Understanding the Nervous System Basics

Hi, Bio32. So we're starting our first lecture on the nervous system. Today is just going to be an introduction to some of the fundamentals of the nervous system, and we will be continuing with the nervous system throughout the rest of the semester. So I'm on page 93 in your lecture notes, page 93, and we're just going to start. with a general overview of the nervous system. So all of our physiological and psychological actions are regulated by the nervous system. It's what we call our fast acting control system. However, the nervous system is also going to be controlling our slow acting control system, which is our endocrine system. So it's essentially mission control, if you will. Everything in our body is regulated by our nervous system. So some general functions. If we're going to break down the nervous system into three main sections, it would be as what you see right here. So we have some sort of sensory input, whether that's visual or taste or hearing or feeling, we have some sort of sensory input. That input gets processed by our brain and our spinal cord in a process we call integration. So integration just means that our brain and our spinal cord are processing this sensory input and deciding what we want to do with that information. After the information has been integrated, then we are going to turn on some sort of effector through a process called motor output. So effectors are going to be causing a response. These effectors can be muscles or glands. So in this case, this person sees a glass of water, their brain decides they're thirsty, and so they're going to be turning on their... somatic muscles, so they're voluntary control muscles, to pick up the glass of water and then take a drink. So that's going to be our motor output in this case is a skeletal muscle. So let's look at the structural and functional classifications of the nervous system. So structurally, we have two main players, the central nervous system, which consists of the brain and the spinal cord, and the peripheral nervous system, which is basically anything outside of the brain and the spinal cord. So those are our two main divisions. So if you flip to page 93, you will see that this chart is already found in your notes. So what I'm doing is I'm just sort of going to break it down for you a little bit. So if you look right here, we have the central nervous system. It can also be referred to as the CNS. So central nervous system, again, that's brain and spinal cord, and peripheral nervous system is everything that's not brain and spinal cord. Then we have some various levels of divisions, functionally classifying the nervous system into what we call sensory or the afferent division and motor or the efferent division. Both of these are part of that peripheral nervous system. So what this means is we have some sort of sensory information coming into the body. Okay. All of the sensory... The input in this graph is represented by the blue arrows, and the output is represented by the red. So we have the sensory afferent division sending information through the peripheral nervous system. That peripheral nervous system is going to send that information towards the central nervous system. So if anything is going towards the central nervous system, we would call that sensory information. At that point... The integration process we mentioned before, which is where the brain is processing, the brain and the spinal cord are processing what to do with the sensory information. That takes place at the level of the CNS. That central nervous system makes a decision to activate an effector. So this is where the divisions get a little more complicated. Depending on the response you want to have, we have many subdivisions of the efferent or motor division. So the brain has made some decision sending it out through that peripheral nervous system, specifically through the motor division of that peripheral nervous system. And then we have a couple of choices. We have our somatic nervous system and we have our autonomic nervous system. The somatic nervous system is going to be 100% our voluntary nervous system. This is where... our skeletal muscles are going to be controlled. So let's add some notes here. So somatic nervous system, this is... skeletal muscle. And so if it's skeletal muscle, that means it is voluntary. Our autonomic nervous system. So autonomic to me kind of sounds like the word automatic. So it means we don't have any control over this side of the system. So it's going to be our involuntary division. In involuntary, we're going to find the control of smooth muscle, cardiac muscle, and then glands. So all of these are regulated by that involuntary autonomic nervous system or our ANS. Now the ANS has... two more divisions in itself, our sympathetic division and our parasympathetic division. So they each have different functions depending on what sort of information was brought in by that sensory division. So the sympathetic division, this is what we call our fight or flight division, which the term fight or flight is slightly outdated because they've actually decided that in times of crisis that people actually do three things. They fight, flight, or they freeze. I feel like I'd probably be a freezer. I'm not too much of a fighter or a runner, at least in all my dreams when I get terrified, it's because I'm paralyzed and I can't move. So fight, flight, or freeze, all of these are regulated by that sympathetic division. So the sympathetic division is going to do things like speed up our heart rate, speed up our respiration rate. So that means how fast we're breathing. Excuse me. I'm going to sneeze. I tried not to do that into the microphone. And then also going to be doing things like elevating our blood pressure. Our parasympathetic division is going to be on the other end of the spectrum. This is our resting and digesting division. And so parasympathetic division is going to be doing things like speeding up up digestion, speeding up urination, slowing down heart rate, slowing down respiration rate, lowering your blood pressure. So these two divisions actually work in opposites of each other. So as we work our way through the nervous system, you're going to find that we spend a lot of time focusing on central peripheral sensory and then this side of the motor division. The reason we're not really talking about the somatic nervous system is because we kind of already did that when we covered all of the skeletal muscles in the last section. So we're primarily, when we get into motor, we're primarily going to be focusing on ANS and the sympathetic and parasympathetic division. But today, again, it's just an introduction into the nervous system itself. So let's continue. Okay, so this is just showing you the two main things. structural classifications of the nervous system. So we have the brain up here, and then we have the spinal cord, and then all of this outside is all starting to branch into that peripheral nervous system. You'll notice, so this is showing you again, sort of what I already showed you in this previous much simple, much more simple figure, is breaking down the different divisions of the nervous system, sensory versus motor. And then I tried to follow the same color coding with blue always being sensory information going towards the CNS. So afferent, again, going towards the CNS. You do have to know both of the names, the sensory afferent division or the motor efferent division. And so then all of the information leaving the central nervous system is highlighted here in red. Okay, so let's talk about nervous tissue. We've already... I've done an intro to this when we were looking at the different types of formin tissue types. We know that the two cell types we would find in nervous tissue are our neurons, which you see right here, and then the neural glial cells, which are the smaller cells surrounding the neurons. And the neural glial cells, as a reminder, those are those support cells. A couple of major differences. Mitosis. Okay, so... Our neuroglial cells, or if you want to abbreviate and call them glial cells, that's okay too. Our glial cells can undergo mitosis. They can keep dividing. Our neurons cannot. They are amyotic. They will not be dividing. The neurons are also capable of carrying electrical signals that we call action potentials, and the neural glial cells are not able to do that. In general, these neural glial cells are going to be supporting the neurons, so linking them to their nutrient sources. They're going to be helping with insulation of the neurons to help them send their action potentials faster, cushioning and protection. These are also the first line of defense if you're going to be using a neural glial cell. There needs to be any sort of repair. So a neuron cannot repair itself, but the glial cells can help to a certain extent. And because they retain the ability to divide, if someone is suffering from a brain tumor, okay, so again, a tumor is an unregulated cell growth. It's a type of benign cancer. If someone is suffering from a brain tumor, it's likely it's going to be in those glial cells because our neurons themselves cannot divide. So the glial cells can. So we have a few different types of neuroglial cells. We have neuroglial cells in that central nervous system. Again, we call that our CNS. And we have neuroglial cells in the peripheral nervous system. And depending on which division you're in, you'll find different types of support cells. So we're going to start with looking at the neuroglia cells in our central nervous system. So again, Glial cells are much smaller than neurons, and they outnumber them in the nervous system by about 10 to 1. So about half your total brain mass is just these support cells. Let's start with the first cell that we call an astrocyte. Cite, again, meaning cell. Astro meaning it sort of has a star shape to it. Okay, so that's what we call these an astrocyte. These are the most abundant and versatile of the glial cells. They link neurons to their nutrient source. So what we can see right here in this figure is this red tube is representing a capillary. We see that the neuroglial cells have wrapped its extracellular extensions around the capillary, and it's also wrapped around the neuron back here. So what they are doing is that they are keeping the neurons constantly fed, if you will. Because neurons are always working, They need a continuous supply of oxygen and nutrients, and the astrocytes make sure that that happens. Because an astrocyte is a cell, it's going to contain that phospholipid bilayer, which again is a semi-permeable membrane, and things are only going to get through if they are small, hydrophobic, and not charged. So that should be... This should be in your brain by now that the only things passing through a semi-permeable membrane are going to be small, hydrophobic, and not charged. So for that reason, we say that the astrocytes form the blood-brain barrier. You'll notice the neurons have no direct connection to the blood capillaries. Everything that they get from our blood has to be filtered through the astrocytes. So again, it allows for some filtration to make sure that our neurons don't get contaminated. anything bad directly out of our blood handed to them. And lastly, the astrocytes are going to be controlling the chemical environment around the neurons, which means that any stray ions that may have leaked out, these astrocytes will be mopping them back up. And the reason we don't want any ions hanging around the neuron that aren't supposed to be there is because we do not want to increase the chance of a neuron firing accidentally. We always want to have a lot of control over when these neurons send their action potentials. Okay, let's go on to page 95. Our next neuroglial cell is called a microglial cell. And these are like the janitors of the central nervous system. They act like Pac-Man. They have this sort of spider shape to them. And they are phagocytic, which means they are going to be eating up. other cells. And we call them phagocytic macrophages, which means large eater. So when a neuron is injured or in trouble, these microglial cells will actually migrate towards the damaged neuron. They dispose of debris and invading microorganisms such as bacteria. And they have a really important role as the immune cells of the central nervous system. Because of that blood-brain barrier, These neurons in our central nervous system are denied access to our immune system. So that's what these microglial cells are doing for us. They are making sure that nothing bad gets to our neurons. appendimal cells. So these should look, I mean, we haven't talked about these specifically, but cells with cilia, whenever you see cilia, you should automatically think, okay, we are pushing some sort of fluid around, right? So these appendimal