| 00:01 | This is our lecture aid of And we spoke about this technique that |
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| 00:07 | called the voltage clamp technique. And voltage clamp technique, what it allows |
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| 00:11 | to do is to hold a a clamp, a potential of the |
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| 00:15 | values. Instead of just recording how mene potential is changing, you're actually |
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| 00:20 | that membrane potential. And we spoke how this technique voltage clamp technique is |
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| 00:26 | in order to tease out or isolate ionic currents. So Hodgkin and Hockley |
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| 00:33 | voltage clamp in order to demonstrate that the depolarization, you have fast inward |
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| 00:39 | transient sodium currents that are followed by activated, late onset and sustained or |
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| 00:46 | activation outward potassium currents. And so needed the voltage clamp to demonstrate the |
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| 00:53 | of these currents and also using the clamp. So you can very clearly |
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| 00:58 | the equilibrium potential at which the value that ion or the direction of the |
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| 01:03 | at that value, the direction of current for that ion reverses ions instead |
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| 01:08 | sodium flowing inward as its potential will blowing outward. Now, this is |
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| 01:16 | composite uh of individual channels that we record. We talked about individual channel |
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| 01:23 | . We'll talk about some more recording briefly uh of the inward current that |
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| 01:27 | followed by the potassium deflux of potassium current. That's what potassium is referred |
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| 01:33 | as delayed rectified. It's trying to the membrane back into the resting membrane |
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| 01:39 | preaction potential levels. We spoke about these voltage gated channels are complex |
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| 01:46 | We spoke about voltage gated sodium So that has certain features. So |
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| 01:51 | transmembrane four subunits. Fourth segment s is a voltage sensor that air can |
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| 01:58 | between us five a six. We'll see that it has six as a |
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| 02:02 | binding site for lidocaine. These channels two gates and they closed with |
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| 02:09 | These channels can open, the depolarization come from excited for synaptic inputs from |
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| 02:15 | neurons. The depolarization can come from external stimulus, a light for |
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| 02:19 | or sound that will cause that initial and cause the opening of in this |
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| 02:26 | voltage gated sodium channel. So I'm about other senses and stimulation of other |
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| 02:30 | just as an example of things that uh open the channels. And in |
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| 02:35 | case, it's the voltage that opens channels, there's a change in voltage |
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| 02:40 | that happens typically either due to stimulus synaptic stimulation from uh from an adjacent |
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| 02:47 | . We also spoke about the fact if you depolarize plasma membrane, these |
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| 02:51 | will open and they will be But as soon as that voltage sensor |
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| 02:56 | up and opens the channel one millisecond , the channel gets inactivated and it |
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| 03:02 | stay inactivated unless the number in control is brought back to the hyper polarized |
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| 03:09 | . In this case, the channel inactivates de inactivated and it closes again |
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| 03:15 | that it can be opened with a depolarization. Again, when we spoke |
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| 03:22 | how there are different mutations along this gated sodium channel. And we talked |
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| 03:27 | the genetic disease, in particular, channelopathy uh that uh mutation to various |
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| 03:35 | of this channel where you have green would result in generalized epilepsy with febrile |
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| 03:41 | plus. So we spoke about what generalized epilepsy, loss of consciousness, |
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| 03:45 | associated with pretty heavy severe seizures, of consciousness, febrile seizures is hypothermia |
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| 03:53 | seizures and having one febrile seizure or does not make you epileptic, but |
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| 03:58 | uh can contribute to you forming epilepsy . And if you have a mutation |
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| 04:04 | these channels, your body temperature doesn't to go up as high in order |
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| 04:08 | you to uh experience this febrile And in addition to GS plus, |
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| 04:14 | is general generalized epilepsy with febrile Plus, we also spoke about SME |
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| 04:25 | SME I which stands for severe myoclonic . OK, of infancy. So |
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| 04:50 | SME I and the where you have where along the red dots along the |
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| 04:59 | of the va child. Um it cause this uh severe meic epilepsy of |
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| 05:07 | or dry syndrome is another name for . This is D syndrome. |
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| 05:27 | Yeah, I use uh so can repeat that? I know we call |
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| 05:38 | how we use data channels are connected the back line. Keep the, |
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| 05:44 | is a single channel. OK. , this is a single channel with |
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| 05:48 | subunits and these four subunits have to together, they're like building blocks and |
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| 05:55 | of them have to come together like , for example, in order to |
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| 06:00 | a, a channel inside. So one of these is a sub unit |
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| 06:05 | six transmembrane segments. Yeah. So not the, the segments are connected |
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| 06:11 | the amino acid cation chain. All right. So this is the |
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| 06:21 | , one of the most fun lectures for me because we get to watch |
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| 06:25 | cartoon and it's The Simpsons. So pretty insulting to everybody and nobody should |
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| 06:33 | insulted. Um It's not as bad South Park and it's a lot of |
