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BIOL 2301 Human Anatomy & Physiology I - BIOL2301 lecture13_0229
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00:00 Oh, good morning y'all. Everyone a nice cold morning. You guys
00:07 for next week? What's next The exam is next week. Uh
00:14 is the exam? Thursday? Do we have class on Tuesday?
00:20 . Is the stuff on Tuesday on exam? No, see,
00:24 You guys are all listeners. There's who haven't shown up to class in
00:27 couple of days, they're gonna be all this muscle stuff and they're gonna
00:30 it's on the exam and they're gonna studying extra hard on stuff. They
00:33 need to know this time. So for you guys. All right,
00:38 , what we're gonna do is we going to cover or talk about the
00:43 potential. All right. So we've talking about the graded potential and the
00:48 potential is um what you get when receive a chemical message from another cell
00:55 it's gonna cause a small depolarization in receiving cell and that greater potential travels
01:01 very, very short distance in the cell. And that's what we ended
01:06 uh when we were uh at the of class on Thur or Tuesday,
01:11 ? And so we were talking about like here, look, there's our
01:14 cell and you can see all the and you can see all the axon
01:20 ending on our receiving cell. All . And so the receiving cell is
01:24 the postsynaptic cell. Because the interaction the sending cell and the receiving
01:28 that interaction is called a synapse. going to talk about that at the
01:32 of class today. All right. we can see here that some of
01:36 are drawn green, some are drawn for the New York color blind.
01:40 , I apologize. It's just an picture. All right. But you
01:44 think about it like this. There some cells that are telling a cell
01:47 activate and there's other cells telling us cell not to activate and so on
01:52 receiving cell, you're getting these greater that we called excitatory post synaptic potentials
01:57 PSPs or you're getting an IP which is an inhibitory postsynaptic potential.
02:02 it's the sum of these Eps PS the IPs PS that result in a
02:07 potential, a sum degraded potential in receiving cell. And we refer to
02:13 as the grand postsynaptic potential. So P, right? So it's
02:18 it's a summer summarized effect and that's of where we ended up. And
02:23 , this idea of summary or summation is something that we can actually uh
02:31 . And so that's what our last was supposed to be, but we
02:34 too slow. And here we we're looking at this and we're
02:37 look, there's different types of And so what I want you to
02:40 is I want you to focus down . All right. So here we
02:44 a two signals that are excitatory. can see the depolarization, right?
02:49 a depolarization. And so what we're is the cell is firing and it's
02:54 a depolarization in the receiving cell. an Epsp occurs and then some time
02:59 and then you get another PSP and you can see nothing's going on,
03:03 get a little blip and then a blip. All right, this dotted
03:07 right here is what is referred to the threshold. This is the point
03:11 an action potential occurs and we're going talk about that more detail in a
03:15 of slides. All right. But idea here is that if you're adding
03:20 or summer uh getting summation and creating grand post synaptic potentials, if that
03:27 is strong enough, it's gonna trigger action potential. All right.
03:32 in other words, what it's saying if, if you get to a
03:35 point, something new is gonna So that's the whole purpose of the
03:40 SPS, right? And the IP are doing the opposite. What they're
03:44 is they're saying we don't want an potential to occur. And so we're
03:48 to prevent that from happening. if we have uh 22 ep SPS
04:00 very, very close together in usually from the same uh excitatory
04:06 What will happen is that we'll get called temporal summation. All right,
04:11 we have uh two different neurons sending excited signal, you're gonna get two
04:17 SPS and their uh their magnitude together be summed up. Now, the
04:22 way to demonstrate this, I hope is an easy way is to think
04:25 the sound you make when you when I clap, do I make
04:28 loud sound? Do I make a sound? Kind of sort of?
04:33 right. What if two of us to clap? All right.
04:38 Is that louder than the first What if we get four people to
04:42 it? 123? Is that Yeah. So this is a spatial
04:47 . Notice we are individuals acting independently together we make a louder sound.
04:53 right. And so if you were get two or three or four or
04:58 ep SPS occurring simultaneously than what you is a much larger sp or a
05:07 grand post synaptic potential. So when dealing with spatial summation, spatial summation
05:13 when two or more action potentials are or two or more greater potentials are
05:20 and creating a larger depolarization event. that's what you see in the picture
05:25 . It's saying, look, here's by itself, here's another one by
05:29 . But if you get the two , they're gonna be large enough to
05:32 to that threshold. And so you an action potential. All right
05:36 we're ignoring the action potential right What I want you to, what
05:39 want you to walk out with is when I'm doing spatial summation, I'm
05:44 an additive effect because two or more are sending an excitatory signal and causing
05:52 EP SPS to occur simultaneously or more or more I should say should be
05:57 on those terms, right, temporal when you're getting the EP SPS occurring
06:05 and closer together. Now, I demonstrate this but I want you
06:09 it's just just it's just not Barbara. All right, but I'm
06:12 do the sound thing again. So I clap, you know, it's
06:15 particularly loud, but if I bring closer together and closer together, it
06:20 an effect that seems like it has greater magnitude. All right, I
06:25 go faster than that. I I could, but it's not going
06:28 do much of a difference. So temporal summation is when you're dealing with
06:33 neuron sending multiple excitatory signals faster and and faster. So you never have
06:39 opportunity for the EPSP. Remember an has that depolarization and on the backside
06:44 has a repolarization. And so what doing, I should do it this
06:48 . So that you can see. as I depolarize, if I get
06:52 stimulus, what that's gonna happen is before I go down, I
06:55 up again. So that's the additive . So the closer they are together
07:00 time, they start adding up and a bigger and bigger, bigger uh
07:05 synaptic potential. So the GPS P result in an action potential.
07:13 there's also something called cancellation and that's the opposite of spatial subs like if
07:19 get an EPSP, that has magnitude direction and I have an IP SP
07:22 has magnitude in that direction, if sum them together a positive and a
07:26 , cancel each other out, So that should be pretty straightforward.
07:31 thing is, is you got to that these EP SPS and the IP
07:34 don't necessarily have the same magnitude. if I have a very large magnitude
07:38 a very small magnitude, you're, still additive or subtractive, it's just
07:44 gonna be nullifying things. And in example that they're showing up here,
07:48 just presuming same magnitude. All So if one is plus 10 and
07:53 is minus 10, then the net would be zero flat and that's what
07:58 showing. OK. So grand or potentials are occurring on the dendrites are
08:07 on the cell body, they're moving , right? Remember how we saw
08:11 ripple effect kind of, it gets and smaller and smaller and it moves
08:15 from the site of stimulation, So this is what's occurring on that
08:20 cell action potentials are only developed in place on the neuron. That ax
08:27 place is the Axon Hillock. Do remember the Axon Hillock? Do you
08:31 when we said that word? I the word. Do you remember the
08:36 ? OK, let me show you the Axon Hillock is actually located.
08:40 is our Axon, here is our . This right there is the Axon
08:47 . OK. It's the base of the axon is located and this is
08:51 only place an action potential can be . All right. And we're going
08:56 see why in just a moment. the goal of the graded potential is
09:00 create a stimulation that can travel far and strong enough to get to the
09:06 hillock to create the events that are to result in an action potential.
09:10 that make sense? Right. So this is the only place I can
09:15 that happen, then this signal, I start a positive signal,
09:18 I'm going to use those. If do a positive signal here, if
09:21 not strong enough to reach there, not going to get anything. So
09:25 we're trying to accomplish is we're trying reach a membrane potential of roughly minus
09:31 it says 50 here, but minus in that receiving cell. And if
09:35 can do that, we're going to an action potential. So what's an
09:39 potential? An action potential, by is a very brief, very
09:45 very large depolarization event that occurs in cell. All right, it's about
09:50 millivolts in terms of its charge. if you're starting at about minus 70
09:55 you're doing is you're going to rise to about plus 30. All
09:58 Now, different cells are going to different types of action potentials.