cells are ciliated. They line the cavity of the brain and the spinal cord, and they circulate a fluid we call cerebrospinal fluid or CSF. And so when we have our next lecture, on just the central nervous system, we will be talking about CSF a lot. So these appendimal cells keep that CSF moving in a circular direction. Our oligodendrocytes. Oligodendrocytes are cells that jump on the axons of neurons and they wrap themselves around. They wrap themselves around forming a myelin sheath in the central nervous system. And so the myelin sheath We'll talk about this in more detail in a few minutes. But the myelin sheath, its main job is to insulate the neuron and to help the signals be sent even faster. Okay. So it helps to send signals much, much faster than if it was not wrapped around the neuron. So those are our main types of neuroglial cells for the central nervous system. Now for the peripheral nervous system, we only have two types of neuroglial cells. that we want you guys to worry about. The satellite cells, which we see right here, they're in purple. Okay. So this is a different type of neuron. So far, every neuron you've looked at is a motor neuron with the cell body on one side and the dendrites on the other side. And they don't all look like that. This is a different type of neuron. So this is our cell body right here. And you'll see that the satellite cells wrap around that cell body. They surround and protect them and they form... they perform similar functions as the astrocytes in the central nervous system. The Schwann cells, which we see right here in blue, the Schwann cells are forming the myelin sheath around the axons in the peripheral nervous system. So they are also going to be playing a very important role in regeneration of the damaged peripheral nerve fibers. So if there's any sort of damage to the fiber underneath the... Schwann cells can help with repair to a certain extent. Okay, so let's talk about the neurons. So these are what we also can refer to as our nerve cells. These are the excitable cells that are specialized to transmit those action potentials, the electrical signals that we call action potentials. They are both irritable and conductive. So irritable means they can respond to stimuli. They can be turned on by certain... influence, influencers in certain stimuli. Conductive means they have the ability to carry an action potential over a long, over a long period of time, over a long distance. And so the ability to transmit an impulse to an effector is the definition of a conductive cell. And that's exactly what these guys do. So some special characteristics is that they have, even though they are amyotic, which means they cannot make more of themselves through mitosis, they have extreme longevity. So they can actually last for a lifetime, over 100 years. So the neurons you are born with are the neurons you are dying with. It's kind of crazy. There are, however, some limitations. So people with spinal cord injuries or if you've suffered a stroke, you will not be able to recover those neurons if they are damaged. Neurons also have an extremely high metabolic rate. So they require, again, a continuous supply of oxygen and glucose. And they literally slow down if they are not properly nourished. So that's why it's really important not to skip breakfast in the morning before you listen to my lectures. Because 25% of the calories you take in are consumed by your brain's activity. Okay, let's talk about some... neuron anatomy. This should be review for you guys. We've already gone over this before. So some major regions. This is our cell body. In the cell body, we can also call it the soma. I don't care which one, which terminology you use. We're going to find the nucleus and we're also going to find your typical organelles. So all the organelles that we covered when we were looking at the generalized cell model are going to be found in the cell body of the neuron. This is also going to be the location that we find that is our metabolic center of the cell. That means that's where all of the metabolism is happening. some specialized structures in the neuron. The first one is called chromatophilic substance or nistle bodies. I do not care which term you use, either of those will work. What they are, they are clusters. If you can see sort of around here, the little dots that we see, the chromatophilic substance or nistle bodies, they're clusters of rough ER and ribosomes, and they do the same thing. They produce membrane and they produce proteins. However, what's really unique about... our neurons is their Golgi apparatus, so their Golgi body. So again, neurons are producing a lot of really complicated proteins called neurotransmitters. And so the Golgi apparatus is responsible for, again, completing the folding of proteins as well as packaging up the neurotransmitters to be shipped out of the cell. And we ship a lot of neurotransmitters in neurons. So the Golgi apparatus actually forms an arc. around the nucleus, it almost encloses it like a cage. And so when we look at the model of the neuron at the end of this lecture, we will be able to see the Golgi body very clearly, completely enclosing that nucleus. In our neurons, we're also going to have a lot of mitochondria. Again, we need a lot of ATP in order to carry out these really complex actions. We're also going to find neurofibrils. So this is a cytoskeleton component. It forms the highways that the synaptic vesicles ride on. So after a Golgi body has processed a neurotransmitter, it packages it up into a synaptic vesicle. Remember, the synaptic vesicles don't get released until they have ridden all the way down the axon and into those axonal terminals. So this is quite a long distance, especially because some of our neurons can be up to a meter in length. So the neurofibrils act as highways carrying those synaptic vesicles to the axon terminals. You're also going to find an excessively large, compared to other cells, nucleolus. And if you recall, the nucleolus is a ribosome factory. So because protein synthesis is a really big deal in our neurons, the nucleolus has to crank out quite a large amount of ribosomes to keep up. So some processes, remember the term process is used for any fiber that extends out of the cell body. So we'll start with the dendrites. So these dendrites we see over here, they are the listeners of the neuron. They're out there waiting for some sort of signal that says, okay, it's time to send an action potential. You'll notice that the dendrites are convoluted and they have all these folds and all these different sort of feelers that reach out. And so what they're trying to do is increase their surface area to accommodate the maximum number of synaptic contacts. So what that means is they want to create synapses on anything they can, other neurons, extending out those processes and making sure that they are picking up any signal that could be potentially sent to them. So they receive signals and they conduct the impulses towards the cell body. So let's take a look at the axon. So this whole long portion right here is the axon. The axon is, if these are our listeners, then the axon is our talker. It's sending the message, okay? It's a single process that conducts impulses away from the cell body. So dendrites are bringing information towards the cell body. axons are bringing information away from the cell body. These are also the reasons we call neurons nerve fibers because they are so long and fibrous. Again, they can range anywhere from a millimeter to one meter in length. The axon hillock is part of the axon. It's this V-shaped funnel that you see right here that sort of transitions the cell body into the axon. So this is our axon hillock. It's what we refer to as the action potential trigger zone. So it determines if that threshold of negative 55 has been achieved. So while the dendrites are picking up their sensory information, so that sensory information is coming in. It's causing a local depolarization of sodium ions, making... the inside of the cell body slightly more positive. Well, all of that sort of funnels into our axon hillock. And then if the axon hillock hits negative 55 millivolts, this is where the action potential begins. So we call it the action potential trigger zone. Okay, page 97. The end of the axon is going to end in our axon terminals. So this is where I'm going to zoom in onto a different picture. So we see axon terminals. What we were looking at last time was the axon terminals synapsing onto a muscle fiber, which they do. However, axon terminals can also synapse directly onto other neurons. And so these synaptic vesicles contain, the synaptic vesicles released from the axonal terminal contain neurotransmitters. So dopamine, serotonin, histamine, norepinephrine, there's up to 50 different types of neurotransmitters. And then if we get a little closer, again, we have our presynaptic neuron with our postsynaptic neuron. We also call this the presynaptic cell membrane or the postsynaptic membrane. I will take either of those terms. And then we have our synaptic cleft, which is that small space in between the two that allows for the communication between the cells to be regulated by our neurotransmitter that is released here. So hopefully that's all review because we talked about the synapse quite a lot. However, now instead of looking at a neuron synapsing onto a muscle fiber, we're looking at two neurons synapsing onto each other. Okay, let's talk about our myelin sheath a little bit and our neurolema. So again, the myelin sheath is, it sort of is white in appearance because it has a very high lipid concentration. Again, the myelin sheath is made out of a cell and cells all have that same phospholipid bilayer. As a review, it's formed by the oligodendrocytes in the CNS and the Schwann cells in the PNS. So what happens is, this example we're looking at right here is in the PNS. So we're looking at a Schwann cell. So we have this Schwann cell. It hops on the axon of a neuron. It begins to wrap itself tightly around the neuron. And then once it's done wrapping, we have two different sort of sections available to us that we can see. This really tight section, which is primarily plasma membrane at this point, is referred to as the myelin sheath. All the other organelles and the cytoplasm has been squeezed to the outside layer. And that's also where we're going to find the nucleus because we still have to keep these Schwann cells alive. Oops, sorry. And so these were all squeezed to the outside layer. And we call this layer the neurolema. So we have the myelin sheath and then we have the neurolema. And if we look at it under a microscope, you can see right here we have, if this is the axon in the center, then this is our myelin sheath. And then all of this outside. is the neurolema. So that's where we would find the cytoplasm and the nucleus. So myelin sheets, again, they are going to be protecting the axons, but they are dramatically increasing the speed of impulse travel. So a myelinated neuron can send a signal at 100 meters per second, whereas an unmyelinated neuron sends a signal at about one meter per second. And so that's a huge difference, 100 times faster. And that's because for certain things, we need an instantaneous response. So walking, talking, learning, all of that requires instantaneous responses. And so it's really important to maintain the myelination in both our central and peripheral nervous system. So on a clinical note, briefly, we'll talk about multiple sclerosis. And so you guys have probably heard about this before. It's also referred to as MS. It's a progressive autoimmune disease where the myelin sheaths are gradually destroyed and reduced to non-functional hardened lesions called scleroses. And so the loss of this myelin as a result of your own immune system attack to the myelin proteins causes a slowdown of impulse travel that eventually completely ceases any conduction of a signal. And so it's a progressive. degenerative disease, which means it's only getting worse over time. And as of right now, there is no cure for it. So symptoms include visual disturbances, problems controlling your muscles, so weakness or clumsiness. Ultimately, it will end in paralysis, speech disturbances, and the like. So it's a very progressive and aggressive disease. Okay, so now let's jump. I'm on page 98. Jumping to nodes of Ranvier. So this is the last bit of neuron anatomy we're going to go over right here. So in between every Schwann cell, you'll find a little bit of open space. That open space is known as the nodes of Ranvier. It breaks in the myelin sheath. And it actually allows to facilitate speeding up the signal even more. So the way that it works, it's almost like if you pick up a stone and skip it across a lake. It's allowing for that signal to sort of skip along our axon and helps to facilitate an