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 00:00:22,805 --> 00:00:23,680 PROFESSOR: All right. 9 00:00:23,680 --> 00:00:27,830 Listen, I didn't much like the way 10 00:00:27,830 --> 00:00:30,010 things went in the last class. 11 00:00:30,010 --> 00:00:36,530 And the reason, it's because of the way I had planned it. 12 00:00:36,530 --> 00:00:42,070 By having a quiz not on the chapter we're 13 00:00:42,070 --> 00:00:45,420 covering in a day, you're always going 14 00:00:45,420 --> 00:00:47,560 to spend your time reviewing for the quiz, 15 00:00:47,560 --> 00:00:50,960 and you're not going to read-- or at least, 16 00:00:50,960 --> 00:00:53,280 you won't all read the chapter for today. 17 00:00:53,280 --> 00:00:56,540 So it's not a very good way to do it. 18 00:00:56,540 --> 00:00:59,860 I asked you to read chapter 12, I believe, for today. 19 00:01:02,750 --> 00:01:05,364 You all should do that if you want to get the maximum out 20 00:01:05,364 --> 00:01:05,905 of the class. 21 00:01:08,440 --> 00:01:11,300 So this is what I would like to change. 22 00:01:11,300 --> 00:01:13,850 There's a number-- I talked to some of the students, 23 00:01:13,850 --> 00:01:15,345 and I talked to Caitlin. 24 00:01:19,410 --> 00:01:22,270 I would like to have a quiz every class, 25 00:01:22,270 --> 00:01:26,930 but only one, occasionally two questions. 26 00:01:26,930 --> 00:01:32,190 One idea would be to have one fairly easy question 27 00:01:32,190 --> 00:01:36,320 on the new chapter, just to make sure you've read it 28 00:01:36,320 --> 00:01:39,490 and get you to read it. 29 00:01:39,490 --> 00:01:44,840 But I also could have a question on the previous class 30 00:01:44,840 --> 00:01:47,700 that you should be able to answer if you've 31 00:01:47,700 --> 00:01:50,250 come to the class and gone over the slides 32 00:01:50,250 --> 00:01:54,050 afterwards that I post online. 33 00:01:54,050 --> 00:02:01,010 Students also suggested perhaps some worksheets 34 00:02:01,010 --> 00:02:03,790 that you can work on. 35 00:02:03,790 --> 00:02:07,290 Any suggested I give some of my pictures, but don't label them. 36 00:02:07,290 --> 00:02:11,145 You label them-- something a little more active 37 00:02:11,145 --> 00:02:14,510 that you can do, trace in certain pathways, for example. 38 00:02:14,510 --> 00:02:17,990 It's a good way to learn it, if you're actively doing it 39 00:02:17,990 --> 00:02:19,800 and not just always passive. 40 00:02:19,800 --> 00:02:21,980 So I think it's a good idea and I 41 00:02:21,980 --> 00:02:25,090 think we should do more of that. 42 00:02:25,090 --> 00:02:27,555 I welcome your suggestions for other things. 43 00:02:31,060 --> 00:02:34,530 So why don't you-- we'll do a practice quiz right now 44 00:02:34,530 --> 00:02:38,610 of this nature, so you know what it could be like. 45 00:02:38,610 --> 00:02:42,290 Take out a piece of paper, and I will put them on the screen. 46 00:02:42,290 --> 00:02:43,320 I will not grade them. 47 00:02:43,320 --> 00:02:45,090 You will grade them afterwards, OK? 48 00:02:58,890 --> 00:02:59,940 Practice quiz. 49 00:03:03,400 --> 00:03:08,270 The first one is actually from the last-- from the midbrain 50 00:03:08,270 --> 00:03:14,634 class, and the second one is from today's class. 51 00:03:14,634 --> 00:03:15,980 Today's chapter, I should say. 52 00:03:27,720 --> 00:03:29,800 So Caitlin, I just went over with them 53 00:03:29,800 --> 00:03:31,510 a little bit what we were talking about, 54 00:03:31,510 --> 00:03:33,360 how to change the class a little bit. 55 00:03:37,540 --> 00:03:40,280 Designed really just to promote your learning. 56 00:04:19,055 --> 00:04:19,555 OK. 57 00:04:19,555 --> 00:04:22,120 You ready to grade them? 58 00:04:22,120 --> 00:04:25,952 OK, the three types of multipurpose movements 59 00:04:25,952 --> 00:04:27,660 can be controlled by midbrain structures. 60 00:04:27,660 --> 00:04:31,000 I'm not even asking you what the midbrain structures are. 61 00:04:31,000 --> 00:04:34,500 I'm just asking you about the function level, which 62 00:04:34,500 --> 00:04:36,645 is quite important in this class. 63 00:04:36,645 --> 00:04:40,730 I always try to relate function to structure. 64 00:04:40,730 --> 00:04:42,500 But the three types we talked about 65 00:04:42,500 --> 00:04:48,230 are locomotion, midbrain locomotor area, 66 00:04:48,230 --> 00:04:51,450 the second one was orienting movements-- 67 00:04:51,450 --> 00:04:53,950 you could say turning movements or turning of head and eyes, 68 00:04:53,950 --> 00:04:58,570 but just orienting movements is a good way to summarize it, 69 00:04:58,570 --> 00:05:03,060 used for many different motivations-- 70 00:05:03,060 --> 00:05:06,180 and the third is grasping-- you could 71 00:05:06,180 --> 00:05:10,750 say reaching and grasping, but grasping 72 00:05:10,750 --> 00:05:13,420 the most basic part of it. 73 00:05:16,410 --> 00:05:20,220 All right, so that was from last time. 74 00:05:20,220 --> 00:05:23,310 Now, what are the two largest subdivisions 75 00:05:23,310 --> 00:05:24,775 of the diencephalon? 76 00:05:24,775 --> 00:05:26,690 It's already come up several times, 77 00:05:26,690 --> 00:05:30,665 but it was a particular part of this chapter for today. 78 00:05:33,760 --> 00:05:36,970 I'm just wanting you to say thalamus and hypothalamus. 79 00:05:39,770 --> 00:05:42,860 Now, there are two other divisions. 80 00:05:42,860 --> 00:05:45,480 And according to gene data, there's actually several more. 81 00:05:45,480 --> 00:05:48,550 But that's because you can subdivide the hypothalamus 82 00:05:48,550 --> 00:05:50,890 into several divisions. 83 00:05:50,890 --> 00:05:54,090 This is a practice quiz, OK? 84 00:05:54,090 --> 00:05:57,494 So they wrote out the answers. 85 00:05:57,494 --> 00:06:00,990 You have just barely time now to look at them, 86 00:06:00,990 --> 00:06:04,330 but you're grading them yourself. 87 00:06:04,330 --> 00:06:07,132 [SIDE CONVERSATION] 88 00:06:24,510 --> 00:06:28,950 All right, so what are the two other subdivisions? 89 00:06:28,950 --> 00:06:32,045 I could have asked you, what are the four main subdivisions? 90 00:06:35,300 --> 00:06:38,670 The epithalamus and subthalamus, right. 