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 00:00:23,680 --> 00:00:28,140 PROFESSOR: Can somebody tell me what the homeobox genes are? 9 00:00:28,140 --> 00:00:30,070 They're often called Hox genes. 10 00:00:33,840 --> 00:00:35,210 What are they code for? 11 00:00:39,160 --> 00:00:40,790 Transcription factors. 12 00:00:43,650 --> 00:00:54,900 And if you delete certain Hox genes or change their position, 13 00:00:54,900 --> 00:00:59,990 you can get abnormalities in the segmentation of the body. 14 00:00:59,990 --> 00:01:01,860 Some of that has been done with flies. 15 00:01:01,860 --> 00:01:03,810 They can produce a fly, for example, 16 00:01:03,810 --> 00:01:09,740 with legs coming out his head or something like that. 17 00:01:12,410 --> 00:01:15,620 And it's interesting that of rearrangement on the chromosome 18 00:01:15,620 --> 00:01:22,730 that the position of the gene and the sequence of genes 19 00:01:22,730 --> 00:01:29,260 on the chromosome, it's always consistent right 20 00:01:29,260 --> 00:01:32,320 across the species. 21 00:01:32,320 --> 00:01:36,220 As we saw last time this slide of a mouse 22 00:01:36,220 --> 00:01:45,280 showing the expression of three different genes. 23 00:01:45,280 --> 00:01:47,727 They were doing immunostaining of the antibodies 24 00:01:47,727 --> 00:01:49,060 for the proteins of those genes. 25 00:01:51,840 --> 00:01:57,350 And here, this is actually not-- it's mesodermal expression. 26 00:01:57,350 --> 00:02:02,360 But these genes are expressed in nervous system and other body 27 00:02:02,360 --> 00:02:02,860 tissues. 28 00:02:06,027 --> 00:02:08,360 But you see each on of them, each of these transcription 29 00:02:08,360 --> 00:02:14,110 factors has a rostral limit for its expression, 30 00:02:14,110 --> 00:02:17,610 less precise than the caudal side. 31 00:02:17,610 --> 00:02:23,380 But now, if you look at the hindbrain, 32 00:02:23,380 --> 00:02:26,130 during development at a certain period, 33 00:02:26,130 --> 00:02:29,672 you see this pattern appearing. 34 00:02:29,672 --> 00:02:34,580 The segmentation is visible in the bulges of the hindbrain. 35 00:02:34,580 --> 00:02:36,050 We call them rhombomeres. 36 00:02:36,050 --> 00:02:42,500 Mere for for the section or segment. 37 00:02:42,500 --> 00:02:45,370 Rhombo, of course, for the rhombencephalon. 38 00:02:45,370 --> 00:02:47,920 These are segmentation of rhombencephalon. 39 00:02:53,920 --> 00:02:58,440 When you look at the expression of transcription factors, 40 00:02:58,440 --> 00:03:01,630 including many of the Hox genes, they 41 00:03:01,630 --> 00:03:02,860 have an interesting pattern. 42 00:03:02,860 --> 00:03:05,735 And here's a little cartoon of the rhombomeres 43 00:03:05,735 --> 00:03:08,325 of the hindbrain from rostral here 44 00:03:08,325 --> 00:03:12,460 on the left, the caudal on the right. 45 00:03:12,460 --> 00:03:19,460 And if you look at the pattern of gene expression this way, 46 00:03:19,460 --> 00:03:22,040 it looks like a bar code. 47 00:03:22,040 --> 00:03:23,600 It's interesting that some of them 48 00:03:23,600 --> 00:03:27,360 are expressed in like one rhombomere, 49 00:03:27,360 --> 00:03:31,850 and then they're not expressed in the next one. 50 00:03:31,850 --> 00:03:36,830 Then they are expressed in the next one down line. 51 00:03:36,830 --> 00:03:38,810 And that's true of a number of them. 52 00:03:38,810 --> 00:03:42,230 You see here, they skipped two. 53 00:03:42,230 --> 00:03:46,590 This one's in one and two, not in three. 54 00:03:46,590 --> 00:03:50,410 Then these two are both present the fourth, 55 00:03:50,410 --> 00:03:53,242 and they're present again in the sixth, and one of them's 56 00:03:53,242 --> 00:03:54,075 also in the seventh. 57 00:03:58,790 --> 00:04:02,100 So that's true about of a number of different genes. 58 00:04:02,100 --> 00:04:05,510 And this is just one experiment showing 59 00:04:05,510 --> 00:04:08,540 an effect of these genes. 60 00:04:08,540 --> 00:04:14,140 Here you are seeing what you saw on the previous slide, 61 00:04:14,140 --> 00:04:18,290 expression of these particular Hox genes. 62 00:04:18,290 --> 00:04:22,390 There's two that have that more limited expression 63 00:04:22,390 --> 00:04:26,980 in certain segments and not others. 64 00:04:26,980 --> 00:04:35,170 If you take stem cells, basically the precursor cells 65 00:04:35,170 --> 00:04:42,100 from the embryo, and infect them in another embryo, 66 00:04:42,100 --> 00:04:46,920 if you do it before those rhombomeres form, 67 00:04:46,920 --> 00:04:50,180 you can inject them near a boundary 68 00:04:50,180 --> 00:04:53,435 and they spread right across that boundary. 69 00:04:53,435 --> 00:04:58,920 Because the boundary i before those genes are expressed, 70 00:04:58,920 --> 00:05:01,510 it doesn't have the reality it does later. 71 00:05:01,510 --> 00:05:06,560 Because after the rhombomeres appear, you inject those cells 72 00:05:06,560 --> 00:05:09,590 and they don't move over the boundary. 73 00:05:12,490 --> 00:05:14,992 Of course, the genes must be doing other things, too. 74 00:05:14,992 --> 00:05:16,950 We know that there's developmental differences. 75 00:05:20,526 --> 00:05:22,640 The motor neurons didn't originate 76 00:05:22,640 --> 00:05:26,320 in a particular rhombomere, just innervate a particular part 77 00:05:26,320 --> 00:05:30,885 of the mesoderm corresponding to the branchial arches 78 00:05:30,885 --> 00:05:31,970 of the embryo. 79 00:05:41,310 --> 00:05:44,230 So now, this entire class is about the hindbrain 80 00:05:44,230 --> 00:05:46,820 and the cranial nerves of the hindbrain. 81 00:05:46,820 --> 00:05:49,600 We've talked a bit about hindbrain specializations 82 00:05:49,600 --> 00:05:52,870 already in chapter six, but we'll 83 00:05:52,870 --> 00:05:57,200 talk a little more about hindbrain specializations 84 00:05:57,200 --> 00:05:59,240 today. 85 00:05:59,240 --> 00:06:03,110 So first, back to the columns of the secondary sensory neurons 86 00:06:03,110 --> 00:06:05,870 and the motor neurons, and compare the hindbrain 87 00:06:05,870 --> 00:06:09,200 with spinal cord. 88 00:06:09,200 --> 00:06:12,540 This is probably the third time I've presented it. 89 00:06:12,540 --> 00:06:15,430 I want you to start to remember it. 90 00:06:15,430 --> 00:06:18,410 In this case, I'm trying here for the spinal cord. 91 00:06:18,410 --> 00:06:20,935 This is based on a figure of [INAUDIBLE], where 92 00:06:20,935 --> 00:06:22,560 I've added the colors. 93 00:06:22,560 --> 00:06:25,150 There are sensory and motor columns, 94 00:06:25,150 --> 00:06:29,970 but also I've colored in the visceral column, 95 00:06:29,970 --> 00:06:34,940 pregangliotic motor neurons of the sympathetic system. 96 00:06:34,940 --> 00:06:36,850 And then, in the hindbrain, I've used 97 00:06:36,850 --> 00:06:40,870 to red color for the visceral sensory and the visceral motor 98 00:06:40,870 --> 00:06:42,970 neurons. 99 00:06:42,970 --> 00:06:50,500 Visceral sensory gets input from the entire gut. 100 00:06:50,500 --> 00:06:56,615 They do have sensory fibers that come in through dorsal roots, 101 00:06:56,615 --> 00:07:02,190 but they reach this nucleaus in the hindbrain. 