WEBVTT 00:00:00.250 --> 00:00:01.800 The following content is provided 00:00:01.800 --> 00:00:04.040 under a Creative Commons license. 00:00:04.040 --> 00:00:06.890 Your support will help MIT OpenCourseWare continue 00:00:06.890 --> 00:00:10.740 to offer high-quality educational resources for free. 00:00:10.740 --> 00:00:13.360 To make a donation or view additional materials 00:00:13.360 --> 00:00:17.241 from hundreds of MIT courses, visit MIT OpenCourseWare 00:00:17.241 --> 00:00:17.866 at ocw.mit.edu. 00:00:23.950 --> 00:00:26.490 PROFESSOR: This is 914, and the people in the back 00:00:26.490 --> 00:00:29.340 may sometimes have trouble hearing me. 00:00:29.340 --> 00:00:32.740 So you should always get-- maybe we should actually 00:00:32.740 --> 00:00:37.940 change tables in the future, so you can all sit closer. 00:00:37.940 --> 00:00:40.300 I don't have a real loud voice. 00:00:40.300 --> 00:00:43.570 I can ask them for an amplifier, but in a small class, 00:00:43.570 --> 00:00:46.698 that's sort of awkward. 00:00:46.698 --> 00:00:49.594 AUDIENCE: [INAUDIBLE]? 00:00:49.594 --> 00:00:51.510 PROFESSOR: Yeah, well, if you stop hearing me, 00:00:51.510 --> 00:00:53.710 just come closer. 00:00:58.160 --> 00:01:00.022 There's one there. 00:01:00.022 --> 00:01:02.055 And there's a few there that are closer. 00:01:08.960 --> 00:01:12.340 So this is the plan. 00:01:12.340 --> 00:01:15.400 I want you to acquire, and by acquire 00:01:15.400 --> 00:01:18.440 I mean in here in your mind, I want 00:01:18.440 --> 00:01:22.980 you to have an outline of vertebrate neuroanatomy, 00:01:22.980 --> 00:01:24.320 especially for mammals. 00:01:24.320 --> 00:01:26.790 But we'll learn enough about non-mammals 00:01:26.790 --> 00:01:31.080 that you'll have some understanding of them, too. 00:01:31.080 --> 00:01:36.790 And neuroanatomy anatomy is not exactly an exciting topic. 00:01:36.790 --> 00:01:38.900 It's usually boring. 00:01:38.900 --> 00:01:46.400 But it doesn't stay that way if you know why it's like that 00:01:46.400 --> 00:01:48.000 and what it does. 00:01:48.000 --> 00:01:51.310 So that's why, and when I wrote the book that's 00:01:51.310 --> 00:01:58.160 the text for the class, I try to explain where this came from, 00:01:58.160 --> 00:02:01.296 how it develops, how it evolved. 00:02:01.296 --> 00:02:04.970 And for evolution, yes, I can use molecular data, 00:02:04.970 --> 00:02:08.600 but that's only in conjunction with comparative anatomy, 00:02:08.600 --> 00:02:14.030 look at a broad range of species, some of which 00:02:14.030 --> 00:02:14.920 are very primitive. 00:02:14.920 --> 00:02:19.520 That is, fossil record can trace them way, way back, 00:02:19.520 --> 00:02:21.005 like the sea lamprey, for example. 00:02:24.991 --> 00:02:27.240 And as far as if you're going to talk about evolution, 00:02:27.240 --> 00:02:28.820 you've got to talk about function, 00:02:28.820 --> 00:02:36.480 because things don't evolve-- they evolve mainly 00:02:36.480 --> 00:02:41.015 to serve adaptive function, that is, by natural selection. 00:02:41.015 --> 00:02:45.070 And I'm assuming that, and I'm a Darwinian in that sense, 00:02:45.070 --> 00:02:48.330 and I recognize there are other mechanisms of evolution that 00:02:48.330 --> 00:02:53.810 result in change, but I believe the major things, especially 00:02:53.810 --> 00:02:59.300 for things like the CNS, which controls function, 00:02:59.300 --> 00:03:07.270 is due to selective survival of species. 00:03:07.270 --> 00:03:10.690 So today, we'll start out with a little terminology. 00:03:10.690 --> 00:03:13.030 And then we're going to talk about cells. 00:03:13.030 --> 00:03:17.030 And the next time we'll be talking about the way 00:03:17.030 --> 00:03:18.520 some of the cellular mechanisms are 00:03:18.520 --> 00:03:22.450 used to study pathways, connections. 00:03:22.450 --> 00:03:26.850 And we'll hear a little bit about that today. 00:03:26.850 --> 00:03:30.080 You should be getting familiar with the Stellar site. 00:03:30.080 --> 00:03:39.990 And you go to the-- you log in, you go to this Materials 00:03:39.990 --> 00:03:42.560 section, and you'll see at the top 00:03:42.560 --> 00:03:46.640 the General section and a Resources section. 00:03:46.640 --> 00:03:48.420 You'll find there a book list. 00:03:48.420 --> 00:03:54.540 Now, this year, I'm really only requiring 00:03:54.540 --> 00:03:58.980 as essential reading of my book, but there 00:03:58.980 --> 00:04:02.350 are some very interesting other books. 00:04:02.350 --> 00:04:04.135 And I post some of those readings 00:04:04.135 --> 00:04:08.320 as supplementary readings, and some of them are very helpful. 00:04:08.320 --> 00:04:11.186 If you get through with the reading 00:04:11.186 --> 00:04:15.970 and you haven't put your nine hours a week in yet, 00:04:15.970 --> 00:04:18.130 do some of the supplementary readings. 00:04:18.130 --> 00:04:21.010 The Allman book is a particularly interesting one. 00:04:21.010 --> 00:04:22.035 It's out of print. 00:04:22.035 --> 00:04:24.910 That was the problem with Freeman Press and Scientific 00:04:24.910 --> 00:04:26.375 American; books. 00:04:26.375 --> 00:04:28.700 They didn't keep books in print. 00:04:28.700 --> 00:04:31.980 Other publishers could pick them up, 00:04:31.980 --> 00:04:34.255 but so far, Allman hasn't been republished. 00:04:34.255 --> 00:04:36.640 And that's true also for [INAUDIBLE] and [INAUDIBLE] 00:04:36.640 --> 00:04:38.000 book. 00:04:38.000 --> 00:04:40.014 [INAUDIBLE] was my teacher in neuroanatomy, 00:04:40.014 --> 00:04:41.430 and he was a great neuroanatomist, 00:04:41.430 --> 00:04:44.530 and wrote a very interesting book 00:04:44.530 --> 00:04:46.650 that's still a good resource. 00:04:46.650 --> 00:04:49.180 So I will be posting those, too. 00:04:49.180 --> 00:04:55.750 I'm not posting the Larry Swanson's book Brain 00:04:55.750 --> 00:04:58.090 Architecture. 00:04:58.090 --> 00:05:01.670 It's a book with similar goals to my book, 00:05:01.670 --> 00:05:04.380 but it's a very different book. 00:05:04.380 --> 00:05:10.000 It doesn't have the general kind of coverage that I have, 00:05:10.000 --> 00:05:12.400 but it's very unique in many things. 00:05:12.400 --> 00:05:17.620 And I did make use of that book in writing mine. 00:05:17.620 --> 00:05:20.760 So some people might want to pick that up. 00:05:20.760 --> 00:05:23.310 And I always list where the relevant things 00:05:23.310 --> 00:05:26.850 are in that book. 00:05:26.850 --> 00:05:29.395 You have a copy in the reserve room, I think. 00:05:29.395 --> 00:05:31.340 AUDIENCE: Well, I have a personal copy. 00:05:31.340 --> 00:05:33.430 PROFESSOR: OK, well, we should check. 00:05:33.430 --> 00:05:36.570 Well, check the reserve room and find out 00:05:36.570 --> 00:05:39.850 to make sure that they put the library's copy on reserve. 00:05:39.850 --> 00:05:42.180 So in case you have time and want to read some of that. 00:05:42.180 --> 00:05:44.090 That's fine. 00:05:44.090 --> 00:05:48.300 Now glossaries are important because you will soon find out 00:05:48.300 --> 00:05:51.510 there's a lot of terms in neuroanatomy. 00:05:51.510 --> 00:05:53.150 And they come from the Greek. 00:05:53.150 --> 00:05:57.160 They come from the Latin, or various combinations. 00:05:57.160 --> 00:06:01.170 And there's a lot of structures. 00:06:01.170 --> 00:06:05.910 A lot more than we have time to mention. 00:06:05.910 --> 00:06:10.910 I doubt if I will mention the bundle of Vicq d'azyr. 00:06:10.910 --> 00:06:13.060 I might mention habenulointerpeduncular tract. 