in this video I'd like to talk a little bit about the structure of a neuron now the neurons when we talk about the nervous system err kind of the stars of the show okay the neurons are the ones that actually do the signaling at least the majority of the signaling in a neuron has three parts it has dendrites or these branching cell extensions they kind of look like hotrod flames a soma or cell body and a thin excellent these are the three major parts of a neuron so we have the dendrites we have the soma or the body of the cell and then we have the axon those are the main parts now where the axon attaches to the soma we have this additional region called the trigger zone or the axon hillock okay and at the end of the axons we're gonna have these branching terminals they could be many thousands per axle on they kind of branch out and right at the ends we have their terminals or where they interact with the next neuron okay so these are the axon terminals okay now usually these dendrites are thought of as the input region but I'm going to have a little caveat there they're not onlys the input region similarly axons are largely thought of as the output but I'm gonna put a little caveat here we can also get signaling that moves up an axon they could be the input as well but in general and how most textbooks teach it dendrites are the input axons are the output and the soma is where the decisions are made this is where the integration is making sense of that input and deciding what to do for output this is much like the general layout of the nervous system as a whole we have a brain and spinal cord which does integration it happens to be loaded with these multipolar neurons I've drawn you a multipolar neuron here and it receives information from the sensory system and then it sends information out through the motor division of pns neurons are like many nervous systems they are the functional unit of the nervous system the smallest thing we can turn to the nervous system down to and still retain all of its functionality okay so we're looking at a multipolar neuron but this also could apply to a pseudo unipolar neuron which is basically a bipolar neuron that's sat upright there's that one pull pseudo unipolar a bipolar neuron has two poles there's my simple layout of it this is multi polar because we're seeing multiple Selleck extensions okay a neuron has a nucleus like most cells it just has one nucleus and inside that nucleus we have the nucleolus the nucleolus is going to be making the ribosomal subunits the ribosomal RNA the nucleus contains the genetic information the genes the chromatin and we have a nuclear membrane that has pores in it to allow messenger RNA and other substances to move in and out of the nucleus so that those ribosomal subunits can escape and they may end up out here in the cytosol and when they end out he up out here in the cytosol well those ribosomal subunits are going to make proteins for within the cell but if they're embedded in some rough ER if these ribosomal subunits are embedded in some rough ER these proteins that are going to be made by these ribosomal subunits are going to be intended to leave the cell this gets a special name in neurons this is called a missile body a missile body which is just extensive rough ER and associated well rough ER has the ribosomes embedded in it and why it gets a special names these are very important in neurons because neurons are going to make proteins they're gonna make neurotransmitters they're gonna make a lots of them and they're going to store them down in vesicles at the axon terminals then these vesicles we're going to have stored proteins or neurotransmitters now we also have smooth ER just like we would in any other so bit of smooth ER we have peroxisomes and we've talked a lot about these different cell organelles we have lysosomes and lysosomes digest materials and sometimes in neurons they can digest so much and as they age we can't really dispose of them well anymore and we get these dark spots of Ryba of lysosomal activity this is like an age spot in the skin and in a neuron we call this lipo fussen light both fussen or aging pigment we see that in our own skin sometimes lipo fussen or aging pigment you can determine the age of a brain in part by how much of this aging pigment you see now surprisingly it doesn't interfere with the function of the neuron at all if you have a little age spot in your skin it's not like it interferes with the primary function of the skin forming a barrier it just is something that happens to B cells over time not that we know of anyway it doesn't interfere so we've gotten a couple new terms like a piece and missile bodies and looking at the structure of this neuron okay what other cellular organelles do we have what we have mitochondria we have mitochondria the mitochondria in these axons all right Golgi apparatus we need some Golgi apparatus here to convert the proteins that were made from the messenger RNA from the nucleus to convert those proteins after they've been translated and modify and label them package them up so that they can be transported to the axon terminals in these vesicles okay now we also have some cytoskeletal elements but before I go over those cytoskeletal elements I want to talk briefly about what organelles we're gonna find where in this cell now in the soma or the cell body we find all the organelles we're gonna find all the types all types of organelles we find all types of organelles in the soma but in the dendrites we actually lack the nucleus can't fit the nucleus in these dendrites okay but all other types we would find we would find a little bit of golgi we would find a little bit of mitochondria we would find some lysosomes the axon is different in the axon there is no rough ER and there is no Golgi apparatus and there certainly isn't a nucleus if you consider the nucleus an organelle many people don't so as far as organelles go we find all types in the soma we find all types in the dendrites but in the axon we don't find rough ER or Golgi apparatus and if we think form and function what that tells us is that proteins that are made from our genes that's what genes do is they code for proteins that messenger RNA when we transcribe the gene travels out and it's going to be made in the soma this is going to