even faster signal. Okay, so now we're sort of shifting topics. We're moving away from the cellular anatomy, and now we're going to talk about some terminology. So I want to talk about neuronal cell body location. So what that means is where are these cells located in the body? Where do we keep the cell bodies depending on if we're looking at CNS or PNS, and then we have some terminology we use for each of them. So I'm going to write central nervous system over here and then PNS over here. Okay. So our first thing we're going to be looking at for CNS is cell body. Oops, that's kind of messy, but I think you guys can read it. It's kind of hard to write with this tablet. Cell body location. This is just some terminology. Okay. So it's just definitions. If. we have a cell body location in the CNS, the term we give them are called nuclei. Okay. So again, this is the cell body of that neuron. If we have a cell body in the PNS, the term we give it is a ganglion. And then ganglia is plural. So again, just straight up terminology. Now, this is looking at the cell body of the neuron. Well, what about the bundles of the nerve fibers? So the axons, okay? So if we're looking at the nerve fibers themselves, if they are in the CNS, okay, we call them tracts. If they're in the PNS, we call them nerves. In the CNS, we have two more types of terminology. These tracks can be called white matter or gray matter. Oops, I'm not writing matter because I'm running out of space. But white matter or gray matter. The white matter are going to be myelinated. oops, that shouldn't be there, myelinated, and the gray matter is going to be unmyelinated. And so again, that just means, are we going to have those oligodendrocytes or those Schwann cells? Well, if we're talking about CNS, it would be oligodendrocytes. Are they present or are they not present? So in the white matter, the oligodendrocytes will be present, wrapping around our neurons. And in the gray matter, they will be not present. So that's all we're trying to break down with this next section. It's just some vocabulary. And that matters because if I'm referring to something as a ganglion, then you can automatically say, okay, I know she's talking about the peripheral nervous system. But if I'm talking about gray matter or white matter, then you always know I'm going to be talking about the central nervous system. On the other side of things, let me clear this out really quick. If I, oops. If I were to present you with a picture of something like this, what we're looking at here is a cross section of a spinal cord. So because we know that the CNS is made up of brain and spinal cord, then I know I'm going to be looking at tracks in this area. Okay, so here we actually in the spinal cord, we have the gray matter. on the deep to the white matter. So this butterfly shape you see here in the center is gray matter, which is unmyelinated. And then out here, the white matter you see is myelinated. Taking a look at a cross section of the brain. So this isn't as nicely color coded as the last one being obviously gray and white. Oops. But here on the brain, the more superficial portion, is going to be that gray matter and the deeper portion is called white matter. So on the brain, the unmyelinated neurons are more superficial to the myelinated neurons. So they're opposites of each other. Gray matters on the inside here, gray matters on the outside here. Okay, so now we're going to classify neurons based on structure and based on function. We love classifying everything twice, structure and function. Oops, you know I got ahead of myself. We will be talking about this in more detail when we get into peripheral nervous system. But when we talk about bundles of nerve fibers in the peripheral nervous system, we call them nerves. And that's because we bundle our nerves by bundling axons. So we have one single axon here. We bundle it. We call that bundle a fascicle. And then we bundle a bunch of fascicles together. wrap it in a connective tissue layer, and that's all called one nerve. So again, I'm gliding over this because we will be covering it in much more detail in a later lecture. But you'll see that the wrapping and the stacking that we do with nerves is very similar to what you saw in our skeletal muscle anatomy. Okay, now let's classify neurons by structure. So We have multipolar, bipolar, and unipolar neurons. So what that means is, it's just referring to how many processes hang off of the cell body. So if we take a look at this first neuron right here, we have the cell body sort of in the center, and then we have the axon hanging off this way, and then we have dendrites all over the place hanging off this way. So we have many. processes. So we call this one multipolar. Bipolar means we have the cell body here, and we have two processes hanging directly off of that cell body. So that's going to be our bipolar. And then lastly, unipolar means here is our cell body, and we have one single process hanging off the cell body. It does split, but as far as what's directly hanging off the cell body, we have only that one. So we refer to that as unipolar. So multipolar neurons are going to be the most common neuron. 99% of all of our neurons are these multipolar neurons. They can be used for both motor neurons, but also something we call an interneuron. So we'll get to that in a little bit later. Our bipolar neurons are going to be much more rare. Bipolar neurons are found in sensory locations like the eyes. And then unipolar neurons. Right here, these are also referred to as our sensory neurons. So a lot of the information bringing, I'm sorry, a lot of the neurons bringing information towards our central nervous system are going to be sensory neurons. Okay, so I think that also sort of covers the next section, which is the functional classification of the neuron. So again, sensory right here. And then we have our motor or our efferent neurons, as well as our inter or our association neurons. So we're going to draw something together. So if you need to pause the video and pull out a piece of paper, now's the time. You're going to be seeing this drawing quite a bit coming up. So I'm just going to draw my cross section of a spinal cord. Okay, it's not great, but you get the idea. Let me change my color here. So I'm going to draw this next stuff in blue because that's going to be representing our sensory information coming in. Okay, so this was my sensory neuron. On the outside here, we have a receptor, and this is where some sort of stimulus is going to get picked up, okay? That's sensory neuron. The information is moving towards the CNS, so from the receptor towards the spinal cord in this case. And because this is, so this is representing my cell body, because this is a collection of cell bodies outside of the central nervous system, going back to that terminology we covered before. This is referred to as a... ganglion. Because realistically, it wouldn't be just one single neuron. It would be a bundle of many of these sensory neurons. So now we brought that information towards the CNS. At this point, it's going to get integrated by what we refer to as a, I'm going to do a line over here. This is my interneuron. And again, that interneuron is going to be a multipolar neuron. So that interneuron is doing a couple of things. It's processing information at the level of the spinal cord. It's also communicating with all of the other interneurons, sending all the information out of the spinal cord towards the brain where it can be. processed. And so lastly, that interneuron is going to be sending information to a motor neuron. Motor neurons are carrying information, oops, not the best arrow, but you get the idea, carrying information away from the central nervous system. And these motor neurons are activating effectors, which again are going to be muscles or glands. Okay, so you'll also notice that I drew the cell body of the motor neuron in a very specific location. It's in the gray matter of the central nervous system because the gray matter, as you will recall, is un... myelinated. So we don't have any myelination around that CNS, or I'm sorry, around that cell body, but we will have myelination around the axon as it leaves. And so this is why spinal cord damage can be so dramatic on our bodies, because if you disrupt anything at the level of the spinal cord, you're cutting off the head, if you will, of our motor neurons. So no signals will ever get sent out to the effectors. which are muscles and glands. Okay, so let's take a look at page 99. And I'm going to clear all this away. We will be coming back to this drawing quite a bit. So please, please become familiar with it. Okay, so now we're getting into a little bit of neurophysiology. So this is going back a lot to our muscles to lecture where we were talking about the neuromuscular junction and how action potentials are transferred from a motor neuron and ultimately into a muscle fiber. But the exact same process happens when we're transferring an action potential from a neuron into another neuron. So we have the exact same. I'm going to go through these a little quick because this should be review. We have that exact same resting membrane potential of negative 70 millivolts. present in our neurons. This is maintained, again, by our sodium-potassium pump, as well as some open sodium-potassium channels. When a stimulus is reached, it first starts with that local depolarization. Some ligand-gated sodium channels are going to open until we hit a threshold of negative 55. So I know your notes say negative 65. Please cross that out. We're going to say negative 55 so it matches your book. And so again, this is the minimum amount of depolarization required to initiate an action potential. Once we hit negative 55, the action potential is fired. As a result, our membrane potentials are temporarily reversed. So wherever the action potential is not, we will have our negative 70 inside. And then right here will be that positive 30 and then negative 70. And this will, it will self. propagate, meaning it will continue. Once it starts at the axon hillock of our neuron, it will continue all the way down to the axon terminals of the neuron. So it is an all-or-one phenomenon. So hopefully this looks familiar. We have negative 70. Some sort of stimulus happens. We hit negative 55. Sodium enters. We peak at positive 30. Potassium leaves. And then we have some hyperpolarization. We can also refer to this as the refractory period, where we will not be sending another signal until the sodium-potassium puns have re-established a negative 70 concentration gradient. Okay, page 100, the synapse. Again, this should be a little bit of review. However, we're going to be focusing specifically on neuron to neuron synapses. So these are the synapses that we find in your brain, in your spinal cord. We have over 100 trillion synapses in the brain alone. This is how we learn. This is how we remember. It's also, unfortunately, the root of many psychiatric disorders. This is why drugs and addictions exist by manipulating the synapses in the brain. So the synapse is going to be mediating information transfer from one neuron to another neuron, which is what we see right here. You don't have to know the names of all these different synapses. You just have to know that you can synapse basically anywhere you want to on a neuron with the exception of the axon. And so... We can synapse directly onto the cell body, onto the dendrites, onto the axon hillock, but not on here. Our three main parts are the axon or the presynaptic terminal or presynaptic membrane. Again, I will take any of those terms. We have that synaptic cleft in the center. And then we have the postsynaptic membrane on the receiving side of the signal. So we transfer information. chemically. So it starts off as an electrical signal and then when we transfer the information from one neuron to the next we are doing that with a chemical signal. So for that reason we call this electrochemical communication and then the reason we want to have both electric and chemical communication is the chemical communication slows things down. It also allows for us to control the synapses. If this was electrical and we just went boom boom we wouldn't really be able to regulate anything at the synapse, at the level of the synapse. So again, this is just should be review. We have the action potential arriving at the axon terminal. This causes a huge influx of calcium as voltage-gated calcium channels open. The influx of calcium is going to cause the release of the synaptic vesicles. By exocytosis, they're going to be... releasing whatever neurotransmitter they carry into the synaptic cleft. The neurotransmitters will diffuse across the synaptic cleft and bind to the receptors on the postsynaptic cell. It's also really important that we regulate how long these neurotransmitters