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00:00 | Okay. So what we discussed the 2 3 lectures were resting number and |
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00:11 | . And of course the action And when we talked about the action |
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00:17 | , we learned that action potential is by two currents. The sodium conductance |
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00:24 | is coming from outside of the south the inside of the cell, the |
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00:28 | word, current positive charge moving inside the awkward current which is a potassium |
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00:37 | from the south of the outside of south. We talked about how puffer |
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00:44 | contain tetrodotoxin. The toxin is produced bacteria and that tetrodotoxin is an |
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00:53 | It binds two potassium channel and blocks trump. Uh sorry sodium channel, |
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01:00 | educated sodium channel in particular the vault sodium channel that is responsible for generating |
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01:06 | action potentials. So in the presence tetrodotoxin you will not see these inward |
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01:13 | is because the sodium current and sodium is going to be blocked. We |
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01:19 | talked about tetra ethyl ammonium A. . A. Has a specific blocker |
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01:24 | the potassium channels and the outward conductance in generating action country. And we |
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01:31 | that these substances uh there's multiple substances lidocaine and we also mentioned cocaine that |
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01:40 | be targeting multi educated sodium channels as . So there's many different things in |
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01:46 | of course is the local anesthetic. when the action potential gets generated, |
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01:54 | gets generated in the acts on initial . So in this scenario what you're |
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02:00 | on the slide as this neuron here active and it sends a signal to |
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02:06 | neuron. There's a synoptic transmission here will start discussing later today neurotransmitter is |
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02:12 | and at the level of the downgrade are postion optic potentials. There is |
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02:16 | great and synaptic potentials and they're either which means that our D polarizing to |
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02:22 | cell and be polarizing plasma membrane or inhibitory. And they're hyper polarizing. |
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02:29 | they are D polarizing enough at the of the soma, then the accident |
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02:35 | segment right here which is located close the soma will generate the action |
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02:42 | This action potential will travel down the which is insulated except for where you |
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02:50 | the nodes of Ron veer and the there is exposed and nodes of ranveer |
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02:56 | with voltage gated sodium and potassium each note of round year the action |
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03:02 | is going to reproduce itself and arrive the external terminal having the same amplitude |
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03:13 | it did. That the acts on segment was initially generated. So this |
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03:18 | referred to assault a Tory conduction or action potential conduction down the axon. |
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03:27 | so each one of these nodes of beers will have the machinery, the |
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03:35 | potassium channel machinery to reproduce these spikes action potentials. Ra Monica. How |
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03:46 | the person that not only made these drawings of neurons and neuronal circus. |
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03:53 | if you recall in his drawings, showed that axons had arrows next to |
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04:00 | and he postulated that gun rights received information are the side of the inputs |
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04:06 | of like an antenna and the axon an output. And there was a |
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04:12 | to the signal flow in his So he proposed his principle of dynamic |
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04:19 | , meaning that there is a directionality the polarity to the flow of the |
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04:26 | to the flow of the dynamics of information that is being carried through the |
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04:32 | . And so he was absolutely The axons where the output. Although |
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04:40 | did not know that physiologically, he derived it from the drawings that he |
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04:46 | with the gold he stay. It also right that action potentials travel in |
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04:53 | direction to the axon terminal. With exception of what has been discovered about |
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05:03 | years ago in the form of what called the action potential that is back |
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05:08 | action to come. In reality this area of the axon because it is |
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05:26 | with very sensitive sodium channels that can polarize and produce this very fast spark |
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05:33 | the form of the action potential, threshold or how much deep polarization the |
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05:39 | initial segment has to see as compared how much deep polarisation has to be |
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05:44 | in dendrites or Soma. It's actually in the sense that the synopsis that |
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05:51 | contact the damn drives. They're far from excellent initial segment. So at |
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05:57 | level of the downgrade downgrade may have be deep polarized, very, very |
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06:01 | levels minus 30 million volts minus 35 bowls. Right? But if there |
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06:08 | an input that is very close to accident initial segment it can actually influence |
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06:17 | also have a very strong effect. , a small deep polarization in the |
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06:23 | are close to the accident. Initial is very meaningful to these sodium channels |
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06:29 | a small deep polarization that is far in the damn right. It's not |
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06:33 | meaningful why? Because gun rights are insulated. And so these great and |
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06:40 | potentials that are produced excitation and they will die down with distance. |
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06:46 | electrical potential on that change will reduce distance. And that's why you need |
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06:51 | or hundreds of synapses activated at the time in order for a cell to |
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06:57 | an action potential. Because those synopsis you saw can be found on the |