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| 06:41 | and you'll understand why we're watching this just about it. Second. |
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| 06:55 | Oh Hey. Mhm. Oh See going on with the volume here? |
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| 07:20 | , what's this Fugu? It is blue pizza. I bet I should |
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| 07:26 | you that. 11 pal fugle They say this cat shafts are |
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| 07:33 | It's not gonna work without sound the . Let me see what can be |
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| 07:38 | here. This is very loud and amazing. Mhm Mhm. Your |
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| 08:27 | But I'm talking about Shaq. You anything, huh? He's a complicated |
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| 08:32 | . But no one understands him but woman and Shaq, oh, she's |
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| 08:40 | to her for me. Want to not fugu, if it is cut |
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| 08:46 | it, yes. Yes. It poisonous. Potentially fat. But inside |
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| 08:51 | can be quite tasty. I must the master. Oh, I might |
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| 09:06 | a sound and it's not. yeah, that's a maximum. So |
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| 09:28 | probably has something to do with these here. Maybe I need to. |
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| 09:34 | no, maybe I need to Mhm. See what happens now. |
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| 09:50 | there. Hopefully the sound will kick because it's a really fun video. |
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| 10:02 | , hey, what's this fugu? is a blue pizza but I should |
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| 10:09 | you that one pal fugle me. say this cat shafts a bad mother |
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| 10:16 | mouth. But I'm talking about chefs I can dig it. He's a |
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| 10:22 | man but this woman can chat. , she's here. Cover for me |
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| 10:33 | to go. Not fugu. If is cut improperly, it's. |
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| 10:37 | Yes. It is poisonous. Potentially . But if sliced properly, it |
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| 10:42 | be quite tasty. I must get master. Oh Miss crab. |
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| 10:50 | your hair smells so master you are in the kitchen. I said cut |
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| 10:57 | only dart but master we need your hands. My skilled hands are |
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| 11:03 | You get. Mhm ah poison poison . Concentrate, concentrate. Mm F |
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| 11:25 | tasting all of beautiful language, isn't ? Don't eat another bite. |
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| 11:44 | I couldn't bother, please, Mr . Son. I shall be |
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| 11:47 | We have reason to believe you have poison poison. Look, what should |
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| 11:53 | do? What should I do? me quick. No need to |
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| 11:56 | There's a map to the hospital on back of the menu. Dry |
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| 12:02 | New Homer. Well, it hurt homer. I never heard of a |
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| 12:05 | pork chop. Your wife agreed that should break this to you. No |
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| 12:10 | doc. I can read Marge like book. It's good news, isn't |
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| 12:17 | ? Simpson? If in fact, consumed the venom of the blowfish. |
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| 12:21 | from what the chef has told it's quite probable. You have 24 |
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| 12:26 | to live 24 hours. Well, . I'm sorry. I kept you |
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| 12:30 | so long. I could have, could have died. Well, if |
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| 12:36 | one consolation, it's that you will no pain at all until sometime tomorrow |
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| 12:41 | when your heart suddenly explodes. a little death, anxiety is |
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| 12:45 | You can expect to go through five . The first is denial. No |
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| 12:49 | because I'm not dying. Second. it you after that comes fear, |
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| 12:56 | . What's after? Fear? Bargaining ? You gotta get me out of |
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| 12:59 | . I'll make it worth your Finally. Acceptance. Well, you |
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| 13:03 | gotta go jump time, Mr Your progress astounds me. I should |
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| 13:07 | you two alone perhaps. This pamphlet be helpful. So you're going to |
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| 13:13 | like, ok, the more exotic in store known to hardly anyone in |
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| 13:28 | West. For example, the the poisonous puffer fish of which there |
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| 13:34 | about 100 species worldwide. You need license to sell puffer fish in |
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| 13:40 | But as a buyer, you need too. Uzo Okamoto has a fugu |
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| 13:50 | and of course a license he's not to buy the increasingly popular non toxic |
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| 13:56 | fugu which can be recognized by its fins. Nor is he interested in |
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| 14:01 | species caught in the wild from Japanese . This true connoisseur is only looking |
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| 14:08 | one thing toxic wild fugu as fresh possible. And that means Tora |
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| 14:14 | tiger puffer fish, the Kobe beef Fugu cuisine, a single specimen of |
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| 14:34 | species which is only found in the of Japan may well cost €100. |
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| 14:48 | of Tokyo's historic districts is located around Temple. Most wild Fuku restaurants are |
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| 14:55 | be found here. There are about restaurants specializing in Fugu in Tokyo today |
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| 15:02 | the outside, they're usually easy to and they're always highly specialized. One |
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| 15:12 | them is Rizo Okamoto restaurant where sometimes prime ministers drop by. Wo say |
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| 15:19 | its name the pure fish place. also need a license to prepare |
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| 15:25 | The poison in Fugu is tetrodotoxin. 1000 times more potent than cyanide and |
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| 15:32 | is no antidote the poison paralyzes its but leaves them fully conscious. Proper |
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| 15:41 | is critical. The skin and entrails the fish are poisonous and they must |
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| 15:46 | contaminate the non toxic meat on the . High concentrations of highly poisonous tetrodotoxin |