91 00:06:38,670 --> 00:06:41,050 One above the thalamus, the other below the thalamus. 92 00:06:41,050 --> 00:06:45,005 And that's how they're named-- epi for above, sub for below. 93 00:07:03,701 --> 00:07:07,566 So there's a little bit to finish up from last time, 94 00:07:07,566 --> 00:07:09,030 and I'd like to do that first. 95 00:07:15,900 --> 00:07:20,050 This is where we ended, pointing out 96 00:07:20,050 --> 00:07:23,630 that both the midbrain and the tweenbrain 97 00:07:23,630 --> 00:07:29,600 can be divided into two major functional regions. 98 00:07:29,600 --> 00:07:32,030 They're not just functional. 99 00:07:32,030 --> 00:07:35,240 Functional divisions correspond to the dominant type 100 00:07:35,240 --> 00:07:39,460 of connection these areas get-- the limbic 101 00:07:39,460 --> 00:07:40,515 and the somatic regions. 102 00:07:43,774 --> 00:07:45,190 And you can see what they include. 103 00:07:45,190 --> 00:07:50,390 In the midbrain, central gray area and ventral 104 00:07:50,390 --> 00:07:52,390 tegmental area. 105 00:07:52,390 --> 00:07:54,750 And these will come up repeatedly now in the class. 106 00:07:58,560 --> 00:08:01,120 Similarly, the somatic regions, which are basically 107 00:08:01,120 --> 00:08:05,510 everything else here, includes at this level, 108 00:08:05,510 --> 00:08:06,750 the superior colliculus. 109 00:08:06,750 --> 00:08:10,950 More caudally, it would be the inferior colliculus, and what 110 00:08:10,950 --> 00:08:15,120 we call the midbrain tegmentum below it, going all the way 111 00:08:15,120 --> 00:08:21,250 down to the base here, substantia nigra 112 00:08:21,250 --> 00:08:26,060 and the axons of the cerebral peduncles there coming 113 00:08:26,060 --> 00:08:27,690 from the cortex. 114 00:08:27,690 --> 00:08:32,190 Now, if you follow those two regions forward-- 115 00:08:32,190 --> 00:08:33,980 and you could do that just by connections, 116 00:08:33,980 --> 00:08:36,334 you could trace connections from either the central gray 117 00:08:36,334 --> 00:08:38,524 or the ventral tegmental area, and you 118 00:08:38,524 --> 00:08:40,039 would see that in the tweenbrain, 119 00:08:40,039 --> 00:08:44,350 they divide and they go up to the top, the epithalamus, 120 00:08:44,350 --> 00:08:45,824 and in through the hypothalamus. 121 00:08:49,730 --> 00:08:55,490 And if you labeled cells in the hypothalamus or epithalamus 122 00:08:55,490 --> 00:08:57,330 and trace connections from there, 123 00:08:57,330 --> 00:08:59,020 you would find that they go largely 124 00:08:59,020 --> 00:09:03,790 to those areas of the midbrain, the caudal projections. 125 00:09:03,790 --> 00:09:06,450 Of course, they go rostrally too. 126 00:09:06,450 --> 00:09:06,950 All right. 127 00:09:06,950 --> 00:09:14,090 So, a few more questions about these somatic regions, 128 00:09:14,090 --> 00:09:17,980 this section of the midbrain. 129 00:09:17,980 --> 00:09:20,196 The first one is, there are motor neurons located 130 00:09:20,196 --> 00:09:22,000 in the midbrain. 131 00:09:22,000 --> 00:09:26,900 What movements do those motor neurons control? 132 00:09:26,900 --> 00:09:28,460 I haven't talked much about them, 133 00:09:28,460 --> 00:09:32,465 but I have mentioned them a few times, 134 00:09:32,465 --> 00:09:34,365 when we talked about cranial nerves, 135 00:09:34,365 --> 00:09:38,830 because it gives rise to the third nerve, 136 00:09:38,830 --> 00:09:39,910 third cranial nerve. 137 00:09:43,650 --> 00:09:45,112 There they are. 138 00:09:45,112 --> 00:09:49,036 I put the label in red here, ocular motor 139 00:09:49,036 --> 00:09:51,410 nuclei, the third nerve nucleus. 140 00:09:51,410 --> 00:09:55,190 Now, the fourth nerve nucleus is also in the midbrain, 141 00:09:55,190 --> 00:09:57,250 so you could have answered that too. 142 00:09:57,250 --> 00:09:58,720 It's another ocular motor nucleus, 143 00:09:58,720 --> 00:10:01,861 but it's called the trochlear nucleus. 144 00:10:01,861 --> 00:10:03,810 It controls a different eye muscle. 145 00:10:07,786 --> 00:10:10,040 The ocular motor nuclei concerned 146 00:10:10,040 --> 00:10:14,980 with lateral eye movements, the trochlear 147 00:10:14,980 --> 00:10:17,790 for the twisting of the eye. 148 00:10:24,240 --> 00:10:28,050 And at the base of the midbrain, you 149 00:10:28,050 --> 00:10:31,900 find this fiber bundle that's hugely 150 00:10:31,900 --> 00:10:34,720 different in different species. 151 00:10:34,720 --> 00:10:36,237 So what's that fiber bundle? 152 00:10:39,039 --> 00:10:40,625 It's at the very bottom. 153 00:10:46,957 --> 00:10:48,790 There's an enlarged picture of the midbrain. 154 00:10:48,790 --> 00:10:51,710 It's this bundle. 155 00:10:51,710 --> 00:10:54,760 We call it the cerebral peduncle. 156 00:10:54,760 --> 00:10:57,570 What does it contain? 157 00:10:57,570 --> 00:11:01,630 All the fibers-- go ahead. 158 00:11:01,630 --> 00:11:02,400 Sorry? 159 00:11:02,400 --> 00:11:04,460 AUDIENCE: [INAUDIBLE]. 160 00:11:04,460 --> 00:11:09,720 PROFESSOR: Always from the cortex, always going down. 161 00:11:09,720 --> 00:11:12,056 So they're efferents from the cortex. 162 00:11:12,056 --> 00:11:12,930 And where do they go? 163 00:11:16,560 --> 00:11:19,615 Spinal cord, and where else? 164 00:11:19,615 --> 00:11:21,852 The corticospinal. 165 00:11:21,852 --> 00:11:25,670 But remember, we keep talking about another main projection 166 00:11:25,670 --> 00:11:27,670 that ends in the hindbrain. 167 00:11:27,670 --> 00:11:31,296 Well, they go to a lot of places in the hindbrain too. 168 00:11:31,296 --> 00:11:33,710 But there's one in the rostral hindbrain that's 169 00:11:33,710 --> 00:11:38,550 particularly important, because it's going to the cerebellum. 170 00:11:38,550 --> 00:11:41,230 To get to the cerebellum, what does it have to terminate? 171 00:11:41,230 --> 00:11:43,420 Where does it go? 172 00:11:43,420 --> 00:11:45,956 Does it go directly to the cerebellar cortex? 173 00:11:45,956 --> 00:11:49,710 No, it goes to the pons, the gray matter 174 00:11:49,710 --> 00:11:53,150 of the pons, the corticopontine axons. 