Overview of Neuroanatomy and Functions

Well I really appreciate the opportunity to be here. I apologize that I'm in scrubs but Christy put me to work by booking two cases for me today too as well as a lecture. And then she gave me the task of making neuroanatomy ridiculously simple. So what I did is I found a video. That's always the easy way to make things simple. the parts of the brain performed by the brain yes neocortex frontal lobe it goes pretty fast so you gotta write all down hippocampus neural node right hemisphere pons and cortex visual brainstem brainstem sylvan fisher pineal left hemisphere cerebellum left cerebellum right synapse hypothalamus striatum dendrite. Alright, this is the part where he scratches a little bit. Axon fibers matter gray. Brainstem! Brainstem! Central tegmental pathway. Temporal load. White core matter. Four brains go. Brainstem! Brainstem! Central fissure quartz... All right, we'll stop. That's too much fun. Okay. So neuroanatomy is fun. It's not that much fun. So what I'd like to do, and obviously it's very difficult to put together a big course into a 45-minute talk, so I apologize for not being very in-depth, but I want to just quickly run over... The basic neuroanatomy that I think all of us need to be familiar with, I'm just going to focus on brain anatomy. And so just as a reminder, the brain obviously is a very complex organ, and it develops from what is a rather simple tube into this very complicated structure with many gyri and sulci and a very complex folding pattern that results in the anatomy that we look at. And so when we look at the brain as a final product, We can generally divide it into regions and we'll try to do that today and talk about what happens in the cerebral hemisphere which is the cortex of the brain which is the area that we we often think of when we talk about the brain but there clearly are some very important deep structures the dying cephalon which is a thalamus and hypothalamus play very critical roles as does obviously the brain stem as Pinky the brain emphasized there and then we'll talk a little bit about the cerebellum as well. So starting with the cerebral hemisphere, this really is the largest portion of the brain. It's about 83% of the total brain mass. It covers the diencephalon, it covers the midbrain, it sits above the cerebellum. And it does have what at first glance looks like a random pattern of gyri and sulci, but as we know there is a very unique characteristic pattern here that does allow us to identify different regions of the brain and different functional areas. And the first level of dividing the brain into regions is dividing it into lobes. So as I'm sure we all remember from school, the frontal lobe and the parietal lobe are separated by the central sulcus, and that's the main sulcus that separates these two regions of the brain. There's a lateral or sylvan fissure that separates the frontal lobe from the temporal lobe. There's an occipital lobe that's defined by the preoccipital notch. And then there is the transverse fissure, which will... divide the supratentorial space from the infratentorial space. So this is a lateral view of the brain. If we look at the brain from above, we can identify again a frontal, parietal, and occipital lobe, and a central sulcus here that's dividing the frontal from the parietal. So this gives us a real general kind of zip code segmentation of the brain. It's important to keep in mind that the brain is not just that lateral surface that we look at. There's a medial surface, so again we can identify a frontal and parietal lobe. separated by a paracentral lobule, which is where the central sulcus dives in. Functionally, that's the leg area. We'll talk a little bit about that. And then we can identify an occipital lobe separate from the parietal lobe, defined again by the preoccipital notch laterally and then the parietal occipital sulcus here. We know this is where vision is, for example. So this kind of general subdividing of the brain has some functional significance. And then if you look at the brain from below, there's a ventral surface as well. Again, a very characteristic pattern of temporal lobe gyri and sulci and interhemispheric fissure. And then now the cranial nerves and the brain stem itself and the cerebellum are more evident. So a lot of complicated anatomy. And there's a long history of trying to understand the anatomy of the brain. And one of the earliest important steps in trying to understand the cortex, since it did seem like a very random... Structure was some of the work that Brodmann did. So Brodmann was a German neurologist, not a neurosurgeon unfortunately, but still very very smart. And he was one of the first to really look at these sub regions and he looked at them histologically, looked at the cell types in those areas and began to divide the brain into regions. And so this is a colorized version of the original diagram that Brodmann published. It was done in black and white. dividing the brain into 52 cortical areas. And this has been refined quite a bit over time and there obviously we have a better understanding than than Brodman had but this was a really important first step forward in understanding that the brain is not just a random gyrated structure but but there is some function here. So here's all the 52 areas we won't go over all of them but this will be on the exam so it's a very important way. I think the the more useful way to look at brain anatomy and what we try to teach our trainees here is to really look at the anatomy functionally rather than structurally. So I think it's very useful to to look at the frontal lobe of the brain and to think about an area that is prefrontal, which is a pink area here, and we can talk about the prefrontal cortex and what happens there. We can talk about the motor region of the frontal lobe. So we can divide this frontal lobe into two regions. We can talk about a sensory area. which is the blue, and we have a primary sensory area here. We also have another primary sensory area in the back of the brain. And then a lot of the light blue are these association areas. And association areas are very interesting because a lot of higher order functioning happens in these association areas. Bless you. And the prefrontal cortex, too, is technically an association area. So these are parts that are taking multiple inputs, associating them with one another to comprehend our world. So what I'd like to do is walk through these. So we'll start with the prefrontal cortex. This is the part of the brain that is the most complex and most developed in humans. And so this really is the closest thing to where our mind sits, if you will. A lot of complex behavior, cognitive behavior, social behavior, personality, expression. Those of you that have taken care of patients with prefrontal lobe injuries know that people change when this part of the brain is not working well. So a lot of executive functions as well lie