102 00:07:02,190 --> 00:07:06,850 The rostral part of the nucleus is the [INAUDIBLE] nucleus, 103 00:07:06,850 --> 00:07:09,110 getting input from the seventh, ninth, 104 00:07:09,110 --> 00:07:10,820 and [INAUDIBLE] cranial nerves. 105 00:07:10,820 --> 00:07:13,410 But here, just across the boundary 106 00:07:13,410 --> 00:07:16,300 between [INAUDIBLE] and basal plates, 107 00:07:16,300 --> 00:07:17,910 you have this motor column. 108 00:07:17,910 --> 00:07:20,685 That's this very long column with the big dorsal motor 109 00:07:20,685 --> 00:07:21,810 nucleus of the vagus nerve. 110 00:07:28,200 --> 00:07:30,870 And you'll note here, here there's 111 00:07:30,870 --> 00:07:34,130 just two roots; the dorsal root and ventral 112 00:07:34,130 --> 00:07:36,020 root at each segment. 113 00:07:36,020 --> 00:07:39,210 That's not true in the hindbrain. 114 00:07:39,210 --> 00:07:42,180 Here, the sensory fibers are coming in 115 00:07:42,180 --> 00:07:44,750 in two different positions. 116 00:07:44,750 --> 00:07:47,806 This is where the input is saved from the auditory 117 00:07:47,806 --> 00:07:51,080 and vestibular senses would come in. 118 00:07:51,080 --> 00:07:54,390 Whereas the somatosensory input from the face 119 00:07:54,390 --> 00:08:04,600 comes in a little further ventrally, the trigeminal 120 00:08:04,600 --> 00:08:07,050 And then you have-- so these are sensory nerves, 121 00:08:07,050 --> 00:08:10,210 but the fifth actually has a motor component, too. 122 00:08:10,210 --> 00:08:12,620 It has a motor nucleus. 123 00:08:12,620 --> 00:08:15,740 It's just on the other side of this boundary. 124 00:08:15,740 --> 00:08:20,030 it's the matiscatory nucleus for chewing movements. 125 00:08:20,030 --> 00:08:20,810 It goes out. 126 00:08:20,810 --> 00:08:24,525 It joins the sensory fibers of fifth nerve. 127 00:08:24,525 --> 00:08:28,220 I don't show it here. 128 00:08:28,220 --> 00:08:32,590 And then you have mixed nerves-- the seventh, ninth, and tenth 129 00:08:32,590 --> 00:08:36,140 primarily, where you have a mixture of sensory fibers 130 00:08:36,140 --> 00:08:37,470 and motor fibers. 131 00:08:37,470 --> 00:08:39,299 So no [INAUDIBLE] roots at all. 132 00:08:39,299 --> 00:08:41,830 But then you have somatic motor column 133 00:08:41,830 --> 00:08:45,780 controlling eye movements and controlling tongue movements, 134 00:08:45,780 --> 00:08:49,910 that just contain the motor neuron axons. 135 00:08:58,790 --> 00:09:02,190 I want to now go through cranial nerves a little bit. 136 00:09:02,190 --> 00:09:04,710 And then we'll talk about hindbrain some more, 137 00:09:04,710 --> 00:09:07,850 naming cell groups, looking at fibers, 138 00:09:07,850 --> 00:09:14,500 going through the cord and fibers of those cranial nerves. 139 00:09:14,500 --> 00:09:18,450 First of all, what is a sensory placode? 140 00:09:18,450 --> 00:09:21,050 Remember how the secondary sensory neurons 141 00:09:21,050 --> 00:09:24,692 of the spinal cord originate from neural crest cells. 142 00:09:27,920 --> 00:09:36,130 The secondary sensory neurons of the cranial nerves 143 00:09:36,130 --> 00:09:39,865 don't just originate in neural crest in the head region, 144 00:09:39,865 --> 00:09:44,650 they also originate from sensory placodes. 145 00:09:44,650 --> 00:09:45,750 What is a placode? 146 00:09:48,702 --> 00:09:51,000 There's several of them. 147 00:09:51,000 --> 00:09:54,416 They contribute to the [INAUDIBLE] nerves, 148 00:09:54,416 --> 00:09:58,200 in addition, in the vestibular sense. 149 00:09:58,200 --> 00:10:01,565 The olfactory neurons originate in a placode. 150 00:10:04,210 --> 00:10:09,960 It's just a piece of the ectodermal tissue, the surface 151 00:10:09,960 --> 00:10:13,810 tissue, that is neurogenic. 152 00:10:13,810 --> 00:10:18,430 It gives rise to, among other things, to neurons. 153 00:10:22,560 --> 00:10:25,090 So they don't-- all those secondary sensory cells 154 00:10:25,090 --> 00:10:28,210 don't come from the [INAUDIBLE] crest. 155 00:10:28,210 --> 00:10:30,490 And then we want to know about the cranial nerves 156 00:10:30,490 --> 00:10:31,480 and their number. 157 00:10:31,480 --> 00:10:35,120 I have a table in the book. 158 00:10:35,120 --> 00:10:38,700 You start studying that table because I'm 159 00:10:38,700 --> 00:10:40,426 going to give you some time, but we're 160 00:10:40,426 --> 00:10:44,190 going to memorize all the cranial nerves and a few things 161 00:10:44,190 --> 00:10:46,570 about them. 162 00:10:46,570 --> 00:10:48,830 I'll give you more instruction about that, 163 00:10:48,830 --> 00:10:51,510 but I want you to start paying attention to that 164 00:10:51,510 --> 00:10:53,510 because when I say seventh nerve, 165 00:10:53,510 --> 00:10:55,000 I expect you to know what it is. 166 00:10:55,000 --> 00:10:58,590 If I say twelfth nerve, you should know what it is. 167 00:10:58,590 --> 00:11:01,930 Now you probably don't, but just start learning it, 168 00:11:01,930 --> 00:11:06,270 and over time, pretty much the numbers and the names 169 00:11:06,270 --> 00:11:08,370 mean the same thing to you. 170 00:11:08,370 --> 00:11:12,560 After all, you need to know the number and the name 171 00:11:12,560 --> 00:11:15,200 and a little bit about the function. 172 00:11:15,200 --> 00:11:16,980 [INAUDIBLE], sensory, or motor. 173 00:11:19,980 --> 00:11:23,560 So these placodes, so a little more about them. 174 00:11:23,560 --> 00:11:26,530 First of all, the dorsal lateral placodes 175 00:11:26,530 --> 00:11:28,155 include the trigeminal placode. 176 00:11:33,010 --> 00:11:35,080 There's two main portions, a thalmic 177 00:11:35,080 --> 00:11:37,060 and the [INAUDIBLE] mandibular portions. 178 00:11:37,060 --> 00:11:39,970 They give rise to the secondary sensory cells 179 00:11:39,970 --> 00:11:44,910 of the trigeminal ganglia, that make up 180 00:11:44,910 --> 00:11:49,165 the trigeminal, the axons of those cells, those neurons, 181 00:11:49,165 --> 00:11:54,030 give rise to trigeminal nerve, fifth cranial nerve. 182 00:11:59,250 --> 00:12:02,630 And then the otic placode, another one 183 00:12:02,630 --> 00:12:04,115 of the dorsal lateral placodes. 184 00:12:04,115 --> 00:12:09,130 They're named according to position in the embryo. 185 00:12:09,130 --> 00:12:12,865 That gives rise to vistibular and auditory segment 186 00:12:12,865 --> 00:12:16,500 of sensory cells, those ganglian cells that 187 00:12:16,500 --> 00:12:19,180 outside the central nervous system. 188 00:12:19,180 --> 00:12:21,907 And then, as I already mentioned, 189 00:12:21,907 --> 00:12:25,170 the olfactory placode gives rise to the olfactory [INAUDIBLE]. 190 00:12:25,170 --> 00:12:26,860 Remember, the primary sensory neurons 191 00:12:26,860 --> 00:12:29,640 are right in epithelial. 