1 00:00:00,250 --> 00:00:01,800 The following content is provided 2 00:00:01,800 --> 00:00:04,040 under a Creative Commons license. 3 00:00:04,040 --> 00:00:06,890 Your support will help MIT OpenCourseWare continue 4 00:00:06,890 --> 00:00:10,740 to offer high quality educational resources for free. 5 00:00:10,740 --> 00:00:13,360 To make a donation or view additional materials 6 00:00:13,360 --> 00:00:17,265 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,265 --> 00:00:17,890 at ocw.mit.edu. 8 00:00:23,160 --> 00:00:24,660 PROFESSOR: Today we're going to talk 9 00:00:24,660 --> 00:00:27,630 about the evolution of the earliest 10 00:00:27,630 --> 00:00:34,100 nervous systems, the evolution. 11 00:00:34,100 --> 00:00:37,570 Why were nervous systems so important with multicellular 12 00:00:37,570 --> 00:00:38,070 organisms? 13 00:00:42,350 --> 00:00:45,900 Single-cell organisms can do a lot, 14 00:00:45,900 --> 00:00:49,260 and they don't have nervous systems. 15 00:00:49,260 --> 00:00:52,320 But remember they have primitive cellular mechanisms. 16 00:00:52,320 --> 00:00:53,750 They respond to inputs. 17 00:00:56,500 --> 00:00:59,840 The effects of inputs are conducted throughout the cell. 18 00:00:59,840 --> 00:01:01,350 They respond to cells. 19 00:01:04,000 --> 00:01:08,385 They do a lot of things multicellular organisms do. 20 00:01:08,385 --> 00:01:11,950 But as soon as you start putting a lot of cells together, 21 00:01:11,950 --> 00:01:13,980 then you have the problem of integration, 22 00:01:13,980 --> 00:01:17,620 one part of the organism with another. 23 00:01:17,620 --> 00:01:18,120 OK. 24 00:01:18,120 --> 00:01:23,290 So what are some multipurpose actions 25 00:01:23,290 --> 00:01:26,780 that every animal, even one-cell organisms, 26 00:01:26,780 --> 00:01:28,127 must be able to perform? 27 00:01:31,170 --> 00:01:32,750 I teach animal behavior. 28 00:01:32,750 --> 00:01:35,690 And so this, to me, even though it's 29 00:01:35,690 --> 00:01:44,370 omitted by a lot of behavioral textbooks and teachers, to me, 30 00:01:44,370 --> 00:01:47,550 you've got to start with the fundamentals. 31 00:01:47,550 --> 00:01:50,283 What do our animals do? 32 00:01:50,283 --> 00:01:51,610 AUDIENCE: Locomotion. 33 00:01:51,610 --> 00:01:54,330 PROFESSOR: Locomotion, big one. 34 00:01:54,330 --> 00:01:56,380 You know, what do they use locomotion for? 35 00:01:59,580 --> 00:02:03,700 To escape from things, to get away from things, 36 00:02:03,700 --> 00:02:07,017 and to grab things, either attack them, 37 00:02:07,017 --> 00:02:11,262 and kill them, and eat them, or find food in some other way. 38 00:02:11,262 --> 00:02:14,240 It requires locomotion, unless-- 39 00:02:14,240 --> 00:02:15,590 There are a few exceptions. 40 00:02:15,590 --> 00:02:18,790 There are some animals that have evolved, 41 00:02:18,790 --> 00:02:22,460 at least at certain stages of their life, sessile forms, 42 00:02:22,460 --> 00:02:23,620 where they just sit. 43 00:02:23,620 --> 00:02:27,600 But most organisms have to locomote towards or away 44 00:02:27,600 --> 00:02:28,470 from things. 45 00:02:28,470 --> 00:02:29,790 What else? 46 00:02:29,790 --> 00:02:32,552 What is another multipurpose action? 47 00:02:32,552 --> 00:02:34,360 AUDIENCE: Reproduction. 48 00:02:34,360 --> 00:02:36,410 PROFESSOR: Reproduction, very basic. 49 00:02:36,410 --> 00:02:38,800 But reproduction-- 50 00:02:38,800 --> 00:02:42,300 Well, that's a broader thing. 51 00:02:42,300 --> 00:02:45,840 I'm talking about fundamental action patterns. 52 00:02:45,840 --> 00:02:48,480 So let's go back from reproduction. 53 00:02:48,480 --> 00:02:50,120 But these things we're talking about 54 00:02:50,120 --> 00:02:51,530 are involved in reproduction. 55 00:02:51,530 --> 00:02:52,530 You're absolutely right. 56 00:02:52,530 --> 00:02:54,530 And that's particularly fundamental 57 00:02:54,530 --> 00:02:59,140 because that's what drives evolution. 58 00:02:59,140 --> 00:02:59,884 Yeah? 59 00:02:59,884 --> 00:03:01,780 AUDIENCE: Responding to a stimulus? 60 00:03:01,780 --> 00:03:04,270 PROFESSOR: Responding to a stimulus, very basic. 61 00:03:04,270 --> 00:03:05,920 But I want the action. 62 00:03:05,920 --> 00:03:11,251 How do they respond to the stimulus besides locomotion? 63 00:03:11,251 --> 00:03:11,750 Yes? 64 00:03:11,750 --> 00:03:12,780 AUDIENCE: Orientation? 65 00:03:12,780 --> 00:03:15,850 PROFESSOR: Orienting, turning. 66 00:03:15,850 --> 00:03:20,316 Animals have to respond to where things are. 67 00:03:20,316 --> 00:03:20,815 OK. 68 00:03:23,880 --> 00:03:29,330 So locomotion, approaching, avoiding, 69 00:03:29,330 --> 00:03:32,880 orienting towards or away again. 70 00:03:32,880 --> 00:03:36,275 And then I've added here exploring, or foraging, 71 00:03:36,275 --> 00:03:38,810 or seeking. 72 00:03:38,810 --> 00:03:41,870 But you see that's just includes the first two. 73 00:03:41,870 --> 00:03:47,040 But what is included in foraging that's not necessarily 74 00:03:47,040 --> 00:03:50,800 in those first two, locomotion and orientation? 75 00:03:50,800 --> 00:03:53,260 There's an element that's involved. 76 00:03:53,260 --> 00:03:55,520 I think I probably asked that-- 77 00:03:55,520 --> 00:03:56,080 Yeah, here. 78 00:03:56,080 --> 00:03:58,380 That's the next question. 79 00:03:58,380 --> 00:03:59,480 OK? 80 00:03:59,480 --> 00:04:01,330 Approach and avoidance with flight movements 81 00:04:01,330 --> 00:04:05,870 are controlled by sensory inputs plus one other thing, one 82 00:04:05,870 --> 00:04:07,590 other important thing. 83 00:04:07,590 --> 00:04:09,700 What is that other thing? 84 00:04:09,700 --> 00:04:12,448 Very important in the evolution of the CNS. 85 00:04:12,448 --> 00:04:14,280 AUDIENCE: Grasping? 86 00:04:14,280 --> 00:04:17,470 PROFESSOR: Grasping is part of-- 87 00:04:17,470 --> 00:04:23,270 Yeah, grasping is actually a third fundamental action. 88 00:04:23,270 --> 00:04:26,440 But grasping isn't always. 89 00:04:26,440 --> 00:04:28,090 I'm thinking of something else. 90 00:04:30,800 --> 00:04:32,160 Anybody? 91 00:04:32,160 --> 00:04:33,926 Yes? 92 00:04:33,926 --> 00:04:34,800 AUDIENCE: Motivation? 93 00:04:34,800 --> 00:04:37,900 PROFESSOR: Motivation, the internal drive, 94 00:04:37,900 --> 00:04:40,610 something that comes from inside. 95 00:04:40,610 --> 00:04:44,240 I mean, why are they locomoting in one direction 96 00:04:44,240 --> 00:04:46,670 now and another direction another time? 97 00:04:46,670 --> 00:04:48,750 Why are they trying to get to food one 98 00:04:48,750 --> 00:04:52,440 time, to a mate another time, and so on and so forth? 99 00:04:52,440 --> 00:04:54,380 It depends on internal states. 100 00:04:54,380 --> 00:04:57,420 All right. 