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07:02 | drives and the good experience on the . Some of them can also be |
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07:09 | in the accidents. So, let's at how the action potential gets generated |
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07:18 | how it travels in the forward And for that. Uh I have |
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07:28 | in your special materials lecture materials and , which is about 12 years |
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07:43 | But the mechanics and the channels behind are involved in generating what is happening |
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07:54 | . Still hold true. So it called Hewlett the spikes out and who |
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08:01 | the spice out room. Uh Which let the spikes out. That's really |
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08:10 | question here. And you'll see, do you mean? Which channel? |
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08:14 | sodium channel sodium channel is responsible for the action potential. And then I |
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08:21 | it to divey plots that drew these lines everywhere. And I said look |
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08:25 | these lines, they're all different types plots. One cell can have all |
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08:29 | these lines as the dialect of that sour. Why can't it have all |
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08:34 | these ivy applause. Because it has variety of different voltage gated and other |
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08:40 | channels. And if you have voltage channels that have different lines, that |
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08:46 | they process information differently. And that are also subtypes of voltage gated sodium |
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08:52 | that there are subtypes of chicken potassium , calcium channels and so on. |
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08:58 | so the way that action potential is at the accident. Initial segments can |
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09:06 | represented by this cartoon. So there have an incoming deep polarization and you |
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09:11 | see this green cloud here over the dendrite is here and this green cloud |
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09:18 | sending the green arrow into the It's trying to excite the cell and |
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09:24 | to de polarize the soul and trying de polarize the actual initial segment. |
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09:30 | this neuron hypothetical model neuron is receiving lot of excitation on it's damned rights |
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09:37 | dendritic spines, that this neuron is receiving a lot of inhibition. And |
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09:44 | it happens in the neuronal circuitry and in the cortical circuitry in the brain |
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09:49 | a lot of the inhibitory synapses and are formed on the selma or around |
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09:56 | selma which we call perry somatic regions neurons And that is also important because |
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10:06 | closer you are to the integrated region the cell which is the selma and |
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10:13 | closer you are to the trigger region is excellent initial segment which triggers action |
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10:21 | . The stronger impact you have, more control you have of what happens |
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10:27 | the summer whether it's deep polarized hyper , whether an action potential gets fired |
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10:31 | not. So when we talked about we looked at the hippocampal circuit we |
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10:38 | there's a variety of these inhibit their . Um Some of them will project |
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10:41 | selma some of them will project and drives. But in reality inhibitory cells |
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10:47 | inhibitory inputs really dominate the paradigmatic regions neurons. There are fewer. There's |
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10:55 | 10-20% of inhibitory into neurons in the regions and the rest 80% 90% of |
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11:05 | cells are excited through phenomenal selves. if you are on the 10% of |
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11:15 | inhibition you want to you structure the and yourself with respect to the projection |
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11:21 | and communicate information and in train and . As much of that information is |
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11:27 | to the integrative and trigger points for south. If however this cloud of |
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11:36 | which is the d polarizing input, excitatory synopsis breakthrough and reach the accident |
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11:49 | segment and you have a deep polarization action initial segment. They're anatomically you |
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11:56 | encounter two types of both is gated channels. And maybe 1.2. sodium |
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12:04 | a V. Stands for voltage 1.2 a subtype And any of you 1.6 |
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12:15 | Maybe 1.2 are located closer to the . But m maybe 1.2 are what |
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12:24 | call high threshold voltage gated channels. means that they have to have high |
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12:30 | of deep polarization in order to open they give you 1.6 channels. They |
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12:37 | further away from the SEA as compared 1.2. But they're low threshold both |
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12:44 | sodium channels. That means that low of deep polarization or input is necessary |
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12:52 | sufficient to open These NAV 1.6 So what happens is if this deep |
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13:05 | reaches the accident initial segment, This charge will actually bypass the 1.2 |
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13:14 | It's not enough to open that 1.2 . But when it encounters and maybe |
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13:23 | this charge is enough because they just a little bit the little threshold voltage |
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13:29 | sodium channel. So low voltage low of changing voltage are okay to open |
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13:36 | and they open. And as they there's a deep polarization they go through |
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13:43 | positive feedback cycle in generating an explosion is the action potential and number |
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13:50 | And this is the forward propagating action . This is the action potential that |
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14:00 | that propagates from the excellent initial segment the way into the external terminal. |
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14:14 | this is the forward propagating action potential it moves in that direction. But |
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14:20 | what happens now? There's still deep input coming in. There's still some |
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14:27 | charge left in this purple zone which to N A. V 1.2 And |
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14:33 | nearby there was an explosion causing further polarization by M 81.6 channels the father |
