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BIOL 2301 Human Anatomy & Physiology I - BIOL2301_lecture09_0616
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00:01 All right. So we get to about our decision to procrastinate. Let's
00:07 if it was worth the effort. right, what we're gonna do today
00:11 we are going to be diving deep how neurons work. What uh what
00:17 of electrical potentials are taking place um the stuff like I said yesterday was
00:25 when we look at this stuff, lot of this is not stuff that
00:28 can visualize, you have to have meters to measure things and you're trying
00:31 imagine the movement of ions which are really perceivable. I mean, can
00:36 picture an ion moving? It's, not something that we think about,
00:41 ? So there's a little difficulty in only in that sense, but in
00:45 of principles, understanding these principles are help us understand not only how the
00:50 system and how the musculature works, it will give us a real understanding
00:54 what cells actually do and how they're to manage um to create these
01:01 to allow them to do things, ? And so what we're gonna do
01:04 we're gonna start here with some principles we've already kind of discussed, you
01:08 , and we're gonna try to put into context so that we can understand
01:12 changes that are gonna take place. gonna see some mathematical stuff. You
01:16 not have to do math on my . Ok. So, just
01:21 But seeing how the relationship between two , uh, might be makes it
01:26 little bit helpful to understand, what's actually going on and then what
01:31 gonna do is we're gonna look at potentials and action potentials and what they
01:34 and, and what, what they're . And then finally, we're gonna
01:37 at how the neuron actually functions and we're gonna talk kind of like wrap
01:43 up around there. All right, the neuron. So it's gonna feel
01:46 it's kind of disjointed, but it's connected together. All right. So
01:49 starting point here is we talked about . We said that cells have a
01:54 membrane, that plasma membrane is impermeable things that are charged ions are the
01:59 that are charged. Um And so order for ions to move back and
02:03 , they're going to use channels or pumps to allow for the movement
02:06 these ions. The second thing we've talked about is we said there is
02:10 uneven distribution here. We can see showing those un even distributions. You
02:15 that versus that, that versus you can see those numbers are not
02:18 same ergo, they're different. And knowing what you know about how
02:22 when things are different, what do want to do they want to
02:26 Then it starts with e and with equilibrium. All right. But when
02:31 have an impermeable or a semi permeable that disallows the movement of ions,
02:36 don't have the ability to bring these things together. So that means there's
02:40 potential for these things to move and time you see the hear the word
02:44 , that means there's a potential All right. Now, this unequal
02:49 leads to these unique concentration gradients. what they're gonna do is they're going
02:54 move from an area of high concentration an area of low concentration. Should
02:58 be a channel or a pump to for that to happen? Now,
03:02 , pumps move things in the direction they don't want to go,
03:04 move things or allow things to move the direction they do want to
03:08 right? So there's a real simple heather that you need to understand.
03:12 if these things are gonna move, there is a channel to allow them
03:15 move, that's great. But the the difference between the two sides,
03:20 greater the flux, the greater the at which things are gonna travel.
03:24 this should make sense to you. , if you get on a skateboard
03:26 Houston, are you gonna move If you stand on a skateboard?
03:32 it's flat, there's equilibrium, But if I put a little bit
03:37 a slope, will you start If I make the slope steeper,
03:42 , faster, faster, right. that's the way you need to think
03:46 this. So for example, here going to see a very, very
03:49 movement. This would probably be even and small. But don't worry about
03:52 speeds for these particular things. That's important for us. But the idea
03:55 that we're creating these gradients and these are going to result in quicker or
04:03 movement. And of course, I to push the button. All
04:08 with that in mind, we talked channels, right. So we said
04:12 channels are those membrane proteins that allow move back and forth across a great
04:17 across the membrane that doesn't allow It's passive. All you gotta do
04:21 open it up. Each of these are going to be selected to what
04:25 them to pass through them. So potassium channel specific to potassium or sodium
04:30 specific to sodiums, a cat ion is specific to ions that are positively
04:35 and ion channels are specific to negatively ions, right? So they can
04:41 less specific, but there's still a to them. The two channels that
04:47 going to be most interested in are are referred to as gated channels and
04:51 channels. The difference between these two very small, right? They're both
04:57 , right. They both have some of door to them, right.
05:00 the gate channels exist in either an or a closed state. And this
05:06 is what allows for an ion to through or no. So when it's
05:09 , ions pass through, when it , ions can't pass through, so
05:12 go back to the impermeable state, leak channel says exactly what it
05:17 It's a type of gated channel, a voltage gated channel and that voltage
05:22 caused the channel to remain in the state. And so if it's in
05:27 open state, ions can pass through they can leak through the plasma
05:32 that's where it gets its name All right. So they are a
05:36 that never closes, or at least the state that we find them,
05:40 mostly open all the time. That's other way to think about it.
05:44 it's unregulated. All right. So can imagine they're always in this state
05:51 and what we're gonna be talking we're gonna be focused on two of
05:55 gated channels. All right. Remember talk, there's more than these two
05:59 of channels out there. Um But specifically going to be talking about the
06:03 gated channel, which is the easy . It's basically, I have a
06:07 key. I put the chemical key the chemical uh uh lock and that
06:12 the door to open. And so can flow through and then after a
06:15 of time, the gates shut and throws out the key, right?
06:20 that's kind of the lion gated These can be found all over the
06:23 . They can be found on the of the cell at the plastic membrane
06:26 be found inside cells. They can the ligand can act from the
06:32 it can act from the inside. just, there's a variety of different
06:35 of, of these channels. But key thing to understand here is that
06:40 have some sort of chemical that binds the channel that causes it to open
06:43 to close because it's typically we're going think about it in this sense where
06:47 bind and you open, but you actually have the reverse. But it's
06:51 what you're looking at here. The gated channel is the one that's conceptually
06:56 little bit more difficult to understand. like, well, I have this
07:00 up of ions, the ions on side are attracted to each other,
07:04 they can't get near each other. what they do is they accumulate and
07:09 you have a, an accumulation of specific type of charge that causes or
07:15 with that channel to cause it to or to close. And so in
07:20 particular case, we have, they're saying it's high positive out here,
07:24 negative or low positive. And now opened the channel because we changed the
07:31 . And so the channel opens up the charges have changed around it.
07:35 the channel has changed its shape. what we say is that in a
07:40 gated channel, the surrounding charge affects opening and the closing of the
07:48 Now, these two types of channels the most common types of channels we
07:51 to deal with. And when we're about neurons and we're talking about
07:56 these are the things that we're going see most active in these types of
08:04 . Now, there are some general that you have to tattoo to your
08:07 . All right, these four ions you see up here, potassium,
08:12 , chlorine and calcium are the big that are, are involved in the
08:17 activation of neurons and the activation of . Now, these aren't the only
08:23 , but these are the ones that the biggest effect on how a neuron
08:27 or how a muscle fires. And fact, the ones that are most
08:31 are the two on the top and are just kind of there and we'll
08:34 them pop up every now and So that's why we can start paying
08:37 to them. All right. So you understand the relationship of sodium and
08:41 to, to each other and into cell, then you're pretty much good
08:45 good to go. But in these are the rules and you can
08:48 of, again, here's the numbers you want to see numbers so that
08:51 can visually understand the differences is typically we look at a cell, we'll
08:56 potassium on the inside of the significantly greater than the potassium on the
09:01 of the cell. So if that's case, then potassium is always trying
09:05 move out of the cell trying to back outside the cell so they can
09:10 equilibrium. All right. And if you need to see that number
09:14 and 40 versus five, you can if I've got 100 and 40 over
09:18 and five over there, I'm trying go down to the five. All
09:21 , with regard to sodium, it's opposite. The concentration of sodium outside
09:24 cell is significantly greater than the concentration sodium on the inside. So sodium
09:29 always trying to go into the All right, and these are passive
09:34 , right? We're just moving down concentration gradients. With regard to
09:39 there is a greater concentration of chlorine the outside versus inside. So chlorine
09:43 to move into the cells and with to the calcium, it's the same
09:47 , there's more calcium outside the cells it's inside the cells. So calcium
09:50 trying to move into the cells. , if you understand these two,
09:54 probably good to go. But these pop up like I said. So
09:57 got to remember these, these are that is just something you have to
10:02 , memorize, memorize and you carry you for the rest of your
10:05 right? It's kind of like people the tattoo of caffeine on their
10:09 just get tattoo potassium and sodium and movement. Now, here's something you
10:17 already understand. All right, these ions that have charges to them.
10:23 so while we can look at concentration to determine the direction things want to
10:28 , we also need to take into when we look at an ion,
10:31 charge charges are important. And you understand the relationship between charges. If
10:36 have two positive charges, are they to each other or do they repel
10:39 other? They repel what about two charges? Yeah. And then we
10:43 down to the positive negative charge because don't care what the ion is.
10:47 they attracted to each other? All right. And so these simple
10:53 that you have learned from, I know how long ago are applicable here
10:58 well. All right. While we this uneven distribution of ions across the
11:03 , there's also an uneven distribution of . We refer to this as an
11:08 gradient. If the number of ions different, that's a concentration gradient.
11:13 the charges are different, that's an gradient. Now, this can be
11:19 difference in the number of charges. if I have five sodium on the
11:22 of the cell and one sodium on inside of the cell. That's a
11:25 of four charges, we just call inside of the cell negative because it's
11:30 than the outside. All right, just a, it's a frame of
11:35 , right? So very often we're gonna be looking at the number of
11:39 , but it could be also the in the number of opposite charges,
11:43 . So I could have five sodiums the outside of the cells and five
11:47 on the inside of the cell. that's a difference in terms of
11:51 right? That's a they're attracted to other. So that electrical gradient refers
11:58 both of these types of differences. of course, ions are gonna move
12:03 the towards their opposite charge. if the ions are capable of passing
12:11 the membrane, right? In other , if the membrane is permeable to
12:13 , they will then go and travel first down their concentration gradient. But
12:20 charge also will have an effect on movement. So for example, if
12:25 have a lot of positive charges over and I have very few positive charges
12:29 there, I'm gonna move this But what I've done is when I've
12:33 , I've moved that charge. And now the electrical gradient has changed and
12:38 going to be a point where I not have reached equilibrium with regard to
12:42 , but I may have reached equilibrium regard to charge. And so the
12:46 eye on that moves is now attracted move the opposite direction because that imbalance
12:52 electrical charges has an effect. And we have this, we'll normally see
12:58 the electrochemical gradient, the two things , they move in opposite directions.
13:05 you might have an electrical attraction one , but you're having a chemical traction
13:08 the other direction. And so there's balance or an equilibrium between the electrical
13:14 and the concentration gradients. OK. , I see the furrow brows because
13:20 like, well, now, wait second, I'm, I'm not quite
13:22 what you're saying here. All So let's do something. That's kind
13:26 simple. All right. I'm gonna the next slide. Yeah. Is
13:29 do this. All right, I you to picture a party. All
13:34 , where it's an equal number of and an equal number of girls.
13:37 yes, I'm going to use the relationship to just demonstrate this.