are here for. And so we actually have to terminate the effects of the neurotransmitters. So this allows for, again, control. We want to maintain regulation of these areas. So we do this in a few ways. We can reuptake the neurotransmitter, which means the presynaptic neuron has proteins on it that act like little vacuums and we'll just suck these guys right back in. Degradation is an enzymatic breakdown. So sort of like how the acetylcholine esterase functions to break down acetylcholine, we also have other enzymes that can break down other neurotransmitters. And then lastly, we have diffusion, which just means, again, going from an area of high concentration to an area of lower concentration, our neurotransmitters simply float away from the synapse. So knowing that, let's talk about how we can either excite or inhibit a neuron at the level of the synapse. So when I say excite, I mean it makes it easier to send a signal, and inhibit makes it more difficult to send a signal. Neurotransmitters are specific for their receptors, okay? So what neurotransmitter gets used and how it affects the body is dependent on the receptors of the receiving cell. Okay, so let's talk about our... excitatory postsynaptic potentials. You'll see this up here. We can also call it an EPSP, okay? Excitatory postsynaptic potential. What this means is a neurotransmitter, so they can be stimulatory in one synapse and inhibitory in another, but it depends on the receptor, okay? So it's all dependent on the receptor. So let's say that we let a neurotransmitter free here in the synaptic cleft. And then these receptors that we see on this side, are what we call excitatory receptors. They are more likely to fire an action potential. They increase the permeability of the postsynaptic neuron to sodium, which basically just means that once a stimulus hits, we have this really quick increase in positive ions. So the inside of the neuron becomes more positive. So it increases the likelihood of us hitting negative 55, and then having that action potential fire. An inhibitory postsynaptic potential works the other way. It's going to be increasing permeability to potassium ions, therefore causing a drop in what will require sort of a drop in voltage. Okay, so if it's more permeable to potassium ions. it's going to make the inside more negative. So it's decreasing the chance of firing an action potential. So EPSPs make the inside more positive. IPSPs make the inside more negative. And again, this is going to depend on the type of receptor that is present on the postsynaptic cell. So IPSP is actually a really great demonstration of how we can... use local anesthetics. So let's talk about this really quick. I'm just going to bring my pen back. So with local anesthetics, pain is processed at the level of the cerebral cortex. Okay, so that's where pain is perceived. So there has to be some sort of receptor picking up the information. That receptor sends that information along a sensory neuron. That sensory neuron is going to send it to an interneuron. The interneuron will send it up the spinal cord. Oops. And then the spinal cord will ultimately send it to the cerebral cortex. Oops. Hang on. Let's see. I don't know how to find the eraser. So what we do with... local anesthetics is that we shut down the sodium channels at the level of the sensory neuron. So we are, so something like Novocaine, okay, shuts down the sodium channels. So if we have no sodium channels, we never get that local depolarization. We never set an action potential. The information never leaves the sensory neuron. So even though our receptors might be detecting pain, It never makes it to the cerebral cortex, which is where pain is actually processed. Okay, let's move on to page 101. We are getting towards the end here. So let's talk about neurotransmitters. Neurotransmitters. are electrical signals or a lot, I'm sorry, neurotransmitters are proteins that along with electrical signals create the language of our nervous system. Again, that electrochemical communication. We have over 50 different neurotransmitters that have been identified. I wouldn't be surprised if there were more we haven't identified yet. They control everything from sleep, rage, appetite, memory, learning. They are most probably famously known for their regulation of our emotions. So we're going to be looking at one specific neurotransmitter. For this class, I don't expect you to know all the different classes of neurotransmitters and what they excite and what they inhibit. That's in your book, but don't have a heart attack that you don't have to know all that stuff. You just have to know EPSPs versus IPSPs. And then we're going to look at norepinephrine as a specific example together. So norepinephrine is sort of one of, it's famously known as a feel good neurotransmitter. It regulates mood and energy. Um, it's what we would call a happy neuron, if you will. So it has many other functions in the peripheral nervous system. It's not just a mood regulator. Um, but for, um, for this course, we're just going to look at it specifically as its function as a mood regulator. Okay. So at the bottom of page 101, you have a figure that should look like this. So, um, make sure You're here with me and we're going to be doing some drawings together. So let's say that we are sending an action potential down a presynaptic cell. So we have our action potential here. It's moving this way along our presynaptic cell. Once that action potential reaches the axon terminal, it's going to open our voltage-gated calcium channels. So that's my channel, and that's calcium. flooding into the cell. Then we also have our synaptic vesicles. So those synaptic vesicles are going to contain, because we're looking at norepinephrine, it's going to contain the neurotransmitter norepinephrine. Once calcium floods the cell, these synaptic vesicles are going to fuse with the axonal terminal. membrane and release neurotransmitters into the synaptic cleft. So on this side, we have our receptors. Okay, so the receptors are going to be receiving those neurotransmitters, which in this case... are norepinephrine. So these receptors have a super easy name. We just call them norepinephrine receptors. Okay. Again, they are still a ligand-gated sodium channel, but because they are receiving norepinephrine, we call them norepinephrine receptors. So just as a reminder, okay, it is a ligand-gated sodium channel. So we have our norepinephrine diffusing across our synaptic cleft, binding with our ligand-gated sodium channels. A local depolarization takes place until we hit that negative 55, and then we start an action potential on this side of the cell in the postsynaptic cell, okay? So that's fantastic. We've started our action potential in this cell. However, let's look at how norepinephrine is regulated for reuptake. Again, we don't want it hanging out in the cell forever. So we have these pumps present on the presynaptic cell and their job is to grab that norepinephrine and reuptake it. Okay. So we want to pump it back into the cell. They are called MAOs, monoamino oxidases. Okay, so it's an enzyme that both pumps more norepinephrine back into the cell, but it also has the ability to degrade it to a certain extent as well. Okay, so if we flip over to page 102, we'll talk about what happens if you have too much norepinephrine. So if these monoamino oxidases are not working, or if certain drugs will block them, things like that, what happens? So it can cause an overexcitation and a euphoria. So this is sort of how cocaine works. What it does is it blocks these monoamino oxidases, so that way norepinephrine spends more time in contact with the receptors, sending action potential after action potential after action potential, making a constant stimulation in the following neurons. These are going to be causing the cells to exhaust themselves. They deplete. their norepinephrine stores. Again, these cells are creating proteins. Protein synthesis is a process. You don't have endless amounts of norepinephrine. So you dump all of your norepinephrine stores, your mood goes up, your energy goes up. However, once all these stores are depleted, your energy is going to significantly drop followed by a period of depression. Sometimes hospitalization or a detox will be necessary to reestablish your homeostatic norepinephrine balance. Now, if someone naturally perhaps doesn't produce enough norepinephrine, we have certain medications that can help with that. So antidepressants, certain antidepressants are actually referred to as MAOIs, and this is monoamino oxidase inhibitors. What they actually do is that they slow down these pumps. They don't stop them. We don't want to stop them. That's what cocaine does, right? But we want to slow down the reuptake of norepinephrine to increase the amount of contact it has or increase the amount of time it has to contact the receptors. And then... we will be able to sort of get a nice action potential on the other side of that synapse. So this is why when someone is taking an antidepressant a lot of times, so this is just one single type of antidepressant focusing on one single type of neurotransmitter. And it's all very, not suggestive, but it's all very flexible. It depends on your own body. how much norepinephrine you're producing or how much serotonin or dopamine, whatever the antidepressant is regulating. And it's sort of playing around with the synapse, trying to figure out the perfect balance of how to create that action potential, how to create that stimulus, how to help with mood elevation, but not making you like overly elevated or maybe not even reaching the elevation you want at all. So that's why if someone you know or... maybe you've had some personal experiences with antidepressants, it can be a lot of trial and error because we have a lot of drugs that manipulate the synapse between our neurons in a lot of different ways. Okay, so the reason I did this entire drawing is because you're going to have to recreate it for your lab homework. Alrighty, so when you get into the lab, you will see some instructions about recreating this with serotonin. And so it's, you're going to be essentially copying this drawing. You're going to have a slightly, the only slight change is that the uptake valves have a different name. Okay. And that's covered in the lab review video as well. Alrighty. So let's move on. We're going to go over just a few things. This is all covered in your lab review video, but I did want to talk about it briefly at the end of today's lecture. just so we know what we're looking at. This portion in the center, this is, so this is our model of our motor neuron. This is our cell body or the soma. These are the dendrites out here. The red dots that we see, those are our nissil bodies. Remember a nissil body or chromatophilic substance, whichever term you like to use. Those are going to be our modified rough endoplasmic reticulum and ribosome. And then this cage that we see around the nucleus, that's our Golgi body. The white boundary is defining the nucleus itself, and then the clear bead in the center is our nucleolus. Here we have the axon, and then because this is a motor neuron, we will see the myelination created here by the Schwann cell. So what we're seeing right here, that's representing a Schwann cell. And then lastly, we have our presynaptic terminals. In this case, it's synapsing directly onto a muscle fiber. which is represented by the red. So this is everything I just mentioned. Let me see if I left anything out. Oh, the axon hillock right here. So again, that V-shaped area, and then the neurofibrils. So again, these are what the vesicles are going to be riding on as they make their way to the axon terminals. Schwann cells, myelin sheath, and the axon. This again should be reviewed, but this is our neuromuscular junction model. So we have the motor neuron right here. The rest of it is all skeletal muscle fiber. This is an individual Schwann cell. We have the nucleus of the Schwann cell seen here and here. This is the axon right in the center. So that right in the center. And then all of these layers are going to be the myelin sheath. And again, we would have the neurolema at the level that we have. the nucleus and the cytoplasm, but you don't have to identify that on this model. This is all, so this is looking again at the neuromuscular junction. So these are our muscle fibers. This dark stripe we see right here is the axon of our motor neuron. And then these are the individual axon terminals synapsing onto the muscle fiber. And then I've also included some review videos. in case you guys want to spend some more time looking at this stuff than you already are. Alrighty guys, so I think that's it for today. Enjoy your jump into the nervous system, and I'll see you shortly for the second part, central nervous system. Talk to you later.