00:06:16.030 --> 00:06:17.760 These are just, they're synonyms. 00:06:17.760 --> 00:06:20.180 They mean the very same thing. 00:06:20.180 --> 00:06:22.400 The second way, that's easy. 00:06:22.400 --> 00:06:23.922 If you know what the habenula is, 00:06:23.922 --> 00:06:25.630 you know what the interpeduncular nucleus 00:06:25.630 --> 00:06:28.270 is because it's the habenulointerpeduncular tract. 00:06:28.270 --> 00:06:30.480 It goes from one to the other. 00:06:30.480 --> 00:06:32.140 And a lot of tracts, fortunately, 00:06:32.140 --> 00:06:35.880 are named that way, but not all. 00:06:35.880 --> 00:06:38.250 And there's a lot of synonyms. 00:06:38.250 --> 00:06:40.800 You will see some of that right away. 00:06:40.800 --> 00:06:43.570 So you just get used to it, a little suffering, 00:06:43.570 --> 00:06:45.790 especially earlier in the class. 00:06:45.790 --> 00:06:50.160 And it might make you feel a little lost once in awhile. 00:06:50.160 --> 00:06:54.410 But be patient with yourself, and just put the time in. 00:06:54.410 --> 00:06:57.220 And I will go over things. 00:06:57.220 --> 00:07:01.600 The more important things I will return to a number of times 00:07:01.600 --> 00:07:03.750 to make it easier for you. 00:07:03.750 --> 00:07:07.710 I use the method in the book, and we'll use it in the class, 00:07:07.710 --> 00:07:12.735 because I'm basically-- the book originated from this class, 00:07:12.735 --> 00:07:15.520 from teaching here at MIT from a number of years. 00:07:20.540 --> 00:07:23.990 I'm posting not only the readings for each class, 00:07:23.990 --> 00:07:27.470 but I'm posting questions on the readings. 00:07:27.470 --> 00:07:32.500 I want you to read before the class. 00:07:32.500 --> 00:07:36.170 Don't just come here and expect me to feed it all to you. 00:07:36.170 --> 00:07:39.080 We will answer questions in this class. 00:07:39.080 --> 00:07:43.300 And you will have a chance to ask me questions. 00:07:43.300 --> 00:07:46.240 But to make sure you're reading, I am sometimes just going 00:07:46.240 --> 00:07:49.275 to say, what's the answer to that question? 00:07:52.300 --> 00:07:56.050 You'll all be embarrassed from time to time, 00:07:56.050 --> 00:07:59.000 but it gets you to read. 00:07:59.000 --> 00:08:02.380 I can also use quizzes for that, but that takes up class time, 00:08:02.380 --> 00:08:03.595 takes up discussion time. 00:08:03.595 --> 00:08:06.920 So we're not going to have time to do too many quizzes. 00:08:06.920 --> 00:08:09.460 I will let in advance when we're going to have one. 00:08:12.190 --> 00:08:16.280 So let's go through the questions. 00:08:16.280 --> 00:08:19.020 And I know this is the first class. 00:08:19.020 --> 00:08:21.410 We had a little trouble getting the book online. 00:08:21.410 --> 00:08:25.360 MIT Press was going to do it, as you probably know. 00:08:25.360 --> 00:08:29.810 And they ended up not being satisfied with their set-up 00:08:29.810 --> 00:08:31.730 for textbooks for a specific class. 00:08:31.730 --> 00:08:36.120 They have a deal with the libraries to make their books, 00:08:36.120 --> 00:08:38.730 their ebooks-- but mine isn't actually even out 00:08:38.730 --> 00:08:42.950 yet, so that will come. 00:08:42.950 --> 00:08:47.010 March 28 is when we can actually get the book, the print book. 00:08:47.010 --> 00:08:50.565 And after a few classes, I'll get all the names of you 00:08:50.565 --> 00:08:54.090 who expect to stay in the class or for other reasons want 00:08:54.090 --> 00:08:55.620 the book. 00:08:55.620 --> 00:08:59.960 And I will give that list to the guy at the MIT Press bookstore, 00:08:59.960 --> 00:09:04.130 to make sure he holds those for you guys. 00:09:04.130 --> 00:09:06.650 And then, anybody else that comes in, 00:09:06.650 --> 00:09:08.620 he'll have to have extra copies for them. 00:09:13.650 --> 00:09:15.770 Should brain structures and their organization 00:09:15.770 --> 00:09:18.860 make sense to you? 00:09:18.860 --> 00:09:21.590 Because it seems a little arbitrary 00:09:21.590 --> 00:09:24.360 a lot of times when you're studying brain structure. 00:09:24.360 --> 00:09:26.500 What kind of sense should it make? 00:09:26.500 --> 00:09:28.822 What kind of sense do you want it to make? 00:09:31.650 --> 00:09:33.960 How would you answer that? 00:09:33.960 --> 00:09:38.350 I want it to make sense in terms of evolution 00:09:38.350 --> 00:09:41.760 and in terms of development and in terms of function. 00:09:41.760 --> 00:09:44.910 I want the connections we talk about, most of them, 00:09:44.910 --> 00:09:46.930 to make some kind of functional sense. 00:09:46.930 --> 00:09:49.320 It will help you remember it. 00:09:49.320 --> 00:09:54.890 And you will build, gradually, this outline in your mind. 00:09:54.890 --> 00:09:59.980 And if it doesn't seem to make any sense, bring it up. 00:09:59.980 --> 00:10:03.760 Just tell me, it doesn't make any sense, OK? 00:10:03.760 --> 00:10:06.790 Put me on the spot. 00:10:06.790 --> 00:10:12.280 So, could somebody define central nervous system for me? 00:10:12.280 --> 00:10:12.904 Yes. 00:10:12.904 --> 00:10:13.820 AUDIENCE: [INAUDIBLE]. 00:10:22.730 --> 00:10:23.610 . 00:10:23.610 --> 00:10:26.410 PROFESSOR: So brain and spinal cord. 00:10:26.410 --> 00:10:28.950 The brain is in the skull. 00:10:28.950 --> 00:10:34.570 The word encephalon means in the skull. 00:10:34.570 --> 00:10:38.260 So we talk about the different main parts of the brain 00:10:38.260 --> 00:10:44.080 as prosencephalon, mesencephalon, rhombencephalon, 00:10:44.080 --> 00:10:49.090 the different three major brain vesicles in the skull. 00:10:49.090 --> 00:10:57.320 And then the marrow, the center of the spinal column, enclosed 00:10:57.320 --> 00:11:03.570 by the vertebrae there's the spinal cord or the medulla 00:11:03.570 --> 00:11:05.820 spinalis. 00:11:05.820 --> 00:11:08.150 That's why the caudal end of the hindbrain 00:11:08.150 --> 00:11:14.230 is actually the medulla oblongata, the elongated center 00:11:14.230 --> 00:11:17.280 medulla of the spinal cord. 00:11:21.340 --> 00:11:23.940 So here are pictures of it. 00:11:23.940 --> 00:11:25.315 This is one from [INAUDIBLE]. 00:11:28.650 --> 00:11:33.870 This is from a dissection at a medical school 00:11:33.870 --> 00:11:38.520 museum in [INAUDIBLE], Switzerland that I visited. 00:11:38.520 --> 00:11:40.110 They have a wonderful museum there. 00:11:40.110 --> 00:11:44.920 And this is a dissection of a child who died. 00:11:44.920 --> 00:11:51.580 And they have exposed the whole spinal cord and the roots 00:11:51.580 --> 00:11:56.910 and the brain, where they sectioned part of it there. 00:11:56.910 --> 00:12:03.960 This is one where-- you know why that 00:12:03.960 --> 00:12:08.200 looks so different from this one? 00:12:08.200 --> 00:12:11.300 What's different there? 00:12:11.300 --> 00:12:16.280 It's encased by the dura mater. 00:12:16.280 --> 00:12:20.870 The dura is the tough mother, the canvas-like covering 00:12:20.870 --> 00:12:23.290 of the brain, the outer meningeal layer. 00:12:27.020 --> 00:12:31.310 And we found this picture after my book. 00:12:31.310 --> 00:12:33.590 I would have liked to use this in my book. 00:12:33.590 --> 00:12:39.760 I've actually used these, but this one probably 00:12:39.760 --> 00:12:41.710 will be in the next edition because it's 00:12:41.710 --> 00:12:46.610 such a beautiful dissection of the adult human spinal cord 00:12:46.610 --> 00:12:52.230 and attached to the brain with the nerve roots, of course, 00:12:52.230 --> 00:12:52.845 all cut off. 00:12:52.845 --> 00:12:55.350 These would lead to the whole network 00:12:55.350 --> 00:12:56.978 of the peripheral nervous system. 