175 00:11:53,150 --> 00:11:57,730 So then there was one here-- the last question 176 00:11:57,730 --> 00:12:00,930 is a more difficult one. 177 00:12:00,930 --> 00:12:05,344 Another pathway that actually occurs-- oh, here's 178 00:12:05,344 --> 00:12:06,510 the one I meant to show you. 179 00:12:06,510 --> 00:12:09,371 This shows the peduncle in three different animals 180 00:12:09,371 --> 00:12:10,370 that I've just sketched. 181 00:12:13,630 --> 00:12:16,815 A rodent like a mouse, or a hamster or rat, 182 00:12:16,815 --> 00:12:18,550 would be like that one at the top. 183 00:12:18,550 --> 00:12:20,300 This would be a hamster. 184 00:12:20,300 --> 00:12:24,150 The rat, the mouse, superior colliculus, just 185 00:12:24,150 --> 00:12:27,720 slightly smaller. 186 00:12:27,720 --> 00:12:31,030 Otherwise, proportionately it's very similar to this. 187 00:12:31,030 --> 00:12:34,950 But look at human, look at the biggest difference. 188 00:12:34,950 --> 00:12:40,140 The huge cerebral peduncle, and also corticopontine fibers, 189 00:12:40,140 --> 00:12:43,330 because of the very large neocortex in humans. 190 00:12:43,330 --> 00:12:46,566 So any animal with very large neocortex 191 00:12:46,566 --> 00:12:51,580 is going to have a pretty large cerebral peduncle too. 192 00:12:51,580 --> 00:12:54,770 But humans, it's relatively the largest. 193 00:12:57,530 --> 00:12:59,230 And then there's a treeshrew. 194 00:12:59,230 --> 00:13:03,070 We used to think the treeshrew was a primitive primate. 195 00:13:03,070 --> 00:13:05,475 It turned out, because of the position 196 00:13:05,475 --> 00:13:07,920 of the corticospinal fibers, we realized 197 00:13:07,920 --> 00:13:12,650 it wasn't a primate, because in primates, the cortical fibers 198 00:13:12,650 --> 00:13:15,624 followed the lateral columns into the cord. 199 00:13:15,624 --> 00:13:18,290 But in the treeshrew, they're at the base of the dorsal columns, 200 00:13:18,290 --> 00:13:21,530 just like in the rat, or in insectivores. 201 00:13:21,530 --> 00:13:24,500 So it eats insects, among other things, 202 00:13:24,500 --> 00:13:27,580 it was classified as an insectivore-- very much, 203 00:13:27,580 --> 00:13:30,560 though, like a squirrel, a rodent. 204 00:13:30,560 --> 00:13:34,300 What characterizes it is that very large superior colliculus, 205 00:13:34,300 --> 00:13:36,510 so large that we could call it an optic lobe, 206 00:13:36,510 --> 00:13:40,910 just like we call it an optical lobe in the predatory fish, 207 00:13:40,910 --> 00:13:44,790 for example, or in birds, because they have 208 00:13:44,790 --> 00:13:51,070 so many important movements, particularly orienting 209 00:13:51,070 --> 00:13:53,120 movements, that depend on the midbrain. 210 00:13:53,120 --> 00:13:58,020 Their innate kind of learning is just short term. 211 00:14:00,630 --> 00:14:01,680 So that's the treeshrew. 212 00:14:01,680 --> 00:14:04,820 And there's the corticospinal tract. 213 00:14:04,820 --> 00:14:07,420 It's not that they don't have a decent size cortex, 214 00:14:07,420 --> 00:14:13,850 but the midbrain is much larger than in these other animals. 215 00:14:13,850 --> 00:14:18,720 Now, the last question then about pathway that 216 00:14:18,720 --> 00:14:22,120 goes forward from the cerebellum. 217 00:14:22,120 --> 00:14:24,170 I drew these in here on this picture 218 00:14:24,170 --> 00:14:28,990 that we're showing with the red circles, the locomotor areas. 219 00:14:28,990 --> 00:14:32,420 So there's the midbrain locomotor area, 220 00:14:32,420 --> 00:14:35,020 defined by electrical stimulation. 221 00:14:35,020 --> 00:14:40,710 And then I've sketched-- the BC means brachium conjunctivum-- 222 00:14:40,710 --> 00:14:44,240 not something you're likely to remember very well right now. 223 00:14:44,240 --> 00:14:48,920 But the axons from cerebellum don't just 224 00:14:48,920 --> 00:14:52,440 go down to the spinal cord in the hindbrain 225 00:14:52,440 --> 00:14:55,520 to affect movement. 226 00:14:55,520 --> 00:14:59,760 The kind of timing coordination, the movements that they do, 227 00:14:59,760 --> 00:15:04,420 is also important for endbrain functions for the neocortex. 228 00:15:04,420 --> 00:15:08,785 So to get there, it goes through the midbrain. 229 00:15:08,785 --> 00:15:11,440 The fibers cross over, because remember, 230 00:15:11,440 --> 00:15:14,280 hindbrain is uncrossed. 231 00:15:14,280 --> 00:15:18,940 So when it gets into the midbrain and forebrain, 232 00:15:18,940 --> 00:15:19,660 they're crossed. 233 00:15:19,660 --> 00:15:22,280 So they cross here-- big bundle of axons 234 00:15:22,280 --> 00:15:24,334 in the caudal part of the midbrain. 235 00:15:24,334 --> 00:15:25,324 AUDIENCE: [INAUDIBLE]. 236 00:15:25,324 --> 00:15:26,490 PROFESSOR: Sorry, ascending. 237 00:15:26,490 --> 00:15:29,330 Yeah, they're coming out of the cerebellum 238 00:15:29,330 --> 00:15:32,550 just behind this level, and now they're crossing over. 239 00:15:32,550 --> 00:15:34,620 And they're going to go to the red nucleus 240 00:15:34,620 --> 00:15:37,990 and then forward into the more anterior 241 00:15:37,990 --> 00:15:40,944 parts of the ventral nucleus of the thalamus. 242 00:15:40,944 --> 00:15:42,777 The posterior parts of that ventral nucleus, 243 00:15:42,777 --> 00:15:45,806 remember, gets somatosensory. 244 00:15:45,806 --> 00:15:51,344 But the more rostral parts get their input 245 00:15:51,344 --> 00:15:53,990 from cerebellum and from corpus striatum, 246 00:15:53,990 --> 00:15:56,262 and it goes to the motor areas of the cortex. 247 00:15:58,761 --> 00:15:59,260 All right. 248 00:15:59,260 --> 00:16:00,770 So that's the brachium conjunctivum. 249 00:16:05,380 --> 00:16:07,430 I'd like you to begin to hear these things 250 00:16:07,430 --> 00:16:09,236 and learn about it. 251 00:16:09,236 --> 00:16:11,960 We will come back to it later. 252 00:16:11,960 --> 00:16:19,140 But we won't be talking in great detail about the cerebellar 253 00:16:19,140 --> 00:16:22,960 pathways because we don't know enough about them. 254 00:16:22,960 --> 00:16:26,480 I'm going to say here a little more about these long axons. 255 00:16:26,480 --> 00:16:32,005 This is a-- let's just look at this picture of the midbrain 256 00:16:32,005 --> 00:16:34,630 and talk about the long axons. 