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 --> 00:00:17,241 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,241 --> 00:00:17,866 at ocw.mit.edu. 8 00:00:23,350 --> 00:00:25,170 PROFESSOR: This is now class five. 9 00:00:25,170 --> 00:00:28,890 We had an introduction to it last time 10 00:00:28,890 --> 00:00:33,620 where I talked about this question, 11 00:00:33,620 --> 00:00:36,790 does ontogeny recapitulate phylogeny? 12 00:00:36,790 --> 00:00:39,010 It's been important in the history of the field. 13 00:00:39,010 --> 00:00:41,990 And we know that, very roughly speaking, 14 00:00:41,990 --> 00:00:46,450 yes there's some correspondence but it's not perfect. 15 00:00:46,450 --> 00:00:50,870 And there's probably no truly phylotypic stage 16 00:00:50,870 --> 00:00:54,390 for all the species in a given phylum. 17 00:00:54,390 --> 00:00:57,890 But nevertheless, there are a lot 18 00:00:57,890 --> 00:01:01,420 of similarities across species, especially when we 19 00:01:01,420 --> 00:01:09,220 deal with spinal cord and hindbrain, midbrain and even 20 00:01:09,220 --> 00:01:10,620 some aspects of the endbrain. 21 00:01:14,520 --> 00:01:18,150 What is the biggest type of difference that does occur? 22 00:01:21,170 --> 00:01:24,330 You've got to discriminate between the topology 23 00:01:24,330 --> 00:01:28,380 of the brain and the detailed topography of the brain. 24 00:01:28,380 --> 00:01:30,870 Relative sizes of structures vary. 25 00:01:30,870 --> 00:01:33,040 And so after we finish this class-- 26 00:01:33,040 --> 00:01:35,560 I don't know if we'll get to it all today. 27 00:01:35,560 --> 00:01:38,240 We're going to go through some of the specializations 28 00:01:38,240 --> 00:01:41,790 where you will see just like we've already 29 00:01:41,790 --> 00:01:43,990 seen for the hindbrain, certain structures 30 00:01:43,990 --> 00:01:45,870 grow a lot bigger in some animals 31 00:01:45,870 --> 00:01:50,630 than others, depending on behavioral specializations. 32 00:01:50,630 --> 00:01:52,310 OK. 33 00:01:52,310 --> 00:01:56,300 We found out what a cynodont was. 34 00:01:56,300 --> 00:01:59,900 They're the mammal-like reptiles. 35 00:01:59,900 --> 00:02:02,430 Mammals evolved from that group. 36 00:02:02,430 --> 00:02:06,140 This is an early cynodont here in the upper left. 37 00:02:06,140 --> 00:02:08,630 So just as a fantasy, we can pretend 38 00:02:08,630 --> 00:02:12,140 we're looking at the brain of an early cynodont. 39 00:02:12,140 --> 00:02:15,020 But it's really based more on amphibian brains 40 00:02:15,020 --> 00:02:19,090 and very primitive reptilian brains. 41 00:02:19,090 --> 00:02:19,590 All right. 42 00:02:19,590 --> 00:02:27,750 So the relevance to mammals is that we still 43 00:02:27,750 --> 00:02:31,820 have that brain, even in the human brain. 44 00:02:31,820 --> 00:02:35,320 It's like it's the older parts of the brain that are still 45 00:02:35,320 --> 00:02:36,430 there. 46 00:02:36,430 --> 00:02:41,220 I already said spinal cord, hindbrain, and midbrain. 47 00:02:41,220 --> 00:02:44,210 You can see the same structures across many different species. 48 00:02:47,180 --> 00:02:49,670 And in fact, even for the endbrain, 49 00:02:49,670 --> 00:02:51,230 there are great similarities. 50 00:02:51,230 --> 00:02:55,060 But think of that. 51 00:02:55,060 --> 00:02:57,440 This primitive brain, we're going to take a look at 52 00:02:57,440 --> 00:03:03,436 is representative of the core of our own brain. 53 00:03:03,436 --> 00:03:08,140 But first, let's just take the cynodont memory 54 00:03:08,140 --> 00:03:10,610 and you tell me what you remember 55 00:03:10,610 --> 00:03:14,240 from what we've learned already. 56 00:03:14,240 --> 00:03:16,105 Look at this brain. 57 00:03:16,105 --> 00:03:20,475 I've wiped out the top part because I want you to remember. 58 00:03:23,880 --> 00:03:28,130 By now, we know that the most caudal part of the CNS, 59 00:03:28,130 --> 00:03:29,500 we have the spinal cord. 60 00:03:29,500 --> 00:03:35,510 And that's just an example of a spinal nerve in the dorsal root 61 00:03:35,510 --> 00:03:39,580 carrying sensory information to the upper part, the dorsal part 62 00:03:39,580 --> 00:03:42,030 of the spinal cord. 63 00:03:42,030 --> 00:03:45,140 And obviously, we've distorted the brain here just 64 00:03:45,140 --> 00:03:46,500 to be able to show connections. 65 00:03:46,500 --> 00:03:48,900 So what do we have about the spinal cord? 66 00:03:48,900 --> 00:03:51,560 Everything between here and here. 67 00:03:51,560 --> 00:03:53,930 What is there? 68 00:03:53,930 --> 00:03:55,070 Hindbrain. 69 00:03:55,070 --> 00:03:55,960 OK. 70 00:03:55,960 --> 00:03:58,960 What do you think that this? 71 00:03:58,960 --> 00:03:59,640 Cerebellum. 72 00:03:59,640 --> 00:04:00,140 OK. 73 00:04:00,140 --> 00:04:02,900 So the rostral part of the hindbrain 74 00:04:02,900 --> 00:04:08,290 is often called the pontine region because cells 75 00:04:08,290 --> 00:04:11,500 down here-- which I don't really depict in this screen, 76 00:04:11,500 --> 00:04:14,610 but we certainly see it in mammalian brain-- 77 00:04:14,610 --> 00:04:17,250 connect to the cerebellum. 78 00:04:17,250 --> 00:04:20,579 It carries input from the cortex. 79 00:04:20,579 --> 00:04:26,140 And the lower part-- the Latin for spinal cord is medulla 80 00:04:26,140 --> 00:04:28,930 spinalis-- the core. 81 00:04:28,930 --> 00:04:34,750 The medulla, the core, the inner core of the spinal column. 82 00:04:34,750 --> 00:04:36,590 So the lower part of the hindbrain 83 00:04:36,590 --> 00:04:43,136 is just an extension of that, the medulla oblongata, 84 00:04:43,136 --> 00:04:45,570 the elongated spinal cord. 85 00:04:45,570 --> 00:04:48,380 Whereas the rostral part now is changed. 86 00:04:48,380 --> 00:04:50,580 That's where the cerebellum develops. 87 00:04:50,580 --> 00:04:53,590 What's above that? 88 00:04:53,590 --> 00:04:56,240 The midbrain or mesencephalon-- well, 89 00:04:56,240 --> 00:04:59,020 what are the bumps up there? 90 00:04:59,020 --> 00:05:03,030 We see it in all of vertebrates. 91 00:05:03,030 --> 00:05:04,270 Sorry? 92 00:05:04,270 --> 00:05:05,450 AUDIENCE: The colliculi? 93 00:05:05,450 --> 00:05:06,090 The colliculi. 94 00:05:06,090 --> 00:05:09,790 What does colliculi mean? 95 00:05:09,790 --> 00:05:11,040 It means little hills. 96 00:05:11,040 --> 00:05:13,152 So if you look down on the surface-- we do a brain 97 00:05:13,152 --> 00:05:15,110 dissection, you'll see that in the sheep brain. 98 00:05:15,110 --> 00:05:17,220 You'll see that in any mammalian brain. 99 00:05:17,220 --> 00:05:20,250 You'll see these four bumps. 100 00:05:20,250 --> 00:05:24,350 And in some animals, one of those bumps, 101 00:05:24,350 --> 00:05:28,460 a pair of those bumps is much larger than in another species. 102 00:05:28,460 --> 00:05:30,600 But the basic structures are the same. 103 00:05:30,600 --> 00:05:31,100 OK. 104 00:05:31,100 --> 00:05:35,250 And then above the midbrain, if we just 105 00:05:35,250 --> 00:05:39,915 take this whole division-- sorry? 106 00:05:39,915 --> 00:05:40,790 AUDIENCE: Tweenbrain. 107 00:05:40,790 --> 00:05:41,706 PROFESSOR: Tweenbrain. 108 00:05:41,706 --> 00:05:43,460 or diencephalon. 109 00:05:43,460 --> 00:05:46,876 And the largest part up here? 110 00:05:46,876 --> 00:05:47,376 Thalamus. 111 00:05:49,960 --> 00:05:53,655 This is really crucial to our functioning. 112 00:05:56,015 --> 00:05:57,140 AUDIENCE: The hypothalamus. 113 00:05:57,140 --> 00:05:58,640 PROFESSOR: Hypothalamus. 114 00:05:58,640 --> 00:06:00,100 Below the thalamus. 115 00:06:00,100 --> 00:06:02,460 OK. 116 00:06:02,460 --> 00:06:12,400 And now above that, above the tweenbrain, 117 00:06:12,400 --> 00:06:15,310 we know that's all what? 118 00:06:15,310 --> 00:06:16,720 AUDIENCE: [INAUDIBLE]. 