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14:42 | of sodium and more deep polarization. now locally here in the membrane The |
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14:49 | the input excitation and deep polarization with deep polarization produced by the low threshold |
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14:57 | 1.6 channels can the two can some . And when they do that deep |
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15:04 | that changes voltage is enough to open high threshold voltage gated sodium channels. |
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15:12 | this back propagating action potential is called propagating because it is not going to |
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15:19 | in the same direction down the Why? Because they're standing strong, |
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15:25 | strong 100 million bowls change and positive that is happening right here. This |
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15:32 | all happening within no second of So the only solution and the only |
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15:40 | in which the this charge from N . B 1.2 can move is back |
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15:47 | propagate back from the acts on initial into the selma and potentially into the |
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15:54 | rights and injury spines. So the propagating action potential a lot of times |
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16:02 | referred as orthodontic and of course the propagating action potential is referred as back |
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16:09 | action potential. Back propagating spike. amplitude of the forward propagating action potential |
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16:16 | what we've already learned on the order 100 million bushels. The amplitude of |
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16:22 | dark propagating spike is small and just a few million volts. So |
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16:28 | will say well how come? It's a greater potential than because it does |
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16:32 | come from a synapse. It comes the neuron channels generating that small potential |
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16:39 | sending it back toward the soma and the gun. Rights. So why |
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16:47 | I care about this not propagating Well because of the rules by which |
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16:59 | learn and some of these rules plasticity that will change the strength of the |
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17:06 | and potentially the number of the So we already talked about dendritic spine |
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17:13 | . We said that during early development is more spines that are grown and |
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17:17 | can be strengthened or potentially ated or can be weakened, depressed are |
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17:24 | You have this process. It's plastic . And really spine plasticity. So |
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17:30 | the back propagating action potential, it's for them to expand plasticity. It |
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17:38 | served in the way as an excited . D polarizing signal that tells the |
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17:45 | that were active within one or two that we produced an action potential. |
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17:53 | the pre synaptic neuron will say I I fired. I fired. And |
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17:57 | the past synaptic neuron doesn't sound the propagating spike then these pre synaptic neuron |
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18:04 | of firing, they don't know whether responding or not. So there is |
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18:08 | linkage that strengthens the back propagating action , strengthens this linkage between the active |
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18:18 | attic neuron saying fire active boston optic and saying I fired an active person |
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18:26 | neuron is saying okay good I'm meaningful you because guess what if the pre |
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18:33 | neuron fires fires, fires, fires and this accident initial segment doesn't produce |
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18:41 | back propagating spike doesn't produce a spike all. These synopsis are meaningless Or |
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18:48 | produces the spike 20 seconds later, is forever in the brain processing |
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18:54 | It's not meaningful. And that's why response has to be also lengthen time |
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19:01 | when the prison optic neurons activate on at the cellar this network and when |
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19:07 | network responds and the closer in time input comes into closer in time and |
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19:15 | in time you produce the action potential the back propagating spike within a few |
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19:21 | to 20 to 40 milliseconds, the plasticity in the system you have, |
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19:26 | more ability. This synopsis and communication the synopsis have the ability to |
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19:33 | Uh huh. So this is what mean by spike farming dependent plasticity. |
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19:39 | the spike timing from the neuron that fire fire fire is short between the |
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19:45 | that says I fired then this plasticity strong and this timing is short. |
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19:53 | if the incoming neurons says I'm firing , firing what what I'm firing, |
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20:02 | , firing her fire. You're gonna up on that. This synopsis is |
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20:10 | going to be meaningful, This communication it can actually weaken because the time |
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20:15 | is too long and for the brain this time period is too long. |
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20:21 | responds window with spike timing dependent plasticity either strengthening potential rating or depressing synapses |
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20:31 | about 40 milliseconds plus minus 1 20 on each side. The ability for |
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20:40 | networks process visual information is seven milliseconds the optimal plasticity in your visual |
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20:51 | Fire response within seven milliseconds the networks to link together, neurons have to |
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20:57 | together in order to process the ongoing visual information such as movies are tv |
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21:04 | and so on. So we talked the propagation of deep polarization and the |
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21:12 | and I have a challenge of the . Do you think dendrites prefer to |
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21:16 | deep polarization and forward or backward how would you test this hypothesis? |
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21:23 | ? S cage neurotransmitter and what is ? So again, if you go |
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21:30 | your glass folder materials you will find an article that talks about caged |
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21:38 | It's a very very cool technique. you may want to look it up |
