here in your occipital lobe we'll talk about it later but this is where vision it terminates that can be sent visual information could be sent to this post here association area right here is where auditory sensation is involved in your temporal lobe that can send that auditory stimulus to the posterior association area and then right here is going to be where sensations like actual somatic sensations are actually kind of recognized and kind of modified here and that can also be sent to this posterior association area so you have visual auditory and somatic sensations all communicating in this area and guess what all this can be sent to your prefrontal cortex to be involved with motor planning because this prefrontal cortex can communicate with the basal ganglia so as you can see the prefrontal cortex can be very complicated when you really dig into the details of it but what i want you to remember is how it is involved particularly with personality and behaviors and your memory is the connection between the hippocampus and your limbic system and then how it's involved particularly with kind of decision making is also via the ventral tegmental area and again some of these limbic structures and then again motor planning is the way it's connected with the posterior association area and the communication with the basal ganglia the reason why i wanted to kind of like talk about all of these things is because there is a very common condition that can affect and plague the frontal lobe let's talk about that quickly all right so i really want to quickly kind of explain why the prefrontal cortex is such an important area to know and the reason why is that there's a condition called frontotemporal dementia so as you can tell this condition is where there's damage of two lobes the frontal lobe and the temporal lobe we're really kind of focusing on the frontal lobe aspect of the frontal temporal dementia but what happens is there's actually going to be damage or atrophy of these areas so all the functions that we discussed are going to be altered so let's explain how and why it's important to know these basic functions remember one of the things that we just said is that there will be personality and behavioral changes what does that mean that means that the patient may have some degree of they might be aggressive right so they may be aggressive they may be hostile right they may be kind of very irritable or agitated and that's because you've damaged the area that's involved with their normal personality and behavior right that's relatively straightforward the other aspect here is their working memory now generally memory becomes affected a little bit kind of later in the disease process usually not early it's usually later in the disease process but if you damage the prefrontal cortex you can bet that later on potentially that they may have some type of memory loss and here's the big thing not just memory loss of you know the past events but also difficulty in learning new things or storing new memories so you can actually decrease their actual ability to remember things and decrease their ability to learn new types of tasks the next thing that you're affecting is their decision making right their reasoning their judgment this is a very important one because sometimes this can cause them to perform certain types of behaviors that they would not normally perform you can think about your prefrontal cortex when it's working really well as an area that says okay i want to do this terrible thing your prefrontal cortex says i don't think that's a good idea to do that but when it's damaged you have no longer this ability to inhibit those thoughts so there's a disinhibition in that sense and so this leads to them having uh kind of inappropriate hypersexual behaviors so this can lead to increased kind of sexual hypersexual behavior but not in a good way in an inappropriate way it also might lead to gambling right because you're taking away that area that is kind of helpful for reasoning and judgment and also it might actually cause the patient to be a little bit apathetic but again that kind of comes with the personality behavior aspect as well the last thing is that sometimes remember what i told you the prefrontal cortex what do we say just so we remember this can communicate it does this motor planning by communicating between the posterior association area to the prefrontal cortex and the prefrontal cortex can communicate with the basal ganglia which communicates with your motor cortex so if you damage the prefrontal cortex you're affecting the communication with your basal ganglia affecting the motor cortex output right particularly this can lead to actually parkinsonian types of symptoms so later on in the disease they also might develop motor deficits but the motor deficits that they actually develop present more in a parkinson's type of presentation parkinson's like so remember we talked about how primarily this frontal temporal dementia affects the frontal lobe and when it affects the temporal lobe it's more likely affecting speech and the ability to comprehend language so that whenever this is damaged it can actually cause aphasia on top of the things that we just talked about all right again just to again remind you that sometimes these can be questions on this in the exams the broadband area for prefrontal cortex there's so many different areas so it's a very wide range of areas so some of the areas that we're going to mention here actually there's a couple of them so it can be anywhere from numbers 8 to 14 right and then you can add on to that 24 25 32 and 45 to 47 so there's a lot of different areas broadband areas for this prefrontal cortex that it actually encompasses okay so that covers our prefrontal cortex let's move on to the frontal eye fields all right the frontal eye feels this is actually a really cool area the frontal eye field so again remember your kind of uh areas here this is our primary motor right then just anterior to that is what your motor association cortex which we said is made up of the pre-motor and the supplementary motor cortex then we've already discussed the prefrontal cortex which is pretty much all of this portion here right all of this and so this next portion that we're going to discuss right now is the frontal eye fields which is about right here okay the frontal eye field is actually really interesting we said it's involved with the voluntary movement voluntary rapid eye movements remember we said it was actually