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BIOL 3324 Human Physiology - BIOL3324_Lecture05b
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00:03 as promised. Here we are with part of lecture that I was not
00:07 to get during class time and really we did we were talking about membrane
00:12 were talking about how we go about changes in them. There are two
00:17 types of membrane potential change. There's is called the action potential and what
00:21 called the grated potential. And so the great next light. So what
00:27 want to just kind of do you to give you the overview and we're
00:29 to see how the greatest potential is . We're going first, kind of
00:33 them, look a great potential. look at the axe potential, see
00:36 to conduct. So the action potential our starting form. We said,
00:40 is its? They change the membrane . This is actually a very large
00:45 . All right, so we're looking something. It's very quick, very
00:49 and very brief for rapid in terms how it moves. And we're looking
00:54 something like 100 million volts change. , Miller votes are very, very
00:59 , but but relative to a it's a fairly large thing. And
01:04 what we're doing here is we're taking cell and what is normally negative membrane
01:11 , and we're reversing. It were bringing it up to 100 mill.
01:15 mean, not 100 levels, but minimal change from that starting point,
01:20 least a neuron. And whenever we're at a potential remembering potential chain,
01:25 , we're not talking about the entire , just going to a member of
01:31 . It starts as a very, small portion remembering. All right,
01:36 we're looking at whenever we see a here or even on the other
01:40 we're looking at just a single point the plaza memory. And then what
01:45 gonna do is we're gonna see how change occurs from that membrane from that
01:51 point. And so when you're looking this graph right here, what you're
01:56 at is you're looking at Miller Volts time. All right, so down
02:00 the bottom, that's time. And you're looking at that single point you
02:04 see here. We've got a little . We're looking at that single
02:07 And what we're saying is look, is the stimulus. So our stimulus
02:11 either on or it's off. So your off position. There's your own
02:16 . So nothing's going on, and we turn it on their simulation.
02:19 we turn off stimulation going. And what you can see here is we
02:24 at a a specific charge. We're doing anything. And then when the
02:28 occurs, what happens? We see rapid rise over time, and it
02:34 this rapid fall that occurs there. her. Okay, so that's kind
02:39 what we're looking at. Three Easy to visualize this. Which is why
02:44 wish you all were in class. you could do this at home.
02:47 just bear with me is I want to picture a wave. I'm not
02:52 a wave like that. The I'm talking about what you do at
02:55 event. All right, so you're in your chair, you're looking
02:58 you have 100,000 people or 40,000 people whatever it is around view, and
03:02 starts the wave and it starts moving the stadium. And so you're gonna
03:06 that wave of people standing up, sitting down, it comes over to
03:11 , and from where you are. you do is you basically take your
03:14 from your side and you lift them and over your head and to the
03:18 tough. And then you bring them again. And that's kind of the
03:20 that we're looking at. We're looking at this particular action potential. We're
03:25 at an individual, lifting their hands in putting their hands back down over
03:30 . And that's what that rapid rises what that rapid fall is. It's
03:35 the flow of ions over that period time, causing that deep polarization that's
03:40 initial phase and then re polarizing back their original position. Now with an
03:47 potential. What's gonna happen is, you produce it, it propagates just
03:51 a wave does at a sporting So you can imagine Here is your
03:55 right. You start the wave and goes around the circle and keeps going
04:01 , and it just keeps going and going. In other words, it's
04:04 in such a way that doesn't diminish strength. It stays the same strength
04:09 entire length that that wave moves, that's what an action potential does.
04:14 starts at a single point. All , so here is your neuron.
04:22 your axe, Exxon. It starts a single point, and then once
04:26 produced, it stays the same And it keeps going the entire
04:33 All right, so you can imagine wave moving entire land. And it
04:37 not diminish in strength and stays at same strength the entire length. All
04:43 now, the key thing about an potential on this is important. It's
04:46 all or nothing response. It either 100% or doesn't respond at all.