13:43 All right. If you have five and five girls, everyone has a
13:47 . Did you ever go to parties this? No, you guys are
13:50 different generation. I keep forgetting, ? But if there's 45 girls over
13:55 and there's five guys over here and a dance, everyone wants to kind
13:58 dance, but everyone's kind of But what's gonna happen is, is
14:01 gonna slowly move towards each other, ? But there's gonna be a point
14:05 when you move over here, There's gonna be an imbalance in terms
14:09 these things. So you're gonna kind move the opposite direction. That was
14:12 really bad example. So I've got come back to the story and it
14:15 make sense when I come to this , how do I put this?
14:25 gonna try to set this up for guys. All right, this is
14:29 story I tell all the time. it'll make more sense this way.
14:35 are not a lot of schools in , in the city of Houston where
14:37 have two high schools next to each . All right. But there are
14:41 couple right? If you go um River Oaks, you have uh Lamar
14:47 School that sits right next to Episcopal School. If you go into um
14:56 in our school district or our, competition district when kids competition. But
15:00 two high schools that are literally side side. And you can imagine in
15:03 schools that you have couples, When you went to a school where
15:07 couples. Yeah, I, I , I need confirmation here.
15:12 I need to know that you guys some point are gonna reproduce because if
15:16 not gonna reproduce, we're, we've got to just stop what we're
15:18 about. We gotta get to the stuff in A MP two because it's
15:22 one generation. All it takes one to stop breeding and it wipes out
15:26 entire. So All right. So can imagine for example, couples get
15:32 , right? So sodium and they're a couple, they like each
15:36 positive charge and negative charge they get , they go the googly eyes,
15:39 walk around each other to go to together, they put their hands in
15:42 pockets, you know the couple I'm about, right? You've seen
15:45 they're annoying, right? And then can imagine at say this is Lamar
15:50 we're just gonna use this as a . You can imagine this is a
15:52 couple. Just ignore that this is sort of, you know, you
15:57 , polyamorous thing. That's not, shooting for here. What we have
16:00 we have another couple there, there's couple. All right. So you
16:03 potassium and it's attracted to these negatively anionic proteins. All right. So
16:09 all doing the googly eyes and stuff that. But you can imagine also
16:12 these schools and this is quite frequent there aren't couples, right? But
16:17 people who aren't couples, they want be couples, don't they? And
16:21 they're walking around the school and they're sad all the time. Right.
16:26 you agree with that? Right. so we have them in both
16:29 See, there's, there's that sad , there's over here and let's imagine
16:33 instead of eating lunch in the you can eat anywhere on campus.
16:37 . And so you go out of school and between Lamar and between Episcopal
16:42 school there is a chain link fence the two schools and you can go
16:47 and here you are, you're outside the couples, they're gonna do what
16:49 do. They go and sit in . They make googly eyes and smoochy
16:53 and stuff like that. But the sacks, the lonely ones, they
16:58 out there a little lonely lunch. know, the little brown bag and
17:01 like, oh woe is me and walk outside and they see across that
17:06 link fence that there's someone they're attracted . All right, that negative charge
17:14 attracted to that positive charge, isn't ? And what does that negative charge
17:19 ? It moves to the fence and positive charge on the other side of
17:28 fence looks over the brown bag is longer the sole thing that's keeping it
17:35 . It comes up to the fence the other side, they look at
17:40 other through the chain link fence, they're not couples yet. Why there's
17:46 chain link fence in the way. right. Now, what we have
17:51 in this situation is what's going on every single solitary cell ions are gonna
17:57 to move across that, that fence attracted. There's gonna be a point
18:03 the movement across is going to be , which is why I was trying
18:07 get out with the electrical gradient. every time a potassium goes across
18:11 you're moving down the concentration gradient. every time that potassium leaves, you're
18:16 behind a negative charge, right? you're, you're following your heart as
18:23 potassium to move down your concentration But you're leaving behind your partner,
18:29 negative charge. And there's gonna be point where, well, I wanna
18:33 hang out with my, my, friends, I'm positively, I
18:37 I'm a, I'm a potassium. need to balance things out. But
18:40 , that negative charge over there is attractive. So I'm just gonna go
18:43 the other direction. All right, what I was talking about. The
18:47 and the, and the, and uh chemical gradients having an effect that
18:53 in the opposite direction. Every time positive bion moves, it leaves behind
18:57 negative charge. It may not be actual ion, but it will be
19:01 absence of that positive charge. in this situation, this is what
19:06 cell is doing. All right. what we now have is we have
19:10 difference in charge aligning up, notice a positive or negative come together and
19:14 neutralize each other out. So they have an effect on the difference in
19:19 when they're paired up. But when all alone, we can see here
19:23 we have a high concentration of positive over here, ignoring all the
19:29 we have a bunch of negative charges have not paired up. And so
19:34 what we have is we have a in charge, the difference between this
19:38 and that side is the membrane potential these could get together except what's in
19:44 way the plasma membrane, right? they could, but they can't,
19:52 couple stuck on either side of the , they can't get together. How
19:56 we get them together? What what would be the one thing we
19:58 do to get them together? What you think at a gate? Let's
20:04 a gate. Oh We can open the gate, flip the gate and
20:06 what's gonna happen if true love will and they come together and they meet
20:10 and everything is hunky dory and life good. If I add a gate
20:16 can flow through now, each of gates are gonna be specific as we
20:20 described, it can be a potassium . And if potassium then the potassium
20:23 gonna flow out right now. When flows out, I'm I'm using
20:28 it flows out. There are no there's very few negative charges which you
20:30 match up. So we're probably not see a lot of potassium. But
20:33 we put up in sodium gate, , sodium has a bunch of negative
20:37 , it could go to you see difference here. So the difference in
20:43 , as I mentioned is the membrane , the membrane itself and this is
20:46 point I need to make does not a charge, the membrane is the
20:51 that's in the interfering. All the charge is found on either side
20:55 every cell that we look at, cell in your body has this thing
20:59 on. There are extra ions on inside and extra ions on the
21:03 They're unmatched. They have this membrane , but it's only the cells that
21:08 open and close channels or gates that allow for these ions to move.
21:15 these are the ones that have electrical . So your neurons and your muscles
21:20 the ones that take advantage of Whereas your other cells in your bodies
21:24 take advantage of this condition. It has this imbalance. All right.
21:31 this is what electrical signaling comes from the movement of these ions, these
21:37 uh materials. Now we can measure with a volt meter. So basically
21:42 put a probe inside the cell and put a probe outside the cell and
21:45 can measure the difference in charge between two sides. All right. That
21:50 how we determine the differences between And it's just you're measuring those charges
21:56 this is gonna be measured in mills it's really the the measure of the
22:01 ability to do work. Have you wondered? I mean, again,
22:05 know that not all of you are up to the higher I say the
22:09 but like to like medical school or school and stuff like that, the
22:13 for, for nursing school is right? But if you're going to
22:16 A school you have to take don't you? All right. Have
22:19 noticed that? You ever wondered So that you understand this, that's
22:23 only reason that didn't know how high get the poles when you do an
22:27 V poll because you understand the pull gravity and stuff like that.
22:34 what we're talking about here is work doing work. All right. So
22:40 measuring potential energy. Now, there's lot of other stuff up here that
22:46 don't think is particularly relevant, you how to read the vault meter and
22:49 like that. I just used to about it. Here's the math,
22:55 is what the physicists or not, physiologists get real excited about this and
22:59 , let's figure out what this all and how we can do mathematics to
23:03 and describe what's going on, not important for you all, but I'll
23:10 you why we look at this when talk about a single ion, what
23:16 can do is we can look at concentration inside the cell and outside the
23:19 like we've done. All right. that's what we see here. All
23:24 . And what we can do is can determine the point at which that
23:29 gradient and that, that electrical gradient and we can find that point and
23:35 point is where where that those two do where the movement of that ion
23:41 . In other words, it's equal both directions, right? So the
23:45 is if I pop over here, like, no, no,
23:48 I'm too attracted. I, I go to this site. We
23:51 no, I, I wanna So now you're fighting between concentration
23:55 So that movement is equal in both . So we can do the math
23:59 this equation, it's called the Nernst . And it helps us to determine
24:04 the equilibrium potential for a particular ion be found. And you can see
24:10 equation here here is the I it the equilibrium of the ion. So
24:13 pick your ion of choice, So it could be potassium is equal
24:16 this, this constant, that constant the valence. Do you remember what
24:22 is? It's the charge? So calcium has a valence of two plus
24:27 has a valence of one since we're with potassium and sodium, they both
24:31 one. So the math gets Remember logs. Do you remember having
24:35 do logs? Right. So you logs, but this is the important
24:39 right here. The concentration of the versus the inside. If this number
24:43 greater than that number, then the of that number is gonna be
24:47 right? Do you remember? And the this number is greater than that
24:50 , then the log becomes negative, ? Do you remember that what?
24:56 way back when I can't remember when first teach you that like ninth grade
25:01 , some time, a long time . So calculating out the number isn't
25:06 important but understanding the the direction and effect that these have. So for
25:14 , potassium has a very, very concentration inside the cell, but a
25:19 low concentration outside the cell. So log of that number is going to
25:23 negative. So this whole number becomes . So the equilibrium potential that we
25:29 is gonna say that when we measure inside of the cell is gonna have
25:35 negative value. In other words, gonna have a negative number to
25:40 And when we calculate it out, it comes out to is about negative
25:44 millivolts. All right. And so difference on the inside to the outside
25:50 negative 90. And that means on inside of the cell is gonna have
25:54 greater pole. And so as potassium out, once you get to negative
26:00 the difference between the two sides and potassium doesn't stop moving. All
26:05 So that's where the difference is where goes out and says no,
26:08 no, I'm now at negative 91 need to go back inside the
26:12 That's the calculation. And you can this for each of the different
26:16 the concentration of sodium is greater on outside than on the inside. So
26:20 , this number becomes positive. So equilibrium potential for sodium is a positive
26:26 . It's actually plus 60 millivolts. so sodium is going to move into
26:29 cell until the difference on the And the outside is plus 60 millivolts
26:35 60 minus 90 is very different And you can do this for
26:38 you can do this for chlorine, can do this for every ion that
26:42 . And you can see where that is where that one ion stops moving
26:48 you're probably sitting there. And so , why should I care about
26:53 Well, each of these values has impact on the total equilibrium potential of
27:02 cell. In other words, what the membrane potential? Where do the
27:06 finally create a balance based upon each their own individual movements? Well,
27:14 have this horrible equation called the Goldman Kaz equation. This is what it
27:19 like. It's basically the nernst but we're using something different. But
27:23 we're also having to take into consideration the permeability of the membrane for the
27:30 ion that you're looking at. You're see I see the look on your
27:34 . You're going, oh my Do I have to actually know this
27:36 ? No, no, I'm not about you being able to do the
27:41 . I want you to understand what's measured here. So again, what
27:44 we looking at? We're looking at , right? But we're also looking
27:48 per abilities. Well, what does mean? What does permeability mean?
