hi everyone dr mike here in this video we're going to take a look at the cerebral hemispheres so when we take a look at the brain itself we know the brain is made up of the cerebrum which is everything colored here the cerebellum which is that little brain that sits underneath and towards the back and the brain stem underneath which sits just above the spinal cord today we're talking about the largest part of the brain which is the cerebrum which has a fissure or segmentation down the middle that separates it into two hemispheres a left hemisphere and a right hemisphere so it's the largest part of the brain but it's also the most developed part of the brain now what do i mean by developed well let's take a look at some of the functions of the cerebrum first of which is that the cerebral hemispheres contain the primary motor and sensory cortices now when i say cortices i'm referring to the cortex and the cortex is simply the outer one to five millimeters of the cerebrum it contains gray matter remember when we look at a neuron you're going to have the cell body of a neuron you have the axon of the neuron and then you're going to have the axon terminals that axon terminal is likely going to talk to another axon or neuron i should say for example so importantly the axon is surrounded by fat myelin and fat in this case looks white so when we look at gray matter gray matter are the cell bodies in the areas of synapsing so that's gray matter and the white matter is actually simply the axons so that means that when you see gray matter this is the site of integration when we make sense of information the white matter is simply just highways this is simply where one signal is sent to the next area all right keeping that in mind when we look at the primary motor and sensory cortices that sit within the cerebral hemispheres this is the highest level of activity for example when we look at the motor cortex cortex or the primary motor cortex which actually sits in this part of the frontal lobe this is the area where we want to initiate some sort of voluntary or conscious motor movement if i want to begin walking this is where it begins so that's why it's the highest level in which motor activity will function when we look at the sensory cortex this is where information coming from the external environment or the internal environment is coming up for us to be consciously aware of it again it's the highest level of integration of sensor information this is where we become aware so think about if you had your hand in your pocket when you feel something in your pocket this is going to the sensory cortex all right now in addition to that i'm going to skip this part here we've got association areas that's part of the cerebral hemispheres now association areas they help the primary motor and sensory cortices by associating previous information and current information it's comparing and contrasting what it already knows so that you now have more information it's basically a way to to analyze complex information so first of all the association areas for the motor cortex so i said you can have the motor cortex here i want to initiate walking for example that's happening there at the primary motor cortex but the association areas allow for you to sequence and plan more complex tasks so if i wanted to go play the piano for example or juggle some balls this is where we have the association areas come into play for the motor cortex allows for us to plan and sequence complex movements when we look at the sensory cortex which i didn't say sits within that parietal lobe here the association cortices help it help you understand what piece of sensory information you are receiving so i said before that primary sensory cortex there you put your hand in your pocket and you feel something what the association cortex does is it analyzes whether it's smooth or rough whether it may be hot or cold have i felt it before what might this be from previous experience so it's an association cortex because it's bringing associations from previous experience and throwing it to that of the primary somatosensory cortex so these are these association areas all part of the cerebral cortex the cerebral hemisphere is the substrate for conscious experience when we become consciously aware of anything it's because it's gone to the cortex of the cerebral hemispheres so if you want to be consciously aware it needs to get to those one to five centimeter thick a millimeter i should say layer of the cerebral hemispheres if you want to be consciously awake this is where consciousness is going to arise where you become aware of experience more deeper areas of the brain may receive sensory information but you will not become aware of it occurring or it may make a decision about conscious may make a decision about motor movement but you're not going to be consciously aware of that for conscious awareness it must get to that one to five centimeter external layer that we call the cortex of our cerebral hemispheres the cerebral hemispheres also contain the limbic system now the limbic system is important for memory and emotional aspects of behavior so think of emotional aspects of things that you do so the emotional aspects of feeding the emotional aspects of relationships the emotional aspects of reproduction the emotional aspects of fight or flight this is the limbic system and you can see part of the limbic lobe sitting here but there's deeper limbic structures as well right near the thalamus that you can see here so we've got the limbic system it's also the highest aspect of cognitive function the cerebral hemispheres the