257 00:16:34,630 --> 00:16:37,020 Well, some of the long axons come in and just 258 00:16:37,020 --> 00:16:39,600 terminate there in the midbrain, like the optic tracts. 259 00:16:39,600 --> 00:16:41,190 I have those at the top here. 260 00:16:41,190 --> 00:16:44,460 You see some indicating that they're terminating there 261 00:16:44,460 --> 00:16:46,617 in the superficial tectum. 262 00:16:46,617 --> 00:16:48,200 But what about the ones going through? 263 00:16:48,200 --> 00:16:51,280 Well, all those pathways from the spinal cord that 264 00:16:51,280 --> 00:16:55,480 carry somatosensory information, to get to the thalamus 265 00:16:55,480 --> 00:16:58,010 and subthalamus, especially the thalamus, 266 00:16:58,010 --> 00:16:59,920 they have to go through the midbrain. 267 00:16:59,920 --> 00:17:04,050 And there, these green axons form 268 00:17:04,050 --> 00:17:11,849 in this C-shaped region that includes, 269 00:17:11,849 --> 00:17:15,105 at this level, medial lemniscus down here 270 00:17:15,105 --> 00:17:20,980 and trigeminal lemniscus, and then spinothalamic tract. 271 00:17:20,980 --> 00:17:28,980 And the spinothalamic includes a spinotectal component. 272 00:17:28,980 --> 00:17:31,800 In other words, many of them don't make it to the thalamus. 273 00:17:31,800 --> 00:17:35,960 They terminate in the superior colliculus or tectum. 274 00:17:35,960 --> 00:17:39,840 But they don't terminate up in the surface layers 275 00:17:39,840 --> 00:17:41,910 like the renal fibers do. 276 00:17:41,910 --> 00:17:44,870 They terminate just where I'm showing you here, 277 00:17:44,870 --> 00:17:48,298 in the deeper layers of the tectum. 278 00:17:48,298 --> 00:17:52,830 It's the tectum-- so important for orientating, 279 00:17:52,830 --> 00:17:56,040 you would expect it to get multiple inputs, 280 00:17:56,040 --> 00:18:02,890 and it does-- visual, somatosensory, and auditory. 281 00:18:02,890 --> 00:18:05,320 The auditory fibers, many of them pass through. 282 00:18:05,320 --> 00:18:08,652 They're way out here at the edge in this bundle. 283 00:18:08,652 --> 00:18:11,470 It's called the arm of the inferior colliculus, brachium 284 00:18:11,470 --> 00:18:13,380 of the inferior colliculus. 285 00:18:13,380 --> 00:18:15,570 Brachium means arms. 286 00:18:15,570 --> 00:18:18,430 But some of them-- I don't show it here, but some of them 287 00:18:18,430 --> 00:18:21,150 terminate right in the middle there. 288 00:18:21,150 --> 00:18:24,940 So you have visual, then auditory, then somatosensory. 289 00:18:24,940 --> 00:18:28,050 And in those deeper layers where the somatosensory input comes 290 00:18:28,050 --> 00:18:33,430 in, the output neurons are all multi-modal, almost all. 291 00:18:33,430 --> 00:18:36,200 They're getting input from various modalities, 292 00:18:36,200 --> 00:18:38,950 but all controlling the same kind of movements. 293 00:18:38,950 --> 00:18:42,440 So they converge on the cells like this, 294 00:18:42,440 --> 00:18:45,121 that give rise to the tectospinal tract. 295 00:18:45,121 --> 00:18:46,870 Most of them are getting converging inputs 296 00:18:46,870 --> 00:18:48,229 from the different modalities. 297 00:18:50,950 --> 00:18:53,810 All right. 298 00:18:53,810 --> 00:18:56,856 What have I indicated in red there? 299 00:18:56,856 --> 00:18:58,780 In these pictures, I'm always using 300 00:18:58,780 --> 00:19:01,580 red for the limbic related things. 301 00:19:01,580 --> 00:19:06,820 That's pathways carrying limbic-type information. 302 00:19:06,820 --> 00:19:11,080 The ascending ones are mostly viscerosensory. 303 00:19:11,080 --> 00:19:14,603 They're coming in from the hindbrain, 304 00:19:14,603 --> 00:19:17,130 and they're traveling into the central gray 305 00:19:17,130 --> 00:19:20,090 but also they go all the way into the hypothalamus 306 00:19:20,090 --> 00:19:21,330 by that route. 307 00:19:21,330 --> 00:19:24,500 They also come through the ventral tegmental area, 308 00:19:24,500 --> 00:19:27,499 and they continue on to the hypothalamus also. 309 00:19:27,499 --> 00:19:28,540 I didn't show those here. 310 00:19:32,560 --> 00:19:34,520 And what are the other ones passing through? 311 00:19:34,520 --> 00:19:37,710 What about fibers in the other direction? 312 00:19:37,710 --> 00:19:42,010 Well, I've shown them in the blue dots. 313 00:19:42,010 --> 00:19:45,020 Almost all those axons are just passing through 314 00:19:45,020 --> 00:19:51,250 from the neocortex to the pons and to the hindbrain 315 00:19:51,250 --> 00:19:52,250 and spinal cord. 316 00:19:55,620 --> 00:19:58,090 So that's just summarized verbally here. 317 00:19:58,090 --> 00:20:00,280 I mentioned cerebellum, but I didn't 318 00:20:00,280 --> 00:20:02,650 show those on that next picture. 319 00:20:02,650 --> 00:20:03,360 All right. 320 00:20:06,228 --> 00:20:15,530 So another question, what two major instigators of action 321 00:20:15,530 --> 00:20:17,950 are discussed in this chapter on the midbrain? 322 00:20:21,630 --> 00:20:24,930 One involves sensory motor pathways. 323 00:20:24,930 --> 00:20:27,340 What are the actions we were talking about here? 324 00:20:31,120 --> 00:20:34,910 First quiz question, sensory motor pathways 325 00:20:34,910 --> 00:20:39,220 for orienting movements, or for locomotor movements, 326 00:20:39,220 --> 00:20:42,752 or for reaching movements. 327 00:20:42,752 --> 00:20:45,560 For reaching, the somatosensory pathways 328 00:20:45,560 --> 00:20:50,390 are dominant in most animals. 329 00:20:50,390 --> 00:20:53,200 For turning movements, it varies. 330 00:20:53,200 --> 00:20:56,680 Usually somatosensory is the most dominant 331 00:20:56,680 --> 00:21:00,870 because that means something's very close to you. 332 00:21:00,870 --> 00:21:03,840 But visual, of course, is very important too, 333 00:21:03,840 --> 00:21:05,780 and also auditory. 334 00:21:05,780 --> 00:21:08,470 All right. 335 00:21:08,470 --> 00:21:11,554 But I say there's two major instigators of action. 336 00:21:11,554 --> 00:21:12,970 All those sensory motor things I'm 337 00:21:12,970 --> 00:21:15,680 just classifying as the one type. 338 00:21:15,680 --> 00:21:18,450 What's the other type? 339 00:21:18,450 --> 00:21:22,480 What makes an animal start to move, 340 00:21:22,480 --> 00:21:25,840 to do one thing rather than another thing? 