101 00:04:57,420 --> 00:05:01,730 And then, as I mentioned, in that earlier slide-- 102 00:05:01,730 --> 00:05:03,870 we didn't get through everything there. 103 00:05:03,870 --> 00:05:05,590 But I asked a question about it here. 104 00:05:05,590 --> 00:05:09,405 What are the ongoing maintenance activities, 105 00:05:09,405 --> 00:05:14,900 or background activities, that are happening all the time? 106 00:05:14,900 --> 00:05:16,960 While their locomotion is happening, 107 00:05:16,960 --> 00:05:21,070 while the orienting is happening, 108 00:05:21,070 --> 00:05:25,700 whatever the motivation, it's independent of motivation. 109 00:05:25,700 --> 00:05:27,860 What are the ongoing background activities? 110 00:05:27,860 --> 00:05:31,300 And what kind of nervous system mechanism is involved? 111 00:05:31,300 --> 00:05:32,260 Yes? 112 00:05:32,260 --> 00:05:37,760 AUDIENCE: Like homeostatic things, like [INAUDIBLE]. 113 00:05:37,760 --> 00:05:39,800 PROFESSOR: Yeah, things that need 114 00:05:39,800 --> 00:05:42,460 to be maintained in a constant state. 115 00:05:42,460 --> 00:05:44,410 That's good. 116 00:05:44,410 --> 00:05:46,060 Can anybody think of other things? 117 00:05:48,670 --> 00:05:52,500 Think of one you're doing one of these fundamental things. 118 00:05:52,500 --> 00:05:53,800 You're locomoting. 119 00:05:53,800 --> 00:05:55,580 You're going to your next class. 120 00:05:55,580 --> 00:05:58,400 What are the background things going on? 121 00:05:58,400 --> 00:05:59,850 What is your body doing? 122 00:05:59,850 --> 00:06:02,830 What's it maintaining in homeostasis? 123 00:06:02,830 --> 00:06:05,870 Temperature, for example. 124 00:06:05,870 --> 00:06:10,490 Even protists will seek places of the right temperature. 125 00:06:10,490 --> 00:06:14,030 They may not have much internal-- 126 00:06:14,030 --> 00:06:18,420 They're not endothermic, like we are. 127 00:06:18,420 --> 00:06:22,310 But they still have some kind of regulation. 128 00:06:22,310 --> 00:06:23,880 They still have to eliminate. 129 00:06:23,880 --> 00:06:24,730 They still have to-- 130 00:06:27,440 --> 00:06:34,209 What about a quadruped now, or a two or four legged animal? 131 00:06:34,209 --> 00:06:35,750 What does he do when he's locomoting? 132 00:06:35,750 --> 00:06:37,980 What is the maintenance? 133 00:06:37,980 --> 00:06:38,850 AUDIENCE: Balance. 134 00:06:38,850 --> 00:06:39,780 PROFESSOR: Balance. 135 00:06:39,780 --> 00:06:41,300 Yeah, posture. 136 00:06:41,300 --> 00:06:45,120 What are the mechanisms now that control these background 137 00:06:45,120 --> 00:06:47,530 things? 138 00:06:47,530 --> 00:06:48,550 What do we call them? 139 00:06:48,550 --> 00:06:53,050 They're lower level mechanisms for the most part. 140 00:06:53,050 --> 00:06:55,250 Many of them are spinal mechanisms, 141 00:06:55,250 --> 00:06:57,451 as we'll be talking about. 142 00:06:57,451 --> 00:06:57,950 Yes? 143 00:06:57,950 --> 00:06:59,280 AUDIENCE: Reflexes? 144 00:06:59,280 --> 00:07:02,190 PROFESSOR: A lot of them are reflexes, very simple, 145 00:07:02,190 --> 00:07:03,390 local pathways. 146 00:07:03,390 --> 00:07:05,024 That's exactly right. 147 00:07:05,024 --> 00:07:06,780 OK? 148 00:07:06,780 --> 00:07:09,350 Simple reflexes and simple programs 149 00:07:09,350 --> 00:07:14,640 that are ongoing so they don't heart race, one. 150 00:07:14,640 --> 00:07:18,970 The heart, of course, has its own ganglion 151 00:07:18,970 --> 00:07:21,060 that's regulating it. 152 00:07:21,060 --> 00:07:24,280 But it's influenced by the central nervous system also. 153 00:07:24,280 --> 00:07:28,310 It's adjusted because you need a lot more blood flow when you're 154 00:07:28,310 --> 00:07:32,840 running than you do when you're not running, things like that. 155 00:07:32,840 --> 00:07:35,670 All right. 156 00:07:35,670 --> 00:07:42,110 So now let's start talking about conduction, nerve cells. 157 00:07:42,110 --> 00:07:44,420 How can conduction between cells occur 158 00:07:44,420 --> 00:07:47,460 without synaptic connections? 159 00:07:47,460 --> 00:07:52,575 We find such conduction before we find real neurons. 160 00:07:52,575 --> 00:07:58,050 It's found in sponges even, as well as in cnidarians, 161 00:07:58,050 --> 00:07:59,857 like hydra. 162 00:07:59,857 --> 00:08:01,690 Most of these things I'm going to talk about 163 00:08:01,690 --> 00:08:04,230 are found in little creatures, like hydra. 164 00:08:04,230 --> 00:08:05,940 We used to call them the coelenterates. 165 00:08:08,544 --> 00:08:09,900 That's been revised. 166 00:08:09,900 --> 00:08:12,022 They're now the cnidarians. 167 00:08:12,022 --> 00:08:16,720 But even sponges have conduction between cells. 168 00:08:16,720 --> 00:08:20,720 You touch a sponge, it's just not the cells 169 00:08:20,720 --> 00:08:22,900 that you're touching that are responding. 170 00:08:22,900 --> 00:08:26,775 Other cells respond too. 171 00:08:26,775 --> 00:08:29,220 AUDIENCE: Like sort of electrical conductions, 172 00:08:29,220 --> 00:08:30,690 like that? 173 00:08:30,690 --> 00:08:33,790 PROFESSOR: Yeah, there is a kind of electrical conduction. 174 00:08:36,770 --> 00:08:40,669 People sometimes call this conduction myoid and neuroid, 175 00:08:40,669 --> 00:08:43,230 just meaning it's like conduction between muscle 176 00:08:43,230 --> 00:08:43,730 cells. 177 00:08:43,730 --> 00:08:46,380 It's like conduction between nerve cells. 178 00:08:46,380 --> 00:08:50,770 But it's not really the same as in advanced organisms. 179 00:08:50,770 --> 00:08:54,280 It's a term used in Nauta and [INAUDIBLE] book. 180 00:08:54,280 --> 00:08:57,710 And it's used by others that talk 181 00:08:57,710 --> 00:09:02,780 about primitive, conductive mechanisms. 182 00:09:02,780 --> 00:09:05,940 And it's done in the study of the anatomy of those creatures 183 00:09:05,940 --> 00:09:11,040 that we get ideas about earliest stages of nervous system 184 00:09:11,040 --> 00:09:12,850 evolution. 185 00:09:12,850 --> 00:09:20,560 I've taken these pictures that I've put in the book 186 00:09:20,560 --> 00:09:30,400 not from George Parker at Yale, who was the guy who first tried 187 00:09:30,400 --> 00:09:34,410 to do it, but Mackie, George Mackie, who updated it, 188 00:09:34,410 --> 00:09:41,780 wrote a nice paper in Quarterly Review of Biology in 1970. 189 00:09:41,780 --> 00:09:43,440 This is his earliest stage. 190 00:09:43,440 --> 00:09:48,760 There you have contracted cells that are also sensory. 191 00:09:48,760 --> 00:09:50,090 So they're sensory and motor. 192 00:09:50,090 --> 00:09:51,800 They're responding to the environment. 193 00:09:51,800 --> 00:09:53,370 They can contract. 194 00:09:53,370 --> 00:09:55,575 But he shows this-- 195 00:09:58,140 --> 00:10:00,810 He indicates this dashed line, where 196 00:10:00,810 --> 00:10:03,140 the membranes are against each other. 