04:52 it's very binary. It's not a , I'll kind of be in
04:57 You don't kind of go up to and then come back down. It's
05:01 away back down, but you have reach a certain threshold. All
05:06 that's what they're showing right here is a threshold. If you can reach
05:10 , you produce the big wave. you can't reach threshold, you don't
05:16 the wave at all. You basically underneath that coin. All right,
05:22 that's one of the key things about the action. The great potential,
05:30 the other hand, is different in it is still remembering potential change,
05:36 it can go in either direction. can either be a deep polarisation or
05:42 . Here was the deep polarisation. the hype. Accorsi. The second
05:46 about a great potential is that whatever causing the triggering event, it's gonna
05:51 different magnitudes that produce that trigger of . And so the response that the
05:58 potential has is equivalent to the So there are magnitude magnitude inal differences
06:05 great potential in grated potentials. But means is that weaker stimuli result in
06:11 responses. And that's what this is to shows like again, Here's our
06:15 graph. This is a responsive It says. Look, here's the
06:19 line. It says. That's a weak signal. Look, I still
06:23 a membrane potential change. It's a , itsy bitsy, teeny tiny
06:27 The larger the stimulus, the stronger potential right. And what you can
06:33 here is I've actually turned it into action potential, which we'll get to
06:37 just a moment. But look at opposite. Here appear this is
06:40 hyper polarization. So this is This is causing hyper polarization, so
06:46 stimulus is weak, larger, larger largest. You can see a moving
06:54 and further and further down that hyper into that for a state. So
07:00 we have here is a member of change that has a variety or
07:07 the responses is equivalent or related to magnitude of the trigger. So in
07:15 , the bigger the trigger, the the response is smaller, the period
07:18 the smaller response. And this is true with regard to duration, which
07:22 not really dealing with here. But , on our grasses time, the
07:28 that that stimulation is there with longer , the greater potential is going to
07:35 . Now again, we're looking at single point, and what we need
07:39 understand is that these ions are moving that single point of stimulation. So
07:45 is kind of what this draft is to show you say, Look,
07:47 is where the point of stimulation probably find a different. So I guess
07:51 have to use something like start purple. All right, so So
08:00 we have, where the stimulation you can see the little channel.
08:05 happens is is stimulation caused the opening the channel. Whatever the channel happens
08:09 be, ions flow in. And are they flowing in while they're trying
08:13 find their partner? And so you imagine the first place that they're going
08:18 have the highest amount of ions is the point of influx, all
08:23 where they're coming in. But as as they partner up, there's there's
08:29 and fewer ions that are cables are to travel further and further away.
08:33 so if you were to measure at and further points, what you find
08:38 that the the membrane potential change is and smaller and smaller. Another would
08:47 . In other words, what's happening is that the membrane potential change is
08:51 out over a very, very short . So there's many reasons for
08:56 One is that pairing, but they the ions are leaking back out,
09:00 out whatever the case may be. this is again, this is deep
09:03 . So this would be true also polarization, but your items might be
09:09 brought back in. But the point this is is that what we have
09:14 with the greatest potential is that that could only travel very, very short
09:21 . Whereas what We're looking at the potential. It can trouble very long
09:26 because of this non Decorah mental, , propagation that occurs as a result
09:32 that. So action potentials are these changes, right? They leads that
09:41 are large island movements that are causing very large membrane potential change.
09:49 then, is a maximum membrane potential that travels. All right. The
09:55 potential is kind of like a rippling you throw. You throw a rock
09:59 a pond, you get ripples that of move outward. And over certain
10:05 that ripple dies out. Ex You don't get that dying out.