341 00:21:25,840 --> 00:21:30,350 Not just the sensory stimuli bombarding its senses 342 00:21:30,350 --> 00:21:33,030 at the moment. 343 00:21:33,030 --> 00:21:36,990 Motivation, yes. 344 00:21:36,990 --> 00:21:47,760 So the limbic areas there, best seen in this picture, 345 00:21:47,760 --> 00:21:50,930 the reddish areas there. 346 00:21:50,930 --> 00:21:57,180 And there is motivational control from the midbrain, 347 00:21:57,180 --> 00:22:01,510 although it's really dominated by the forebrain components 348 00:22:01,510 --> 00:22:07,200 of the limbic system, which these areas get input from. 349 00:22:07,200 --> 00:22:10,090 Hypothalamus and the connections of the endbrain 350 00:22:10,090 --> 00:22:12,600 that connect to the hypothalamus. 351 00:22:12,600 --> 00:22:17,520 So that's what I mean by the two instigators of action. 352 00:22:20,880 --> 00:22:23,960 And I just made a note there where you in the book 353 00:22:23,960 --> 00:22:25,650 actually say this. 354 00:22:28,940 --> 00:22:30,970 And I usually include old slides. 355 00:22:30,970 --> 00:22:32,700 Some of you might find them useful, 356 00:22:32,700 --> 00:22:35,598 but we don't need to go through them in the class. 357 00:22:38,980 --> 00:22:45,180 Because I want to talk a bit about the forebrain now 358 00:22:45,180 --> 00:22:47,220 and the comparative studies that have given us 359 00:22:47,220 --> 00:22:50,610 some idea about the evolution of the forebrain. 360 00:22:50,610 --> 00:22:55,250 These are the major topics, the major subdivisions, 361 00:22:55,250 --> 00:22:59,486 with an overview of the tweenbrain or diencephalon. 362 00:22:59,486 --> 00:23:03,660 This is basically the quiz question-- thalamus 363 00:23:03,660 --> 00:23:06,020 and hypothalamus are the dominant regions, 364 00:23:06,020 --> 00:23:08,540 and then subthalamus and epithalamus 365 00:23:08,540 --> 00:23:16,980 are the two other major regions of the tweenbrain. 366 00:23:16,980 --> 00:23:23,560 Then we'll talk about two pathways originating 367 00:23:23,560 --> 00:23:29,010 in the endbrain that actually correspond to this subdivision. 368 00:23:29,010 --> 00:23:31,200 It has a reality of the organization 369 00:23:31,200 --> 00:23:33,454 of axons in the brain. 370 00:23:33,454 --> 00:23:35,370 And then I'll say a little bit about evolution 371 00:23:35,370 --> 00:23:38,740 of the forebrain, especially from genetic data. 372 00:23:43,150 --> 00:23:43,650 All right. 373 00:23:46,770 --> 00:23:49,070 That's question two, the two largest subdivisions 374 00:23:49,070 --> 00:23:50,190 of the diencephalon. 375 00:23:50,190 --> 00:23:52,345 That was the quiz question. 376 00:23:52,345 --> 00:23:53,730 And then two additional ones. 377 00:23:53,730 --> 00:23:55,500 But there's another question before that-- 378 00:23:55,500 --> 00:23:58,155 what are the ganglionic eminences of the developing 379 00:23:58,155 --> 00:23:59,320 endbrain? 380 00:23:59,320 --> 00:24:02,250 I don't think we've used that term before. 381 00:24:02,250 --> 00:24:08,470 It's a term from embryology, the ganglionic eminences. 382 00:24:08,470 --> 00:24:11,610 They actually disappear with development. 383 00:24:11,610 --> 00:24:15,150 So that means they must be what? 384 00:24:19,450 --> 00:24:21,374 They're big collections of dividing cells. 385 00:24:24,010 --> 00:24:27,275 Oh, and I forgot to bring the book on my shelf. 386 00:24:27,275 --> 00:24:28,995 I wanted to show you actual pictures 387 00:24:28,995 --> 00:24:30,286 so you see what they look like. 388 00:24:30,286 --> 00:24:34,230 I'll try to remember that next time. 389 00:24:34,230 --> 00:24:37,030 OK, so here is a cross-section. 390 00:24:37,030 --> 00:24:40,490 Notice a huge ventricles that's very far anterior. 391 00:24:40,490 --> 00:24:42,040 It's through the endbrain. 392 00:24:42,040 --> 00:24:45,670 There's no diencephalic structures here. 393 00:24:45,670 --> 00:24:52,505 And you see in the outline by the little dash lines there, 394 00:24:52,505 --> 00:24:56,300 the separation of the dividing cells, the ventricular 395 00:24:56,300 --> 00:25:03,400 layer of cells, cells undergoing mitosis, 396 00:25:03,400 --> 00:25:08,470 and the cells where axons are present 397 00:25:08,470 --> 00:25:10,860 and cells that are post-migratory, 398 00:25:10,860 --> 00:25:15,090 they've already migrated into this region. 399 00:25:15,090 --> 00:25:17,840 So just like in the spinal cord, you 400 00:25:17,840 --> 00:25:22,810 have cell division happening mainly near the ventricles. 401 00:25:25,330 --> 00:25:28,870 So if these areas are so big, they 402 00:25:28,870 --> 00:25:30,960 can't all be going to the striatum. 403 00:25:30,960 --> 00:25:34,020 The striatum isn't the biggest structure of the endbrain. 404 00:25:34,020 --> 00:25:36,660 And yet there they are, just where 405 00:25:36,660 --> 00:25:38,145 the striatum would be in an adult. 406 00:25:41,120 --> 00:25:44,600 So large that they get this special name, 407 00:25:44,600 --> 00:25:47,520 because at the more anterior levels, 408 00:25:47,520 --> 00:25:52,640 they can be divided and form these two main bumps. 409 00:25:52,640 --> 00:25:57,550 We call it the lateral and medial ganglionic eminence. 410 00:25:57,550 --> 00:26:00,905 And then there's a little region-- at least in mammals 411 00:26:00,905 --> 00:26:04,860 it's small-- that could be called part 412 00:26:04,860 --> 00:26:07,250 of the lateral ganglionic eminence, 413 00:26:07,250 --> 00:26:09,420 but it's often given a special name 414 00:26:09,420 --> 00:26:11,400 because it's right at the angle there 415 00:26:11,400 --> 00:26:16,735 between the subpallial region and the pallium. 416 00:26:19,510 --> 00:26:21,650 The lateral ventricular angle region-- 417 00:26:21,650 --> 00:26:24,380 that's a particularly interesting region because some 418 00:26:24,380 --> 00:26:32,060 of those cells move up into the cortex with development. 419 00:26:32,060 --> 00:26:34,171 This just shows you where that section was taken. 