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| 16:02 | found in the innards, especially the and ovaries. Special disposal is |
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| 16:11 | Mhm. A seasoned Fugu chef like Sam takes about 10 minutes to neatly |
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| 16:28 | . A tour of Fugu most commonly fish is cut into thin slices and |
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| 16:33 | raw as sashimi. In fact, taste of unprepared puffer fish is unspectacular |
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| 16:40 | bland. The U Ozai restaurant exclusively its guest. Fugu captured in the |
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| 16:49 | in small doses. The poison of Fugu fish triggers numbness in the mouth |
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| 16:54 | is intoxicating. But here they do cater for guests who might be eager |
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| 17:00 | try out tiny doses of this What we serve here is 100% non |
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| 17:15 | . If we break this law, ruined. A real Fugu meal consists |
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| 17:25 | at least six courses. This ultimate gourmet pleasures is mainly enjoyed in Japan |
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| 17:36 | there is something to celebrate. the chances of being poisoned at a |
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| 17:42 | restaurant are practically zero. Thanks to high demands placed on the chefs. |
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| 17:54 | I see what on 50 years more than 100 Japanese died each year |
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| 18:02 | fugo poisoning. Today, there are three a year. All victims of |
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| 18:07 | amateur and recreational cooks. I'm not at all. I ate a Fugu |
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| 18:20 | a child and it always tasted very to me. Fu is a delicacy |
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| 18:30 | eaten in Japan despite earthquakes, tsunamis nuclear disasters. Rizo Okamoto will not |
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| 18:37 | out of work. And in the too, it's likely to remain quite |
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| 18:55 | . So that's pretty, pretty And you'll never forget that. Tur |
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| 18:59 | Thomson lives in Fugu fish. All have to do is remember Simpsons or |
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| 19:06 | video, which is really neat. always wanted to go to the Asakusa |
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| 19:11 | area. There isn't a restaurant here my knowledge in Houston. Although we |
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| 19:15 | such an incredible diverse uh um ethnic from all over the world. That's |
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| 19:21 | of the best things about Houston foods around the world. But there's no |
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| 19:27 | fish that is being certain. So puffer fish, it contains TT |
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| 19:35 | What TT X is is we didn't except that it blocked action potentials and |
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| 19:42 | it's potent. It can be deadly ingested. It is a part of |
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| 19:47 | food chain and puffer fish do not tetrodotoxin. And that's why they talked |
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| 19:55 | how there are toxic species of And we're not interested in these farm |
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| 20:01 | species that don't have any TT So it's not something that the fish |
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| 20:08 | . It's a part of the bacteria bacteria as a part of these animals |
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| 20:14 | their entrails in their liver and other , ovaries and skin that has high |
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| 20:21 | of that TT X. And that's those animals are susceptible to carrying that |
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| 20:30 | . And the species are farm they're raised differently. Those other |
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| 20:34 | they, they don't contain TT X them. There's a little bit of |
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| 20:38 | conflicting information there in that documentary, we don't serve anything toxic here and |
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| 20:44 | commentator says, but they have high of this toxin in there. So |
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| 20:49 | going on here? There's obviously a bit of leftover somehow of that toxin |
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| 20:54 | the, in the muscle and the of the fish. And the thrill |
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| 20:59 | to consume it so that you get mouth numb for some moments. It's |
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| 21:05 | interesting. Uh It's uh obviously a cultural thing, but I would, |
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| 21:11 | would, I would really like to it, but you have to try |
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| 21:14 | from a licensed chef. Obviously, recreational fugu peddlers. They are, |
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| 21:20 | know, they don't know how to the meat, right? So, |
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| 21:23 | that's why people were getting poisoned some ago because there was a, a |
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| 21:28 | that later was established to get certifications cut and uh and, and prepare |
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| 21:34 | fish by the chefs and it takes a bit of skills to do |
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| 21:38 | Uh OK. So it's in, bacteria. Yeah. Is that the |
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| 21:42 | place that, that bacteria is No, it's, it's, it's |
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| 21:47 | in other places and there's also other toxins that are produced by other organisms |
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| 21:54 | we talk on the next slide So now the interesting thing about this |
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| 22:02 | is that when Toji Nahai found this , he saw that it blocks |
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| 22:08 | So you took a vial of this to the United States in the late |
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| 22:13 | . And he needed to get a of voltage clown. When he got |
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| 22:17 | hold of voltage clown, he was to isolate inward sodium and outward potassium |
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| 22:24 | using voltage clown. And when he tetrodotoxin, it specifically and exclusively blocked |
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| 22:32 | gated sodium channels and it did not , it does not affect the outward |
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| 22:38 | channels, the outward carb with So this toxin is specific to voltage |
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| 22:44 | sodium channels. And that's how Doctor Hashi answered the question that it blocks |
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| 22:49 | potentials by blocking the voltage gated sodium . It's called a blocker or |
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| 22:58 | So something that blocks the channel or the channel activity, it's an |
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| 23:04 | In this case, this antagonist is . So TT X is a reversible |