10:10 does this happen? Well, it back to those irons that we talked
10:13 the sodium and potassium, All And what we have here is we
10:17 channels that are going to be depended the change in the membranes state toe
10:22 up. In other words, what have here is a special type of
10:25 that responds to the membrane potential. called a voltage gated channels all
10:31 And these have lots of charge groups them, and what they do is
10:34 the membrane potential changes. It causes change in the shape of the
10:39 which opens up, which allows more to flow in or out, which
10:43 further changes in their shape. And that's kind of the positive feedback loop
10:47 allows for the membrane potential change to . All right, And these particular
10:52 are gonna be located a very specific called the Axon Hillock. Now
10:57 we said, there's two different types channels. We have the voltage gated
11:00 channel, all right, and this kind of a unique channel in that
11:03 has two gates, all right, there's not one gate through which arms
11:08 to flow. There's two of them one is called an activation gig one's
11:12 inactivation. You can see here in initial state. What we have is
11:17 have a closed activation gate button open gate so before stimulus ions can flow
11:24 because the activation gate is closed. when you're stimulate the channel, what
11:30 is that the gate opens up all , so I owns can flow
11:34 but at the same time that you that that channel that the inactivation gate
11:40 to close, but it takes a bit more time. And so the
11:44 state is you're now back in a steak, but it's a result of
11:47 second gate and then what you have do to bring yourself capable of
11:53 And you have to reset yourself all way back here. You don't go
11:57 this middle state. It's a than , then see, and then all
12:03 way back to a There's no middle in there. Okay, so the
12:11 picture here, the full city gated channel has three configurations. We call
12:16 closed, capable of opening, opened then closed but incapable of opening.
12:22 you have to come all the way from the inactivated state to the ready
12:26 open state before anything else happens. system multi tasking channel makes more
12:36 It's one that's easy to identify. has won gates, so you have
12:39 states. It's either open or When the clothes tasking can't flow
12:44 open tasking can flow out all And so what I want to do
12:48 I want to break down this action . Alright, we're just gonna walk
12:52 . So remember, we're looking at single point, and what we're asking
12:56 is what is happening over this period time. At this single point,
13:01 our starting point is gonna be here rest, so just follow the
13:04 All right? So at rest we This is at the Axon Hillock.
13:09 right, These voltage gated sodium channels bull escaped tasking channels are closed.
13:15 close to know our own passes but we do have the natural flow
13:20 we would get because we have the the study and potassium leak channels.
13:24 have the sodium potassium, 80 Ace. So these leak channels and
13:31 pump are basically maintaining that membrane potential the resting potential right here.
13:38 That's what you're seeing now, at period of time, remember, we've
13:42 said that there is a relative permeability between sodium and potassium, right?
13:50 supersedes sodium movement by almost 50 to to one. And the reason for
13:56 is because you have so many potassium . Very few, uh, sodium
14:04 . Make sure I said that, . Many, many potassium channels very
14:07 sodium channels. All right, so the key thing. So what's keeping
14:12 at that Near that minus 70 is that that strange ratio, all
14:18 but we still have these channels, they're closed. And because their
14:22 that doesn't affect probability permeability right now rest permeability is a constant. So
14:29 have a triggering event. When is trigger have been simply the stimulus that
14:33 along and causes the opening of these ? Now we're gonna open up a
14:38 bunch of different types channel We don't not talking about what the triggering event
14:42 . But generally speaking, the triggering opens up a different type of
14:46 usually at the at the dendrite, then causes a grated potential to be
14:53 , which moves towards the acts on . It's here at the Axon
14:57 where we have these voltage gated And if it's a deep polarisation
15:03 what's gonna happen is you're gonna open the voltage gated sodium channels. And
15:06 when that happens, more sodium comes the cell, and when you open
15:10 more voltage gated sodium channels and studying , sodium is coming into the
15:14 That's gonna cause further deep polarisation, causes more voltage gated sodium channels to
15:18 , which causes more sodium come which causes more Holzer gated sodium channels
15:22 create system positive feedback loop to the where all the voltage gated sodium channels
15:29 open. And so as a what we're doing is we are moving
15:35 and upward enough word, all so sodium is basically feeding back through
15:42 mechanism because all the voltage gated sodium to open. So threshold is really
15:50 point. Win that voltage gated All voltage Gated city and channels are
15:55 So what you've done now is you the permeability, all right, so
16:02 just making up a number. It's a real number, but let's say
16:05 1000 channels, right. And you start off with one's sodium Leak
16:11 to 75. I'll just use It's an easier number 50 potassium leave
16:16 . And then now what you've done this stimulation is you resulted opening up
16:23 sodium or voltage gated sodium channel. instead of being 1 to 50 now
16:28 1000 of 50 and so it's now is that the permeability of sodium is
16:35 the member and so sodium is rushing the south, and that's why you're
16:39 to start seeing this massive climb. Threshold represents the point when these all
16:45 channels have opened up now. So gonna keep coming in until it reaches
16:51 60 given the opportunity to do All right, that's what that's what
16:55 trying to do. But something happens it ever gets there. And what's
17:01 is, is that that channel? , we said it has two gates
17:06 voltage gated sodium channel. It opened activation gate to allow the sudden a
17:10 . But at the same time, when that voltage gated inactivation gate begins
17:16 close. It's just slower. And what happens is while those gates are
17:22 , you're getting sodium to come But when it closes, it ceases
17:25 allow any more sodium to come and you were turned membrane potential back
17:29 to its original state. All so what we've done here is basically
17:35 reached the peak of flow, all , because he slammed all the doors
17:40 . If nothing else were to then because leak channels in the
17:43 We slowly moved back then, but don't do that. Instead, we
17:48 this massive return this very quick And again, look at the relative
17:54 here. We're looking at roughly a for all this to take place.