27:52 , permeability means the number of gates you have available for this particular
27:59 All right. So for example, and if you look over here,
28:03 is a terrible way to do So you should never have a fraction
28:06 here. The lowest number should be one that you're comparing to. But
28:11 this to this, there's a difference 25 right? This is their 25
28:17 difference between 250.4 and one, So four times 25 is 100
28:23 So there's 25 fold difference. That for every sodium channel you have,
28:28 are 25 potassium channels. So if were to ask the question, which
28:34 moves more frequently across the membrane, one would you say it is
28:39 So you might expect that potassium would the greatest effect on the membrane
28:45 right? So its equilibrium potential has most profound point where the cell finds
28:52 at rest. Now, if you're envisioning this, we're gonna use the
28:56 dumb example I have of this. all been to a football game.
29:01 . OK. Yes, I wanna sure. So if we, if
29:04 haven't been to a football game, isn't gonna make a lot of
29:07 You might have to think about a , right? So half time comes
29:12 around, it's bathroom time. All . Guys, when we go to
29:17 bathroom, I'm talking to the guys . How long does it take us
29:19 get in and out of the bathroom we're at a football game? 30
29:25 ? Ladies, how long does it to get you in and out of
29:26 bathroom? Hour? Hour and a ? Yeah, that's, that's,
29:31 why now I'm gonna, I'm gonna away the guy's secrets so that you
29:34 why? All right, in the restroom, we have troughs,
29:40 When we go in there, we we have this wall of troughs and
29:44 walk in, we don't make eye to anybody. We don't talk to
29:47 . This is not the place where make friends. We walk up to
29:51 trough, we go shoulder to we do our business, we take
29:54 step back and then we wash our and we get out of there.
29:58 right. Now, ladies, when go to the restroom, you have
30:03 , you cannot put three ladies in stall right? There is one toilet
30:08 each of those stalls and I'm just about whatever business you're doing in
30:11 right? So that means a stall to become available and there is less
30:18 with regard to the number of people can use a restroom at any given
30:22 , even though the same space is used, right? Because women's restroom
30:26 not bigger than a men's restroom or versa. The difference is the trough
30:32 the stall. And so we can it out in and out in 30
30:36 . You guys have to wait hours hours and hours. It's like the
30:42 is over and there's still a line to get in from half time,
30:47 ? That's like what permeability is? . So, permeability here has a
30:54 effect on the membrane potential, the the permeability ion, the greater its
31:01 potential has on moving the needle. other words, how much effect that
31:08 or how much effect that ion has the balance between the two sides of
31:12 membrane. And we can calculate it using this horrible equation here. But
31:16 don't have to do that. I'm trying to point out it has to
31:19 with this permeability. And so here can kind of see this thing.
31:26 this right here, this line represents , the what we're saying, the
31:31 types of potentials that we're looking at membrane potential of a neuron is around
31:36 70 millivolts. So what that means that when the inside of the cell
31:42 more negative than the outside of the ? All right, that's, that's
31:46 negative part. So there's more positive on the outside than there is on
31:50 inside. And the cell is in at minus 70 millivolts. And the
31:56 it's at minus 70 millivolts is because equilibrium potential of potassium has the greatest
32:04 on that membrane potential. We said about minus 90. So what it
32:09 instead of being here at perfect balance you say, oh it's zero,
32:12 know, no. What we've done we're saying potassium is leaking out of
32:15 cell as fast as it can leaving negative ions. And so what it's
32:20 is it's dragging the membrane potential way this direction, but it doesn't drag
32:25 all the way to minus 90 because have sodium that wants to go into
32:30 cell. Sodium wants to go into cell and until it reaches a balance
32:34 around plus 60 but there's only one channel for every 25 potassium channels.
32:41 25 go out, one goes in so that drags it away a little
32:46 from this direction and then you can in chlorine, you can put in
32:49 and they would also have an effect you get to this value. And
32:53 calculated it all from that equation right . We're not worried about that.
32:58 just want you to understand where the comes from. Why do I care
33:02 the number comes from? Because when was sitting in your seats and I
33:05 a professor up here saying the because was German, the uh a membrane
33:12 was minus 70. And then we talking about something else. And
33:15 what, why, why do I about this number? What, why
33:19 this important. And I want you understand why it's important because this is
33:23 cell at rest. And if I activity to occur, if I want
33:29 make the neuron do something, I to change permeability. Because when I
33:35 permeability, then this membrane potential starts . And that is when this thing
33:43 sliding, that's going to affect the of these ions, they're either gonna
33:48 flowing or they're gonna flow more. the only way that's gonna happen is
33:51 I affect permeability. So here we in this room, we have two
33:55 . How would I affect permeability in room? If I had to affect
33:59 per I gotta go open the right? Or I have to put
34:04 doors in. All right. So cell at rest has in theory gated
34:13 and these gated channels just need to open and when they open, that's
34:17 change the ratio that we're seeing here now. It's 1 to 25
34:26 Maybe if I open up some more channels, I will now make the
34:29 closer to 1 to 1 which would things this way and that's going to
34:34 the movement of the ions, more will be able to get in and
34:39 sodium gets in things happen. So we look at a cell, this
34:49 what what I've been describing to you far. All right, we got
34:52 these positive charges hanging out all these charges hanging out, they're all attracted
34:56 each other trying to, trying to together these things right here. The
35:00 minus is a protein. It's a that is negatively charged, it cannot
35:05 the cell, it is left OK? So things that, that
35:10 charge can never leave. All So it's just stuck there. So
35:13 only way we can balance out that charge is the potassium stays there or
35:17 goes in now, potassium wants to . So screw potassium. So all
35:22 got to do is we want to in sodium to help balance out those
35:25 charges. That's why sodium wants to in that minus 70 that we describe
35:30 is insufficient to counterbalance that concentration gradient that uh a potassium, right.
35:36 this is right right over here. potassium is always going to be leaving
35:40 to get to minus 90 but sodium always going into the cell trying to
35:45 to plus 65 or 61. And we have pumps, sodium potassium
35:53 So if all things being equal, like wait, wait, wait,
35:55 , no, I want the sodium the cell and I want potassium inside
35:58 cell. So we have pumps that no, no, you just
36:00 I'm gonna put you right back where put you the first time. And
36:04 now at the expense of energy A P, I'm constantly putting sodium out
36:09 the cell. I'm constant putting potassium the cell. So I have a
36:13 movement of material always, always, going on with every cell. And
36:21 I'm doing that, I'm stuck at point. Unless I open or close
36:26 , they're all moving potassium. Yeah, potassium and sodium are moving
36:30 they're moving through these leak channels that already there. That's what that permeability
36:35 is the result of. So we this, this equilibrium this at minus
36:42 because of the natural movement of sodium out of cell, the natural movement
36:48 sodium into the cell at different rates of the presence of different channels.
36:53 then this thing coming along saying, , eventually you would reach equilibrium,
36:59 know, a concentration equilibrium, but not going to allow that to
37:02 I'm going to pump you right back where you started from. I'm
37:06 I'm going to fix the leak as were. So with that in
37:12 well, I'm gonna stop here for second and if I just said something
37:15 is horribly confusing to you, and recognize that this is confusing material.
37:21 I have I clarified it a little . Do you need a little bit
37:25 explanation? Are there questions about And it's OK to say, I
37:30 , I'm not getting this. All . I don't want you to walk
37:33 going well, I I'll figure it on my own because it's not material
37:37 you can just kind of get, might have to watch like six youtube
37:42 and they may explain it even worse me. So questions, do you
37:49 what you're trying to understand here? of membrane potential potential is important because
37:55 gonna use it. That's the key to walk away from. All
37:58 And where do the potentials come So potassium are the big boys and
38:03 other ones have effects, but we're gonna worry about them right now.
38:10 . Ok. Yes. Ok. . Negative. Mhm. Right.
38:27 , so again, remember the idea whenever you have an electrical potential,
38:32 difference, right? That's a a in charge and the difference in charge
38:37 be one of two things if all have are positive ions, it's the
38:41 in the number of ions on either of that membrane. So if I
38:44 20 positive ions over here and one here, that is a difference in
38:50 . And we just say, you that difference is 20 to 1.
38:53 that's a negative charge relative to that there. All right. The other
38:58 we can do it is we can at the number of charges positive versus
39:02 , right? So if I have positive charges and 20 negative charges,
39:07 , you'd say, well, they're in terms of the number of
39:10 Yes, but these are all So we have a great difference between
39:14 two sides, right? And those things want to get together. But
39:18 charges aren't the only thing that we're about. We're concerned about concentration.
39:22 concentrations and electric and electrical gradients or gradients, electrical gradients are two things
39:28 we have to consider with every single that we look at, right.
39:32 when a potassium leaves the cell, leaving behind that negative charge it was
39:38 to right. What it's doing right is it's favoring the movement along its
39:44 gradient. But in doing so it a negative gradient, an electrical gradient
39:49 the opposite direction. Does that kind make sense so far? Yeah.
39:57 , no, no, it's it's, it passively moves through that
40:01 . All right. So it it's not gonna have a carrier,
40:04 just gonna move, you know, the laws of diffusion. So remember
40:07 we talk about diffusion and all those things, well, so the don't
40:12 about the, the channel itself right , just presume that there's something that
40:15 us to move back and forth. just so there's a, there's a
40:17 there but it's open. All So that's all we're concerned about right
40:21 . All right. So when that is moving, it's, it's,
40:25 has to consider two things, I'm moving down my concentration gradient,
40:31 I might be pulled back by my gradients, right? That's, that's
40:36 idea of those because those two forces in opposite directions of each other.
40:40 every time a potassium moves out of cell, it leaves behind a negative
40:45 to which it was attracted. But concentration gradient may be greater than the
40:50 gradient. But over time, the gradient will get bigger and bigger as
40:54 concentration gradient gets smaller and smaller. eventually there's going to be a point
40:58 those two things cross, right. that crossing point is that equilibrium potential
41:04 potassium for whatever it is that you're at. All right. So that's
41:09 thing that we're kind of describing here we can calculate that value out to
41:14 out what effect it has on a because it's a real number. You
41:17 , when you go out and measure cell and say here it has a
41:20 potential. The membrane potential is this that value comes from something. And
41:26 those differences in the concentrations of the and the difference in the electric,
41:32 electrical potential or the electrical gradients of side of that cell, both the
41:37 and the outside. So when we're at a cell with the resting membrane
41:42 , that's really what we're measuring is is the potential for these ions to
41:46 rolling out or rolling into the And that number, whether it's negative
41:51 positive tells you the direction which the are gonna go. So when you
41:56 it negative, then the ions are be trying to move into the
42:00 When it's positive, the ions are try to be moving out of the
42:03 to reach the membrane potential of the . So again, I understand this
42:11 a difficult concept, but we're gonna it put in practice and I hope
42:17 understand why we talk about it because less important for you to know all
42:22 little tiny details about this. It's important to understand that it exists and
42:27 it has an impact on the Now, what we're doing is we're
42:30 shift gears for a second and we're start talking about the neuron. All
42:35 , because the neuron is the first where we're gonna see it the first
42:39 cell. All right. And we're talk about the neuron because it helps
42:43 understand not only the neuron, but also will help us understand what's going
42:47 in muscles a little bit later. right. So this is an excitable
42:50 . What that means is is that uses the movement of ions to create
42:54 impulses that it can then use to long distance signals. All right.