192 00:12:29,640 --> 00:12:32,430 That is a specialized region, [INAUDIBLE] 193 00:12:32,430 --> 00:12:37,770 region of the ectoderm that gives rise to them. 194 00:12:37,770 --> 00:12:40,840 There's also, I don't stress this, 195 00:12:40,840 --> 00:12:43,162 but there's an epibranchial, sometimes 196 00:12:43,162 --> 00:12:46,935 called epipharyngeal placode that gives rise 197 00:12:46,935 --> 00:12:51,030 to some of the ganglia cells of nerves seven, nine and 10, 198 00:12:51,030 --> 00:12:55,380 but those are more complicated because the neural crest also 199 00:12:55,380 --> 00:12:58,480 contributes to them. 200 00:12:58,480 --> 00:13:04,380 So let's talk about these cranial nerves. 201 00:13:04,380 --> 00:13:06,620 The 12 cranial nerves is actually 202 00:13:06,620 --> 00:13:09,650 not a full description at all. 203 00:13:09,650 --> 00:13:13,060 Even humans have more than that, especially in the embryo. 204 00:13:16,360 --> 00:13:19,150 So why is it so traditional to name just 12? 205 00:13:19,150 --> 00:13:22,310 It's because it is pretty adequate 206 00:13:22,310 --> 00:13:24,120 to describe the adult brain. 207 00:13:27,040 --> 00:13:30,050 There's a table in the Bulter and [INAUDIBLE] book 208 00:13:30,050 --> 00:13:32,616 that lists 25 different cranial nerves. 209 00:13:35,410 --> 00:13:38,020 Some of them are found only in certain groups of vertebrates. 210 00:13:38,020 --> 00:13:41,210 We've mentioned a few times here the lateral line 211 00:13:41,210 --> 00:13:45,150 nerves, there's up to six of them in animals, 212 00:13:45,150 --> 00:13:47,140 say with [INAUDIBLE] reception. 213 00:13:47,140 --> 00:13:52,130 There's also mechanical lateral line organs, 214 00:13:52,130 --> 00:13:53,055 mechanosensory organs. 215 00:13:55,750 --> 00:14:00,010 But most vertebrates don't have those. 216 00:14:00,010 --> 00:14:07,620 But some of our cranial nerves in mammals, the facial 217 00:14:07,620 --> 00:14:10,500 or the glassopharyngeal or the vagus nerve. 218 00:14:10,500 --> 00:14:13,310 There's actually two distinct parts. 219 00:14:13,310 --> 00:14:20,530 The nerve forms the fibers of those two components 220 00:14:20,530 --> 00:14:24,070 are together in many vertebrates and in humans. 221 00:14:28,630 --> 00:14:33,210 So the tradition is to name just 12 for human. 222 00:14:33,210 --> 00:14:34,920 We know they're very tiny nerves, 223 00:14:34,920 --> 00:14:37,283 but we don't know much about the function. 224 00:14:37,283 --> 00:14:41,480 It is certainly accounts for all of the things 225 00:14:41,480 --> 00:14:45,100 that are well known and well studied in the vertebrates. 226 00:14:45,100 --> 00:14:46,680 So we just learn 12. 227 00:14:49,790 --> 00:14:54,060 So let's take now a look at all the hindbrain 228 00:14:54,060 --> 00:15:05,010 of an adult mammal, and look at the locations of cell groups, 229 00:15:05,010 --> 00:15:07,890 look at those columns of secondary sensory neurons 230 00:15:07,890 --> 00:15:10,780 and motor neurons, and also where 231 00:15:10,780 --> 00:15:12,950 the axons are that are passing through. 232 00:15:19,542 --> 00:15:23,272 We're going to look at figure 10 [INAUDIBLE] in the book. 233 00:15:23,272 --> 00:15:28,616 It's a slice through the adult caudal hindbrain. 234 00:15:28,616 --> 00:15:29,990 That is the part of the hindbrain 235 00:15:29,990 --> 00:15:35,826 we call the medulla or medulla oblongata, the elongation 236 00:15:35,826 --> 00:15:39,130 of the spinal cord, not-- below the cerebellar 237 00:15:39,130 --> 00:15:42,910 region, the prompting region. 238 00:15:42,910 --> 00:15:45,370 First of all, what are the sensory modalities 239 00:15:45,370 --> 00:15:48,040 that you know about from that caudal hindbrain region? 240 00:15:52,117 --> 00:15:54,310 I mentioned them a number of times already. 241 00:15:54,310 --> 00:15:56,080 I've even mentioned them in this lecture. 242 00:15:59,470 --> 00:16:07,845 Auditory, vestibular, what about somatosensory? 243 00:16:07,845 --> 00:16:13,330 Of course, that's a hindbrain nerve, too, the trigeminal. 244 00:16:13,330 --> 00:16:15,340 That starts in the rostral hindbrain, 245 00:16:15,340 --> 00:16:18,956 but you still see it in the caudal hindbrain because 246 00:16:18,956 --> 00:16:23,500 of the very long descending nucleus of that system. 247 00:16:23,500 --> 00:16:27,300 And in addition, you have visceral sensory. 248 00:16:27,300 --> 00:16:30,057 And we include in that the taste sense. 249 00:16:30,057 --> 00:16:31,140 All of that's represented. 250 00:16:36,120 --> 00:16:37,890 I know you can answer this one. 251 00:16:40,590 --> 00:16:42,553 Which cranial nerves carry somatosensory input 252 00:16:42,553 --> 00:16:45,710 from the face into the brain? 253 00:16:45,710 --> 00:16:48,100 You should by now know the number 254 00:16:48,100 --> 00:16:50,760 and the name of that nerve. 255 00:16:50,760 --> 00:16:53,630 What is it? 256 00:16:53,630 --> 00:16:57,940 Trigeminal nerve, the fifth nerve, fifth nerve. 257 00:17:00,620 --> 00:17:02,790 Sp we want to look-- first of all, where 258 00:17:02,790 --> 00:17:06,810 are the primary sensory neurons, like every dorsal root, 259 00:17:06,810 --> 00:17:10,069 every cranial nerve, [INAUDIBLE] sensory fibers? 260 00:17:10,069 --> 00:17:13,290 The answer to this question is always the same. 261 00:17:13,290 --> 00:17:16,589 Where are the cell bodies? 262 00:17:16,589 --> 00:17:20,000 In a-- what's the word? 263 00:17:22,530 --> 00:17:30,520 Not nucleus, if you're outside the CNS, what's it called? 264 00:17:30,520 --> 00:17:32,520 A ganglion, right. 265 00:17:32,520 --> 00:17:36,845 So it's in the trigeminal ganglia. 266 00:17:36,845 --> 00:17:38,910 It's a big ganglion. 267 00:17:38,910 --> 00:17:42,240 It's on either side of the hypothalamus, 268 00:17:42,240 --> 00:17:45,660 but it has nothing to do with the hypothalamus. 269 00:17:45,660 --> 00:17:48,300 It just happens to be there at the base of the brain. 270 00:17:48,300 --> 00:17:52,140 That's because the nerves are coming in from the head region, 271 00:17:52,140 --> 00:17:56,610 from the face, and they're coming 272 00:17:56,610 --> 00:18:00,240 in under the [INAUDIBLE], and they 273 00:18:00,240 --> 00:18:02,060 enter the rostral part of the hindbrain. 274 00:18:02,060 --> 00:18:07,105 They actually penetrate through the rostral pontine region, 275 00:18:07,105 --> 00:18:07,980 below the cerebellum. 276 00:18:12,470 --> 00:18:15,400 So where are the secondary sensory neurons? 277 00:18:15,400 --> 00:18:21,690 Well, they're in the hindbrain, and they've 278 00:18:21,690 --> 00:18:29,508 got to be in this region here, in that column. 279 00:18:29,508 --> 00:18:33,450 So let's look now at the adult hindbrain here. 280 00:18:33,450 --> 00:18:37,130 This is where those trigeminal nerve cells are. 281 00:18:37,130 --> 00:18:41,090 We see them in that position every section of the hindbrain, 282 00:18:41,090 --> 00:18:47,010 in the rostral portion, where the cerebellum distorts 283 00:18:47,010 --> 00:18:48,275 the whole picture so much. 284 00:18:48,275 --> 00:18:51,730 And we'll take a look at that maybe in the class. 285 00:18:51,730 --> 00:18:58,750 And it just continues, because axons 286 00:18:58,750 --> 00:19:03,300 form follow this area right here. 287 00:19:03,300 --> 00:19:06,810 A lot of axons come in from the rostrum. 288 00:19:06,810 --> 00:19:11,950 You only see them penetrating varied [INAUDIBLE]. 