17:59 right, so 11 thousands of a . That's a quick. So while
18:04 sodium channels cultivated sitting shells have slammed at the same time, What we're
18:10 is we're opening up the potassium Now. The easiest thing to think
18:16 is that the voltage gated potassium channel being stimulated because we reached a certain
18:21 way up there that's actually know what . The voltage gated potassium channel is
18:27 your your ignorant friend, the one a little slow, you know,
18:31 that you tell jokes to. It about a minute before they figure it
18:35 . That's what's going on because the stimulus that occurred there that caused the
18:40 gated sodium channel open is the exact stimulus that causes the voltage gated
18:46 It just takes more time to do . It's a slow gait, and
18:50 why it takes this long before it gets there, so it's almost a
18:55 a millisecond before the potassium Channel But it's also the same amount of
19:00 that that sodium channel closes. So two events simultaneously results in the flipping
19:08 the membrane back towards re polarization. so, just to put this in
19:14 , what are we doing? We the channel, which prevents more sodium
19:19 coming in, and we open up vault scape. Taxing channel, which
19:22 allowing the potassium to leave, which shoots it down, allows it to
19:29 back down. And that's what's going as we're returning to rest now.
19:35 can see in the graph here, that here's rest and we overshoot for
19:43 reason. What happens well again. low, close, it's It's a
19:49 opening channels, also slow closing and as a result, it takes
19:53 little bit of time for those things close. So even though it should
19:56 closed by this point to get us to their, we overshoot a little
20:00 , and so we kind of hyper for a little bit. Before we
20:03 back to normal, you can see showing a slow rise there. That's
20:07 the artist, um, artists freedom do so. All right, so
20:14 sodium channels, they're slow closing results a transient hyper polarization. All
20:22 so we have a couple of Vince , very simple, right? We
20:26 result. Me, we started rest . Rest is the stimulus that seamless
20:33 up to control to get sodium positive feedback loop what we're seeing down
20:39 , right? All the channels are , so we have rapid, deep
20:44 . Those channels closed at the same . The voltage gated potassium channels
20:48 which causes the rapid falling phase. channels closed, but they're a little
20:54 . So we get this light hyper . Um, um after we've returned
21:00 rest. So that is the events the resting potential. What you can
21:05 to help you understand this is to at where change is occurring and ask
21:11 why? Why does the graft change this point? And that's an easy
21:16 to think about this. So there's couple of other ideas that I
21:23 you understand for the action. All . So an action potential is simply
21:28 electrical signal. Remember, traveling from cell body down the axe onto the
21:32 on terminal. And what you wanted do is you want to ensure that
21:36 signal is gonna be maintained in terms size, and it goes in the
21:41 that you want to go into wanted go to. And so to do
21:45 , what we have is what is a refractory period and the pure definition
21:49 refractory. Here is that period of when something has to be reset before
21:56 can be repeated, that whatever it that you're looking at, so with
21:59 to an action potential, it's that of time when an action potential can
22:03 produced under normal circumstances. Win that of that accident has already undergone an
22:10 . And so what that means is when I produce an action potential,
22:13 actress tensions to move away before I produce another one. Because there's a
22:19 of time when I can't do there's actually two halves to it.