specifically called sakads so it's actually more particularly involved in cicada eye movement and this is basically saying rapid eye movement but to be more specific because we're an engineers we like to know a little bit about this stuff not going into crazy detail how does this frontal eye field cause cicada guy movements well in the actual brain stem you have a couple areas here that we have to talk about really briefly this one here this red nucleus here is actually the nucleus of cranial nerve three this green nucleus here that we're going to kind of zoom in on here is actually cranial nerve 6 abducens and then this pink structure here which we're going to talk about definitely going to abbreviate this one it's called the paramedian pontine reticular formation you definitely know why we're abbreviating that bad boy but again these are the three areas that the frontal eye fields are going to communicate with all right so now what i want us to do is pretend that we're looking here at the frontal eye field and kind of zooming in on it so imagine here i have a frontal eye field right and this particularly is the right frontal eye field over here we'll have another portion this would just be the left which we can't see but this would be your left frontal eye field the right frontal eye field will actually send its neurons to the left paramedian pontine reticular formation which we discussed here this is our left paramedian pontine reticular formation this would be our right paramedian pontine reticular formation so again in that sense these cross the basically the the truth of the matter is is that these send contralateral pathways to the paramedium pontine reticular formation all right let's mainly focus just for the sake of it since we talked about right here we're mainly going to focus on the pathway involved with this right side so let's get rid of this one here okay so if we follow this through we have the right frontal eye field sending connections down to the what to the left pair medium pontine particular formation when it acts on that left paramedium pontine reticular formation this sends its axons to this nucleus here what is this this is your sixth nerve nucleus but it's which one your left your left cranial nerve six right then two things happen here when you stimulate the left sixth nerve it does two things one it actually will send axons that go over here to the contralateral third nerve nucleus so this is now your right cranial nerve three okay the other thing it will do is if you stimulate the sixth cranial nerve is it will send axons out via the abducens nerve to the muscle that the sixth nerve supplies what is that muscle lr6 right so if you remember l r six that means that the sixth cranial nerve supplies the lateral rectus and the lateral rectus is responsible for abducting the eye so this left lateral rectus will be stimulated if the left lateral rectus is stimulated which direction will the eye pull it'll pull to the left right now watch this the sixth nerve nucleus not only does it simulate the left lateral rectus it stimulates the right third nerve now if we stimulate the right third nerve nucleus it's going to do what it's going to go to what muscle here the medial rectus on the opposite eye so it's going to stimulate the right medial rectus what does the right medial rectus do it adducts the eye so now which direction will pull the eye medially which direction is the eyes moving to the left and which frontal eye field stimulated this process the right so the right frontal eye field causes contralateral conjugate meaning that these two are moving in coordination contralateral conjugate deviation of the eyes that is so darn cool how it does that so the reason why i want you guys to know this is that if someone has a lesion of the frontal eye field now what happens you damage this pathway now the left paramedium pontine reticular formation can't stimulate the six nerve so this is inhibited that means that the sixth nerve can't inhibit the third nerve that means this is inhibited that means that the sixth nerve can't stimulate the lateral rectus that means this is inhibited and if the third nerve is inhibited it can't stimulate the right medial rectus so now the eyes won't be able to move towards the left what does that mean if the eyes can't move towards the left conjugately which way will they start to deviate to the opposite side and so because they no longer have those muscles pulling in the same direction the eyes will start deviating to the opposite side if they start naturally kind of deviating we'll draw here with this pink arrow to the other side which direction are they deviating with respect to the actual lesion the same side which is where the right frontal eye field is so this is called ipsi lateral conjugate gaze deviation and that is why this is so important sometimes to just understand basic functions here all right so that covers our frontal eye field now the broadband area for this one it's actually technically a part uh considered a part of the prefrontal cortex but the broadband area for this is actually number eight okay so broadman area number eight for the frontal line field now let's talk about broca's area all right the last area that we got to talk about of the frontal lobe within the cerebral cortex is this last area right so we talked about this one a little bit we said it was called the broca's area right because we've already talked about the primary motor the supplementary and pre-motor the frontal eye fields and the prefrontal cortex the only area that's left is the broca's area now here's what i want you to remember we said that the broca's area is involved with basically stimulating muscles of speech right and the big thing i want you to remember is we said that the broca's area is located on the dominant hemisphere so what does that mean that means kind of if you have a right-handed person that means that broca's area is most likely going to be on the left frontal lobe in the inferior frontal gyrus so left broca's right now the question is is how does it stimulate muscles of speech how does it help with this process well the broca's area it communicates with a couple other areas it actually communicates with this area we'll talk about when we talk about the temporal lobe called wernicke's area so this is called wernicke's and wernicke's is where we comprehend language because it receives information from your visual cortex it receives information from your auditory cortex basically under