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21:43 | may have a question about that on quiz or what is engaging. And |
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21:48 | can also go over a little bit the following lecture if anybody remembers |
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21:59 | So orthodontic is moving from Selma. . Uh It's used mostly. You |
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22:21 | you could it's not necessarily for testing the strength of the pathways as much |
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22:27 | testing the strength of the synopsis. can say it's a path line but |
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22:32 | not really looking at the conduction velocity axons that interconnect to networks. So |
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22:41 | you're looking at is you're looking at close in time is the pre synaptic |
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22:45 | firing? In the past, synaptic has responded if they're firing and responding |
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22:51 | close in time that synapse strengthens if order is reversed that synapse weekends. |
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23:02 | the time period gets longer between prison saying, fire and for synoptic saying |
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23:11 | then that synopsis too long of a and it's not going to do either |
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23:20 | nor strengthen or weaken. It's just of a signal that's out there that's |
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23:25 | unrelated. Oh yeah. You know is one of the mechanisms or you |
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23:43 | see this is one of the cellular for learning and memory. Despite |
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23:56 | Spike timing plasticity in particular by timing . First testament is one of the |
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24:05 | by which Meuron strengthened synopsis and weakened and by which they learn and when |
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24:14 | strengthen synopsis and there's repeated activity and response. It can be likened to |
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24:21 | studying new material that's really difficult and happens if you repeat it 34 times |
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24:28 | somebody will just give you a trigger when you quit somebody just you can |
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24:33 | the first Two words of a definition 20 words long and the person will |
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24:39 | you an answer. But that will on the fourth time. And that's |
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24:44 | equivalent of the synapses. Now repeating, repeating and strengthening. And |
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24:52 | rules. Some of them are short learning rules, short term memory that |
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24:57 | have, others are long term Uh Learning rules will come back to |
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25:01 | a little bit later in the Talk about more about plasticity. The |
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25:05 | way that the brain encodes strengthens the so weakens them using what we call |
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25:13 | rate code or the frequency. So the timing this is spike timing the |
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25:21 | code is this is high frequency stimulation represents high stimulus, strong stimulus or |
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25:29 | infrequent stimulation which represents maybe a week or inconsequential stimulus. This is another |
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25:37 | of learning. And in reality the takes advantage of both of those learning |
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25:45 | , Their rate card, the timing and also the directionality of communication pre |
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25:52 | and post pre. So I hope answers your question. That's really good |
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26:00 | . And I think some of these will keep coming out during the course |
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26:05 | I'll address them uh in a little more detail in a couple of |
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26:09 | But if you're interested in what happens them. Rights. Look up this |
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26:16 | about caged neurotransmitters because you can actually a neurotransmitters in the cage and lock |
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26:23 | up. You can put chemicals in cage and lock them up and you |
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26:28 | release them using lasers and you can in it just singled and riddick |
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26:33 | That single synopsis, which is incredible . Okay so we have this propagation |
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26:40 | drama. It is moving in the from the soma into accident to draw |
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26:45 | . If you shocked the axon, will also move into the into the |
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26:50 | . But that doesn't happen physiologically. Korea conduction refers to the regenerative action |
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26:58 | it knows of ranveer and there are actions that are non violent nated and |
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27:04 | non myelin ated and the signal will on overtime. Um And the reason |
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27:11 | nose over and beer can regenerate this potentials is as is shown by the |
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27:16 | and green and red. It's a high density of voltage gated sodium channels |
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27:22 | voted to get potassium channels that are to produce action production. So, |
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27:30 | channel diversity already talked about this but is an illustration of a channel |
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27:38 | C. N. One channel It doesn't really matter what kind of |
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27:42 | it is. Ih current doesn't doesn't us what type of channel it |
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27:48 | The principle is what concerns us. is this HCM expressed in the |
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27:56 | So first of all let's look at prom. It'll Soller favorite criminal sell |
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28:00 | pickle vendor is have the most of . The cell has a strategy and |
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28:05 | cellular early in places. Most of receptors in the optical generals. External |
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28:12 | to sell. You will see that receptors. Okay these channels if CNN |
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28:20 | density call them receptors well let's call ion channels, they're distributed evenly. |
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28:27 | did they trade? Underwrite summer everywhere see red the channel is there. |
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28:34 | we can pull basque itself only on external terminals, cerebellum basket self very |
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28:45 | expression on the film and strong expression the external terminals and these cups |
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28:52 | So first of all each cell has own sub cellular ionic channel distribution. |
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28:58 | has its own strategy. If you to produce a lot of action potentials |
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29:03 | an action potential you load Jackson initial with voltage gated sodium and both educated |