10:02 memorizing the number, it is not important. The idea here is in
10:06 on this is what it looks All right. And so you're going
10:09 get this rapid depolarization that then reverses itself and returns. And in doing
10:15 , what we've done is we've changed inside of the cell for a very
10:20 moment because remember the inside of the is always minus 70 right at
10:24 And then what we're doing is we're it plus 30. It is approaching
10:28 close to what we see if we're with the equilibrium potential of sodium.
10:33 how do we get it? Like said, it is generated as a
10:37 of the summing of these greater If I can get greater potentials,
10:42 can reach a threshold of minus 55 I'm going to get an action
10:48 If I can't reach minus 55 I . And this is what it's referred
10:52 as the all or none rule. is a binary situation. Either I
10:55 an action potential or I don't. no in between. There is
11:00 I kind of have one. I'm wake some of you guys up
11:03 It's like virginity. You either are you aren't. There is no in
11:09 . There's no kind of, it's pregnancy. You are pregnant or you
11:13 not pregnant. There is no I might be kind of pregnant.
11:17 , you are either pregnant or you're pregnant. You are either a virgin
11:22 you are not a virgin. It an all or none response. So
11:26 is something that you must remember. or none. Yeah, action potential
11:32 all or none. If I get graded potential or get a summation of
11:36 potentials and they get just shy, instead of 55 they're minus 56.
11:42 again, I'm just, I'm using values for us to understand you're not
11:46 an action potential. But if you minus 55 action potential and you're shooting
11:50 the way up to plus 30. . All are non response. All
11:56 . Now, the reason this happens because of the presence of voltage gated
12:02 , right? Remember we made a deal about them. I fussed about
12:05 . Oh, voltage gated channels, , blah, blah. And so
12:08 we're going to be doing is we're to affect the, the the
12:13 the ability or the permeability of the by opening channels. So remember we
12:19 normal sodium leaking into the cell. have normal potassium leaking out of the
12:24 , right. We talked about that on Tuesday and we said that permeability
12:29 and there's this threat, this ratio roughly about 50 to 75 to
12:34 So every time one sodium moves in to 50 potassium move out. And
12:39 is why we're at rest. And only way we can affect that is
12:43 we open up some channels and allow sodium to come in or more potassium
12:47 leave the rest of the membrane potential going to change at that point.
12:51 so the action potential is a function opening up more channels, we change
12:56 permeability. OK. So this is excitable cells have. They have the
13:02 to change permeability because of these voltage channels. So how do we do
13:08 ? Well, again, it has do with the net depolarizing GP
13:14 right? If we can get enough post synaptic potentials to travel the distance
13:19 to the axon hillock, then and strong enough, it has the magnitude
13:23 reach that threshold, then that's where gonna get an action potential. So
13:27 big players in this and when we at this chart, so I'm going
13:33 point out a couple of things about chart here in just a second,
13:35 big players here are going to be voltage gated channels. One that's going
13:38 be a voltage gated sodium channel and that's going to be a voltage gated
13:41 channel. When we open up voltage sodium channels, we're gonna get
13:47 All right. So, depolarization is this direction, we're going to see
13:52 . When we open up vulture gated cha channels, we're gonna get repolarization
13:57 hyper polarization. So that's gonna be with this side. All right.
14:03 , how many of you guys were at some point in your academic
14:07 And I say train or taught would a better way to say how to
14:10 a graph. Anyone taught how to a graph. So the first thing
14:14 you see a graph is you should and ask two questions. What is
14:18 X axis? What is my Y ? Right? And you are going
14:21 learn more by looking at a graph reading the text. I guarantee it
14:25 single time graphs are wonderful things. makes me not have to read stuff
14:29 I love it when I don't have read stuff. All right. So
14:32 I look at this graph, you see they marked this, they
14:34 look on this side, what we is we have voltage measured in mills
14:38 down over here, it's over here the side because of the space.
14:41 they're saying, look, we have on this side and it's measured in
14:46 . So we're talking really, really periods of time. All right.
14:50 , the other thing I want to out about this graph, it looks
14:52 a bunch of uh fruit stripes, fruit stripe gum. You remember fruit
14:56 gum, you know, whenever it's awful, awful gum, right?
15:00 what you see is you have different and what they're really trying to show
15:03 is the artist said, hey, know, it would be a really
15:05 idea to show you the points where take place, right? Because when
15:09 looking at a line graph, that's all the interesting stuff happens. And
15:13 each of these borders right here, here they're saying change occurs there.
15:18 new happens. Oh Over here, new happens right up here, something
15:22 happens down here. Something new happens they just happen to color it so
15:25 you would focus in on it. right? But very often we don't
15:28 that stuff we just want to get the picture. And so what I'm
15:31 you is that's what you should be on. When I look at this
15:35 , I'm looking for where change Because if I'm looking to see where
15:38 line changes shape, then something unique happened. And that's where we need
15:42 focus our, our attention. And they've actually drawn down here, the
15:48 things that are happening to the different . All right. So each slide
15:51 we're gonna go through, it's I'm gonna just focus in on that
15:55 little thing so that you can see . All right. Now, what
15:59 want to do here is I want point out some weird things about these
16:03 . All right. The first channel looking at here is the voltage gated
16:06 channel. Well, aren't all channels same Dr Wayne? No, they're
16:10 . In fact, they're all weird strange in their own rights. But
16:13 one in particular is very strange when look at a door, how many
16:17 , how many actual structures inside that ? Do I see? How many
16:22 you see in that one? I one. This is a, a
16:26 that has two doors weird. All . The first door is what we
16:33 to as an activation gate. All . So when this, when the
16:36 is activated, this gate normally sits the closed state. And what happens
16:42 when I activate it, I open that gate and now things can go
16:46 . But I also have a second and that second gate is called an
16:50 gate. It activates or it changes as soon as you ch change the
16:55 of the first gate. So this how it exists in the simulated
17:03 I am closed but capable of right? See my door here,
17:08 closed. If I am the this is my gate and I'm
17:12 I get stimulated. I open So now ions can flow through
17:17 All right. Great. But the that I open up that gate,
17:20 other gate begins to close and it a little bit of time, couple
17:25 milliseconds, but then it will close . And now I'm in another closed
17:30 . So the three states that this because I have two gates, it's
17:33 but capable of opening, opened, , incapable of opening must be
17:41 Ok. So closed, open, again. Feel like a cheerleader up
17:48 . Ok. Now, in my brain, I just want to
17:53 oh, well, all I gotta to get back to the original stage
17:55 I'll just go back here and then do that again, but that's not
17:57 this works. You have to go stage A stage B stage C and
18:03 you come all the way back around stage A again. So I'm
18:07 Capable of opening, open, incapable of opening. And then something
18:12 happens where it's like this, So I stay in the closed state
18:16 I'm reset. All right. So means there's gonna be this lag time
18:22 when I can be reopened again. kind of makes sense. All
18:28 Yeah. Say again. Yeah. I do the cheerleader thing again?