in here. So a lot of our higher cognitive processing, trying to follow rules, perform multiple tasks at a time, control impulses. And again, a lot of personality lies in the prefrontal cortex. And a lot of working memory is here too. So for those of us that have had patients that have a hard time with working memory, hanging on to a rule, hanging on to short-term memory and being able to retrieve it while doing a task. It's very difficult when you have a prefrontal cortex injury. When patients have a head injury, for example, which is one of the most common causes for brain injury, this prefrontal cortex, especially the frontal lobe and the orbital frontal surface, are very prone to moving within the cranial vault and getting damaged. So that's why we see quite a bit of that. So that's a brief kind of idea of what happens in the prefrontal area. If we move back to this darker red area, this is the more posterior portion of the frontal lobe. And this is the motor area. And so the motor area has multiple regions. There's a primary motor cortex, which is Brodmann area 4. And then there are premotor areas. There's an eye field and a language field here. So the primary motor cortex is the one we all learned back in school. This is the precentral gyrus. So it's right in front of that central gyrus. So it's right at the very back of the frontal lobe. Very large pyramidal cells here, which is why Brodmann identified this as region 4. It's a very distinct anatomic region. And it does have a somatotopic organization, so a lot of us remember the homunculus, this idea of a little map of the body within the frontal lobe. So the more lateral parts of this are areas that are controlling movement of hand and face and mouth. The more medial and superior areas are where the leg area is located. And this becomes important in patients that have a stroke or a tumor, where out here you're going to expect more facial droop, hand weakness. An ACA stroke, for example, which would affect more of the paracentral lobule may result in just leg weakness, but the arm and hand and face may be okay. So this organization is very important functionally. And the motor cortex is a very simple and basic starting point for motor movement, but there's a lot of motor planning that's involved, and that's where the premotor area comes into play. And it's really closer to that prefrontal area where you're cognitively engaged that's also where you become where you're focusing your planning and your access to motor plans and selecting different motor plans and inhibiting competing plans. So a lot of that happens here in this premotor cortex area, which is a very important area and as you know if you've had a patient that's had a premotor cortex injury, a lot of times they may even look like someone that has a complete motor paralysis because they just have a very hard time with initiating and having a drive to move. Moving the eyes is a very complex motor function, so that occurs in the frontal eye field, which is located right here. And then Broca's area, which is this area here, is a speech area. And it's a pretty large area because speech production can happen with your mouth. It can also happen with your hand. You can sign speech, you can write, and you can speak. And so Broca's area is a very complex area. It's not a coincidence that it's located right next to the part of the homunculus where your mouth and hand is. So it makes sense that an area that's going to initiate that type of motor plan is going to be right next to that part of the homunculus. So then if we move back behind the central sulcus, we get into the sensory areas, and a lot of the brain is dedicated to sensory processing, to understanding the world around us and understanding stimuli as they come in. And a lot of it happens in this primary... sensory cortex or this post central gyrus, the gyrus right behind the central sulcus. And the primary somatosensory cortex is very similar to the motor cortex in that it also has a somatotopic organization. So there is a similar organization where the medial portion is the leg, the more lateral portion is the hand and face. And again, the distribution here is biased towards areas like the fingers, the hand, the face, the mouth, where your sensory discrimination is very high. Areas like your back, your sensory discrimination is much lower. And so most of us in school did the kind of sensory discrimination test where you take two little paper clips and you see how far apart you've got to get them before they feel like two pokes versus one. And if you do that on your fingertips, you're really, really good at that. On your back, it's very hard. You've got to really separate them out because the plots are much bigger. It's just not a high resolution area. So this is the primary somatosensory cortex, but then this large light blue area are these other sensory areas, these association areas, and there's a lot going on in here. There are areas that are associating input from the hands, perhaps from the eyes as well, or from the ears as well, where the primary auditory region is. There are areas that are going to get input from vision as well, so areas that lie within here are going to access input from the primary somatosensory, primary auditory, primary visual. So again, it makes sense functionally why you would put these sensory association areas here. And so we can plot out primary association areas for every sensation we have. So there's going to be an olfactory cortex for smell, a vestibular cortex for balance, a gustatory cortex for taste, and so on. And these are going to land in these dark blue areas, and then they're going to come into this sort of parieto-temporal association area where it's going to be processed and comprehended. Now vision is an interesting one because it lies on that medial surface of the brain. So if you look at the lateral surface, it's this tip all the way back here at the occipital pole. But if you look at the medial surface of the brain, you can see that actually the sensory cortex has a very interesting orientation. It lies right along this calcarine sulcus, which is a nice dominant sulcus right in the middle of the medial occipital lobe. And this is area 17, and this is primary visual cortex, so the visual input that comes from the eyes. Relays through the thalamus and comes back to the occipital lobe, comes here. And so it's the same idea where you have a primary area. So this is an area that's going to detect a flash of light, for example, in a certain area. But understanding what you're seeing in that area, understanding movement, and then identifying an object is going to happen in association areas. So when we take care of patients, it's important to keep in mind that a lesion of a primary area and a lesion of an association area are going to have different deficits. and the association areas where a lot of comprehension is going to occur. One example of that is the visual input that comes