So all of our physiological and psychological actions are regulated by the nervous system. It's what we call our fast acting control system. However, the nervous system is also going to be controlling our slow acting control system, which is our endocrine system. So it's essentially mission control, if you will. Everything in our body is regulated by our nervous system.

So some general functions. If we're going to break down the nervous system into three main sections, it would be as what you see right here. So we have some sort of sensory input, whether that's visual or taste or hearing or feeling, we have some sort of sensory input.

That input gets processed by our brain and our spinal cord in a process we call integration. So integration just means that our brain and our spinal cord are processing this sensory input and deciding what we want to do with that information. After the information has been integrated, then we are going to turn on some sort of effector through a process called motor output.

So effectors are going to be causing a response. These effectors can be muscles or glands. So in this case, this person sees a glass of water, their brain decides they're thirsty, and so they're going to be turning on their... somatic muscles, so they're voluntary control muscles, to pick up the glass of water and then take a drink.

So that's going to be our motor output in this case is a skeletal muscle. So let's look at the structural and functional classifications of the nervous system. So structurally, we have two main players, the central nervous system, which consists of the brain and the spinal cord, and the peripheral nervous system, which is basically anything outside of the brain and the spinal cord.

So those are our two main divisions. So if you flip to page 93, you will see that this chart is already found in your notes. So what I'm doing is I'm just sort of going to break it down for you a little bit. So if you look right here, we have the central nervous system. It can also be referred to as the CNS.

So central nervous system, again, that's brain and spinal cord, and peripheral nervous system is everything that's not brain and spinal cord. Then we have some various levels of divisions, functionally classifying the nervous system into what we call sensory or the afferent division and motor or the efferent division. Both of these are part of that peripheral nervous system.

So what this means is we have some sort of sensory information coming into the body. Okay. All of the sensory...

The input in this graph is represented by the blue arrows, and the output is represented by the red. So we have the sensory afferent division sending information through the peripheral nervous system. That peripheral nervous system is going to send that information towards the central nervous system. So if anything is going towards the central nervous system, we would call that sensory information. At that point...

The integration process we mentioned before, which is where the brain is processing, the brain and the spinal cord are processing what to do with the sensory information. That takes place at the level of the CNS. That central nervous system makes a decision to activate an effector. So this is where the divisions get a little more complicated. Depending on the response you want to have, we have many subdivisions of the efferent or motor division.

So the brain has made some decision sending it out through that peripheral nervous system, specifically through the motor division of that peripheral nervous system. And then we have a couple of choices. We have our somatic nervous system and we have our autonomic nervous system.

The somatic nervous system is going to be 100% our voluntary nervous system. This is where... our skeletal muscles are going to be controlled.

So let's add some notes here. So somatic nervous system, this is... skeletal muscle.

And so if it's skeletal muscle, that means it is voluntary. Our autonomic nervous system. So autonomic to me kind of sounds like the word automatic.

So it means we don't have any control over this side of the system. So it's going to be our involuntary division. In involuntary, we're going to find the control of smooth muscle, cardiac muscle, and then glands. So all of these are regulated by that involuntary autonomic nervous system or our ANS. Now the ANS has...

two more divisions in itself, our sympathetic division and our parasympathetic division. So they each have different functions depending on what sort of information was brought in by that sensory division. So the sympathetic division, this is what we call our fight or flight division, which the term fight or flight is slightly outdated because they've actually decided that in times of crisis that people actually do three things. They fight, flight, or they freeze.

I feel like I'd probably be a freezer. I'm not too much of a fighter or a runner, at least in all my dreams when I get terrified, it's because I'm paralyzed and I can't move. So fight, flight, or freeze, all of these are regulated by that sympathetic division. So the sympathetic division is going to do things like speed up our heart rate, speed up our respiration rate.

So that means how fast we're breathing. Excuse me. I'm going to sneeze. I tried not to do that into the microphone.

And then also going to be doing things like elevating our blood pressure. Our parasympathetic division is going to be on the other end of the spectrum. This is our resting and digesting division.

And so parasympathetic division is going to be doing things like speeding up up digestion, speeding up urination, slowing down heart rate, slowing down respiration rate, lowering your blood pressure. So these two divisions actually work in opposites of each other. So as we work our way through the nervous system, you're going to find that we spend a lot of time focusing on central peripheral sensory and then this side of the motor division.

The reason we're not really talking about the somatic nervous system is because we kind of already did that when we covered all of the skeletal muscles in the last section. So we're primarily, when we get into motor, we're primarily going to be focusing on ANS and the sympathetic and parasympathetic division. But today, again, it's just an introduction into the nervous system itself.

So let's continue. Okay, so this is just showing you the two main things. structural classifications of the nervous system.

So we have the brain up here, and then we have the spinal cord, and then all of this outside is all starting to branch into that peripheral nervous system. You'll notice, so this is showing you again, sort of what I already showed you in this previous much simple, much more simple figure, is breaking down the different divisions of the nervous system, sensory versus motor. And then I tried to follow the same color coding with blue always being sensory information going towards the CNS.

So afferent, again, going towards the CNS. You do have to know both of the names, the sensory afferent division or the motor efferent division. And so then all of the information leaving the central nervous system is highlighted here in red.

Okay, so let's talk about nervous tissue. We've already... I've done an intro to this when we were looking at the different types of formin tissue types. We know that the two cell types we would find in nervous tissue are our neurons, which you see right here, and then the neural glial cells, which are the smaller cells surrounding the neurons.

And the neural glial cells, as a reminder, those are those support cells. A couple of major differences. Mitosis.

Okay, so... Our neuroglial cells, or if you want to abbreviate and call them glial cells, that's okay too. Our glial cells can undergo mitosis.

They can keep dividing. Our neurons cannot. They are amyotic.

They will not be dividing. The neurons are also capable of carrying electrical signals that we call action potentials, and the neural glial cells are not able to do that. In general, these neural glial cells are going to be supporting the neurons, so linking them to their nutrient sources.

They're going to be helping with insulation of the neurons to help them send their action potentials faster, cushioning and protection. These are also the first line of defense if you're going to be using a neural glial cell. There needs to be any sort of repair.

So a neuron cannot repair itself, but the glial cells can help to a certain extent. And because they retain the ability to divide, if someone is suffering from a brain tumor, okay, so again, a tumor is an unregulated cell growth. It's a type of benign cancer. If someone is suffering from a brain tumor, it's likely it's going to be in those glial cells because our neurons themselves cannot divide.

So the glial cells can. So we have a few different types of neuroglial cells. We have neuroglial cells in that central nervous system. Again, we call that our CNS.

And we have neuroglial cells in the peripheral nervous system. And depending on which division you're in, you'll find different types of support cells. So we're going to start with looking at the neuroglia cells in our central nervous system. So again, Glial cells are much smaller than neurons, and they outnumber them in the nervous system by about 10 to 1. So about half your total brain mass is just these support cells.

Let's start with the first cell that we call an astrocyte. Cite, again, meaning cell. Astro meaning it sort of has a star shape to it.

Okay, so that's what we call these an astrocyte. These are the most abundant and versatile of the glial cells. They link neurons to their nutrient source.

So what we can see right here in this figure is this red tube is representing a capillary. We see that the neuroglial cells have wrapped its extracellular extensions around the capillary, and it's also wrapped around the neuron back here. So what they are doing is that they are keeping the neurons constantly fed, if you will. Because neurons are always working, They need a continuous supply of oxygen and nutrients, and the astrocytes make sure that that happens. Because an astrocyte is a cell, it's going to contain that phospholipid bilayer, which again is a semi-permeable membrane, and things are only going to get through if they are small, hydrophobic, and not charged.

So that should be... This should be in your brain by now that the only things passing through a semi-permeable membrane are going to be small, hydrophobic, and not charged. So for that reason, we say that the astrocytes form the blood-brain barrier.

You'll notice the neurons have no direct connection to the blood capillaries. Everything that they get from our blood has to be filtered through the astrocytes. So again, it allows for some filtration to make sure that our neurons don't get contaminated.

anything bad directly out of our blood handed to them. And lastly, the astrocytes are going to be controlling the chemical environment around the neurons, which means that any stray ions that may have leaked out, these astrocytes will be mopping them back up. And the reason we don't want any ions hanging around the neuron that aren't supposed to be there is because we do not want to increase the chance of a neuron firing accidentally.

We always want to have a lot of control over when these neurons send their action potentials. Okay, let's go on to page 95. Our next neuroglial cell is called a microglial cell. And these are like the janitors of the central nervous system. They act like Pac-Man. They have this sort of spider shape to them.

And they are phagocytic, which means they are going to be eating up. other cells. And we call them phagocytic macrophages, which means large eater.

So when a neuron is injured or in trouble, these microglial cells will actually migrate towards the damaged neuron. They dispose of debris and invading microorganisms such as bacteria. And they have a really important role as the immune cells of the central nervous system. Because of that blood-brain barrier, These neurons in our central nervous system are denied access to our immune system. So that's what these microglial cells are doing for us.

They are making sure that nothing bad gets to our neurons. appendimal cells. So these should look, I mean, we haven't talked about these specifically, but cells with cilia, whenever you see cilia, you should automatically think, okay, we are pushing some sort of fluid around, right? So these appendimal cells are ciliated.

They line the cavity of the brain and the spinal cord, and they circulate a fluid we call cerebrospinal fluid or CSF. And so when we have our next lecture, on just the central nervous system, we will be talking about CSF a lot. So these appendimal cells keep that CSF moving in a circular direction.

Our oligodendrocytes. Oligodendrocytes are cells that jump on the axons of neurons and they wrap themselves around. They wrap themselves around forming a myelin sheath in the central nervous system. And so the myelin sheath We'll talk about this in more detail in a few minutes.

But the myelin sheath, its main job is to insulate the neuron and to help the signals be sent even faster. Okay. So it helps to send signals much, much faster than if it was not wrapped around the neuron.

So those are our main types of neuroglial cells for the central nervous system. Now for the peripheral nervous system, we only have two types of neuroglial cells. that we want you guys to worry about.