197 00:10:03,140 --> 00:10:05,515 That simply means gap junctions. 198 00:10:05,515 --> 00:10:07,590 It's something equivalent to gap junctions 199 00:10:07,590 --> 00:10:09,570 in our own nervous systems. 200 00:10:09,570 --> 00:10:11,690 It's electrical conduction working. 201 00:10:11,690 --> 00:10:15,150 Charged ions can flow from one cell to the other. 202 00:10:15,150 --> 00:10:19,020 So an electrical change that starts here 203 00:10:19,020 --> 00:10:22,690 can spread down the line. 204 00:10:22,690 --> 00:10:24,640 And here's the second stage, where 205 00:10:24,640 --> 00:10:28,050 there are some contractile cells now 206 00:10:28,050 --> 00:10:31,700 that are no longer directly responsive to the environment. 207 00:10:31,700 --> 00:10:33,182 We call these the protomyocytes. 208 00:10:33,182 --> 00:10:35,710 They separate from the epithelium. 209 00:10:35,710 --> 00:10:37,070 They're below the epithelium. 210 00:10:37,070 --> 00:10:42,190 But you can see they're still joined 211 00:10:42,190 --> 00:10:45,910 to these epithelial cells by these gap 212 00:10:45,910 --> 00:10:52,535 junction-type contacts that allow 213 00:10:52,535 --> 00:10:54,620 the electrical changes in one cell 214 00:10:54,620 --> 00:10:57,967 to influence the cell that it's next to. 215 00:11:01,450 --> 00:11:03,840 It's not like external conduction. 216 00:11:03,840 --> 00:11:07,475 The effect doesn't always spread to the entire organism. 217 00:11:07,475 --> 00:11:13,880 It often diminishes the further you get from the source. 218 00:11:13,880 --> 00:11:19,680 And here, the contractile cells are no longer 219 00:11:19,680 --> 00:11:21,750 directly connected. 220 00:11:21,750 --> 00:11:25,730 To most of these cells, there are 221 00:11:25,730 --> 00:11:30,410 neurons in epithelium that are like neurons in that they have 222 00:11:30,410 --> 00:11:35,000 an axon process, an axon-like process that extends down 223 00:11:35,000 --> 00:11:36,685 to the muscle cells. 224 00:11:36,685 --> 00:11:41,050 The connections are still all electrical in nature. 225 00:11:41,050 --> 00:11:43,870 There's no chemical secretion yet triggering 226 00:11:43,870 --> 00:11:47,801 a response in the next cell. 227 00:11:47,801 --> 00:11:48,925 He calls them protoneurons. 228 00:11:52,260 --> 00:11:56,560 They are epithelial cells. 229 00:11:56,560 --> 00:11:59,770 We have some primary sensory neurons 230 00:11:59,770 --> 00:12:00,980 that are just like this. 231 00:12:00,980 --> 00:12:03,810 We can talk about that in a minute. 232 00:12:03,810 --> 00:12:06,290 And there is an electrical contact 233 00:12:06,290 --> 00:12:11,390 with the contractile cell, which are now 234 00:12:11,390 --> 00:12:13,710 completely sub-epithelial. 235 00:12:13,710 --> 00:12:16,280 Their only contact with the epithelium 236 00:12:16,280 --> 00:12:20,970 is through these axon-like processes. 237 00:12:20,970 --> 00:12:23,910 And then he has real neurons appearing, 238 00:12:23,910 --> 00:12:30,000 motor neurons with a chemical synapse. 239 00:12:30,000 --> 00:12:33,530 When he looked at hydra, he found things 240 00:12:33,530 --> 00:12:36,910 like evidence for chemical synapses 241 00:12:36,910 --> 00:12:38,690 contacting the contractile cells. 242 00:12:38,690 --> 00:12:45,140 And it was those cells then that got input from the epithelium. 243 00:12:45,140 --> 00:12:49,570 Now you can call it a primary sensory neuron. 244 00:12:49,570 --> 00:12:56,330 So now you've got a two-synapse nervous system. 245 00:12:56,330 --> 00:12:58,140 What was missing? 246 00:12:58,140 --> 00:13:02,040 Nauta studied the earlier-- 247 00:13:02,040 --> 00:13:03,550 He knew Mackie's work. 248 00:13:03,550 --> 00:13:05,525 He knew the George Parker work. 249 00:13:05,525 --> 00:13:08,500 He cites mainly Parker. 250 00:13:08,500 --> 00:13:10,710 But he realized there's something missing. 251 00:13:10,710 --> 00:13:13,170 There's no intermediate network. 252 00:13:13,170 --> 00:13:15,890 And so that's what I've added. 253 00:13:15,890 --> 00:13:17,400 I added the question here. 254 00:13:17,400 --> 00:13:19,280 The addition emphasized by Nauta-- 255 00:13:19,280 --> 00:13:19,820 I'm sorry. 256 00:13:19,820 --> 00:13:21,240 I answered it for you. 257 00:13:21,240 --> 00:13:24,520 This is the picture then that Nauta added. 258 00:13:24,520 --> 00:13:29,980 So in Nauta's book, he has those earlier stages. 259 00:13:29,980 --> 00:13:38,120 And then he has cells in between sensory neuron. 260 00:13:38,120 --> 00:13:41,710 He has the axon now not directly contacting 261 00:13:41,710 --> 00:13:44,580 either a muscle cell or a motor neuron, 262 00:13:44,580 --> 00:13:48,960 but contacting a neuron in between. 263 00:13:48,960 --> 00:13:52,120 So this is a neuron now that's not 264 00:13:52,120 --> 00:13:54,860 in direct contact with the environment outside. 265 00:13:54,860 --> 00:13:57,520 And it's not contacting improper cells. 266 00:13:57,520 --> 00:14:02,220 It is really an intermediate neuron. 267 00:14:02,220 --> 00:14:04,165 So we would define this is a motor 268 00:14:04,165 --> 00:14:06,585 neuron, of course the muscle cell. 269 00:14:06,585 --> 00:14:09,540 This we could call primary sensory. 270 00:14:09,540 --> 00:14:11,720 But then these are the intermediate. 271 00:14:11,720 --> 00:14:13,490 And that's the beginning of what Nauta 272 00:14:13,490 --> 00:14:16,530 refers to as the great intermediate network. 273 00:14:20,800 --> 00:14:27,340 So now, let's define for every nervous system, 274 00:14:27,340 --> 00:14:30,520 including mammalian, primary sensory neuron, 275 00:14:30,520 --> 00:14:34,040 secondary sensory neuron, motor neuron, 276 00:14:34,040 --> 00:14:38,320 and intermediate network neuron. 277 00:14:38,320 --> 00:14:40,700 Just summarize. 278 00:14:40,700 --> 00:14:43,400 I've done it in a diagram. 279 00:14:43,400 --> 00:14:46,850 But can you define them now? 280 00:14:46,850 --> 00:14:49,450 Remember, I want you to read before you come to class. 281 00:14:49,450 --> 00:14:52,870 You should already be able to do this. 282 00:14:52,870 --> 00:14:55,590 There's one person, three, two people 283 00:14:55,590 --> 00:14:59,600 that have not said anything yet. 284 00:14:59,600 --> 00:15:01,631 So speak up. 285 00:15:01,631 --> 00:15:03,084 Define just one of these. 286 00:15:03,084 --> 00:15:04,000 What's a motor neuron? 287 00:15:07,890 --> 00:15:09,139 Define any of them. 288 00:15:09,139 --> 00:15:09,680 AUDIENCE: OK. 289 00:15:09,680 --> 00:15:11,946 So primary sensory neuron is the neuron 290 00:15:11,946 --> 00:15:18,792 that is in the epithelium. 291 00:15:18,792 --> 00:15:24,500 And if the first [INAUDIBLE]. 