43:00 , really, these cells talk to other like. So here's the end
43:04 the neuron, it uses a chemical talk from one cell to the
43:07 But this portion right here, this where the electrical activity is done allows
43:15 to send a very, very quick over a very long distance because the
43:19 is actually fairly long. Just to you an example, the nerves that
43:26 there innervating your big toe to tell muscles to contract are as long as
43:32 legs, they start in your spinal and actually they start really high up
43:37 your spinal cord ends right about And then they travel down your back
43:41 that operator for amen and they keep all the way down as a bundle
43:45 they get down to your big So that cell, that one cell
43:48 almost, well, however long that from my, from there to
43:52 What was that? 2.5 ft, ft. I don't know, something
43:56 that. That's a long cell. if I was relying on chemicals or
44:02 blood stream to send that chemical along way, it would take a really
44:06 time. And so an electrical signal me to create a very, very
44:11 signal to move that long distance. , how that signal is done is
44:17 be done through the presence of channels pumps to move ions back and forth
44:22 they're gonna be found along the length that cell. All right. And
44:29 , at the very end, that's you're going to use that neurotransmitter.
44:31 the chemical signal. So the two talk to each other with a
44:35 But to release a neurotransmitter, what really doing is I'm telling one part
44:39 the cell to tell another part of cell what to do. So that's
44:43 the electrical signal comes along. neurons have extreme longevity. Basically,
44:49 neurons that you're born with are the that you end up with. There's
44:53 that are being produced over time as develop and stuff like that. But
44:58 , once you hit adulthood, you're not going to be making any new
45:02 . All right, they're ayo, they do not divide and there's very
45:06 exceptions to that rule. And they're , very uh they have a high
45:09 of metabolism. They're highly metabolic, they consume most of the oxygen and
45:14 of the glucose in your body. the reason you eat and, and
45:19 and stuff is because these cells need fuel to power what they do now
45:24 terms of structure, uh we have names because the neurologists back in the
45:29 , you know, we didn't understand all cells have the same stuff.
45:31 they gave cells parts, different It was really weird. So these
45:36 just words, you have to start . All right, the cytoplasm of
45:39 neuron is called a Pericar on. right. So that's just the para
45:43 on. All right. It's found the SOMA. The SOMA is the
45:48 body, the portion of the cell all the stuff is. All
45:52 So here this is where all the making machine and this is where the
45:57 partum is. This is where the this is where mitochondria are located.
46:01 these things are primarily found in the within the para caron, the ribosomes
46:07 stained uh with a unique stain. at the time, they had all
46:11 little tiny dots and the guy who got to name it, they call
46:13 bodies but the ribosomes. So when see those names, you just have
46:19 apply it to the right word, ? It's, that's, that's all
46:21 is to this. Now, when look at this, you can see
46:24 we have all these extensions. All , these processes have names. We
46:29 dendrites and axons. The dendrites typically to the receiving side of the
46:37 All right, the axon is the side. So when a neuron is
46:43 information, it's receiving it from its for the most part and then it
46:47 send a signal along the length of axon. Now, neurons are typically
46:52 together. So when you're looking in central nervous system, which we haven't
46:57 today, and we won't describe until little bit later when we get into
47:00 nervous system in the central nervous these clusters of these cell bodies together
47:06 called nuclei, not to be confused nucleus, right? It's the same
47:11 word, right. But it it's saying a bunch of cell bodies found
47:16 the central nervous system when you're in peripheral nervous system, we give it
47:22 different name, we call it All right. So it's just a
47:28 to tell the reader where part of system, what part of the body
47:31 actually looking. All right. when you have a series of axons
47:38 together, those processes, these axons together form what is called a
47:46 All right. So from the you'll see tracks of axons. All
47:52 , that's the language. And then bunch of tracks put together collectively are
47:58 to as a nerve. So this a nerve, a bunch of these
48:04 together form a nerve. And I've kind of said this in terms of
48:11 dendrites and the axons, the dendrites be producing what are called graded
48:16 They're basically conveying a message received on external side of the cell to the
48:22 to the region here called the Hi, that's kind of the receptive
48:27 of the cell. If we produce strong enough signal, the axon hili
48:32 produce a um a signal that then along the length of the axon.
48:39 we're going to get graded potential. these are membrane potential changes that are
48:43 that are big enough will produce a enough signal to produce what is called
48:49 action potential that will travel along the of the axon. So this is
48:53 axon hili, that's where that The axon is the length the axon
48:57 actually divide along its length. These called collaterals. So it could be
49:02 collateral axon. And then what you is you travel down to the
49:06 these are called the telo indri. right, there's a little tiny branches
49:11 at the very, very end of tele, that's the axon terminal.
49:16 you can see here this is the terminal or what may be called sometimes
49:20 synaptic knob. All right. So are terms that you will see over
49:26 over and over again. So it invaluable that you learn what these terms
49:32 . OK. So I'm I'm just so make sure you don't gloss over
49:39 the axon hili is. I may you a question, what is the
49:42 of the neuron from which action potentials ? The answer is the axon
49:48 what is the portion of the neuron which an a an action potential
49:54 That would be the axon? So it's, it's simple language that
50:00 just uh uh using here. All . So the axon is the conducting
50:07 of the neuron. It generates the impulse here at the Axon Hillock and
50:11 are transmitting the ax potential away from cell body to the terminal ends.
50:17 the cell body, the SOMA is all the structure is. So basically
50:24 niel bodies, everything that's making all proteins, all the things that are
50:28 , all the things that cells The axon has none of that.
50:33 sole purpose is the signaling or sending signal. All right, it has
50:40 cytoplasm. We call the cytoplasm the peron as well as the
50:45 Down here, we refer to the material of the cytoplasm. We call
50:48 the axoplasm because reasons. OK. then we give the plasma membrane a
50:58 name as well. We call it axolemma. All right. So you
51:02 see the term plasma lima plasma lemma refers to the plasma membrane people who
51:07 working on axons. Well, this a special cell. So it gets
51:10 axolemma. So what we're looking at is an example of a neuron.
51:19 right, and you can see there's sum over there on the left moving
51:23 direction is the axon poorly drawn because want to look at stuff on the
51:28 and down here, this is the terminal. And what we can see
51:32 is that materials move through the axon the cyto skeletons that we described
51:40 And we can move things in one two directions. If we're moving away
51:44 the cell body towards a terminal, refer to that as anterograde. And
51:51 if we're moving back towards the cell , we call that retrograde, the
51:57 is taking place over there. But need to sometimes send materials back to
52:01 processed, to be destroyed, to repaired, so on and so
52:05 So you're gonna use these two Now, there are two different rates
52:10 two different speeds at which things are travel. We have what is called
52:13 axonal transport. Here, we're gonna using microtubules, right? You can
52:17 the microtubules and you're gonna use energy T P and motor proteins. You
52:21 see a little motor proteins are all the planes. And what we're doing
52:24 we're carrying things in either direction, interior grade and retrograde to move things
52:30 through that cell. Because these can very, very long processes and the
52:36 at which this is about 400 millimeters day. That's roughly four centimeters.
52:43 that long. So, is that ? No, that's 40 centimeters
52:51 40 centimeters. Is that right? don't know, think about a
52:59 What's a meter? Meters? three , right? So a meter is
53:07 millimeters. So 40% of that per . Ok. So this is how
53:15 get all the neurotransmitters and all the materials down to the Axon terminal.
53:19 that's where we're gonna store things up it's time to release them. All
53:24 . So that's one way slow. transport is much, much slower.
53:27 can see it's very, very This is like you getting on a
53:31 river in an inner tube. If ever get on tubing, you
53:35 you get in the tube, you there, have your cold drink,
53:41 you cold drink, but have your drink and you sit there in the
53:44 and what do you do? look rapids. All right, very
53:53 . This only moves in the interior direction. So very, very
53:57 That way, this is a result the axoplasm flow. So the fluid
54:02 the materials in there, you're not the highways, you're taking your sweet
54:07 to get there. Now, a , this is again, this is
54:17 definition slide. A membrane has different states. In third grade, you
54:26 exposed to the number line. Do remember the number line? The dreaded
54:30 line, you had a zero and you had the line with the arrow
54:34 then you had to like draw the and the arrow and try to figure
54:37 , do you remember that stuff? ? Ok. So if you had
54:40 in the middle, you had negative one direction and you had positive in
54:44 other direction, right? Ok. is a state where you lack
54:51 right? You are neutral, you're positive nor are you negative?
54:57 So if you were to measure a and you'd see no difference between either
55:02 , you would say that you are , see it's not up there
55:07 it's not up there. All But the moment you step off,
55:11 other words, the moment there's any of difference between the two sides of
55:15 membrane, you are now polarized. if this is negative and that's
55:20 If I step over here, I'm polarized, I'm negatively polarized.
55:27 If I come back to zero, rep polarized. All right, I
55:35 back to actually ignore that last If I'm at zero and I go
55:39 direction, I'm now positively polarized. . Now, we already know that
55:45 cells are in a polarized state. use the example of the neuron.
55:50 number I gave you for a neuron , what number do you remember?
55:59 70? OK, good. So long as you're getting in that
56:02 all right. So most of the in the body are gonna be found
56:05 a polarized state way over here at 70. All right. Now,
56:12 that cell moves towards zero, I'm less polarized. So if I become
56:20 polarized, I have b polarized, I return back to my original polarized
56:27 , I have re polarized. And if I become more polarized, I
56:34 going to hyperpolarize and then if I back to my original polarized state,
56:40 re polarizing once again. OK. here I'm at minus 70. But
56:46 if I have a weird cell that's over here at plus 35. What
56:51 am I? Am I beginning in 35 millivolts? I am. Am
56:57 polarized? Am I non polarized? I rep polarizing? I am
57:05 And if I become more positive, have I happened to me? I've
57:12 more. So it is hyper polarized then I returned back to plus
57:18 And so I've gone from my hyper state back to my original state.
57:21 have I done? I've rep And then if I become less
57:26 I am depolarizing. Notice what depolarizing doing is I'm moving towards zero.
57:33 right, I'm becoming less polarized than was before. All right, if
57:39 hyper polarizing, I'm becoming more So I'm moving away from zero.
57:45 , having said that this is gonna weird, right? So that's the
57:49 that is normally used. But what gonna see, we're gonna see sometimes
57:53 gonna see cells go from minus So I'm way over here at minus
57:57 and they're gonna depolarize. So if depolarize which direction do I go to
58:02 ? And then I'm gonna hit So here's zero and I keep
58:07 I don't change the terminology. I'm depolarizing. OK? And then when
58:11 return back, it's gonna be re once again. OK. So it's
58:16 the original movement. You don't, don't say, oh well, I've
58:20 zero. So now I'm hyper It's just the same thing. All
58:25 . Now, generally speaking, when see these terms and what they're doing
58:28 what we're applying them for. If is a net inward flow of positive
58:36 , then we call that depolarization. ? Well, because we're starting at
58:40 70 we're making the inside less negative it was we're becoming more positive.