119 00:06:16,720 --> 00:06:18,620 PROFESSOR: Forebrain. 120 00:06:18,620 --> 00:06:19,770 OK. 121 00:06:19,770 --> 00:06:22,720 The most rostral of the brain vesicles. 122 00:06:22,720 --> 00:06:24,330 But I've got to divided up here. 123 00:06:27,300 --> 00:06:33,940 This is the biggest subcortical components. 124 00:06:33,940 --> 00:06:36,320 This is mostly pallium up here. 125 00:06:39,390 --> 00:06:43,720 And in this schematic here from Streeter, 126 00:06:43,720 --> 00:06:47,520 he names a few more of these things. 127 00:06:47,520 --> 00:06:50,480 And he explains that the pallium, the word 128 00:06:50,480 --> 00:06:51,990 means a cloak. 129 00:06:51,990 --> 00:06:55,970 What's a similar word that we use for pallium? 130 00:06:55,970 --> 00:06:57,180 Cortex. 131 00:06:57,180 --> 00:06:59,080 What does cortex mean? 132 00:06:59,080 --> 00:07:02,140 It means the bark, like the bark of a tree. 133 00:07:02,140 --> 00:07:02,640 OK. 134 00:07:02,640 --> 00:07:06,555 So the pallium is the older word and we use it often 135 00:07:06,555 --> 00:07:07,300 in embryology. 136 00:07:11,410 --> 00:07:13,720 So this is the older parts of the pallium. 137 00:07:13,720 --> 00:07:16,020 There's no neocortex below mammals. 138 00:07:16,020 --> 00:07:18,100 This is a pre-mammalian brain. 139 00:07:18,100 --> 00:07:20,921 But that doesn't mean there's no pallium. 140 00:07:20,921 --> 00:07:21,420 OK. 141 00:07:21,420 --> 00:07:24,090 There's our dorsal pallium, a medial pallium, 142 00:07:24,090 --> 00:07:26,790 a lateral pallium, and there's even a ventral pallium. 143 00:07:26,790 --> 00:07:28,130 But I have this down here. 144 00:07:33,380 --> 00:07:36,890 An olfactory structure, this ventral pallium. 145 00:07:36,890 --> 00:07:41,230 And then these are sub-pallial components 146 00:07:41,230 --> 00:07:44,690 that are connected with the pallium there. 147 00:07:44,690 --> 00:07:46,730 That would include structures like the amygdala 148 00:07:46,730 --> 00:07:48,480 and the mammalian brain. 149 00:07:48,480 --> 00:07:49,982 Yes? 150 00:07:49,982 --> 00:07:53,141 AUDIENCE: Can you remind me how they figured out 151 00:07:53,141 --> 00:07:55,340 which part is which? 152 00:07:55,340 --> 00:07:58,850 PROFESSOR: How do we know which part is which? 153 00:07:58,850 --> 00:08:00,700 Well, that's basically what you're learning. 154 00:08:00,700 --> 00:08:04,180 But we know it from cytoarchitecture. 155 00:08:04,180 --> 00:08:06,380 We know it from fiber architecture 156 00:08:06,380 --> 00:08:09,880 and very important for this class, 157 00:08:09,880 --> 00:08:12,020 we know it from connections. 158 00:08:12,020 --> 00:08:13,600 OK. 159 00:08:13,600 --> 00:08:17,077 We're interested in how these structures evolved 160 00:08:17,077 --> 00:08:18,660 and how they're interconnected and how 161 00:08:18,660 --> 00:08:20,120 those connections evolved. 162 00:08:20,120 --> 00:08:23,035 So that's what we'll be dealing with. 163 00:08:23,035 --> 00:08:26,846 AUDIENCE: But these are made up of more recent amphibian 164 00:08:26,846 --> 00:08:27,680 brains? 165 00:08:27,680 --> 00:08:29,640 PROFESSOR: That's right. 166 00:08:29,640 --> 00:08:32,580 But we know from the skull shapes and everything 167 00:08:32,580 --> 00:08:35,980 of these ancient animals that they were pretty similar. 168 00:08:35,980 --> 00:08:37,880 OK. 169 00:08:37,880 --> 00:08:41,490 If you read on Google online and you do searches for cynodont, 170 00:08:41,490 --> 00:08:44,130 for example, you'll see some fairly ridiculous things. 171 00:08:44,130 --> 00:08:47,245 They'll say mammals are cynodont and things like this. 172 00:08:47,245 --> 00:08:49,370 And that they suckle their young and this and that. 173 00:08:49,370 --> 00:08:51,650 We don't know that. 174 00:08:51,650 --> 00:08:52,990 OK. 175 00:08:52,990 --> 00:08:55,640 As I point out in that previous slide, 176 00:08:55,640 --> 00:08:57,220 just read what I had at the bottom. 177 00:08:57,220 --> 00:08:58,680 I summarized that. 178 00:08:58,680 --> 00:09:01,120 We only have the fossil record. 179 00:09:01,120 --> 00:09:04,350 So soft tissue isn't preserved in the fossil record. 180 00:09:04,350 --> 00:09:06,550 So the brain isn't preserved. 181 00:09:06,550 --> 00:09:10,530 Well, neither are mammary glands or any other soft tissue. 182 00:09:10,530 --> 00:09:13,080 All right. 183 00:09:13,080 --> 00:09:16,260 So this is meant to represent corpus striatum. 184 00:09:16,260 --> 00:09:17,840 This is the pallium above it. 185 00:09:17,840 --> 00:09:22,010 And of course, olfactory system. 186 00:09:22,010 --> 00:09:24,930 At least remember those three things. 187 00:09:24,930 --> 00:09:26,560 And remember that the pallium here 188 00:09:26,560 --> 00:09:29,775 is not neo-pallium or neocortex yet. 189 00:09:32,350 --> 00:09:36,440 And here was the original figure and that 190 00:09:36,440 --> 00:09:39,350 is in the book, or a more modernized version of it. 191 00:09:39,350 --> 00:09:43,600 And you can see, I've labeled there the different parts 192 00:09:43,600 --> 00:09:47,300 of the pallium you find out there. 193 00:09:47,300 --> 00:09:51,560 Even the most primitive of all the vertebrates, 194 00:09:51,560 --> 00:09:59,370 like the sea lamprey, has a pallium. 195 00:09:59,370 --> 00:10:01,850 But we can only really see a dorsal pallium 196 00:10:01,850 --> 00:10:03,146 and the ventrical pallium. 197 00:10:08,830 --> 00:10:11,530 And this is the more realistic view 198 00:10:11,530 --> 00:10:14,120 where I take an embryonic brain. 199 00:10:14,120 --> 00:10:17,030 I've shown a dorsal view, except I've taken the hemispheres 200 00:10:17,030 --> 00:10:18,260 and I pushed from apart. 201 00:10:18,260 --> 00:10:22,410 This is before there's any corpus callosum that's evolved. 202 00:10:22,410 --> 00:10:24,920 So this isn't a section. 203 00:10:24,920 --> 00:10:25,550 OK. 204 00:10:25,550 --> 00:10:29,300 It's a surface view with the hemispheres pushed apart. 205 00:10:29,300 --> 00:10:31,550 So if you want that to look more like the embryo 206 00:10:31,550 --> 00:10:40,850 would look, like in 12 or 13 embryonic day hamster or mouse, 207 00:10:40,850 --> 00:10:44,010 take these and push them together. 208 00:10:44,010 --> 00:10:50,310 The striations there represent a thin one-layer thick layer 209 00:10:50,310 --> 00:10:50,810 of cells. 210 00:10:50,810 --> 00:10:55,260 It's one cell layer thick as the roof plate. 211 00:10:55,260 --> 00:10:56,920 Remember how the roof plate there you 212 00:10:56,920 --> 00:11:01,010 see in the cross section of the hindbrain. 213 00:11:01,010 --> 00:11:03,190 The roof plate where the cerebellum actually 214 00:11:03,190 --> 00:11:05,570 forms rostrally. 215 00:11:05,570 --> 00:11:07,480 But in the early embryo I'm showing in here 216 00:11:07,480 --> 00:11:10,660 before the cerebellum is grown. 217 00:11:10,660 --> 00:11:13,340 And the cerebellum does develop relatively late. 218 00:11:16,200 --> 00:11:18,380 And this roof plate-- there's an area 219 00:11:18,380 --> 00:11:20,990 of thin roof plate in the medial side the hemisphere 220 00:11:20,990 --> 00:11:26,990 and on the dorsal part of the tweenbrain 221 00:11:26,990 --> 00:11:28,530 that you see right there. 222 00:11:34,140 --> 00:11:37,660 So now can anyone answer this for me? 223 00:11:37,660 --> 00:11:39,925 Let's talk about some of these neurons 224 00:11:39,925 --> 00:11:42,500 that we see in that diagram. 225 00:11:42,500 --> 00:11:45,710 What are three different types of primary sensory neuron 226 00:11:45,710 --> 00:11:48,060 structures? 227 00:11:48,060 --> 00:11:51,950 And then we'll talk about where we find them, even in mammals. 