292 00:15:27,307 --> 00:15:27,890 PROFESSOR: OK. 293 00:15:27,890 --> 00:15:30,100 The primary sensory neuron. 294 00:15:30,100 --> 00:15:32,260 And what is it contracting? 295 00:15:32,260 --> 00:15:35,706 Where does its axon go? 296 00:15:35,706 --> 00:15:37,812 AUDIENCE: To a secondary neuron. 297 00:15:37,812 --> 00:15:39,520 PROFESSOR: To a secondary sensory neuron. 298 00:15:39,520 --> 00:15:40,510 And where is that one? 299 00:15:43,060 --> 00:15:44,240 Is it also in the periphery? 300 00:15:47,480 --> 00:15:48,275 No. 301 00:15:48,275 --> 00:15:52,280 The secondary sensory neuron is in the CNS. 302 00:15:52,280 --> 00:15:55,770 The primary sensory neuron is not. 303 00:15:55,770 --> 00:15:59,170 Major difference between those two types. 304 00:15:59,170 --> 00:16:01,891 Otherwise, what you said is completely right. 305 00:16:01,891 --> 00:16:02,390 OK. 306 00:16:02,390 --> 00:16:05,580 Now, what about the motor neuron? 307 00:16:05,580 --> 00:16:09,300 I've defined it maybe three times so far in the class. 308 00:16:09,300 --> 00:16:13,455 In the corner, what is the motor neuron? 309 00:16:13,455 --> 00:16:15,880 AUDIENCE: I'm actually not sure. 310 00:16:15,880 --> 00:16:20,249 I'm coming in to audit the class, 311 00:16:20,249 --> 00:16:22,330 and don't actually know much about it at all. 312 00:16:22,330 --> 00:16:23,230 PROFESSOR: OK. 313 00:16:23,230 --> 00:16:23,790 OK. 314 00:16:23,790 --> 00:16:26,080 Well, if you don't want to answer it, somebody else. 315 00:16:26,080 --> 00:16:27,600 But if you come to the class, I do 316 00:16:27,600 --> 00:16:29,670 expect you to be able to answer some questions. 317 00:16:29,670 --> 00:16:30,720 OK? 318 00:16:30,720 --> 00:16:33,440 So somebody else. 319 00:16:33,440 --> 00:16:35,709 You want to go on? 320 00:16:35,709 --> 00:16:36,625 AUDIENCE: [INAUDIBLE]. 321 00:16:40,350 --> 00:16:43,100 PROFESSOR: So define it again, the motor neuron. 322 00:16:43,100 --> 00:16:46,859 Where is the cell body of the motor neuron? 323 00:16:46,859 --> 00:16:49,180 AUDIENCE: It is in the central nervous system. 324 00:16:49,180 --> 00:16:52,170 PROFESSOR: In the central nervous system, and the axon 325 00:16:52,170 --> 00:16:54,550 goes out and contacts the muscles. 326 00:16:54,550 --> 00:16:55,370 Exactly. 327 00:16:55,370 --> 00:16:58,430 So that's how I came up with this diagram. 328 00:16:58,430 --> 00:17:00,960 There's one other cell type in here though. 329 00:17:00,960 --> 00:17:02,930 It's not primary sensory neuron. 330 00:17:02,930 --> 00:17:04,500 It's not secondary sensory neuron. 331 00:17:04,500 --> 00:17:06,050 It's not a motor neuron. 332 00:17:06,050 --> 00:17:08,810 Actually, there's two others. 333 00:17:08,810 --> 00:17:11,245 There's cells like this. 334 00:17:15,530 --> 00:17:17,130 And even the second sensory neuron 335 00:17:17,130 --> 00:17:21,180 is sometimes included in that intermediate network. 336 00:17:21,180 --> 00:17:22,829 OK? 337 00:17:22,829 --> 00:17:26,220 But since we defined secondary sensory already, 338 00:17:26,220 --> 00:17:30,590 we'll include all the rest that are not motor neurons 339 00:17:30,590 --> 00:17:32,385 as intermediate network neurons. 340 00:17:35,360 --> 00:17:36,650 And I should point out-- 341 00:17:36,650 --> 00:17:38,640 This is a good way to do it right now. 342 00:17:38,640 --> 00:17:40,500 --that many neuroanatomists, when 343 00:17:40,500 --> 00:17:43,250 they talk about an interneuron, they always 344 00:17:43,250 --> 00:17:45,820 mean a short axon interneuron, like these. 345 00:17:45,820 --> 00:17:48,240 Of course, I've greatly simplifies. 346 00:17:48,240 --> 00:17:52,750 I'm not showing the dendrites, simplifying the axon. 347 00:17:52,750 --> 00:17:54,660 But still, basically, that's the way 348 00:17:54,660 --> 00:17:57,540 a short axon interneuron connects. 349 00:18:00,370 --> 00:18:03,976 But broadly speaking, these are all interneurons 350 00:18:03,976 --> 00:18:08,070 if they're not primary sensory and they're not motor. 351 00:18:08,070 --> 00:18:10,370 Everything else is an interneuron. 352 00:18:10,370 --> 00:18:15,180 We define secondary sensory separately. 353 00:18:15,180 --> 00:18:19,150 Most neuroanatomists would talk about the long axon 354 00:18:19,150 --> 00:18:21,710 cells in the central nervous system. 355 00:18:21,710 --> 00:18:24,020 They usually don't bother to call them interneurons, 356 00:18:24,020 --> 00:18:25,720 but they actually are. 357 00:18:25,720 --> 00:18:27,331 They just have much stronger axons. 358 00:18:27,331 --> 00:18:27,830 OK. 359 00:18:27,830 --> 00:18:31,670 Now, we've got another cell type here. 360 00:18:31,670 --> 00:18:35,210 It's not in the central nervous system. 361 00:18:35,210 --> 00:18:38,110 It's in contact with a motor neuron, 362 00:18:38,110 --> 00:18:41,270 at least it's a neuron that looks like a motor neuron 363 00:18:41,270 --> 00:18:45,940 because its axon is leaving the central nervous system. 364 00:18:45,940 --> 00:18:48,800 What is it? 365 00:18:48,800 --> 00:18:51,300 It's in a peripheral ganglion. 366 00:18:54,930 --> 00:19:00,850 It's a preganglionic motor neuron here 367 00:19:00,850 --> 00:19:03,860 and a ganglionic motor neuron here. 368 00:19:03,860 --> 00:19:07,980 And the ganglionic motor neurons contact the smooth muscle, 369 00:19:07,980 --> 00:19:11,690 or gland cells, causing glandular secretions, 370 00:19:11,690 --> 00:19:17,444 causing contraction of the gut or some other organ. 371 00:19:17,444 --> 00:19:20,137 AUDIENCE: So are they considered interneurons? 372 00:19:20,137 --> 00:19:20,720 PROFESSOR: No. 373 00:19:20,720 --> 00:19:22,700 They are not. 374 00:19:22,700 --> 00:19:25,720 We call these environments here-- 375 00:19:25,720 --> 00:19:27,926 Of course, it's a type of interneuron. 376 00:19:27,926 --> 00:19:32,050 But it's defined as a motor neuron in contact 377 00:19:32,050 --> 00:19:36,220 with the central nervous system through a preganglionic motor 378 00:19:36,220 --> 00:19:37,345 neuron. 379 00:19:37,345 --> 00:19:40,090 We call this a motor because it's 380 00:19:40,090 --> 00:19:45,010 got an axon that causes some kind of movement or contraction 381 00:19:45,010 --> 00:19:47,510 or secretion. 382 00:19:47,510 --> 00:19:51,310 Secretion is considered an output. 383 00:19:51,310 --> 00:19:53,090 So it's an output neuron. 384 00:19:53,090 --> 00:19:58,610 But it exerts its action through a peripheral ganglion. 385 00:19:58,610 --> 00:20:02,990 So it's synthetic ganglion or a parasynthetic ganglion, 386 00:20:02,990 --> 00:20:05,410 which we will be defining in more detail soon. 387 00:20:13,690 --> 00:20:18,850 So just remember for me now the answer to question five. 388 00:20:18,850 --> 00:20:20,695 Where are neuronal cell bodies of 389 00:20:20,695 --> 00:20:23,242 the peripheral nervous system located? 