The satellite cells, which we see right here, they're in purple. Okay. So this is a different type of neuron.

So far, every neuron you've looked at is a motor neuron with the cell body on one side and the dendrites on the other side. And they don't all look like that. This is a different type of neuron. So this is our cell body right here. And you'll see that the satellite cells wrap around that cell body.

They surround and protect them and they form... they perform similar functions as the astrocytes in the central nervous system. The Schwann cells, which we see right here in blue, the Schwann cells are forming the myelin sheath around the axons in the peripheral nervous system. So they are also going to be playing a very important role in regeneration of the damaged peripheral nerve fibers. So if there's any sort of damage to the fiber underneath the...

Schwann cells can help with repair to a certain extent. Okay, so let's talk about the neurons. So these are what we also can refer to as our nerve cells.

These are the excitable cells that are specialized to transmit those action potentials, the electrical signals that we call action potentials. They are both irritable and conductive. So irritable means they can respond to stimuli.

They can be turned on by certain... influence, influencers in certain stimuli. Conductive means they have the ability to carry an action potential over a long, over a long period of time, over a long distance.

And so the ability to transmit an impulse to an effector is the definition of a conductive cell. And that's exactly what these guys do. So some special characteristics is that they have, even though they are amyotic, which means they cannot make more of themselves through mitosis, they have extreme longevity.

So they can actually last for a lifetime, over 100 years. So the neurons you are born with are the neurons you are dying with. It's kind of crazy. There are, however, some limitations. So people with spinal cord injuries or if you've suffered a stroke, you will not be able to recover those neurons if they are damaged.

Neurons also have an extremely high metabolic rate. So they require, again, a continuous supply of oxygen and glucose. And they literally slow down if they are not properly nourished. So that's why it's really important not to skip breakfast in the morning before you listen to my lectures. Because 25% of the calories you take in are consumed by your brain's activity.

Okay, let's talk about some... neuron anatomy. This should be review for you guys.

We've already gone over this before. So some major regions. This is our cell body. In the cell body, we can also call it the soma.

I don't care which one, which terminology you use. We're going to find the nucleus and we're also going to find your typical organelles. So all the organelles that we covered when we were looking at the generalized cell model are going to be found in the cell body of the neuron. This is also going to be the location that we find that is our metabolic center of the cell. That means that's where all of the metabolism is happening.

some specialized structures in the neuron. The first one is called chromatophilic substance or nistle bodies. I do not care which term you use, either of those will work.

What they are, they are clusters. If you can see sort of around here, the little dots that we see, the chromatophilic substance or nistle bodies, they're clusters of rough ER and ribosomes, and they do the same thing. They produce membrane and they produce proteins.

However, what's really unique about... our neurons is their Golgi apparatus, so their Golgi body. So again, neurons are producing a lot of really complicated proteins called neurotransmitters.

And so the Golgi apparatus is responsible for, again, completing the folding of proteins as well as packaging up the neurotransmitters to be shipped out of the cell. And we ship a lot of neurotransmitters in neurons. So the Golgi apparatus actually forms an arc. around the nucleus, it almost encloses it like a cage.

And so when we look at the model of the neuron at the end of this lecture, we will be able to see the Golgi body very clearly, completely enclosing that nucleus. In our neurons, we're also going to have a lot of mitochondria. Again, we need a lot of ATP in order to carry out these really complex actions. We're also going to find neurofibrils.

So this is a cytoskeleton component. It forms the highways that the synaptic vesicles ride on. So after a Golgi body has processed a neurotransmitter, it packages it up into a synaptic vesicle. Remember, the synaptic vesicles don't get released until they have ridden all the way down the axon and into those axonal terminals. So this is quite a long distance, especially because some of our neurons can be up to a meter in length.

So the neurofibrils act as highways carrying those synaptic vesicles to the axon terminals. You're also going to find an excessively large, compared to other cells, nucleolus. And if you recall, the nucleolus is a ribosome factory.

So because protein synthesis is a really big deal in our neurons, the nucleolus has to crank out quite a large amount of ribosomes to keep up. So some processes, remember the term process is used for any fiber that extends out of the cell body. So we'll start with the dendrites. So these dendrites we see over here, they are the listeners of the neuron. They're out there waiting for some sort of signal that says, okay, it's time to send an action potential.

You'll notice that the dendrites are convoluted and they have all these folds and all these different sort of feelers that reach out. And so what they're trying to do is increase their surface area to accommodate the maximum number of synaptic contacts. So what that means is they want to create synapses on anything they can, other neurons, extending out those processes and making sure that they are picking up any signal that could be potentially sent to them. So they receive signals and they conduct the impulses towards the cell body.

So let's take a look at the axon. So this whole long portion right here is the axon. The axon is, if these are our listeners, then the axon is our talker.

It's sending the message, okay? It's a single process that conducts impulses away from the cell body. So dendrites are bringing information towards the cell body.

axons are bringing information away from the cell body. These are also the reasons we call neurons nerve fibers because they are so long and fibrous. Again, they can range anywhere from a millimeter to one meter in length.

The axon hillock is part of the axon. It's this V-shaped funnel that you see right here that sort of transitions the cell body into the axon. So this is our axon hillock. It's what we refer to as the action potential trigger zone.

So it determines if that threshold of negative 55 has been achieved. So while the dendrites are picking up their sensory information, so that sensory information is coming in. It's causing a local depolarization of sodium ions, making... the inside of the cell body slightly more positive.

Well, all of that sort of funnels into our axon hillock. And then if the axon hillock hits negative 55 millivolts, this is where the action potential begins. So we call it the action potential trigger zone. Okay, page 97. The end of the axon is going to end in our axon terminals. So this is where I'm going to zoom in onto a different picture.

So we see axon terminals. What we were looking at last time was the axon terminals synapsing onto a muscle fiber, which they do. However, axon terminals can also synapse directly onto other neurons. And so these synaptic vesicles contain, the synaptic vesicles released from the axonal terminal contain neurotransmitters. So dopamine, serotonin, histamine, norepinephrine, there's up to 50 different types of neurotransmitters.

And then if we get a little closer, again, we have our presynaptic neuron with our postsynaptic neuron. We also call this the presynaptic cell membrane or the postsynaptic membrane. I will take either of those terms. And then we have our synaptic cleft, which is that small space in between the two that allows for the communication between the cells to be regulated by our neurotransmitter that is released here. So hopefully that's all review because we talked about the synapse quite a lot.

However, now instead of looking at a neuron synapsing onto a muscle fiber, we're looking at two neurons synapsing onto each other. Okay, let's talk about our myelin sheath a little bit and our neurolema. So again, the myelin sheath is, it sort of is white in appearance because it has a very high lipid concentration. Again, the myelin sheath is made out of a cell and cells all have that same phospholipid bilayer. As a review, it's formed by the oligodendrocytes in the CNS and the Schwann cells in the PNS.

So what happens is, this example we're looking at right here is in the PNS. So we're looking at a Schwann cell. So we have this Schwann cell. It hops on the axon of a neuron. It begins to wrap itself tightly around the neuron.

And then once it's done wrapping, we have two different sort of sections available to us that we can see. This really tight section, which is primarily plasma membrane at this point, is referred to as the myelin sheath. All the other organelles and the cytoplasm has been squeezed to the outside layer.

And that's also where we're going to find the nucleus because we still have to keep these Schwann cells alive. Oops, sorry. And so these were all squeezed to the outside layer.

And we call this layer the neurolema. So we have the myelin sheath and then we have the neurolema. And if we look at it under a microscope, you can see right here we have, if this is the axon in the center, then this is our myelin sheath.

And then all of this outside. is the neurolema. So that's where we would find the cytoplasm and the nucleus. So myelin sheets, again, they are going to be protecting the axons, but they are dramatically increasing the speed of impulse travel. So a myelinated neuron can send a signal at 100 meters per second, whereas an unmyelinated neuron sends a signal at about one meter per second.

And so that's a huge difference, 100 times faster. And that's because for certain things, we need an instantaneous response. So walking, talking, learning, all of that requires instantaneous responses.

And so it's really important to maintain the myelination in both our central and peripheral nervous system. So on a clinical note, briefly, we'll talk about multiple sclerosis. And so you guys have probably heard about this before. It's also referred to as MS. It's a progressive autoimmune disease where the myelin sheaths are gradually destroyed and reduced to non-functional hardened lesions called scleroses. And so the loss of this myelin as a result of your own immune system attack to the myelin proteins causes a slowdown of impulse travel that eventually completely ceases any conduction of a signal.

And so it's a progressive. degenerative disease, which means it's only getting worse over time. And as of right now, there is no cure for it. So symptoms include visual disturbances, problems controlling your muscles, so weakness or clumsiness. Ultimately, it will end in paralysis, speech disturbances, and the like.

So it's a very progressive and aggressive disease. Okay, so now let's jump. I'm on page 98. Jumping to nodes of Ranvier.

So this is the last bit of neuron anatomy we're going to go over right here. So in between every Schwann cell, you'll find a little bit of open space. That open space is known as the nodes of Ranvier.

It breaks in the myelin sheath. And it actually allows to facilitate speeding up the signal even more. So the way that it works, it's almost like if you pick up a stone and skip it across a lake. It's allowing for that signal to sort of skip along our axon and helps to facilitate an even faster signal.

Okay, so now we're sort of shifting topics. We're moving away from the cellular anatomy, and now we're going to talk about some terminology. So I want to talk about neuronal cell body location. So what that means is where are these cells located in the body?

Where do we keep the cell bodies depending on if we're looking at CNS or PNS, and then we have some terminology we use for each of them. So I'm going to write central nervous system over here and then PNS over here. Okay.

So our first thing we're going to be looking at for CNS is cell body. Oops, that's kind of messy, but I think you guys can read it. It's kind of hard to write with this tablet.

Cell body location. This is just some terminology. Okay. So it's just definitions.