228 00:11:51,950 --> 00:11:54,980 What am I talking about? 229 00:11:54,980 --> 00:11:58,080 Primary sensory neurons. 230 00:11:58,080 --> 00:12:00,540 Let me start at the answer just by saying 231 00:12:00,540 --> 00:12:04,100 some primary sensory neurons are right in the epithelium, 232 00:12:04,100 --> 00:12:05,570 just like in an earth worm. 233 00:12:10,240 --> 00:12:14,900 Where do we have those in our brains, in our nervous system? 234 00:12:14,900 --> 00:12:17,605 Where is the primary sensory neuron right in the surface? 235 00:12:20,540 --> 00:12:23,570 The cell body right in the surface. 236 00:12:23,570 --> 00:12:28,090 In here, in the nasal epithelium, OK. 237 00:12:28,090 --> 00:12:31,550 Your receptor cells, olfactory receptor cells 238 00:12:31,550 --> 00:12:34,170 are the primary sensory neurons. 239 00:12:34,170 --> 00:12:37,220 And their dendrites are highly specialized to respond 240 00:12:37,220 --> 00:12:41,115 to things dissolved in the nasal mucosa. 241 00:12:41,115 --> 00:12:44,990 It responds to odorant molecules that we breath in. 242 00:12:44,990 --> 00:12:47,250 But you don't respond to those odor molecules 243 00:12:47,250 --> 00:12:48,880 directly from the air. 244 00:12:48,880 --> 00:12:54,040 They have to dissolve and stimulate receptors 245 00:12:54,040 --> 00:12:58,010 in the dendritic components of those primary sensory neurons. 246 00:12:58,010 --> 00:13:01,182 What are the other types? 247 00:13:01,182 --> 00:13:02,170 AUDIENCE: Bipolar. 248 00:13:02,170 --> 00:13:04,270 PROFESSOR: Bipolar cells. 249 00:13:04,270 --> 00:13:07,510 In some animals, that's the main type 250 00:13:07,510 --> 00:13:10,250 of neuron carrying sensory information from the body 251 00:13:10,250 --> 00:13:11,940 surface. 252 00:13:11,940 --> 00:13:13,820 OK. 253 00:13:13,820 --> 00:13:15,000 Where do we have those? 254 00:13:18,470 --> 00:13:20,950 Anybody remember? 255 00:13:20,950 --> 00:13:21,770 Sorry? 256 00:13:21,770 --> 00:13:23,210 AUDIENCE: Vision? 257 00:13:23,210 --> 00:13:24,210 PROFESSOR: Not in there. 258 00:13:24,210 --> 00:13:27,860 Well, that's a good-- that's actually a pretty good answer. 259 00:13:27,860 --> 00:13:30,410 Because they are bipolar cells. 260 00:13:30,410 --> 00:13:32,190 That's right. 261 00:13:32,190 --> 00:13:33,270 We often forget that. 262 00:13:33,270 --> 00:13:35,861 Because the retina is so highly specialized. 263 00:13:35,861 --> 00:13:36,360 OK. 264 00:13:36,360 --> 00:13:39,540 But yes, in the retinal cells, we have bipolar neurons. 265 00:13:39,540 --> 00:13:40,200 Where else? 266 00:13:44,980 --> 00:13:46,940 For primary sensory neurons, no. 267 00:13:50,788 --> 00:13:54,710 Here, in the auditory system. 268 00:13:54,710 --> 00:13:55,400 And where else? 269 00:14:00,100 --> 00:14:01,081 Vestibular. 270 00:14:01,081 --> 00:14:01,580 OK. 271 00:14:01,580 --> 00:14:04,050 Auditory and vestibular are bipolar. 272 00:14:04,050 --> 00:14:07,000 And this is the way Cajal depicts them. 273 00:14:07,000 --> 00:14:11,150 He's showing different animals here. 274 00:14:11,150 --> 00:14:13,830 Besides, it's the only one I have here. 275 00:14:13,830 --> 00:14:17,080 He's showing different animals. 276 00:14:17,080 --> 00:14:20,150 OK, but we have all these in mammals. 277 00:14:20,150 --> 00:14:24,140 In the epithelium, a bipolar cell sub-epithelium, 278 00:14:24,140 --> 00:14:27,230 and bipolar , cells where the cells are collected 279 00:14:27,230 --> 00:14:30,040 into the ganglia. 280 00:14:30,040 --> 00:14:32,470 And then the fourth type is the major type in us 281 00:14:32,470 --> 00:14:35,965 and most in mammals and birds. 282 00:14:40,590 --> 00:14:44,450 They're called pseudo unipolar. 283 00:14:44,450 --> 00:14:50,470 They're unipolar in their shape but in fact, they still 284 00:14:50,470 --> 00:14:52,955 have a peripheral process and a central process. 285 00:14:56,480 --> 00:14:59,930 As a big advantage, conduction can 286 00:14:59,930 --> 00:15:04,390 be faster because the axon is continuous here 287 00:15:04,390 --> 00:15:08,702 and this is now the metabolic support system. 288 00:15:08,702 --> 00:15:12,860 It has nothing to do with the action potential, OK. 289 00:15:12,860 --> 00:15:15,180 But it supports the cells, of course. 290 00:15:15,180 --> 00:15:18,299 You kill the ganglion cell on this axon will die. 291 00:15:24,900 --> 00:15:27,670 So there's most of the neurons carrying input 292 00:15:27,670 --> 00:15:31,690 from the skin are unipolar in mammals. 293 00:15:31,690 --> 00:15:33,090 There's a bipolar cell. 294 00:15:36,150 --> 00:15:39,760 And here's the olfactory epithelial primary sensory 295 00:15:39,760 --> 00:15:42,720 neuron, carrying input in for the CNS. 296 00:15:46,160 --> 00:15:46,660 All right. 297 00:15:49,400 --> 00:15:52,405 Now here's a different kind of question 298 00:15:52,405 --> 00:15:55,900 but still sticking to the more peripheral parts 299 00:15:55,900 --> 00:15:59,340 in the nervous system. 300 00:15:59,340 --> 00:16:02,190 What are the different types of muscle cells? 301 00:16:02,190 --> 00:16:07,590 Now in the chapter, I talk about just two major types. 302 00:16:07,590 --> 00:16:12,180 We could come up with sub-types of these two. 303 00:16:12,180 --> 00:16:13,595 But what are the two main types? 304 00:16:18,450 --> 00:16:19,760 These? 305 00:16:19,760 --> 00:16:21,896 What types of these? 306 00:16:21,896 --> 00:16:23,150 AUDIENCE: Striated? 307 00:16:23,150 --> 00:16:26,441 PROFESSOR: Striated muscle cells. 308 00:16:26,441 --> 00:16:26,940 OK. 309 00:16:31,490 --> 00:16:35,050 And there's muscles here, too. 310 00:16:35,050 --> 00:16:38,630 This is a cross section of the gut. 311 00:16:38,630 --> 00:16:40,030 OK. 312 00:16:40,030 --> 00:16:42,150 That's lined with muscle cells. 313 00:16:42,150 --> 00:16:44,010 What kind of cell is that? 314 00:16:44,010 --> 00:16:46,995 You see them in the lungs, in the diaphragm. 315 00:16:49,815 --> 00:16:51,250 AUDIENCE: [INAUDIBLE]. 316 00:16:51,250 --> 00:16:55,130 PROFESSOR: It's called smooth muscle. 317 00:16:55,130 --> 00:16:56,880 Not striated muscles. 318 00:16:56,880 --> 00:16:59,980 And the microscopic appearance is very different. 319 00:16:59,980 --> 00:17:06,060 You don't have the alignment of the cells-- 320 00:17:06,060 --> 00:17:08,069 it forms these striations that you 321 00:17:08,069 --> 00:17:10,730 have on the striated muscle. 322 00:17:10,730 --> 00:17:15,270 There is a major type of striated muscle cell that 323 00:17:15,270 --> 00:17:19,720 actually is innervated by the system that 324 00:17:19,720 --> 00:17:21,315 innervates the visceral. 325 00:17:21,315 --> 00:17:25,329 What type am I talking about? 326 00:17:25,329 --> 00:17:27,050 Heart cells, right. 327 00:17:27,050 --> 00:17:31,790 Cardiac muscle cells are striated cells. 328 00:17:31,790 --> 00:17:35,220 But their innervated differently. 329 00:17:35,220 --> 00:17:35,720 OK. 330 00:17:43,260 --> 00:17:47,760 Let's see if anybody knows-- let's do seven here 331 00:17:47,760 --> 00:17:50,110 because that's related to what we just talked about. 332 00:17:50,110 --> 00:17:52,190 What are the two main types of motor neurons 333 00:17:52,190 --> 00:17:55,400 depicted in this introductory chapter? 334 00:17:55,400 --> 00:17:57,490 And you see them here. 335 00:17:57,490 --> 00:18:01,031 Two major types of motor neurons. 336 00:18:01,031 --> 00:18:03,840 AUDIENCE: Ganglion-- 337 00:18:03,840 --> 00:18:06,960 PROFESSOR: Well, that's one way to call them. 338 00:18:06,960 --> 00:18:11,150 These are the alpha motor neurons 339 00:18:11,150 --> 00:18:15,500 with the axon of the motor neuron defined as we already 340 00:18:15,500 --> 00:18:17,160 defined it-- the axon that leaves 341 00:18:17,160 --> 00:18:19,260 the central nervous system. 