22:23 the refractory period you can see here kind of demarcated as two halves.
22:27 has what is referred to as an period of one is referred for the
22:31 , period. All right, we're looking at a single point on
22:36 Ansan, and we're asking what's happening that period of time? Well,
22:41 the first part of that action potential what we would call the absolute.
22:47 this is that period of time, said, is when all those sodium
22:50 are open. We said, all open. And so if you've opened
22:55 all the channels and all the sodium could be rushing in is rushing
23:01 it doesn't matter how much you stimulate sell. You can't open with air
23:06 . They're already in the open so you can't get another action potential
23:10 stimulation. It's already happening. But also need to remember that these channels
23:16 , go through those three stages. so once you start the stage
23:21 you have to go from stage one stage two to Stage Three. Or
23:24 I said earlier was ABC. So you started, you have to go
23:28 that whole thing before you can even to try to stimulate that cell
23:34 So the absolute refractory period is a of time when there's no responsiveness to
23:40 . You've already gotten your stimulus so seem most was enough to produce the
23:45 . And so what this does it that the action potential cannot occur until
23:51 preceding one has moved away. So the absolute curry. The relative refractory
23:58 is during that period of time when are in our re polarization and in
24:04 hyper polarization re polarization stage All in those two things. So here
24:09 we've done is we're article on through resetting of those sodium channels was voted
24:16 get excited. They're not 100% but there's some that are so we're
24:23 at, like maybe 90% of them . So what we're doing is way
24:27 get 100% responsiveness because of those channels being in their clothes statement to be
24:34 . All right. But the other that we have to overcome So even
24:38 we have enough voltage gated sodium channels be able to overcome the threshold,
24:45 still dealing with our slow friend, ? That potassium, that voltage gated
24:51 channel still is in the open And so even if you've opened up
24:54 channels, you saw open potassium and so you're seeing no real net
25:00 , so you have to be able have a stronger, stronger responsiveness.
25:07 word. Mawr voltage gated sodium channels relative to the potassium. So it
25:14 possible. So let's let's just kind put this into visual, right?
25:19 this is threshold, if high in , it's going to take longer form
25:25 stimulus to get me up there that did when I was there. All
25:30 , maybe it's a five extra Maybe it's 10 extra millet balls,
25:34 I need tohave mawr of a signal order for me for that to
25:39 All right, so what this It limits the frequency of when we
25:45 action potential, because we have to be really, really strong to produce
25:50 one in our relative period, or have the wait for the absolute period
25:55 move past. And so that means a mass commemorated, which you can
26:00 action. But what this also means that you can actually in code because
26:07 , action potential are fairly far You can actually increase the frequency and
26:12 the action potentials closer and closer and together. That's one way that the
26:19 system in codes information is in the of the action. How often are
26:24 being put together that encodes some of information that should produce it. Now
26:29 frack, your periods have different lengths different types of neurons in different types
26:33 tissues. So we can't say they look the same. They're just
26:37 but they all deal with the same . It's basically a period of time
26:42 you can't produce an extra potential in normal of circumstances. So this is
26:48 home stretch. It was basically an 30 minutes. It looks like and
26:53 over. Dealing, you know, how does it action potential conducted And
26:57 you can see here what we're looking . This would be your excellent.
27:00 look right here. All right, is your acts on. You can
27:04 . We got a whole bunch of lined up trying to come in when
27:07 open up enough of those sodium What they're gonna do is the sodium
27:11 in like a great potential, and it finds its partner and said
27:16 ? I found a partner, but ones that don't move forward and they
27:20 moving forward, and it causes that . Potential change causes a deep
27:25 which results in the opening of more gated channels because he's voltage gated,
27:29 channels lying the entire length of the as good a vulture gave. And
27:35 what happens is is, as the flows in it keep propagating the action
27:41 . Ford. So you can imagine here that it's there and then it's
27:45 , and I know that the driver great, but you can kind of
27:47 the sense is the wave begins propagating the length of the action, all
27:54 ? And the reason don't go backwards because, remember, we're dealing with
27:57 refractory region on the backside, so only allows the action potential move in
28:03 direction. Now there are two different that actually propagated Easy. One to
28:09 about is what is called continuous All right, And so here we
28:14 the entire axe on exposed to the cellular fluid. And so you can
28:19 that I own all or not thes gated channels along the entire length,
28:24 so basically I have to open and each single one of them is kind
28:27 like in a continuous mode would be of like walking across the floor.