be translated by the rough ER ribosomes in the soma it then leaves and it goes to the Golgi and from the sis face of the Golgi to the trans face so from this sis to the trans face that protein is going to move through the Golgi apparatus from the sis face to the trans face that translated protein is going to move through and it's going to be modified it's going to be labeled it's going to be tagged and then it's going to make its way down to the axon terminals of the neural where it will be stored until this neuron is told to release it now how does it get there it gets there via our first cytoskeletal element microtubules microtubules are very prevalent in axons and they're going to allow motor proteins either kinesins or diamines to carry these little motor proteins can wrap their legs around these vesicles and they're going to carry these vesicles they're much smaller than the vesicle that's not really to scale down the axon to those axon terminals it's gonna carry these vesicles that contain the neurotransmitter it can also move mitochondria can with other organelles that's why we also find tubulin throughout the cell body tubulin resists compressive forces and that's why it's part of the cytoskeleton now axons have a particularly high amount of tubulin these are like railways at Disneyland they can transport things down into those axon terminals and get things to their locations this is a very energy intensive property or process of neurons neurons use an enormous amount of energy because they fulfill the requirements of cells that need a lot of energy they have a lot of sodium potassium ATPase bombs they make a lot of proteins neurotransmitters okay the only feature that they don't do a lot that's very energy demanding is mitosis now it is possible for some neurons to undergo mitotic events like in the hippocampus or some neurons and our nasal mucosa will divide quite often a lot of times it's taught that neurons are a mitotic no mitosis and I think that that theory has been changed over the years we do have examples of neurons actually entering mitosis and dividing they can be replaced if they're destroyed they can change their structure and adapt give this dogma of neuroscience that our brains are fixed has gone by the wayside and it's redirected the risk research which kind of dead ended on false presumptions and we're shifting the way that we think about the nervous system have for quite a long time the nervous system is plastic it can change okay these characteristics of the neurons mean that they need a lot of energy they're very active when I'm studying very hard for exams or thinking very deeply about things over weeks at a time all acts would actually lose body weight the way that I would lose body way to find working out more and it's because the brain consumes an enormous amount of our body's resources and energies like the kidney does like the heart does okay let's look at the other side of skeletal elements we have some actin that underlines the membrane some active it helps give shape to the neuron I described in my in-person class about how this is like the toy where you go in and it's this lattice it's a small and you can expand it out and it you can actually bounce this ball it's a lot of structure and then you can press on it and actually shrink it back down this gives structure to the cell remember the actin is the one that's responsible for amoebic motion if we break down the actin the cytoplasm will push or the cytosol will push the membrane out and then we can reconstruct that actin reshape the South and neurons do this especially at their axon terminals we can reshape membrane reorient the cell okay we also have a keratin and keratin kind of runs within the cell and it prevents tensile forces so where tubulin or microtubules act as kind of highways and also prevent compressive forces the keratin resists tensile forces on this neuron okay we've seen the major parts of the neuron I want to add one additional structure it's actually not part of the neuron but closely associated with it and that's the myelin that's that myelin that I've talked about before because of these Schwann cells or oligodendrocytes if we're in the CNS and what this myelin ultimately allows for is increased speed and conductivity and I'm going to talk in a future video about the different types of axons type a B and C but one of the things that determines the type of axon is not only its diameter but also its degree of myelination and with more myelination we get faster signaling so this is actually a different type of cell this is a Schwann cell this is the Schwann cell and between I always spell that I'm not even sure that's right I got to look that one up between the adjacent cells we have something called a node of ranvier a node of ranvier these are breaks or gaps between the Schwann cells okay this is the overall structure of a multipolar neuron but the same organelles and cell structures apply to a bipolar neuron or pseudo unipolar neuron now when we get into circuits when we start talking a little bit about functions of neurons we represent the cell body as a little dot and then we represent the axon as a line and then we represent the axon terminals as this little mouth again you can think of that axon as the output we can think of this axon as the mouth and it's speaking the dendrites we can kind of think of more as like the ears or the input or the listening so you're gonna be the dendrites yeah dendrites these are where the signals come in the listening okay so these are the basic components but do you remember dendrites are not always then employed dendrites in theory and sometimes can also be that that amount or that output similarly there are circumstances where the axons are actually gonna do some listening but in general I guess I should have drawn me here from the other side they're gonna do some listening but in general the dendrites are thought of as the input and backs on the output and that's why when we're tracing circuits we can see which cells are talking to which cells and we represent that with a cell body an axon and that axon terminal mouth now it's supposed on the back end of this we have some dendrites listening but for simplicity we just draw a cell body an axial on and that axon terminal did you know our network