342 00:18:19,260 --> 00:18:21,730 They innervate the striated muscles. 343 00:18:21,730 --> 00:18:24,360 And here's another motor neuron. 344 00:18:24,360 --> 00:18:27,430 But it doesn't contact the muscle. 345 00:18:27,430 --> 00:18:30,430 It's still called the motor neuron. 346 00:18:30,430 --> 00:18:34,130 It leaves the central nervous system, the axon 347 00:18:34,130 --> 00:18:37,660 and it contacts the ganglion cell out there. 348 00:18:37,660 --> 00:18:43,040 This is a neuron that's located in peripheral ganglia. 349 00:18:43,040 --> 00:18:47,470 And then that's the way the gut is innervated. 350 00:18:50,550 --> 00:18:52,810 The same is true of the heart. 351 00:18:52,810 --> 00:18:55,340 It's always an innervation of the ganglion 352 00:18:55,340 --> 00:18:57,700 first, the ganglion cell. 353 00:18:57,700 --> 00:19:01,160 So we call this the postganglionic axon. 354 00:19:01,160 --> 00:19:05,390 This is the preganglionic axon. 355 00:19:05,390 --> 00:19:07,070 OK. 356 00:19:07,070 --> 00:19:09,920 So those are the two major types of motor neuron. 357 00:19:09,920 --> 00:19:13,620 There is another that we don't depict. 358 00:19:13,620 --> 00:19:17,720 I don't depict in these diagrams but these 359 00:19:17,720 --> 00:19:22,380 are cells that secrete something into the blood. 360 00:19:22,380 --> 00:19:25,060 They could be called motor neurons. 361 00:19:25,060 --> 00:19:27,310 But here, we're just calling them motor neurons 362 00:19:27,310 --> 00:19:29,990 because they have something to do with movement. 363 00:19:29,990 --> 00:19:32,920 It's not secretion. 364 00:19:32,920 --> 00:19:36,990 But it is a major type of output of the central nervous system. 365 00:19:39,530 --> 00:19:40,030 OK. 366 00:19:40,030 --> 00:19:43,740 And does anybody know what secondary sensory nuclei 367 00:19:43,740 --> 00:19:47,070 receive input from axons of the eighth cranial nerve? 368 00:19:47,070 --> 00:19:49,430 They're in the diagram. 369 00:19:49,430 --> 00:19:50,950 The eighth cranial nerve. 370 00:19:53,690 --> 00:19:59,075 This is an axon of the eighth cranial nerve. 371 00:19:59,075 --> 00:20:02,510 You know when you're a neuroanatomist, if someone 372 00:20:02,510 --> 00:20:06,470 gives you just the number of a nerve, you know what it is. 373 00:20:06,470 --> 00:20:11,660 The eight nerve always means what? 374 00:20:11,660 --> 00:20:16,080 Auditory and vestibular, OK. 375 00:20:16,080 --> 00:20:21,140 So I put there a spinal nerve, the eighth cranial nerve 376 00:20:21,140 --> 00:20:22,640 and the first cranial nerve. 377 00:20:22,640 --> 00:20:24,830 That's what I show here in this diagram. 378 00:20:31,090 --> 00:20:36,760 Now in this diagram, I want you to remember 379 00:20:36,760 --> 00:20:40,265 what we said about interneurons an what I write about it. 380 00:20:40,265 --> 00:20:43,150 I want you to discuss the term interneuron. 381 00:20:43,150 --> 00:20:46,710 It has a broader meaning and a more commonly used meaning 382 00:20:46,710 --> 00:20:48,210 in discussions of neuron anatomy. 383 00:20:50,810 --> 00:20:55,690 So a simple way-- the broader definition, 384 00:20:55,690 --> 00:20:58,700 how would you define it most broadly? 385 00:20:58,700 --> 00:21:00,260 What is an interneuron here? 386 00:21:03,180 --> 00:21:04,698 Yes? 387 00:21:04,698 --> 00:21:08,690 AUDIENCE: Anything that's not primary sensory or primary 388 00:21:08,690 --> 00:21:09,690 motor. 389 00:21:09,690 --> 00:21:10,810 PROFESSOR: Exactly. 390 00:21:10,810 --> 00:21:11,310 OK. 391 00:21:11,310 --> 00:21:14,430 So it's not one of these that I show black in here 392 00:21:14,430 --> 00:21:17,340 at the bottom. 393 00:21:17,340 --> 00:21:19,270 Because its axon, those axons are 394 00:21:19,270 --> 00:21:20,890 leaving the central nervous system. 395 00:21:20,890 --> 00:21:24,250 And it's not these that also have a cell body outside. 396 00:21:28,030 --> 00:21:30,260 Normally from the term interneuron though, 397 00:21:30,260 --> 00:21:35,150 we exclude the secondary sensory neurons. 398 00:21:35,150 --> 00:21:37,070 Although they could be called interneurons 399 00:21:37,070 --> 00:21:39,070 in the very broadest sense. 400 00:21:39,070 --> 00:21:42,810 They're in between primary sensory and motor. 401 00:21:42,810 --> 00:21:46,460 But now if we also exclude the secondary sensory cell, 402 00:21:46,460 --> 00:21:48,900 it's everything else. 403 00:21:48,900 --> 00:21:50,790 But what is the more common meaning 404 00:21:50,790 --> 00:21:55,284 when you hear an anatomist talk about an interneuron? 405 00:21:55,284 --> 00:21:57,090 AUDIENCE: A smaller-- 406 00:21:57,090 --> 00:21:58,134 PROFESSOR: A short-- 407 00:21:58,134 --> 00:21:59,050 AUDIENCE: [INAUDIBLE]. 408 00:21:59,050 --> 00:22:01,800 PROFESSOR: Yes, short axon is the term we use. 409 00:22:01,800 --> 00:22:04,340 The short axon interneurons. 410 00:22:04,340 --> 00:22:07,095 Sometimes we abbreviate short axon interneuron 411 00:22:07,095 --> 00:22:09,540 and just call them interneurons. 412 00:22:09,540 --> 00:22:14,330 But actually, every cell of the great intermediate network, 413 00:22:14,330 --> 00:22:19,470 even these with the long axons here, are all interneurons. 414 00:22:22,110 --> 00:22:25,210 But sometimes, we would use the more-- 415 00:22:25,210 --> 00:22:29,460 we'll just be talking about short axon interneurons. 416 00:22:29,460 --> 00:22:34,060 The most common way for any axon in the brain to affect movement 417 00:22:34,060 --> 00:22:37,730 is through a short axon interneuron. 418 00:22:37,730 --> 00:22:40,780 That's true here in the spinal cord. 419 00:22:40,780 --> 00:22:42,600 We always think of primates and we think, 420 00:22:42,600 --> 00:22:45,300 oh, but the motor cortex controls the motor neurons 421 00:22:45,300 --> 00:22:46,320 directly. 422 00:22:46,320 --> 00:22:47,950 That's even in primates. 423 00:22:47,950 --> 00:22:50,300 It's not the most common type of connection. 424 00:22:50,300 --> 00:22:52,380 It goes through interneurons. 425 00:22:52,380 --> 00:22:57,490 We call it the interneuron pool, a pool of neurons 426 00:22:57,490 --> 00:22:59,120 that all innervates the motor neurons. 427 00:22:59,120 --> 00:23:01,460 It causes movement. 428 00:23:01,460 --> 00:23:03,980 Very important in talking about how 429 00:23:03,980 --> 00:23:07,610 the motor system is organized. 430 00:23:07,610 --> 00:23:08,410 OK. 431 00:23:08,410 --> 00:23:11,900 Now let's talk about the local reflex channel of conduction. 432 00:23:11,900 --> 00:23:15,360 You can talk about different channels 433 00:23:15,360 --> 00:23:19,020 where information coming in, like through one 434 00:23:19,020 --> 00:23:22,340 of these axons, is rooted. 435 00:23:22,340 --> 00:23:28,120 And the first one is a local reflex channel. 436 00:23:28,120 --> 00:23:30,880 So what is it in the strictest sense? 437 00:23:30,880 --> 00:23:33,050 A local reflex channel here? 438 00:23:39,520 --> 00:23:41,420 Here's the axon coming in. 439 00:23:48,890 --> 00:23:53,641 I'm just going to draw the shortest pathway to a motor 440 00:23:53,641 --> 00:23:54,140 neuron. 441 00:23:57,374 --> 00:23:59,750 So you could get movement now. 442 00:23:59,750 --> 00:24:02,170 That's a local reflex pathway. 443 00:24:05,000 --> 00:24:09,130 So when we deal with spinal cord, 444 00:24:09,130 --> 00:24:16,670 we could define it as a limited-- 445 00:24:16,670 --> 00:24:22,910 where the conduction is limited to one segment of the cord. 446 00:24:22,910 --> 00:24:25,050 OK. 447 00:24:25,050 --> 00:24:28,750 So we talk about segmental reflexes. 