00:12:59.970 --> 00:13:04.270 So now, beginning at the caudal end of the CNS, 00:13:04.270 --> 00:13:06.940 what are the names of all the major subdivisions? 00:13:06.940 --> 00:13:14.240 Let's name them-- the most caudal, spinal cord. 00:13:14.240 --> 00:13:15.322 So what's just above it? 00:13:15.322 --> 00:13:16.780 I've already mentioned it in class. 00:13:16.780 --> 00:13:19.760 I've actually mentioned all the main answers here. 00:13:19.760 --> 00:13:22.320 But I want to see now. 00:13:22.320 --> 00:13:24.570 You've had 901. 00:13:24.570 --> 00:13:26.940 You've had brain pics before. 00:13:26.940 --> 00:13:29.290 You should know all these. 00:13:29.290 --> 00:13:31.040 So don't be too embarrassed if you forget. 00:13:31.040 --> 00:13:34.460 The neuroanatomy doesn't stick with some people very well, 00:13:34.460 --> 00:13:36.500 but that's why you're taking the class, right? 00:13:36.500 --> 00:13:37.950 So what's above the spinal cord? 00:13:41.550 --> 00:13:42.800 The brain stem. 00:13:42.800 --> 00:13:47.440 The brain stem is a general name for everything 00:13:47.440 --> 00:13:50.510 in the encephalon, inside the skull, 00:13:50.510 --> 00:13:54.380 that's not cerebral hemispheres. 00:13:54.380 --> 00:13:58.190 These are cerebral hemispheres. 00:13:58.190 --> 00:14:01.400 There's the cerebellum. 00:14:01.400 --> 00:14:03.500 Those are the cortical areas. 00:14:03.500 --> 00:14:06.300 It's everything else that's not those two things. 00:14:09.210 --> 00:14:17.300 So let's start at the bottom and name the most caudal one, 00:14:17.300 --> 00:14:19.965 simplest in English; hindbrain, midbrain, forebrain. 00:14:22.880 --> 00:14:27.060 The hindbrain, the lower part, is the medulla oblongata. 00:14:27.060 --> 00:14:31.080 The rostral part is often called the pons, 00:14:31.080 --> 00:14:32.630 just because of the structure called 00:14:32.630 --> 00:14:35.510 the pons that's located there. 00:14:35.510 --> 00:14:38.740 And we'll be talking about that and its connections. 00:14:38.740 --> 00:14:41.785 And then above the hindbrain, the midbrain. 00:14:44.510 --> 00:14:48.530 And we'll be studying that in a special unit, 00:14:48.530 --> 00:14:52.380 and it will come back in various chapters of the book. 00:14:52.380 --> 00:14:55.190 And then, the forebrain, but what 00:14:55.190 --> 00:14:59.150 are the major parts of the forebrain? 00:14:59.150 --> 00:15:02.740 The hemispheres we've already named, cerebral hemispheres. 00:15:02.740 --> 00:15:05.130 That's the endbrain. 00:15:05.130 --> 00:15:09.370 It contains a little more than the hemispheres. 00:15:09.370 --> 00:15:12.380 It contains the olfactory bulbs and what 00:15:12.380 --> 00:15:15.170 we call the basal forebrain. 00:15:15.170 --> 00:15:21.140 And what's in between the endbrain and the midbrain? 00:15:21.140 --> 00:15:22.840 The tween brain, of course. 00:15:22.840 --> 00:15:25.590 The between brain. 00:15:25.590 --> 00:15:28.020 Sure, it's between the midbrain and the endbrain. 00:15:28.020 --> 00:15:30.870 It's also between the hemispheres. 00:15:30.870 --> 00:15:34.680 The hemispheres kind of blossom out of the tween brain. 00:15:34.680 --> 00:15:40.650 All right, so here's a picture of the embryonic neural tube, 00:15:40.650 --> 00:15:43.480 where I've taken the developing hemispheres 00:15:43.480 --> 00:15:45.940 and I've sort of pushed them apart. 00:15:45.940 --> 00:15:50.480 So you can see the thin of what we call the roof plate here 00:15:50.480 --> 00:15:52.640 on the rhombencephalon. 00:15:52.640 --> 00:15:57.900 There you see the hindbrain right there. 00:15:57.900 --> 00:16:03.060 And you see how it's got that sort of one-cell thick membrane 00:16:03.060 --> 00:16:03.910 across the top? 00:16:03.910 --> 00:16:05.060 It's a tube. 00:16:05.060 --> 00:16:07.940 The whole nervous system is a tube. 00:16:07.940 --> 00:16:10.960 But the walls get very thick with development. 00:16:10.960 --> 00:16:12.340 This is early in development. 00:16:12.340 --> 00:16:14.800 They're not that thick yet. 00:16:14.800 --> 00:16:21.050 But that roof plate never gets thick in much of the hindbrain, 00:16:21.050 --> 00:16:23.490 only in the rostral part where the cerebellum develop. 00:16:23.490 --> 00:16:24.520 Then it gets huge. 00:16:27.320 --> 00:16:27.890 Sorry? 00:16:27.890 --> 00:16:30.375 AUDIENCE: [INAUDIBLE]? 00:16:30.375 --> 00:16:31.500 PROFESSOR: The tween brain. 00:16:31.500 --> 00:16:32.690 AUDIENCE: Is that your term? 00:16:32.690 --> 00:16:35.500 PROFESSOR: No, no, that's what di-encephalon means. 00:16:35.500 --> 00:16:38.320 AUDIENCE: Oh. 00:16:38.320 --> 00:16:42.230 PROFESSOR: I'm just giving you here the equivalent 00:16:42.230 --> 00:16:48.010 English and classical names. 00:16:48.010 --> 00:16:49.215 These are basically Greek. 00:16:51.850 --> 00:16:54.540 And the Romans imported a lot of the terms 00:16:54.540 --> 00:16:57.640 from the Greek language, and they have their own. 00:17:00.900 --> 00:17:02.400 So the other question is here, why 00:17:02.400 --> 00:17:06.410 is the hindbrain called the rhombencephalon. 00:17:06.410 --> 00:17:10.750 Hindbrain, rhombencephalon-- well, rhombencephalon 00:17:10.750 --> 00:17:11.800 doesn't mean hindbrain. 00:17:14.349 --> 00:17:15.730 Sorry? 00:17:15.730 --> 00:17:19.230 For that rhombic shape there. 00:17:19.230 --> 00:17:22.630 It's the shape of the roof plate seen from the top. 00:17:22.630 --> 00:17:28.530 And that stretches out like that when the development of the two 00:17:28.530 --> 00:17:31.730 develops flexures, bends. 00:17:31.730 --> 00:17:34.195 It's like a peapod that you've bent 00:17:34.195 --> 00:17:41.630 and it stretches out part of the top there. 00:17:41.630 --> 00:17:43.550 So what are the coordinates we use now? 00:17:43.550 --> 00:17:47.810 We want directions when we're looking at brain sections, 00:17:47.810 --> 00:17:51.920 and we want to know what the common planes of section are. 00:17:51.920 --> 00:17:54.960 Of course, we talk about anterior and posterior, 00:17:54.960 --> 00:17:56.360 rostral and caudal. 00:17:56.360 --> 00:17:58.160 Do those always mean the same thing? 00:17:58.160 --> 00:17:59.720 No, not for humans. 00:17:59.720 --> 00:18:02.520 They do for most animals. 00:18:02.520 --> 00:18:04.790 Now here, anterior and posterior, 00:18:04.790 --> 00:18:07.716 same as rostral and caudal. 00:18:07.716 --> 00:18:09.880 Do you have trouble remembering those names? 00:18:09.880 --> 00:18:12.220 Rostrum, do you know the term rostrum? 00:18:12.220 --> 00:18:13.600 He's at the rostrum. 00:18:13.600 --> 00:18:16.190 He's at the front. 00:18:16.190 --> 00:18:18.980 Caudal actually means tail. 00:18:22.650 --> 00:18:25.492 Dorsal, ventral-- dorsal towards the back, 00:18:25.492 --> 00:18:26.575 ventral towards the belly. 00:18:32.680 --> 00:18:34.690 But look at the human here. 00:18:34.690 --> 00:18:37.490 The only way the terms are really equivalent for the human 00:18:37.490 --> 00:18:40.710 is when he's in that position. 00:18:40.710 --> 00:18:47.220 Because if he's standing up, now ventral is also anterior, 00:18:47.220 --> 00:18:49.120 you see? 00:18:49.120 --> 00:18:50.050 Not so here. 00:18:55.690 --> 00:18:58.210 And it's similar for the bird. 00:18:58.210 --> 00:19:02.370 And so that's the reason we normally-- and by the way, 00:19:02.370 --> 00:19:07.540 you can use the term oral, too, instead of rostral. 