okay so for today we are going to talk about the action potential so last class we covered all about neurons and basic functions of cells okay now we're going to extend this information to chapter two to learn more about the action potential and what happens when the cell actually fires as we were talking about in the last material is everybody okay with the lighting should i turn one down i don't want to turn them both down because then they can't see me at home okay so everybody at home can yo
u see the uh slideshow fine can you hear me okay give me a thumbs up thank you guys okay so let's talk about the action potential there is a lot of chemistry in this there's a lot of biology in this but i'm going to try to do it in a simple way so that everybody is on board who doesn't you know maybe not necessarily have biology i'm going to try to do this as best i can uh if you have questions you know you can always ask them um but here we go all right so let's first talk a little bit about ch
emistry and how it works with the cells in the brain okay so when we look at how the cell communicates we have to first understand how the cell is made up in terms of electrical components okay and then that will then help us understand how the action potential or self-firing works electrically speaking so we're going to talk about two kinds of movements okay one is one is called electrostatic pressure okay which we refer to as electrical gradient and one is diffusion through concentration gradi
ent okay so we're going to talk about how the cells both inside and outside the cell walls are made up of different electrical atoms and how the movement of those atoms and of the um uh liquid determines of what state that cell is in okay so it's accomplished through two processes electrical gradient and concentration gradient okay so electrical gradient is the same concept as using mag so has anybody played with magnets as a kid or maybe even if you have access to a magnet you're gonna play wit
h it right okay you take opposite ends and what do you do when you put them together if you have opposite polar polarized magnets what do they do when you bring them close together they're attractive right okay and they'll still hit together what happens if you have two different polarities and you put them together they push each other they push each other away they rep repel each other right so when we talk about electrical gradients this is the same process there are atoms that are positively
charged and atoms that are negatively charged and those were the opposite charges wait did they say that backwards those have the same so if you have no i said it right right did i say that right about opposite and recall okay now i got myself questioning okay so the same idea happens with electrical gradients okay those particles with opposite charges so if you have a positively charged uh atom and a negatively charged atom they're going to attract each other okay and they're going to want to
get uh you know the same area okay those atomic particles that are negatively charged for example they're going to repel each other you have other atoms that are positively charged it's the same charge they're going to repel each other okay and so if you have a a liquid okay and you have electrically charged molecules in that liquid you're going to see that all the ones that are the same charge are going to repel each other and move away from each other versus if you have oppositely charged they
're going to bunch together okay kind of like when you put salt mixture into water you're going to see it disperse differently based off of the electrical uh atoms within the makeup of the salt in comparison to the water okay and it distributes differently uh throughout the water the idea is to be balanced right so the whole thing will eventually balance out when we talk about concentration gradients okay so this is a different concept concentration gradient is when you see higher concentrations
of something moving throughout a liquid to an area of lower concentration what happens if you take a cup of water and you drop a drop of food coloring in it what's going to happen to the food color it's going to disperse out and eventually what is that cup of water going to look like it's going to look like the coloring it's going to look like the color that you dropped in so let's say you have a drop of blue food coloring okay when you see it hit the water it's going to be super concentrated a
nd very blue right now you're going to see it start to disperse throughout the water and spread itself out to areas that don't have food coloring so then eventually the whole thing will be a lighter shade because it's all dispersed completely into that liquid area that makes sense so your brain and the cells and the molecules in the cells all work with both of these processes to stay regulated okay and we see that these processes jump in when we start to see changes in the concentrations of the
atoms and other molecules in the brain okay everybody good with me so far and understand the difference between electrical gradient and concentration gradient everybody understand that great okay now in the brain you have what's you guys follow along with the um slides you should be able to see the top menu they're very good okay so in the brain we have fluid okay we have extracellular fluid that's outside of the cell and we have intracellular fluid that's inside of the cell okay extra being out
intra being in okay these concentrations of fluid okay contain different ions some of the most uh the the biggest concentrations are sodium or n a plus right okay so i'm going to probably refer to almost all of these by their like their actual chemical name uh symbol so just make sure that you know if you keep forgetting just write it on the side okay of your notes notice that sodium is has what charge positive okay potassium in the brain has what charge positive and chloride in the brain has a