58:45 why it's a depolarization. And then opposite is true. If I have
58:48 outward flow of positive ions, that the inside of the cell is getting
58:53 and more negative because the positive ions leaving. So I am hyper
58:59 All right, that language is what gonna be using when we talk about
59:04 next two things which are the greatest and the action potentials. And this
59:09 the thing that throws everybody is and not trying to say that to make
59:12 go oh no, this is It's just again, when you're sitting
59:15 going, I wanna see things moving the body, you're not gonna see
59:18 oh there's a wave of stuff going . It's not easy. All
59:23 So a change in the membrane potential what gives rise to these electrical
59:28 So when ions move, this is we get the electrical signals. All
59:32 . So anything that can change the permeability or anything that alters the ion
59:38 on the two sides of the So I'm gonna give you an example
59:41 the latter one which we don't ever to happen. All right is if
59:45 take a whole bunch of salt and it into your bloodstream, that's going
59:49 change the concentration of salts outside of cells and that will have an effect
59:55 the membrane potential, I'm going since that never really happens. We're
59:59 gonna give anyone a bolus of I'll tell you an example of something
60:02 did happen once. It's a horrible . You ready for the horrible
60:05 Yeah. All right. So do remember what you guys are really
60:08 So you may actually remember, do remember when the Wii actually came
60:12 You remember that? It was, was a weird Christmas because it was
60:15 the same year that the Xbox came and like the P S two,
60:19 think, I can't remember which. everyone was focused in on the Xbox
60:23 the P S two and the Nintendo the Wii and everyone was like,
60:27 the Wii it's cheaper by 100 bucks , oh, and you couldn't find
60:30 anywhere in stores. It was the item for Christmas that year. All
60:35 . And so like, people would a hold of these things. And
60:38 there was like a radio station in that had like, you know,
60:41 contest and we, you know how have those contests. Like you put
60:44 hand on the, let's like the Beast contest where you put your hand
60:47 the car and the last person takes hands off, you know, gets
60:50 keep the car or whatever. It the same sort of thing. It
60:52 like, what we're gonna do is gonna give you guys a whole bunch
60:55 water to drink. And then the person to go to the bathroom.
60:59 the wii right. So it's p the wii is how I always think
61:02 it. Right. He had all of people doing this and there was
61:06 woman in the contest who was smaller the rest, you know,
61:09 by size. So, like four something and they had, she had
61:12 drink the same amount of water that else did. And so it was
61:16 everyone drank like a gallon of water whatever it is, they had a
61:19 amount of time to do it. then after a couple of minutes,
61:22 killed over and she went into convulsions then she ultimately died, right?
61:26 she did was drink water. why did that happen? All
61:30 it has to do with this latter . So when you put water in
61:34 body, it goes into your digestive from the digestive system, it goes
61:37 into the bloodstream. All right. then it's gonna distribute throughout your whole
61:41 . But by volume, a gallon water is quite a bit of
61:47 And especially when you're smaller, you're in a greater volume by, by
61:53 relative to someone who say six ft . All right. It's kind of
61:58 ladies, when you go out and alcohol, you can't drink as much
62:01 your buddies do your guy friends because , they have more muscle mass and
62:06 , they have a couple of pounds you and probably a couple of inches
62:09 you. So they have a greater to for which that alcohol can go
62:13 . All right. And the same happened to her, the water she
62:16 in her body diluted out all the in her body. And so all
62:20 systems that are dependent upon electrical breathing and heart rate and everything else
62:27 haywire because you change the concentrations. so she basically drowned in the water
62:35 she drank. That doesn't mean don't too fast. It's just, you
62:40 , be cognitive, you're gonna feel it with. So if you get
62:43 contest to P four, we you know, just understand, you're
62:49 at me like this is horrid told it was a sad story. All
62:54 . So when we're talking about membrane change, there's two ways that we
62:58 do, we can do what is a greater potential or an action
63:00 So we're coming to these definitions what is the greater potential? This
63:03 a short distance signal within the All right. And a potential is
63:08 long distance signal within the cell. right. So here we're going to
63:12 try to make a signal go from to here. Whereas with an a
63:16 , it's going to have a much longer distance it can travel.
63:18 here is an example of the greater you can see here here is our
63:23 cell body right here. You can I have my axon terminal, this
63:28 going to be the SOMA there is point of contact where we can uh
63:34 a ligand be released. So that's going on. The ligand is coming
63:37 and causing that channel to open. when that channel opens, this is
63:42 to be a cat ion channel. a sodium channel. And what happens
63:45 sodium comes into the cell. And that sodium looking for just a negative
63:50 ? Right? It's like, you , so so right here where there's
63:55 to be where this channel is that is coming in and it can come
63:59 and find its partner. It's like and then the next sodium comes in
64:02 to travel a little bit further and little bit further and a little bit
64:04 . But what's happening is you're seeing of ions. So the greatest amount
64:08 flow of ions is here where the opened up and as they start partnering
64:12 with a negative ion, there's fewer fewer ions to travel further and further
64:17 . That kind of makes sense. when we measured, if we were
64:20 put a volt meter along different points that cell, we could actually measure
64:25 flow of these ions. So at point of stimulus, that's gonna be
64:30 greatest amount of flow. And as move further and further away, the
64:33 of flow gets less and less and . Now, this flow of ions
64:39 this graded potential, right? It's signal or a change in the membrane
64:46 because remember what's the membrane potential? difference in charge on either side of
64:50 membrane? So mo most ions there's the greatest amount of change.
64:55 out here there's less change, less , even less change, fewer
64:59 no change out here. All I see that for, for a
65:04 . There's a f fa brow. ever thrown a rock into a still
65:10 ? All right. Take a little . Don't, not, not a
65:13 rock. I know that's what you do. But start with the
65:16 If you take that little pebble and throw it in the middle of the
65:19 , what you're gonna see where it ? You're gonna see a, you'll
65:21 a little tiny splash, right? where the highest activity is.
65:26 And then what's gonna happen where that went into the pond? You'll see
65:29 ripple and that ripple then moves away the point of origin in all
65:35 doesn't it? Yeah. But if pool or that pond was infinite in
65:42 , would that ripple eventually die Yeah. Now the reason it dies
65:46 the pool is because of the resistance the water. The reason it dies
65:50 is because the ions pair up and their partner. Remember they're all staring
65:56 , staring at their partner across the , we opened up the gate,
65:59 walked in, they found their they can go sit down and make
66:03 eyes with each other. All the greater potential represents the movement of
66:08 ions. And it's that difference in that we use that movement that makes
66:16 signal. All right. So what looking at in this particular model is
66:21 depolarization of it. This is the common, but it's not the only
66:25 . And this depolarization is occurring in very specific location. It's a very
66:30 location and it's moving outward from the of stimulation. All right.
66:38 there it is. Greater potentials have characteristics. First magnitude and duration,
66:50 ? What is magnitude? How big are? All right. The bigger
66:54 stimulus, the bigger the potential took little tiny pebble threw in the pond
66:59 a little tiny splash. The ripple like this, go take a £20
67:03 walk up to the pond, throw into the pond. What are you
67:06 get a little tiny splash, massive splash differences in magnitude result in
67:15 magnitudes and greater potential. So the the stimulus, the greater the
67:20 So this was showing you small, medium, medium, big, big
67:27 maybe it's the opposite. So this the stimulus, that's the actual potential
67:32 there duration, the longer I stimulate cell, the longer the greater potential
67:39 . Ok. So as duration is , so is the duration of the
67:44 potential. In other words, if keep stimulating that channel, it stays
67:48 . And so ions continue to flow and keep doing the same thing.
67:54 that's a characteristic of all the greater , they have duration of magnitude are
67:58 upon the duration of magnitude of the . All right, we've already talked
68:04 this greater potentials decrease in intensity of distance that they travel. All
68:08 And the reason for that is because ions are kind of matching are not
68:11 of matching up, are matching up the opposite charge. The other thing
68:16 greater potential is that they're very short , meaning that what happens is is
68:21 I create the event and then the is kind of a rippling outward and
68:25 dies off. It doesn't stay around a long period of time. It
68:29 dependent upon the duration of the but most stimuli is very, very
68:33 . So your grade potentials are So what you'll see are things like
68:37 where it's like here's my stimulus, get something like up down and that's
68:41 . But if I kept this going , then this thing would stay on
68:44 a long period of time. But great potential for the most part are
68:48 lived graded potentials, we said are to decrease. Oh there's the same
68:55 , but this is just showing you different. So here we can see
68:58 is the stimulation taking place if you and measure it, look at how
69:02 that graded potential is very, very . But notice it goes in both
69:06 . It's not just going towards the , it's going towards the end of
69:08 dendrite, but nothing happens at the of the dendrite. It's just gonna
69:11 and disappear up there. But as comes down, we see the further
69:15 is the smaller and smaller it And that's true in both directions.