18:37 . Give me an r I don't , so closed but capable of
18:42 open closed. Incapable of opening. . Statements. Well, so,
18:54 what we have here in this particular doesn't do do it justice because you
18:59 see what they're doing is they're saying I am closed and then here I
19:02 open, they're not showing the two , right? I don't know why
19:06 artist chose it this way. But you can think of it is
19:09 um it's like the old timey drains there's a plug that gets kind of
19:14 in place and that's kind of what does. It, it literally just
19:19 uh its shape so that either one gate is blocking or the other gate
19:24 blocking the differences in the timing. everything you're gonna look at here is
19:28 timing. It's not about, everything I'll just say everything is gonna
19:36 dependent upon time. So it's kind like these doors. You can see
19:39 all have the, the arm at top of the door. That's
19:43 the automatic closing arm, right? you can tune that to close quickly
19:47 you can close it uh sh uh right on here. And that's the
19:52 thing. It's tuned to close at specific rate, right? So what
19:57 do is you open quickly and then like click, click, click,
19:59 , click, click, click, . And so what it does is
20:01 allows for the passage of a certain of ions to pass through over a
20:05 period of time. Yeah. ma'am. Well, so that's,
20:12 , again, that's more of a structural question. I don't really
20:15 the answer to every time I've ever any sort of drawing about this.
20:19 kind of looks like what I've just here, but it could literally be
20:22 what this guy did where it's I'm manipulating the shape. So it's
20:25 , jammed close and open. That's real deep structural question that I'm not
20:29 be able to answer. All It's an interesting question, but not
20:35 I paid attention. All right. that's number one. All right.
20:39 one, voltage gated sodium channels have states. The opening and closing of
20:44 are gonna occur in sequence and you to go all the way back around
20:48 reset, which is important. We'll to that in a moment. Number
20:52 is more easier. This is the gated potassium channel. It just exi
20:55 has one gate. So it exists an open closed state, right?
20:58 it's like here I am closed, I am open, closed,
21:01 closed. So the number of gates have equal the number of states that
21:04 exi uh is number of states plus . OK. So most of your
21:10 gated channels are like this. Just voltage gated sodium channel is not.
21:16 , why do I care about All right. First off, let's
21:22 the first state. All right. we're, we're gonna be sitting over
21:25 in this flat zone. All And you can see the flat zone
21:27 over here and then it just keeps around the other side and this is
21:30 resting state. So this is where can see the cell is at
21:34 I'm at my resting membrane potential. I'm at minus 70. There's that
21:38 , that means sodium is slowly moving potassium is is is leaking out.
21:42 that means there's leak channels, There's always going to be leaked
21:46 The ratio of the leak channels is 50 to 175 to 1, whichever
21:52 you read is basically for potassium versus . And this is why we're at
21:55 rest state. All right. So are few leak channels, no sodium
22:01 flow through the voltage gated channels because both exist in their closed state,
22:06 ? And so that whole, that resting membrane potential is dependent upon the
22:12 moving in and the potassium moving out leak channels. So leak channels are
22:17 there. All right now, those others, right? I guess that's
22:25 gate. So that's, that's really focus here. All right. And
22:28 if you want to look at the , you can see, oh look
22:30 leak channel is open but my uh gated sodium channel, my voltage gated
22:35 channel are closed. All right. that's at rest. And then we
22:39 the A TP A. So what's doing? It saying? No,
22:41 , you go back to where you and we're just sitting in this
22:44 All right. Now, the first that we're going to deal with is
22:48 trigger, the triggering event is simply EPSP that comes along and gets to
22:53 Axon Hillock. So it kind of its way down, right. So
22:58 having this ripple or wave of, membrane potential change, right? That's
23:05 each of these represent. And if can get it to an Axon
23:08 what's going to happen is, is going to see a short or small
23:13 arrive at the Axon Hillock. So other words, if I can get
23:17 little bit of that wave to get the Axon Hillock, what it's gonna
23:20 is it's gonna cause a membrane potential . So let's go from minus 70
23:24 say minus 69. That that's one of change. All right.
23:30 located in the Axon Hillock is a of voltage gated sodium channels and a
23:36 of voltage gated potassium channels. But focusing on the voltage gated sodium channels
23:40 now. All right. Now what a voltage gated sodium channel? What
23:44 up any voltage gated channel tells you the name membrane potential. A change
23:50 the membrane potential is gonna open up voltage gated channel. OK? Because
23:55 dependent upon charge. And so if closed at minus 70 if I change
24:00 minus 70 I'm changing the membrane potential that. So I'm changing the state
24:05 the voltage gated channel. So what's happen is is if I can get
24:09 change to occur to kind of find way to the axon heo, what's
24:13 happen is is I'm gonna open up voltage gated sodium channel. And if
24:17 open up a voltage gated sodium what comes into the cell sodium?
24:22 ? And if sodium comes into the , what happens to my membrane potential
24:31 ? OK. And so if I , if I went from minus 70
24:34 minus 69 and I open up a and more sodium goes in, I'm
24:38 to depolarize further to minus 68 and 67 which is going to cause more
24:45 gated sodium channels to open, which more sodium to come in, which
24:50 more depolarization, which causes more sodium come in which or more channels to
24:55 , which causes more sodium to come . Do you see what we have
24:58 ? Do you see this positive feedback ? All right. Question.
25:08 they are. But remember what we're now is we're increasing permeability. So
25:13 we have this is a good It's like wait a second. Do
25:15 have pumps to deal with this? , we do. All right,
25:17 going to deal with those pumps. right. Can I time out for
25:20 second? All right, I'm gonna with a lot of hyperbole. All
25:25 , hyperbole is exaggeration. All So when I say ions are rushing
25:31 , I I'm trying to create an so you can see dominance,
25:35 So when I say sodium is rushing the cell, you get this impression
25:38 there's like thousands of ions moving It's like one or two ions.
25:45 ? But I want you to envision I want you to envision the dominance
25:49 . All right, if it was 1000 ions, pumps wouldn't matter,
25:53 couldn't keep up with it. All . So again, what's going
26:00 Epsp results in a membrane potential A depolarization that causes the opening of
26:06 gated sodium channels which are concentrated in region which causes sodium to come
26:12 which causes further depolarization. And we a positive feedback loop. And that's
26:17 we see. We start off very and then we see the slow
26:23 But then we see that massive curve place. You see that it starts
26:29 up like this. And what happens is that depolarization increases so quickly and
26:36 fast that we end up opening up the vulture gated sodium channels. When
26:41 occurs, we've reached threshold. All . Now your brains in my brain
26:48 I first started learning about this oh, all I've got to do
26:51 reach a number. No, no. The number tells you the
26:55 where that happens. So when all vol voltage gated sodium channels are
27:00 that's at minus 55 millivolts. So action potential actually occurs when I've stimulated
27:06 voltage gated sodium channels to be All right, but you can use
27:11 , whichever works best for you. is, is when we are no
27:16 seeing the, the uh slow curve , we've now opened everything. And
27:21 now what we're doing is we are up and this is what we
27:24 this is this depolarization event. All . So this, this rise is
27:30 dependent upon sodium coming into the As a result of opening up all
27:33 voltage gated sodium channels, we have the permeability in favor of sodium.
27:39 we started off with the permeability favoring roughly 50 to 1. Now we
27:45 it over to about 1000 to 1 favor of sodium. And that's why
27:49 keep shooting up. And if everything stayed as it is right near,
27:54 would be the value that we'd eventually up here? Does anyone remember?
27:58 told you you didn't need to memorize ? But does, does anyone remember
28:01 value plus 60? Right? Because the the equilibrium constant for sodium,
28:10 ? It would just keep going up up and then once you get up
28:11 plus 60 it say OK, I've balance. I don't need to go
28:14 anymore and I'm stopped and that's where would stop, but it doesn't.