00:19:07.540 --> 00:19:12.570 But that's why I prefer just the dorsal, ventral, rostral, 00:19:12.570 --> 00:19:15.990 caudal terms because you can use them 00:19:15.990 --> 00:19:19.840 right across all the vertebrates, 00:19:19.840 --> 00:19:23.180 and even for invertebrates. 00:19:23.180 --> 00:19:27.160 And for the planes of section, very simple. 00:19:27.160 --> 00:19:30.200 But just notice the synonymous terms. 00:19:30.200 --> 00:19:33.750 And I will sometimes, without even thinking, 00:19:33.750 --> 00:19:35.710 switch from one of these to the other. 00:19:35.710 --> 00:19:41.070 Transverse, frontal, coronal-- the all mean the same thing. 00:19:41.070 --> 00:19:43.785 Horizontal always means horizontal. 00:19:43.785 --> 00:19:46.010 You have midsaggital and parasaggital. 00:19:46.010 --> 00:19:49.740 But parasaggital, people don't bother with that. 00:19:49.740 --> 00:19:52.500 They still just call them all saggital, 00:19:52.500 --> 00:19:56.105 whether they're midsaggital or parasaggital, at the midline 00:19:56.105 --> 00:19:56.995 or off the midline. 00:20:00.070 --> 00:20:05.470 And then, oblique sections are just used for special purposes 00:20:05.470 --> 00:20:08.545 in order to get certain axons all in the plane of sections 00:20:08.545 --> 00:20:09.960 and so forth. 00:20:09.960 --> 00:20:14.080 And here I'm just showing-- what you 00:20:14.080 --> 00:20:18.050 see here are the drawings that I based the textbook figures on. 00:20:18.050 --> 00:20:20.740 We did redraw a lot of them for the book. 00:20:20.740 --> 00:20:23.730 But here I just sketched the brains 00:20:23.730 --> 00:20:25.465 used in the lab the most, the mouse, rat, 00:20:25.465 --> 00:20:27.710 or hamster, from the side. 00:20:27.710 --> 00:20:31.080 And showing if you make a series of frontal sections 00:20:31.080 --> 00:20:34.310 and cut like that, this would be the horizontal plane. 00:20:34.310 --> 00:20:36.110 And then I turn the brain around. 00:20:36.110 --> 00:20:37.740 You're looking at it from the front. 00:20:37.740 --> 00:20:40.254 The olfactory bulbs in front. 00:20:40.254 --> 00:20:45.520 And the sagittal sections would look like that. 00:20:45.520 --> 00:20:48.990 So what kind of education tissue makes up the CNS? 00:20:48.990 --> 00:20:52.545 It's not really a lump of porridge. 00:20:52.545 --> 00:20:57.790 It just looks like that if it's not fixed. 00:20:57.790 --> 00:20:59.655 So what kind of tissue is it? 00:20:59.655 --> 00:21:03.390 You can say it's ectodermal tissue 00:21:03.390 --> 00:21:07.555 because it arises from the embryonic ectoderm. 00:21:10.140 --> 00:21:15.850 And part of that ectoderm fronds the central nervous system 00:21:15.850 --> 00:21:18.880 and peripheral nervous system. 00:21:18.880 --> 00:21:22.250 And we will see that because one of our early topics 00:21:22.250 --> 00:21:23.425 is spinal cord development. 00:21:29.600 --> 00:21:32.690 When you do histology of nervous system tissue, 00:21:32.690 --> 00:21:36.039 it's very much like histology of skin 00:21:36.039 --> 00:21:37.330 because the skin is ectodermal. 00:21:42.260 --> 00:21:46.060 So how do we define and recognize cell groups? 00:21:46.060 --> 00:21:47.670 Anybody? 00:21:47.670 --> 00:21:49.350 What do we do? 00:21:49.350 --> 00:21:51.700 How were they initially named? 00:21:51.700 --> 00:21:58.980 Well, of course dissection, but you can't see a lot of detail 00:21:58.980 --> 00:22:02.570 with dissection that you can see with anatomical methods. 00:22:02.570 --> 00:22:05.221 Well, what kind of anatomical methods? 00:22:05.221 --> 00:22:05.720 Yeah? 00:22:08.960 --> 00:22:10.040 Yeah, you. 00:22:10.040 --> 00:22:12.090 You were indicating you were going to tell me. 00:22:15.380 --> 00:22:16.105 Speak louder. 00:22:23.020 --> 00:22:27.010 Anybody, give me some methods. 00:22:27.010 --> 00:22:29.000 Sorry? 00:22:29.000 --> 00:22:30.670 I can't hear very well. 00:22:30.670 --> 00:22:33.300 I can't hear well with any background noise. 00:22:33.300 --> 00:22:37.359 I have more trouble than you do, I think, in hearing me. 00:22:37.359 --> 00:22:39.630 AUDIENCE: Stains, we can look at stains. 00:22:39.630 --> 00:22:44.330 PROFESSOR: Stains, one word, histological stains. 00:22:44.330 --> 00:22:48.660 Give me an example of a-- a Nissl stain. 00:22:48.660 --> 00:22:51.040 What does it stain for? 00:22:51.040 --> 00:22:52.040 Well, a Nissl substance. 00:22:52.040 --> 00:22:54.830 Where is the Nissl substance? 00:22:54.830 --> 00:22:56.710 In the cell body. 00:22:56.710 --> 00:22:59.320 Not very much of it gets into the dendrites, 00:22:59.320 --> 00:23:02.960 maybe the large proximal dendrites get a little of it. 00:23:02.960 --> 00:23:05.520 And it doesn't enter much of the axon either. 00:23:05.520 --> 00:23:07.390 So when we stain for Nissl substance, 00:23:07.390 --> 00:23:10.300 we're seeing the cell bodies. 00:23:10.300 --> 00:23:14.043 So you'll see whether the neurons are big or small, 00:23:14.043 --> 00:23:17.330 and whether they have a lot of Nissl substance or less, 00:23:17.330 --> 00:23:20.280 so there'll be dark staining or lighter staining. 00:23:20.280 --> 00:23:25.720 And just those properties help us define different cell 00:23:25.720 --> 00:23:29.880 groups, and they help us define layers. 00:23:29.880 --> 00:23:32.477 So we will see more pictures of that. 00:23:32.477 --> 00:23:34.560 There's many pictures in the book of these things. 00:23:34.560 --> 00:23:40.070 And you will see more pictures next time and in chapter two. 00:23:40.070 --> 00:23:42.620 Some of you have read it already. 00:23:42.620 --> 00:23:43.745 What other kinds of stains? 00:23:46.810 --> 00:23:51.640 Well, Golgi, but if you just take a more general stain, 00:23:51.640 --> 00:23:56.640 other than the Nissl stain, we could stain for fibers. 00:23:56.640 --> 00:24:00.270 And the fiber stains might just stain for myelin, 00:24:00.270 --> 00:24:02.960 so that's only the thicker myelinated fibers, 00:24:02.960 --> 00:24:06.290 but they might stain for all the fibers, 00:24:06.290 --> 00:24:08.750 like silver stains for axons. 00:24:08.750 --> 00:24:11.390 That gives you a different picture. 00:24:11.390 --> 00:24:17.160 Like for example, when I wanted to map the whole neocortex 00:24:17.160 --> 00:24:20.640 of the hamster, I found the Nissl substances 00:24:20.640 --> 00:24:23.140 not to be all that clear. 00:24:23.140 --> 00:24:28.370 I could see boundaries, but it was pretty hard to make out. 00:24:28.370 --> 00:24:32.860 So I used a silver stain for axons, 00:24:32.860 --> 00:24:37.010 and found suddenly I could really see clear boundaries. 00:24:37.010 --> 00:24:42.720 And I was able to map, using a lot of quantitative care 00:24:42.720 --> 00:24:46.000 in the histology, I was able to map the cortical areas. 00:24:46.000 --> 00:24:51.210 And you'll see results of both of those kinds of methods 00:24:51.210 --> 00:24:54.350 applied to mapping different parts of the brain. 00:24:57.510 --> 00:25:01.990 If we use the term primitive cellular mechanisms, the way 00:25:01.990 --> 00:25:05.330 I do in the book, what's it mean when 00:25:05.330 --> 00:25:07.037 we're talking about nervous system? 00:25:10.700 --> 00:25:14.770 What is a primitive cellular mechanism? 00:25:14.770 --> 00:25:20.080 Basically, I'm talking about mechanisms 00:25:20.080 --> 00:25:23.670 that we see in single-celled animals, 00:25:23.670 --> 00:25:25.290 that we still see in neurons. 00:25:27.950 --> 00:25:31.270 And here I list them, as the way I list them and discuss them 00:25:31.270 --> 00:25:33.580 in chapter one. 00:25:33.580 --> 00:25:35.850 They're all present in one-celled organisms. 