289 00:19:11,950 --> 00:19:14,475 Sp this would have to be a section of the embryonic brain, 290 00:19:14,475 --> 00:19:17,068 to actually be coming in at this point. 291 00:19:22,810 --> 00:19:26,350 So what else can we ask there? 292 00:19:26,350 --> 00:19:27,530 We've already answered. 293 00:19:27,530 --> 00:19:31,410 Here's where you see the special senses coming in, vestibular, 294 00:19:31,410 --> 00:19:33,610 auditory. 295 00:19:33,610 --> 00:19:39,150 And that's exactly the position, at the very caudal end, 296 00:19:39,150 --> 00:19:40,900 when you're entering the spinal cord. 297 00:19:40,900 --> 00:19:43,910 That's where the dorsal column nuclei are. 298 00:19:43,910 --> 00:19:46,390 But the dorsal column nuclei are really 299 00:19:46,390 --> 00:19:49,820 in the very rostrum end of the spinal cord. 300 00:19:49,820 --> 00:19:52,660 Some people still call that hindbrain. 301 00:19:55,220 --> 00:19:59,560 Here's where the motor axons come out. 302 00:19:59,560 --> 00:20:02,680 So all the eye muscles are controlled 303 00:20:02,680 --> 00:20:06,060 by neurons like this. 304 00:20:06,060 --> 00:20:07,610 There's only one that doesn't exit 305 00:20:07,610 --> 00:20:13,215 that way, the fourth nerve, the trochlear nucleus, 306 00:20:13,215 --> 00:20:17,230 but otherwise, it's the same as all the others. 307 00:20:17,230 --> 00:20:21,990 And then the nuclei controlling the tongue, hypoglossal. 308 00:20:21,990 --> 00:20:26,720 So that's very much [INAUDIBLE] ventral view. 309 00:20:26,720 --> 00:20:32,640 But look at the axons now going through. 310 00:20:32,640 --> 00:20:35,050 I show them all here. 311 00:20:35,050 --> 00:20:38,480 The descending pathway's, here is 312 00:20:38,480 --> 00:20:43,090 the sort of pyramidal shape of the pyramidal tract coming 313 00:20:43,090 --> 00:20:46,150 from the cortex, corticospinal accents, 314 00:20:46,150 --> 00:20:48,800 pyramidal tract, right at the base. 315 00:20:48,800 --> 00:20:51,530 They always run on either outside 316 00:20:51,530 --> 00:20:53,290 when you're looking in at a sheep brain. 317 00:20:53,290 --> 00:20:57,730 If you turn it over and look at the ventral side, 318 00:20:57,730 --> 00:20:59,527 you'll see these grooves. 319 00:20:59,527 --> 00:21:01,110 They're little grooves on the midline. 320 00:21:01,110 --> 00:21:04,880 The basilar artery might be there 321 00:21:04,880 --> 00:21:06,130 if it hasn't been pulled away. 322 00:21:07,030 --> 00:21:09,681 But then you'll see a little bit of an indentation 323 00:21:09,681 --> 00:21:11,180 and the edge of the pyramidal tract. 324 00:21:11,180 --> 00:21:13,634 And this will have a slightly whitish appearance 325 00:21:13,634 --> 00:21:14,550 because of the myelin. 326 00:21:18,010 --> 00:21:21,400 And then right above it, you see the sensory fibers 327 00:21:21,400 --> 00:21:30,410 coming from the spinal cord and from the dorsal column nuclei. 328 00:21:30,410 --> 00:21:34,220 Dorsal column nuclei give rise to the medial lemniscus. 329 00:21:34,220 --> 00:21:36,980 So, if is this is the medial lemniscus here 330 00:21:36,980 --> 00:21:40,100 on the right side, where are the cells that 331 00:21:40,100 --> 00:21:43,810 give rise to those medial lemniscus stem cells? 332 00:21:43,810 --> 00:21:50,730 Remember, dorsal column, medial lemniscus, those two names 333 00:21:50,730 --> 00:21:53,160 should be starting to link in your mind. 334 00:21:53,160 --> 00:21:56,040 Dorsal column, medial lemniscus [INAUDIBLE]. 335 00:21:56,040 --> 00:21:57,935 So where would the cells be? 336 00:21:57,935 --> 00:22:00,110 They would be at the top of the spinal cord 337 00:22:00,110 --> 00:22:03,840 in the dorsal column nuclei, but on the other side 338 00:22:03,840 --> 00:22:05,690 because there's a [INAUDIBLE] the hindbrain. 339 00:22:08,816 --> 00:22:13,120 You drew that out in your homework. 340 00:22:15,970 --> 00:22:20,720 And then we have-- I drew the descending pathways on the left 341 00:22:20,720 --> 00:22:22,360 here. 342 00:22:22,360 --> 00:22:27,025 And I'm showing you where, for example, the tectospinal axons 343 00:22:27,025 --> 00:22:34,380 are, axons from the vestibular nucleus. 344 00:22:34,380 --> 00:22:38,820 I'll also follow those axons from the cerebellum. 345 00:22:38,820 --> 00:22:43,010 Now if you imagine that the brainstem is transparent, 346 00:22:43,010 --> 00:22:49,160 and you want to see where each of these groups of nuclei are, 347 00:22:49,160 --> 00:22:50,210 study this. 348 00:22:50,210 --> 00:22:57,970 And this, I used color coding to see them. 349 00:22:57,970 --> 00:23:01,600 So I've shown the sensory cell groups here. 350 00:23:01,600 --> 00:23:03,210 This figure is based on [INAUDIBLE]. 351 00:23:06,830 --> 00:23:11,070 And the motor group's on the left. 352 00:23:11,070 --> 00:23:14,760 So that's where you see the cochlear nuclei. 353 00:23:14,760 --> 00:23:20,080 And a little below the cochlear nucleus and a little more 354 00:23:20,080 --> 00:23:24,167 medial, you see the vestibular nuclei, fairly large nuclei. 355 00:23:24,167 --> 00:23:25,750 There's actually four separate nuclei. 356 00:23:25,750 --> 00:23:28,000 We just lump them together and call 357 00:23:28,000 --> 00:23:30,660 them the vestibular nuclei. 358 00:23:30,660 --> 00:23:34,040 Cochlear nuclei, there's two main-- two or three depending 359 00:23:34,040 --> 00:23:36,660 on how you divide it up. 360 00:23:36,660 --> 00:23:40,290 We just call them the cochlear nuclei here. 361 00:23:40,290 --> 00:23:45,635 And then trigeminal-- see there is the principal nucleus. 362 00:23:45,635 --> 00:23:49,870 But here's the axons that come in way up here. 363 00:23:49,870 --> 00:23:54,532 They keep going all the way down into the top 364 00:23:54,532 --> 00:23:56,840 of the spinal cord. 365 00:23:56,840 --> 00:24:00,660 They go a little further than this picture shows. 366 00:24:00,660 --> 00:24:03,670 That's all secondary sensory cells 367 00:24:03,670 --> 00:24:06,630 representing inputs coming at the face. 368 00:24:06,630 --> 00:24:10,330 And then, and what is the remaining one? 369 00:24:10,330 --> 00:24:12,050 Well, it's a red color. 370 00:24:12,050 --> 00:24:17,110 It's got to be this'll visceral [INAUDIBLE]. 371 00:24:17,110 --> 00:24:21,120 It has a particular name because of its appearance 372 00:24:21,120 --> 00:24:23,020 in [INAUDIBLE]. 373 00:24:23,020 --> 00:24:27,920 It's called the nucleus of the solitary tract. 374 00:24:27,920 --> 00:24:31,040 Because the tract that does standout, even in [INAUDIBLE] 375 00:24:31,040 --> 00:24:32,030 can be seen. 376 00:24:32,030 --> 00:24:37,070 Right next to it, solitary tract. 377 00:24:37,070 --> 00:24:42,050 Many taste fibers in that track as well as 378 00:24:42,050 --> 00:24:44,460 visceral sensory fibers coming in from cranial nerves, 379 00:24:44,460 --> 00:24:50,300 cranial nerve 10, primarily but also from seven and nine. 380 00:24:50,300 --> 00:24:53,580 And then the various motor neuron groups are shown here. 381 00:24:56,780 --> 00:24:59,300 It includes some that weren't in the other picture 382 00:24:59,300 --> 00:25:01,405 because they're very small nuclei. 