highest aspect of cognitive function so when we look at cognitive function we're thinking about planning judgment emotion making sense being reasonable making sure that your behavior is appropriate for the scenario in which you're in most of this sits within the frontal lobe specifically an area called the prefrontal cortex if that area is damaged we have issues when it comes to behavior and planning and things like that all right so highest aspect of cognitive function now like i said when we take the cerebrum it's going to have the one to five millimeter layer and there's going to be some deeper structures the one to five millimeter layer like i said is the gray matter that's the side of integration and making sense and consciousness but we've got deeper layers of the cerebrum where we project information these are the highways these are the axons this is the white matter all right now you can send information from one side of one from this one cerebral hemisphere to the other and if you do this you're sending it through white matter tracks or fibers they're called commisural fibers they are predominantly going to be through what we call the corpus callosum that's the connection between those two hemispheres some people had a corpus callosum otomy otomy means the cut it separates those hemispheres these individuals had very severe cases of epilepsy and epilepsy is this misfiring of neurons if you cut it it stops it from spreading across the two hemispheres and help mitigate the severity of their epilepsy but it also separated the hemispheres anatomically and if you have a look at the split brain experiment studies you'll find some very interesting things when it comes to splitting the consciousness of the brain so you've got the commissural fibers from one hemisphere to the other we've also got projection fibres these fibres take it from more superficial areas of the brain to deeper aspects of the brain brain stem and spinal cord these are going to be projection fibers you can see that they're going to cross over to the other side because the right hemisphere controls the left hand side of the body left hemisphere controls the right or the right side of the body sends information to the left hemisphere and vice versa which means these projection fibers must cross at some point usually they're going to cross at around about the medullary region association fibers i spoke about association areas association fibers allow for one part of the cortex to speak to another part of the cortex so that we can make more sense of what's happening in the situation if i want to sequence a motor task i need these association fibers if i want to make sense of what i'm feeling in my pocket again we need these association fibers so when we look at the cerebral hemispheres it's made up of cerebral cortex one to five millimeter layer this is the site of what is it consciousness experience integration it's made up of lobes and these lobes which you should probably look at before we finish i'm going to focus more attention on those lobes in future videos these lobes are made up of the frontal lobe the parietal lobe the occipital lobe at the back the temporal lobe near the temple and we've also got an insular lobe if i were to sort of pull that temporal lobe away from the frontal you could see the insula underneath i'm going to do videos on each of these lobes more specifically but final point is that when we look at the superficial or surface anatomy of the brain you're going to find that there's areas which have a bump up and a dip down now the bump up is known as a gyrus that's singular if it's pleural it's gyri the dip down is known as a sulcus again that singular a sulci is plural and this is what gives the brain its wrinkled appearance it just increases the surface area of the brain which means there's more room to fit more neurons more sites of integration all that type of fun stuff so a couple of points because i said you've got the frontal lobe the parietal lobe the occipital lobe of the temporal lobe how do we separate them out how do we anatomically know where their demarcation points are well we use gyri and sulci for example we separate out the frontal lobe from the parietal lobe with a sulcus called the central sulcus central sulcus now wherever there's a sulcus in front and behind is going to be a gyrus right so this central sulcus we've got a gyrus in front called the pre-central gyrus and that's that primary motor cortex we've got a gyrus behind it and that's going to be called the postcentral gyrus that's going to be the somatosensory cortex that we spoke about as well when we look at the parietal lobe separated out by the occipital lobe we're going to have the parietal occipital sulcus parietal occipital sulcus and again separating out the occipital to the parietal lobe we've also got the temporal lobe here how is that separated out from the frontal and parietal lobe above it we have a lateral sulcus here also known as a lateral fissure or sylvanian fissure situated there all right in a future video i'm going to focus on each of those lobes but to summarize the cerebral hemispheres is the largest and most complex and most developed part of the brain it allows for us to have conscious awareness it has lobes and these lobes have particular functions it has cognitive higher order cognitive function it has limbic areas for emotional and behavioral understanding it has association areas primary motor primary sensory areas but more deeper to this it has fibers axons that can project to other parts of the cerebral hemispheres but also deeper parts of the brain as well