weight charge negative so it's important to understand that these different um molecules have different um charges okay that's going to play into importance a little bit later as we start to talk about uh the the actual charges also these sides these um molecules are different sizes and we're going to get to that in a few minutes too and why that's important so these ions sodium potassium chloride and other ones like large protein molecules move in and around the cell according to those those p
rinciples that we just talked about electrical gradients and concentration gradients okay they move according to diffusion and we're going to talk about specifically how it does that in and outside of the cell when you see movements of these ions across the whole cell membrane okay we're going to see the action potential and the action potential is the firing of the cell so when i say that if a cell a neuron is firing i am saying that it is displaying an action potential okay so those are two te
rms i'm going to use interchangeably so i might say when you see the action potential and i might say when the cell fires they mean the same thing okay did everybody know that or did most people are familiar with that kind of sort of yeah maybe okay i'm just trying to judge what how how how much you guys are familiar okay so any questions so far trying to go through this kind of slowly so that everybody can have the same sort of foundation is everybody good am i going too slow okay good i'm gett
ing some head shapes it's like nah just go slower okay now remember probably back when we learned science and maybe i don't know sixth or seventh grade we talked maybe even later i don't know i have zero capacity of understanding science now uh in relation to grades you guys remember we talked the the thing a resting potential okay a resting potential of something okay it's just sitting there waiting to be used okay so in the membrane of the cell we have something called a resting potential and
it sits at about a negative 70 millivolts so the resting state of the cell is actually negative it's a negative charge okay so why negative seven okay if you look at different books of biopsychology and physiological psychology and all the other names that you can call it you may say see slight variations of negative 70. negative 70 is the number that we've kind of settled on for teaching purposes because of experiments done on different neurons so if you go into this field you might find that d
ifferent neurons have different resting potentials and it might vary you might see some say negative 50 negative 60. they all fit at a negative level but we're going to settle with negative 70. so if i ask you like on a test what is the resting potential of a cell what's the answer negative 70 millivolts okay negative 70 millivolts so how we've come to determine this particular number is through a series of experiments and we've been able to identify this by using a recording electrode in a gian
t squid cell and i'll go over how that's been done how is it that resting potential is maintained first of all diffusion unless you're static pressure okay so electrical gradient concentration gradient all factors in there and the fact that there is leakage of certain ions across the cell membrane to keep it at a negative 70. okay so there's more negative ions within the cell for it to sit at a negative resting potential and we're going to go into what those are and how they move and how that ch
anges the nature of the cell okay so we're good so far yes why does the number vary it depends on the cell it depends on where it is in the brain it depends on the species because everything that we really are basing the teaching stuff off is up a giant squid cell um so there's a little bit of a variation based on species but generally speaking it's just at a pretty you know a negative level uh and also you know everything that we teach in neuroscience is like based on the study that we did 50 y
ears ago you know and it's been replicated and you know we're pretty confident of it but we're always learning new things about the brain so um you guys might somebody in here might be like super into neuroscience and go into grad school and learn well i was taught this way but there's a lot of exceptions to the rule and it's just based off of what we're gathering and learning about ourselves okay good question any other questions everybody good so far we're going at a good pace this stuff can b
e kind of heavy so i want to kind of walk us through okay because we're building up our knowledge and then i'm gonna bam hit you with action potential okay all right so let's look at this real quick so this is the cell membrane okay so this is the cell membrane okay this is what makes up the outer portion of the cell so at the outside of the membrane this is the actual outside of the cell okay so this is all that's fluid that's sitting outside in between each cell okay here is the barrier and th
en here we have the inside of the cell so this would be all the intracellular fluid and components within the cell so we're basically looking at inside the cell and here's the cell here [Music] outside the cell and that's the outside of the memory okay everybody good so far now outside of the cell what you're going to see is there's a high concentration of chloride and sodium and a relatively low concentration of potassium okay and notice that the sizes of the molecules here are the size of the
box represent like the concentration of them okay so you have a lot of chloride and a lot of sodium and that in a high concentration is pressing on the outside of the cell okay so using electrostatic pressure and diffusion it is maintaining these ions in the extracellular fluid low concentration of potassium notice that outside of the cell it is more positive right everybody see that outside the cell is more positive because you have a high concentration of sodium and you have a low concentratio
n of potassium but that's going to outweigh how much chloride is there so it's going to maintain a positive charge outside of the cell does everybody see that so far now inside of the cell we have a large concentration of large we call them large proteins which is a negative charge a and then we have a large uh concentration of potassium which is a positive charge large a small concentration of chloride small concentration of sodium here this the large proteins and the um amount of chloride okay