28:19 right. So the depolarization is a of sodium rushing into the cell and
28:26 boom, we hit this point right and it stops if it goes the
28:30 direction. So what's happening here at peak? Well, two things are
28:37 at the peak. The first thing happening is that those voltage gated sodium
28:43 are closing. Remember we had three , right? We had the close
28:49 of opening. So that's at the event. We've opened those up,
28:53 open them all up. And so we are in the depolarization state and
28:57 tick tick, tick, tick, , tick, tick tick, they
29:00 and now we're at the top of peak. Now, what did I
29:03 about this? Is this a timed ? I said they open and then
29:08 close. It's a timed event. right. The timing just happens to
29:13 from this point right here to about point right there. Now, it's
29:18 to see that you don't really need memorize. Oh, this is a
29:20 event. But I want you to about, yes, the gate opens
29:25 then the gate closes just like if open that door, it would naturally
29:29 on its own over a period of . All right. That's when I
29:32 it's a timed event. All So if that was the only thing
29:37 was involved, then what we would is we'd see this graph kind of
29:40 like that, that, that, , that and it would slowly return
29:43 to normal, but it doesn't do what does it do? It turns
29:47 itself and goes exactly the opposite direction fast as it rose or roughly as
29:51 as it rose, right? Is what it looks like? It goes
29:53 like this and comes back down like ? Yeah. So the second thing
29:57 happening here is we're opening up the gated potassium channels. Now, you
30:05 think that this is the stimulation to up the vulture gated potassium channel.
30:10 is not. All right. Do have a friend that you can tell
30:15 joke to? That's a little bit . You know, you tell them
30:18 joke and they kind of stare at for a second and then a couple
30:21 seconds later, they, then they probably because they feel like they should
30:24 because it was a joke. They don't get it. Well, the
30:28 gated potassium channel is your slow All right, it is stimulated to
30:34 at the exact same time as the gated sodium channel is. So they're
30:38 supposed to open roughly or they're both to open at the same time.
30:42 when sodium channels open, potassium channels closed because they're still trying to figure
30:46 things. And then it's at when you're that time passes. So
30:51 this is when I'm starting and it's when time passes, when I get
30:54 about right there, that's when all voltage gate potassium channels have started opening
30:58 . So what happens? They're opening just as the voltage gated sodium channels
31:02 to close. And so that's why reverse it back and go the opposite
31:07 . Sodium is no longer rushing into cell. Sodium is prevented from going
31:11 the cell. And now I'm going allow a lot of potassium to leave
31:16 cell and that's what happens and out goes. So you climb quickly because
31:23 sodium, you drop quickly because of . And in both cases, what
31:28 done is we've changed permeability, permeability for sodium. Secondly, permeability for
31:36 and removing the permeability of sodium so . Are you with me?
31:42 And notice each one of these is a point that we're identifying with these
31:48 . Yeah. No, no, I'm what did I tell you on
31:52 ? Did I say this? This is stuff you have to grind through
31:55 think about because it's not a picture easy to understand. This is not
31:59 but it's not visual. So go . Mhm Then we stop it
32:14 then you first you stop it and correct. So think about it.
32:21 what's happened is is first, I've having positive charges. Just think in
32:26 of charge, right? I I'm off negative. Why was it
32:30 Do you remember we had all those proteins that are sitting around begging for
32:35 positive charge to come in. So goes in chasing after that negative
32:41 All right. And so the inside the cell becomes very positive, very
32:44 because of those positive charges entering then you slam the door shut and
32:49 no more positive charges can come Now remember sodium is attracted to the
32:54 charge on the inside potassium. On other hand, while it's attracted to
32:59 negative charge on the inside, there's much potassium, it wants to get
33:03 from all the other potassium. So I open up its gate, what
33:06 gonna do is it's gonna rush out behind the negative charge so that you
33:12 so it can create equilibrium along the line. So when we talk about
33:16 electrical chemical gradient, remember I said two parts to it. We have
33:20 think about the chemical and we have think about the charge itself. So
33:25 is coming in for two reasons. , not enough sodium two, there's
33:29 charge I'm chasing potassium is leaving for reasons. Way too much potassium in
33:34 . I want to get some elbow , right? And oh there's lots
33:39 positive charges now. So I can ahead and leave and not be afraid
33:43 do so because where do I find minus 90? That's where I
33:48 that's where my balance is gonna be . All right. So all that
33:52 stuff that I talked about is why do I have to memorize this
33:55 ? It's not so much about It's understanding what the driving force is
33:59 all this stuff, right? Sore , a function of opening up the
34:08 channels, the vulture gated potassium channels closing the Vulture gated sodium channels.
34:15 right. So this is kind of it looks like during the action
34:18 right? It's saying look, here's voltage gated sodium channel, here it
34:23 close, this is at the front , you can just follow the
34:27 Oh, here I am in this , right? So now I'm opening
34:31 and sodium is coming through massive Sodium is coming through. Oh Now
34:37 the rep polarized state, I'm closed . So it shows you the three
34:42 relative to where the curve is So it's an easy way to look
34:46 it. Now, if you've been attention, you're going wait a
34:51 I shoot way beyond my resting How many of you speed on our
34:59 Roads? Anyone? All right. many of you have come up to
35:03 yellow light and didn't know what to , right? You get, you
35:07 in that zone where it's like if speed up, I'm gonna, I'm
35:11 cause a problem. But if I on my brakes, I'm not gonna
35:13 my light. Have you ever done ? And you kind of slid into
35:16 intersection accidentally maybe crossed over that white where people are trying to cross the
35:22 . Yeah. OK. That's what polarization is like, look remember what
35:27 said, the potassium channel is a bit slow, right? So when
35:31 open it, it takes a little of time to open. When I
35:34 , it takes a little bit of to close. And so what we're
35:36 here is it taking its sweet time close. And what we do is
35:41 slide past the point of rest. right. So in other words,
35:46 hyper polarization is a function of those gated potassium channels staying open too
35:53 And so we slide past our normal and then eventually, what they're gonna
35:57 is they'll get down here and they'll completely. And then the uh sodium
36:02 pumps are sitting there going um we to get things back into balance and
36:05 they start moving the ions back and . They're always doing that. But
36:09 is what allows us to return back the resting point right here.
36:16 Now again, are the leak channels ? Yes, leak channels are always
36:21 . Are the leak channels open Yes. Are leak channels open
36:25 Yes. Are leak channels open This but they're o they're superseded by
36:29 other channels. OK. So the here is in hyper polarization, I'm
36:35 taking my sweet time to close the channels, the voltage gated potassium
36:42 And so that causes the overshoot or hyper polarization. And then the repolarization
36:49 here to there is just simply the doing their job. Okay. So
36:57 action potential is not particularly complicated. one of the things that is difficult
37:05 see, you know is if all got to do is again, look
37:08 the candy coated chart, right? you can go OK. What's happening
37:12 ? That stimulation, what's happening Everything's open. What's happening here?
37:15 closing voltage gated sodium channels, but up potassium channels down here, I'm
37:20 up the potassium channels down here is all closed completely and I'm just returning
37:25 to rest and everything is back to . That's all that does,
37:30 But it's not always easy to understand we're looking at is we're looking at
37:34 graph over time, right? We're at voltage over time. And I
37:41 there's an easy way to visualize this that you can carry this forward to
37:46 the rest of your lives because I you this is probably the toughest thing
37:50 you ever experience in biology. I , it's not, but for most
37:54 , this is where you guys like I don't visual, I don't get
37:57 . And so what I recommend doing let's make something that's visual for us
38:01 understand. And have you guys ever the Wave? Yeah, you done
38:06 at a sporting event. It's really at soccer events, but not so
38:10 at other ones. But one year went to the uh Sugar Bowl uh
38:14 Texas A and M lose to Ohio . It was a really, really
38:17 game. But if you've ever been the Super Dome, um there's three
38:22 and at that game, because it so boring, the fans started doing
38:26 wave and we had one wave going on the bottom level. We had
38:29 go in this direction in the middle and we had one. So it
38:31 like a wild carousel of waves. I recommend we just do the
38:36 You don't have to stand up. I wanna see participation especially to the
38:40 right over there. That's where the usually kind of gives up. They're
38:43 , yeah, we're not gonna do . All right. We're not too
38:45 for school. This is how we stuff ready to do the wave.
