now we're going to talk about some of the cells in the nervous system and we'll begin with the neural glia neuro Malia now neuroglia suggest that these nervous system cells are just merely the glue that helps hold the neurons in place but we'll find out is what was once thought of is just the glue actually has a lot of other important functions and we can group them based on where they're found we're going to have some glia that are only found in the brain and spinal cord just in the CNS and then we're also going to have some glia that are actually found out in the pianos or peripheral nervous system and those spinal nerves or those cranial nerves okay out here in the pianist you get the idea okay so we have pianist and seeing us and the first one I'm going to talk about are the astrocytes astrocytes and like the name suggests Astro star sights cells these cells are shaped somewhat like stars so here's an astrocyte here and here's another hosta site here okay astrocytes have a few different important functions first they're going to provide a scaffolding a scaffolding to guide the growth cone of a neuron so that the neuron can basically climb this lattice the way that some kind of body would climb a lattice in the yard and give some structure or scaffolding when construction workers climb up buildings to build the building taller and taller they climb on scaffolding it's going to provide a scaffolding to guide growth cones of neurons okay astrocytes also can take up toxic waste from the cerebrospinal fluid this fluid that surrounds the brain and then turns up the spinal cord and also fills the ventricles I actually works in more reverse it forms and the ventricles and it moves down and then it covers and saturates the outside of the brain as well this cerebrospinal fluid can be modified by these astrocytes by their ability to take up excess neurotransmitters from that cerebrospinal fluid and waste products okay and that's because they're actually connected to one another and this feature allows them to take up excess waste and excess neurotransmitter without becoming toxic themselves they can kind of form these compartments by attaching to one another through gap junctions and sharing that load we call this a syncytium about astrocytes a syncytium a little city of astrocytes okay this is a very important feature that they have for example glutamate we'll learn is the most excited Tory neurotransmitter in the bottle it's very excited Tory - practically all cells except for in the eye in the eye it's actually inhibitory but glutamate in excessive amounts can over excite neurons when it's released on to a neuron by some other neuron so here I have a neuron coming down this isn't quite to scale and not neuron released some neurotransmitter onto this neuron and excited it using that is he'll call order that glutamate now glutamate can be toxic we can actually over excite cells so much that they fatigue and then their risk if there's any kind of insult or injury and they can die and perish and what happens is this astrocyte will take up well there's three molecules of it one two three three molecules of that glutamate so that it's not so toxic to the surrounding neurons so we have finer control when we do want to stimulate this neuron it's not just being stimulated all the time but this can also share the load one too with this guy who can share the load with this guy and with these two so now we've moved those two down here now nobody's carrying any excessive load of this neurotransmitter or any kind of waste product produced in this cerebrospinal fluid I think if that seen from guardians of the galaxy where star Lord grabs the Infinity stone and it starts peeling off the skin and melting them basically but then Nomura comes over and holds his hand and it disperses the energy throughout their two bodies and then Drax comes in and dramatically puts his hand on star-lord shoulder and shares that load and then rocket grabs his pinky and they're able to withstand the energy of the nice tone it's not too toxic to any one individual they're sharing that level and if we look more closely at the connection between astrocytes something that we'll see is these extensions of the astrocytes come together and they actually have connects on proteins these proteins that form a ring and connect the cytosol of one cell to the next cell so that any materials for example glue to me they come into the astrocyte can move from one cell to the next okay glutamate might be a little large smaller would be calcium and that brings us to another function of astrocytes astrocytes can actually propagate charge throughout the sensation they can signal using calcium waves neroli is not just merely the glue it actually takes on some similar function as actual neurons and what you see when you look at this under the microscope you'll see a lightning bolt go by which is an action potential traveling down a neuron and then you'll see this reverberating wave through the astrocytes and across the tissue this may help compartmentalize the signals so that things that are occurring in the thalamus don't trickle into the epithalamus or the hypothalamus or things that are occurring in premotor cortex don't trickle into the frontal lobe with frontal cortex or the primary motor cortex without a direct connection through neurons these help compartmentalize different areas of the brain and that way they are a lot like connective tissue and structural components but they can also send signals themselves these calcium waves one of the last functions all cover if not the last is the astrocytes form the blood-brain barrier and you may have heard of this thing called a blood-brain barrier essentially what it is is a barrier that prevents neural tissue of the brain from being directly exposed to the blood no we want to filter that blood the way we do it a joint and then bathe the neuron not in synovial fluid the way the cartilage is bathed in synovial fluid or rather in cerebrospinal fluid and how that happens is when we take a blood vessel here in the brain we can look at it and it's