00:25:35.850 --> 00:25:39.460 They're retained in the evolution of neurons. 00:25:39.460 --> 00:25:42.680 Irritability and conduction-- irritability 00:25:42.680 --> 00:25:46.450 means it responds in some way to stimulation, like even just 00:25:46.450 --> 00:25:49.480 simple mechanical stimulation, but also other kinds 00:25:49.480 --> 00:25:52.200 of stimulation, chemical stimulation, 00:25:52.200 --> 00:25:54.370 electrical stimulation. 00:25:54.370 --> 00:25:56.720 Something changes in the membrane, 00:25:56.720 --> 00:26:00.100 and it conducts those changes to other parts of the cell. 00:26:00.100 --> 00:26:01.910 It happens in the amoeba. 00:26:01.910 --> 00:26:05.380 It happens in other protozoa. 00:26:05.380 --> 00:26:08.620 It happens in neurons. 00:26:08.620 --> 00:26:10.220 And then we get specializations. 00:26:10.220 --> 00:26:13.150 That happens in single-celled organisms, too. 00:26:13.150 --> 00:26:15.880 Parts of the membrane respond better to some stimuli. 00:26:19.100 --> 00:26:22.550 And we see that in neurons, of course. 00:26:22.550 --> 00:26:26.126 Specializations at the synapse, of course, specializations 00:26:26.126 --> 00:26:31.140 for responding to stimulation from the outside world, 00:26:31.140 --> 00:26:33.390 movements themselves, specialize in movement. 00:26:33.390 --> 00:26:36.300 You say, well, that applies only to muscle cells. 00:26:36.300 --> 00:26:38.170 No, it applies to neurons, too. 00:26:38.170 --> 00:26:42.020 They have to move a lot when they develop. 00:26:42.020 --> 00:26:44.260 And they still use contractile proteins, just 00:26:44.260 --> 00:26:46.630 like the muscle cells. 00:26:46.630 --> 00:26:51.270 And then secretion, single-cell organisms secrete. 00:26:51.270 --> 00:26:56.060 They use that in catching prey, for example. 00:26:56.060 --> 00:26:58.080 Secretions-- many neurons specialize. 00:26:58.080 --> 00:27:01.350 And even central nervous system neurons, some of them 00:27:01.350 --> 00:27:04.600 don't just secrete chemicals at at the synapses, 00:27:04.600 --> 00:27:08.910 but they secrete into the bloodstream. 00:27:08.910 --> 00:27:11.090 They are neurosecretory cells. 00:27:14.150 --> 00:27:16.075 And then parallel channels of information 00:27:16.075 --> 00:27:19.150 is some way to integrate different information coming 00:27:19.150 --> 00:27:20.710 in different parts. 00:27:20.710 --> 00:27:23.140 Single-cell organisms, it's easier for them 00:27:23.140 --> 00:27:24.810 because they're all one cell. 00:27:24.810 --> 00:27:26.700 When you get a multicellular organism, 00:27:26.700 --> 00:27:29.270 especially if it's big, then it becomes a real problem. 00:27:29.270 --> 00:27:33.070 How do you integrate different things? 00:27:33.070 --> 00:27:34.790 Different stimuli can be contradictory. 00:27:37.327 --> 00:27:39.910 Your left hand might be touching one thing, and the right hand 00:27:39.910 --> 00:27:41.800 something that doesn't make any sense in terms 00:27:41.800 --> 00:27:42.980 of what's in your left hand. 00:27:42.980 --> 00:27:44.290 How do you solve a problem? 00:27:44.290 --> 00:27:45.800 How do you integrate? 00:27:45.800 --> 00:27:48.190 Well, you need connections, the soul 00:27:48.190 --> 00:27:50.460 of what we'll be dealing with. 00:27:50.460 --> 00:27:54.510 And then the last property, endogenous activity-- 00:27:54.510 --> 00:27:57.810 we'll come back to that one. 00:27:57.810 --> 00:28:00.840 Can someone answer question 11 for me? 00:28:00.840 --> 00:28:03.780 Contrast the meaning of synapse and boutons 00:28:03.780 --> 00:28:08.050 in descriptions of neuronal structures. 00:28:08.050 --> 00:28:10.090 You find both of them. 00:28:10.090 --> 00:28:15.670 You find a bouton near the axon ending, or at the axon ending. 00:28:15.670 --> 00:28:17.870 Often many boutons associated with one 00:28:17.870 --> 00:28:22.170 axon because it branches and has many ending. 00:28:22.170 --> 00:28:25.106 And we talk about synapses. 00:28:25.106 --> 00:28:27.480 What is the difference in the way we use those two terms? 00:28:32.661 --> 00:28:33.603 AUDIENCE: [INAUDIBLE]. 00:28:35.030 --> 00:28:39.745 PROFESSOR: Yeah, let's make an even simpler answer. 00:28:39.745 --> 00:28:40.245 Sorry? 00:28:44.610 --> 00:28:47.550 You know, I can hardly hear any of you. 00:28:47.550 --> 00:28:49.846 AUDIENCE: Is a synapse different after the gap? 00:28:49.846 --> 00:28:51.220 PROFESSOR: Yeah, but you're still 00:28:51.220 --> 00:28:52.940 not getting the major point. 00:28:52.940 --> 00:28:54.370 You're looking at details. 00:28:54.370 --> 00:28:56.100 I want the main picture. 00:28:56.100 --> 00:28:59.530 What's the difference between a bouton and a synapse? 00:28:59.530 --> 00:29:02.780 A bouton can have a lot of synapses. 00:29:02.780 --> 00:29:05.610 The synapse is just one little area 00:29:05.610 --> 00:29:07.350 of the membrane that's specialized 00:29:07.350 --> 00:29:09.850 for it's content and communication 00:29:09.850 --> 00:29:10.725 with another cell. 00:29:14.300 --> 00:29:16.840 The bouton is the enlargement of part 00:29:16.840 --> 00:29:24.470 of the axon where most synapses occur. 00:29:24.470 --> 00:29:29.570 So let's say it's an axon going along like this, 00:29:29.570 --> 00:29:32.670 and along its way, it has an enlargement, 00:29:32.670 --> 00:29:34.650 and then it just keeps going. 00:29:34.650 --> 00:29:36.330 And at that enlargement, that would 00:29:36.330 --> 00:29:38.560 be the place to look for synapses. 00:29:38.560 --> 00:29:44.630 They're called boutons en passage, boutons in passage. 00:29:44.630 --> 00:29:48.040 Often we use the French because it sounds so nice. 00:29:48.040 --> 00:29:51.480 And that's where the word, of course, bouton 00:29:51.480 --> 00:29:56.010 is a French word; bouton, terminal, the terminal bouton. 00:29:56.010 --> 00:29:57.850 Now we talked about a bouton a passage. 00:30:00.620 --> 00:30:02.570 So it's where synapses are formed usually. 00:30:06.010 --> 00:30:09.835 Do all axons end in boutons and synapses? 00:30:14.800 --> 00:30:20.300 No, you will see, we'll talk about this different types 00:30:20.300 --> 00:30:22.400 of ending. 00:30:22.400 --> 00:30:26.080 But we're talking about even peripheral nervous system, 00:30:26.080 --> 00:30:28.120 an axon going to a muscle cell, it 00:30:28.120 --> 00:30:31.620 ends in a type of enlargement, but there it's 00:30:31.620 --> 00:30:33.870 more specialized. 00:30:33.870 --> 00:30:36.595 It's the endplate, the muscle endplate. 00:30:36.595 --> 00:30:38.980 It's a flat structure, but it has 00:30:38.980 --> 00:30:40.635 all the synapses on the muscles. 00:30:45.130 --> 00:30:48.240 Next question there, what membrane structure 00:30:48.240 --> 00:30:53.210 had to evolve in order for action potentials in axons 00:30:53.210 --> 00:30:55.590 to evolve? 00:30:55.590 --> 00:30:59.860 You know that dendrites, most of them, 00:30:59.860 --> 00:31:01.450 don't conduct action potentials. 00:31:01.450 --> 00:31:03.840 A few of them actually do, but not very many. 00:31:06.720 --> 00:31:08.630 They conduct differently from axons. 00:31:08.630 --> 00:31:11.250 Axons conduct by action potentials. 00:31:11.250 --> 00:31:14.720 Now I want to know what membrane structure 00:31:14.720 --> 00:31:18.620 had to evolve for this to happen? 00:31:18.620 --> 00:31:20.754 Sorry? 00:31:20.754 --> 00:31:21.670 AUDIENCE: Myelin? 00:31:21.670 --> 00:31:23.930 PROFESSOR: No, no, no, no, myelin 00:31:23.930 --> 00:31:28.750 didn't exist when axons first evolved 00:31:28.750 --> 00:31:32.930 and when action potentials evolved. 