also lead to it being a more negative chart inside sitting at that negative 70 millivolts okay and again the forces of um electrostatic pressure and diffusion are keeping those molecules in place large proteins cannot get through the cell membrane because the molecular size is too big they cannot freely go back and forth okay all right and we're going to talk about pumps and how things move through here in a minute okay now inside of the cell is mostly potassium outside of the cell is mostly so
dium and chloride now what is sodium chloride salt okay this is kind of gross but if you were to lick the solution outside of the cell what would it taste like kind of salty right okay so if this helps you remember that all the fluid outside of the cell is made up of sodium and chloride and that together gives us salt okay and that tastes salty okay then if you were to look the outside of the cell it would taste kind of salty i don't suggest it but if you will so concentration gradient allows fo
r these ions to stay in place potassium being outside of the cell uh excuse me inside the cell and sodium chloride outside of the cell electrostatic pressure explains why the inside of the cell sits at this negative 70 millivolts because potassium and sodium want to stay inside of the cell okay and chloride which is negatively charged wants to get out of the cell and away from all this potassium and sodium because it is oppositely charged does everybody understand so far so these two processes a
re explaining why the inside of the cell sits at a negative 70 okay because the chloride is continuously trying to escape okay and the concentration gradient is maintaining the cell voltage uh inside and outside the cell as well now there okay so the question is off topic but i'll attempt to answer it the question is if you were to lick the outside of a brain would it be considered cannibalism and very odd question but i'll take a stab out of it no pun intended um i'm pretty positive that cannib
alism by definition is the consumption of human flesh so i think if you lick it you're good and you're not considered a cannibal unless you're somehow getting some of that ingesting very odd uh answer first time i've had that question uh now why is the brain exposed i don't know and perhaps the fact that you exposed it might start to teeter you over to the cannibalism realm i don't know but i believe it's actual consumption very interesting question did i answer your question okay great i do not
uh advise any kind of licking or consuming of human flesh just my disclaimer so everybody's aware okay so finally there has to be a balance of concentration gradient and electric uh static pressure in order to keep it all balanced and at um a uh homeostatic right now let's talk about how we maintain this status okay so the topics says sodium potassium transporters so the sodium potassium transporters help to keep the cell at its resting membrane potential of negative 70 millivolts okay because
it's constantly pushing sodium out of the cell and pushing potassium back in now remember these are different concentrations of the two okay and how we're able to maintain the balance and so if you look at the the the figure okay here number one you see that and atp is adenosine transporter transport proteins which we won't really get into right now we'll get into this later but atp is what we use for energy in the cell and it requires this process of transport requires energy so this is why we'
re going to see atp being included in this process because without it it can't function okay the cell can't work so what you're going to see this process working here we have step one three sodium ions and an atp being uh uh uh transported through this particular pump okay so the atp is going to bind to allow it to actually give it energy to do this okay step number two okay we're gonna see uh the atp change shape to allow for it to um process to to give it the energy that it needs to send these
three potassium um excuse me these three sodium ions out of the cell okay remember this is inside the cell we're throwing these bad boys out okay so three sodiums get pumped out with the use of atp okay now you're going to see that the shape change of the transporter pump pick is allowing the sodium to push out of the cell but also enables the potassium to bind okay so the three sodium get booted out and then the two potassium is allowed to bind change shape again and push that into the cell so
for every three sodium molecules that the cell pushes outside it brings in two potassium molecules now what does that do to the charge if we're pushing out three positively charged molecules and only accepting two positively charged uh molecules in what is this doing to the cell inside the cell charge-wise it's it's keeping it negative because it's dumping out not all the positive but it's dumping out more positive than it's taking it does that make sense everybody got that okay so these very s
pecific sodium potassium transporters are allowing three sodiums to throw out with the use of atp changes the shape of the transporter uh uh the pump and allows two sodium to bind keep saying so two potassium divides three sodium go out two potassium okay and allows it to come inside the cell i know i keep switching it but you guys see it on the thing and have it right here excellent another cannibalism question here [Music] because we can act we can actually witness this um and you can measure
the concentrations and you can measure how much is going in and out so we can actually take a sort of a snapshot of this in different levels and be able to to tag those those ions in this protein okay all right any other questions are we good now this process is going to keep repeating and cycling through maintaining that resting potential of the cell now let's talk about ion channels okay so there are proteins that are embedded okay in the um cell membrane wall that can allow certain ions to le