69:21 it's like that ripple in a Now, we have different types of
69:27 potentials depending upon where you are. this is where we get to play
69:30 soup time, we get to learn abbreviations. All right, the first
69:36 of, of graded potential is called long word words, excitatory postsynaptic
69:46 A lot of unpack there, excitatory it's stimulating the cell, which cell
69:52 it stimulating the one on the opposite of the synapse. All right,
69:55 got to pause here because we're going come to this definition here. So
69:59 is our interaction between the cell. our synaptic knob. This is the
70:02 cell. So this is the sending , sending cell receiving cell. This
70:08 between the two is referred to as synapse. This is the presynaptic cell
70:13 it's the sending cell. This is postsynaptic cell. So the excitatory postsynaptic
70:20 is occurring in the receiving cell, postsynaptic cell. What type of
70:26 Am I creating excitatory? I'm causing here and it's just say it's a
70:35 . So we abbreviated E P S cry posting after potential because writing that
70:41 would suck, right? You're kind like, I don't know,
70:48 here, we can see this The cell at rest, we get
70:52 stimulation, the cell depolarizes and it back to rest. That is the
70:58 P S P. All right. E P S P occurs as a
71:04 of the opening of a sodium So sodium rushes in the cell causing
71:09 depolarization. Right? IP S If E S E P S P
71:18 excitatory, IP S P is Yeah. All right, you're gonna
71:23 getting this now. All right. again, here at the synapse,
71:26 in the postsynaptic cell. So if E P S P causes depolarization,
71:30 IP S P causes hyper polarization. right, I move away from
71:40 I move the opposite direction. So the same sort of thing. And
71:45 what I'm doing and an E P P is opening up sodium channels,
71:48 most common thing that happens is I up potassium channels, but I can
71:52 have chlorine channels. And what's gonna is when I open up a potassium
71:56 , potassium leaves the cell which causes cell to become more and more negative
72:02 the inside. That's why you see . So E P S P excitatory
72:09 IP S P inhibitory negative charge de or sorry, hyper polarization, primarily
72:16 , but chlorine can do the same . All right, the truth is
72:25 a greater potential can't do much of on its own. All right,
72:28 just a small depolarization or small hyper . And if you look at the
72:34 body of a neuron, you'll notice it's not just 1 to 1
72:37 like in all the pictures that we've showed you, it's more like
72:40 there's like one cell and like, don't know, several synapses, several
72:45 or thousands of synapses on that postsynaptic . So this cell is receiving thousands
72:54 thousands of signals at the same So it's, it's receiving these signals
72:59 it's creating E P SPS, it's other signals and it's creating IP
73:03 So when we take the sum of the E P SPS and the IP
73:06 together, we call that the GPS , the grand postsynaptic potential. And
73:13 the sum of the changes inside that that determine whether or not we're going
73:19 produce a response in that cell. , just to make this a little
73:24 simple for you. This is harder harder because I first off, I
73:28 never interested in social media. I I had a Facebook page that I
73:32 for like eight days and then I looked at it ever again, finally
73:37 a couple of years ago just because , but I, I don't know
73:41 about social media. But one of things I do know is that you
73:43 to be able to do polls. I don't know if in your current
73:46 media, do you get to do ? All right. So you get
73:49 ask you and your 4000 favorite friends . Like, for example, let's
73:53 you're dating someone. You're like, don't know if I should break up
73:56 this person. And so you just your 4000 closest friends say,
73:59 should I break up with this And then they all get to
74:02 It's a, it's a yes or vote, right? So if you
74:05 create a yes, that would be or I don't know which one's positive
74:08 this case, right? One's one's negative. Yes or no,
74:13 ? And so your 4000 friends all to send you a signal roughly at
74:17 same time. And then you are to respond based upon that signal,
74:22 ? That's what a grand postsynaptic potential for the cell. It's saying stimulate
74:26 or, or prevent me from being and then whatever all the sum of
74:31 those signals are, that's gonna be I respond. Now, the response
74:40 meeting a certain threshold. In other , when I change the membrane
74:45 can you tell I really want to here, the response in the cell
74:53 when the change in membrane potential reaches certain level, a certain height,
74:57 we call a threshold. Now, nuance to that. But just for
75:03 now, just say when the membrane depolarizes enough that threshold being met,
75:08 when I'm gonna get a response. this membrane potential response is a result
75:13 the sum of all the E P and the IP SPS. The thing
75:17 , is that E P P S the IP SPS come not all at
75:21 same time, they might be uh might, some might come at the
75:24 time, some might come uh at times or from multiple sources. And
75:30 what we do is we look at , these different signals and we
75:34 how, how do we put them ? So if I have two or
75:42 signals coming at the same time, we do is refer to that as
75:47 summation. All right. So here is an example and you can imagine
75:52 , if we have all these uh these uh synapses and I have say
75:59 one and this one acting at the time. So each one of them
76:03 their own like. So you can there's their E P SPS. I'm
76:07 talking E P SPS right now. one fires, it produces this E
76:10 S P, another one fires that an E P S P of the
76:13 size, right? So if they at the same time, those two
76:18 are additive. So you don't get tiny thing. What you do is
76:21 get one thing that gets bigger and we've reached this threshold. So we're
76:25 get the signal in that postsynaptic All right. So this would be
76:32 example of uh well, here's So I should be looking at
76:36 not this. So here's spatial. here one by itself, the other
76:39 by itself, but the two at same time, they stack enough to
76:42 threshold. So that gives me that . All right. So spatial is
76:47 two things are occurring at the same , here's an easy way to do
76:51 , right? You and I were clap. So if I clap,
76:54 you clap and we clap at the time, was that a little bit
76:59 ? Let's how about if we have person clap you clap to one,
77:02 gonna do this. 123, try again. 123. Was that
77:07 Yeah. How about four of 123, all right. Six of
77:12 . How about all of us that than the first one? So you
77:17 see spatial summation results in the larger . And so you get large GP
77:22 here we're reaching threshold so we can summation. All right. So that'd
77:27 spatial summation. Temporal summation. I give you a good example of
77:30 But here what we have is we a single axon resulting, you
77:35 creating a signal that causes E P in greater periods of time. In
77:39 words, faster and faster and closer together. So what's happening
77:43 as you can see here, I a period of excitation, I get
77:45 period of relaxation. You see So that's the up and that's the
77:49 , right? If I cause stimulation , it causes to go up.
77:53 before it starts coming down, I the cell again, I can make
77:56 go up again. That would be . So what I'm doing is I'm
78:01 the amount of time in between that E P S P. So if
78:06 using the clapping as an example and a bad one. If it be
78:09 here, there's one, there's So you can hear that space in
78:13 the two, right? But what I start? There's still too much
78:18 in between. But if I'm going fast that it becomes one sound,
78:23 ? That would be the example like , it's a success of firing so
78:28 the cell doesn't ever get a moment rest so that I I reach threshold
78:32 that way. And then the term is when I'm using E P SPS
78:36 IP SPS together. So here you see the E P S P here
78:39 the IP S P because they have same magnitude. Uh the two things
78:44 together basically results in staying at rest , keep in mind E P SPS
78:49 IP SPS will have different magnitudes. . So I could have one that
78:53 a magnitude of 51 that has a of 10 together. They equal
78:57 Right? I could have one that's five, one that's negative 10.
79:00 I end up with a grand poten postp potential of minus five. They're
79:05 upon their magnitudes. We're just using examples to understand simple concepts.
79:13 Cancellations when they cancel each other All right. So graded potentials have
79:24 . They have duration, they, diminish over time. They have short
79:30 . You can change the strength based the the degree of stimulation. You
79:34 change the duration based on the duration the stimulus action potential are very,
79:39 different. Right here, an action is going to be generated at the
79:45 hili or the initial segment. That's other term for it. All
79:49 And what it's gonna do is once create an action potential, then it
79:53 be propagated at the same uh magnitude the entire length of that action
80:01 All right. So in other the length of the axon, all
80:05 , they're very brief, they're very . There are massive changes in the
80:10 potential. They're roughly 100 millivolts in neuron. So you go from minus
80:14 to plus 30 and once you create , it will stay that way the
80:18 time. Now, when you look this, what you're looking at,
80:23 have to kind of look at the . A lot of people see the
80:25 and go, OK. It's kind a weird thing. This is time
80:29 the bottom, this is magnitude over . OK. So what we're looking
80:36 is we're looking at a single point the cell and we're asking the
80:40 what's going on at this point over in the cell, the membrane potential
80:45 changing it, nothing's going on, going on. And then all of
80:48 sudden it rises, it goes up high and then it comes right back
80:52 again and then it comes to rest then resets itself. But all I'm
80:56 is I'm looking at a single point that cell when that happens. All
81:02 , when this occurs, if we at different points on the cell,
81:06 would see that this wave is maintained a non detrimental fashion, meaning it
81:12 change in terms of its size or . Now me saying that doesn't give
81:19 a good visual representation of what this like. So I've come up with
81:24 way to demonstrate this to you. you guys know how to do the
81:28 ? All right, we're gonna do wave. Now, most of you
81:31 over there. So you're just gonna to bear with me. All
81:35 this is a lot more fun when have 450 people in the large
81:39 right? You don't need to stand , you just need to do your
81:42 . Ok? So we're gonna do wave and we're gonna start over here
81:46 no one is too cool for We'll keep doing it until everyone does
81:51 . Ok? You're like, damn . And I'm watching, I always
81:55 the people. I know who doesn't it. You ready? Here we
82:02 . Uh we, we failed over . OK. We're gonna try this
82:05 . All right, ready. Here go. See, it's not as
82:10 when there's only 40 students in the , but one more time because it's
82:13 fun. Who, who, who the wave at college? I
82:18 in, in school, it's We did the wave. Now,
82:23 I'm gonna do is I'm gonna initiate wave and I'm gonna say pause and
82:26 you are in the wave, I you to pause. You ready?
82:30 pause. All right. Keep your where you are. So your hands
82:35 up or going down, going What are your hands doing? What
82:39 your hands doing? What are your doing? And they're going down?
82:46 right. Keep your hands where you . This is an exercise to make
82:52 brain think about what's going on up . Remember? This is a time
82:57 , right? So where are you the graph? You're over here?
83:04 me when. No, you're I know. I, I wanna
83:10 where do you think you are? me when about right there? You'll
83:19 right. Where are you? That way, that way.
83:28 Right there. What about you? are you? You're about right there
83:31 where are you? You're right over . Where are you over there?
83:37 why was, why it's kind of to think about this is you remember
83:40 said your hands are coming down You are, you all are,
83:43 can put your hands down now. right. So here you are,
83:46 at rest, right? You're waiting turn and my hands go up,
83:50 reach their zenith and then I'm putting hands down right now. What I
83:58 you pause is because remember we are a snapshot of what's happening at a
84:05 point on the membrane. You are parts of the membrane. We're gonna
84:08 the, the, the um wave more time and we're gonna focus
84:13 Everyone watch her but we're gonna everyone's gonna do the wave. All
84:17 . And I want you to watch we are now watching the graph over
84:22 . OK. Ready go. You ? So she was down here,
84:29 waited her turn, then her hands all the way up and then they
84:32 all the way back down again. that's what happened there. But we
84:35 it, we could count what we're . One Mississippi two Mississippi and we
84:39 see there's a time frame as which happening. So with an action
84:46 that's what's going along the membrane of cell. It's starting at the Axon
84:52 . It gets initiated because we reach threshold and once we reach that
84:58 we're gonna create the action potential. has what we call the all or
85:02 response, right? It happens or doesn't. All right. This is
85:07 I make people uncomfortable. It's like , it's like pregnancy. You're either
85:14 virgin or you're not, you're either or you're not, you cannot be
85:18 , you cannot be, I'm kind right. There is no kind of
85:23 potential. You are either not an potential, you don't reach the threshold
85:28 you reach the threshold and you become action potential. All right. So
85:35 potentials have an all or none They always move in this fashion over
85:42 . It's not gonna be plus It is gonna be plus 100.
85:46 right, just as it was over when it started, right. We
85:50 up, we go down, we this entire movement along the entire length
85:54 the cell over which the actual potential travels. Now, the reason this
85:58 is because we're now dealing not with gated channels like we would see with
86:02 graded potential. Instead we're using voltage channels and that's what all these next
86:09 actually talk about. All right. when we get a GPS P that
86:14 G F P S P it initiated a result of opening up a channel
86:19 these postsynaptic potentials, degraded potentials if travel far enough and get to the
86:25 . Hi, what they'll start doing they'll start opening or causing the opening
86:28 voltage gated channels. The big players in this this event, this ax
86:34 is the voltage gated sodium and potassium . All right. The depolarizing event
86:43 you're going to see here is a of the voltage gated sodium channels.
86:46 then this rep polarizing event here is result of the potassium channels opening plus
86:51 resetting of and the closing of the channels. If you're wondering why we
86:57 all these color codes and stuff right . It is because the author is
87:02 to show you points of interest changes are taking place on the graph.