00:31:32.930 --> 00:31:38.804 I'm talking about a molecular structure in the membrane. 00:31:38.804 --> 00:31:40.280 AUDIENCE: Ion channel? 00:31:40.280 --> 00:31:43.330 PROFESSOR: Exactly, a particular type of ion channel, 00:31:43.330 --> 00:31:46.080 a voltage-gated ion channel. 00:31:46.080 --> 00:31:49.240 It appeared in even jellyfish, which 00:31:49.240 --> 00:31:52.250 have been around longer than any chordate. 00:31:55.820 --> 00:32:01.620 And that just means that when the membrane potential 00:32:01.620 --> 00:32:05.830 changes-- remember the cell is irritable. 00:32:05.830 --> 00:32:07.500 It responds to input. 00:32:07.500 --> 00:32:13.530 And what's the usual response of a neuron to stimulation? 00:32:13.530 --> 00:32:17.900 Or an axon-- take an axon in my arm and I pinch it, 00:32:17.900 --> 00:32:21.720 especially if I pinch right here, I get an effect. 00:32:24.610 --> 00:32:28.450 I'm causing depolarization, simple word. 00:32:28.450 --> 00:32:31.210 Think in terms of the main thing here. 00:32:31.210 --> 00:32:33.320 Depolarization, the main response 00:32:33.320 --> 00:32:35.810 of a neuronal membrane to stimulation. 00:32:39.110 --> 00:32:47.570 So now, what about let's deal with these, 00:32:47.570 --> 00:32:51.490 and you'll see examples of that in a minute here. 00:32:51.490 --> 00:32:53.180 I want you to be able to contrast 00:32:53.180 --> 00:32:55.850 excitatory and inhibitory postsynaptic potential, 00:32:55.850 --> 00:32:59.340 you should all be able to do that by now with the studies 00:32:59.340 --> 00:32:59.840 you've done. 00:32:59.840 --> 00:33:05.035 Unless you're from another department amd 00:33:05.035 --> 00:33:07.660 you just wondered what the brain is all about, and you're here. 00:33:07.660 --> 00:33:10.210 Well, we'll teach you, but I don't 00:33:10.210 --> 00:33:12.830 expect you to be able answer here. 00:33:12.830 --> 00:33:14.360 Contrast the nature of conduction 00:33:14.360 --> 00:33:19.220 in a dendrite and an axon; just what we were talking about. 00:33:19.220 --> 00:33:20.680 And what's the functional purpose 00:33:20.680 --> 00:33:25.100 of an active pumping mechanism in the axonal membrane? 00:33:25.100 --> 00:33:27.480 Usually people say, oh, action potentials. 00:33:27.480 --> 00:33:29.555 And the answer is, no. 00:33:29.555 --> 00:33:32.590 It's not its purpose. 00:33:32.590 --> 00:33:34.500 So first of all, excitatory, inhibitory 00:33:34.500 --> 00:33:36.350 post synaptic potentials, this is 00:33:36.350 --> 00:33:41.080 from an introductory biological psychology textbook. 00:33:43.660 --> 00:33:47.400 It shows intracellular recordings 00:33:47.400 --> 00:33:53.405 with a microelectrode, where they record from this axon. 00:34:04.199 --> 00:34:04.990 I'm wondering here. 00:34:04.990 --> 00:34:05.490 Yeah. 00:34:08.280 --> 00:34:10.760 So the presynaptic recording shows 00:34:10.760 --> 00:34:14.270 the action potential, big potential that 00:34:14.270 --> 00:34:19.590 goes from minus 60, minus 70, becomes momentarily positive 00:34:19.590 --> 00:34:24.699 and then the membrane potential recovers. 00:34:24.699 --> 00:34:28.090 And if you record on the other side of the synapse, 00:34:28.090 --> 00:34:30.679 you get a little bit of depolarization. 00:34:30.679 --> 00:34:32.389 If you're getting depolarization, 00:34:32.389 --> 00:34:34.350 it's excitatory. 00:34:34.350 --> 00:34:38.020 Why are those two things are equivalent? 00:34:38.020 --> 00:34:39.925 Because it moves. 00:34:39.925 --> 00:34:46.260 There's one point here where the axon begins, 00:34:46.260 --> 00:34:50.250 where if the depolarization, reaches a critical level, 00:34:50.250 --> 00:34:53.770 it triggers the action potential. 00:34:53.770 --> 00:35:00.760 And these little EPSPs summate at the beginning 00:35:00.760 --> 00:35:05.330 of the axon, the axon hillock, we call it. 00:35:05.330 --> 00:35:09.130 So the more of them there-- and the conduction in the cell body 00:35:09.130 --> 00:35:11.110 is decrimental. 00:35:11.110 --> 00:35:14.900 So if it's happening way over here, 00:35:14.900 --> 00:35:18.350 and there's a depolarization, it has less effect 00:35:18.350 --> 00:35:21.540 on the axon hillock here than something 00:35:21.540 --> 00:35:24.974 happening right there. 00:35:24.974 --> 00:35:26.390 So it makes a big difference where 00:35:26.390 --> 00:35:28.830 the terminal is on the axon. 00:35:28.830 --> 00:35:33.340 But the EPSPs look the same everywhere. 00:35:33.340 --> 00:35:36.110 They might be a little bigger, or a little smaller, 00:35:36.110 --> 00:35:39.090 but they're conducted decrementally 00:35:39.090 --> 00:35:41.680 by the dendrites and cell body membrane. 00:35:45.480 --> 00:35:49.350 Inhibitory post synaptic potential is opposite. 00:35:49.350 --> 00:35:52.330 It's when there's a hyperpolarization, 00:35:52.330 --> 00:35:55.460 as you see here. 00:35:55.460 --> 00:35:58.800 The membrane, if it was polarized as minus 70, 00:35:58.800 --> 00:36:01.690 might go to minus 80. 00:36:01.690 --> 00:36:04.760 And it's inhibitory because it takes the membrane further 00:36:04.760 --> 00:36:08.980 from the point where an action potential will be triggered. 00:36:08.980 --> 00:36:11.610 So let's talk a little bit more about that difference 00:36:11.610 --> 00:36:13.810 in conduction in dendrites and axon. 00:36:13.810 --> 00:36:19.030 Looking this picture, I drew it without myelin for a reason. 00:36:19.030 --> 00:36:23.770 Axons don't need myelin to conduct. 00:36:23.770 --> 00:36:28.600 So here I'm drawing functionally equivalent parts 00:36:28.600 --> 00:36:31.850 of two neurons, a dorsal root ganglion 00:36:31.850 --> 00:36:36.000 cell that conducts from the body surface, where there are 00:36:36.000 --> 00:36:39.740 endings here, and then the long axon 00:36:39.740 --> 00:36:43.510 goes right by the cell body into the central nervous system, 00:36:43.510 --> 00:36:47.760 where it ends in terminals with synapses 00:36:47.760 --> 00:36:51.700 on the cells, secondary sensory neurons. 00:36:51.700 --> 00:36:53.320 So it's a sensory neuron. 00:36:53.320 --> 00:36:54.920 And here I have a motor neuron. 00:36:54.920 --> 00:36:59.580 So here, you're inside the CNS, and there is the cell body. 00:36:59.580 --> 00:37:03.880 There is the axon going to a muscle cell. 00:37:03.880 --> 00:37:17.580 So this part of both of those cells is the receptive part. 00:37:17.580 --> 00:37:20.550 This part, where I show the arrows, is the conductive part. 00:37:20.550 --> 00:37:23.868 And here transmissions occur in, the transmission part. 00:37:32.660 --> 00:37:38.010 And so now let's take a little piece of that. 00:37:38.010 --> 00:37:42.670 First of all, the conduction here-- now, in some cases, 00:37:42.670 --> 00:37:44.640 the axon might begin further out. 00:37:44.640 --> 00:37:47.840 But here, I have it at the beginning right here. 00:37:47.840 --> 00:37:50.240 You get decremental conduction there. 00:37:50.240 --> 00:37:52.980 What are the characteristics of decremental conduction, other 00:37:52.980 --> 00:37:54.705 than the fact that gets less and less 00:37:54.705 --> 00:37:58.214 the further away from the sight of stimulation you get? 00:37:58.214 --> 00:37:59.880 The other characteristic you should know 00:37:59.880 --> 00:38:06.660 is it's very, very fast, almost instantaneous. 00:38:06.660 --> 00:38:11.180 Not like light, but it's close, very fast. 00:38:11.180 --> 00:38:15.480 And then the point where the action potential 00:38:15.480 --> 00:38:17.300 begins, what is an action potential? 