If. we have a cell body location in the CNS, the term we give them are called nuclei. Okay.

So again, this is the cell body of that neuron. If we have a cell body in the PNS, the term we give it is a ganglion. And then ganglia is plural. So again, just straight up terminology. Now, this is looking at the cell body of the neuron.

Well, what about the bundles of the nerve fibers? So the axons, okay? So if we're looking at the nerve fibers themselves, if they are in the CNS, okay, we call them tracts.

If they're in the PNS, we call them nerves. In the CNS, we have two more types of terminology. These tracks can be called white matter or gray matter.

Oops, I'm not writing matter because I'm running out of space. But white matter or gray matter. The white matter are going to be myelinated.

oops, that shouldn't be there, myelinated, and the gray matter is going to be unmyelinated. And so again, that just means, are we going to have those oligodendrocytes or those Schwann cells? Well, if we're talking about CNS, it would be oligodendrocytes. Are they present or are they not present?

So in the white matter, the oligodendrocytes will be present, wrapping around our neurons. And in the gray matter, they will be not present. So that's all we're trying to break down with this next section. It's just some vocabulary. And that matters because if I'm referring to something as a ganglion, then you can automatically say, okay, I know she's talking about the peripheral nervous system.

But if I'm talking about gray matter or white matter, then you always know I'm going to be talking about the central nervous system. On the other side of things, let me clear this out really quick. If I, oops.

If I were to present you with a picture of something like this, what we're looking at here is a cross section of a spinal cord. So because we know that the CNS is made up of brain and spinal cord, then I know I'm going to be looking at tracks in this area. Okay, so here we actually in the spinal cord, we have the gray matter.

on the deep to the white matter. So this butterfly shape you see here in the center is gray matter, which is unmyelinated. And then out here, the white matter you see is myelinated.

Taking a look at a cross section of the brain. So this isn't as nicely color coded as the last one being obviously gray and white. Oops. But here on the brain, the more superficial portion, is going to be that gray matter and the deeper portion is called white matter. So on the brain, the unmyelinated neurons are more superficial to the myelinated neurons.

So they're opposites of each other. Gray matters on the inside here, gray matters on the outside here. Okay, so now we're going to classify neurons based on structure and based on function.

We love classifying everything twice, structure and function. Oops, you know I got ahead of myself. We will be talking about this in more detail when we get into peripheral nervous system.

But when we talk about bundles of nerve fibers in the peripheral nervous system, we call them nerves. And that's because we bundle our nerves by bundling axons. So we have one single axon here. We bundle it.

We call that bundle a fascicle. And then we bundle a bunch of fascicles together. wrap it in a connective tissue layer, and that's all called one nerve. So again, I'm gliding over this because we will be covering it in much more detail in a later lecture. But you'll see that the wrapping and the stacking that we do with nerves is very similar to what you saw in our skeletal muscle anatomy.

Okay, now let's classify neurons by structure. So We have multipolar, bipolar, and unipolar neurons. So what that means is, it's just referring to how many processes hang off of the cell body.

So if we take a look at this first neuron right here, we have the cell body sort of in the center, and then we have the axon hanging off this way, and then we have dendrites all over the place hanging off this way. So we have many. processes. So we call this one multipolar. Bipolar means we have the cell body here, and we have two processes hanging directly off of that cell body.

So that's going to be our bipolar. And then lastly, unipolar means here is our cell body, and we have one single process hanging off the cell body. It does split, but as far as what's directly hanging off the cell body, we have only that one.

So we refer to that as unipolar. So multipolar neurons are going to be the most common neuron. 99% of all of our neurons are these multipolar neurons.

They can be used for both motor neurons, but also something we call an interneuron. So we'll get to that in a little bit later. Our bipolar neurons are going to be much more rare. Bipolar neurons are found in sensory locations like the eyes. And then unipolar neurons.

Right here, these are also referred to as our sensory neurons. So a lot of the information bringing, I'm sorry, a lot of the neurons bringing information towards our central nervous system are going to be sensory neurons. Okay, so I think that also sort of covers the next section, which is the functional classification of the neuron.

So again, sensory right here. And then we have our motor or our efferent neurons, as well as our inter or our association neurons. So we're going to draw something together. So if you need to pause the video and pull out a piece of paper, now's the time. You're going to be seeing this drawing quite a bit coming up.

So I'm just going to draw my cross section of a spinal cord. Okay, it's not great, but you get the idea. Let me change my color here.

So I'm going to draw this next stuff in blue because that's going to be representing our sensory information coming in. Okay, so this was my sensory neuron. On the outside here, we have a receptor, and this is where some sort of stimulus is going to get picked up, okay? That's sensory neuron. The information is moving towards the CNS, so from the receptor towards the spinal cord in this case.

And because this is, so this is representing my cell body, because this is a collection of cell bodies outside of the central nervous system, going back to that terminology we covered before. This is referred to as a... ganglion. Because realistically, it wouldn't be just one single neuron.

It would be a bundle of many of these sensory neurons. So now we brought that information towards the CNS. At this point, it's going to get integrated by what we refer to as a, I'm going to do a line over here. This is my interneuron.

And again, that interneuron is going to be a multipolar neuron. So that interneuron is doing a couple of things. It's processing information at the level of the spinal cord. It's also communicating with all of the other interneurons, sending all the information out of the spinal cord towards the brain where it can be.

processed. And so lastly, that interneuron is going to be sending information to a motor neuron. Motor neurons are carrying information, oops, not the best arrow, but you get the idea, carrying information away from the central nervous system.

And these motor neurons are activating effectors, which again are going to be muscles or glands. Okay, so you'll also notice that I drew the cell body of the motor neuron in a very specific location. It's in the gray matter of the central nervous system because the gray matter, as you will recall, is un... myelinated.

So we don't have any myelination around that CNS, or I'm sorry, around that cell body, but we will have myelination around the axon as it leaves. And so this is why spinal cord damage can be so dramatic on our bodies, because if you disrupt anything at the level of the spinal cord, you're cutting off the head, if you will, of our motor neurons. So no signals will ever get sent out to the effectors.

which are muscles and glands. Okay, so let's take a look at page 99. And I'm going to clear all this away. We will be coming back to this drawing quite a bit.

So please, please become familiar with it. Okay, so now we're getting into a little bit of neurophysiology. So this is going back a lot to our muscles to lecture where we were talking about the neuromuscular junction and how action potentials are transferred from a motor neuron and ultimately into a muscle fiber. But the exact same process happens when we're transferring an action potential from a neuron into another neuron.

So we have the exact same. I'm going to go through these a little quick because this should be review. We have that exact same resting membrane potential of negative 70 millivolts. present in our neurons. This is maintained, again, by our sodium-potassium pump, as well as some open sodium-potassium channels.

When a stimulus is reached, it first starts with that local depolarization. Some ligand-gated sodium channels are going to open until we hit a threshold of negative 55. So I know your notes say negative 65. Please cross that out. We're going to say negative 55 so it matches your book.

And so again, this is the minimum amount of depolarization required to initiate an action potential. Once we hit negative 55, the action potential is fired. As a result, our membrane potentials are temporarily reversed. So wherever the action potential is not, we will have our negative 70 inside.

And then right here will be that positive 30 and then negative 70. And this will, it will self. propagate, meaning it will continue. Once it starts at the axon hillock of our neuron, it will continue all the way down to the axon terminals of the neuron. So it is an all-or-one phenomenon.

So hopefully this looks familiar. We have negative 70. Some sort of stimulus happens. We hit negative 55. Sodium enters. We peak at positive 30. Potassium leaves.

And then we have some hyperpolarization. We can also refer to this as the refractory period, where we will not be sending another signal until the sodium-potassium puns have re-established a negative 70 concentration gradient. Okay, page 100, the synapse.

Again, this should be a little bit of review. However, we're going to be focusing specifically on neuron to neuron synapses. So these are the synapses that we find in your brain, in your spinal cord. We have over 100 trillion synapses in the brain alone.

This is how we learn. This is how we remember. It's also, unfortunately, the root of many psychiatric disorders.

This is why drugs and addictions exist by manipulating the synapses in the brain. So the synapse is going to be mediating information transfer from one neuron to another neuron, which is what we see right here. You don't have to know the names of all these different synapses.

You just have to know that you can synapse basically anywhere you want to on a neuron with the exception of the axon. And so... We can synapse directly onto the cell body, onto the dendrites, onto the axon hillock, but not on here. Our three main parts are the axon or the presynaptic terminal or presynaptic membrane. Again, I will take any of those terms.

We have that synaptic cleft in the center. And then we have the postsynaptic membrane on the receiving side of the signal. So we transfer information.

chemically. So it starts off as an electrical signal and then when we transfer the information from one neuron to the next we are doing that with a chemical signal. So for that reason we call this electrochemical communication and then the reason we want to have both electric and chemical communication is the chemical communication slows things down.

It also allows for us to control the synapses. If this was electrical and we just went boom boom we wouldn't really be able to regulate anything at the synapse, at the level of the synapse. So again, this is just should be review.

We have the action potential arriving at the axon terminal. This causes a huge influx of calcium as voltage-gated calcium channels open. The influx of calcium is going to cause the release of the synaptic vesicles.

By exocytosis, they're going to be... releasing whatever neurotransmitter they carry into the synaptic cleft. The neurotransmitters will diffuse across the synaptic cleft and bind to the receptors on the postsynaptic cell. It's also really important that we regulate how long these neurotransmitters are here for. And so we actually have to terminate the effects of the neurotransmitters.

So this allows for, again, control. We want to maintain regulation of these areas. So we do this in a few ways. We can reuptake the neurotransmitter, which means the presynaptic neuron has proteins on it that act like little vacuums and we'll just suck these guys right back in.