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29:10 | channels. If you want to release affects on all terminal you load the |
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29:16 | with voltage gated sodium charleston voltage gated channels which you learn is necessary for |
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29:22 | release. It's a similar strategy. am channel distributions of cellular early After |
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29:29 | different types of iron channels can be by one cell indifference of cellular |
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29:36 | That's a lot of channels that's a of I. D. Plots that |
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29:41 | exist. Coexist in one south and the diversity of these channels. This |
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29:46 | going to account for the collect the behavior of neurons or the dialects that |
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29:53 | described to you from from Very early and how neurons fire and produces action |
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30:00 | . So have slightly different sub paths will express an 81.2 others will one |
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30:05 | long. Others will number 1.6, their action potential dynamics are going to |
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30:11 | different. The frequency at which they produce action potentials. The activation and |
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30:17 | models are going to be different for subtypes of these channels. And that's |
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30:22 | you get this incredible diversity and communication dialects among neurons that you're seeing. |
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30:32 | , synaptic transmission, we're gonna start about synaptic transmission. We'll come back |
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30:38 | review a little bit of back propagation time. But I encourage you to |
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30:42 | at that article who let the spikes fully understand it. It's not the |
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30:48 | and the people that are really responsible defining it. Thinking about it hypothesizing |
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30:57 | and drawing, testing, measuring Good Cathal familiar goals is student drew these |
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31:08 | networks and said there's snap the There's directionality, the principle of dynamic |
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31:16 | , which he wasn't 100 right because that propagating action potential but he was |
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31:24 | much right. The major signal and chemical communication happens down the axon and |
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31:32 | terminal search all shankman who coined this of a synapse is a specialist location |
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31:39 | communication between the cells. Even in 19 twenties, ra Monica ha fault |
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31:45 | the synapses of plastic that the connections plastic. That means that new synopsis |
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31:53 | form and certain synopsis can go away that they can strengthen. He postulated |
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32:00 | of that 100 years ago. Ultra . We finally was the person that |
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32:06 | discovered the chemical that is involved in synaptic transmission Examine two weeks. That's |
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32:14 | true. Officer necessary to. That's true. It's from all slide the |
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32:19 | is still the same if you need email me. Uh huh. Um |
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32:26 | of 100 billions of neurons in the . That's what synaptic transmission is, |
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32:37 | . Mhm. I think I can like a billion. I don't know |
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32:44 | I can write 100 billion. How many Zeros is that? |
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32:55 | Mhm. 12 Oh let's try so hundreds of billions of neurons in the |
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33:10 | . 100 billion. They form Synopsis you're on can have 100,000 synopsis. |
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33:20 | we're talking about trillions of synaptic trillions of sites in the cns or |
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33:30 | communication, this electrochemical communication to take . If you were to lay out |
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33:36 | membrane of the brain. All of neurons that you were unfolded them dries |
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33:43 | then it expires all flat. It cover four soccer fields. The total |
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33:51 | in the area of the brand. . Mhm. Or pretty much for |
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33:58 | fields. Yeah this is what we the fabric of our minds. Think |
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34:06 | it you lay it out flat. covers four football fields and then you |
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34:12 | it up and put it in. scholar that has all of the |
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34:17 | drives billions of south trillions of neuron synapses neurotransmitters from the maximum initial |
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34:25 | produces this action potential. An action arise of external terminal. Now we |
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34:30 | that there is a release of the . But to get there, this |
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34:36 | one of the really cool stories that should uh never give up on your |
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34:43 | and on your visions. In the of Easter Saturday 1920 100 years |
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34:52 | bottle of champagne. I walk, down the light, enjoyed it. |
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35:00 | a few miles from the tiny slip paper. Then I fell asleep again |
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35:06 | it occurred to me at 6:00 AM during the night I had written down |
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35:12 | most important but I was enabled to for this crawl that sunday was the |
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35:19 | desperate day in my whole scientific life the next night however, I awoke |
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35:26 | at 3:00 and I remembered what it this time. I did not take |
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35:32 | risk. I got up immediately. to the laboratory, made the experiment |
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35:39 | the frog's heart, described the below at five o'clock the chemical transmission of |
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35:47 | impulse was conclusively proved quoted from OTA 1953 Ratings. Uh how cool is |
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36:00 | ? So what did you do? he woke up and went to the |
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36:06 | in the middle of the night, the vagus nerve Vagus nerve is one |
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36:15 | the cranial nerves and in this class actually learn about the 12 cranial |
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36:20 | And you'll certainly learn about the vagus because you're learning about it today. |
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36:24 | cranial nerve tan it runs from the stone and it innovates extensively most extensively |
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36:33 | the body and the viscera which has strong input including into the heart. |