ave and enter in and remember that the whole point of this is to keep cells at a resting potential of negative 70 millivolts until it is ready for the action potential to send the electrical signal through the first step of the action potential is the opening of those sodium channels to allow for a change in charge of the inside of the cell now some neurotransmitter receptors remember these are chemical receptors actually contain allow for quicker function and faster distribution of electrical s
ignal and not necessarily the signal is faster the reaction faster okay so we're going to talk about two voltage-gated and chemical or ligand-heated um types of um resemblance okay all right so we good so far this is a really nice visual here this is an ion channel that's closed not accepting any ions in this one right here is open okay and that's allowing for the change in molecular distributions so in order for us to make um conclusions about what an action potential is and how it works okay i
'm gonna just very briefly describe the process of how we look at this and how it's studied um sort of bench science so what do you need to learn about the neuron obviously you need to start with a cell you need a neuron you need some way to measure electrical current in the neuron to be able to actually test this and you need an ionic solution to store this in um so that you can basically replicate what you're seeing the brain so this particular experiment is done with a squid giant accent not
a giant squids accent a squid's giant accent the way that it's heard it is actually very particular this action is is large enough that you don't need a as highly powered microscope um to use this is why they use specifically the giant accent and then you need the ability to be able to record uh the the process and you also need stimulating electrodes in order to um again follow the the process the action potential so this is what the setup looks like it's actually um really interesting to see t
his so you're seeing that we have petri dish with the giant squid x in here and then we have the voltmeter so that you can actually test to see what voltage it is we have the wire electrode that's placed in this saltwater solution and then we're able to conduct the electricity this is actually put into the axon itself then we have the simulator and then we have the ability to record it this here is basically where we record the uh electrical impulse okay and then we're able to determine at the r
esting state and then we're able to determine an action potential what the voltage change is what it looks like across the axis okay so that's how we would do this in a lab um so there have been you know you can you can take neurons out of the brain and you can you can observe them um they're so much smaller that it's hard to get a good idea of what this looks like um a lot of what we do with this we call translational research is we make assumptions we say well the structure is the same or iden
tical the process appears to be identical when observing it in other fashions um so that's kind of like taking what we know and building on it based off of these kinds of experiments if you take sensation and perception with me you'll see that we do the same sort of thing with animal work and looking at things like the visual system of hearing things like that these experiments are done with a brain as close as we can get to a human brain which is usually non-human primates um and looking at the
structures and the makeup and saying well these are basically identical so you take the information that you learn there and you apply it to the human membrane so we're taking what we learn on a larger scale and applying it to the same cell structure as a human and saying this is how it works does that make sense any other questions okay all right so what did we learn from doing these experiments on on a squish giant action okay so we've learned that the resting potential okay is a different ch
arge when the neuron is at rest versus when it's active okay so we're we're we're settling on that negative 70 millivolts being the resting state and then that the uh inside of the shark the cell is charged negatively in comparison to the outside of the cell which is a positive charge any um stimulus that elicits an action potential um which we call a sufficient stimulus that crosses that threshold is caused by the movement of those positively charged ions the potassium and the sodium we know th
at the axon um is what carries the electrical impulse to the end of the neuron and we know that the change in the membrane's potential and charge happens as it moves down the axis okay so you actually see it change from a negative 70 millivolts to a positive charge as it moves that electrical impulse down the axis okay i have a youtube video on here it's a like a not a cartoon but it's like a computer graphic of what a uh electrical impulse probably looks like in a human brain so that's just a n
eat way to kind of visualize how we do that has anybody been able to access the self-service human anatomy app yet is it on there excellent so you guys now have access to the uh human anatomy app it's called human anatomy atlas um it should be able to be installed from self-service if you don't see it let me know but you should should be able to see it because if you're enrolled in the class we won't be messing with that yet because we can't look at molecular stuff on it we can only look at kind
of big big brain stuff so we'll we'll be using that in class probably uh next week or the week after okay any questions so far all right now let's look at what the action potential looks like on a on a graph okay so when you chain the inside of a cell a negative charge to a more positive charge okay you're changing when you change the charge you're basically causing it to engage in an electrical stimulation [Music] that follows all the way down the accent of the cell in the next step stimulates
the next cell and if it's a strong enough signal to the next cell it will then potentially cause the next one to fire as well depends on where it's attached to the cell the next cell and um what the other cell is doing okay so we're going to talk about that here in a minute here's what it looks like on a graph so this is the threshold okay so this is right here this is the threshold this right here is the resting state so if you look at where the cursor is pointed here okay everyone states of t