448 00:24:28,750 --> 00:24:31,520 What would be a possible function 449 00:24:31,520 --> 00:24:33,568 of that pathway I just drew? 450 00:24:36,436 --> 00:24:39,304 AUDIENCE: That you adapt faster than you're 451 00:24:39,304 --> 00:24:41,220 able to have processed. 452 00:24:41,220 --> 00:24:43,990 PROFESSOR: OK, but can we name the type of reflexes? 453 00:24:43,990 --> 00:24:45,770 One synapse here. 454 00:24:45,770 --> 00:24:47,320 Another synapse here. 455 00:24:47,320 --> 00:24:50,660 Another synapse here. 456 00:24:50,660 --> 00:24:53,372 What might be the function? 457 00:24:53,372 --> 00:24:55,120 AUDIENCE: Pain? 458 00:24:55,120 --> 00:24:57,120 PROFESSOR: Yeah, a response to pain. 459 00:24:57,120 --> 00:24:58,730 That's a good answer. 460 00:24:58,730 --> 00:25:00,740 But what kind of reflex is that? 461 00:25:00,740 --> 00:25:01,880 How do we respond? 462 00:25:01,880 --> 00:25:04,280 If I reach out here and something suddenly 463 00:25:04,280 --> 00:25:09,040 hurts my finger, what kind of reflex is that? 464 00:25:09,040 --> 00:25:10,510 It's got two names. 465 00:25:10,510 --> 00:25:14,650 Withdrawal reflex or flexion reflex. 466 00:25:14,650 --> 00:25:15,520 OK. 467 00:25:15,520 --> 00:25:19,920 Withdrawal or reflection reflex. 468 00:25:19,920 --> 00:25:23,820 It always involves more than one synapse 469 00:25:23,820 --> 00:25:27,495 between the primary sensory neuron and the motor neuron. 470 00:25:30,210 --> 00:25:33,320 There is a reflex that only has one synapse, 471 00:25:33,320 --> 00:25:35,730 the mono-synaptic reflex. 472 00:25:35,730 --> 00:25:37,180 What kind of reflex is that? 473 00:25:41,130 --> 00:25:43,130 You learn this in 901. 474 00:25:43,130 --> 00:25:44,960 At least when I taught 901, I always 475 00:25:44,960 --> 00:25:46,552 made sure everybody knew this. 476 00:25:49,210 --> 00:25:53,050 The axon, I actually showed you a picture of it already, 477 00:25:53,050 --> 00:25:54,190 from Cajal. 478 00:25:54,190 --> 00:25:56,960 Except he drew it the input coming from skin 479 00:25:56,960 --> 00:25:59,255 and I said that was wrong, it comes from muscle. 480 00:26:02,240 --> 00:26:04,900 These little sensory receptors in our muscles, 481 00:26:04,900 --> 00:26:07,900 especially the muscles of fine movement. 482 00:26:07,900 --> 00:26:10,510 OK, we've got a lot of little receptors 483 00:26:10,510 --> 00:26:15,096 in those muscles that detect muscle stretch. 484 00:26:15,096 --> 00:26:17,420 The stretch receptors. 485 00:26:17,420 --> 00:26:22,900 They give rise to secondary-- the primary sensory neurons 486 00:26:22,900 --> 00:26:28,855 innervating them have very large axons, the 1a axons. 487 00:26:28,855 --> 00:26:33,410 They're fast conducting and they go right to the motor neuron. 488 00:26:33,410 --> 00:26:35,865 A motor neuron innervates the very same muscle 489 00:26:35,865 --> 00:26:38,988 where it came from. 490 00:26:38,988 --> 00:26:41,310 And the reason it's such a nice system 491 00:26:41,310 --> 00:26:45,390 is that there's a little muscle inside each spindle organ. 492 00:26:45,390 --> 00:26:48,090 So the sensitivity to stretch can 493 00:26:48,090 --> 00:26:51,870 be varied from the central nervous system 494 00:26:51,870 --> 00:26:55,700 by a little motor neuron in the ventral horn called the gamma 495 00:26:55,700 --> 00:26:58,110 efferent neuron. 496 00:26:58,110 --> 00:27:01,820 You're constantly adjusting those muscle spindles. 497 00:27:01,820 --> 00:27:03,473 So you can actually-- your brain can 498 00:27:03,473 --> 00:27:08,426 set the link at which the spindle starts firing. 499 00:27:08,426 --> 00:27:13,880 It's very nice way to get stable, control the movement. 500 00:27:13,880 --> 00:27:14,465 All right. 501 00:27:17,790 --> 00:27:29,320 So this kind of axon that enters one segment of the cord 502 00:27:29,320 --> 00:27:34,510 comes from that. 503 00:27:34,510 --> 00:27:36,000 What does that mean? 504 00:27:36,000 --> 00:27:37,530 A dermatome. 505 00:27:37,530 --> 00:27:40,960 AUDIENCE: It's like a map of where 506 00:27:40,960 --> 00:27:46,274 the sensory inputs into the spinal cord are laid out. 507 00:27:46,274 --> 00:27:46,940 PROFESSOR: Yeah. 508 00:27:46,940 --> 00:27:50,440 It's true. 509 00:27:50,440 --> 00:27:55,880 But I want you to be a little more specific. 510 00:27:55,880 --> 00:28:00,010 How is a dermatome defined? 511 00:28:02,630 --> 00:28:06,440 How is the first thoracic dermatome defined? 512 00:28:06,440 --> 00:28:07,970 Now I'm giving you a huge hint. 513 00:28:10,500 --> 00:28:15,089 It's an area-- what does derm mean? 514 00:28:15,089 --> 00:28:15,880 AUDIENCE: The skin. 515 00:28:15,880 --> 00:28:17,590 PROFESSOR: The skin. 516 00:28:17,590 --> 00:28:19,250 Tome-- section. 517 00:28:19,250 --> 00:28:21,330 So it's got to be a section of skin. 518 00:28:21,330 --> 00:28:24,120 What kind of section of skin? 519 00:28:24,120 --> 00:28:26,970 There's a dermatome map. 520 00:28:26,970 --> 00:28:31,810 What do each of those little sections represent? 521 00:28:31,810 --> 00:28:38,790 The skin innervated by the dorsal root of one segment. 522 00:28:38,790 --> 00:28:41,530 OK. 523 00:28:41,530 --> 00:28:45,520 Meaning, we should find eight cervical dermatomes. 524 00:28:48,500 --> 00:28:51,930 We should find 12 thoracic dermatomes. 525 00:28:51,930 --> 00:28:54,800 We should find five lumbar dermatomes, 526 00:28:54,800 --> 00:28:57,970 five sacral dermatomes. 527 00:28:57,970 --> 00:29:02,176 Some people might define one [INAUDIBLE] dermatome. 528 00:29:02,176 --> 00:29:04,660 But generally, it doesn't. 529 00:29:04,660 --> 00:29:08,000 Usually, we just talk about down to the sacral. 530 00:29:08,000 --> 00:29:15,790 Why does it have such a peculiar arrangement on the limbs 531 00:29:15,790 --> 00:29:19,410 and such irregular arrangements on the trunk? 532 00:29:19,410 --> 00:29:20,390 That's one question. 533 00:29:20,390 --> 00:29:24,930 Another question is, what about the face? 534 00:29:24,930 --> 00:29:26,400 Why isn't the face included? 535 00:29:29,125 --> 00:29:31,250 AUDIENCE: There's no connection to the spinal cord. 536 00:29:31,250 --> 00:29:32,060 PROFESSOR: Sorry? 537 00:29:32,060 --> 00:29:33,690 AUDIENCE: There's no connection to the spinal cord. 538 00:29:33,690 --> 00:29:34,356 PROFESSOR: Yeah. 539 00:29:34,356 --> 00:29:36,885 It's not innervated by the spinal cord at all. 540 00:29:36,885 --> 00:29:37,560 That's right. 541 00:29:37,560 --> 00:29:39,874 What is it innervated by? 542 00:29:39,874 --> 00:29:43,610 AUDIENCE: The cranial neuron? 543 00:29:43,610 --> 00:29:46,660 PROFESSOR: By what kind of nerve? 544 00:29:46,660 --> 00:29:47,950 Cranial nerve. 545 00:29:47,950 --> 00:29:49,050 Which cranial nerve? 546 00:29:56,420 --> 00:29:58,960 What's another name for the fifth nerve? 547 00:30:01,770 --> 00:30:04,410 It's got three main branches so we 548 00:30:04,410 --> 00:30:07,520 call it the trigeminal nerve, exactly. 549 00:30:07,520 --> 00:30:08,550 OK. 550 00:30:08,550 --> 00:30:09,300 Very good. 551 00:30:14,990 --> 00:30:19,620 Put the human in this position and now imagine he's 552 00:30:19,620 --> 00:30:26,690 still an embryo, and the limbs are just little stubs here. 553 00:30:26,690 --> 00:30:30,590 Then you will see that the lines are all pretty straight. 554 00:30:30,590 --> 00:30:31,260 OK. 555 00:30:31,260 --> 00:30:33,080 And if he tilts his head up a little bit, 556 00:30:33,080 --> 00:30:35,210 that line is straight, too, the line 557 00:30:35,210 --> 00:30:42,290 between trigeminal and the uppermost cervical nerve input. 558 00:30:42,290 --> 00:30:44,700 So it's an embryological phenomenon 559 00:30:44,700 --> 00:30:48,131 that you end up with this kind of map. 560 00:30:48,131 --> 00:30:48,630 All right. 