38:47 we go. Do you see that ? I'll get it for you if
38:53 don't have to get up. Oh . All right. So let's describe
39:00 we just did. I'm a triggering , right? I was a GPS
39:04 that said we're gonna have an action . And so I created the action
39:08 , right? And then you as cell. Really? Axon Hillock started
39:13 action potential here and then it traveled the Axon, right? And what
39:17 we do? Our hands went up then they came back down again.
39:20 the wave, right? Very, simple. It's a wave form.
39:26 do we got up here, we a wave form, don't we?
39:29 have hands going up to the they reach the peak and then they
39:32 back down again, don't they? so you can think about what is
39:37 an action potential is literally picking a in the cell and saying, let
39:41 see what's happening at the cell at particular point in the cell. I'm
39:45 over time. So we're going to the wave again, but we're going
39:48 focus right here. So sorry, going to focus on her as we
39:51 do the wave and you can see time as it passes right here we
39:55 again. We gotta try it We gotta do it right.
40:00 123. I know it's embarrassing. eyes on you. Let's try it
40:09 more time. All right. Do you see as we went?
40:15 , and we're gonna do this one time and I'm gonna say pause,
40:18 gonna say stop and wherever your hands , keep them there ready.
40:23 stop. Where are your hands? they coming up or coming down?
40:27 going down. What are your hands going? They're going up. Where
40:31 your hands? They're at the right? What are your hands
40:34 They're starting to go up, aren't ? All right. Look at where
40:38 are on the graph. All That's who you are on this graph
40:43 . You are literally watching this over . You can imagine there's A P
40:48 what you're doing is going up and back down again. And what we
40:52 is we are a specific point in cell. And we're asking over
40:56 what is the change that's taking place time? OK. So when you
41:01 at that, don't think of, it being like this solid state,
41:06 ? It is literally a ripple of that's occurring along the length of the
41:11 . And you're just watching that ripple by. It's as if you're watching
41:14 wave past you in the ocean. . So it's not just one
41:23 It is, you are literally watching point in the cell as that,
41:28 wave of deportation passes by. So is, it is literally what you're
41:43 here. So I'm, that's why moving ahead one. All right.
41:46 what you're looking at is now we're at an Axon, we could be
41:49 on this Axon. We could be at the Axon Hillock, but we're
41:52 the Axon here because it's showing three points, right? There's a after
41:58 , there is an at point and is a before point, right?
42:01 that's what you're saying because if the potential moves from the Axon Hillock down
42:04 the Axon terminal and it always, , always, always moves in that
42:08 , right? It's always created up , it always terminates down here.
42:14 right, So if the middle represents the action potential is, then this
42:20 the point before where that action potential . I'm trying to make sure that
42:23 drew the picture, right? And , OK. I'm just making sure
42:30 where the action potential has passed up . And so what you can see
42:34 like look at where the action is there, it's going there, it's
42:37 there, right? Boom, boom. And so you can see
42:40 the action potential, you can see potassium uh coming out at the where
42:46 potential is, you see the sodium in. And so this ripple effect
42:50 taking place is literally as that wave moving forward. So you could say
42:56 right here is the peak of the and look at what the peak of
42:59 wave did. It started up then it came to here and then
43:02 came to here. All right, is a propagation event. All
43:07 So what we're looking at is we're at the wave moving along the length
43:11 the cell. And when you're looking that graph, you're looking at that
43:16 as it passes past you. That's idea. All right, now,
43:25 already said everything that's said on that , right? Sequential opening of the
43:29 gated sodium channel, followed by the closing of the sodium channel, followed
43:33 well simultaneous opening of the Vulture gated channels. And this propagation is going
43:39 occur along the length of the just like when I started over there
43:43 said, we're going to do a . It started over here and it
43:46 the length of the room. We it's an all or none response.
43:50 you get an action potential, it , it does not, it does
43:55 decrease in size. It's always stays same height. All right. It's
43:59 like the ripple of the graded potential dies out. It just goes until
44:04 nothing there. And the reason for is because you have the same concentration
44:07 voltage gated sodium channels and the same of voltage gated potassium channels. I
44:11 up the channels, ions are gonna . All right, it doesn't
44:15 It's an all or none response is idea here. And so once I
44:20 up on top, sorry, once start it there, it will arrive
44:24 the same strength as when it Can I make it any more
44:29 No? All right. It is complete or doesn't happen at all.
44:35 the idea. All right. for every action potential there is what
44:44 would call a refractory period. The period follows the action potential. It
44:50 behind it. All right. So this is your action potential, a
44:54 period is going to be back All right. And what a refractory
44:58 is, is simply the period of where in another action potential cannot occur
45:04 right. In other words, it's short period of time where no amount
45:08 stimulation is going to allow me to another action potential. It has to
45:12 before I can get another action All right. And there's two halves
45:16 it. All right, the first is called the absolute. So when
45:21 hear absolute, what does that If someone says you absolutely cannot do
45:25 ? Are there any exceptions to the ? No? All right. So
45:29 absolute refractor period is under no Will you ever get another action potential
45:37 this little space of, of, , of uh refraction? All
45:42 Now there's a reason for this. . So the action potential while it's
45:49 . So you can imagine it's going right, as it's going by,
45:52 we've done is we've opened up voltage sodium channels and we have closed our
45:58 voltage gated sodium channels. Did I that? Right? Potassium, did
46:01 say potassium first? OK. All . So let's think about the voltage
46:05 sodium channel, both voltage gated sodium . I've opened it and then I've
46:09 it. And what did I call state closed but incapable of opening.
46:14 I have to completely reset, don't ? So during the refractory period,
46:18 is the state of my voltage gated channels. I have to go through
46:22 process of resetting them. I can't them. I have to totally
46:26 So one of the reasons I cannot an action potential. There is because
46:31 can't open. And what was the that caused the action to start in
46:35 first place is the opening of those ? Does that make sense? Something
46:39 can't open? I can't open. I can't stimulate. So absolute refractory
46:45 is dependent upon that. The second that's causing the issue is I've got
46:48 and tons of potassium rolling into the or rolling out of the cell,
46:52 me. And as a result of , I'm, I'm, I'm dominated
46:57 that potassium um um uh permeability. so those two things together are gonna
47:04 any sort of, of action potential occurring on the backside of the action
47:11 . Now, when you look at graph and when you look at something
47:14 this, where they're gonna put the period is they'll always draw it on
47:18 side because this is the backside of action potential, the action potential is
47:25 in this direction. But what you say is, hey, um once
47:29 gone through this event, this is I would see on the back
47:34 So you would kind of flip it , this is the front end,
47:37 is the back end over time. right. Now, if that's confusing
47:41 you just think in terms of what first, which side happens first,
47:46 side or that side, that So that's the thing that you're doing
47:50 . All right. The other half the refractory period is called the relative
47:54 period, which is more of the it could happen. All right.
47:57 here what we've done is the sodium have started resetting themselves, right?
48:03 the potassium channels have started closing. , if I have some sodium channels
48:10 they've reset themselves, is it possible me to open them again?