383 00:25:01,405 --> 00:25:05,360 They're part of that visceral motor cell group 384 00:25:05,360 --> 00:25:07,900 column that controls salivation. 385 00:25:12,910 --> 00:25:19,380 Now those kinds of figures, this one and this one, 386 00:25:19,380 --> 00:25:21,070 don't memorize them. 387 00:25:21,070 --> 00:25:25,580 Use them for reference if you forget, and you're 388 00:25:25,580 --> 00:25:27,550 reading something about these nuclei, 389 00:25:27,550 --> 00:25:32,430 you want to remember where they were, look back at chapter 10 390 00:25:32,430 --> 00:25:34,070 and look up where they are. 391 00:25:34,070 --> 00:25:36,800 And notice, they go all the way up in to the midbrain. 392 00:25:39,610 --> 00:25:43,907 I mentioned that one in red there, the [INAUDIBLE] nucleus. 393 00:25:43,907 --> 00:25:44,990 Remember what it controls? 394 00:25:48,250 --> 00:25:49,765 The pupils, pupillary cells. 395 00:25:52,340 --> 00:25:57,330 Not the blink of the eye, but just the pupils 396 00:25:57,330 --> 00:26:00,180 of the eye, the iris. 397 00:26:00,180 --> 00:26:04,472 And then the oculomotor nuclei, the third and fourth, and then 398 00:26:04,472 --> 00:26:08,036 one more down here, the sixth, controlling 399 00:26:08,036 --> 00:26:09,577 different directions of eye movement. 400 00:26:13,330 --> 00:26:23,500 So we want to look more at these trigeminal nuclei. 401 00:26:23,500 --> 00:26:27,180 But I want to say a little-- go back 402 00:26:27,180 --> 00:26:30,620 to this topic about the evolution of the system. 403 00:26:30,620 --> 00:26:33,785 Because these pathways really terminated 404 00:26:33,785 --> 00:26:36,625 with pretty important factors that 405 00:26:36,625 --> 00:26:40,978 influenced the evolution of the hindbrain and also more rostral 406 00:26:40,978 --> 00:26:41,478 structures. 407 00:26:46,124 --> 00:26:47,790 So first of all, where's the information 408 00:26:47,790 --> 00:26:51,040 go when it comes in the trigeminal nerve? 409 00:26:51,040 --> 00:26:54,220 There should be local reflexes. 410 00:26:54,220 --> 00:26:56,050 I just mentioned eye blink. 411 00:26:56,050 --> 00:26:59,260 That' a reflex that depends on input 412 00:26:59,260 --> 00:27:03,760 coming in to the trigeminal nerve. 413 00:27:03,760 --> 00:27:06,780 It could come from the cornea, from there, 414 00:27:06,780 --> 00:27:08,260 it will cause an eye blink. 415 00:27:08,260 --> 00:27:10,570 It could be a touch of the eyelashes 416 00:27:10,570 --> 00:27:13,140 or a touch of the face. 417 00:27:13,140 --> 00:27:15,115 But it also could just be visual input. 418 00:27:19,850 --> 00:27:23,560 We're concerned with this somatosensory input. 419 00:27:23,560 --> 00:27:26,470 There's got to be a pathway for the eye blink, so look at that. 420 00:27:30,250 --> 00:27:31,890 I mentioned that it could be considered 421 00:27:31,890 --> 00:27:33,786 a [INAUDIBLE] pattern. 422 00:27:33,786 --> 00:27:36,890 There's actually a drive associated with it. 423 00:27:36,890 --> 00:27:38,420 You blink your eyes periodically. 424 00:27:38,420 --> 00:27:42,190 It's very important in keeping the cornea lubricated. 425 00:27:42,190 --> 00:27:44,350 And then we have the lemniscal pathways. 426 00:27:44,350 --> 00:27:46,920 Remember the lemniscal pathways in the spinal cord. 427 00:27:50,670 --> 00:27:55,990 There was a spinoreticular pathway. 428 00:27:55,990 --> 00:27:59,950 There were spinal [INAUDIBLE] tract, 429 00:27:59,950 --> 00:28:02,960 and then the dorsal column the the lemniscus system. 430 00:28:02,960 --> 00:28:06,150 There must equivalent systems here for the trigeminal system. 431 00:28:09,040 --> 00:28:12,790 But first, let's go through this hypothesis, the [INAUDIBLE] 432 00:28:12,790 --> 00:28:15,900 of the axons to the midbrain and forebrain evolved 433 00:28:15,900 --> 00:28:21,050 with or after the evolution of the cross retinal projection 434 00:28:21,050 --> 00:28:23,750 to the tween brain and midbrain, and that 435 00:28:23,750 --> 00:28:28,040 led to cross projections in the trigeminal system as well, 436 00:28:28,040 --> 00:28:31,770 and even the auditory system has been affected by that. 437 00:28:31,770 --> 00:28:33,965 So, in fact, the entire midbrain and forebrain 438 00:28:33,965 --> 00:28:38,420 in the sensory world is represented side opposite 439 00:28:38,420 --> 00:28:40,330 to where brain representation is, 440 00:28:40,330 --> 00:28:42,410 but not in the hindbrain and spinal cord. 441 00:28:46,410 --> 00:28:49,920 So what is the most ancient descending pathway 442 00:28:49,920 --> 00:28:53,350 from secondary sensory neurons to the trigeminal system? 443 00:28:53,350 --> 00:28:54,350 What did I just call it? 444 00:28:59,050 --> 00:29:01,450 What was the oldest one from the spinal cord? 445 00:29:05,870 --> 00:29:07,265 Can you say it louder than that? 446 00:29:07,265 --> 00:29:09,390 AUDIENCE: [INAUDIBLE]. 447 00:29:09,390 --> 00:29:10,587 PROFESSOR: Spinal reticular. 448 00:29:10,587 --> 00:29:12,420 So what do we call it here in the hindbrain? 449 00:29:15,765 --> 00:29:16,640 Trigeminal reticular. 450 00:29:20,710 --> 00:29:23,720 And then you should be able to at least give 451 00:29:23,720 --> 00:29:29,700 a quick description of the hypothesis for how 452 00:29:29,700 --> 00:29:33,210 somatosensory and [INAUDIBLE] pathways 453 00:29:33,210 --> 00:29:36,260 evolved to become predominantly crossed. 454 00:29:36,260 --> 00:29:41,310 The simplest possible way the hypothesis 455 00:29:41,310 --> 00:29:48,049 is that it was to increase the speed of the escape movements. 456 00:29:48,049 --> 00:29:50,090 So let's go through that in a little more detail. 457 00:29:50,090 --> 00:29:52,920 First of all, in these little diagrams, 458 00:29:52,920 --> 00:29:58,420 I've sketched spinal reticular and trigeminal reticular 459 00:29:58,420 --> 00:29:59,770 pathways. 460 00:29:59,770 --> 00:30:04,750 Mostly it's lateral pathways, but a few axons, spinal 461 00:30:04,750 --> 00:30:08,140 and even brain levels have reached the other side. 462 00:30:08,140 --> 00:30:10,640 And then, here, I show the same. 463 00:30:10,640 --> 00:30:16,150 I leave the spinal reticular and I add to it, 464 00:30:16,150 --> 00:30:20,780 here in black, the trigeminal reticular, 465 00:30:20,780 --> 00:30:22,320 axons that [INAUDIBLE] this. 466 00:30:23,477 --> 00:30:25,060 [INAUDIBLE] the very caudal forebrain. 467 00:30:25,060 --> 00:30:27,590 I don't show that here because there's so few of them. 468 00:30:27,590 --> 00:30:32,330 But I show them mainly in the midbrain and hindbrain, going 469 00:30:32,330 --> 00:30:34,761 into the reticular formation, and a few of the axons 470 00:30:34,761 --> 00:30:35,760 going to the other side. 471 00:30:39,140 --> 00:30:43,107 That's all you have in the most primitive vertebrates. 472 00:30:47,200 --> 00:30:48,580 That's the somatosensory pathway. 473 00:30:48,580 --> 00:30:51,040 There 474 00:30:51,040 --> 00:30:54,430 In all the more advanced creatures 475 00:30:54,430 --> 00:30:59,290 you end up with these crossed pathways. 