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| 23:14 | . They said that there is no antidote but reversible antagonist means that the |
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| 23:21 | binds to the receptor and can be away this in form of covalent |
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| 23:26 | And so if you get to the after uh TT X poisoning within 45 |
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| 23:33 | , there's a chance they could actually some of it away. Um iii |
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| 23:38 | if, if it's in time apart from the toxins that are found |
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| 23:44 | nature that we already talked about scorpion . Remember that Roderick mckinnon used scorpion |
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| 23:51 | to block and target voltage gated potassium . And he was using those toxins |
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| 23:57 | order to deduce and understand the three structure of those channels. Uh So |
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| 24:04 | are also substances that are synthetic or , synthesized, chemicals, chemicals from |
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| 24:09 | , chemicals from natural precursors. But is a tetra ammonium which we abbreviate |
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| 24:16 | te a and that's a specific blocker potassium current. So there are many |
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| 24:22 | chemical substances that will target different parts channel, the same channel or different |
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| 24:29 | , different substances, some that are to sodium, blocking sodium carbs. |
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| 24:34 | of them are specific and they're blocking cars, of course, a lot |
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| 24:41 | these channels, voltage gated sodium different subtypes of them will be found |
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| 24:45 | other parts of the body. We're talking about the brain here, but |
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| 24:49 | be also found in the heart and diaphragm. And so the death from |
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| 24:54 | toxin comes typically from uh being paralyzed uh not having the ability to breathe |
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| 25:05 | . So other toxins, there's a of toxins. There's a whole menu |
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| 25:11 | uh there are toxins, multiple toxins will target sodium channels. So during |
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| 25:19 | red tides, what we call in southern waters, especially here in uh |
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| 25:25 | coast waters, Texas, Florida on other side in the Atlantic, not |
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| 25:31 | much, but it can be also the southern States. On the Atlantic |
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| 25:37 | . During warm temperatures, there's a up of uh bacteria and there's bacteria |
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| 25:44 | often inhabit themselves in the shellfish such oysters or clams. And quite often |
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| 25:55 | the hot months of the year, going to be recommended not to consume |
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| 26:00 | shellfish. And I was taught when moved here to Texas first, actually |
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| 26:06 | Louisiana, then to Texas that all the months that have r in |
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| 26:13 | you can consume shellfish. So February, March, April, not |
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| 26:19 | May, not in June, not July, not in August. September |
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| 26:23 | still questionable but as in are and onwards all the way to November, |
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| 26:27 | to December. Uh we love oysters the half shell down here in Louisiana |
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| 26:35 | . We love everything on the half . We love red fish on the |
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| 26:38 | shell, love oysters on the half . It's very popular way to consume |
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| 26:43 | raw. Uh It's very tasty. has incredible amount of protein. Some |
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| 26:48 | the highest concentration of protein is in oysters. Uh but it can |
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| 26:55 | this toxin, which is called saxy , saxitoxin, saxitoxin and it's also |
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| 27:05 | sodium channel blocking toxin. There are dark frogs that live in, in |
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| 27:12 | America and they're called dark frogs. They contain Bacot toin, they're called |
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| 27:21 | frogs is because some of the indigenous populations would have little darts that they |
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| 27:31 | put poison from these frogs on the of the dart. And they would |
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| 27:37 | these poisoned darts to hunt for other or to fight against intruders or |
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| 27:46 | including humans. So that's why they them dart frogs. They have daco |
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| 27:52 | . Now that acts on the same gated sodium channel, but it does |
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| 27:57 | very different. It blocks inactivation. is inactivation. So if there is |
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| 28:06 | act inactivation, if the channel opens doesn't inactivate, the channel will continue |
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| 28:14 | open. So that's what it So the channel remains open. There |
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| 28:20 | differential toxin binding sites, they bind different parts of this channel which just |
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| 28:28 | , some of them will bind to part of the channel, it blocks |
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| 28:31 | , two of them saxitoxin tt Others bind to inactivation gate of the |
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| 28:36 | , but actually keeps it open for time. And all of this can |
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| 28:42 | us just like with Robert mckinnon's experiments he used those different techniques to deduce |
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| 28:47 | three dimensional structure of potassium channels. of this helps us in the older |
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| 28:53 | to deduce the three dimensional structure of sodium channels as well. Here's another |
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| 29:00 | common substance is a common local anesthetic you would have for local minor |
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| 29:08 | It would be used, there's lidocaine for pain relief. Uh There's use |
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| 29:15 | lidocaine at the dentist's office when they're some dental work, uh they will |
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| 29:21 | it and rub it on your Typically it, it has some flavoring |
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| 29:25 | it or maybe a little bit of taste and, and some clove power |
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| 29:31 | add it on to it. But has its own distinct binding side. |
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| 29:34 | it binds to s 610 numbering segments uh it is a blocker of voltage |