into the primary visual cortex actually goes forward to the association areas in two different streams. There's a dorsal stream which actually goes towards the parietal lobe, and that's a part of the brain that is focused more on where something is, where an object is, where you are geographically, where structures are within your world. And then there's a ventral stream that goes towards the temporal lobe, which is an association area that's more of a what area. So a lot of our recognition of a face, of an object, naming things, is going to occur here. So one example of how input coming to the primary visual cortex. might make you blind, cortically blind, if you weren't able to get that input to begin with. But if you get that input, you may have a hard time identifying where something is versus what something is, depending on whether you have dysfunction in your dorsal stream or your ventral stream. And so these are things that do come into play again when we're seeing patients with injuries to different brain areas. And then these association areas, which we've kind of talked about multiple times, again, they... Occupy different areas of the brain. The prefrontal cortex really is a very large complicated association area because identifying objects in your world but then formulating a plan, initiating a response, and trying to do that in the context of the information you've just processed is very complex and so we're talking about information coming into sensory and then perhaps going to prefrontal where you may decide how you feel about it, how you want to respond to it, what your mother or father told you you're supposed to do during a situation like this. This is all prefrontal cortex. And then you're going to go to premotor to plan a response, if it's a motor response, and then go to your motor cortex. So this really is a very complex association area. These are really complex sensory association areas where you're trying to interpret that information and identify what it is. And then language, both the motor language and the sensory language, so that's the... the Wernicke's area, which is our sensory language, and then Broca's, our motor language, these are association areas. These are areas which are taking input from multiple primary areas to either understand what you've seen or formulate a response. There is an area called the insula, which we're kind of ignoring because it's hidden under the lateral sulcus here, but the insula is a very interesting area where there's not a great understanding of what it does. It clearly plays a role in language, does play a role in some visceral kind of organ sensation, some of the autonomic type of responses in the limbic cortex and the way we respond to things. Now we talked a lot about gray matter here, but there's white matter connecting everything. And so those of us that have taken care of patients with diffuse axonal injury know that you can have a great cortex, but if white matter tracks are damaged, then function is compromised. So there are a lot of important white matter tracks to keep in mind. The ones that cross the brain. like the corpus callosum or the smaller anterior and posterior commissure. These are called commissures. These are ones that connect the left and right brain together. Those are very, very important for association and comprehension of complex input. There are association fibers which run within one hemisphere, one like the superior longitudinal fasciculus, for example. And there are projection fibers which are actually kind of the input-output from the brain. And so these white matter tracks are absolutely critical, and many of us have seen patients where... The cortical process might be fine. For example, a patient with a conductive aphasia, you know, Wernicke's is okay, Broca's is okay, but that arcuate fasciculus that connects it to is not okay. So you can see a dramatic dysfunction, even though the cortical regions are working okay. So if the connections are not there, you know, this complex computer falls apart. So it's very important to keep in mind that this anatomy is there. It can be affected by injury, and as surgeons, you know, we can actually map this. We can image this with tractography, diffusion tensor imaging. We're much more thoughtful now about white matter tracks in the brain. To kind of finish off this walk through the anatomy of the cortex, we talked about gray matter areas, we talked about white matter. It's important to keep in mind that when you take a slice through the brain, either imaging on an MRI or CAT scan or anatomically in the laboratory, you see a lot of gray matter that's deep in the brain as well. So it's not just gray matter on the surface, white matter underneath. There are areas of deep gray matter and there are many areas in the brain. These are very complex areas. Some examples are the basal forebrain nuclei, which sit in the lower back part of the frontal lobe. They're deep structures. These are areas that are very important in acetylcholine-mediated transmission. We think in Alzheimer's disease this is an area that does not function well and we lose cholinergic transmission. The basal ganglia is another great example, which is a group of many structures, including the caudate, the putamen, the globus pallidus, the subthalamic nucleus. These are areas that are involved in motor processing, kind of scaling movement, picking different motor plans. So patients with Parkinson's disease, with Huntington's disease, the cortex is fine, but movement is still affected because of these basal ganglia, these deep structures. So having just a normal motor cortex and intact white matter tracks doesn't mean the motor function is going to work well. You also have to have this deeper cortical relay working well in these deeper gray matter structures being able to regulate and control the cortex. So those are the hemispheres and then we'll kind of move a little bit deeper to some of these deeper areas as we head to the homestretch here. So the thalamus is a very important structure and this is one of the two parts of the diencephalon. So the diencephalon is made up of the thalamus and the hypothalamus. The thalamus, which means inner room, is a very interesting structure located deep in the brain. There's two of them. They look like these small hard-boiled eggs connected to each other. They form the walls of the third ventricle and they're really kind of a cut-off person, if you will, between the brain and the peripheral nervous system. So information that comes up to the brain almost always relays through the thalamus. So sensory information, visual information coming up will almost always synapse in the thalamus and then the thalamus shoots it up to the cortex. So the thalamus plays a very important role in that way. If you look at a brain, the thalamus is this structure here, so it's sitting right in the middle of the brain. If we look at a cartoon here, the thalamus are these two