476 00:30:59,290 --> 00:31:02,130 I just have a few drawings to illustrate that. 477 00:31:02,130 --> 00:31:04,270 We'll start with this one. 478 00:31:04,270 --> 00:31:08,480 These are the basis for those figures. 479 00:31:08,480 --> 00:31:10,830 So what I'm showing here is, first of all, here's 480 00:31:10,830 --> 00:31:12,730 the trigeminal input. 481 00:31:12,730 --> 00:31:15,880 And here I show spinal reticular pathways and note, 482 00:31:15,880 --> 00:31:17,990 a few of them are getting to the other side. 483 00:31:17,990 --> 00:31:20,880 Most of them are [INAUDIBLE]. 484 00:31:20,880 --> 00:31:22,880 Here's the retinal, primitive retinal input, 485 00:31:22,880 --> 00:31:27,630 the most ancient pathway, coming into the hypothalamus. 486 00:31:27,630 --> 00:31:31,360 And even in modern mammals, that pathway 487 00:31:31,360 --> 00:31:36,400 goes pretty much equal to the two sides. 488 00:31:36,400 --> 00:31:39,050 In the hamster where I've studied it 489 00:31:39,050 --> 00:31:41,050 with several different methods, I 490 00:31:41,050 --> 00:31:43,640 can't discriminate the quantity in the two sides. 491 00:31:43,640 --> 00:31:46,980 It's a bilateral projection. 492 00:31:46,980 --> 00:31:50,495 It's a little nucleus and it sits above the optic chiasm. 493 00:31:50,495 --> 00:31:54,910 And the fibers go mainly to the suprachiasmatic nucleus, 494 00:31:54,910 --> 00:31:58,510 but they also spread outside it and go to the adjacent areas. 495 00:32:01,115 --> 00:32:04,395 So the question is, why with further evolution, 496 00:32:04,395 --> 00:32:06,630 do they end up mainly crossed? 497 00:32:10,970 --> 00:32:14,010 Here's what the animal had to do if it's 498 00:32:14,010 --> 00:32:16,687 going to get away from something coming here 499 00:32:16,687 --> 00:32:17,520 from the right side. 500 00:32:17,520 --> 00:32:21,160 It causes a shadow affecting the lateral eye. 501 00:32:21,160 --> 00:32:27,690 It could be touching the animal or causing water currents. 502 00:32:27,690 --> 00:32:30,880 So you get a trigeminal as visual input. 503 00:32:30,880 --> 00:32:36,530 What we want to do is turn away and swim like hell. 504 00:32:36,530 --> 00:32:40,250 OK The turning away was critical, 505 00:32:40,250 --> 00:32:43,420 and people have generally ignored this in studying it. 506 00:32:43,420 --> 00:32:45,935 They studied the, what they call a startle response 507 00:32:45,935 --> 00:32:50,080 or rapid swimming, but they forget 508 00:32:50,080 --> 00:32:52,960 they don't want to swim right towards the attacking animal. 509 00:32:52,960 --> 00:32:54,670 They want to turn. 510 00:32:54,670 --> 00:32:57,480 So I think the speed of that was very important. 511 00:32:57,480 --> 00:32:59,490 That's my own hypothesis. 512 00:32:59,490 --> 00:33:03,445 So the result was, to get turning, 513 00:33:03,445 --> 00:33:06,280 you need to contract muscles on the left 514 00:33:06,280 --> 00:33:09,459 for input coming into the right. 515 00:33:09,459 --> 00:33:11,500 So you've got to reach motor neurons on the left. 516 00:33:15,950 --> 00:33:18,510 And if you're doing that with forebrain input, put 517 00:33:18,510 --> 00:33:20,220 in the case of the visual system, 518 00:33:20,220 --> 00:33:24,229 there were no long pathways going all the way 519 00:33:24,229 --> 00:33:26,020 down the spinal cord or even the hindbrain. 520 00:33:26,020 --> 00:33:29,430 They did [INAUDIBLE] in the midbrain. 521 00:33:29,430 --> 00:33:32,870 They went directly to hindbrain and spinal cord. 522 00:33:32,870 --> 00:33:35,680 So that I'm showing in red. 523 00:33:35,680 --> 00:33:40,520 So the most rapid pathway to get there was a cross pathway. 524 00:33:44,040 --> 00:33:47,210 Even saving a very small fraction of a second 525 00:33:47,210 --> 00:33:50,607 can make the difference between living and dying. 526 00:33:50,607 --> 00:33:51,107 Yes? 527 00:33:51,107 --> 00:33:52,023 AUDIENCE: [INAUDIBLE]? 528 00:33:58,100 --> 00:34:00,610 PROFESSOR: There are. 529 00:34:00,610 --> 00:34:05,070 Again, for hindbrain and spinal cord, they don't cross. 530 00:34:08,190 --> 00:34:10,380 And what's critical here is what's 531 00:34:10,380 --> 00:34:12,690 in the hindbrain and the spinal cord. 532 00:34:12,690 --> 00:34:16,370 So the midbrain pathway that reaches those, is uncrossed. 533 00:34:20,489 --> 00:34:23,239 And that's very clear, even in modern mammals. 534 00:34:23,239 --> 00:34:26,449 So this is the behavior. 535 00:34:26,449 --> 00:34:29,110 These are the pathways that had to evolve 536 00:34:29,110 --> 00:34:31,710 ti get that very rapid response. 537 00:34:31,710 --> 00:34:34,860 The question is then, how did that evolve afterwards? 538 00:34:34,860 --> 00:34:39,130 And I'll just go through that quickly here. 539 00:34:44,440 --> 00:34:58,920 We know-- this just says what I've already gone through. 540 00:34:58,920 --> 00:35:01,410 We know that the projections of the midbrain surface 541 00:35:01,410 --> 00:35:04,460 became typographically organized. 542 00:35:04,460 --> 00:35:10,270 With topographic input, first of all, 543 00:35:10,270 --> 00:35:13,830 it could add a little bit of directionality 544 00:35:13,830 --> 00:35:15,160 to that escape response. 545 00:35:15,160 --> 00:35:18,085 I'm not sure just how important that would have been. 546 00:35:18,085 --> 00:35:20,220 But one thing's very clear, that once you 547 00:35:20,220 --> 00:35:22,480 have a topographic projection, it become useful 548 00:35:22,480 --> 00:35:26,840 for a lot of things besides just rapid escape. 549 00:35:26,840 --> 00:35:29,620 When you look at escape responses in animals, 550 00:35:29,620 --> 00:35:35,390 the direction they turn in doesn't differ that much. 551 00:35:35,390 --> 00:35:42,000 It generally is away from the animal, 552 00:35:42,000 --> 00:35:44,050 but it doesn't vary that much. 553 00:35:44,050 --> 00:35:47,329 But if you want to find food, turn 554 00:35:47,329 --> 00:35:48,870 toward something that's not dangerous 555 00:35:48,870 --> 00:35:51,840 or [INAUDIBLE] approach another fish. 556 00:35:51,840 --> 00:35:55,240 Then, of course, the topography becomes critical. 557 00:35:55,240 --> 00:35:59,220 And for that, again, the most efficient 558 00:35:59,220 --> 00:36:04,590 was you've got to contract the muscles on the opposite side. 559 00:36:04,590 --> 00:36:07,180 Instead of doing this, you want to orient towards something 560 00:36:07,180 --> 00:36:09,260 if it's not dangerous. 561 00:36:09,260 --> 00:36:13,230 You're going to have to contract the muscles on the other side. 562 00:36:13,230 --> 00:36:15,270 So that led to the evolution. 563 00:36:15,270 --> 00:36:17,940 This is from our earlier class where 564 00:36:17,940 --> 00:36:21,080 I show the input to the surface in midbrain. 565 00:36:21,080 --> 00:36:23,500 Here is the ipsilateral descending 566 00:36:23,500 --> 00:36:26,400 pathway, controlling locomotion. 567 00:36:26,400 --> 00:36:31,020 Here, then, is the cross pathway controlling turning 568 00:36:31,020 --> 00:36:33,150 [INAUDIBLE]. 569 00:36:33,150 --> 00:36:35,840 That's the tectospinal [INAUDIBLE]. 