48:16 All right. Now where this occurs primarily down here. OK. So
48:22 this point, I can start opening voltage gated sodium channels. All
48:27 But the problem is, is I'm further away from threshold. Why am
48:32 further away from threshold? Because I have some potassium channels open and I
48:37 have other sodium channels that I need reset. They're still in that
48:41 But if I have enough of a , a strong enough stimulation, I
48:45 overcome that threshold variance. So if threshold from here to here is 15
48:52 , let's just make up a Let's call that 20 millivolts. Let's
48:56 say, oh, if I get strong enough epsp, I may be
48:59 to overcome that deficit and then reach threshold to then get an action
49:05 All right. So action potentials um this period of time where you can't
49:13 another action potential, right? You to wait for it to pass before
49:19 can do that. Now, I'm gonna demonstrate this with the wave who
49:22 who should I pick on this You're like, no way. All
49:26 . Can I pick on you for bit? All right, I'm,
49:28 gonna, I'm gonna stimulate everyone. . All right. So this would
49:30 like the triggering event. When I that. You do your wave?
49:33 . Ready. And you have to a whole wave. All right.
49:37 . Go and uh go. Can keep up with me? Do you
49:45 there's remember what is an action potential has two parts to it,
49:49 It has the up and it has down. If you're going up,
49:52 you go start going up again? , if you're up here, can
49:55 start going up if you're coming Can you go up? No,
49:58 have to go all the way back . And that's kind of what the
50:01 period is, is saying, there are already certain motions that
50:05 have started and have to go through before you can do that again.
50:10 that's what the refractory period does and it does is it limits the frequency
50:15 an action potential, which is why can't sum action potentials. That's why
50:19 get an all or none response. you get the full thing or you
50:23 get anything at all. You can't too close together and stack them like
50:27 SPS because they're already complete and then you're creating this, this, this
50:34 period, they prevent them from getting closer to each other. All
50:39 And one of the ways that your talk to each other is in the
50:43 of those action potentials. When you're at this chart up here and remember
50:48 it says is in milliseconds, It says milliseconds up there. The
50:53 of this from here to there is four milliseconds. All right, we
50:58 get uh action potential pretty close It can get about two milliseconds
51:02 but that's about it. All So one of the ways that cells
51:05 to each other, they code in frequencies of those action potentials. In
51:10 words, the timing of them, how they know what the messages
51:15 All right. Now, action potentials dependent upon two things in terms with
51:22 to their speed, dependent upon two . All right. The first is
51:25 diameter of the fiber. Now, I've been a professor here,
51:33 music and uh music devices have changed a bit. All right, you
51:40 your music on your phone now and you wear ear buds, which is
51:46 . All right. But in the old days, if you built a
51:49 system, you'd get these big old , right? If you, you
51:54 the cars that go boom, you where there's fewer and fewer of those
51:59 , right, with the big But if you look at the wiring
52:03 those cars, if you want good for your sound systems. What type
52:08 wires do you want? You want tiny thin wires, you want big
52:10 wires. What do you think? thick? Right. And the reason
52:14 that is they produce less resistance, smaller the wire, the more
52:18 the more resistance, the less the signals are gonna be able to move
52:21 them. Right? And so big provide for easy movement. That's an
52:27 way to kind of think about it terms of the uh the ions passing
52:31 that. This is also true for , the thicker or bigger the diameter
52:38 the axon, the faster the signal . Now, on average, we're
52:43 about roughly 1.5 to 2 m in . We got to send signals from
52:48 brains down to our big, our toes. And you can imagine if
52:51 need, if I step on a or something like that, I want
52:53 get that information up, my brain quick, wouldn't you? Right.
52:56 just know that you have to lift foot up, right. So that's
53:01 . So you would think that maybe want that signal to go through a
53:04 thick axon. Would you agree with on that? Yeah. Ok.
53:09 you can imagine that's not the only that I have in my body.
53:12 got hundreds of thousands of fibers in body. And if all the information
53:16 important, I'm gonna need a bunch thick fibers aren't I? And the
53:19 , more fibers I need that are and thick, the bigger and thicker
53:22 gonna have to become, right? the bigger and thicker I become,
53:27 I'm gonna need bigger and thicker Do you see the problem here?
53:30 happens? Right. So the larger fibers, the more space I need
53:34 provide for that fiber to be in then that makes me bigger. So
53:38 the fiber has to be bigger and just doesn't end. So the workaround
53:43 that is we use another type of material called myelin. All
53:49 So myelin is uh produced by So here you can see the myelin
53:54 going to be. So here is normal neuron with no myelin. And
53:58 you can see I've had these cells are wrapped around and they're creating this
54:02 of insulation. All right. So is formed by two different types of
54:07 . We're going to learn more about in the next unit. But what
54:10 do is they wrap around and produce insulated regions where action potentials cannot
54:17 All right. So this is what a better look of it. There's
54:20 better vision of it and there's two types of cells we have in the
54:23 nervous system. So outside of the nervous system. So where your nerves
54:28 , this is what you'd see. see neural lites. They also have
54:31 different name called Schwann cells. And individual cells that are wrapped around the
54:36 like you see here and they leave little tiny spaces in between them.
54:40 it's in those little tiny spaces where action potentials can occur doesn't occur
54:45 the myelin myelin is insulation. All , that prevents action potentials. And
54:49 what would happen here is that action could only occur at those individual spots
54:55 between the cells. All right, between the myelin. These spots where
55:02 actions occur are called nodes of Named after the guy who discovered them
55:07 the central nervous system. We have cell that's called an oligodendrocyte. It
55:12 the exact same thing except it sends multiple extensions and those multiple extensions are
55:17 wrapped around individual cells. So you see here here's one cell, you
55:21 see it's wrapped around multiple cells along way, but it still leaves those
55:25 tiny spaces in between. And those the nodes of Ranvier and this speeds
55:30 transmission. All right. So this of gives you a better visual.
55:35 you can see it, there's the in there. That's a node of
55:38 node of Ranvier node of Ranvier. right. And that's where the action
55:41 are occurring. Myelin, nothing's happening the myelin occurs. All right.
55:46 it's only at the note of Ranvier you're going to see the actual
55:51 And now the reason it does. is that first an action potential is
55:56 propagated, just like what we saw the class when we did the wave
55:59 a propagation when there is no an action potential has to occur over
56:05 entire length of the cell. All . So the example I like to
56:09 of is like if I'm walking across stage, I have to, if
56:12 stage is an axon and there's no , nothing in the way I have
56:16 cover the entire length. And the that I would do that is I'd
56:19 toe to heel, right. And I walk toe to heel, that's
56:23 slow, isn't it prime? the node of Ranvier covers up portions
56:31 the axon. So the only place the channels are located are in the
56:36 of Ranvier. So what an ax does it literally hops from one node
56:41 Ranvier to the next? This is to me walking. Normally when I
56:46 , normally, what do I do I step over portions of the
56:49 don't I like? So am I when I walk? Like this?
56:56 answer is yes. Normally, what do is I'd pull one of you
56:58 up here and erase me. I lose because I do the toe to
57:03 . All right. When there is myelin, the type of propagation is
57:09 to as contiguous propagation or continuous either is correct. All right. So
57:15 whole Axon everything is going through these . It uses more energy and it's
57:21 when you're dealing with my Allen. you have is saltatory conduction, saltatory
57:27 to jump. All right. And what it's doing is it's jumping from
57:30 of Ranvier to note of Ranvier. the space of the my Allen is
57:34 far enough so that you can get action potential um and not have a
57:40 or something like that. And so perfectly spaced. So you're basically
57:45 hop, hop, hop. So just like I can't walk like
57:49 that would be too hard, They're just just like that. And
57:55 you end up going a lot So here's the example of the
57:59 You can see moving from point to to point here in South Victoria.
58:04 are you doing? I'm jumping from of Ranvier to note of Ranvier to
58:08 of Ranvier. This is so much advantage advantageous and the reason it's about
58:18 times faster. So you can get really, really tiny fiber and you
58:24 make it behave like a very fat and it saves energy and the body
58:31 to sage energy. OK. So it comes to propagation fat fibers with
58:41 , our fastest thin fibers without myelin slowest. And then there's ranges in
58:50 . All right. So the presence myelin, the fatness or the thickness
58:54 the diameter very, very important so . So good with that.