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| 29:45 | sodium channel and by blocking voltage gated channel. Now, we're talking about |
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| 29:49 | the periphery on the nerves and is . So it has analgesic numbing an |
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| 29:57 | analgesic properties, really more anesthetic blocking perception of pain if you make. |
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| 30:04 | we already know how to probe these and how to use different techniques such |
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| 30:09 | voltage cloud. And this is what talked about. There are several techniques |
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| 30:13 | you attach yourself to a cell, mode is called cell attached mode. |
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| 30:18 | the way this happens is that you a neuron and that neuron has an |
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| 30:25 | . And that electrode is if the of a neuron this time is not |
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| 30:30 | very well. The size of a is about 10 micrometers in diameter. |
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| 30:41 | tip of the electrode is only one , but the size of this electric |
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| 30:47 | to the South is on the water centimeters. And so we have this |
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| 30:53 | giant pool filled with water. This that now latches on to the number |
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| 31:01 | the cell attach mode. When you a cell attach mode, you're just |
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| 31:05 | to what the cells are receiving. , it's like an antenna. Your |
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| 31:10 | serves like an antenna. And this is actually connected to the tube. |
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| 31:19 | connected to a little tube and that tube is connected to another tube and |
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| 31:26 | it's connected to a syringe and it inside the syringe like like this. |
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| 31:33 | on this syringe, the experimenter puts lips on the syringe, it produces |
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| 31:39 | suction and the suction allows for this to attach to neuron all the great |
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| 31:46 | to learn. So you would use microscopy because you can visualize neurons without |
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| 31:50 | stain electrophysiology, patch, clamp recordings cell attached recordings. And this is |
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| 31:59 | you do this. So if you a little bit of suction, you |
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| 32:03 | onto the plasma membrane, you're in cell attached mode. If you apply |
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| 32:08 | little bit more suction in the the experimenter puts their lips on this |
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| 32:13 | you like this suctions, it you break into the cell and this is |
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| 32:19 | the whole cell recorded. It's very that during wholesale recordings, the solution |
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| 32:28 | the electrode which we call the reporting solution is exactly the same composition as |
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| 32:34 | cytoplasm of this neuron. Because you know all the good things about osmosis |
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| 32:39 | things like that. If there is molarity or too much water, the |
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| 32:44 | shrink or they swell or they explode they die from shrinkage. So it |
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| 32:50 | to be precisely tuned with what is the cytoplasm. So the, it's |
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| 32:56 | what is in the extracellular solution. if you want to, you have |
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| 33:00 | huge reservoir, put, if you too much water concentration in this |
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| 33:06 | the cell is going to die. , but if you have a whole |
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| 33:10 | access, you're recording all of the going in and out of the cell |
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| 33:16 | in another configuration, you can attach with a syringe on the membrane and |
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| 33:21 | some other ritual whatever magic you for a couple of times, bang |
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| 33:27 | the table and then maybe drop the sideways. And if you're lucky and |
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| 33:33 | the electrode, you will actually have patch of the membrane that you would |
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| 33:37 | . Now you can do single channel in here and there's an advantage to |
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| 33:44 | ear because if you do this kind uh electrophysiological preparation, you expose the |
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| 33:51 | of this channel to the experimental not just to the ear but to |
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| 33:56 | solution. So there are some sub like pharmacological substances that can cross the |
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| 34:04 | membrane, but they do it in very slow fashion. So if you're |
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| 34:09 | a wholesale recording and you apply that , you may have to wait for |
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| 34:13 | minutes that present some other variables and to experiment, to wait 20 minutes |
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| 34:19 | order to to to see an effect that molecule, because that molecule very |
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| 34:25 | will cross through the plasma membrane and very small amount will cross and then |
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| 34:30 | will attach on the inside of the . But here you have the inside |
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| 34:36 | the channel exposed to the outside That's what's called the inside out |
|
| 34:40 | Now, you can put that substance interest that you're studying and see really |
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| 34:45 | , what effect significant effect has. if I had a lot more of |
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| 34:49 | on the inside of the cell? does it affect it? You can |
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| 34:52 | substances and see you have substances that to the extracellular domains here and you |
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| 34:59 | substances that bind to cytoplasmic domain. this is a very important technique for |
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| 35:06 | or for any pharmacological development of drugs target channels or target cellular occurrence of |
|
| 35:14 | . In another situation, you actually to the cell, you have cell |
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| 35:19 | , recording, you take this piece the membrane, you withdraw the electrode |
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| 35:24 | the piece of the membrane and then apply stronger section in the electrodes and |
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| 35:29 | break the piece of the membrane, whatever ritual you need to do, |
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| 35:33 | a few times. And if you're and that it is very difficult for |
|