87:07 don't know if you've ever been taught to read a graph. Have you
87:10 been taught how to read a So when you look at a
87:13 you look for where do changes take ? I'm flat. Now I'm starting
87:18 curve upwards. So there's a change occurs there. Something happens here where
87:22 no longer cur curving slowly. Now going through a steep incline and then
87:26 get up here to the top. I'm changing direction. Now I'm going
87:30 down here. Oh, the speed which I'm coming down changes. All
87:35 . And then what we're gonna see is really the change that takes place
87:38 . They're just kind of marking off . OK? And so what we're
87:43 is we're saying different things are happening these different points. If I know
87:46 these different things are, I can the action potential. I've told you
87:52 . Vulture gated channels are involved. have the Vulture gated sodium channel.
87:55 gated sodium channel is the weird voltage gated channels. Sodium channels have
88:00 gates. They have an activation gate they have an inactivation gate. That
88:04 weird two gates. In the same , think of my arms as being
88:08 activation gate and an inactivation gate I at rest with my activation gate
88:15 Nothing can go through me. But I have a change in the membrane
88:19 that causes the activation gate to open can now flow through me. But
88:25 happens is is that as ions as gate opens, that causes the other
88:30 to start closing just slower. And I'm in a closed state. So
88:35 have three states that I exist in gates. Three states closed, capable
88:39 opening, open closed, have to reset. All right, I cannot
88:46 back through the open state. I to go all the way back around
88:49 the closed, capable of opening All right. So that's the I
88:56 123, I have to go all way back around to this state.
89:00 this gate can be opened up OK. I can't go back through
89:03 middle. There are no shortcuts. right. The Vulture gated sodium channel
89:09 important because it is what defines how actual potential works. Why we get
89:14 particular thing? Vated potassium channel is lot easier. Just one gate.
89:19 you have two states open, be easy. All right, pretty
89:24 . Yeah. OK. So we're walk through all these different states.
89:28 goodness, we have 20 minutes. see if we can get through all
89:31 stuff because there's quite a bit All right, first up when I
89:35 at rest. All right, what have is I have both voltage gated
89:39 closed, no sodium and no potassium through those channels. But instead I
89:43 leak channels, leak channels are So remember I'm dominated primarily by potassium
89:48 channels. So I've got more potassium out the cell than I have sodium
89:51 into the cell. So my membrane at minus 70. This is
89:56 OK. Still have my pumps pumping on keeping things in that perfect
90:02 All right. So here I am here at rest. Second state triggering
90:08 takes place. So somehow I get signal that arrives to the Axon
90:13 So if I get a strong grade potential that membrane potential change causes or
90:19 reaches the Axon Hili in the Axon , I have a high concentration of
90:24 gated sodium channels, what opens up voltage gated channel, the change in
90:32 potential or if you want to be simple voltage. OK. So a
90:36 potential is a change in voltage. if I get a greater potential that
90:42 at the axon heli that's strong it's gonna cause the opening of some
90:47 channels, these voltage gated sodium So if I open up a voltage
90:51 sodium channel, sodium comes into the , which causes a change in the
90:55 potential. If I have a change the membrane potential, what's going to
91:00 to vol gated channels they're gonna So sodium comes into the cell which
91:07 voltage gated channels to open, which sodium to come in. Do you
91:10 what I have here? I got positive feedback loop. So if I
91:13 get a signal to the axon I can begin a positive feedback loop
91:19 results in more and more and more more voltage gated sodium channels opening.
91:24 right. So this is that loop we're trying to describe. So what
91:28 see here is I see a slight which results in a bigger depolarization which
91:33 in a bigger depolarization which results in bigger depolarization, which results in a
91:37 to the point where all the voltage sodium channels are now open. When
91:42 happens, I've reached the threshold. really what the threshold is. We
91:47 measure it. And So that's how usually do. They talk about the
91:50 itself. So when you get to 55 millivolts, you've reached the
91:54 you've reached the threshold. Uh It's the opposite. When I've opened up
91:58 the channels, the flow of sodium the cell is much, much greater
92:02 the flow of potassium out of It's at minus 55. And now
92:06 have no choice but sodium just rushes the cell. And that's what we're
92:11 here. We're seeing this massive depolarization it. So here what I've done
92:16 I've taken that activation gate for all voltage gated sodium channels in the
92:20 Hi and I've opened them all Sodium is rushing into the cell,
92:24 the amount of potassium leaving the That's why we see this massive
92:28 But we said something about these voltage channels are weird. They have the
92:33 gate. The activation gates opens and but slower. The the inactivation gates
92:41 . All right. And if you up here at the top, what
92:46 ? The flow of ions is pretty until you get right up here and
92:49 the flow of ions changes direction, it kind of it slows down?
92:56 what you're witnessing there is the closing the voltage gated sodium channels.
93:01 if nothing else were to happen, slowly but surely we would return back
93:06 rest. But we don't just slowly surely turn back to rest.
93:12 what we see is we see us return the opposite direction. So here
93:22 getting a positive feedback at threshold, get massive influx of sodium and then
93:29 get to the peak and then at that point, that's when we
93:32 all the fated sodium channels. But we're gonna see this massive repolarization
93:41 Now remember we have this other this voltage gated potassium channel. Do
93:46 have a friend that you can tell joke to? And they just kind
93:49 stare at you for a second before get it. You know your slow
93:54 , you know, you let them around with you because they're fun but
93:57 don't, they don't always get things the time. It takes them a
94:00 . Do you know that person? what voltage gated potassium channels is a
94:05 front here. All right, the that causes the opening of the voltage
94:09 sodium channels. The same trigger that up the voltage gated potassium channels,
94:14 just slower if this is the Remember this is time. If this
94:20 the point where all the Vulture gated channels open, that's the point where
94:24 Vulture gated potassium channels open. Same is slower. And so what happens
94:30 as you get that depolarization as a of sodium rushing in those gate slams
94:35 and then at the same time, the same point where the Vulture gated
94:38 channel finally opened. That's when he the joke. Oh yeah. And
94:44 so potassium starts rushing in or really , potassium rushes out, not rushes
94:51 . Sodium is rushing in. Potassium out. So now potassium rushes out
94:54 the cell and out it goes and gonna take a little bit of time
94:58 it to close up. And so what's happening here is we're actually over
95:03 because our slow friend is slow at everything down. Now, during the
95:09 period of time, we have to through that reactivation, right? So
95:14 we took the gates, we open up, we close them up in
95:16 in the sodium vulture gated sodium we have to go back and reset
95:20 back to the state. So that's what's going on also at the same
95:25 . So we're dominated by the opening the potassium vated potassium channel and they'll
95:32 a little bit extra time before they up. And here we are at
95:37 . Look what we've done. We're shooting that rest. So as as
95:42 rushes out of the cell, it's basically returning everything back towards
95:47 But because we slow things or because overshoot because it takes us a little
95:53 longer to close things out. This just trying to show you the states
95:57 the voltage gated channel so that you see what's going on. So here
96:01 are at rest. Here, we opening up the channel. So we're
96:04 up here, all the channels are and then right here during this
96:08 that's when the voltage gated sodium channel closed. Yes, ma'am.
96:21 No, but yeah, but you're gonna reach the action potential. So
96:25 action potential occurs once you get past what we call this threshold. So
96:30 you have a really small grade of , you might stimulate a couple of
96:36 of uh vated channels to open, you may not get enough to,
96:39 reach that threshold. So if you a strong enough signal, that's the
96:43 where you're getting to the point where the channels are opening, that's the
96:46 or none response. So that's a good point. A lot of people
96:50 of miss that, right. So we are, we say we are
96:54 that hyper polarized state. Like I , that's when we've overshot too much
96:58 is leaving the cell, but we those things shut and then they slowly
97:02 things will start moving back and forth on their equilibrium potential. So that
97:07 give us uh get us right back where we are at rest. And
97:11 to aid the whole process, we have that sodium potassium A T P
97:13 pump that says, hey, hey, all you sodium that went
97:16 the cell, you're supposed to go out of the cell, all the
97:19 , hey, you went in, back into the cell. So it's
97:22 things out. And I used a of hyperbole here when I use the
97:26 , you know, sodium and potassium in and out of the cell.
97:29 really talking about a couple of That's how big of AAA difference a
97:33 of ions can make. But I to use the hyperbole because it gives
97:38 , a real sense of movement, it? All right? So during
97:43 period of time, during this hyper state, we're still moving those sodium
97:48 back into the original configurations. You open them yet. They have to
97:52 back to that original configuration. We've seen this happen when we did the
97:58 , did the action did, did wave propagate itself appropriately in this
98:04 I mean, it wasn't great but it do so well. I
98:07 in the right way, in other , when you guys were coming
98:10 you guys were waiting to start, , right. Yeah. And then
98:14 they were already down, were you kind of at your peak?
98:19 So that propagation is how an action propagates along the cell basically along the
98:25 of the cell, you have these gated channels. And so in an
98:28 where the voltage gated sodium channels are , the areas to which you're moving
98:33 gates are closed. And as sodium into the cell, it's going to
98:38 those channels to open so that you getting the action potential moving forward and
98:45 just like the way that we did . All right. So it's a
98:49 opening and closing of voltage sodium voltage gated sodium channels. And it's
98:53 , the closing of the uh of sodium channel and the opening of the
98:57 gated potassium channel, then the closing the potassium channel and this is just
99:01 along the length of that axon from axon, he all the way down
99:05 the axon terminal and I just turned the light there go. All
99:12 Now we have what is uh in thing to prevent the actual potential from
99:17 backwards. It can only go one , it only moves forward. Notice
99:20 we started the wave, you didn't oh well, I need to go
99:23 this direction. You didn't start doing , it just went in one
99:26 And the reason for that is because have what is called a refractory
99:30 something that prevents the opening of those in the opposite direction, right.
99:35 that's where that voltage gated sodium channel that inactivation gate and prevents things from
99:40 in the backwards direction. We can at this and we can say,
99:45 , this refractory period which exists over period right here occurs because we have
99:51 region that we refer to as being , we can never ever,
99:56 ever ever get another a potential during same period of time. All
100:00 In other words, I can't open the sodium channels and then open them
100:05 more. Does that make sense? . So there's a period of time
100:11 I can't create an extra because there's else I can do it. It
100:15 is. And when those gates are , there's nothing I can do.