561 00:30:48,630 --> 00:30:54,210 But now here's one little caveat to this whole story. 562 00:30:54,210 --> 00:30:59,280 Each dermatome actually overlaps with two adjoining dermatomes, 563 00:30:59,280 --> 00:31:00,710 as you see here. 564 00:31:00,710 --> 00:31:03,210 That's usually not depicted in the map. 565 00:31:07,430 --> 00:31:09,980 Why is the dermatomal map so important 566 00:31:09,980 --> 00:31:11,320 in clinical neurology? 567 00:31:15,786 --> 00:31:19,620 Can you think of a reason? 568 00:31:19,620 --> 00:31:24,780 When you get a neurological exam, 569 00:31:24,780 --> 00:31:30,660 they test for sensation in various parts of the body. 570 00:31:30,660 --> 00:31:34,051 They're not just playing around. 571 00:31:34,051 --> 00:31:39,640 If you get pain that corresponds to a dermatome 572 00:31:39,640 --> 00:31:44,080 or a few dermatomes, it could mean pressure 573 00:31:44,080 --> 00:31:45,160 on the spinal nerve. 574 00:31:45,160 --> 00:31:47,350 If someone has a slipped disc, he's 575 00:31:47,350 --> 00:31:51,990 going to have a hypersensitive nerve. 576 00:31:51,990 --> 00:31:57,360 And if it's affecting only the spinal root, the dorsal root 577 00:31:57,360 --> 00:32:02,610 on one side, it will go right to the midline 578 00:32:02,610 --> 00:32:08,535 and then go around the body to the midline in the back. 579 00:32:08,535 --> 00:32:09,035 All right. 580 00:32:12,870 --> 00:32:16,000 So the neurologist needs to know these things 581 00:32:16,000 --> 00:32:19,520 and will always look for pain for example 582 00:32:19,520 --> 00:32:21,330 that follows the dermatome map. 583 00:32:26,770 --> 00:32:29,450 All right. 584 00:32:29,450 --> 00:32:31,450 How are they mapped? 585 00:32:31,450 --> 00:32:34,790 Well, I mentioned one region, the irritation 586 00:32:34,790 --> 00:32:37,095 of the single spinal root will cause pain 587 00:32:37,095 --> 00:32:42,110 in the corresponding dermatome or herniated disk. 588 00:32:42,110 --> 00:32:45,400 But you also-- there's data in the literature 589 00:32:45,400 --> 00:32:51,780 from pathological cases where many nerves have been severed 590 00:32:51,780 --> 00:32:54,780 but there's a spared nerve. 591 00:32:54,780 --> 00:32:56,190 OK. 592 00:32:56,190 --> 00:33:02,400 So that's the method of remaining sensibility 593 00:33:02,400 --> 00:33:07,380 where the many roots have been severed but one has spared. 594 00:33:07,380 --> 00:33:10,220 Of course, the dermatome sensation and the dermatome 595 00:33:10,220 --> 00:33:12,180 will be spared, too. 596 00:33:12,180 --> 00:33:16,340 The term myotome is sometimes here, a section of muscle 597 00:33:16,340 --> 00:33:19,150 that simply is the same definition as the dermatome. 598 00:33:19,150 --> 00:33:21,650 But now, it corresponds to the ventral root. 599 00:33:21,650 --> 00:33:27,530 It's the muscles innervated by one ventral root 600 00:33:27,530 --> 00:33:30,470 or one pair of ventral roots. 601 00:33:30,470 --> 00:33:35,410 So they usually are pretty closely 602 00:33:35,410 --> 00:33:36,580 aligned with the dermatomes. 603 00:33:40,360 --> 00:33:44,125 And so there you see this spinal nerve 604 00:33:44,125 --> 00:33:47,210 in a dissection of a young human. 605 00:33:50,180 --> 00:33:54,370 We define local-- when we talk about a local reflex 606 00:33:54,370 --> 00:33:57,440 in the periphery, in terms of dermatomes. 607 00:33:57,440 --> 00:34:01,290 But in the CNS, we talk about the segment. 608 00:34:01,290 --> 00:34:05,465 Segments were originally defined just by the vertebrae. 609 00:34:08,719 --> 00:34:12,080 The nerve tend to come out just below the spinal vertebrae 610 00:34:12,080 --> 00:34:16,000 except for the upper cervical ones. 611 00:34:16,000 --> 00:34:17,700 Which come on just above the vertebrae. 612 00:34:21,550 --> 00:34:26,469 Now let's talk about the longer pathways. 613 00:34:26,469 --> 00:34:29,909 What's the oldest ascending somatosensory pathways that 614 00:34:29,909 --> 00:34:30,670 reaches the brain. 615 00:34:33,770 --> 00:34:37,380 It's actually a couple of them that are very ancient. 616 00:34:37,380 --> 00:34:39,440 When I was studying their anatomy, 617 00:34:39,440 --> 00:34:42,920 I learned that the paleo lemniscus 618 00:34:42,920 --> 00:34:46,230 was a cross pathway coming through spinal cord called 619 00:34:46,230 --> 00:34:49,080 the spinothalamic tract. 620 00:34:49,080 --> 00:34:51,610 But in studying it further, I realized 621 00:34:51,610 --> 00:34:54,340 that there's actually an older one. 622 00:34:54,340 --> 00:34:57,270 In fact, that spinothalamic tract across pathways 623 00:34:57,270 --> 00:35:03,350 doesn't even exist in the most ancient of the chordates. 624 00:35:03,350 --> 00:35:07,950 And certainly not in amphioxus, the lancelets. 625 00:35:07,950 --> 00:35:08,450 OK. 626 00:35:11,480 --> 00:35:15,850 These are the two-- if I just talk 627 00:35:15,850 --> 00:35:21,830 about sensory lemniscii that mediate touch sensation. 628 00:35:21,830 --> 00:35:27,700 We've got the two types of lemniscal pathways. 629 00:35:27,700 --> 00:35:29,920 These are suprasegmental pathways 630 00:35:29,920 --> 00:35:34,450 above the segments of the spinal cord. 631 00:35:34,450 --> 00:35:39,290 So you'll sometimes hear talk about a suprasegmental reflex. 632 00:35:39,290 --> 00:35:41,700 A response is just like a reflex but it 633 00:35:41,700 --> 00:35:44,970 involves the brain in some ways, about the segments 634 00:35:44,970 --> 00:35:47,260 of the chord. 635 00:35:47,260 --> 00:35:53,600 The oldest connections terminate in reticular formation. 636 00:35:53,600 --> 00:36:02,130 The core neurons of the brain stem, hindbrain, and midbrain. 637 00:36:02,130 --> 00:36:03,322 OK. 638 00:36:03,322 --> 00:36:05,990 But even both of these old pathways 639 00:36:05,990 --> 00:36:10,760 have some axons that do reach the thalamus. 640 00:36:14,450 --> 00:36:17,160 And of these two pathways, one of them decussates and one 641 00:36:17,160 --> 00:36:19,210 doesn't. 642 00:36:19,210 --> 00:36:24,170 So let's talk about the oldest one-- spinal reticular. 643 00:36:24,170 --> 00:36:30,110 It's bilateral but most of the axons never cross the midline. 644 00:36:30,110 --> 00:36:31,280 OK. 645 00:36:31,280 --> 00:36:34,170 Most of them stay ipsilaterally. 646 00:36:34,170 --> 00:36:36,370 They go to the core of the brain stem, 647 00:36:36,370 --> 00:36:40,900 almost all them terminating in the reticular formation. 648 00:36:40,900 --> 00:36:42,800 It's the least studied of the pathways 649 00:36:42,800 --> 00:36:47,200 but you always find in any study of the ascending spinal 650 00:36:47,200 --> 00:36:50,250 pathways, in any chordate. 651 00:36:50,250 --> 00:36:52,120 You look at an amphioxus, you see 652 00:36:52,120 --> 00:36:54,750 most of the axon stay on the same side, a few of them 653 00:36:54,750 --> 00:36:56,590 reach the other side. 654 00:36:56,590 --> 00:37:01,530 So we know in animals what was most important for them, 655 00:37:01,530 --> 00:37:04,390 control of their blood pressure and heart rate, 656 00:37:04,390 --> 00:37:08,160 breathing rate and volume, autonomic and defensive 657 00:37:08,160 --> 00:37:10,340 behavioral response to pain inputs, 658 00:37:10,340 --> 00:37:13,610 temperature regulation, control of sexual behavior. 659 00:37:13,610 --> 00:37:17,690 These had to be functions of that pathway. 660 00:37:17,690 --> 00:37:19,790 I can say that even in the absence 661 00:37:19,790 --> 00:37:24,940 of very specific studies of the functions of the pathways. 