tries to comprehend and understand that language and then send that information from the wernicke's area to the broca's area via a connection called the arcuate fasciculus but basically the broca's area now will then take that information that it received from wernicke's area about the language and the comprehension of it and send that information so that we can speak basically give a response to what we are hearing or seeing right so how does that work well broca's area is actually going to be sending down it actually contributes a little bit to those uh kind of those the corticospinal cortical bulbar tracts if you remember right here is our primary motor cortex so coming down from that primary motor cortex you're going to get some contribution from the broca's area and what this is going to do is it's going to come down you know to your actual brain stem and it's going to give stimulation to particular nuclei located within the brainstem one of these nuclei is actually called your facial nerve now the muscle that we're actually talking about here that the facial nerve stimulates is actually called the orbicularis oris which basically helps to kind of change the shape of the mouth right that's important in speech because it kind of changes the way that we enunciate the process of speech right the other nucleus it stimulates is actually called the nucleus ambiguous but that comes out via a couple nerves one of the nerves is called cranial nerve what nine the glossopharyngeal nerve the other one is called cranial nerve 10 which is the vagus nerve and the last one here is the cranial part of the accessory nerve all of these make up what's called the pharyngeal plexus and this supplies a bunch of muscles it supplies the soft palate it supplies the uvula it supplies the pharynx it supplies the larynx and this is the big one the larynx but all of these structures are important for voice for basically speech production okay i'll explain all of it as we come to the end of it but that's another thing that it stimulates via the broca's area the last area is the hypoglossal nucleus which comes out via the hypoglossal nerve which is cranial nerve 12. and this stimulates the muscles of the tongue so now if you have stimulation of all of these areas think about that whenever you are basically pushing air from your lungs out it has to go from the through the larynx the larynx has little vocal cords the vocal cords they're basically the tension on them is dependent upon the muscles which is stimulated by the vagus vagus nerve and the a little bit of the accessory nerve so now when these muscles are stimulated it'll change the tension in the vocal cords it also may change the shape of the pharynx a little bit it may help to move the uv in the soft palate a particular way and now that speech that's coming up and hitting the vocal cords and resonating through the larynx through the pharynx across the soft palate and uvular area is all going to have to go through a specific resonating pathway carried out through these nerves then the tongue we might move the tongue in a particular way that helps us to articulate speech particularly right then as this this speech is moving out across all of these structures past the tongue then we have the orbicularis oris which kind of changes the shape of our mouth maybe to enunciate or maybe change the way that we speak particular words so now how is broca's area involved with muscles of speech it stimulates all of these nerves which stimulate all of these muscles that are involved in the speech production which all have different types of functions right why is this important when someone damages the broca's area maybe because of a middle cerebral artery lesion you lose the ability to speak properly right all of these muscles of speech are now going to be damaged in some way shape or form so because of that speech is interrupted but how is it interrupted these people they're having difficulty getting these muscles going and really helping to get the speech moving so because of that their speech is not really it doesn't flow perfectly so it's called non-fluent speech and another thing is they have a hard time being able to make their speech kind of grammatically correct so it's non-fluent speech but the other aspect of it is that it is completely grammatically incorrect and the last thing here remember i told you that wernicke's area is involved in what the comprehension of language this area is fine all we did was damage the broca's area so the communication from all of these areas from your vision from your auditory and then the comprehension of those things being sent to the broca's area is all intact we didn't touch that area all we touched was the broca's area so comprehension of language will be understandable so they do have comprehension of language so this is intact now there's another name for broca's aphasia that sometimes needs to be uh kind of expressed here no pun intended it is actually sometimes referred to as because you can't kind of say what you want to say it's called expressive aphasia okay and so this basically gives us everything we need to know about broca's area also if you guys want to know what broca's aphasia looks like we're going to have a link down in the description box to a video where you guys can go ahead and see how these people have difficulty with their non-fluent and grammatically incorrect speech but understand what you're trying to say or what you're trying to show them okay all right ninjas so in this video which i know was long i'm sorry but i wanted to make sure all of this stuff makes sense and it's understandable and if it is understandable it does make sense it did help please hit that like button comment down in the comment section and please subscribe also down in the description box we have links to our facebook instagram patreon account you guys want to go check that out follow us help us out in any way that you guys can we would truly appreciate it all right ninjas as always we thank you love you and until next time [Music] you

Channel: Ninja Nerd Lectures

Views: 63,675

Rating: 4.9733238 out of 5

Keywords: Ninja Nerd Lectures, Ninja Nerd, Ninja Nerd Science, brain, neurology, frontal lobe, neuroanatomy, cerebrum, anatomy, nervous system, neuroscience, cerebral cortex, occipital lobe, central nervous system, temporal lobe, cerebrum series, usmle, physiology, medical school, medicine, Zach Murphy

Id: 1CCNldjSEXs

Length: 53min 59sec (3239 seconds)

Published: Mon Nov 16 2020