420 00:26:42,040 --> 00:26:47,100 And talks about endbrain evolution 421 00:26:47,100 --> 00:26:51,820 always involve some discussion on where these cells go, 422 00:26:51,820 --> 00:26:56,450 because they don't do the same things in mammals 423 00:26:56,450 --> 00:26:58,341 and non-mammals. 424 00:26:58,341 --> 00:27:01,492 So we will talk about that today. 425 00:27:01,492 --> 00:27:04,630 Now, some of the evidence on that 426 00:27:04,630 --> 00:27:10,140 have come from gene expression data, homeobox gene 427 00:27:10,140 --> 00:27:13,530 expression in particular. 428 00:27:13,530 --> 00:27:17,620 This was one of the earliest studies of that nature. 429 00:27:17,620 --> 00:27:26,052 They just studied two genes-- these two, EMX1 and DLX1, 430 00:27:26,052 --> 00:27:27,620 and there's several related genes 431 00:27:27,620 --> 00:27:30,510 that they've also studied later. 432 00:27:30,510 --> 00:27:33,510 But in this study, they were looking 433 00:27:33,510 --> 00:27:40,380 at frog, turtle, chick, and mouse. 434 00:27:40,380 --> 00:27:43,270 And EMX1, they found, was expressed 435 00:27:43,270 --> 00:27:49,310 in the areas that became neocortex, also 436 00:27:49,310 --> 00:27:52,990 hippocampal cortex, also olfactory cortex. 437 00:27:52,990 --> 00:27:59,000 This whole pallial region expressed that gene. 438 00:27:59,000 --> 00:28:01,710 And if they looked at the corresponding area 439 00:28:01,710 --> 00:28:09,000 in the chick, they found it was a thick region that 440 00:28:09,000 --> 00:28:16,980 included parts of the brain that actually were labeled striatum 441 00:28:16,980 --> 00:28:19,581 in the early studies. 442 00:28:19,581 --> 00:28:23,230 If they looked at a turtle, you'll 443 00:28:23,230 --> 00:28:26,560 see the region included, and then a frog. 444 00:28:26,560 --> 00:28:29,470 And if they looked at the one labeled green here, 445 00:28:29,470 --> 00:28:33,190 DLX1, you'll see it's labeling the striatum. 446 00:28:33,190 --> 00:28:36,526 Now, this is showing the adult. 447 00:28:36,526 --> 00:28:37,900 But of course the gene expression 448 00:28:37,900 --> 00:28:43,350 data, what's important it what's expressed very early. 449 00:28:43,350 --> 00:28:49,170 So this is the striatum, but that gene is expressed also 450 00:28:49,170 --> 00:28:54,915 all the way down to the base, and also the medial area, 451 00:28:54,915 --> 00:28:57,160 the area we call the septum. 452 00:28:57,160 --> 00:29:00,355 So the basal forebrain, the septum, and the corpus striatum 453 00:29:00,355 --> 00:29:02,780 are all included. 454 00:29:02,780 --> 00:29:06,610 But then there are regions that don't express either one. 455 00:29:06,610 --> 00:29:09,420 And notice how different they are. 456 00:29:09,420 --> 00:29:13,410 It includes this area in the turtle and in the chick 457 00:29:13,410 --> 00:29:17,460 that we call the dorsal ventricular ridge. 458 00:29:17,460 --> 00:29:21,510 Whereas in mammal, the only corresponding area 459 00:29:21,510 --> 00:29:23,485 in this initial study that they found 460 00:29:23,485 --> 00:29:29,180 was the amygdala of the mouse, the amygdala and the claustrum, 461 00:29:29,180 --> 00:29:33,390 which is near the amygdala-- and some studies 462 00:29:33,390 --> 00:29:35,910 have even included it with the amydala-- 463 00:29:35,910 --> 00:29:38,560 and part of the septum here. 464 00:29:38,560 --> 00:29:40,540 All right. 465 00:29:40,540 --> 00:29:47,014 So we'll come back to that kind of study later. 466 00:29:47,014 --> 00:29:49,908 I want to talk about major features of these forebrain 467 00:29:49,908 --> 00:29:51,700 structures. 468 00:29:51,700 --> 00:29:54,780 And then we'll pause just to review 469 00:29:54,780 --> 00:29:58,200 what I consider some of the important concepts we've 470 00:29:58,200 --> 00:30:01,580 been covering in the class so far. 471 00:30:01,580 --> 00:30:07,890 But first, here's the embryonic mammal stretched out, 472 00:30:07,890 --> 00:30:11,710 hemispheres pushed apart. 473 00:30:11,710 --> 00:30:15,710 And these are what the sections look like, 474 00:30:15,710 --> 00:30:17,500 the one that includes the diencephalon. 475 00:30:17,500 --> 00:30:20,330 And there you have the cerebral hemispheres up above, 476 00:30:20,330 --> 00:30:22,430 and then here, the more anterior picture. 477 00:30:27,020 --> 00:30:34,340 So first, four regions of diencephalon, thalamus 478 00:30:34,340 --> 00:30:39,340 and hypothalamus, subthalamus and epithalamus. 479 00:30:39,340 --> 00:30:42,390 You know the relationships, visceral. 480 00:30:46,320 --> 00:30:47,940 We call them limbic because they're 481 00:30:47,940 --> 00:30:53,801 related to the limbic or fringe structures of the hemispheres. 482 00:30:53,801 --> 00:30:56,950 We'll talk about pathways related now 483 00:30:56,950 --> 00:30:59,030 to these two divisions. 484 00:30:59,030 --> 00:31:02,100 Now, that hypothalamus and epithalamus on the one hand, 485 00:31:02,100 --> 00:31:05,400 thalamus and subthalamus on the other. 486 00:31:05,400 --> 00:31:08,440 Limbic and somatic. 487 00:31:08,440 --> 00:31:10,630 So there's that picture we saw earlier. 488 00:31:20,560 --> 00:31:24,900 It's this question now I want to deal with. 489 00:31:24,900 --> 00:31:27,410 The division of pallial and subpallial regions 490 00:31:27,410 --> 00:31:31,560 of the endbrains, this division into somatic and limbic, 491 00:31:31,560 --> 00:31:36,140 supported by evidence of two pathways followed 492 00:31:36,140 --> 00:31:38,015 by their output axons. 493 00:31:38,015 --> 00:31:43,345 And you find these two pathways not just in mammals 494 00:31:43,345 --> 00:31:45,660 but in all the other vertebrates you 495 00:31:45,660 --> 00:31:48,400 can find, at least in development, 496 00:31:48,400 --> 00:31:54,026 but usually right into adulthood these two kinds of pathways. 497 00:31:54,026 --> 00:32:02,240 So let's go through these. 498 00:32:02,240 --> 00:32:11,340 First of all, this pathway, these 499 00:32:11,340 --> 00:32:13,090 are pathways coming from neocortex. 500 00:32:15,635 --> 00:32:17,420 We'll just color it in there. 501 00:32:17,420 --> 00:32:20,190 We'll use blue for the somatic. 