epithelial cells here by drawing a capillary and this capillary here this capillary [Music] and not one of my best capillaries but hopefully you get the idea that this has been I mean this capillaries been cut tearing the blood and other nutrients allows well we know we have continuous capillaries in the in the brain they're the most common capillaries that we have in our body and in breaks in the tight junctions these little particles can move out of the bloodstream little breaks in tight junctions these particles can move out of the bloodstream and feed the surrounding tissue also waste products waste products can make their way back into the bloodstream and be swept away but in the brain we want to tightly regulate what this neural tissue gets exposed to and so these astrocytes here's one astrocyte is going to send an extension and it's going to cover those epithelial cells using one of its arms oops well you get the idea and now particles can't move so easily in or out let me put another Oster site over on this side and let me send its arm and it's gonna cover right here and then we sew these two astrocytes together using actin in tight junctions so what this looks like in cross-section I'll do a better cross-section here I have one epithelial cell of the capillary and then I have another epithelial cell of the capillary and capillaries usually have tight junctions holding them together themselves but sometimes they have little breaks in those tight junctions where particles can move out and what this astrocytes going to do is it's going to send in its arm and it's going to surround this capillary and the other astrocytes going to sign in its arm and it too is going to surround this capillary and then we have tight junctions sealing them up we've reinforced we've created a blood barrier that separates the cerebrospinal fluid what this brain is being bathing in from the actual blood stream okay any molecules any nutrients and anything from the blood needs to actually leave the blood stream and then be actively transported across the cytosol in order to end up in the cerebrospinal fluid it's not just going to diffuse it now lipid-soluble products can and that's why a lot of neurotropic or drugs that change the brain they tend to be lipid soluble because they can get right through the brain barrier right through those plasma membranes but for anything that's polar you need an actual receptor for that chemical you transport it into the cytosol you may even modify it before you safely put it into the cerebrospinal fluid nothing toxic its contact with the brain this is actually why baby food is banned or uh glutamate is banned from baby food it takes the nervous system about 24 to 26 years to fully develop but it takes months and maybe even a year or two to fully form these tight junctions between cells the blood-brain barrier is actually leaky in newborns and if they add too much glutamate or mono sodium glutamate this food additive that makes foods taste savory if they add that to baby food there's a potential that it moves from the bloodstream because these astrocytes haven't fully formed out into the cerebrospinal fluid and it can be toxic to the neurons these astrocytes are still guiding neurons to their appropriate position humans are quite special in that were born with underdeveloped brains to be able to fit through the birth canal you don't see that in other animals a horse is standing up and walking its first day by one or two years they're competing in the whole portraits erasing their fully mature and their being bred by age three four five four humans we're having trouble lifting our faces off the floor before the first year of life and that's because we have very underdeveloped brains our brains become so advanced that they would never fit through the birth canal if we were born mature the way that other animals are so these tight junctions need some time to form these growth cones from a neuron needs some time to be guided along these astrocytes and this is why they bought ban monosodium glutamate from baby food the blood-brain barrier isn't fully formed okay I'm gonna talk about two more glial cells that are found in the CNS the first one's gonna be microglia small Lea to me these kind of look like the tapper in Harry Potter that screams Neville Longbottom pulls them out of the ground they call them screaming Mandrax I think in Harry Potter these are very small cells and they have voracious appetites these are actually the resident macrophage the resident macrophage of the CNS these are the mean cells that will travel around and eat up damaged cells pretty simple and straightforward job they have the third one I'd like to talk about our oligodendrocytes when I did research on astrocytes I would grow these from rock grains in a petri dish I was always on the lookout for these microglia because they could destroy my culture by eating up all the nutrients and also all my cells that I was trying to grow but often I would get knocks on the lab door or people coming by to see if I had any old Legos or any oligodendrocytes oligodendrocytes are an area of really intense research because they form the myelin in the CNS there the myelin eating cells in the CNS and the way that they look is they're going to kind of send out these bedsheets or these little blankets and these are very rich in lipid and when an axon or an extension from a neuron is passing by we've actually kind of gave it a nice blanket to comfort it and with a second oligo we can kind of [Music] cover that up a bit more on the other side like a sandwich and so what we've done is we've taken this axon and we've created a lipid rich membrane around it and we'll talk a lot more about myelin and its function but it actually allows neurons to signal more quickly it speeds up signaling and there's a lot of demyelination diseases out there that people are trying to treat and those of the central nervous system really the target is to enhance the function or preserve the function of these oligodendrocytes okay we'll pick up with the glial cells of the P NS in the next video