Dr. Jacqueline Pal (she/her): Hello, welcome to physiology on demand. For today. We are going to learn about neuronal structures and location in great detail. Start with a little bit of review and then getting some new content. So we can dive deeper into our neuronal physiology. And so this picture is just kind of a precursor for our next slide, where I'm going to do just a little bit of a review about pumps and channels, and Dr. Jacqueline Pal (she/her): I know this is information you learn for
test one when we talk about the plasma membrane. But in this case I'm going to apply it directly to the neuron. So please don't skip ahead, but listen Dr. Jacqueline Pal (she/her): for its specific application. So pumps, as you recall, require energy and are going to move things against a concentration gradient or up the gradient. And in the neurons we're going to have our typical sodium potassium pump. But we also have calcium pumps. We haven't talked much about calcium pumps. but calcium pump
s are really important, not only in the neuron but also in muscle to reduce the level of calcium and the cytosol, because it's really important to keep the cytosol levels of calcium blue, so that when we have an influx in of calcium Dr. Jacqueline Pal (she/her): through a calcium channel, we then will have the reaction either in the muscle or the neuron to have Dr. Jacqueline Pal (she/her): the release of a neurotransmitter, or to have Dr. Jacqueline Pal (she/her): the start of excitation coupli
ng Cross Bridge to occur. Dr. Jacqueline Pal (she/her): That's all we need to know about pops as far as channels. They do not require Dr. Jacqueline Pal (she/her): Atp. They are facilitating diffusion, allowing substances to move down a concentration gradient, and in the neuron. We are going to have leaky channels. We're going to have chemically gated channels which you may have learned as ligand channels. Those 2 terms are synonymous with each other. Dr. Jacqueline Pal (she/her): chemically ga
ted. You can call Ligand ligand. You can call chemically gated no reduction for using either term, and I will use both terms. During this course, and then the third type are going to be voltage gated channels. And then there's a fourth time. I will mention briefly at the end. Dr. Jacqueline Pal (she/her): Link. Dr. Jacqueline Pal (she/her): Channels are passive channels that are always open, and they allow a continuous diffusion, and examples of these are going to be sodium channels which are go
ing to allow sodium, which is extra cellar, to slowly leak into the cell and potassium, which is mostly intracellular, to slowly leak out of the cell. And that's why we have to have the sodium potassium pump constantly moving those substances in the opposite direction Dr. Jacqueline Pal (she/her): as far as Ligand channels. These are normally closed, and in response to the binding of a neural transmitter they will temporarily open, allowing their specific ions to diffuse. Dr. Jacqueline Pal (she
/her): So we can have a ligand gated sodium channel. We can have a Ligand gated potassium channel, and we can have a Ligand gated chloride channel. All 3 of those exist in the neuron Dr. Jacqueline Pal (she/her): for voltage, gated channels. These also are normally closed, and once again they will temporarily open this time in response to electrical charges allowing their specific ions to diffuse, and examples of these are sodium gated. When we have depolarization, the sodium gated channels open
, when we have repolarization, the potassium gated channels open. Dr. Jacqueline Pal (she/her): and the calcium channels open, and those are really important. as far as allowing the influx of salvium which is going to allow Dr. Jacqueline Pal (she/her): the synaptic vesicles containing the neurotransmitters to release the neural transmitters. Okay. Dr. Jacqueline Pal (she/her): and then in some of our sensory neurons on their dendritic endings, we have modality gated channels. Dr. Jacqueline Pa
l (she/her): Okay? And they function into response to very unique sensory stimuli. For instance. Dr. Jacqueline Pal (she/her): in our eye, the presence or absence of light as them function. We have temperature Dr. Jacqueline Pal (she/her): changes, they can have them function. We have pressure, the absence or pressure of continuous pressure or deep pressure. We have Ph changes. They can do this. So these are very specific ones. And when we go through our Dr. Jacqueline Pal (she/her): are on spec
ial senses, I will talk about, for instance. with vision how these work. Okay. So don't worry about those unless I specifically talk about those later on. Dr. Jacqueline Pal (she/her): We will also be talking about Dr. Jacqueline Pal (she/her): how CO. 2, and Ph work with specific Dr. Jacqueline Pal (she/her): central and peripheral chemo receptors and baro receptors Dr. Jacqueline Pal (she/her): to keep your body in homeostasis. But that's Dr. Jacqueline Pal (she/her): much later in the course.