59:00 Yeah. Sure. So fat fibers myelin, very, very fast.
59:06 . Thin fibers. No, very, very slow. All
59:11 And then there's a range of stuff between. All right. Those are
59:16 two extremes. All right. So increases, speed, diameter increases
59:21 Those two things together. How we on time. Uh, we're
59:27 I was getting panicky. I thought was running out of time. Are
59:30 any questions so far about this Is the action potential? Scary.
59:36 , just think in terms of if drew it out, what is it
59:39 , what has been going up, has it been going down? Just
59:42 look at those points of change. you know where those points of
59:45 what's happening at those points of you are golden. You are the
59:48 who actually understand what's going on. right, if you look at the
59:52 of change, that's the key secret the action potential. All right,
59:59 period, understand, I can't, just can't get another one. There's
60:02 point where I can, but there's point also where I cannot at
60:07 absolute versus relative. So what we've of done, let me see if
60:14 can go back. All right, we've kind of done is we've
60:16 hey, today's lecture has been about an action potential up here at the
60:22 Hillock and sending that action potential down Axon down to the axon terminals.
60:28 we're asking the question, what is action potential really doing? Why do
60:31 even care and remember what an a is. It's a long distance signal
60:37 the length of the cell. And the end, what it's going to
60:40 is it's going to cause the release a chemical message. All right.
60:45 that's where we're kind of going, dealing with what is called the chemical
60:49 . And so here we are down the axon terminal. All right.
60:53 here at the axon terminal, this where we are going to have a
60:56 bunch of vesicles filled with neurotransmitter. what we're doing is we're going to
61:00 this neurotransmitter be released into this space the synaptic cleft. And we want
61:06 chemical to then travel across that synaptic to bind to the receptor on the
61:12 cell. And when you bind to receptor on the receiving cell, you're
61:16 a post synaptic potential, right? excitatory. So that would be an
61:24 or inhibitory. So we've come back circle, haven't we? We started
61:30 saying, hey, what happens when receive a message? If I receive
61:33 message, can I produce a an action potential that then travels down
61:38 length of the cell to cause what message to be released so that it
61:42 be received? All right. So where we are, we're back where
61:48 started. So the sending cell the that's releasing the message we said is
61:53 . The one that's receiving is post . There are fourth steps that occur
62:00 you are in the uh cell, you're trying to send the signal.
62:04 this is pre synaptic. So here can see here's my potential action potentials
62:09 down action potentials are the result of opening of voltage gated sodium channels and
62:15 closing of voltage gated potassium channels. as long as they have sodium channel
62:21 a potassium channel, they're gonna just swapping back and forth. I'm gonna
62:24 an action potential. When you get to the uh this the uh axon
62:31 , there are no more voltage gated channels. So do I get action
62:36 down in the terminal? No, I don't have the channel, I
62:42 get the action potential, but this a signal and the signal is going
62:46 for a reason. And what we're to see down here at the very
62:49 are voltage gated calcium channels. All . So I'm changing something up
62:56 Whoa, it's just another ion Ah Calcium is a unique ion in
63:01 body. It can serve as a just like what we're seeing right now
63:05 terms of depolarization stuff or, and often it is used as a signaling
63:14 . We're gonna have to backtrack a bit to the previous unit. You
63:18 when we talked about vesicles and I out hey, these vesicles are all
63:23 up and they're sitting there and they're waiting for a signal. And what
63:26 were they waiting for? Calcium. the action potentials job is to come
63:32 here and open up the channels that calcium to come in. When calcium
63:37 flowing into the cell, it binds to the machinery, holding the vesicles
63:42 place to tell them to open. so they released the neurotransmitter out into
63:47 space. Right. So calcium is signaling molecule, neurotransmitter goes out in
63:53 space. It doesn't know where it's . It's just a simple diffusion,
63:56 just goes out there and goes, . I'll just go wherever I go
64:00 some of it will make it across synaptic cleft. It's a very,
64:04 small distance, right, very, short distance. And they will find
64:08 receptors and they'll bind to that And what we've done is we've now
64:11 a neurotransmitter, a chemical that's acting activate another channel to cause a depolarization
64:19 a hyper polarization in the receiving OK. So that's what you see
64:25 or what neurotransmitter can do is it flow away and if it flows
64:28 it's not doing anything. So those the four steps a potential arrives at
64:33 axon terminal causes the opening of voltage channels. Calcium flows in because those
64:39 vultures gated calcium channels, calcium binds those um uh vesicles or to the
64:46 that are monitoring or regulating the vesicles then they open up and they release
64:50 . New neurotransmitter floats across and binds the channel. And this is how
64:54 cell talks to another cell. This how neurons talk to neurons or neurons
64:59 to muscle cells or the glands through release of this neurotransmitter. Now,
65:07 takes a little bit of time for to happen because the uh neurotransmitter doesn't
65:13 where it's going. It's just kind floating around through the process of
65:16 So the opening of this channel to time of binding takes about 0.3 to
65:21 milliseconds to get there. And so can imagine if I have a series
65:26 neurons at each point of interaction, synapse, there's going to be a
65:30 . And so the more neurons there in the system, the greater the
65:34 for something to be processed. So you have something really, really
65:39 you want fewer neurons involved, you fewer synapses. All right.
65:44 synaptic delay is something that must be through these signaling mechanisms. So many
65:51 the systems in your body are designed the synaptic delay. No, as
66:01 as neurotransmitters in the synaptic cleft, going to continue binding to and activating
66:07 cell, we do not want that happen. We want signals to be
66:12 and, and just absolute like turn , turn off. That's, that's
66:19 it is. You don't want it say, hey, turn on and
66:21 let you know when it's time to off. That's, that's a bad
66:24 of signaling. And so we have in place that turn off the
66:31 All right. So everything that's been on must be turned off.
66:35 the most common way of turn uh of, of dealing with this
66:40 is listed up here. Now, you look at this picture, this
66:43 , what you'll see is we have types of neurons and they have different
66:46 . Do you need to know which does? Which, what do you
66:50 ? I like that? See, I ask that question, you
66:52 the answer is gonna be no. right. No, do not memorize
66:55 picture. What I want you to is the different ways that happen.
66:59 first one that was ever discovered was here in cholinergic neurons. So,
67:04 is the neurotransmitter that allows your muscles move. It's a very common
67:09 And so it was one of these that we discovered very early on and
67:13 looked in there and they said, wow, in the synaptic class,
67:16 have this enzyme. So we're releasing and this enzyme is acetycholine esterase.
67:22 basically chews up acetylcholine as soon as released. So I'm destroying the
67:27 It's like, oh man, so must be the most common way that
67:29 happens and they start looking everywhere else it doesn't happen anywhere else. All
67:33 . Very rare. Do we see ? But this is a mechanism of
67:38 . It's like I release the I destroy the signal that I'm being
67:41 . And so only a couple of neurotransmitters can get across that space.
67:45 like the single most dangerous game of Rover you'll ever see, you
67:50 Red Rover. Did you guys play Rover? One person anyone,
67:53 you guys play Red Rover? Red , red rubber? Let Bobby come
67:56 and they come running and you, close line them. It's the most
68:00 game. You never played Red man. You guys missed out,
68:03 me guess for, for uh for . Did you guys even have
68:08 Yeah. Did they make you like with your hands folded outside the school
68:11 something? I mean, we've tried find ways to break other people's
68:15 Red Rover is a game where you up groups of kids and they hold
68:19 and you say, hey, you over here and see if you can
68:22 our arms and they come running at speed and you close line them and
68:25 like kids are like crap, you , or you break somebody.