he cell is sitting at a negative 70 millivolts okay so this cell is just sitting there minding its own business nothing's happening it's just resting okay now another cells um connections possibly connected onto the cell's dendrites or cell body okay it's sending a signal to the cell saying hey wake up okay so what we're seeing is okay so we gotta hit that did nothing you see that okay we got hit number one that's nothing hit number two did nothing hit number three did nothing still maintaining
its resting state so each time this cell gets hit its charge changes a little so each time it gets hit the charge are starting to make this cell a little bit more positive so hit number one changes it from a negative 70 to maybe like a negative 65 okay but that's not enough for the cell to respond right then another hit no another more sodium and potassium come in okay and it's for it to hit so the threshold in this case and again this is something that you might see the number change a little b
it based on the book in this case the negative the negative 60 is the threshold of excitation so when it hits when the charge changes from negative 70 and in this graph in this case to negative 60 it starts the process of the action potential once the process starts once the threshold is hit it's an all or none thing everything starts to work it doesn't need any more stimulation it doesn't need any more signaling doesn't mean any more messages the cell takes over from this point okay now we're s
tarting to see ions flood the cell positively charged ions flood the cell so if the cell was at a negative 70 binding its own business it got enough stimulation to drop it to a negative 60. okay so increase negative 60. what happens to the charge if positively charged ions rush the cell does the solvent come more positive or more negative it becomes more positive so if it's sitting at a negative resting state of negative 70 it gets stimulation to set it at a negative 60 it's becoming more positi
vely charged now it hits the threshold and all the sodium and potassium rush in now it's going to change the charge of the inside of the cell to be more positive in fact it happened so fast and there's so many ions that rush in it becomes positively charged it passes zero so it goes from the resting state of negative 70 to the threshold of negative 60 hits the switch now it's going to rush in to hit a positive 40. so it's going to get so positively charged but it's actually going to cause the in
side to now be positive does everybody see that so starts to the negative 70 and then the peak starts for you okay so if i were to ask you what's the peak positive charge that the cell membrane gives you the number gets to what is your answer a what you get at home too if you want to answer as well positive 40 very good positive 40. so once it hits that peak positive charge okay once it hits the peak positive charge it will then [Music] hit its max and start pushing out that positive those posit
ive ions okay so it's going to push out the positive ion what happens to the charges of the cell if it's pushing out all the positive ions what does the cell now become more negative exactly so now the cell is becoming more negative okay and then it hits the resting state again at negative 70. but this process remember we all talked about regulation homeostatic regulation it actually overshoots in this process of hyperpolarization and actually dips below even more than negative 70 it hits about
negative 80 or so and it's got to kind of regulate itself back to negative 7. okay and during this process of hyperpolarization okay it does not have the ability to fire again it's got to regulate itself okay and we'll talk about this in just a second does everybody see that as the cell gets the stimulation it's going to change from a negative 70 hit the threshold to negative 60 or so that's going to start the process it's going to it's going to change its charge to a negative to a positive 40 a
nd then it's going to dip down all the way below negative 70 and then it's going to be upright again and now at this point it's ready to go to to fire again and this whole thing takes about three milliseconds okay and it fires over and over and over again yes yeah we're i have another graph of that and so that'll explain that yeah okay any questions so far are we good i should have another graph of that that actually has three terms on it so if i don't i'm gonna put that in there because it's re
ally easy to tell the difference between all right so here is the steps here are the steps at each point okay here all right so we're at negative 70 the threshold of negative 16 is hit at this point the sodium channels open and then sodium starts to flood the cell and then at step two the potassium channels are going to flood this up so first we have the sodium channels opening that's going to start getting it to a more positive charge right after that potassium is going to open up continuing to
make the inside of the cell more positive and then here the peak is next now the sodium channels are refractory they can't do anything right now they're kind of stuck in this refractory state so no more sodium enters the cell so then that means that the cell can't become more positive because it's not accepting in any more positively charged ions then what we see is that potassium so that heat is hits potassium will start leaving the cell and we have that the met the the potential starts to go
to resting levels this step here we the potassium channels are closing sodium channels are resetting but in the process of those sodium channels resetting it's going to dip a bit below and then those extra potassium cells ions excuse me are going to then diffuse and get it back to the negative 70 thrusting state okay everybody good so far and here again here are the different steps here this is step one with the channels opening here's the refracted period where it's closed and then the the sodi