390 00:20:23,242 --> 00:20:27,660 If you have cell bodies, and they're in the periphery, 391 00:20:27,660 --> 00:20:31,115 we say they are in a ganglion. 392 00:20:33,810 --> 00:20:35,730 OK? 393 00:20:35,730 --> 00:20:38,420 What about these words? 394 00:20:38,420 --> 00:20:39,640 What is a nerve? 395 00:20:39,640 --> 00:20:40,980 And what is a tract? 396 00:20:40,980 --> 00:20:43,150 And there are some other names we could add to that. 397 00:20:46,480 --> 00:20:50,340 But just take those two, nerve and tract. 398 00:20:50,340 --> 00:20:54,540 Define nerve for me. 399 00:20:54,540 --> 00:20:57,222 Anybody want to try? 400 00:20:57,222 --> 00:21:00,413 AUDIENCE: A group of axons that have 401 00:21:00,413 --> 00:21:04,590 a common origin and [INAUDIBLE]. 402 00:21:04,590 --> 00:21:10,960 PROFESSOR: That's very good, except it's not always true. 403 00:21:10,960 --> 00:21:14,750 Many nerves don't have a common origin. 404 00:21:14,750 --> 00:21:15,560 They can be mixed. 405 00:21:15,560 --> 00:21:18,030 They can come from various sources. 406 00:21:18,030 --> 00:21:21,780 In fact, they might not even end up at the same place. 407 00:21:21,780 --> 00:21:24,750 That's not what defines them. 408 00:21:24,750 --> 00:21:28,270 First of all, where is a nerve? 409 00:21:28,270 --> 00:21:31,430 In the periphery. 410 00:21:31,430 --> 00:21:34,490 If you hear people talking about nerves 411 00:21:34,490 --> 00:21:36,870 in the brain or the spinal cord, you'll 412 00:21:36,870 --> 00:21:38,710 know that they're not neuroanatomists, 413 00:21:38,710 --> 00:21:40,410 and they've never had this class. 414 00:21:40,410 --> 00:21:41,197 OK? 415 00:21:41,197 --> 00:21:44,360 Because we don't call them nerves 416 00:21:44,360 --> 00:21:46,820 unless they're in the periphery. 417 00:21:46,820 --> 00:21:48,900 OK? 418 00:21:48,900 --> 00:21:55,810 In the central nervous system, we call them a tract 419 00:21:55,810 --> 00:21:58,280 or we give them some other name. 420 00:21:58,280 --> 00:22:04,220 We call them a bundle, a tract, a fasciculus, a lemniscus. 421 00:22:04,220 --> 00:22:08,460 All very descriptive terms of what these are like. 422 00:22:08,460 --> 00:22:11,670 Bundle, that's clear. 423 00:22:11,670 --> 00:22:12,170 OK. 424 00:22:15,200 --> 00:22:17,245 Lemniscus means ribbon. 425 00:22:17,245 --> 00:22:20,440 So they're a ribbon of fibers. 426 00:22:20,440 --> 00:22:23,120 Fasciculus is basically a term meaning 427 00:22:23,120 --> 00:22:24,780 a group or bundle of axons. 428 00:22:29,550 --> 00:22:32,420 So they all mean bundles of axons. 429 00:22:32,420 --> 00:22:35,360 But you've got to keep separate the terms 430 00:22:35,360 --> 00:22:37,534 we use for central nervous system 431 00:22:37,534 --> 00:22:38,926 and peripheral nervous system. 432 00:22:38,926 --> 00:22:42,070 So on this slide, I just put a bunch of these things. 433 00:22:42,070 --> 00:22:45,790 They're all defined in chapter three. 434 00:22:45,790 --> 00:22:49,280 There's a few things we haven't mentioned, like different cell 435 00:22:49,280 --> 00:22:49,780 groups. 436 00:22:49,780 --> 00:22:53,320 We call them ganglia outside the central nervous system. 437 00:22:53,320 --> 00:22:56,020 But in the central nervous system, 438 00:22:56,020 --> 00:22:58,380 yes, we violate our rules sometimes 439 00:22:58,380 --> 00:23:01,560 when we talk about the basal ganglia. 440 00:23:01,560 --> 00:23:04,490 That has to do with the history of the field. 441 00:23:04,490 --> 00:23:06,760 But usually, in the central nervous system, 442 00:23:06,760 --> 00:23:12,210 groups of cells that are functionality distinct 443 00:23:12,210 --> 00:23:16,710 or anatomically distinct, or usually both, 444 00:23:16,710 --> 00:23:20,180 we call them nuclei just to confuse you more because it 445 00:23:20,180 --> 00:23:23,170 doesn't-- in the nucleus of the cell at all. 446 00:23:23,170 --> 00:23:24,645 It's a grouping of cells. 447 00:23:28,770 --> 00:23:32,077 And we give them various specific names. 448 00:23:32,077 --> 00:23:34,880 OK. 449 00:23:34,880 --> 00:23:39,810 We'll get to know the cord and neural tube very soon. 450 00:23:39,810 --> 00:23:43,840 What's the animal that is called in my book the simplest living 451 00:23:43,840 --> 00:23:44,340 chordate? 452 00:23:46,940 --> 00:23:49,570 There are others in the group, the cephalochordates. 453 00:23:54,280 --> 00:23:56,180 They have a similar structure, but there's 454 00:23:56,180 --> 00:23:57,670 this particular one-- 455 00:23:57,670 --> 00:24:00,152 [LAUGHTER] 456 00:24:00,152 --> 00:24:00,860 PROFESSOR: Sorry. 457 00:24:00,860 --> 00:24:01,476 What did I do? 458 00:24:01,476 --> 00:24:02,392 AUDIENCE: [INAUDIBLE]. 459 00:24:05,800 --> 00:24:06,724 PROFESSOR: Yeah. 460 00:24:06,724 --> 00:24:08,580 AUDIENCE: [INAUDIBLE]. 461 00:24:08,580 --> 00:24:12,510 PROFESSOR: What's the animal that's pointed at both in this? 462 00:24:12,510 --> 00:24:13,884 Amphioxus. 463 00:24:13,884 --> 00:24:14,800 AUDIENCE: There we go. 464 00:24:14,800 --> 00:24:16,650 PROFESSOR: OK. 465 00:24:16,650 --> 00:24:20,860 And that little amphioxus can be found even 466 00:24:20,860 --> 00:24:25,200 in waters around here. 467 00:24:25,200 --> 00:24:25,915 It's very common. 468 00:24:29,480 --> 00:24:33,950 I may have said in the book that it was mostly southern waters, 469 00:24:33,950 --> 00:24:37,944 but we do now find them fairly far North as well. 470 00:24:40,790 --> 00:24:48,320 It has another name that's more common among systematic people 471 00:24:48,320 --> 00:24:49,805 who do systems in biology. 472 00:24:53,130 --> 00:24:54,680 Well, chordate is the phylum. 473 00:24:54,680 --> 00:24:56,720 They are called the simplest living chordate. 474 00:24:56,720 --> 00:24:59,490 The branchiostoma is the other name. 475 00:24:59,490 --> 00:25:02,340 So when you look things up on amphioxus, 476 00:25:02,340 --> 00:25:04,423 you want to try searching both. 477 00:25:04,423 --> 00:25:08,050 But because amphioxus is so popular 478 00:25:08,050 --> 00:25:12,345 because it's so descriptive, meaning sharp at both ends. 479 00:25:12,345 --> 00:25:16,720 But still both are used, so I use both. 480 00:25:16,720 --> 00:25:20,500 You can see it is sort of sharp at both ends. 481 00:25:20,500 --> 00:25:24,140 This is a picture of its nervous system. 482 00:25:24,140 --> 00:25:29,390 Notice it's not much bigger than it is anywhere. 483 00:25:29,390 --> 00:25:29,890 OK? 484 00:25:35,170 --> 00:25:38,690 It is a chordate. 485 00:25:38,690 --> 00:25:40,950 So what is a chordate? 486 00:25:40,950 --> 00:25:44,170 What defines a chordate? 487 00:25:44,170 --> 00:25:44,960 We are a chordate. 