| 35:37 | , there's an element of luck in technique but also luck this membrane, |
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| 35:42 | break and broken membrane will re anneal because it's possible at the bilayer. |
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| 35:49 | when it does, so it will re anneal in such a fashion that |
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| 35:53 | extracellular side, the extracellular domain of protein channel is now exposed. So |
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| 36:01 | , you can again do pharmacological use voltage plan a very precise environment |
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| 36:09 | which you can submerge these channels to what effect different chemicals have on the |
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| 36:14 | of cytoplasmic domain versus the extracellular domain the channel. So all of these |
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| 36:21 | including the voltage clamp will allow us study um and the diversity of these |
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| 36:29 | allow you to study substances that can the inside of the channel versus the |
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| 36:34 | of the channel action potential. We about action potential a lot, but |
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| 36:40 | didn't actually talk about where it happens where it is initiated. We just |
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| 36:46 | that action, initial segment goes to SOMA spike initiation zone right here, |
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| 36:51 | Saxon villa, that's where the actual is gonna be generated. Uh |
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| 36:58 | And that's because this area and the in general will contain high densities of |
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| 37:05 | gated sodium channels as well as voltage potassium channels. And if you look |
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| 37:10 | it in great detail in a in slide, except for sensory neuron, |
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| 37:16 | you recall sensory neurons such as dorsal neuron has the peripheral axon that is |
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| 37:22 | the periphery and it also has a axon. So these sensory cells sometimes |
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| 37:27 | initiation can actually happen and usually at end of the axon and that's just |
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| 37:33 | different functional arrangement for these cells uh a different morphology for these types of |
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| 37:40 | . But typically, and what we'll discussing, we'll be discussing one of |
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| 37:44 | favorite cells is this parameter cell. campus, you all know everything about |
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| 37:50 | cell and of this neuron and a cell projection cell releases glutamate excitatory. |
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| 37:58 | aren't that many different subtypes of the , but it actually comes the majority |
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| 38:03 | cells in the calpol and in the . And you also know this |
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| 38:09 | it's a pseudo polar cell, it's , it has uh peripheral central |
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| 38:17 | it releases I'm excited to a neurotransmitter in your table. You have to |
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| 38:24 | to remind your cells. I know just tell you. And then you |
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| 38:29 | have motor neuron which is multipolar cell it's a projection cell out of the |
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| 38:35 | cord goes into the muscles and it the neurotransmitter that I won't tell you |
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| 38:40 | I know then you have the inter that is local circuit cell inside the |
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| 38:46 | cord is also multipolar cell and it release an inhibitor neurotransmitters that are in |
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| 38:55 | table for you to review. But is where action potential gets generated in |
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| 39:01 | very special area called the axon hillock here right next to the. |
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| 39:09 | so what happens is that this as we mentioned, this neuron will |
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| 39:15 | receiving a lot of inputs, some these synaptic inputs and some of the |
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| 39:20 | is going to be depolarizing, it's to be excitatory. And that's another |
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| 39:26 | to remind yourself. And this is we'll study when we study synoptic transmission |
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| 39:32 | that once there is a neurotransmitter released and if there's enough activation of the |
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| 39:40 | , it reaches the threshold, it produce the action potential. So |
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| 39:44 | the cell is maybe sitting at minus millivolts or so at risk. |
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| 39:53 | And resting number of potential of minus and the cell is not sitting there |
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| 40:05 | this. So it may receive a input sanitary input. But the threshold |
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| 40:11 | action potential generation is this minus 45 value. So it may receive a |
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| 40:20 | depolarization. It may receive a small polarization, it may receive a little |
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| 40:25 | depolarization, small hyper polarization. So are synaptic potentials and they're graded |
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| 40:35 | And if there is enough depolarization in selma and this Axon hila right, |
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| 40:43 | the depolarization is winning because the cell receiving both excited or an inhibitory inputs |
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| 40:50 | each input is really small. So have to activate many different synapses in |
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| 40:55 | to reach the threshold. If once the action potential gets produced in |
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| 40:59 | Axon hillock. Axon Hillock is shown contains a high density of voltage gated |
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| 41:06 | channels and potassium channels. And this potential gets regenerated at each node of |
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| 41:12 | deer and each node of on the is packed again with high densities of |
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| 41:19 | gated sodium channels and voltage gated potassium . So you generate the action |
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| 41:25 | it stays within the actual the axon being insulated. Uh the flow of |
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| 41:32 | information and the forward manner called orthodromic potential travels in one direction down as |
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| 41:40 | terminal. And that's exactly what Ramona proposed. He said that there's a |
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| 41:46 | of dynamic uh polarization. So he that inputs come into the dendrites, |
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| 41:51 | get processed by the SOMA and the goes the AXON. So we call |