570 00:36:35,840 --> 00:36:38,280 It only reaches the rostrum-most part 571 00:36:38,280 --> 00:36:44,915 of of the spinal cord in the animals that I know about 572 00:36:44,915 --> 00:36:48,760 and it's been studied a number of different animals. 573 00:36:48,760 --> 00:36:52,120 So you end up with a cross pathway from the tectum 574 00:36:52,120 --> 00:36:56,174 and an uncrossed pathway with very different functions. 575 00:36:59,850 --> 00:37:05,730 And once this visual pathway became crossed, 576 00:37:05,730 --> 00:37:10,170 the somatosensory pathways and even auditory 577 00:37:10,170 --> 00:37:14,440 that also gave information about the space around the head, 578 00:37:14,440 --> 00:37:15,550 had to match it. 579 00:37:15,550 --> 00:37:19,585 Otherwise, there was a mismatch between somatosensory and 580 00:37:19,585 --> 00:37:22,740 visual, and between auditory and visual. 581 00:37:22,740 --> 00:37:24,966 And that's exactly what happened in evolution. 582 00:37:28,090 --> 00:37:32,350 And that is how all the senses, midbrain and forebrain, 583 00:37:32,350 --> 00:37:37,044 became represented on the opposite side. 584 00:37:37,044 --> 00:37:37,960 AUDIENCE: [INAUDIBLE]? 585 00:37:45,140 --> 00:37:48,330 PROFESSOR: Yes, it is. 586 00:37:48,330 --> 00:37:52,980 So that is simply arguing for the importance of visual system 587 00:37:52,980 --> 00:37:54,150 very clearly. 588 00:37:54,150 --> 00:37:57,695 There is some variation when we look across species, 589 00:37:57,695 --> 00:38:01,810 that some species have projections 590 00:38:01,810 --> 00:38:04,380 that are more bilateral in the forebrain. 591 00:38:04,380 --> 00:38:06,635 But they're more specialized species. 592 00:38:06,635 --> 00:38:10,100 I'm talking about sort of the main line that 593 00:38:10,100 --> 00:38:11,986 led to modern mammals. 594 00:38:11,986 --> 00:38:13,740 But there is some variation. 595 00:38:13,740 --> 00:38:17,420 And I don't know of any review that's gone through. 596 00:38:17,420 --> 00:38:19,470 I know individual studies that show 597 00:38:19,470 --> 00:38:22,140 some of these odd pathways. 598 00:38:22,140 --> 00:38:25,990 But most of the vertebrates have the kind 599 00:38:25,990 --> 00:38:28,176 of pathways I'm talking about. 600 00:38:28,176 --> 00:38:33,250 In the very ancient ones, this is what you have. 601 00:38:33,250 --> 00:38:34,935 Well, the most ancient ones don't even 602 00:38:34,935 --> 00:38:43,190 have spinal [INAUDIBLE] tract crossed yet. 603 00:38:43,190 --> 00:38:46,270 They just have spinal reticular. 604 00:38:46,270 --> 00:38:49,200 There's a lot more study that could be done, especially 605 00:38:49,200 --> 00:38:54,600 on those primitive animals, to look for more evidence of this. 606 00:38:54,600 --> 00:38:58,030 And animals like amphioxus, you don't see any. 607 00:38:58,030 --> 00:38:58,986 We don't know much. 608 00:38:58,986 --> 00:39:00,737 There's just little pigmented areas. 609 00:39:00,737 --> 00:39:03,880 They would respond to shadows. 610 00:39:03,880 --> 00:39:06,650 There were animals after amphioxus, 611 00:39:06,650 --> 00:39:11,106 before the hagfish and the sea lampreys though, 612 00:39:11,106 --> 00:39:13,920 but we only have fossil records. 613 00:39:13,920 --> 00:39:23,560 [INAUDIBLE] did appear long, long before the hagfish 614 00:39:23,560 --> 00:39:26,230 and lampreys. 615 00:39:26,230 --> 00:39:29,200 AUDIENCE: [INAUDIBLE]? 616 00:39:29,200 --> 00:39:31,048 PROFESSOR: You have to talk louder. 617 00:39:31,048 --> 00:39:31,964 AUDIENCE: [INAUDIBLE]? 618 00:39:38,779 --> 00:39:40,362 PROFESSOR: Good question. [INAUDIBLE]. 619 00:39:44,420 --> 00:39:49,430 Let's see what else. 620 00:39:49,430 --> 00:39:53,870 I want to say a little more about the trigeminal system. 621 00:39:53,870 --> 00:39:57,264 In this picture, I'm showing where they are in the embryo. 622 00:39:57,264 --> 00:39:59,180 And then here they are in the hindbrain again. 623 00:40:03,940 --> 00:40:08,850 And here, I've just shown the trigeminal, 624 00:40:08,850 --> 00:40:10,840 left the others out . 625 00:40:10,840 --> 00:40:13,280 But I've included the facial motor nucleus 626 00:40:13,280 --> 00:40:16,510 because I want to show the simplest pathways for the eye 627 00:40:16,510 --> 00:40:22,520 blink, going directly from interneurons here 628 00:40:22,520 --> 00:40:28,370 in the trigeminal nucleus, going to either, by way 629 00:40:28,370 --> 00:40:32,560 of interneurons, or to this neuron 630 00:40:32,560 --> 00:40:36,550 directly to the facial motor nucleus, causing the eye blink. 631 00:40:36,550 --> 00:40:38,212 I assume that some of the pathways 632 00:40:38,212 --> 00:40:41,200 are probably direct because it's very important functionally 633 00:40:41,200 --> 00:40:42,940 for that to be a rapid movement. 634 00:40:45,680 --> 00:40:47,830 It's a little bit like the escape response. 635 00:40:47,830 --> 00:40:49,130 It's protective. 636 00:40:49,130 --> 00:40:53,330 It's preserving the eyes, so it's very rapid. 637 00:40:56,240 --> 00:40:59,080 Now I want you to be able to contrast the trigeminal nerve 638 00:40:59,080 --> 00:41:03,120 and the trigeminal lemniscus. 639 00:41:03,120 --> 00:41:08,810 Think of the meaning of each of those terms, trigeminal nerve, 640 00:41:08,810 --> 00:41:11,315 primary sensory cell axons. 641 00:41:15,840 --> 00:41:18,940 These are the axons themselves in trigeminal ganglia. 642 00:41:18,940 --> 00:41:20,700 Then what is the trigeminal lemniscus? 643 00:41:24,950 --> 00:41:30,800 What is the secondary sensory axons, exactly. 644 00:41:30,800 --> 00:41:33,250 Just like from the spinal cord. 645 00:41:33,250 --> 00:41:36,230 But now we're talking about pathways 646 00:41:36,230 --> 00:41:38,390 that originate in the hindbrain. 647 00:41:38,390 --> 00:41:40,780 This looks complicated only because I 648 00:41:40,780 --> 00:41:43,400 added some other nuclei here and a bunch of words. 649 00:41:43,400 --> 00:41:47,040 But I can very simply show you what I'm talking about. 650 00:41:47,040 --> 00:41:49,350 Here's the trigeminal ganglion, sitting, 651 00:41:49,350 --> 00:41:54,050 remember, below the brain in humans. 652 00:41:54,050 --> 00:41:58,500 Here's its three branches, opthalmic, maxillary, 653 00:41:58,500 --> 00:42:01,010 and mandibular branches of trigeminal nerve. 654 00:42:03,580 --> 00:42:05,820 There the cell bodies are in that ganglion. 655 00:42:05,820 --> 00:42:09,380 And here the axon comes in and terminates 656 00:42:09,380 --> 00:42:10,880 in the trigeminal nuclei. 657 00:42:10,880 --> 00:42:15,170 Sometimes it's called the brainstem trigeminal complex. 658 00:42:15,170 --> 00:42:20,050 They're just secondary sensory cells of the trigeminal nuclei. 659 00:42:20,050 --> 00:42:23,623 principal nucleus at the top and then the descending nucleus. 660 00:42:23,623 --> 00:42:25,517 They're all getting direct input from 661 00:42:25,517 --> 00:42:27,110 those primary sensory axons. 662 00:42:27,110 --> 00:42:33,250 Now the cells here, they're not performing reflex, 663 00:42:33,250 --> 00:42:36,225 like that eye blink reflex, they may 664 00:42:36,225 --> 00:42:39,480 be sending an axon across the midline 665 00:42:39,480 --> 00:42:44,440 and descending in the lemniscus. 