502 00:32:20,190 --> 00:32:26,350 And these axons are going to and coming 503 00:32:26,350 --> 00:32:31,390 from the thalamus and also the subthalamus, 504 00:32:31,390 --> 00:32:34,462 coming from subthalamus. 505 00:32:34,462 --> 00:32:40,710 But we associate the most with this bundle of axons. 506 00:32:40,710 --> 00:32:42,660 This is the bundle we're talking about here. 507 00:32:42,660 --> 00:32:46,545 It's called embyologically the lateral forebrain bundle. 508 00:32:46,545 --> 00:32:49,310 And we'll talk about all the fiber components 509 00:32:49,310 --> 00:32:52,450 of the lateral forebrain bundle now in a minute. 510 00:32:52,450 --> 00:32:56,210 And then, the medial forebrain bundle is here. 511 00:32:56,210 --> 00:33:00,220 This bundle here is the fornix coming from the hippocampus, 512 00:33:00,220 --> 00:33:01,972 but it includes all these fibers that 513 00:33:01,972 --> 00:33:05,780 come in and out of the hypothalamus. 514 00:33:05,780 --> 00:33:11,190 It also includes a bundle right here coming in and out 515 00:33:11,190 --> 00:33:12,140 of the epithalamus. 516 00:33:12,140 --> 00:33:14,850 And of course it's on both sides. 517 00:33:14,850 --> 00:33:20,310 So that's the medial forebrain bundle, and as you can expect, 518 00:33:20,310 --> 00:33:25,670 it's in a more medial position when we look at the endbrain, 519 00:33:25,670 --> 00:33:29,735 or here at this level, the more caudal forebrain. 520 00:33:29,735 --> 00:33:33,270 But remember, it includes both the epithalamic 521 00:33:33,270 --> 00:33:36,980 and hypothalamic components. 522 00:33:36,980 --> 00:33:39,500 So here's the more anterior picture. 523 00:33:39,500 --> 00:33:41,605 You see the same bundles. 524 00:33:44,890 --> 00:33:50,580 so now, the medial forebrain bundle is down here. 525 00:33:50,580 --> 00:33:52,390 And on the left side, I'm showing 526 00:33:52,390 --> 00:33:54,396 where the axons are coming from. 527 00:33:58,890 --> 00:34:01,290 AUDIENCE: The medial forebrain-- because you 528 00:34:01,290 --> 00:34:03,540 had some at the top and the bottom-- 529 00:34:03,540 --> 00:34:11,540 they both end up projecting to where you're showing 530 00:34:11,540 --> 00:34:15,050 the medial forebrain now because you have some at the top? 531 00:34:15,050 --> 00:34:16,570 So both of those come together? 532 00:34:16,570 --> 00:34:17,760 PROFESSOR: Yes. 533 00:34:17,760 --> 00:34:18,830 That's right. 534 00:34:18,830 --> 00:34:25,730 These axons here are going both up here and down here. 535 00:34:25,730 --> 00:34:28,320 Think of it that way. 536 00:34:28,320 --> 00:34:31,870 When they came into the thalamus, they were together. 537 00:34:31,870 --> 00:34:37,520 But then one goes over the top, one stays below. 538 00:34:37,520 --> 00:34:39,675 One below goes to the hypothalamus. 539 00:34:39,675 --> 00:34:42,000 The one above goes to the epithalamus. 540 00:34:42,000 --> 00:34:45,440 And it has a special name, the stria medullaris. 541 00:34:45,440 --> 00:34:46,790 And that's what this is called. 542 00:34:46,790 --> 00:34:49,909 This is the stria medullaris. 543 00:34:49,909 --> 00:34:52,510 So here's the medial forebrain bundle. 544 00:34:52,510 --> 00:34:54,830 And see where the axons are coming from? 545 00:34:54,830 --> 00:34:58,920 They're coming from the ventral parts of the striatum. 546 00:34:58,920 --> 00:35:01,940 They're coming from olfactory regions. 547 00:35:01,940 --> 00:35:04,450 So ventral striatum and olfactory regions-- 548 00:35:04,450 --> 00:35:07,070 but also, there's the medial pallium. 549 00:35:07,070 --> 00:35:09,230 This is the position of the hippocampus. 550 00:35:11,930 --> 00:35:15,370 In most mammals, it's very tiny at this level, 551 00:35:15,370 --> 00:35:17,996 mostly it's larger, more caudally. 552 00:35:17,996 --> 00:35:20,190 But it's definitely hippocampus. 553 00:35:20,190 --> 00:35:24,530 And the larger hippocampus in most mammals 554 00:35:24,530 --> 00:35:27,080 gives rise to a pathway that goes forward, 555 00:35:27,080 --> 00:35:31,340 goes right through this region and then down, 556 00:35:31,340 --> 00:35:34,270 joining the medial forebrain bundle. 557 00:35:34,270 --> 00:35:40,720 And then these axons, many of them 558 00:35:40,720 --> 00:35:44,110 coming out of the hemisphere there as I show on the left 559 00:35:44,110 --> 00:35:44,610 here. 560 00:35:44,610 --> 00:35:49,160 I show them coming from neocortex, many different 561 00:35:49,160 --> 00:35:51,000 regions of neocortex. 562 00:35:51,000 --> 00:35:53,630 They're going into the lateral forebrain bundle. 563 00:35:53,630 --> 00:35:56,815 They're coming also from the output structures 564 00:35:56,815 --> 00:35:58,160 of the corpus striatum. 565 00:36:01,310 --> 00:36:03,030 When I talk about striatum here, I'm 566 00:36:03,030 --> 00:36:05,070 going to lump together at this point 567 00:36:05,070 --> 00:36:09,240 the output structures which are called the globus pallidus. 568 00:36:09,240 --> 00:36:12,330 We'll just include them as part of the striatum, 569 00:36:12,330 --> 00:36:16,950 because they are very closely tied to the striatum. 570 00:36:16,950 --> 00:36:19,340 All right. 571 00:36:19,340 --> 00:36:21,080 So this just gives all this in words. 572 00:36:21,080 --> 00:36:24,430 It's giving you the origin of these two pathways. 573 00:36:24,430 --> 00:36:34,140 Now, this is a picture of the lateral forebrain bundle. 574 00:36:34,140 --> 00:36:36,570 Now you'll see it's really a lot of words 575 00:36:36,570 --> 00:36:38,465 that you're very familiar with already. 576 00:36:38,465 --> 00:36:43,610 It includes fibers coming from the neocortex, the white matter 577 00:36:43,610 --> 00:36:44,740 of the neocortex. 578 00:36:44,740 --> 00:36:48,560 And then they come down through the striatum. 579 00:36:48,560 --> 00:36:50,840 And when they come down through the striatum, 580 00:36:50,840 --> 00:36:54,390 we call them internal capsule. 581 00:36:54,390 --> 00:36:58,990 They're capsulated by the corpus striatum. 582 00:36:58,990 --> 00:37:03,785 They're joined by fibers from the striatum. 583 00:37:03,785 --> 00:37:05,640 It's all part of this somatic system. 584 00:37:11,610 --> 00:37:13,330 So here they are at the tweenbrain level. 