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36:40 | if you stimulate the vagus nerve in case on the frog heart the heart |
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36:47 | will slow down. So he had heart because the donor heart sitting in |
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36:57 | dish and he stimulates the vagus nerve he collects the fluid that is bathing |
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37:06 | heart. Following the stimulation he takes fluid removes it from the donor heart |
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37:16 | he applies it onto the recipient part heart is not being stimulated and does |
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37:24 | have vagus nerve attached to it. wrote the vagus nerve off of it |
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37:28 | he's not stimulating anything. Instead it's in the solution and he brings this |
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37:35 | stimulated donor heart solution and drips on of the recipient heart. And the |
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37:42 | is the same. The heart rate down. And so he definitively demonstrates |
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37:48 | it's not the electricity that gets transferred the nerve and the heart or between |
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37:56 | neuron to another neuron there is electricity gets transferred. We know that there's |
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38:02 | junctions called gap junctions. But he that there is fluid and that once |
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38:09 | stimulate the vagus nerve, that there's in that fluid. There's some substance |
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38:14 | that fluid that if you apply it the virgin recipient in stimulated heart, |
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38:22 | has the same effect. It's the in the chemical that has the |
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38:29 | So one of my PhD postdoc mentors to say that sleep is for the |
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38:37 | , I think you realize that when have your own kids at some point |
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38:42 | then sleep is for the weak or too weak if you need to |
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38:49 | The other thing is if you have vision, don't go back to |
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39:00 | wake up and execute on it, out who cares? It's one night |
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39:06 | am. Forget it. Sometimes you your best fish at night. Sometimes |
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39:12 | take your best nails at night doesn't to be all the time. You |
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39:15 | have to be a lunatic walking around the time, but an all nighter |
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39:20 | or there can make you can help in, you know, not just |
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39:26 | nighter, but something that you're working , but you have to resolve that |
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39:31 | have to be confirmed experimentally and it wait. So this is quite an |
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39:41 | story. What is the neurotransmitter that ? We discovered cecile Colin? It |
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39:52 | and the city of Colin. This a neuromuscular junction. It's a junction |
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40:00 | the nerve the vagus staff and the muscle which is the heart neuromuscular junction |
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40:11 | it's a single Colin on a single , inhibits or slows down their heart |
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40:19 | . So if you learned about the Colin in the skeletal muscles it actually |
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40:26 | contraction speeds up the contraction of the . But in the heart it has |
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40:34 | different effect that slows it down. as you will learn over the next |
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40:40 | of lectures as we talk about synaptic , the response off the cell muscle |
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40:48 | a neuron depends on the receptors that carries not on the chemical stimulus that |
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40:56 | civil clothing for certain cells can be turning for other cells that can be |
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41:02 | . Acetylcholine also has different subtypes of and some of those receptors will help |
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41:08 | cells get more excited and others will them. Mm So we'll come back |
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41:14 | talk about the pseudo Comey and cycle receptors. But sometimes later there was |
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41:23 | a discovery that neurons indeed past the from one another. That there are |
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41:33 | very specialist locations just like you have synopsis that have a synoptic left. |
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41:40 | it's a specialist zone of 20 nm space. That's a part that's where |
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41:46 | neurotransmitter goes and the receptors are on other side. Gap junctions or electrical |
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41:54 | are also present in neurons and they very interesting because for gap junction to |
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42:04 | two. How many channels. One one neuron cell one You're on one |
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42:12 | of plasma membrane and neuron to Has come together and form a continuous channel |
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42:19 | between the two selves. It was . Connex Solutions connection is a sub |
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42:26 | that makes a single connects on and connect since make a gap junction or |
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42:31 | electrical synapse electrical junction. Why is an electrical synapse and electrical junction? |
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42:38 | if you were to inject current into top sell here and to place a |
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42:44 | electrode. This is your injected Remember? It's a square wave like |
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42:50 | that's electronic and the cell will respond its resistance capacity of properties. We'll |
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42:56 | a strong response in this cell in you pass the current but in the |
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43:03 | cell if you place another electrode immediately any delay, you'll also see a |
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43:12 | current. But this this neuron that bottom is not being stimulated, it's |
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43:17 | the top neuron is being stimulated. , gap junctions, there are certain |
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43:24 | of the gap junctions. Gap past ions through them. So do |
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43:30 | islands. Hyper polarizing islands. Gap also passed small chemicals and molecules through |
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43:38 | . They even can pass the secondary like cycling a. Mp. Who |
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43:44 | junctions. It is somewhat voltage gated there for the most part open all |
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43:51 | time. It's just sit there a bit more open or less open. |
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43:57 | would you want that signal to be so rapidly. And why is it |
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44:03 | ? Why there's no delay because there no sin. Ops the two cells |