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| 41:56 | the orthodromic action potential or forward propagating potential, it propagates from the SOMA |
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| 42:04 | the external terminal. It regenerates each of round here. So we refer |
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| 42:10 | it as saltatory conduction as it reaches external terminal. The purpose of this |
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| 42:16 | propagating action potential is going to be cause depolarization here in external terminal and |
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| 42:21 | cause neurotransmitter release, which is going cause synaptic potentials on the adjacent |
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| 42:28 | And the difference is that if you this threshold of action potential, action |
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| 42:34 | is all or non even, you reach minus 40 millivolts and go |
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| 42:39 | It will always, if you reach level, you will generate an action |
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| 42:43 | here. So the synaptic inputs, come in different sizes, smaller, |
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| 42:48 | . That's why we call them graded , post synaptic potentials. But this |
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| 42:54 | all or non enough to action typical conduction velocities, 10 m. |
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| 42:59 | second typical length of action potential is in the sense of the duration of |
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| 43:05 | action potential is two milliseconds. And we also know that in in, |
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| 43:12 | addition to this forward propagating action potential causes the vesicular release and neurotransmission. |
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| 43:20 | also small action potential, we call propagating action potential that travels in the |
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| 43:27 | direction. We call anti drama And for a while they, if |
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| 43:32 | stimulate the axon, you can make the anti dr flow of information back |
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| 43:37 | the SOMA in the opposite direction. you also have a little bit of |
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| 43:41 | of the back propagation for this action back into the SOMA. So it's |
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| 43:46 | propagation. So you can have it from axon initial segment that we'll just |
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| 43:51 | about. In the next slide, can also force by stimulating the axon |
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| 43:56 | it to for the signal to flow the opposite direction. So it calls |
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| 44:00 | question this principle of dynamic polarization by Cajal and informs us that currents can |
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| 44:07 | including the action potential. A small in the opposite direction from what he |
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| 44:12 | original. Remember that we have insulation Sos and PN ss O Ligo Denroy |
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| 44:20 | CNS. It's Salvator conduction and you a lot of voltage gated sodium channels |
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| 44:25 | are concentrated, that have nodes of that allow for that action potential to |
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| 44:31 | regenerated in each node of Ron And uh there, there was a |
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| 44:38 | for an explanation of how this back action potential happens. How can you |
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| 44:44 | , can you actually have two action coming from the same Axion Hill of |
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| 44:48 | that is going to be forward propagating other one that is going backward, |
|
| 44:52 | . How does that happen? So 2009, uh a very good uh |
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| 44:59 | and colleague of mine, Dr Chris , who is a professor of Neuroscience |
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| 45:03 | Tufts University in Boston. And John , his previous boss at Stanford |
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| 45:09 | They came up with this explanation in . So I I was speaking with |
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| 45:15 | last year on the phone and I , hey, Chris, has anybody |
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| 45:19 | up with like better explanation? Both is based on experiment and theoretically of |
|
| 45:24 | forward back getting action potential. Uh somebody tried to challenge it in some |
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| 45:29 | , but it's still kind of the explanation, both that we observe experimentally |
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| 45:35 | also explanation that we, we still somewhat theoretically and the way that Chris |
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| 45:42 | and John explained this is that when can have a very strong depolarizing |
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| 45:48 | notice that it shows a lot of excitatory inputs on the apo dentes of |
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| 45:54 | cell. And it shows quite a of inhibition surrounding the selma. And |
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| 46:00 | is actually the case, a lot inhibition will be targeting the SOMA regions |
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| 46:04 | remember that inhibition is controlling the output the cell is going to produce. |
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| 46:09 | if the cell receives strong enough excitation this excitation wins over and depolarizes the |
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| 46:17 | , depolarizes the cell and depolarizes the hila in Axon Hillock, it will |
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| 46:24 | the forward propagating action potential and the propagating action potential by using two subtypes |
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| 46:31 | volt educated sodium channels. So, it happens that this Axon Hillock has |
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| 46:37 | sub types of voltage gated sodium NAV 1.6 which we call low threshold |
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| 46:45 | gated sodium channel, low threshold voltage sodium channel. 1.6 is the subtype |
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| 46:51 | A sodium V volt voltage 1.6 it's located in Axon Hillock, but |
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| 46:58 | located some distance away from the selma closer to the selma, we have |
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| 47:04 | subtype of voltage gated sodium channel of . And this 1.2 channel is referred |
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| 47:10 | as a high threshold voltage gated sodium , high threshold versus low threshold, |
|
| 47:16 | threshold means that in order to open channel, you need a lot of |
|
| 47:22 | . Remember think about what we talked how these channels are gated, they're |
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| 47:26 | by voltage. So if you have very uh positively charged S four voltage |
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| 47:34 | that can move very freely, then quite reactive to a change in |
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| 47:39 | What if you have much larger, cumbersome S four transmembrane segment possibly charged |
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| 47:46 | takes some time and more current in for it to feel more depolarization |