paired blue structures. There's an interthalamic adhesion that connects the two, and then the thalamus, just like everything else in anatomy, is broken up into sub-regions. We're not going to go over these. This is, you know, a whole lecture itself. Thalamic anatomy is a big textbook I have, which is very scary, that goes over the thalamus. But, you know, some kind of just basic things just to put it in the context of what we talked about. Sensory input, for example, from the hands and feet comes into the thalamus, and it goes to the VPL, the ventral posterior lateral nucleus of the thalamus, which is this big blue area, and then this shoots it up to that primary sensory cortex. So all the input that the primary sensory cortex gets gets from the thalamus. So, again, you can think about someone that's had a thalamic stroke or a thalamic tumor. You know, they have major, major deficits. Cortex is fine. Sensory in the hand is fine, but input doesn't get there if you don't have the cutoff person. Vision, for example, runs through the thalamus. It goes to the lateral geniculate nucleus. Auditory input goes to the medial geniculate nucleus. So a lot of the sensory information has to run through the thalamic relay. And the thalamus, for that reason, is an area that we're very interested in with deep brain stimulation and neuromodulation because it is a very critical cutoff or relay structure that can be modulated. So you can maybe turn it up or turn it down. One interesting area of the thalamus is this intralaminar nuclei, which kind of run in the middle here. This is an area that in a patient, gosh, it's been 10 years now, I think, that was minimally responsive in a vegetative state. A group of surgeons put a stimulator in this area and actually were able to increase wakefulness in that patient. This was someone that started feeding themselves and communicating, and before they weren't doing that at all. Because the intralaminar nuclei are an area that... that take input from the activating system, the reticular activating system that wakes you up in the morning and relays it to the brain to turn on the brain. So the thalamus is a very interesting area and it's one that a lot of very smart people are researching to try to better understand how we can modulate thalamic function. Below the thalamus is the hypothalamus. So if this is the thalamus, then below it is the hypothalamus. Hypothalamus is a very more basic area of the brain. It's... It functions on its own, so it's not a relay center like the thalamus. And it's really focused on a lot of autonomic type of basic functions in the brain. So emotional responses, body temperature, hunger, thirst, sex drive, sleep-wake cycle, controlling your hormones. The pituitary gland is under the control of the hypothalamus. These are very important structures. if you've had someone with a hypothalamic injury, if you've seen a child with hypothalamic seizures, for example, those manifest as a gelastic kind of laughing seizure. I mean, it's a very, very interesting area of the brain. If a young child has injury to the hypothalamus, like with a tumor like a cranial pharyngioma, they can become severely obese because they have total disruption of their normal satiety function. So hunger and thirst are here. So very, very critical deep brain structure. different from the thalamus because it's not focused on interfacing with the cortex. It's a very basic function in the brain that lies below that. And then moving beyond the diencephalon now we'll go down to the brainstem. So we're working our way down. So the brainstem really sits now in the posterior fossa. So we're below the cortex, below the diencephalon, and a lot of automatic, programmed, reflexive type of behaviors come from here. So this is not conscious processing in the brain stem. And it is broken down into three areas as you know, so if we look at that ventral surface of the brain, we can take that brain stem and break it up into a midbrain, a pons, and a medulla. And the anatomy in these is very complex. You can't really see them much from the outside, so a lot of the anatomy that we learned in school is to slice through this and look at the slice, which means on a good MRI you could also see this and you can identify different structures within the midbrain. The midbrain is going to sit right on this upper third of the brain stem. Same thing with the pons, it occupies this middle third of the brain stem. If you kind of slice through it, you can see the anatomy within the pons, which is also very complex. And then if you get down to the medulla, which is just the very, very bottom, where we transition to the spinal cord, again, very, very complex. To summarize the brain stem, I didn't want to go into brain stem a lot, because it is very complicated. But all the cranial nerves come from the brain stem. So all the nerves that go to the head, face, neck, so control of. Eye movement, control of hearing, speaking, speech, swallow, even shrugging your shoulders, the cranial nerve 11 that goes to your neck muscle, the sternocleidomastoid, are coming from the brainstem. The brainstem is also taking sensory input from the head and neck and face. So hearing, taste, balance, these are things that are going to come into the brainstem and then get sent up to the thalamus before they go up to the cortex. So the brain stem is a very important direct communication through the cranial nerves. And then finally is the cerebellum. The cerebellum means the little brain. It kind of is a little brain. It sits down below. It's connected to the brain stem. It doesn't have a complicated prefrontal cortex, so fortunately it's not thinking for you. But what it does do primarily is coordinate movement. It does have other functions too. There's a lot of interesting work on it. the cerebellum but the most basic function that it performs is coordinating movement and the cerebellum has a very complicated structure of what we call folia. They look like leaves so they don't have the gyri and sulci but they have the folia and fissures in them and the more central part of the cerebellum controls movement in the head and neck and trunk so it's more axial coordination whereas the more lateral cerebellum is more appendicular or arms, hands, and legs. So those of you that have had patients with either cerebellar tumor, cerebellar stroke, you've certainly seen that if it involves the medial part of the cerebellum, you're going to have more truncal instability, but patients might do really well with their arms and hands. If it's more lateral cerebellum, then you see things like dysmetria, dyssynergia, dysthytocokinesia, these deficits of distal appendicular arm and hand movement. And the cerebellum does also... process some sensory input, most of it is balance related and proprioception related because that's really critical for coordinating movement. Okay, so that is my neuroanatomy made ridiculously simple. I preferred the cartoon but...