Degradation is an enzymatic breakdown. So sort of like how the acetylcholine esterase functions to break down acetylcholine, we also have other enzymes that can break down other neurotransmitters. And then lastly, we have diffusion, which just means, again, going from an area of high concentration to an area of lower concentration, our neurotransmitters simply float away from the synapse. So knowing that, let's talk about how we can either excite or inhibit a neuron at the level of the synapse.

So when I say excite, I mean it makes it easier to send a signal, and inhibit makes it more difficult to send a signal. Neurotransmitters are specific for their receptors, okay? So what neurotransmitter gets used and how it affects the body is dependent on the receptors of the receiving cell.

Okay, so let's talk about our... excitatory postsynaptic potentials. You'll see this up here. We can also call it an EPSP, okay? Excitatory postsynaptic potential.

What this means is a neurotransmitter, so they can be stimulatory in one synapse and inhibitory in another, but it depends on the receptor, okay? So it's all dependent on the receptor. So let's say that we let a neurotransmitter free here in the synaptic cleft. And then these receptors that we see on this side, are what we call excitatory receptors.

They are more likely to fire an action potential. They increase the permeability of the postsynaptic neuron to sodium, which basically just means that once a stimulus hits, we have this really quick increase in positive ions. So the inside of the neuron becomes more positive. So it increases the likelihood of us hitting negative 55, and then having that action potential fire.

An inhibitory postsynaptic potential works the other way. It's going to be increasing permeability to potassium ions, therefore causing a drop in what will require sort of a drop in voltage. Okay, so if it's more permeable to potassium ions.

it's going to make the inside more negative. So it's decreasing the chance of firing an action potential. So EPSPs make the inside more positive. IPSPs make the inside more negative. And again, this is going to depend on the type of receptor that is present on the postsynaptic cell.

So IPSP is actually a really great demonstration of how we can... use local anesthetics. So let's talk about this really quick.

I'm just going to bring my pen back. So with local anesthetics, pain is processed at the level of the cerebral cortex. Okay, so that's where pain is perceived. So there has to be some sort of receptor picking up the information. That receptor sends that information along a sensory neuron.

That sensory neuron is going to send it to an interneuron. The interneuron will send it up the spinal cord. Oops.

And then the spinal cord will ultimately send it to the cerebral cortex. Oops. Hang on.

Let's see. I don't know how to find the eraser. So what we do with...

local anesthetics is that we shut down the sodium channels at the level of the sensory neuron. So we are, so something like Novocaine, okay, shuts down the sodium channels. So if we have no sodium channels, we never get that local depolarization.

We never set an action potential. The information never leaves the sensory neuron. So even though our receptors might be detecting pain, It never makes it to the cerebral cortex, which is where pain is actually processed. Okay, let's move on to page 101. We are getting towards the end here. So let's talk about neurotransmitters.

Neurotransmitters. are electrical signals or a lot, I'm sorry, neurotransmitters are proteins that along with electrical signals create the language of our nervous system. Again, that electrochemical communication. We have over 50 different neurotransmitters that have been identified. I wouldn't be surprised if there were more we haven't identified yet.

They control everything from sleep, rage, appetite, memory, learning. They are most probably famously known for their regulation of our emotions. So we're going to be looking at one specific neurotransmitter. For this class, I don't expect you to know all the different classes of neurotransmitters and what they excite and what they inhibit.

That's in your book, but don't have a heart attack that you don't have to know all that stuff. You just have to know EPSPs versus IPSPs. And then we're going to look at norepinephrine as a specific example together. So norepinephrine is sort of one of, it's famously known as a feel good neurotransmitter.

It regulates mood and energy. Um, it's what we would call a happy neuron, if you will. So it has many other functions in the peripheral nervous system. It's not just a mood regulator.

Um, but for, um, for this course, we're just going to look at it specifically as its function as a mood regulator. Okay. So at the bottom of page 101, you have a figure that should look like this. So, um, make sure You're here with me and we're going to be doing some drawings together. So let's say that we are sending an action potential down a presynaptic cell.

So we have our action potential here. It's moving this way along our presynaptic cell. Once that action potential reaches the axon terminal, it's going to open our voltage-gated calcium channels. So that's my channel, and that's calcium.

flooding into the cell. Then we also have our synaptic vesicles. So those synaptic vesicles are going to contain, because we're looking at norepinephrine, it's going to contain the neurotransmitter norepinephrine. Once calcium floods the cell, these synaptic vesicles are going to fuse with the axonal terminal.

membrane and release neurotransmitters into the synaptic cleft. So on this side, we have our receptors. Okay, so the receptors are going to be receiving those neurotransmitters, which in this case... are norepinephrine. So these receptors have a super easy name.

We just call them norepinephrine receptors. Okay. Again, they are still a ligand-gated sodium channel, but because they are receiving norepinephrine, we call them norepinephrine receptors.

So just as a reminder, okay, it is a ligand-gated sodium channel. So we have our norepinephrine diffusing across our synaptic cleft, binding with our ligand-gated sodium channels. A local depolarization takes place until we hit that negative 55, and then we start an action potential on this side of the cell in the postsynaptic cell, okay? So that's fantastic.

We've started our action potential in this cell. However, let's look at how norepinephrine is regulated for reuptake. Again, we don't want it hanging out in the cell forever. So we have these pumps present on the presynaptic cell and their job is to grab that norepinephrine and reuptake it.

Okay. So we want to pump it back into the cell. They are called MAOs, monoamino oxidases.

Okay, so it's an enzyme that both pumps more norepinephrine back into the cell, but it also has the ability to degrade it to a certain extent as well. Okay, so if we flip over to page 102, we'll talk about what happens if you have too much norepinephrine. So if these monoamino oxidases are not working, or if certain drugs will block them, things like that, what happens?

So it can cause an overexcitation and a euphoria. So this is sort of how cocaine works. What it does is it blocks these monoamino oxidases, so that way norepinephrine spends more time in contact with the receptors, sending action potential after action potential after action potential, making a constant stimulation in the following neurons.

These are going to be causing the cells to exhaust themselves. They deplete. their norepinephrine stores.

Again, these cells are creating proteins. Protein synthesis is a process. You don't have endless amounts of norepinephrine. So you dump all of your norepinephrine stores, your mood goes up, your energy goes up. However, once all these stores are depleted, your energy is going to significantly drop followed by a period of depression.

Sometimes hospitalization or a detox will be necessary to reestablish your homeostatic norepinephrine balance. Now, if someone naturally perhaps doesn't produce enough norepinephrine, we have certain medications that can help with that. So antidepressants, certain antidepressants are actually referred to as MAOIs, and this is monoamino oxidase inhibitors.

What they actually do is that they slow down these pumps. They don't stop them. We don't want to stop them.

That's what cocaine does, right? But we want to slow down the reuptake of norepinephrine to increase the amount of contact it has or increase the amount of time it has to contact the receptors. And then...

we will be able to sort of get a nice action potential on the other side of that synapse. So this is why when someone is taking an antidepressant a lot of times, so this is just one single type of antidepressant focusing on one single type of neurotransmitter. And it's all very, not suggestive, but it's all very flexible.

It depends on your own body. how much norepinephrine you're producing or how much serotonin or dopamine, whatever the antidepressant is regulating. And it's sort of playing around with the synapse, trying to figure out the perfect balance of how to create that action potential, how to create that stimulus, how to help with mood elevation, but not making you like overly elevated or maybe not even reaching the elevation you want at all.

So that's why if someone you know or... maybe you've had some personal experiences with antidepressants, it can be a lot of trial and error because we have a lot of drugs that manipulate the synapse between our neurons in a lot of different ways. Okay, so the reason I did this entire drawing is because you're going to have to recreate it for your lab homework. Alrighty, so when you get into the lab, you will see some instructions about recreating this with serotonin. And so it's, you're going to be essentially copying this drawing.

You're going to have a slightly, the only slight change is that the uptake valves have a different name. Okay. And that's covered in the lab review video as well. Alrighty. So let's move on.

We're going to go over just a few things. This is all covered in your lab review video, but I did want to talk about it briefly at the end of today's lecture. just so we know what we're looking at.

This portion in the center, this is, so this is our model of our motor neuron. This is our cell body or the soma. These are the dendrites out here.

The red dots that we see, those are our nissil bodies. Remember a nissil body or chromatophilic substance, whichever term you like to use. Those are going to be our modified rough endoplasmic reticulum and ribosome.

And then this cage that we see around the nucleus, that's our Golgi body. The white boundary is defining the nucleus itself, and then the clear bead in the center is our nucleolus. Here we have the axon, and then because this is a motor neuron, we will see the myelination created here by the Schwann cell. So what we're seeing right here, that's representing a Schwann cell. And then lastly, we have our presynaptic terminals.

In this case, it's synapsing directly onto a muscle fiber. which is represented by the red. So this is everything I just mentioned.

Let me see if I left anything out. Oh, the axon hillock right here. So again, that V-shaped area, and then the neurofibrils.

So again, these are what the vesicles are going to be riding on as they make their way to the axon terminals. Schwann cells, myelin sheath, and the axon. This again should be reviewed, but this is our neuromuscular junction model.

So we have the motor neuron right here. The rest of it is all skeletal muscle fiber. This is an individual Schwann cell. We have the nucleus of the Schwann cell seen here and here.

This is the axon right in the center. So that right in the center. And then all of these layers are going to be the myelin sheath.

And again, we would have the neurolema at the level that we have. the nucleus and the cytoplasm, but you don't have to identify that on this model. This is all, so this is looking again at the neuromuscular junction. So these are our muscle fibers. This dark stripe we see right here is the axon of our motor neuron.

And then these are the individual axon terminals synapsing onto the muscle fiber. And then I've also included some review videos. in case you guys want to spend some more time looking at this stuff than you already are. Alrighty guys, so I think that's it for today. Enjoy your jump into the nervous system, and I'll see you shortly for the second part, central nervous system.

Talk to you later.

Transcript for:Understanding the Nervous System Basics

Transcript for:
Understanding the Nervous System Basics