28:32 hell, All right, so you're to see this whenever you have accents
28:37 lack my Alan. It's a fairly process because just, like watch walking
28:42 Hill while there's a distance to you have no gap between your in
28:47 stride. You're basically toe to heel heel, and it's a very slow
28:51 , all right, but it zey typical it's what we would think about
28:55 be occurring. But the problem is that in order to get signals
29:01 go faster, there's really only two to do that. All right,
29:06 come back to this slide right. first way is to increase the dynamic
29:12 of of the of the Axe on right, which means you have to
29:17 it wider. It's kind of like . If you feel you are audio
29:21 will know this. The thicker the less resistance, the better the
29:25 the thinner the wire. The more you have, the harder it is
29:30 get good sound out of it. of wire. And so so the
29:34 here is I need big fat fibers I want to speed up the process
29:39 propagation. Problem is, if I make a bigger, fatter axe
29:43 it means I need a bigger If I have a bigger neuron,
29:45 need a bigger space to put that got thousands upon millions of these things
29:50 your body so you can imagine your would have to be bigger as a
29:54 of that. And so it just probably means a further distance that up
29:59 travel with me, they need a neuron in the audio, so that
30:03 not a solution. It's a solution you have a same size critter or
30:08 same size person. So a bigger is faster than a smaller neuron.
30:14 you can't make all neurons bigger. so what the body came up with
30:18 this plan that's called my Elonis all , and my l. A.
30:24 is using those Schwann cells or those ago dinner sites in the central nervous
30:28 to cover up a portion of that . So there's only a very,
30:34 small portion of the axe on exposed the extra cellular fluid. And so
30:41 is where the action potential they're gonna place the distance between one note in
30:46 next and these air called the nodes Randhir. So that little space,
30:50 there is a note of ranveer That's note of ranveer. That's another
30:54 This is a mile in sheep. right, action, petition action potentials
30:59 being produced at the nodes of All right? And so what happens
31:06 , is that instead of covering the length of the axe on what we
31:12 is we leap from note of Randhir note of Rand view. It's kind
31:17 like a stride, and the distance these nodes is just far enough that
31:23 action potential could be stimulated each All right, so there, as
31:28 as they can be. So it's life. He stride once you stand
31:32 right now, I don't want you walk across the room, toted hell
31:35 see how long it takes you. then I want you walk across the
31:37 the other direction using a regular stride see how much faster it iss all
31:43 . So when my illness present, going to get salvatori, which literally
31:49 to jump. All right. This is a better representation of
31:56 You can see here all my channels can see I'm insulated from the
32:01 So I'm opening and closing the voltage channels IOM's air flowing through, which
32:06 a change in the membrane so that could get the next one and then
32:09 next one. And that's why I'm from one to the neck. And
32:14 allows that signal to move incredibly fast increasing the size of the fiber.
32:20 you can keep your are your your I were small, The other thing
32:25 does incredibly beneficial because it consumes less . And, of course, the
32:29 is always looking for reasons for using energy. So our goal here to
32:36 is that the action potential is going travel, um, quicker with Miles
32:44 because of these little regions in between mile and called nodes of ranveer.
32:50 right, That's what I wanted to to. And so that catches us
32:55 . I hope you enjoy this. was 30 extra minutes. I'm
32:59 I've just been talking slow all Maybe I will be caught up after
33:05 unit. You can come and ask questions at office hours. That's going
33:09 Thursday from 11 to noon. Or can ask questions in class. I
33:16 more questions begin classes slower ago. not a reason not to ask
33:20 I'm just letting you know that. thank you for tuning in
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