So what I did is I found a video. That's always the easy way to make things simple. the parts of the brain performed by the brain yes neocortex frontal lobe it goes pretty fast so you gotta write all down hippocampus neural node right hemisphere pons and cortex visual brainstem brainstem sylvan fisher pineal left hemisphere cerebellum left cerebellum right synapse hypothalamus striatum dendrite. Alright, this is the part where he scratches a little bit.

Axon fibers matter gray. Brainstem! Brainstem! Central tegmental pathway.

Temporal load. White core matter. Four brains go. Brainstem!

Brainstem! Central fissure quartz... All right, we'll stop.

That's too much fun. Okay. So neuroanatomy is fun. It's not that much fun.

So what I'd like to do, and obviously it's very difficult to put together a big course into a 45-minute talk, so I apologize for not being very in-depth, but I want to just quickly run over... The basic neuroanatomy that I think all of us need to be familiar with, I'm just going to focus on brain anatomy. And so just as a reminder, the brain obviously is a very complex organ, and it develops from what is a rather simple tube into this very complicated structure with many gyri and sulci and a very complex folding pattern that results in the anatomy that we look at. And so when we look at the brain as a final product, We can generally divide it into regions and we'll try to do that today and talk about what happens in the cerebral hemisphere which is the cortex of the brain which is the area that we we often think of when we talk about the brain but there clearly are some very important deep structures the dying cephalon which is a thalamus and hypothalamus play very critical roles as does obviously the brain stem as Pinky the brain emphasized there and then we'll talk a little bit about the cerebellum as well. So starting with the cerebral hemisphere, this really is the largest portion of the brain.

It's about 83% of the total brain mass. It covers the diencephalon, it covers the midbrain, it sits above the cerebellum. And it does have what at first glance looks like a random pattern of gyri and sulci, but as we know there is a very unique characteristic pattern here that does allow us to identify different regions of the brain and different functional areas. And the first level of dividing the brain into regions is dividing it into lobes.

So as I'm sure we all remember from school, the frontal lobe and the parietal lobe are separated by the central sulcus, and that's the main sulcus that separates these two regions of the brain. There's a lateral or sylvan fissure that separates the frontal lobe from the temporal lobe. There's an occipital lobe that's defined by the preoccipital notch. And then there is the transverse fissure, which will... divide the supratentorial space from the infratentorial space.

So this is a lateral view of the brain. If we look at the brain from above, we can identify again a frontal, parietal, and occipital lobe, and a central sulcus here that's dividing the frontal from the parietal. So this gives us a real general kind of zip code segmentation of the brain.

It's important to keep in mind that the brain is not just that lateral surface that we look at. There's a medial surface, so again we can identify a frontal and parietal lobe. separated by a paracentral lobule, which is where the central sulcus dives in. Functionally, that's the leg area.

We'll talk a little bit about that. And then we can identify an occipital lobe separate from the parietal lobe, defined again by the preoccipital notch laterally and then the parietal occipital sulcus here. We know this is where vision is, for example. So this kind of general subdividing of the brain has some functional significance. And then if you look at the brain from below, there's a ventral surface as well.

Again, a very characteristic pattern of temporal lobe gyri and sulci and interhemispheric fissure. And then now the cranial nerves and the brain stem itself and the cerebellum are more evident. So a lot of complicated anatomy. And there's a long history of trying to understand the anatomy of the brain. And one of the earliest important steps in trying to understand the cortex, since it did seem like a very random...

Structure was some of the work that Brodmann did. So Brodmann was a German neurologist, not a neurosurgeon unfortunately, but still very very smart. And he was one of the first to really look at these sub regions and he looked at them histologically, looked at the cell types in those areas and began to divide the brain into regions. And so this is a colorized version of the original diagram that Brodmann published. It was done in black and white.

dividing the brain into 52 cortical areas. And this has been refined quite a bit over time and there obviously we have a better understanding than than Brodman had but this was a really important first step forward in understanding that the brain is not just a random gyrated structure but but there is some function here. So here's all the 52 areas we won't go over all of them but this will be on the exam so it's a very important way.

I think the the more useful way to look at brain anatomy and what we try to teach our trainees here is to really look at the anatomy functionally rather than structurally. So I think it's very useful to to look at the frontal lobe of the brain and to think about an area that is prefrontal, which is a pink area here, and we can talk about the prefrontal cortex and what happens there. We can talk about the motor region of the frontal lobe.

So we can divide this frontal lobe into two regions. We can talk about a sensory area. which is the blue, and we have a primary sensory area here. We also have another primary sensory area in the back of the brain. And then a lot of the light blue are these association areas.

And association areas are very interesting because a lot of higher order functioning happens in these association areas. Bless you. And the prefrontal cortex, too, is technically an association area.

So these are parts that are taking multiple inputs, associating them with one another to comprehend our world. So what I'd like to do is walk through these. So we'll start with the prefrontal cortex.

This is the part of the brain that is the most complex and most developed in humans. And so this really is the closest thing to where our mind sits, if you will. A lot of complex behavior, cognitive behavior, social behavior, personality, expression. Those of you that have taken care of patients with prefrontal lobe injuries know that people change when this part of the brain is not working well. So a lot of executive functions as well lie in here.

So a lot of our higher cognitive processing, trying to follow rules, perform multiple tasks at a time, control impulses. And again, a lot of personality lies in the prefrontal cortex. And a lot of working memory is here too.