Alright. let's back up and look at these voltage gated channels because there's one type of voltage gauge channel that is different from the others, and that is the sodium channel. And even if you took Dr. Jacqueline Pal (she/her): anatomy with me, I didn't tell you that the sodium channel is special. Okay, whereas the other ones are either open or pose. Dr. Jacqueline Pal (she/her): The sodium channel actually has 2 gates in it, and each gate can be open or closed, so you can have both gates o
pen, both gates closed, or you can have one gate open and one gate closed. and because of that Dr. Jacqueline Pal (she/her): the sodium channel can be in 3 different states. And so I'm going to show the picture. And then I'm going to tell you how this works. So here we've got 3 different states. Dr. Jacqueline Pal (she/her): So in this first one, we can see extra cellular. We have sodium on the outside here at the bottom. This is inside the cell. And here's the plasma membrane in the middle. And
so when you look at the sodium, we have what's called an activation gate. And then we have what's called an inactivation gate. And Dr. Jacqueline Pal (she/her): in the normal state what happens is the activation gate is closed and the inactivation gate is open. and because the activation gate is closed, sodium cannot enter the cell. And that's why most of the sodium is outside the cell. Dr. Jacqueline Pal (she/her): Now, when the cell reaches threshold there is rapid opening of the activation g
ate. Now remember, the inactivation gate is already open. Dr. Jacqueline Pal (she/her): and now the activation gate opens in response to the threshold. And so, since both gates are open, sodium can enter the cell. Dr. Jacqueline Pal (she/her): So that's the second state that the Voltage gate itself could be at Dr. Jacqueline Pal (she/her): now. The third stage is Dr. Jacqueline Pal (she/her): the activation gate is still open, but the inactivation gate sorry temporarily closes Dr. Jacqueline Pal
(she/her): for milliseconds. Dr. Jacqueline Pal (she/her): So this rapid opening at threshold, this rapid opening of the activation state. Also triggers this Dr. Jacqueline Pal (she/her): in activation gate Dr. Jacqueline Pal (she/her): just slowly make its way up here and block it. But then the weight kind of pulls it back out. So it's only closed for milliseconds Dr. Jacqueline Pal (she/her): and it can't be stimulated to reopen. So how does this look with the activation energies at resting?
But potential, minus 70 millivolts. The activation gate is closed Dr. Jacqueline Pal (she/her): as its depolarizing from minus months 50 to positive plus 30. Both gates are open Dr. Jacqueline Pal (she/her): and from peak plus 30 going down to minus 78. Dr. Jacqueline Pal (she/her): The inactivation gate is closed. Dr. Jacqueline Pal (she/her): and then this one will open Dr. Jacqueline Pal (she/her): and the activation gate will close, and it will return back to the first state. Dr. Jacqueline
Pal (she/her): So most of the time sodium can't enter. But it's for 2 different reasons. 2 different gates. All right. So I hope you understand that? Alright. So now let's look at all these different channels and pumps and see where they are in the neuron. Dr. Jacqueline Pal (she/her): So let's start first on this left side, where all this yellow part is of the neuron. Okay? Cause some of these pumps and channels are all over the place, and some of them are only in specific areas. And it's all r
elated to the function. So in this yellow area, what we can see throughout the entire plasma membrane of the entire neuron. We are going to be having our sodium leak channels and our potassium leak channels. The entire license diffusing potassium is going to diffuse out and and Dr. Jacqueline Pal (she/her): addition, we are going to be having the study potassium returning the stuff where it belongs at all of this is going to establish and maintain that resting member potential Dr. Jacqueline Pal
(she/her): which I will be talking about in more detail in the next video. Dr. Jacqueline Pal (she/her): Okay. Dr. Jacqueline Pal (she/her): then, if we look up here where the dendrite and the cell body is. This is called the receptive segment of the neuron. And up here we have chemically gated channels. Specifically, we have potassium Dr. Jacqueline Pal (she/her): channels. Chloride channels and what we call Cation channels. And what a Cation channel is. It's one channel that lets sodium go in
and potassium go out in the same channel. Dr. Jacqueline Pal (she/her): Yeah, so those are the 3 types of channels that are found up there. And this also lets it establish and maintain the resting membrane potential Dr. Jacqueline Pal (she/her): continuing on in the neuron. The most important part of the neuron for an action potential is this area right here the Axon hillock. Dr. Jacqueline Pal (she/her): which physiologically is known as the initial segment, because this is where the action po
tential is generated. So if you are asked, where is the action potential generated in the neuron, it is the Axon hillock. Dr. Jacqueline Pal (she/her): That's where the action starts. Dr. Jacqueline Pal (she/her): Okay, that's where the nerve impulses started doesn't start in. The dendroids doesn't start in the cell body. It starts in the Axon helic. and this has both voltage, gated sodium channels and voltage, gated Dr. Jacqueline Pal (she/her): potassium channels, and those are the exact same