100:19 have to wait for them to I can't make a gate that doesn't
100:23 to open to open. So during absolute refracted refractory period, I cannot
100:30 another action potential. And what this , it creates a period of time
100:35 only one action potential occur. So when we looked at graded potentials,
100:40 we add graded potentials on top of other? Yeah, because there's nothing
100:45 them from doing so. But with potentials, we can't add action potentials
100:50 . You get one or you get . And that's it. It's a
100:54 binary. There's a period where you though get an action potential even though
101:00 not in a perfect state. And is the relative period. So I
101:03 you to consider yourself down here In this region of hyper polarization,
101:09 already started resetting my voltage gated sodium . So some of them have already
101:14 themselves so they could be open, I have to overcome the outflow of
101:23 , right. So over here, membrane potential is much, much lower
101:26 it is at rest. So if open up all my sodium channels I
101:30 not or the ones that are I may not be get to a
101:33 where I'm reaching that threshold. I to have a really strong stimulus to
101:37 me up to that point. So the relative period I'm dealing with some
101:44 inactivation, inactivated sodium gates, you , voltage gated sodium channels. And
101:49 got those potassium channels still open. I have to do a little bit
101:52 extra work to get me up to . All right, does that kind
101:57 make sense? But when that I could get another action potential
102:02 So the way you can think about is action potentials have a period of
102:07 where there's, there's rest in between . And so what that means is
102:11 the cells are signaling in a way I can speed up signaling, but
102:15 can't stack the signaling, I can down signaling that makes sense. But
102:21 idea is that I'm coding my signals the number of action potentials that I
102:30 . So the action potential can move and then the refractory period prevents the
102:38 one from stacking up directly behind Is really what this is trying to
102:42 you that allows for you to have period so that you can encode signals
102:49 the the number of action potentials that actually occurring during a given period of
103:05 . Speed of an a potential is upon two things. I'm speeding
103:08 You're gonna start hearing me talk like auctioneer. You ready if you think
103:12 been talking fast so far. I welcome you to speed though. All
103:16 , I want to deal with the of an, a potential two things
103:20 going to deal with that diameter and or not my is present diameter,
103:24 an easy thing. The fatter, signal, the faster things can
103:28 the smaller the neuron, the slower are going to go. But there's
103:32 limit to the size of a um a neuron. You can't keep making
103:37 neuron bigger and bigger and bigger. have a finite body. If I
103:39 a fatter neuron, I gotta get a bigger body. So now I'm
103:43 need a fatter neuron, which means bigger body. And you can see
103:46 a mouse trap problem, right? this is where myelin comes into
103:50 And what we're gonna do is we're take one of those glial cells in
103:54 or a neural side depending upon whether in the central nervous system or the
103:58 nervous system. And what you're gonna is you're gonna wrap that uh cell
104:03 the axon. And what that does it creates an environment where that portion
104:09 the axon doesn't interact with the surrounding . So it limits where action potentials
104:14 take place. All right. So is the myelin, the white
104:20 This is not a great picture. is a better one. So here
104:23 is the myelin, you can see little spaces in between that little space
104:27 between is called the node of And that node of Ranvier is where
104:32 action potential can take place. So a better view of this. You
104:36 see there's a little tiny space in , a little tiny space, a
104:38 tiny space, a little tiny So now when action potential occurring,
104:43 this serves as an insulation to prevent potentials. But the spaces between the
104:50 of Ranvier are close enough together. that when I'm stimulating here, I
104:54 stimulate the next area which can stimulate next area. This speeds up the
104:58 of transmission. Normally I'd get you walking in here. So you can
105:03 if I'm walking toe to heel, move slowly, right? But to
105:09 over that same distance, if I have a normal gate, I move
105:13 . And that's what the does, allows me to skip over portions of
105:17 axon so that the signal moves Be aware of which type of
105:23 all Goden sites are going to be the central nervous system. Neuroma sites
105:28 going to be in the peripheral nervous . So this leads us to two
105:33 types of propagation when I'm walking to hill. When I don't have my
105:38 , I'm doing contiguous. It sounds continuous. So you gotta imagine.
105:41 just stimulating the entire cell along the . If I'm doing saltatory, saltatory
105:47 to jump. All right. That's or something. I don't know if
105:51 might be Greek, but the idea I'm skipping over the areas of
105:56 So what is the myelin? It as insulation. It is not where
106:00 action potential is taking place, the potentials take place at the nodes of
106:05 beer between the myelin. All don't get the two things confused.
106:11 this is just trying to show you contiguous would look like that would be
106:15 . You could see us jumping from to point here. And again,
106:21 example, point to point. The thing that this does is that it
106:25 only does it allow the uh impulses travel faster, you use less
106:30 So anything in the body that causes energy that's like for the body last
106:38 bit deals with what happens. What we do with this action potential?
106:41 do we care? Remember the cells to each other through the chemicals?
106:45 , that action potential is taking a from the cell body along the length
106:49 the axon down to the axon And what it's going to do is
106:53 going to serve as a signal to the vesicles with the neurotransmitter to open
106:59 and release that neurotransmitter so that it then stimulate the next cell we're actually
107:04 right back to the graded potential because release of this neurotransmitter binds to a
107:09 on the next cell that causes the of sodium or in flow of
107:14 which results in a graded potential. do you see this kind of a
107:19 and egg thing? There are four here that are involved. So the
107:23 potential travels down. And so remember opening and closing voltage gated sodium potassium
107:28 . But when we get down to axon terminal, there's a new channel
107:31 . It's voltage gated. But now a calcium channel. When you get
107:35 that, you open up calcium flows calcium then serves as a signal.
107:40 you remember when we talked about the ? Remember we said calcium is
107:43 So calcium serves as a signal to up that vesicle that's lined up.
107:47 what happens is that the vesicle opens and it releases the neurotransmitter, the
107:52 flows into the synaptic cleft, which what this space is called. And
107:58 just flows by rule like like um through the rules of diffusion. And
108:03 as it goes across, it will or may not come into contact with
108:08 ligand or sorry with a channel, serves as that ligand which causes the
108:12 to open and whatever type of channel is, it will allow for the
108:16 or the outflow of an ion. it's, if it's a sodium
108:20 it's going to allow for the inflow an ion into that next cell causing
108:23 E P S P. If this is a potassium channel, it's going
108:27 cause the outflow of potassium, it's cause an IP S P. It
108:35 a little bit of time for this happen. So there's a synaptic
108:38 you know how long it's very, short. But the more cells you
108:43 in series like this, you can now how you can actually cause delays
108:48 these pathways. All right. So , they become additive over time.
108:58 know I'm getting close to the end . How far do I have?
109:03 many slides? Three? Thank All right. In terms of terminating
109:08 signal, any time we create a , we have to turn it
109:10 There are different mechanisms to which this . All right. So what I
109:16 to do this is the first one discovered it was enzymatic destruction. So
109:19 that synaptic cleft, you can imagine an enzyme that's there to that recognizes
109:23 destroys the neurotransmitter. So this one the first that one discovered. So
109:27 thought that this is how it So this is the example, you
109:29 not need to know these, these just examples. So for example,
109:33 with Aceto Cole, this is one the neurotransmitters. There was an enzyme
109:36 colon Aase that chewed up the acetic . And then that's how you kill
109:40 signal. Everyone said. All Now, we just got to start
109:42 for these enzymes. Turns out this the only one that does it this
109:46 . All right, the rest of use other things. Now, a
109:49 can diffuse away when it diffuses it can't bind to its receptor.
109:53 it doesn't cause an effect. diffusion is a, is a kind
109:56 default way of, of termination. right. But the other thing that
110:00 is once neurotransmitter is released, it be taken in by either the,
110:05 neuron that actually released it or it be taken up by other cells in
110:09 nearby area. When you take up neurotransmitter, you're removing it so that
110:13 can't interact. And then what you do is you can either recycle it
110:16 or destroy it or whatever. And what these other systems are trying to
110:20 you. And these are the basic of neurotransmitters and the neurons that are
110:24 used. And you'll notice that most them do exactly the same thing.
110:27 just taking it up, taking it , taking it up, taking it
110:30 . So that seems to be the common way to do so. But
110:34 thematic destruction, diffusion or I can it up either in the neuron itself
110:39 in the surrounding cells around it. are chemically signaling cells. But we
110:48 there and talk about electrical potentials all time. But I want you to
110:53 that ultimately, that the cell that's doing this electrical potential is releasing
110:57 chemical signal. These chemical signals are neurotransmitters. They're um a whole bunch
111:03 different types and they act in this fashion. So we saw here's my
111:08 , I'm releasing the chemical that go the next cell. There are hundreds
111:12 hundreds of neurotransmitters and they fall into these different types of categories.
111:18 The ones that are most important for to understand is first acetal colon,
111:23 going to see a sea of colon and over again. It was the
111:25 one discovered. Everyone thought, we don't know what neurotransmitters look
111:28 We want, we know if we this first one, that means we're
111:32 to be able to start discovering them because they're all gonna have the same
111:35 . Turns out aceta colon is, by itself, it's like all alone
111:38 it's all over the place. This the, this is the neurotransmitter that
111:42 use these a neurotransmitter that you're going see in the brain as well.
111:46 second group that you should probably be with is the amino acids.
111:51 glutamate, asperate, glycine are amino that you probably have heard of.
111:56 actually serve directly as a neurotransmitter and you can also take glutamate and modify
112:02 . And that's where you get we'll talk more about these a little
112:05 later in terms of uh which ones inhibitory and excitatory. And the last
112:10 are the monoamine. And I mentioned because you're gonna see these all the
112:13 . You've probably heard about them. guys heard of histamine before?
112:17 that antihistamine. Take my antihistamines, . Um, Serotonin. You've heard
112:22 serotonin? Yeah. Have you heard dopamine? Yeah. Have you heard
112:26 Epinephrine? If you haven't? You've of adrenaline? Yeah, that's
112:30 That's, it's close cousin. this group of mono means they take
112:34 amino acid and they modify it and how they get these. But you
112:37 see there's other types as well. mean, a T P uh there's
112:41 gasses, nitric oxide, for fats, there's proteins that can all
112:46 as neurotransmitters. All right. here's that list I just gave you
112:51 . Here's the acetycholine. There's the acids, glue. I, I
112:54 I would get to it. So is the excitatory one, glutamate and
112:57 tape. Those are the excitatory and Gaba is primarily inhibitory. So if
113:02 making a lot of, you can it inhibitory and then glycine is another
113:07 that's inhibitory. All right. So you know these two, then you
113:11 know those two. So just decide memorize one of them since glutamate is
113:16 . That's an easy one to It's like 90% of the synapses.
113:19 then again, we'll see these a bit later. But I want to
113:23 point out that you already know Um, and you should be familiar
113:28 them. This is my last isn't it? Yeah, I'm so
113:32 . It took you to how see if, when I slow
113:35 this is what happens I told you was gonna be a hard day.
113:37 last thing I want to just mention is that there are such things as
113:40 synapses. We're 99% of the things you're gonna be looking at are going
113:45 be chemical synapses. But there's also thing as an electrical synapse. There's
113:49 synaptic delay here, but you can't or change these. This is how
113:53 cells and smooth muscles work. They their uh signaling molecules through gap junctions
114:00 make the all, all the cells the same way. But it's the
114:04 thing as a chemical junction in the that you're using chemicals to make two
114:08 behave. The difference here is that not a chemical, it's an ion
114:13 instead of of causing action potentials, you're doing is you're creating greater potential
114:19 move from cell to cell to cell cell. All right. See,
114:26 we should have done this seven minutes . I'm so sorry. I kept
114:29 . If your T A gets mad you, tell him to F off
114:33 to call me. Maybe not. , but, but, but just
114:39 them we had to get through this thing. Remember, test is
114:43 Not Monday, you have the day , so, find a way to
114:46 . Ok. Yeah. Have a
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