um channels are then reset okay allows for us to do it over and over and over again until we die okay any questions about that so far okay see we have repolarization hyperpolarization depolarization and i thought i had a table on here that should all break i'm gonna have to i'm gonna have to go back when it comes to refractory periods okay there are two types of refractory periods that occur after an action potential happens so we have an absolute refractory period where the cell is essentially
halted for just about a half a millisecond where it can't do anything else okay how many of you have ever flushed the toilet and then realized that you probably need to flush it again for whatever reason okay and you tried to do the little flusher and it just went to you anybody ever experienced that okay what that toilet is doing is experiencing an absolute refractory period what has to happen to the toilet for it to be able to flush again it has to fill back up with water in the back right so
in the process of it filling back with water that toilet's going dude nothing okay you're just gonna have to sit there and watch right and then once the toilet's ready and filled back up with water then when you push the flood you know when you when you what is that called uh flusher uh handle right once you do the handle of the toilet it's gonna then flush again same process with the with the neuron it goes through this absolute refractory period where it cannot fire again it just physically ca
n't now why do you think we should have an absolute refractory period for our brain cells why is a support it needs time to rest absolutely what happens if a brain cell can't rest okay what if it can't go back to homeostasis what happens to itself i'm hearing some bumble burns out essentially it gets frag what happens to fried cells they die right exactly so when you have cells that are firing too often and not experiencing this absolute refractory period essentially what you're having is you're
you're burning your cells out and that's not a good thing that's not a healthy cell okay you can actually see this happen with conditions like um epilepsy okay so epilepsy is when you have excessive firing of neurons okay that's not good for your brain it's not good for your brain to have the success of firing in areas that aren't supposed to be firing right now okay and that is not um that's not going to be conducive to a healthy uh set of cells for your brain now we also have a relative perio
d which we call the relative refractory period where it's unlikely that the cell can then uh fire again it can happen but there is a period of time where it isn't a resting period where it it normally does not fire okay and what drives these are the opening and closing of the of the sodium channels okay so in in cases where we have close close off channels we can't have that rush of positive ions and therefore it will not allow for it to change in charge to allow for an actual potential to occur
okay any questions about that yes that's a good question so what cells have the absolute versus the relative uh uh uh refractory period i want to say i don't know the answer on top of my head i i don't know if it's always self-specific um i think it's more uh sometimes location specific and i think it's based off of some motor versus reflective cells um i think we might cover this a little bit later but i can't take off the top of my head one having one over the other it's more of like there's
a period of time right before the absolute period where there's a refractory and then a period after this you know what i'm saying yeah so um that's probably a better explanation of the two together than cells having cells yeah any other questions yeah what causes the change in the status of the positive versus negative okay so the whole thing starts with a stimulation from another cell so and we're gonna get to that so you'll see so um the exchange of information from cell to cell is chemical t
hat chemical message could say fire or don't fire when enough message is received that stimulation will will signal the cell that i have an electrical impulse and that's where this all occurs and we're going to talk specifically about what is enough and what where where is where it is in order to get this process started okay all right any other questions about refractory periods or the processing of itself are we all good so far okay however we're good give me a thumbs up if you're following al
ong yay thank you guys all right now very important feature of the action potential is something called the all or none wall once the action potential begins once it is triggered it goes down the length of the axon it either happens or it doesn't we don't have a partial action potential we don't have a graded action potential we don't have a sort of kind of action potential we either have the message is sent or the message is not sent okay one or the other all or not it either happens or it does
n't happen now we do have something called the rate law and that's about intensity of the stimulus and that can change the rate and variation of firing so the rate law is not does it fire or not necessarily or how fast fires the rate law is lots of firings back back or slow it's not like how strong each one is it's the rate and frequency of the fire that's the rate okay so variations in intensity how fast and how quickly are they from back to back as well as variation in the rate of the accident
itself in terms of fire okay so here we see a shorter period versus longer period weight of actual fire does that make sense and that is taken through the um giant uh accent of the script any questions so far are we good all right now we've talked about this a little bit before but this is where we're going to explain how this works with the myelin sheath action potentials are regenerated down the length of the axis so as it hops from node to node we're seeing those ions move in the membrane of