So for those of us that have had patients that have a hard time with working memory, hanging on to a rule, hanging on to short-term memory and being able to retrieve it while doing a task. It's very difficult when you have a prefrontal cortex injury. When patients have a head injury, for example, which is one of the most common causes for brain injury, this prefrontal cortex, especially the frontal lobe and the orbital frontal surface, are very prone to moving within the cranial vault and getting damaged. So that's why we see quite a bit of that.

So that's a brief kind of idea of what happens in the prefrontal area. If we move back to this darker red area, this is the more posterior portion of the frontal lobe. And this is the motor area. And so the motor area has multiple regions.

There's a primary motor cortex, which is Brodmann area 4. And then there are premotor areas. There's an eye field and a language field here. So the primary motor cortex is the one we all learned back in school. This is the precentral gyrus. So it's right in front of that central gyrus.

So it's right at the very back of the frontal lobe. Very large pyramidal cells here, which is why Brodmann identified this as region 4. It's a very distinct anatomic region. And it does have a somatotopic organization, so a lot of us remember the homunculus, this idea of a little map of the body within the frontal lobe.

So the more lateral parts of this are areas that are controlling movement of hand and face and mouth. The more medial and superior areas are where the leg area is located. And this becomes important in patients that have a stroke or a tumor, where out here you're going to expect more facial droop, hand weakness.

An ACA stroke, for example, which would affect more of the paracentral lobule may result in just leg weakness, but the arm and hand and face may be okay. So this organization is very important functionally. And the motor cortex is a very simple and basic starting point for motor movement, but there's a lot of motor planning that's involved, and that's where the premotor area comes into play. And it's really closer to that prefrontal area where you're cognitively engaged that's also where you become where you're focusing your planning and your access to motor plans and selecting different motor plans and inhibiting competing plans.

So a lot of that happens here in this premotor cortex area, which is a very important area and as you know if you've had a patient that's had a premotor cortex injury, a lot of times they may even look like someone that has a complete motor paralysis because they just have a very hard time with initiating and having a drive to move. Moving the eyes is a very complex motor function, so that occurs in the frontal eye field, which is located right here. And then Broca's area, which is this area here, is a speech area. And it's a pretty large area because speech production can happen with your mouth.

It can also happen with your hand. You can sign speech, you can write, and you can speak. And so Broca's area is a very complex area. It's not a coincidence that it's located right next to the part of the homunculus where your mouth and hand is.

So it makes sense that an area that's going to initiate that type of motor plan is going to be right next to that part of the homunculus. So then if we move back behind the central sulcus, we get into the sensory areas, and a lot of the brain is dedicated to sensory processing, to understanding the world around us and understanding stimuli as they come in. And a lot of it happens in this primary...

sensory cortex or this post central gyrus, the gyrus right behind the central sulcus. And the primary somatosensory cortex is very similar to the motor cortex in that it also has a somatotopic organization. So there is a similar organization where the medial portion is the leg, the more lateral portion is the hand and face.

And again, the distribution here is biased towards areas like the fingers, the hand, the face, the mouth, where your sensory discrimination is very high. Areas like your back, your sensory discrimination is much lower. And so most of us in school did the kind of sensory discrimination test where you take two little paper clips and you see how far apart you've got to get them before they feel like two pokes versus one. And if you do that on your fingertips, you're really, really good at that.

On your back, it's very hard. You've got to really separate them out because the plots are much bigger. It's just not a high resolution area.

So this is the primary somatosensory cortex, but then this large light blue area are these other sensory areas, these association areas, and there's a lot going on in here. There are areas that are associating input from the hands, perhaps from the eyes as well, or from the ears as well, where the primary auditory region is. There are areas that are going to get input from vision as well, so areas that lie within here are going to access input from the primary somatosensory, primary auditory, primary visual.

So again, it makes sense functionally why you would put these sensory association areas here. And so we can plot out primary association areas for every sensation we have. So there's going to be an olfactory cortex for smell, a vestibular cortex for balance, a gustatory cortex for taste, and so on.

And these are going to land in these dark blue areas, and then they're going to come into this sort of parieto-temporal association area where it's going to be processed and comprehended. Now vision is an interesting one because it lies on that medial surface of the brain. So if you look at the lateral surface, it's this tip all the way back here at the occipital pole. But if you look at the medial surface of the brain, you can see that actually the sensory cortex has a very interesting orientation.

It lies right along this calcarine sulcus, which is a nice dominant sulcus right in the middle of the medial occipital lobe. And this is area 17, and this is primary visual cortex, so the visual input that comes from the eyes. Relays through the thalamus and comes back to the occipital lobe, comes here.

And so it's the same idea where you have a primary area. So this is an area that's going to detect a flash of light, for example, in a certain area. But understanding what you're seeing in that area, understanding movement, and then identifying an object is going to happen in association areas. So when we take care of patients, it's important to keep in mind that a lesion of a primary area and a lesion of an association area are going to have different deficits.

and the association areas where a lot of comprehension is going to occur. One example of that is the visual input that comes into the primary visual cortex actually goes forward to the association areas in two different streams. There's a dorsal stream which actually goes towards the parietal lobe, and that's a part of the brain that is focused more on where something is, where an object is, where you are geographically, where structures are within your world.