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44:06 | touching each other. The car in is now immediately on the other side |
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44:10 | the gap junction there's no synaptic There's no neurotransmitter binding release and travel |
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44:17 | synaptic cleft which takes 5 to 10 for this synaptic process and the response |
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44:23 | take place. This is almost almost immediate. That's very important because |
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44:30 | many instances neurons and neuronal networks need respond and need to synchronize to that |
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44:39 | in a very fast fashion. Therefore junctions electrical synapse allow for fast synchronization |
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44:49 | the neurons through the gap junctions. if you excite one part of the |
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44:55 | network it's connected to the gap junctions another side. The other side of |
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45:00 | network who almost instantaneously get excited and in synchronized to be active at the |
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45:07 | time. Mm So electrical synapses No synaptic delay. Great for synchronization |
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45:19 | the south. But only a fraction this current gets transferred. So there's |
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45:25 | a small amount of that town gets into adjacent south to the gap |
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45:32 | And with the chemical neural transmission as will see there is a delay. |
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45:38 | that's because when the oxen terminal produces terminal of the final action potential. |
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45:48 | action potential will cause the deep polarization the plasma number and opening of the |
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45:53 | gated calcium channels which is necessary for vesicles binding and the transmitter released And |
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46:00 | neurotransmitter gets released and it will cross space of 20 nanometers before it bounces |
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46:06 | synaptic response and then you will have Matic response. So there's a synoptic |
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46:12 | in chemical synaptic transmission which you don't . And the gap junctions. But |
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46:18 | chemical neural transmission you will amplify that . And in gap junctions only a |
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46:24 | of that signal gets transferred. But any delay. There's another homework question |
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46:31 | the year that I actually answer. it's not that much of a homework |
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46:36 | but it's something that will show up the quiz or exam what a dance |
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46:41 | vesicles are. They different from neurotransmitter . So first of all let's talk |
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46:46 | neurotransmitter vesicles. And you have these here and you can see in the |
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46:53 | you have loads of mitochondria. the lows of mitochondria right here and |
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47:01 | you have these active zones, pre active zones and you can see that |
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47:07 | sort of a stacking of these around bubbles. There's the neurotransmitter vesicles that |
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47:13 | the chemical molecules and you can see they're mostly densely populated here and on |
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47:19 | past synaptic side you see also passed density is there's a boston optic |
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47:24 | This is an electron microscope image if look closer at these dots circles and |
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47:33 | synapses. The rounded vesicles and the number and differentiations meaning that the boston |
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47:42 | zone is so much thicker than the synaptic zone. They actually most of |
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47:48 | time will identify with excited to ourselves electron microscopy serve you an electron microscope |
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47:55 | vesicles and this estimate trickle number and . It's an excited tourists announced. |
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48:03 | you see symmetrical number of differentiation You see that the pre synaptic and |
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48:08 | fast synaptic sides are both both equal thickness so to speak in size. |
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48:15 | you can see that these vesicles are flattened. Those are typically the inhibitory |
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48:21 | inhibitor Anthony so excited her would be glutamate vesicles from the vesicles and the |
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48:27 | flattened ones. The symmetrical number and will be that Gabber bicycles. And |
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48:37 | we talked about the synopsis chemical synopsis form on the soma and mostly form |
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48:46 | the damn dries. And if the on the so most are called access |
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48:51 | . If they are formed on the are called accident riddick. Sometimes they're |
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48:57 | formed on the axons and they're called . Oxymoronic. And then there are |
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49:03 | cases to done rights can communicate to other through these chemicals analysis. So |
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49:11 | part of most of the things that be studying is related to accident during |
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49:16 | access synaptic and this actual external synapses gender the drinks synapses we won't really |
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49:23 | time to talk about. Excuse Two improvement. Yeah. Mhm. |
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49:40 | And so again a very good Um It is a microscopic awhile observation |
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49:47 | the level of the I like to . Not certain why there's higher densities |
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49:55 | the excited heard. Uh Plus synoptic are bigger. May have to do |
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50:02 | the fact that and M. A. Receptors are quite large. |
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50:09 | receptors that received glutamate fasten optical are large. It could be one of |
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50:15 | reasons but I don't really have a answer why one is symmetrical. Why |
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50:20 | is a symmetrical. But from anatomically is sort of a classical description of |
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50:26 | excited her inhibitor synopsis. Mhm. So most of the excited their synopsis |
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50:41 | contain when we come to coordinate neural and one or two electricity. There's |
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50:48 | NBA channels. There's an emperor There's tiny channels and most of them |
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50:53 | co express all three subtypes of these actually. So it's not that it's |
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50:59 | than M. D. A. synapse but it's more specific to the |