68:29 it's the best game ever. You why my generation so tough. This
68:35 what we did. That's just one . I mean, oh, if
68:41 could just tell you all the stuff did. All right. So that's
68:44 it is. It's like, all , I want you to run over
68:46 and bind to the receptor. But the meantime, someone's gonna try to
68:49 you while you try to do That's, that's what these enzymes are
68:52 . OK. All right. Another is diffusion. Diffusion simply says,
68:58 , um, as you're going um you may not stay in the
69:01 and you'll kind of go away and the way that uh uh any
69:05 of ligand works is that you have have the receptor for it to
69:08 And so if you float away from synapse, there's no place to
69:12 And so eventually you'll be destroyed by enzyme circulating in the body, usually
69:16 quickly. Most of these things are , very short half life. So
69:19 is the the other thing and it's shown in any of these pictures.
69:22 if you're trying to find it, other two ways that you can do
69:25 is simply by taking up that neuron that neurotransmitter by either the neuron that
69:31 it or nearby glial cells, these nearby support cells. And so that's
69:35 these all are showing you is Look here, I'm being released.
69:37 look, I'm being taken up again . I'm being released, taken
69:39 Oh, and other cells are taking up, taken up, taken
69:42 taken up, taken up. So you kind of see what's kind of
69:46 over? And over again is like cell that's releasing it is taking it
69:49 up and, and recycling it. those are usually the more common ways
69:55 at least they appear. So the thing here to walk away with is
70:00 , enzymatic activity can destroy, I diffuse that neurotransmitter away or I can
70:05 it back up, not in the cell, but in either the sending
70:08 or surrounding cells. So that, neurotransmitter can't act. And this is
70:13 I kill the signals so that I really precise, turn on, turn
70:17 uh signals. There are a lot different neurotransmitters. All right. So
70:28 are about 100 of them and I'm going to show you a couple of
70:32 and again, which ones you have know I really have over here.
70:36 right. But typically, what we is we look at neurotransmitters and they
70:40 a structure to them. Again, very first one that was discovered was
70:44 acetylcholine. All right. So it's ACH um If you wanna look,
70:48 don't even know if it's even Oh, there it is. Acetycholine
70:51 right there. All right. If wanna look at their chemical structure,
70:54 great. I'm never gonna ask you structure. That's not important for this
70:57 . But this one was the first discovered and they were so excited.
70:59 was like, oh, we finally out how neurons work. And so
71:02 gonna start looking for things that look a cedar choline and there's no other
71:06 that's related to Cedar Colline. It its own little category and it's
71:10 so disappointing because you've discovered like the , the, the one that's most
71:14 and there's nothing like it. All . But then you have things that
71:18 based on amino acids, right? , like the mono means and the
71:22 acids themselves can serve as neurotransmitters. , some of these, you've heard
71:27 , we have the catecholamines. You not have heard of that, but
71:29 probably heard of dopamine. Have you heard of dopamine? Yeah. All
71:33 . You may not have heard of or, nor epinephrine. But you've
71:37 of their common names. At least of their common names. Adrenaline.
71:41 you heard of adrenaline? That is . And it has a cousin called
71:46 Adrenaline or norepinephrine. All right. you heard of serotonin? Yeah.
71:51 you heard of histamine? Yeah. that they get big, you
71:54 those get all topped up. You the theist, right? So,
71:59 , these are neurotransmitter. You've heard glutamate and you've heard of aspartate,
72:02 heard of Glycine. These are amino and there's, they serve as
72:10 A TP. We talked about it the molecule of energy, but it
72:13 serve as a neurotransmitter. So, are the purines, there's gasses that
72:18 bodies can use. They're called gas collectively. But nitric oxide for
72:24 hydrogen sulfide, carbon monoxide are all that can be used by cells as
72:31 . Hydrogen sulfide is what makes a egg smell like a rotten egg,
72:36 your body uses it as a Now, there again, very,
72:39 small quantities, you have things that uh peptides or proteins. So,
72:45 heard of opioids and probably you've heard of an endorphin, right? But
72:49 a whole class of these things. right. And there's lots of different
72:54 and then some of the lipids that mentioned, we said there's these
72:58 these can be used as neurotransmitters. you can see that neurotransmitters follow along
73:04 these different types of groups of They're not just limited to a simple
73:10 like acetylcholine. There are these So for you, this is what
73:16 should know. You should know a of Colline. You're gonna see it
73:18 and over and over again. Ace Colline can be excitatory or inhibitory depending
73:22 where you're looking and what you're looking . All right. And again,
73:25 not gonna look at it today, it's coming down the pike. All
73:30 . It's found both in the central system and the peripheral nervous system with
73:34 to the amino acids. These are ones you need to know. All
73:38 , you need to know glutamate, and aspartate. These are excitatory.
73:43 if it ends with a te, probably in good shape, glycine and
73:49 . Gaba is a modification of All right. These two are
73:55 All right. So when you see particular amino acids, like,
73:57 if I'm looking at this system and has glutamate, it's an excitatory
74:01 it's turning on things downstream. And lastly, the biogenic means this is
74:06 group that includes the catecholamines. They're related to each other. They're
74:11 um, uh modifications. So, is the serotonin, there's the
74:15 here's the catecholamines right there. And could just see if you go and
74:20 at them closely, you can see small modifications, we're gonna see them
74:23 and over again. So you should when you hear biogenic means is oh
74:27 . I'm I'm referring to those neurotransmitters are that I'm familiar with dopamine,
74:33 cetera, epinephrine. So with chemical , you're going to be using neurotransmitters
74:40 this is our last slide. This the last thing you need to know
74:42 the exam. There's another type of in the body. It's the electrical
74:46 . They're not particularly common. Most the synapses in your body are going
74:50 be using chemical messaging the chemical message dependent upon the action potential. The
74:57 potential is dependent upon graded potentials produced the cell. Do you see the
75:02 here? So I get a greater that results in the production of action
75:06 that results in the release of a message so that I can create a
75:10 that's going to stimulate the next cell be a greater potential. Again,
75:14 may change the activity inside the cell upon where I'm looking with electrical
75:19 You don't need a chemical. All here, what you're doing is you're
75:23 gap junctions, you're moving ions between , the two cells are interconnected and
75:29 the ions moving between the cells allows the proliferation of and propagation of those
75:36 electrical signals along the length of the , the easiest. And and I
75:40 example to think about is what happens your heart, your heart, the
75:45 are interconnected by these gap junctions. action potential is produced in a group
75:51 cells in the heart which are then from cell to cell to cell to
75:54 to cell to cause the pump of heart. Ok. The contraction of
76:00 heart. All right. So this the weird one they exist but this
76:07 where you see electrical synapses, action are not part of that process.
76:13 right, action potentials are dealing primarily the release of that chemical signal.
76:19 , ma'am. Yes. So the thing would uh result in it like
76:25 the in the case of the muscle , muscle cells contract, right.
76:29 so here the actual potential or really the potential moving from cell to cell
76:33 cell results in the group of cells simultaneously. Ok? Now, there
76:40 actual potential in cardiac cells I just want to get into it just right
76:43 . Ok. So with that in , everything we talked up to this
76:47 will be on the exam when we in on Tuesday. I'm just introducing
76:51 the idea of muscles for the next . So zam, if you haven't
76:57 up yet will be next Thursday you meet here. Yes, sir.
77:01 . Yeah. Oh, wrong There you go. Yeah. Got
77:10 question about it or anything. You're . OK. Uh No,
77:17 no, no. So this from to about there is the refractory
77:24 OK. Right. So go deep repo hyper and there you go.
77:32 then you'd say right about here, relative. It's hard to write like
77:39 relative and this is absolute. I . Thank you. You're welcome.
77:48 in regards
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