00:38:21.410 --> 00:38:22.790 Here I pictured it. 00:38:22.790 --> 00:38:26.400 I've taken a snapshot of it at one little plane 00:38:26.400 --> 00:38:29.720 and enlarged the tube or the axon, 00:38:29.720 --> 00:38:35.970 and I'm just showing how ion distributions are polarizing 00:38:35.970 --> 00:38:41.000 the membrane, positive on the outside, mainly because 00:38:41.000 --> 00:38:46.290 of the accumulation of sodium ions, negative on the inside. 00:38:46.290 --> 00:38:49.520 There are potassium ions in there that are positive also. 00:38:49.520 --> 00:38:51.890 But a lot of name are going to be charged anions, 00:38:51.890 --> 00:38:56.560 large ones, and [INAUDIBLE] here. 00:39:00.250 --> 00:39:04.350 What happens when, at the beginning of the action 00:39:04.350 --> 00:39:09.530 potential, there's an implosion of sodium ions? 00:39:09.530 --> 00:39:11.970 Momentarily reverses the potential. 00:39:11.970 --> 00:39:17.210 This curve matches that piece of axon. 00:39:17.210 --> 00:39:19.780 So there's the beginning of the action potential. 00:39:19.780 --> 00:39:24.070 The sodium ions rush in, an implosion of sodium ions. 00:39:24.070 --> 00:39:27.750 The potential, remember, reverses, momentarily, 00:39:27.750 --> 00:39:30.160 and then it rapidly recovers. 00:39:30.160 --> 00:39:32.790 And the first reason it starts recovering 00:39:32.790 --> 00:39:35.670 is potassium ion channels are also voltage-gated, 00:39:35.670 --> 00:39:40.240 and so potassium, which is in high concentration inside, 00:39:40.240 --> 00:39:41.230 rushes out. 00:39:41.230 --> 00:39:44.650 The channels open up. 00:39:44.650 --> 00:39:46.560 You see, it's a semipermeable membrane. 00:39:46.560 --> 00:39:50.780 It's not-- all these ions can't get through very rapidly, 00:39:50.780 --> 00:39:54.470 unless the channels open up. 00:39:54.470 --> 00:39:57.984 So that's why the voltage-gated ion channels are so important. 00:39:57.984 --> 00:39:59.650 And then so then, the membrane recovers. 00:40:03.130 --> 00:40:08.200 And there's another way to look at that membrane, 00:40:08.200 --> 00:40:11.740 where I show the polarization indicated a lot of sodium ions 00:40:11.740 --> 00:40:12.580 on the outside. 00:40:12.580 --> 00:40:14.520 There's also chloride ions. 00:40:14.520 --> 00:40:16.540 And then, in the inside the negatively charged 00:40:16.540 --> 00:40:19.170 anions, the big ones that don't pass through the membrane 00:40:19.170 --> 00:40:24.730 at all, and the positively charged potassium ions. 00:40:24.730 --> 00:40:27.430 But there are molecules in the membrane, 00:40:27.430 --> 00:40:29.720 I'm just showing a couple of sites here, 00:40:29.720 --> 00:40:34.480 we call the sodium potassium pump. 00:40:34.480 --> 00:40:40.090 It's always moving sodium ions out and potassium ions in. 00:40:40.090 --> 00:40:44.230 Because with a lot of action potentials, 00:40:44.230 --> 00:40:47.930 you basically lose that concentration 00:40:47.930 --> 00:40:50.630 of sodium on the outside and potassium on the inside 00:40:50.630 --> 00:40:53.510 if you get a lot of action potentials. 00:40:53.510 --> 00:40:56.220 So eventually, it'll just stop. 00:40:56.220 --> 00:41:02.030 Unless, you use energy to redistribute those ions. 00:41:02.030 --> 00:41:04.620 And that's why we need an active pumping mechanism. 00:41:11.900 --> 00:41:16.920 So now we've answered those questions, at least tried to. 00:41:16.920 --> 00:41:18.320 Where's the dorsal root ganglia? 00:41:18.320 --> 00:41:19.370 I've mentioned it here. 00:41:22.290 --> 00:41:26.790 Actually, I said a dorsal root ganglia cell. 00:41:26.790 --> 00:41:29.110 Let's answer that a little better, talk 00:41:29.110 --> 00:41:32.560 about the oligodendrocytes and Schwann cells. 00:41:32.560 --> 00:41:34.089 Somebody already mentioned myelin. 00:41:34.089 --> 00:41:35.630 These are the cells that make myelin. 00:41:40.060 --> 00:41:44.240 And then I want to talk about the main function of the myelin 00:41:44.240 --> 00:41:45.910 sheath. 00:41:45.910 --> 00:41:49.040 First of all, what's the dorsal root ganglia? 00:41:49.040 --> 00:41:50.600 This is a picture from [INAUDIBLE] 00:41:50.600 --> 00:41:51.930 that I put in the book. 00:41:51.930 --> 00:41:54.240 Here you see in an earthworm and mollusk, 00:41:54.240 --> 00:41:57.090 primary sensory neurons, the neurons responding 00:41:57.090 --> 00:41:58.130 to the outside world. 00:41:58.130 --> 00:42:02.220 These are neurons at the surface layer of the body, 00:42:02.220 --> 00:42:04.160 so in the skin of the animal. 00:42:04.160 --> 00:42:06.270 Here are the cell primary sensory neurons 00:42:06.270 --> 00:42:08.520 right in the epothelium. 00:42:08.520 --> 00:42:10.980 Here, the cell body below the epothelium, 00:42:10.980 --> 00:42:16.036 but it extends right out into the epothelium. 00:42:19.160 --> 00:42:23.360 But as soon as you get to the vertebrates-- 00:42:23.360 --> 00:42:26.320 this is the central ganglion here. 00:42:26.320 --> 00:42:28.010 We don't talk really about a CNS, 00:42:28.010 --> 00:42:30.446 but sometimes we do, just because 00:42:30.446 --> 00:42:31.820 of similarity to the vertebrates. 00:42:35.620 --> 00:42:39.680 Here's a fish and amphibian, reptile, bird, or mammal. 00:42:39.680 --> 00:42:43.640 The fish has these bipolar cells that 00:42:43.640 --> 00:42:45.140 contain the primary sensory neuron, 00:42:45.140 --> 00:42:47.800 and they are collected in a ganglia. 00:42:47.800 --> 00:42:50.410 You talk about a collection of cells 00:42:50.410 --> 00:42:54.590 outside the central nervous system as ganglia. 00:42:54.590 --> 00:43:01.200 So here, in us and in these other mammals and also 00:43:01.200 --> 00:43:05.450 amphibians and reptiles, the primary sensory neurons 00:43:05.450 --> 00:43:08.785 carry input from the skin are in a dorsal root ganglion. 00:43:08.785 --> 00:43:14.160 From the dorsal roots because the roots of the spinal nerves 00:43:14.160 --> 00:43:18.510 that enter the CNS will always divide. 00:43:18.510 --> 00:43:23.050 The more dorsal one contains the sensory axons, the more ventral 00:43:23.050 --> 00:43:27.590 ones, the motor axons going to the muscles. 00:43:27.590 --> 00:43:31.820 So that's the dorsal root ganglia. 00:43:31.820 --> 00:43:34.120 So now what about oligodendrocytes 00:43:34.120 --> 00:43:35.110 and Scwann cells. 00:43:39.110 --> 00:43:45.300 When axons acquire myelin, it is the Schwann cell 00:43:45.300 --> 00:43:49.830 that myelinites these axons of the periphery, 00:43:49.830 --> 00:43:52.550 the peripheral nervous system. 00:43:52.550 --> 00:43:55.860 But as soon as you enter the central nervous system, 00:43:55.860 --> 00:43:58.240 it's really a very different type of tissue, 00:43:58.240 --> 00:44:01.490 and you get a different glial cell making the myelin. 00:44:01.490 --> 00:44:03.786 It's now an oligodendrocyte. 00:44:03.786 --> 00:44:05.160 There are other differences, too. 00:44:05.160 --> 00:44:11.120 One Schwann cell will form the myelin in one little stretch. 00:44:11.120 --> 00:44:13.610 And then there will be a little place with no myelin. 00:44:13.610 --> 00:44:17.090 And then another Schwann cell wil myelinate the next segment. 00:44:17.090 --> 00:44:22.720 In the CNS, one oligodendrocyte can myelinate or form 00:44:22.720 --> 00:44:27.430 a segment of myelin in a whole bunch of axons nearby, 00:44:27.430 --> 00:44:28.760 so quite different. 00:44:28.760 --> 00:44:32.030 But the function is quite similar. 00:44:32.030 --> 00:44:33.950 What is the function? 00:44:33.950 --> 00:44:35.765 It's a kind of insulator. 