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51:03 | . There are synopsis per set person will have a combination of receptor |
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51:09 | So again a very very good Um So let's talk about what what |
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51:18 | different about when you're contacting at Right? You're basically sending the information |
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51:25 | an antenna to done right and that is going to inform the soma. |
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51:30 | going to integrate information, accent initial is going to produce an action potential |
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51:36 | you are contacting the soma. You're the integrated region directly saying I got |
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51:43 | talking I'm talking to you inhibiting I'm exciting you. Very tight control |
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51:48 | the integration of what happens to the . A very tight control whether this |
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51:53 | post synaptic cell will fire an action or not. If you excited stem |
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51:59 | it's enough it will fire an action If you're excited so much enough it |
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52:02 | fire an action production. But it's different situation where you have an accent |
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52:08 | another accident. We call this arrangement module a Tory and in this case |
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52:13 | you're doing, you're modulating the output this neuron onto the other south. |
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52:20 | not modulating the integrative properties of this because your Axiron these axons contact dem |
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52:35 | in soma. They are affecting the of the summer. This axon is |
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52:43 | another accident. So what is it ? Is it affecting integration? No |
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52:50 | affecting the output of the cell onto cell. So it's modulating the output |
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52:56 | the sell. It could be that cell produces very high frequency of action |
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53:03 | . This guy comes in as an guy. And all of a sudden |
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53:09 | the cell only here did did did modulated the number of action potentials of |
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53:16 | frequency that was produced by the Yes. Uh huh. But accidents |
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53:28 | DeAndre relax into Selma are the two common ones. Yeah and accented dendritic |
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53:37 | . Um Gun rights accident to Axiron also relatively common. I would say |
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53:43 | done right and done right is relatively type of the synapse. A connection |
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53:57 | . Yes. Yes. It's another commentary question that you will have these |
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54:07 | arrangements. Whether it's an integration. fact a module a Tory effect on |
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54:12 | output depending on the brain region on function and what you're trying to do |
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54:18 | how you're trying to modulate that and fact that specific brain region and what |
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54:22 | of cell you are, you're excited inhibitor itself. So yes. |
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54:28 | Right. How did he says that's problem? Uh Yes. You know |
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54:45 | you know what what my answer Everything is possible. And I say |
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54:51 | because in every science, especially in science, there is rules and there |
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54:58 | always exceptions to the rules And that not be a regular, normal physiological |
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55:04 | . It could be a part of beginning of the physiological state. It |
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55:08 | be a breakdown of some of the . It could be abnormal uh gap |
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55:15 | information because the cells are pushed close physically because of the uh something encroaching |
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55:22 | the territory like a tumor and stuff that. So yes, you |
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55:30 | There are situations, there are models show that I don't know if there |
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55:35 | probably few experiments and accent another accent how it can affect the other cells |
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55:41 | also present. But in general a of things can happen. And I'm |
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55:49 | believer that especially in the brain that pretty complex processing. There are rules |
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55:53 | there's many different exceptions to these rules how the signal moves. And what |
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55:59 | the brain is that when for example seller or brain network is experiencing a |
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56:07 | . I don't channel selectivity is out door. Everything goes everywhere. Those |
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56:16 | interactions with them in acid residues and for engaging out the door numbers are |
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56:23 | . The charges crazy. You everything is open is shunting inhibition that |
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56:28 | talk about where you that's excited to and inhibitory receptor channels can open and |
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56:36 | to signal legs it out. So yeah, so it depends on the |
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56:41 | of the brain but and most of things that that happened or that we |
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56:47 | be learning about is in this realm mostly really on the gun rights and |
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56:52 | symbols. But all of these are great questions. I really appreciate them |
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56:56 | even if I don't have complete answers okay, our next stop was going |
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57:03 | be neuromuscular junction and to understand your junction and we'll talk about the civil |
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57:09 | but we will leave it for our lecture. So they had enough I |
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57:14 | of the material today And again. you for being here. Thank you |
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57:20 | being in zoom. I will see on monday. We'll continue covering synaptic |
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57:27 | and start going into the neurotransmitter systems criteria. Start talking about a single |
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57:37 | and quite a great detail but we'll touch on some other neurotransmitters and when |
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57:42 | talk about neurotransmitter systems we'll come back make it relevant again to some of |
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57:47 | pathologies and diseases that we started For example, when we talk about |
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57:52 | Colin will come back and discuss it the context of Alzheimer's disease as |
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57:58 | Alright, so have a great evening I'll see you next week. |
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