488 00:25:50,580 --> 00:25:53,780 I basically simplified a reconstruction 489 00:25:53,780 --> 00:25:55,528 done of amphioxus. 490 00:25:59,150 --> 00:26:05,620 It has, along the back, a nerve cord. 491 00:26:05,620 --> 00:26:08,900 That is its central nervous system. 492 00:26:08,900 --> 00:26:12,540 You can see it runs almost the entire length. 493 00:26:12,540 --> 00:26:15,200 I've indicated, just to emphasize there, 494 00:26:15,200 --> 00:26:18,590 a very slight something different way at the front end. 495 00:26:18,590 --> 00:26:22,600 Yes, it does have a brain. 496 00:26:22,600 --> 00:26:26,600 It's a little hard to make out if you don't study it 497 00:26:26,600 --> 00:26:28,610 with the microscope. 498 00:26:28,610 --> 00:26:31,750 But what is that? 499 00:26:31,750 --> 00:26:35,840 It has no skeleton except that. 500 00:26:35,840 --> 00:26:38,600 It's another cord. 501 00:26:38,600 --> 00:26:40,920 It's not a nerve cord. 502 00:26:40,920 --> 00:26:42,310 OK? 503 00:26:42,310 --> 00:26:45,390 It's cartilage. 504 00:26:45,390 --> 00:26:47,740 It's called the notochord. 505 00:26:47,740 --> 00:26:53,260 And all chordates, at some stage in their development, 506 00:26:53,260 --> 00:26:55,280 usually at least early in development, 507 00:26:55,280 --> 00:27:01,600 have a notochord along the dorsal side. 508 00:27:01,600 --> 00:27:02,670 OK? 509 00:27:02,670 --> 00:27:05,060 That's the notochord. 510 00:27:05,060 --> 00:27:09,070 And the dorsal nerve cord, or the central nervous system, 511 00:27:09,070 --> 00:27:17,250 develops in all chordates just above or just dorsal 512 00:27:17,250 --> 00:27:21,290 to that notochord. 513 00:27:21,290 --> 00:27:23,480 Notice it's got an odd spelling. 514 00:27:23,480 --> 00:27:26,805 It's like music, notochord. 515 00:27:26,805 --> 00:27:28,700 But that is the way it's spelled. 516 00:27:28,700 --> 00:27:29,200 OK. 517 00:27:33,980 --> 00:27:37,190 So what does that central nervous system, that nerve 518 00:27:37,190 --> 00:27:39,220 cord, look like? 519 00:27:39,220 --> 00:27:45,010 This is another picture I simplified from a recent study. 520 00:27:45,010 --> 00:27:52,810 And I've shown in blue there the central nervous system. 521 00:27:52,810 --> 00:27:58,240 It's basically a tube with somewhat thickened walls. 522 00:27:58,240 --> 00:28:02,405 That's the neural tube with a ventricle in the middle, 523 00:28:02,405 --> 00:28:04,990 that you can't really see there very well. 524 00:28:04,990 --> 00:28:10,520 But you do see purple nerves that 525 00:28:10,520 --> 00:28:17,050 are extending into that nerve cord. 526 00:28:17,050 --> 00:28:22,720 You also see outputs mostly on the ventral side here. 527 00:28:22,720 --> 00:28:30,250 And note that they're, unlike all the vertebrates, 528 00:28:30,250 --> 00:28:32,730 and we didn't notice in the early studies. 529 00:28:32,730 --> 00:28:34,240 Nah, they didn't know it actually 530 00:28:34,240 --> 00:28:37,150 because the electron microscopic reconstructions 531 00:28:37,150 --> 00:28:39,420 hadn't been done. 532 00:28:39,420 --> 00:28:41,290 These are muscle cells. 533 00:28:41,290 --> 00:28:43,820 These are groups of muscles. 534 00:28:43,820 --> 00:28:45,825 And these are muscle processes that 535 00:28:45,825 --> 00:28:48,750 extend right up to the nerve cord. 536 00:28:48,750 --> 00:28:50,910 And they poke right into the nerve cord. 537 00:28:50,910 --> 00:28:53,645 And they directly contact the motor neurons 538 00:28:53,645 --> 00:28:58,390 in the ventral part of that nerve cord. 539 00:28:58,390 --> 00:29:00,200 That's a peculiarity of amphioxus. 540 00:29:04,350 --> 00:29:04,930 OK. 541 00:29:04,930 --> 00:29:08,970 What's the Bell-Magendie Law? 542 00:29:08,970 --> 00:29:10,600 There's something in what I was just 543 00:29:10,600 --> 00:29:14,180 saying was almost getting to that. 544 00:29:14,180 --> 00:29:18,610 The Bell-Magendie Law, what is it? 545 00:29:18,610 --> 00:29:23,200 What do we usually call it more popularly and less 546 00:29:23,200 --> 00:29:25,190 historically? 547 00:29:25,190 --> 00:29:31,540 Discovered by Charles Bell and Francois Magendie. 548 00:29:31,540 --> 00:29:34,390 Bell, 1811. 549 00:29:34,390 --> 00:29:41,410 Magendie, 1823. 550 00:29:41,410 --> 00:29:45,530 It was a discovery about mammals, 551 00:29:45,530 --> 00:29:50,490 about the nerves that come in and attach 552 00:29:50,490 --> 00:29:54,660 to the central nervous system, the spinal cord. 553 00:29:54,660 --> 00:29:59,335 They always divide into a dorsal root and a ventral root 554 00:29:59,335 --> 00:30:02,270 as they approach the cord. 555 00:30:02,270 --> 00:30:06,420 The dorsal root contains actually the dorsal 556 00:30:06,420 --> 00:30:08,313 root ganglion cells. 557 00:30:08,313 --> 00:30:12,640 So we'll see pictures of that in a minute. 558 00:30:12,640 --> 00:30:16,642 Sensory fibers, the inputs coming into dorsally. 559 00:30:16,642 --> 00:30:20,544 The outputs, those axons are the motor neurons. 560 00:30:20,544 --> 00:30:22,460 Remember in the picture of Cajal I showed you. 561 00:30:22,460 --> 00:30:25,002 The axons were growing out ventrally. 562 00:30:25,002 --> 00:30:26,325 OK? 563 00:30:26,325 --> 00:30:27,920 That's the ventral root. 564 00:30:27,920 --> 00:30:28,575 It's motor. 565 00:30:31,410 --> 00:30:32,720 But then I ask you here. 566 00:30:32,720 --> 00:30:35,880 So that's the law of roots, the Bell-Magendie Law. 567 00:30:35,880 --> 00:30:37,213 Is it always true? 568 00:30:40,600 --> 00:30:41,680 It's mostly true here. 569 00:30:41,680 --> 00:30:45,010 I mean, yeah, there are not actual axons going out. 570 00:30:45,010 --> 00:30:50,640 But the motor outputs are going out ventrally. 571 00:30:50,640 --> 00:30:52,640 The sensory inputs are coming in dorsally. 572 00:30:56,200 --> 00:30:58,230 But one thing really odd about amphioxus 573 00:30:58,230 --> 00:31:03,590 is one level of the nervous system, the nerves come 574 00:31:03,590 --> 00:31:07,710 in on one side, and they go out the other side. 575 00:31:07,710 --> 00:31:10,275 You go to the next nerve. 576 00:31:10,275 --> 00:31:12,140 It does have multiple nerves. 577 00:31:12,140 --> 00:31:14,260 You see here are all the different roots. 578 00:31:19,130 --> 00:31:22,890 The next segment down, you would find 579 00:31:22,890 --> 00:31:26,770 the input, the nerve from the periphery coming in dorsally, 580 00:31:26,770 --> 00:31:31,490 and the muscles being driven from the ventral part 581 00:31:31,490 --> 00:31:33,000 of the cord. 582 00:31:33,000 --> 00:31:35,420 So it alternates. 583 00:31:35,420 --> 00:31:41,740 Not only that, there are a few motor axons 584 00:31:41,740 --> 00:31:44,860 in that dorsal root. 585 00:31:44,860 --> 00:31:45,950 There are violations. 