00:44:35.765 --> 00:44:39.910 It prevents ion flow. 00:44:39.910 --> 00:44:42.160 The ions can't flow through the membrane 00:44:42.160 --> 00:44:44.162 where the myelin is there. 00:44:44.162 --> 00:44:44.870 It's a tight fit. 00:44:47.720 --> 00:44:53.740 So if you get depolarization just before myelin begins-- 00:44:53.740 --> 00:44:58.390 if we're talking here about space, so at one end-- 00:44:58.390 --> 00:45:00.990 you get depolarization. 00:45:00.990 --> 00:45:01.895 What happens? 00:45:01.895 --> 00:45:04.860 It triggers the action potential right there 00:45:04.860 --> 00:45:06.990 on that little piece of bare axon. 00:45:06.990 --> 00:45:13.010 And then, the only way I can conduct down the axon 00:45:13.010 --> 00:45:19.320 is by a flow of ion by decremental conduction, 00:45:19.320 --> 00:45:23.030 until it reaches the next node where there's no myelin. 00:45:23.030 --> 00:45:29.610 And if the decrement of the depolarization isn't so great, 00:45:29.610 --> 00:45:31.490 it will depolarize that membrane, 00:45:31.490 --> 00:45:33.990 trigger an action potential there. 00:45:33.990 --> 00:45:36.550 And then same thing will happen, and the conduction 00:45:36.550 --> 00:45:41.430 will go bloop, bloop, bloop, bloop, like jumps. 00:45:41.430 --> 00:45:45.110 That's what saltatory conduction is. 00:45:45.110 --> 00:45:47.070 So [INAUDIBLE] means dumps. 00:45:47.070 --> 00:45:50.610 OK And that's why it speeds up, because 00:45:50.610 --> 00:45:55.180 the decremental conduction is very fast, like I said before. 00:45:55.180 --> 00:45:57.099 The action potential is not so fast 00:45:57.099 --> 00:45:58.265 that it's self-regenerating. 00:46:00.840 --> 00:46:04.910 So in a picture like this, you just 00:46:04.910 --> 00:46:07.450 get this continuous movement of the action potential, 00:46:07.450 --> 00:46:09.950 all the way down the axon. 00:46:09.950 --> 00:46:12.070 But it's limited in how fast it can go. 00:46:12.070 --> 00:46:16.340 It goes faster if the axon's bigger. 00:46:16.340 --> 00:46:19.470 So in animals without myelin, the axons 00:46:19.470 --> 00:46:21.725 get huge if they need rapid conduction, 00:46:21.725 --> 00:46:24.740 for an escape response. 00:46:24.740 --> 00:46:27.050 But we don't have-- mammals generally 00:46:27.050 --> 00:46:30.620 don't have such huge axons. 00:46:30.620 --> 00:46:35.090 It would be very-- it would cost too much energy and space. 00:46:35.090 --> 00:46:37.600 The myelin was the invention that solved that problem. 00:46:43.050 --> 00:46:46.120 Receptor cells, I said many receptor cells are not actually 00:46:46.120 --> 00:46:48.620 neurons. 00:46:48.620 --> 00:46:50.120 So how do they differ from neurons? 00:46:50.120 --> 00:46:53.320 How do they interactive with neurons? 00:46:53.320 --> 00:46:55.740 They depolarize, just like neurons. 00:46:55.740 --> 00:46:59.880 But they don't have the membrane of an axon. 00:46:59.880 --> 00:47:03.360 They don't have any action potentials, 00:47:03.360 --> 00:47:08.200 but their depolarization affects neurons that contact them, 00:47:08.200 --> 00:47:12.490 and can trigger an action potential in those neurons. 00:47:12.490 --> 00:47:14.510 So that's a receptor cell. 00:47:14.510 --> 00:47:17.675 Some receptors, like in the nasal epithelium 00:47:17.675 --> 00:47:21.860 or olfactory receptors, the primary sensory cell 00:47:21.860 --> 00:47:22.590 is a receptor. 00:47:25.640 --> 00:47:28.720 You have the same thing in the retina, where 00:47:28.720 --> 00:47:30.570 the specialization is even greater. 00:47:34.090 --> 00:47:38.450 And here's just a list of various specializations. 00:47:38.450 --> 00:47:41.240 You already should know about various kinds. 00:47:41.240 --> 00:47:43.660 Some of them here are mechanical in nature, 00:47:43.660 --> 00:47:47.590 also response to light, chemicals, to heat or cold 00:47:47.590 --> 00:47:52.260 are all specialized receptor cells, 00:47:52.260 --> 00:47:54.977 except in the case of chemicals, where it's the neuron itself. 00:47:54.977 --> 00:47:56.560 But it's still a specialized receptor. 00:48:00.800 --> 00:48:05.500 What kind of molecules are actin and myosin? 00:48:05.500 --> 00:48:09.010 What kind of molecule is that that we're talking about? 00:48:09.010 --> 00:48:11.780 Contractal porteins. 00:48:11.780 --> 00:48:16.055 When is actin found most abundantly in neurons? 00:48:19.530 --> 00:48:23.860 During development, when the axon's growing. 00:48:23.860 --> 00:48:25.950 The axon has to move a lot. 00:48:25.950 --> 00:48:28.780 The growth cone is very active. 00:48:28.780 --> 00:48:31.195 And we will see that when we study development. 00:48:33.840 --> 00:48:36.680 You should know about the Otto Loewi's discovery. 00:48:36.680 --> 00:48:38.880 Don't have time to describe his dream. 00:48:38.880 --> 00:48:40.140 I like to describe it. 00:48:40.140 --> 00:48:41.820 It's a lot of fun. 00:48:41.820 --> 00:48:42.950 But you should read. 00:48:42.950 --> 00:48:45.260 I have a little bit in the book about it. 00:48:45.260 --> 00:48:49.950 And you can find things online very easily. 00:48:49.950 --> 00:48:53.780 He discovered-- he didn't know he was discovering 00:48:53.780 --> 00:48:56.740 acetylcholine and norepinephrine, 00:48:56.740 --> 00:48:58.280 but that's what it was. 00:48:58.280 --> 00:49:00.260 That's what the molecules turned out to be. 00:49:00.260 --> 00:49:06.280 He was the one who settled a big argument in neuroscience 00:49:06.280 --> 00:49:08.660 in the early part of the 20th century 00:49:08.660 --> 00:49:11.220 about whether conduction in synapse 00:49:11.220 --> 00:49:13.570 was electrical or chemical. 00:49:13.570 --> 00:49:17.390 And there were a lot of arguments on both sides. 00:49:17.390 --> 00:49:21.570 He proved that-- now we know they both exist, 00:49:21.570 --> 00:49:24.590 but for the most part, most synapses, 00:49:24.590 --> 00:49:26.886 the conduction is the transmission 00:49:26.886 --> 00:49:28.510 from one cell to the other is chemical. 00:49:28.510 --> 00:49:31.740 He discovered that in this experiment on frogs. 00:49:34.720 --> 00:49:40.070 By just stimulating the axon of a heart, 00:49:40.070 --> 00:49:45.640 and accelerator nerve, one heart in a Petri dish, 00:49:45.640 --> 00:49:47.820 taking a little fluid from that Petri dish 00:49:47.820 --> 00:49:49.362 and putting it in another Petri dish, 00:49:49.362 --> 00:49:50.778 here he hadn't stimulated a nerve, 00:49:50.778 --> 00:49:52.280 but the heart speeded up anyway. 00:49:59.490 --> 00:50:03.180 The reason I said it is high and maybe a few of you 00:50:03.180 --> 00:50:05.990 want to go to the [INAUDIBLE]. 00:50:05.990 --> 00:50:10.260 [INAUDIBLE] didn't discover, didn't talk about-- 00:50:10.260 --> 00:50:13.866 I wanted you to read this and you ask me questions about it. 00:50:13.866 --> 00:50:15.240 If there's anything about the way 00:50:15.240 --> 00:50:17.690 I portrayed synapses and their various types 00:50:17.690 --> 00:50:19.360 in the central nervous system. 00:50:19.360 --> 00:50:21.640 The hardest thing is probably the concept 00:50:21.640 --> 00:50:25.840 of presynaptic facilitation and inhibition. 00:50:25.840 --> 00:50:31.570 So, see if you can get some understanding of that. 00:50:31.570 --> 00:50:33.050 The rest of this, I think, is quite 00:50:33.050 --> 00:50:37.970 clear from the book, endogenous activity also. 00:50:37.970 --> 00:50:39.720 Just read it in the book. 00:50:39.720 --> 00:50:43.550 You can look at the slides to know what I'm stressing here. 00:50:43.550 --> 00:50:48.930 And these concepts will recur later in the class.