662 00:37:24,940 --> 00:37:27,780 Because I know that the sensory input from the body surface 663 00:37:27,780 --> 00:37:30,350 control these things and the animals 664 00:37:30,350 --> 00:37:33,130 had to have those functions even before they 665 00:37:33,130 --> 00:37:36,490 had a-- even the ones that don't have any other descending 666 00:37:36,490 --> 00:37:38,870 pathways. 667 00:37:38,870 --> 00:37:42,630 So here in our simplified diagram, 668 00:37:42,630 --> 00:37:45,990 these axons would be the ones that belong to that pathway. 669 00:37:45,990 --> 00:37:49,800 And notice I do show a long here going to the thalamus. 670 00:37:49,800 --> 00:37:54,430 Others are terminating in the midbrain and hindbrain. 671 00:37:54,430 --> 00:37:57,060 This picture was revised a little bit 672 00:37:57,060 --> 00:38:00,020 from the one in the book. 673 00:38:00,020 --> 00:38:01,730 OK. 674 00:38:01,730 --> 00:38:04,440 It actually could represent spinal reticular 675 00:38:04,440 --> 00:38:06,790 or the spinothalamic. 676 00:38:06,790 --> 00:38:10,200 And if we talk now about what are these most 677 00:38:10,200 --> 00:38:12,840 ancient animals-- I keep mentioning them. 678 00:38:12,840 --> 00:38:14,720 These are the main ones. 679 00:38:14,720 --> 00:38:19,075 Amphioxus, a group of species called the lancelets 680 00:38:19,075 --> 00:38:21,030 that we talked about earlier. 681 00:38:21,030 --> 00:38:23,720 And then there's a hagfish and there's a sea lamprey. 682 00:38:23,720 --> 00:38:30,450 These are eel-like animals that are not bony vertebrates. 683 00:38:30,450 --> 00:38:32,350 They don't have a bony skull. 684 00:38:32,350 --> 00:38:33,225 It's just cartilage. 685 00:38:36,310 --> 00:38:42,390 And these are pictures of their brain you can see. 686 00:38:42,390 --> 00:38:44,930 Hindbrain is the biggest here. 687 00:38:44,930 --> 00:38:48,480 There's the midbrain, here's the forebrain 688 00:38:48,480 --> 00:38:50,720 with the telencephalon, about the same size 689 00:38:50,720 --> 00:38:53,340 of the diencephalon, about the same size 690 00:38:53,340 --> 00:38:55,540 as the olfactory bulbs. 691 00:38:55,540 --> 00:38:58,510 And it's similar for the sea lamprey, which 692 00:38:58,510 --> 00:39:02,480 is more studied then the hagfish. 693 00:39:02,480 --> 00:39:06,010 A little less specialized so there's 694 00:39:06,010 --> 00:39:11,070 been more focus of studies on that animal. 695 00:39:11,070 --> 00:39:15,260 And all of these animals all have a spinal reticular 696 00:39:15,260 --> 00:39:16,305 pathway. 697 00:39:16,305 --> 00:39:19,820 But not much of the spinothalamic pathways, if any 698 00:39:19,820 --> 00:39:20,400 at all. 699 00:39:20,400 --> 00:39:22,820 What's interesting about those three-- 700 00:39:22,820 --> 00:39:27,050 so I marked them here on the cladogram, is that you can 701 00:39:27,050 --> 00:39:36,600 trace animals in those three groups in the fossil record 702 00:39:36,600 --> 00:39:40,660 back to the earliest, earliest chordates. 703 00:39:40,660 --> 00:39:46,175 Only amphioxus is an invertebrate chordate. 704 00:39:49,730 --> 00:39:52,040 The hagfishes and lampreys are vertebrates 705 00:39:52,040 --> 00:39:53,970 but they're not bony vertebrates. 706 00:39:53,970 --> 00:39:56,700 Or jawed vertebrates. 707 00:39:56,700 --> 00:40:00,660 The animal is bony, jaw and skull. 708 00:40:00,660 --> 00:40:01,160 OK. 709 00:40:01,160 --> 00:40:03,210 Start here. 710 00:40:03,210 --> 00:40:06,955 And they include all the other vertebrates. 711 00:40:11,380 --> 00:40:13,060 So this is, as I already mentioned, 712 00:40:13,060 --> 00:40:15,945 that amphioxus has something like this spinal reticular 713 00:40:15,945 --> 00:40:16,445 pathway. 714 00:40:20,740 --> 00:40:23,430 You can find this spinal reticular type pathway 715 00:40:23,430 --> 00:40:26,470 in hagfish and sea lampreys but they don't apparently 716 00:40:26,470 --> 00:40:28,360 have any cross pathways. 717 00:40:31,460 --> 00:40:33,770 They have a few axons that do cross to the other side 718 00:40:33,770 --> 00:40:35,800 but it's not a specific lemniscus. 719 00:40:35,800 --> 00:40:37,405 It's not a major pathway. 720 00:40:40,400 --> 00:40:42,450 You get, though, that cross pathway 721 00:40:42,450 --> 00:40:52,330 in most of the vertebrates that evolve later, including 722 00:40:52,330 --> 00:40:55,930 both mammals and non-mammals and certainly 723 00:40:55,930 --> 00:40:58,540 the cartilage in these fishes. 724 00:40:58,540 --> 00:41:03,150 So that cross pathway we called spinothalamic. 725 00:41:07,550 --> 00:41:09,320 Remember when it was discovered, people 726 00:41:09,320 --> 00:41:11,790 didn't know anything specifically 727 00:41:11,790 --> 00:41:14,330 about the spinal reticular. 728 00:41:14,330 --> 00:41:19,600 And it's been more studied and it's more important in humans. 729 00:41:19,600 --> 00:41:21,360 I'm not totally convinced of that 730 00:41:21,360 --> 00:41:24,670 because they just don't study people 731 00:41:24,670 --> 00:41:29,530 without both of these pathways. 732 00:41:29,530 --> 00:41:31,140 So there they are. 733 00:41:31,140 --> 00:41:35,420 And this, if we look at it on this kind of diagram, 734 00:41:35,420 --> 00:41:38,610 this is what spinothalamic tract is like. 735 00:41:38,610 --> 00:41:42,110 Spinal reticular would be axons that go on this, mostly 736 00:41:42,110 --> 00:41:45,770 on the same side, with a few crossing over at all levels. 737 00:41:45,770 --> 00:41:47,500 Here's the spinothalamic. 738 00:41:47,500 --> 00:41:52,330 It's a cross pathway but the decussation 739 00:41:52,330 --> 00:41:54,000 is at all levels of the chord. 740 00:41:54,000 --> 00:41:56,020 Because they're decussated immediately. 741 00:41:56,020 --> 00:41:58,130 At every level of the cord, you can 742 00:41:58,130 --> 00:42:03,300 find secondary sensory neurons with axons 743 00:42:03,300 --> 00:42:06,740 that crossover and ascend in the lateral columns 744 00:42:06,740 --> 00:42:10,120 on the opposite side towards the brain. 745 00:42:10,120 --> 00:42:13,010 And a few of the axons do reach the thalamus, 746 00:42:13,010 --> 00:42:17,071 so you get-- it does provide input to the [INAUDIBLE]. 747 00:42:25,700 --> 00:42:28,550 So I want you to keep in mind we're not talking here 748 00:42:28,550 --> 00:42:32,124 about earliest chordates. 749 00:42:32,124 --> 00:42:34,560 It's a very long period of evolution 750 00:42:34,560 --> 00:42:37,920 in order to get there. 751 00:42:37,920 --> 00:42:42,740 I think it probably evolved as a specialization of the widely 752 00:42:42,740 --> 00:42:45,900 branch in the spinal reticular axons. 753 00:42:45,900 --> 00:42:50,340 So there must have been some big advantage to crossing over, 754 00:42:50,340 --> 00:42:52,070 which I mentioned earlier and we'll 755 00:42:52,070 --> 00:42:55,250 talk about that when we discuss the hindbrain in more detail. 756 00:42:58,190 --> 00:42:59,800 So now I've mentioned a few times 757 00:42:59,800 --> 00:43:02,240 that spinal reticular, there's not a lot of research. 758 00:43:02,240 --> 00:43:06,300 So these are simply questions related to that research 759 00:43:06,300 --> 00:43:10,530 questions that haven't been fully answer. 760 00:43:10,530 --> 00:43:11,470 OK. 761 00:43:11,470 --> 00:43:14,480 Here's another sensory lemniscal pathway, 762 00:43:14,480 --> 00:43:16,450 carrying information to the cerebellum. 763 00:43:19,300 --> 00:43:22,020 Why did the cerebellum evolve? 764 00:43:22,020 --> 00:43:26,610 What's the suggestion, the hypothesis 765 00:43:26,610 --> 00:43:30,170 that's actually fairly popular. 766 00:43:30,170 --> 00:43:31,740 In my reading of that literature, 767 00:43:31,740 --> 00:43:33,710 though, many people that study it 768 00:43:33,710 --> 00:43:36,355 focus on more very specific functions. 769 00:43:40,750 --> 00:43:43,690 What is the hypothesis I talk about? 