And then there's a ventral stream that goes towards the temporal lobe, which is an association area that's more of a what area. So a lot of our recognition of a face, of an object, naming things, is going to occur here. So one example of how input coming to the primary visual cortex. might make you blind, cortically blind, if you weren't able to get that input to begin with.

But if you get that input, you may have a hard time identifying where something is versus what something is, depending on whether you have dysfunction in your dorsal stream or your ventral stream. And so these are things that do come into play again when we're seeing patients with injuries to different brain areas. And then these association areas, which we've kind of talked about multiple times, again, they...

Occupy different areas of the brain. The prefrontal cortex really is a very large complicated association area because identifying objects in your world but then formulating a plan, initiating a response, and trying to do that in the context of the information you've just processed is very complex and so we're talking about information coming into sensory and then perhaps going to prefrontal where you may decide how you feel about it, how you want to respond to it, what your mother or father told you you're supposed to do during a situation like this. This is all prefrontal cortex.

And then you're going to go to premotor to plan a response, if it's a motor response, and then go to your motor cortex. So this really is a very complex association area. These are really complex sensory association areas where you're trying to interpret that information and identify what it is. And then language, both the motor language and the sensory language, so that's the...

the Wernicke's area, which is our sensory language, and then Broca's, our motor language, these are association areas. These are areas which are taking input from multiple primary areas to either understand what you've seen or formulate a response. There is an area called the insula, which we're kind of ignoring because it's hidden under the lateral sulcus here, but the insula is a very interesting area where there's not a great understanding of what it does.

It clearly plays a role in language, does play a role in some visceral kind of organ sensation, some of the autonomic type of responses in the limbic cortex and the way we respond to things. Now we talked a lot about gray matter here, but there's white matter connecting everything. And so those of us that have taken care of patients with diffuse axonal injury know that you can have a great cortex, but if white matter tracks are damaged, then function is compromised.

So there are a lot of important white matter tracks to keep in mind. The ones that cross the brain. like the corpus callosum or the smaller anterior and posterior commissure. These are called commissures.

These are ones that connect the left and right brain together. Those are very, very important for association and comprehension of complex input. There are association fibers which run within one hemisphere, one like the superior longitudinal fasciculus, for example.

And there are projection fibers which are actually kind of the input-output from the brain. And so these white matter tracks are absolutely critical, and many of us have seen patients where... The cortical process might be fine.

For example, a patient with a conductive aphasia, you know, Wernicke's is okay, Broca's is okay, but that arcuate fasciculus that connects it to is not okay. So you can see a dramatic dysfunction, even though the cortical regions are working okay. So if the connections are not there, you know, this complex computer falls apart. So it's very important to keep in mind that this anatomy is there.

It can be affected by injury, and as surgeons, you know, we can actually map this. We can image this with tractography, diffusion tensor imaging. We're much more thoughtful now about white matter tracks in the brain.

To kind of finish off this walk through the anatomy of the cortex, we talked about gray matter areas, we talked about white matter. It's important to keep in mind that when you take a slice through the brain, either imaging on an MRI or CAT scan or anatomically in the laboratory, you see a lot of gray matter that's deep in the brain as well. So it's not just gray matter on the surface, white matter underneath.

There are areas of deep gray matter and there are many areas in the brain. These are very complex areas. Some examples are the basal forebrain nuclei, which sit in the lower back part of the frontal lobe. They're deep structures.

These are areas that are very important in acetylcholine-mediated transmission. We think in Alzheimer's disease this is an area that does not function well and we lose cholinergic transmission. The basal ganglia is another great example, which is a group of many structures, including the caudate, the putamen, the globus pallidus, the subthalamic nucleus.

These are areas that are involved in motor processing, kind of scaling movement, picking different motor plans. So patients with Parkinson's disease, with Huntington's disease, the cortex is fine, but movement is still affected because of these basal ganglia, these deep structures. So having just a normal motor cortex and intact white matter tracks doesn't mean the motor function is going to work well. You also have to have this deeper cortical relay working well in these deeper gray matter structures being able to regulate and control the cortex.

So those are the hemispheres and then we'll kind of move a little bit deeper to some of these deeper areas as we head to the homestretch here. So the thalamus is a very important structure and this is one of the two parts of the diencephalon. So the diencephalon is made up of the thalamus and the hypothalamus. The thalamus, which means inner room, is a very interesting structure located deep in the brain. There's two of them.

They look like these small hard-boiled eggs connected to each other. They form the walls of the third ventricle and they're really kind of a cut-off person, if you will, between the brain and the peripheral nervous system. So information that comes up to the brain almost always relays through the thalamus.

So sensory information, visual information coming up will almost always synapse in the thalamus and then the thalamus shoots it up to the cortex. So the thalamus plays a very important role in that way. If you look at a brain, the thalamus is this structure here, so it's sitting right in the middle of the brain. If we look at a cartoon here, the thalamus are these two paired blue structures. There's an interthalamic adhesion that connects the two, and then the thalamus, just like everything else in anatomy, is broken up into sub-regions.

We're not going to go over these. This is, you know, a whole lecture itself. Thalamic anatomy is a big textbook I have, which is very scary, that goes over the thalamus. But, you know, some kind of just basic things just to put it in the context of what we talked about. Sensory input, for example, from the hands and feet comes into the thalamus, and it goes to the VPL, the ventral posterior lateral nucleus of the thalamus, which is this big blue area, and then this shoots it up to that primary sensory cortex.