666 00:42:44,440 --> 00:42:46,990 That's the trigeminal lemniscus. 667 00:42:46,990 --> 00:42:50,620 We can't separate the spinal, [INAUDIBLE] in the spinal cord, 668 00:42:50,620 --> 00:42:53,290 we had the spinal [INAUDIBLE] in the dorsal column [INAUDIBLE] 669 00:42:53,290 --> 00:42:54,260 lemniscus. 670 00:42:54,260 --> 00:42:57,180 There are axons in different sides. 671 00:42:57,180 --> 00:42:59,280 Obviously, the ones from come up here 672 00:42:59,280 --> 00:43:03,031 are going to reach this [INAUDIBLE] cortex a lot more 673 00:43:03,031 --> 00:43:03,530 rapidly. 674 00:43:03,530 --> 00:43:06,416 They're more like the dorsal column system 675 00:43:06,416 --> 00:43:08,970 and meet in the medial lemniscus. 676 00:43:08,970 --> 00:43:12,115 Whereas the ones down here, including pain input, 677 00:43:12,115 --> 00:43:16,110 that goes down into the spinal cord. 678 00:43:16,110 --> 00:43:18,440 Those pathways to the brain are slower, more 679 00:43:18,440 --> 00:43:20,850 like the spinothalamic tract. 680 00:43:20,850 --> 00:43:24,485 But they're all called the trigeminal lemniscus. 681 00:43:24,485 --> 00:43:25,960 You can see them. 682 00:43:25,960 --> 00:43:29,230 They simply join the medial lemniscus 683 00:43:29,230 --> 00:43:32,190 and the spinothalamic tract axon as they 684 00:43:32,190 --> 00:43:35,735 cross there through the midbrain into the caudal thalamus 685 00:43:35,735 --> 00:43:38,680 terminate in the ventral posterior nucleus, 686 00:43:38,680 --> 00:43:42,572 where the cells then project the [INAUDIBLE] somatosensory 687 00:43:42,572 --> 00:43:46,392 cortex, very much like the spinal cord. 688 00:43:49,230 --> 00:43:50,960 I'm leaving out the spinal reticular 689 00:43:50,960 --> 00:43:55,430 here, just showing these more recently evolved pathways that 690 00:43:55,430 --> 00:44:00,164 are so important in getting to the forebrain. 691 00:44:00,164 --> 00:44:02,580 And I already mentioned this is where the pain in the foot 692 00:44:02,580 --> 00:44:04,840 goes. 693 00:44:04,840 --> 00:44:08,176 And this enlarges a little bit. 694 00:44:08,176 --> 00:44:11,650 Here you see the crossing. 695 00:44:11,650 --> 00:44:15,050 These are trigeminal [INAUDIBLE] axons. 696 00:44:15,050 --> 00:44:18,850 Notice here in the ventral basal or ventral posterior nucleus, 697 00:44:18,850 --> 00:44:22,210 those two names mean the something thing. 698 00:44:22,210 --> 00:44:25,120 I'm showing green here. 699 00:44:25,120 --> 00:44:28,350 I omit the lateral most part. 700 00:44:28,350 --> 00:44:30,390 Why? 701 00:44:30,390 --> 00:44:33,430 Because the ventral posterior nucleus gets input 702 00:44:33,430 --> 00:44:38,470 from the body surface, too, from the spinal cord. 703 00:44:38,470 --> 00:44:40,280 This one goes out here. 704 00:44:40,280 --> 00:44:44,510 The body is topographically represented in that nucleus. 705 00:44:44,510 --> 00:44:48,480 Caudal parts of the body are here, the more medial parts 706 00:44:48,480 --> 00:44:52,860 here, the very medial most is input from the tongue 707 00:44:52,860 --> 00:44:58,110 and is the taste area there, the most medial part 708 00:44:58,110 --> 00:45:01,230 of that nucleus. 709 00:45:01,230 --> 00:45:06,690 And I describe there what you're seeing at each level. 710 00:45:06,690 --> 00:45:09,680 We talked about [INAUDIBLE] I just mentioned here 711 00:45:09,680 --> 00:45:12,510 the masticatory nucleus of feeding. 712 00:45:12,510 --> 00:45:15,650 And we talk about these specializations 713 00:45:15,650 --> 00:45:20,190 before, except this one I didn't have the picture. 714 00:45:20,190 --> 00:45:23,870 Amy mentioned this star nosed mole. 715 00:45:23,870 --> 00:45:27,800 And notice, here's that specialized organ. 716 00:45:27,800 --> 00:45:30,182 But here is proportionally how it's 717 00:45:30,182 --> 00:45:31,390 represented in the neocortex. 718 00:45:33,930 --> 00:45:37,870 All this is, is the [INAUDIBLE]. 719 00:45:37,870 --> 00:45:40,690 If they distort the picture according 720 00:45:40,690 --> 00:45:44,580 to how much brain is taken up by representing-- 721 00:45:47,953 --> 00:45:48,869 AUDIENCE: [INAUDIBLE]. 722 00:46:14,350 --> 00:46:17,915 PROFESSOR: I didn't actually plan 723 00:46:17,915 --> 00:46:21,320 to copy the figure from the paper, the most recent paper 724 00:46:21,320 --> 00:46:23,815 that mapped this [INAUDIBLE] cortex. 725 00:46:23,815 --> 00:46:25,740 That was done by John [INAUDIBLE]. 726 00:46:25,740 --> 00:46:31,260 Amy found the paper, but I didn't pull the figure out yet. 727 00:46:31,260 --> 00:46:35,250 And then, the trigeminal system representing whiskers-- 728 00:46:35,250 --> 00:46:37,510 so here it shows the face. 729 00:46:37,510 --> 00:46:41,150 And then it shows the barrel fields in cortex. 730 00:46:41,150 --> 00:46:43,160 But here they are in the thalamus. 731 00:46:43,160 --> 00:46:44,350 We don't call them barrels. 732 00:46:44,350 --> 00:46:46,250 We call them barelliods. 733 00:46:46,250 --> 00:46:49,700 And down in the brainstem, you call them barrelettes. 734 00:46:49,700 --> 00:46:55,640 Just cute names to represent the fact that you can actually 735 00:46:55,640 --> 00:46:58,580 see these little clumps of cells for each whisker 736 00:46:58,580 --> 00:47:03,360 in the hindbrain, in the thalamus, and in the cortex. 737 00:47:03,360 --> 00:47:04,880 We've seen this in the cortex. 738 00:47:04,880 --> 00:47:07,125 I wanted to show you a few more of the axons. 739 00:47:07,125 --> 00:47:10,965 This is from a frontal section, where each little puff of axons 740 00:47:10,965 --> 00:47:15,380 there labeled with [INAUDIBLE], It which 741 00:47:15,380 --> 00:47:18,320 diffuses through the axons even in a fixed brain. 742 00:47:18,320 --> 00:47:24,040 And you can see the little puffs, one puff per whisker. 743 00:47:24,040 --> 00:47:25,950 And here they are cut tangentially. 744 00:47:25,950 --> 00:47:27,730 We see the axons, the barrels. 745 00:47:27,730 --> 00:47:32,940 The cells will be mainly in the dark areas there. 746 00:47:32,940 --> 00:47:35,200 Here they are in acetylcholinesterase, 747 00:47:35,200 --> 00:47:37,292 and here they are in cytochrome c. 748 00:47:37,292 --> 00:47:39,500 You just keep seeing them with these various methods. 749 00:47:44,510 --> 00:47:48,830 And then we talked about distortions. 750 00:47:48,830 --> 00:47:50,500 Why don't we do the distortions. 751 00:47:50,500 --> 00:47:53,090 We've already seen these. 752 00:47:53,090 --> 00:47:56,790 But I want to talk about the distortions 753 00:47:56,790 --> 00:48:00,217 from the incredible development of the cerebellum, which 754 00:48:00,217 --> 00:48:02,980 is particularly prominent in animals 755 00:48:02,980 --> 00:48:06,860 with [INAUDIBLE], manual dexterity, 756 00:48:06,860 --> 00:48:10,750 dexterity of other body movements. 757 00:48:10,750 --> 00:48:13,390 So we'll look at it for human and go 758 00:48:13,390 --> 00:48:14,557 through some of these terms. 759 00:48:14,557 --> 00:48:15,973 So we're going to end right there, 760 00:48:15,973 --> 00:48:18,050 and we'll come right back here next time.