770 00:43:43,690 --> 00:43:46,330 It's very simple. 771 00:43:46,330 --> 00:43:50,570 We know all output, all movement depends on the motor neurons, 772 00:43:50,570 --> 00:43:52,030 right? 773 00:43:52,030 --> 00:43:57,520 So if I flex my arm, OK, every time I flex my arm, 774 00:43:57,520 --> 00:44:01,610 it depends on flex or motor neurons in the spinal cord. 775 00:44:01,610 --> 00:44:03,640 What's causing me to flex my arm? 776 00:44:03,640 --> 00:44:06,000 Well, it can be caused by a result 777 00:44:06,000 --> 00:44:11,000 of visual input, auditory input, input from speech, for example. 778 00:44:11,000 --> 00:44:14,425 It could be doing a lot of different kinds of inputs. 779 00:44:14,425 --> 00:44:18,170 It could be input generated from within the brain. 780 00:44:18,170 --> 00:44:22,160 How do we make sure that the various inputs that 781 00:44:22,160 --> 00:44:26,060 are coming in simultaneously, in very different parts 782 00:44:26,060 --> 00:44:30,920 of the body, are all causing that movement at the same time? 783 00:44:30,920 --> 00:44:33,346 Because it may be part of a sequence of movements. 784 00:44:33,346 --> 00:44:34,470 It's got to be coordinated. 785 00:44:37,170 --> 00:44:40,200 And that is a big problem, especially in large animals. 786 00:44:40,200 --> 00:44:43,820 As they're growing, the length of these pathways is changing. 787 00:44:43,820 --> 00:44:46,100 And we know that axonal conduction is not 788 00:44:46,100 --> 00:44:47,060 instantaneous. 789 00:44:47,060 --> 00:44:48,920 It's not like life. 790 00:44:48,920 --> 00:44:50,820 It takes some time. 791 00:44:50,820 --> 00:44:53,880 So I believe the cerebellum evolved in order 792 00:44:53,880 --> 00:44:57,570 to adjust the relative timing of these pathways. 793 00:44:57,570 --> 00:45:02,870 There are our major inputs in these various senses. 794 00:45:02,870 --> 00:45:04,990 They reach cerebellum. 795 00:45:04,990 --> 00:45:07,940 There's an amazing timing mechanism 796 00:45:07,940 --> 00:45:12,700 in the cerebellum for adjusting timing and major outputs 797 00:45:12,700 --> 00:45:13,620 to the spinal cord. 798 00:45:21,110 --> 00:45:24,050 So that's what I described in this slide 799 00:45:24,050 --> 00:45:27,765 and this is the pathway we're talking about. 800 00:45:37,070 --> 00:45:40,460 You can see it goes directly to the cortex of the cerebellum. 801 00:45:56,760 --> 00:45:59,810 The basic cell types and the circuitry 802 00:45:59,810 --> 00:46:02,020 are highly conserved in evolution. 803 00:46:02,020 --> 00:46:04,270 And you look at widely different animals 804 00:46:04,270 --> 00:46:07,300 and you keep seeing the cerebellar structure. 805 00:46:07,300 --> 00:46:09,720 The layering does become more regular. 806 00:46:09,720 --> 00:46:13,580 You get new inhibitory cell types in tetrapods. 807 00:46:13,580 --> 00:46:15,880 And also the deep nuclei that provide 808 00:46:15,880 --> 00:46:18,830 the output in the tetrapods aren't 809 00:46:18,830 --> 00:46:22,090 present before tetrapods. 810 00:46:22,090 --> 00:46:29,600 You also see tremendous variation and relative size, 811 00:46:29,600 --> 00:46:31,856 as we'll see in when we talk about some 812 00:46:31,856 --> 00:46:34,190 of the specializations. 813 00:46:34,190 --> 00:46:37,910 Now it's generally true that the larger 814 00:46:37,910 --> 00:46:40,760 the cerebral hemispheres, the biggest 815 00:46:40,760 --> 00:46:45,010 part of our brain, 80% percent, the cerebral cortex 816 00:46:45,010 --> 00:46:46,660 and related structures in the endbrain. 817 00:46:49,620 --> 00:46:53,910 The larger that is, the bigger the cerebellum. 818 00:46:53,910 --> 00:46:58,240 But there are some interesting exceptions. 819 00:46:58,240 --> 00:47:00,700 There are a few species of animals 820 00:47:00,700 --> 00:47:02,950 without the large cerebral hemispheres, 821 00:47:02,950 --> 00:47:06,150 in which a greatly enlarged cerebellum is found. 822 00:47:06,150 --> 00:47:09,314 What animals am I talking about? 823 00:47:09,314 --> 00:47:12,204 AUDIENCE: Isn't it a type of fish? 824 00:47:12,204 --> 00:47:12,870 PROFESSOR: Yeah. 825 00:47:12,870 --> 00:47:14,580 It's a fish, great. 826 00:47:14,580 --> 00:47:16,050 With what? 827 00:47:16,050 --> 00:47:21,520 It's got a specialization in the type of sensory input. 828 00:47:21,520 --> 00:47:25,690 It's an input we have no direct experience because we 829 00:47:25,690 --> 00:47:26,650 don't have it. 830 00:47:26,650 --> 00:47:28,934 In fact, they have a lot of cranial nerves. 831 00:47:28,934 --> 00:47:29,850 AUDIENCE: [INAUDIBLE]? 832 00:47:29,850 --> 00:47:30,808 PROFESSOR: Sorry? 833 00:47:30,808 --> 00:47:33,150 AUDIENCE: [INAUDIBLE]? 834 00:47:33,150 --> 00:47:34,610 PROFESSOR: It's not taste. 835 00:47:34,610 --> 00:47:36,110 That's another area where there's 836 00:47:36,110 --> 00:47:38,250 been great specialization, but taste 837 00:47:38,250 --> 00:47:41,330 doesn't lead to enlargement of the cerebellum. 838 00:47:41,330 --> 00:47:42,990 This sense does. 839 00:47:42,990 --> 00:47:44,910 It's electroreception and we spend 840 00:47:44,910 --> 00:47:48,280 a lot of interesting studies of electroreception. 841 00:47:48,280 --> 00:47:53,410 Here I've drawn, from a published picture, 842 00:47:53,410 --> 00:47:55,910 I've drawn so I could simplify it a little bit 843 00:47:55,910 --> 00:47:57,660 and point out the main points. 844 00:47:57,660 --> 00:48:00,940 The enlarged cerebellum of a mormyrid fish. 845 00:48:00,940 --> 00:48:05,680 The mormyrids and the gymnotus have electroreceptions. 846 00:48:05,680 --> 00:48:07,630 They have a number of cranial nerves 847 00:48:07,630 --> 00:48:10,450 that are the electrosensory cranial nerves. 848 00:48:10,450 --> 00:48:13,970 And the input comes in to the lateral line 849 00:48:13,970 --> 00:48:17,020 lobe, electrosensory lateral line lobe, 850 00:48:17,020 --> 00:48:19,300 which also becomes quite large. 851 00:48:19,300 --> 00:48:20,760 That's not cerebellum. 852 00:48:20,760 --> 00:48:23,030 It's a hindbrain structure. 853 00:48:23,030 --> 00:48:23,880 OK. 854 00:48:23,880 --> 00:48:28,210 But everything shown in green there almost covers 855 00:48:28,210 --> 00:48:29,580 the entire brain. 856 00:48:29,580 --> 00:48:33,700 This is one part of the cerebellum in these animals. 857 00:48:33,700 --> 00:48:36,910 So we think that relative timing is 858 00:48:36,910 --> 00:48:40,190 used in the analysis of electrosensory input. 859 00:48:40,190 --> 00:48:44,340 But there is a lot of work going on right now. 860 00:48:44,340 --> 00:48:47,420 It has been going on for awhile for the mormyrid fish, 861 00:48:47,420 --> 00:48:50,480 especially in Canada in the laboratory of Leonard 862 00:48:50,480 --> 00:48:52,370 Mailer, who is a graduate of this department. 863 00:48:55,710 --> 00:48:58,730 And I hope he gets-- he's trying to work it out. 864 00:48:58,730 --> 00:49:01,470 And of course, computational work is being done also. 865 00:49:04,140 --> 00:49:07,570 So this is just a little about that 866 00:49:07,570 --> 00:49:12,240 and I point out that coordinated timing is important, 867 00:49:12,240 --> 00:49:16,010 even in our imagery, even in our dreams. 868 00:49:16,010 --> 00:49:20,780 And the entire neocortex involved in that projects 869 00:49:20,780 --> 00:49:26,078 to the cerebellum by way of the pons. 870 00:49:26,078 --> 00:49:28,540 All right. 871 00:49:28,540 --> 00:49:30,170 That is all for today. 872 00:49:34,380 --> 00:49:36,580 We'll continue with this story. 873 00:49:36,580 --> 00:49:39,110 We'll be talking about-- we'll take a little break 874 00:49:39,110 --> 00:49:41,990 and talk about specializations and then go on 875 00:49:41,990 --> 00:49:44,140 to the hindbrain.