type that are continued the entire length of the axon, and also all the way down through the axon terminals. And those are where the Dr. Jacqueline Pal (she/her): action potential continues to be transmitted. And so those parts of the neuron are known as the conductive segment, because that's where the action potential is conducted Dr. Jacqueline Pal (she/her): alright. So that continues all the way down to these little Novi things at the end of the Axon terminals, and they have a specific name
. Dr. Jacqueline Pal (she/her): and their specific name is the terminal Bhutan, also known as synaptic bulbs. So pick which one personally, I like going from the Axon hillock to the Exxon to Axon terminal. So the terminal bouton, which just means terminal buttons. It's just a French word sounds really fancy terminal bouton, but you can call it synaptic bulbs. Dr. Jacqueline Pal (she/her): if you prefer. And here we have a change. Dr. Jacqueline Pal (she/her): Here we have voltage, gated calcium
channels, and you should remember this because these are required in order to get the calcium to enter the synaptic knob which is required when we have that massive influx of calcium that is the signal for the synaptic vesicles filled with that neurotransmitter acetyl to undergo so cytosis Dr. Jacqueline Pal (she/her): and release those neurotransmitters into the synaptic clip where they're looking for their receptors Dr. Jacqueline Pal (she/her): on the postsynaptic cell. Dr. Jacqueline Pal (sh
e/her): Okay, if you don't have that influx of calcium, then acetocoline cannot be released. Dr. Jacqueline Pal (she/her): But that, then, gives us the problem that we have all this calcium and the cytosol there in the synaptic knob. And so that is why we need a calcium pump which is going to use a bunch of atp to send that calcium back outside the neuron. Dr. Jacqueline Pal (she/her): It needs to be kicked outside the neuron so that we can have another action potential. Come down and bring it i
n so you can release more acetylcholine. Dr. Jacqueline Pal (she/her): Alright. So hopefully. Now you understand all that. So let's look. Add a different picture of the neuron. and relate all this to Dr. Jacqueline Pal (she/her): voltage and current and all that kind of stuff I mentioned before. So if you recall voltage was the difference in electrical charges. And when we talked about the neuron, we said the outside of the cell had a very positive charge, whereas the inside of the charge was ex
tremely negative. Dr. Jacqueline Pal (she/her): Yeah, it wasn't having a good day. It was very negative. Dr. Jacqueline Pal (she/her): Okay? And when we looked at this. This gave us resistance, which was the opposition to movement of the charged particles. And basically all this resistance was due to the plasma membrane there Dr. Jacqueline Pal (she/her): alright. And so, in order to have Dr. Jacqueline Pal (she/her): this action potential, we had to generate a current. Dr. Jacqueline Pal (she/h
er): and what the current was was a movement of charged particles across the plasma membrane, through these open channels. through these sodium channels and potassium channels. These were voltage, gated sodium channels and potassium channels, and that gave us a current. And so I think you understood all this. And so now we're gonna throw on that little physics thing. Ohm's law. Okay. Dr. Jacqueline Pal (she/her): Now, I'm not gonna ask you what is ohms law. But I know that we've got a bunch of p
eople of physiology who love to throw in ohms law when they're teaching the lab. So in case your lab professors, one of those people that asked you, what's Ohm's law? Now, I told you what Ohm's law is which basically it tells you that current technically is a voltage divided by resistance. Dr. Jacqueline Pal (she/her): So it's the difference in electrical charge divided by the resistance. Dr. Jacqueline Pal (she/her): Okay, so what does that exactly mean when we're talking about a neuron. So let
's look at this neuron, we had this neuron. And in this neuron, according to the previous slide, we talked about. We had all these leaky channels of sodium, all these leaky channels of potassium, and we had all these sodium potassium pumps. Dr. Jacqueline Pal (she/her): and based on all that we talked about. We had the neuron had a resting member potential of minus 7 days. So basically, the current maintain the neurons resting member potential minus 7, 8 through all these leaky channels and blos
som. Dr. Jacqueline Pal (she/her): That is where we were. Dr. Jacqueline Pal (she/her): That's the bottom line. Dr. Jacqueline Pal (she/her): Alright. So take all this information, the previous slides, and look at this overview, read all these words, make sure you understand it. Make sure you can apply all these concepts and build on what you learned previously and anatomy. When I was reading a lot of the answers from the concept, from the quiz questions number one, I noticed a lot of the answer
s you were just giving me the answers that you would have learned in anatomy, and not diving deeper. This Dr. Jacqueline Pal (she/her): is not anatomy. 2 point. O, this is physiology! You need a deeper dive in physiology. So I'm challenging you, cause I know you can do it Dr. Jacqueline Pal (she/her): all right. Have a great day, and I will see you for the next video. Thank you for all your hard work, and I'll see you soon. Bye.
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