So all the input that the primary sensory cortex gets gets from the thalamus. So, again, you can think about someone that's had a thalamic stroke or a thalamic tumor. You know, they have major, major deficits.

Cortex is fine. Sensory in the hand is fine, but input doesn't get there if you don't have the cutoff person. Vision, for example, runs through the thalamus.

It goes to the lateral geniculate nucleus. Auditory input goes to the medial geniculate nucleus. So a lot of the sensory information has to run through the thalamic relay. And the thalamus, for that reason, is an area that we're very interested in with deep brain stimulation and neuromodulation because it is a very critical cutoff or relay structure that can be modulated. So you can maybe turn it up or turn it down.

One interesting area of the thalamus is this intralaminar nuclei, which kind of run in the middle here. This is an area that in a patient, gosh, it's been 10 years now, I think, that was minimally responsive in a vegetative state. A group of surgeons put a stimulator in this area and actually were able to increase wakefulness in that patient. This was someone that started feeding themselves and communicating, and before they weren't doing that at all.

Because the intralaminar nuclei are an area that... that take input from the activating system, the reticular activating system that wakes you up in the morning and relays it to the brain to turn on the brain. So the thalamus is a very interesting area and it's one that a lot of very smart people are researching to try to better understand how we can modulate thalamic function. Below the thalamus is the hypothalamus.

So if this is the thalamus, then below it is the hypothalamus. Hypothalamus is a very more basic area of the brain. It's...

It functions on its own, so it's not a relay center like the thalamus. And it's really focused on a lot of autonomic type of basic functions in the brain. So emotional responses, body temperature, hunger, thirst, sex drive, sleep-wake cycle, controlling your hormones. The pituitary gland is under the control of the hypothalamus.

These are very important structures. if you've had someone with a hypothalamic injury, if you've seen a child with hypothalamic seizures, for example, those manifest as a gelastic kind of laughing seizure. I mean, it's a very, very interesting area of the brain. If a young child has injury to the hypothalamus, like with a tumor like a cranial pharyngioma, they can become severely obese because they have total disruption of their normal satiety function.

So hunger and thirst are here. So very, very critical deep brain structure. different from the thalamus because it's not focused on interfacing with the cortex. It's a very basic function in the brain that lies below that.

And then moving beyond the diencephalon now we'll go down to the brainstem. So we're working our way down. So the brainstem really sits now in the posterior fossa. So we're below the cortex, below the diencephalon, and a lot of automatic, programmed, reflexive type of behaviors come from here.

So this is not conscious processing in the brain stem. And it is broken down into three areas as you know, so if we look at that ventral surface of the brain, we can take that brain stem and break it up into a midbrain, a pons, and a medulla. And the anatomy in these is very complex. You can't really see them much from the outside, so a lot of the anatomy that we learned in school is to slice through this and look at the slice, which means on a good MRI you could also see this and you can identify different structures within the midbrain. The midbrain is going to sit right on this upper third of the brain stem.

Same thing with the pons, it occupies this middle third of the brain stem. If you kind of slice through it, you can see the anatomy within the pons, which is also very complex. And then if you get down to the medulla, which is just the very, very bottom, where we transition to the spinal cord, again, very, very complex.

To summarize the brain stem, I didn't want to go into brain stem a lot, because it is very complicated. But all the cranial nerves come from the brain stem. So all the nerves that go to the head, face, neck, so control of. Eye movement, control of hearing, speaking, speech, swallow, even shrugging your shoulders, the cranial nerve 11 that goes to your neck muscle, the sternocleidomastoid, are coming from the brainstem.

The brainstem is also taking sensory input from the head and neck and face. So hearing, taste, balance, these are things that are going to come into the brainstem and then get sent up to the thalamus before they go up to the cortex. So the brain stem is a very important direct communication through the cranial nerves. And then finally is the cerebellum. The cerebellum means the little brain.

It kind of is a little brain. It sits down below. It's connected to the brain stem.

It doesn't have a complicated prefrontal cortex, so fortunately it's not thinking for you. But what it does do primarily is coordinate movement. It does have other functions too. There's a lot of interesting work on it.

the cerebellum but the most basic function that it performs is coordinating movement and the cerebellum has a very complicated structure of what we call folia. They look like leaves so they don't have the gyri and sulci but they have the folia and fissures in them and the more central part of the cerebellum controls movement in the head and neck and trunk so it's more axial coordination whereas the more lateral cerebellum is more appendicular or arms, hands, and legs. So those of you that have had patients with either cerebellar tumor, cerebellar stroke, you've certainly seen that if it involves the medial part of the cerebellum, you're going to have more truncal instability, but patients might do really well with their arms and hands.

If it's more lateral cerebellum, then you see things like dysmetria, dyssynergia, dysthytocokinesia, these deficits of distal appendicular arm and hand movement. And the cerebellum does also... process some sensory input, most of it is balance related and proprioception related because that's really critical for coordinating movement.

Okay, so that is my neuroanatomy made ridiculously simple. I preferred the cartoon but...

Transcript for:Overview of Neuroanatomy and Functions

Transcript for:
Overview of Neuroanatomy and Functions