the axon continuously to allow for that electrical impulse to continue down the length of the axis so what you're seeing here is that the sodium and potassium channels okay open along the length of the axon okay and they open and open they open the open here here here here open here here here over here here and at each section of the exposed accent okay we're seeing this process repeat and we call this a regeneration because we're essentially recreating the action potential at each open spot be
cause the myelination occurs the myelinated fatty tissue here is going to change the conduction okay and it can't do it in that particular spot so it's got to regenerate and jump nodes at every point of the nodes of ranvier so here these nodes of ranvier allow for the electrical impulse to continue to regenerate until it hits the end of the axis okay so the myelination or the myelin sheaths are going to increase the speed of conduction conduction and allow it to go faster from node to node okay
through saltatory conduction so at this point there are fewer sodium and potassium channels that have to open at each node allowing for faster conduction if we had no myelin cheese imagine this we have no myelin sheath that would mean that every sodium and potassium pump and channel along the entire length his job would have to be open open open open that would take a long time and it's not smooth and if we have a disruption that's going to cause a problem for that electrical impulse to go down
the length of the axis however if we only have sections of sodium and potassium channels that have to open at any given time it's going to allow for faster processing of those ion movements to allow for faster conduction down the length of the axis because now we've got up and up open first you see how that changes how fast that message can jump from node to node if we're like i'm gonna have an open i'm gonna open versus so the myelin sheath are giving it the opportunity to cover the cell in suc
h a way that speeds that electrical impulse up from node to node does that make sense is everybody seeing that sure any questions at home so everybody see how the myelin sheath work to allow for less surface area of the nodes of ranvier to require those starting potassium channels to open along the way so to summarize all of this together okay the activation of a neuron through the signal from another cell and enough stimulation occurs to cause an action potential to happen the action potential
will then propagate down the length of the accent jumping from node to node of the nodes of ranvier to the end of the cell what happens now when it gets to the end so the cell has got this electrical impulse that runs throughout it now it's going to hit the end of the cell and then release the chemicals to send a message to the next cell whether or not to fire and what kind of chemicals for it to release if it does fight okay so it's a complex message of what the next cell's job needs to do and
the kind of cell and the location of the cell is going to give us information as to what kind of chemicals that cell is producing and synthesizing and what messenger is getting sent from point to point okay so it's going to depend on what kind of cell it is it's going to depend on what kind of chemicals it's synthesizing to determine what that message is going to be and it will quantity okay so if we look at this right here this is ascending cell this is the terminal button here we have the micr
otubules that's coming from the accent and then we have different um ways that the chemicals can be transported and synthesized whether it's the cell body whether they get transported through the accent or whether they're synthesized and housed here in the terminal button this is the receiving end this is the dendrite the cell body here the postsynaptic area where it's going to then receive the chemicals from that action potential message does everybody get that does that seem clear then we're g
oing to go over this process and how cells uh get this information and what they do with it okay everybody good so far we might have we'll do one last slide and then we'll end for today and i'll open for questions okay so the very crux of this why do we care about the actual potential and then sending a signal the sound of itself has sent the actual potential now what does it do the next cell has to determine if it's going to also fire an action potential but it takes the information from the pr
evious cell to determine that okay so in order to receive information and chemicals it has to have the ability to have receptors to accept the kinds of molecular shapes that the cell is trying to give to so here we have the terminal button of one cell the dendrite or cell body of the receiving cell okay so the message has been set and this electrical impulse has activated the cell the action potential occurred now we have these chemicals to relay another message so this right here is the pre-syn
aptic membrane okay it contains vesicles or sacs that contain chemicals known as neurotransmitters so neurotransmitters are things like dopamine serotonin acetylcholine choline these are all different kinds of chemicals okay and then here we have the synaptic cleft or synaptic gap which is essentially a very very tiny open area not physically attached to the cell it's an open area of physical space between neurons where the chemicals then get sort of exchanged and then finally we have the postsy
naptic receiving end and this has receptors that are designed to take in very specific chemical structures so if you have a cell that's giving you dopamine you have to have a dopaminergic receptor to accept that chemical message like a lock and key so think of the chemical like dopamine as the key and the law would be the receptors that are on the cell they got to lock into place in order for it to take that information okay so next time we will talk about specifically the vesicles and how the c
hemicals are generally synthesized within the cell where they're synthesized and all that does anybody have any questions about the material everybody good okay at home does anybody have any questions about the material all right i'm gonna go ahead and end the recording
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