586 00:31:45,950 --> 00:31:49,790 And if you study other creatures in great detail, 587 00:31:49,790 --> 00:31:52,760 you will find even in higher vertebrates, 588 00:31:52,760 --> 00:31:55,790 you will find a few exceptions to the law of roots. 589 00:31:55,790 --> 00:31:58,830 But for the most part-- 590 00:31:58,830 --> 00:32:04,100 And you know, in neuroanatomy, it's not quite like physics, 591 00:32:04,100 --> 00:32:06,750 in case you're from physics or engineering. 592 00:32:06,750 --> 00:32:10,030 There are a lot of exceptions. 593 00:32:10,030 --> 00:32:13,020 And that's a lot of the times what we're describing 594 00:32:13,020 --> 00:32:18,560 is by and large true. 595 00:32:18,560 --> 00:32:21,840 So think of the Bell-Magendie Law that way. 596 00:32:21,840 --> 00:32:24,650 It's usually true. 597 00:32:24,650 --> 00:32:27,140 What is it in primary brain vesicles? 598 00:32:29,980 --> 00:32:33,242 I indicated something odd here about the very front end. 599 00:32:33,242 --> 00:32:34,595 That's his brain. 600 00:32:37,400 --> 00:32:39,240 The amphioxus does have the beginning 601 00:32:39,240 --> 00:32:41,100 of primary brain vesicles. 602 00:32:41,100 --> 00:32:43,672 What are they? 603 00:32:43,672 --> 00:32:46,550 We defined it before. 604 00:32:46,550 --> 00:32:50,330 I don't expect you necessarily to remember it. 605 00:32:50,330 --> 00:32:54,120 But now you've read about it again because in chapter three. 606 00:32:57,210 --> 00:33:01,190 What are the three primary brain vesicles? 607 00:33:01,190 --> 00:33:02,070 Now, I've added. 608 00:33:02,070 --> 00:33:03,780 I've told you there's three of them. 609 00:33:07,070 --> 00:33:09,912 Hindbrain, midbrain, and forebrain. 610 00:33:09,912 --> 00:33:11,240 OK. 611 00:33:11,240 --> 00:33:13,620 Those are the primary brain vesicles. 612 00:33:13,620 --> 00:33:17,440 They generally are vesicles, in that they swell a little bit. 613 00:33:17,440 --> 00:33:21,710 They're a little bit bigger than the spinal cord below. 614 00:33:21,710 --> 00:33:26,940 And they usually get a little smaller at their boundary. 615 00:33:26,940 --> 00:33:28,440 So you can see a-- 616 00:33:28,440 --> 00:33:31,606 In brain development of human, and just 617 00:33:31,606 --> 00:33:32,980 about every other vertebrate, you 618 00:33:32,980 --> 00:33:35,700 do see three at least early in development. 619 00:33:43,870 --> 00:33:48,965 Now, number 10 there asks for a little more detail. 620 00:33:48,965 --> 00:33:51,960 But this is another question that the answer 621 00:33:51,960 --> 00:33:56,880 would be the same for amphioxus and for mammals. 622 00:33:56,880 --> 00:34:02,710 In what subdivision of the CNS do visual inputs enter? 623 00:34:02,710 --> 00:34:07,505 Describe or name the two visual inputs found in many chordates. 624 00:34:11,679 --> 00:34:15,770 The diencephalon, yeah, tweenbrain. 625 00:34:15,770 --> 00:34:18,965 Which of the brain vesicles is diencephalon in? 626 00:34:22,530 --> 00:34:24,361 Part of the forebrain. 627 00:34:24,361 --> 00:34:24,860 OK. 628 00:34:24,860 --> 00:34:28,556 It's the caudal part of the forebrain. 629 00:34:28,556 --> 00:34:30,969 It's not part of the cerebral hemispheres. 630 00:34:30,969 --> 00:34:34,090 They balloon out from the diencephalon. 631 00:34:37,699 --> 00:34:38,969 So here's an amphioxus. 632 00:34:38,969 --> 00:34:41,739 This is from Allman. 633 00:34:41,739 --> 00:34:45,850 And he shows the arrangement of cells near there a little 634 00:34:45,850 --> 00:34:49,600 pigmented area, you see, right at the front end. 635 00:34:54,310 --> 00:34:57,540 And these are pigmented cells. 636 00:34:57,540 --> 00:35:05,750 Next to them are receptor cells responding to light. 637 00:35:05,750 --> 00:35:10,110 Next to them are neurons that have 638 00:35:10,110 --> 00:35:15,310 axons that travel to other parts of the nervous system. 639 00:35:15,310 --> 00:35:17,280 The arrangement, that arrangement, 640 00:35:17,280 --> 00:35:19,660 that very simple arrangement in amphioxus 641 00:35:19,660 --> 00:35:26,570 is very much like the developing retina in vertebrates. 642 00:35:26,570 --> 00:35:27,905 Here's the pigment epithelium. 643 00:35:31,270 --> 00:35:33,940 Here are the receptor cells. 644 00:35:33,940 --> 00:35:34,935 Here are the neurons. 645 00:35:38,536 --> 00:35:44,070 Receptor cells, they're really primary sensory neurons, 646 00:35:44,070 --> 00:35:48,940 very specialized for responding to light energy. 647 00:35:48,940 --> 00:35:51,070 And then the neurons in the retina, 648 00:35:51,070 --> 00:35:53,220 besides the interneurons, the main ones 649 00:35:53,220 --> 00:35:56,960 are the bipolar cells and the retina ganglion cells. 650 00:35:56,960 --> 00:36:02,430 And it's the ganglion cells that give rise to these long axons, 651 00:36:02,430 --> 00:36:06,140 just like these cells in amphioxus. 652 00:36:06,140 --> 00:36:07,280 OK. 653 00:36:07,280 --> 00:36:11,680 Now, these are cartoons of amphioxus on top 654 00:36:11,680 --> 00:36:16,550 and a kind of invertebrate on the bottom. 655 00:36:16,550 --> 00:36:19,760 It was based originally just on structural studies. 656 00:36:19,760 --> 00:36:23,060 But gene expression studies have shown now 657 00:36:23,060 --> 00:36:29,200 and confirmed that amphioxus has a region that 658 00:36:29,200 --> 00:36:31,855 expresses the genes of the spinal cord. 659 00:36:34,550 --> 00:36:37,930 He has a small region that expresses 660 00:36:37,930 --> 00:36:42,580 the genes of the midbrain, the segments of the midbrain, 661 00:36:42,580 --> 00:36:46,260 mainly one segment in invertebrates. 662 00:36:46,260 --> 00:36:50,170 And then, more rostrally, the rest of it 663 00:36:50,170 --> 00:36:53,690 is like between brain. 664 00:36:53,690 --> 00:37:00,940 But he doesn't have the endbrain or an olfactory bulb. 665 00:37:00,940 --> 00:37:02,060 OK? 666 00:37:02,060 --> 00:37:08,030 The olfactory bulb is part of the endbrain in vertebrates. 667 00:37:08,030 --> 00:37:10,320 And notice here there using the retina. 668 00:37:10,320 --> 00:37:14,380 It's ballooning out another kind of output gene, 669 00:37:14,380 --> 00:37:17,220 like the hemispheres, but now it remains 670 00:37:17,220 --> 00:37:18,510 part of the diencephalon. 671 00:37:18,510 --> 00:37:19,650 That's the retina. 672 00:37:22,480 --> 00:37:26,796 So there you have that visual area of the amphioxus. 673 00:37:26,796 --> 00:37:29,342 And here you have it in a vertebrate. 674 00:37:29,342 --> 00:37:31,430 And here is the other area. 675 00:37:31,430 --> 00:37:34,350 Remember, I said there were two. 676 00:37:34,350 --> 00:37:39,830 Well, at the opposite side of the tweenbrain 677 00:37:39,830 --> 00:37:42,510 you have what we call an epithalamus. 678 00:37:42,510 --> 00:37:47,981 It's the most caudal segment of the developing tweenbrain. 