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| 47:53 | in order for it to be repelled move. So it more, more |
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| 47:58 | is higher threshold in order to open channel. So these are high threshold |
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| 48:04 | this is low threshold sodium channel. means you need a little bit of |
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| 48:08 | and that sensor will move in the over. And so what happens is |
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| 48:13 | depolarizing current comes in, enters into soma depolarizes the axon and it actually |
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| 48:21 | in this direction. But it bypasses 1.2 does not activate NAV 1.2. |
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| 48:30 | it bypasses and it triggers the activation NAB 1.6. This is not enough |
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| 48:37 | , it's not enough threshold to open channels, but it's enough for NAV |
|
| 48:43 | and they open and they produce this explosion in the form of the action |
|
| 48:49 | . And this action potential is going be traveling in this forward propagating fashion |
|
| 48:55 | cause neurotransmitter release. Now, as as this explosion happens and the low |
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| 49:04 | sodium channels are open, you still depolarization that's coming in here. |
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| 49:11 | you have a lot of depolarization nearby of the sodium current through the N |
|
| 49:17 | 1.6 the two. Now some together and this depolarization now is high enough |
|
| 49:27 | the threshold in order to open high of the depolarization to open this channel |
|
| 49:34 | this channel opens. So he rushes and you'd say well, then sodium |
|
| 49:38 | gonna go this direction except that you have this massive depolarization. This is |
|
| 49:44 | happening within a fraction of millisecond. still have massive depolarization here. So |
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| 49:51 | current is not gonna move where there action potential, positive current is gonna |
|
| 49:55 | where there is closer to the threshold it moves in the opposite direction. |
|
| 50:01 | is back propagating it back propagates from axon into the SOMA and potentially into |
|
| 50:09 | dendrites. So if the purpose of action potential, the forward propagating action |
|
| 50:18 | is to release the neurotransmitter to cause release. What is the purpose of |
|
| 50:24 | back propagating action? And as it out this back propagating action potential is |
|
| 50:31 | important for the cell to know and this communicating cells to know that this |
|
| 50:39 | has responded positively to this depolarizing Otherwise, this of these synaptic inputs |
|
| 50:46 | not have any backflow of the any information. So it's very important |
|
| 50:51 | binding the information from pre synoptic inputs this post synoptic response. And it's |
|
| 50:58 | important for plasticity. And in when we learned about plasticity, strengthening |
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| 51:05 | or weakening synopsis, that's why it's important as back propagating action potential. |
|
| 51:11 | in particular, there is a form plasticity called spike timing, dependent |
|
| 51:16 | So everything that neurons do is very , we're talking on the order of |
|
| 51:21 | . So if this depo horizon current in here produces an action potential within |
|
| 51:27 | , gets a back propagating spike within , it starts tuning, it starts |
|
| 51:32 | stronger, it has strong communication and inputs and strong pontic response. And |
|
| 51:39 | has to happen within a certain short of milliseconds within about 10 to 20 |
|
| 51:45 | to be meaningful for neurons. for you, you know, you |
|
| 51:49 | in the room and you say hello somebody, you know, and that |
|
| 51:52 | says hi, you know, then continue the conversation. How's it |
|
| 51:55 | Good? You know, what are doing and so on, you walk |
|
| 51:57 | the room and you look at the in the eye and you say |
|
| 52:00 | that person just looks at you, know, so like 10 seconds, |
|
| 52:03 | even 20 seconds gets a little You know, you just go on |
|
| 52:08 | your day and start doing things that doing and then that person says five |
|
| 52:11 | later, oh hello. You like what is that? Is that |
|
| 52:15 | to me? Are you talking to ? You know, like is that |
|
| 52:18 | ? Is that so long ago you're responding, I'm on to doing something |
|
| 52:23 | . So this is how neurons have communicate. But they have to do |
|
| 52:26 | within milliseconds. There has to be response and the inputs have to know |
|
| 52:31 | this response happens. So this is simplistic explanation of backing spike. There |
|
| 52:37 | a much more uh um technical explanation spike, founding dependent plasticity. In |
|
| 52:44 | , I have a paper on spike dependent plasticity that I published uh together |
|
| 52:49 | my mentor from Johns Hopkins University. I was opposed to uh it's really |
|
| 52:54 | cited paper. We studied this type synaptic plasticity um to test that it's |
|
| 53:00 | that you have this back propagating We did a lot of studies using |
|
| 53:05 | kind of a experimental paradigm. But now you understand that there are essentially |
|
| 53:11 | ways in which actions potential can This is the large 100 mill of |
|
| 53:16 | fast uh forward propagating spy. This much smaller, it's on the order |
|
| 53:22 | a hum mia. So this depolarization much smaller just on the order of |
|
| 53:28 | compared to forward propagating pipe. And back propagation is really important in binding |
|
| 53:33 | presynaptic input posy, responsive and making those connections plastic between communicating |
|
| 53:44 | All right. So we learned a in this section, we learned how |
|
| 53:50 | are what they are neurons glia notice when we talk about action potentials, |
|
| 53:56 | talk about neurons, we don't talk glia because glia do not produce action |
|
| 54:04 | . Glia had different means of We uh pass ions, they have |
|
| 54:10 | waves, they can have potassium waves there is a high rising potassium |
|
| 54:16 | but they do not produce it. is specific to neurons, the action |
|
| 54:20 | and the action potentials in the cns are really, really fast. So |
|
| 54:25 | to a few milliseconds, you have potentials in the cardiac muscle, you |
|
| 54:30 | action potentials in the skeletal muscle, are much longer in duration. Uh |
|
| 54:37 | of milliseconds in duration. They involve mechanisms. For example, muscular contraction |
|
| 54:42 | involve influx of calcium, not just . So it will be different dynamics |
|
| 54:48 | you will see in neuromuscular junction from muscle action potential or from the cardiac |
|
| 54:54 | . We also learned that we have ways of subtyping these cells. So |
|
| 55:01 | talked about different dyes Golgi stain Nel . Uh how we reveal the morphology |
|
| 55:08 | these cells. How action platon trolls like a code, it's a neuronal |
|
| 55:15 | , the frequency, the pattern of action platon tras the pattern of firing |
|
| 55:20 | very important because the pattern of action will determine the pattern of chemical neurotransmitter |
|
| 55:28 | , which will determine the pattern of pattern of the response from another |
|
| 55:33 | So it is like a code. And next uh section, what we |
|
| 55:39 | do is when we come back, will draw ourselves back into sort of |
|
| 55:45 | gross anatomical view of the brain. talk briefly very basic things about the |
|
| 55:51 | of the brain and major parts and of the CNS. And then we |
|
| 55:58 | start understanding how neurons communicate with each through synaptic transmission, different chemical synaptic |
|
| 56:06 | . What it means that will set up for the third section of |
|
| 56:10 | which is going to be the the system. Thank you very much for |
|
| 56:15 | here. Good luck studying and good on your exam on Thursday. I'll |
|
| 56:22 | everyone next week. Uh |
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