679 00:37:47,981 --> 00:37:48,480 OK. 680 00:37:52,060 --> 00:37:59,530 That's where many chordates have a pineal eye, an eye on top 681 00:37:59,530 --> 00:38:01,740 of their head that responds to light. 682 00:38:01,740 --> 00:38:08,566 It's involved in control of photoperiodic behavior. 683 00:38:08,566 --> 00:38:16,660 Even in us, that region controls the daily cycle 684 00:38:16,660 --> 00:38:21,530 of secretion of melatonin, even though it doesn't directly 685 00:38:21,530 --> 00:38:23,830 respond to light anymore. 686 00:38:23,830 --> 00:38:27,980 The animals we use in the lab, like the mouse, like a rat-- 687 00:38:27,980 --> 00:38:29,960 The mouse has got a pretty thin skull. 688 00:38:29,960 --> 00:38:32,690 And he's got cells there that actually do directly 689 00:38:32,690 --> 00:38:35,280 respond to light that gets through the skull. 690 00:38:35,280 --> 00:38:40,309 But the main inputs come through the lateral eyes, these eyes, 691 00:38:40,309 --> 00:38:41,475 through an indirect pathway. 692 00:38:44,095 --> 00:38:44,595 OK. 693 00:38:47,720 --> 00:38:53,250 You should be able to summarize the basic rules of evolution. 694 00:38:53,250 --> 00:38:56,120 I do it on the next slide here. 695 00:38:58,830 --> 00:39:01,575 You should know the basic processes 696 00:39:01,575 --> 00:39:03,490 that govern evolution. 697 00:39:03,490 --> 00:39:07,150 And it's all right if you assume that natural selection, just 698 00:39:07,150 --> 00:39:11,240 like Darwin believed, is the major factor that 699 00:39:11,240 --> 00:39:12,360 causes gene sorting. 700 00:39:15,200 --> 00:39:18,120 Survival of some genes and not of others, 701 00:39:18,120 --> 00:39:20,530 the decrease in the frequency of some genes, 702 00:39:20,530 --> 00:39:22,030 increase in the frequency of others. 703 00:39:24,640 --> 00:39:26,000 So I just summarized that. 704 00:39:26,000 --> 00:39:30,250 And I write it out in a pretty straightforward way 705 00:39:30,250 --> 00:39:31,140 in the book. 706 00:39:34,300 --> 00:39:37,160 In the animal behavior class, I do talk a little bit 707 00:39:37,160 --> 00:39:39,600 about other mechanisms of genetic change 708 00:39:39,600 --> 00:39:43,880 that can result in changes outside of natural selection 709 00:39:43,880 --> 00:39:47,180 that still are important in evolution. 710 00:39:47,180 --> 00:39:49,620 There's various arguments about just how important 711 00:39:49,620 --> 00:39:50,680 those things are. 712 00:39:57,800 --> 00:40:01,530 So when you think now about that very simple neural tube 713 00:40:01,530 --> 00:40:03,830 at the beginning of the central nervous system, 714 00:40:03,830 --> 00:40:10,710 you've got to say, how did that little worm-like animal, 715 00:40:10,710 --> 00:40:18,892 or animals like that, how did that end up evolving primates? 716 00:40:18,892 --> 00:40:23,215 You've got to think about the highest priority's evolution. 717 00:40:23,215 --> 00:40:25,800 And I've consistently done that through the book. 718 00:40:28,600 --> 00:40:33,590 And I've taken a nice phrase from Chandler Elliott, 719 00:40:33,590 --> 00:40:36,030 who wrote this book in '69. 720 00:40:36,030 --> 00:40:38,590 He has this phrase near the beginning of the book. 721 00:40:38,590 --> 00:40:42,180 "Every brain system grows logically from the tube." 722 00:40:42,180 --> 00:40:45,280 What he simply meant was that, by small steps, 723 00:40:45,280 --> 00:40:48,810 by processes of natural selection, 724 00:40:48,810 --> 00:40:51,770 that neural tube developed the way 725 00:40:51,770 --> 00:40:56,770 we have it into current species. 726 00:40:59,740 --> 00:41:04,740 So it's mostly speculation. 727 00:41:04,740 --> 00:41:09,070 These are the questions I was following, just looking 728 00:41:09,070 --> 00:41:14,960 across the existing animals and also using some paleontology. 729 00:41:14,960 --> 00:41:17,922 So that's what we're going to do next time. 730 00:41:17,922 --> 00:41:22,635 We're going to talk about the ancestors of mammals. 731 00:41:22,635 --> 00:41:25,610 We'll sketch a simple premammalian brain. 732 00:41:25,610 --> 00:41:28,830 Well, how could I guess what a premammalian brain is like? 733 00:41:28,830 --> 00:41:32,330 It's actually based mostly on an amphibian brain. 734 00:41:32,330 --> 00:41:32,830 OK? 735 00:41:32,830 --> 00:41:38,590 But we do have skulls of the group of animals 736 00:41:38,590 --> 00:41:41,670 that led to the evolution of mammals. 737 00:41:41,670 --> 00:41:44,730 They were running around the forest floor 738 00:41:44,730 --> 00:41:47,016 at the time of the big dinosaurs. 739 00:41:47,016 --> 00:41:50,602 They evolved with the dinosaurs. 740 00:41:50,602 --> 00:41:52,640 They were the cynodonts. 741 00:41:52,640 --> 00:41:55,415 OK? 742 00:41:55,415 --> 00:41:57,930 We'll talk about that other stuff next time. 743 00:41:57,930 --> 00:42:00,810 These are the cynodonts. 744 00:42:00,810 --> 00:42:02,850 This is just a few of them. 745 00:42:02,850 --> 00:42:06,180 Reconstructed, we don't really know their colors. 746 00:42:06,180 --> 00:42:07,540 We just have the skulls. 747 00:42:07,540 --> 00:42:09,490 But we do know a little about their brain 748 00:42:09,490 --> 00:42:13,880 because the inside of the skull preserves 749 00:42:13,880 --> 00:42:17,810 the shape of the central nervous system, 750 00:42:17,810 --> 00:42:20,110 just like we find the vertebrae, and we 751 00:42:20,110 --> 00:42:23,725 know how big the spinal cord was. 752 00:42:23,725 --> 00:42:27,300 We know in brontosaurus is lumbar 753 00:42:27,300 --> 00:42:32,900 in large was probably bigger than his brain. 754 00:42:32,900 --> 00:42:35,086 But he was a very, very large animal, 755 00:42:35,086 --> 00:42:37,325 and he needed a lot of neurons there 756 00:42:37,325 --> 00:42:42,160 to control those enormous rear legs. 757 00:42:42,160 --> 00:42:43,530 But OK. 758 00:42:43,530 --> 00:42:48,276 So we'll be talking about a brain that we'll assume-- 759 00:42:48,276 --> 00:42:50,675 If you don't like thinking in terms of evolution, 760 00:42:50,675 --> 00:42:54,250 you can think of it as an amphibian. 761 00:42:54,250 --> 00:42:59,344 But we think it's something like the early cynodonts. 762 00:42:59,344 --> 00:43:01,010 By the time you have the late cynodonts, 763 00:43:01,010 --> 00:43:03,202 they're pretty similar to mammals. 764 00:43:03,202 --> 00:43:05,130 OK? 765 00:43:05,130 --> 00:43:09,350 So that's what we'll be doing next time. 766 00:43:09,350 --> 00:43:12,317 And that's all the time we have. 767 00:43:12,317 --> 00:43:14,150 AUDIENCE: Can you just go around and tell me 768 00:43:14,150 --> 00:43:15,650 the right names for things? 769 00:43:15,650 --> 00:43:18,100 Because I just want to make sure--