585 00:37:13,330 --> 00:37:17,010 You'll see them up there in the white matter of the cortex, 586 00:37:17,010 --> 00:37:20,980 and now the peduncle is coursing along the side 587 00:37:20,980 --> 00:37:24,030 of the tweenbrain. 588 00:37:24,030 --> 00:37:26,030 That's the cerebral peduncle. 589 00:37:26,030 --> 00:37:30,350 That's simply the same axons right here, 590 00:37:30,350 --> 00:37:33,910 coursing along the side of the tweenbrain. 591 00:37:33,910 --> 00:37:35,730 Then they keep going. 592 00:37:35,730 --> 00:37:42,220 They go on that big bundle at the base of the midbrain. 593 00:37:42,220 --> 00:37:48,190 So I show that in the embryonic midbrain here, in this section. 594 00:37:48,190 --> 00:37:50,130 Then they keep going. 595 00:37:50,130 --> 00:37:51,880 They get to the pons. 596 00:37:51,880 --> 00:37:55,820 They course through the middle of the pons. 597 00:37:55,820 --> 00:37:59,710 And they emerge from the caudal end of the pons and keep going. 598 00:37:59,710 --> 00:38:03,680 There they are at the base of the hindbrain. 599 00:38:03,680 --> 00:38:05,590 There, they get a different name. 600 00:38:05,590 --> 00:38:09,260 Now we call them the pyramidal tract. 601 00:38:09,260 --> 00:38:13,970 Same axons, just changing names because of the way 602 00:38:13,970 --> 00:38:17,340 they look at different levels and where they are. 603 00:38:17,340 --> 00:38:23,590 They reach the caudal end of the hindbrain and they decussate. 604 00:38:23,590 --> 00:38:25,300 You can say, well, why didn't they 605 00:38:25,300 --> 00:38:28,210 decussate as they entered the hindbrain? 606 00:38:28,210 --> 00:38:29,420 Well, they don't. 607 00:38:29,420 --> 00:38:31,930 That's all I can say. 608 00:38:31,930 --> 00:38:33,695 They don't decussate until later. 609 00:38:38,440 --> 00:38:43,610 There they decussate in all the vertebrates, they cross over, 610 00:38:43,610 --> 00:38:49,257 and in the primates, they travel in the lateral columns. 611 00:38:49,257 --> 00:38:51,465 When we studied spinal cord, I showed that big bundle 612 00:38:51,465 --> 00:38:54,910 in the lateral columns of the spinal cord. 613 00:38:54,910 --> 00:38:56,690 That's where the corticospinal axons are. 614 00:38:56,690 --> 00:39:00,582 We just call them corticospinal axons after that decussation. 615 00:39:00,582 --> 00:39:02,600 We stop calling them pyramidal tract, 616 00:39:02,600 --> 00:39:04,300 although some anatomy books might 617 00:39:04,300 --> 00:39:07,310 say this is the pyramidal tract. 618 00:39:07,310 --> 00:39:10,075 Strictly speaking, they're only called pyramidal tract 619 00:39:10,075 --> 00:39:11,920 at the base of the hindbrain when 620 00:39:11,920 --> 00:39:13,690 they have that pyramidal shape. 621 00:39:16,446 --> 00:39:18,652 If they're a rodent, they're in the ventral part 622 00:39:18,652 --> 00:39:20,801 of the dorsal columns. 623 00:39:20,801 --> 00:39:21,300 OK. 624 00:39:21,300 --> 00:39:24,060 So there I have the different names 625 00:39:24,060 --> 00:39:27,100 given for the very same axons of the lateral forebrain 626 00:39:27,100 --> 00:39:30,210 bundle at all these different levels. 627 00:39:30,210 --> 00:39:33,480 They're all descending. 628 00:39:33,480 --> 00:39:37,820 Now, since you brought that up, remember here 629 00:39:37,820 --> 00:39:44,820 at these rostral levels, the internal capsule fibers, 630 00:39:44,820 --> 00:39:48,340 that's a two-way street, because many fibers come 631 00:39:48,340 --> 00:39:49,300 from the thalamus. 632 00:39:49,300 --> 00:39:51,680 They're going up into the cortex. 633 00:39:51,680 --> 00:39:53,910 They are part of the internal capsule, 634 00:39:53,910 --> 00:39:56,310 and they are part of the white matter of the cortex. 635 00:39:56,310 --> 00:39:59,580 They are part of the lateral forebrain bundle there. 636 00:39:59,580 --> 00:40:03,650 But here, we're just dealing with the ones going down. 637 00:40:03,650 --> 00:40:06,480 And once we're past the diencephalon, 638 00:40:06,480 --> 00:40:08,860 almost all of the axons in that bundle 639 00:40:08,860 --> 00:40:13,391 are descending all the way down into the spinal cord. 640 00:40:13,391 --> 00:40:13,890 OK. 641 00:40:13,890 --> 00:40:18,460 Now the other system, the limbic system, we just review here. 642 00:40:18,460 --> 00:40:20,600 Not showing the details. 643 00:40:20,600 --> 00:40:22,680 The axons tend to be a little different. 644 00:40:22,680 --> 00:40:25,070 They're much shorter connections. 645 00:40:25,070 --> 00:40:28,490 So we will never be able to follow pathways 646 00:40:28,490 --> 00:40:31,010 like this for the limbic system. 647 00:40:31,010 --> 00:40:35,110 With a few exceptions, the hypothalamus in many species 648 00:40:35,110 --> 00:40:38,960 has evolved a few long connections to the spinal cord. 649 00:40:38,960 --> 00:40:41,884 For example, the one controlling urination 650 00:40:41,884 --> 00:40:45,925 goes directly into the spinal cord. 651 00:40:48,680 --> 00:40:49,180 All right. 652 00:40:49,180 --> 00:40:54,110 So this is just reviewing what we already 653 00:40:54,110 --> 00:40:58,440 said for these two systems. 654 00:40:58,440 --> 00:41:01,780 So this division into somatic and limbic, you see, 655 00:41:01,780 --> 00:41:04,200 is supported by the neuroanatomy very strongly. 656 00:41:08,670 --> 00:41:12,850 So here's another question about these pathways. 657 00:41:12,850 --> 00:41:16,080 What is a striking difference in the outputs 658 00:41:16,080 --> 00:41:18,760 from the neocortex on the one hand 659 00:41:18,760 --> 00:41:20,576 and the corpus striatum on the other? 660 00:41:24,950 --> 00:41:29,480 If you had to answer that, I put you on the spot 661 00:41:29,480 --> 00:41:32,100 and say, give me a quick answer to that, 662 00:41:32,100 --> 00:41:39,374 something really simple, can you guess? 663 00:41:39,374 --> 00:41:43,327 AUDIENCE: [INAUDIBLE] directly to it? 664 00:41:43,327 --> 00:41:44,160 PROFESSOR: Directly? 665 00:41:46,955 --> 00:41:51,392 AUDIENCE: So the neocortex goes like directly 666 00:41:51,392 --> 00:41:53,860 to the [INAUDIBLE]? 667 00:41:53,860 --> 00:41:56,030 PROFESSOR: Longer axons. 668 00:41:56,030 --> 00:41:58,027 Where do the longer axons from the cortex go? 669 00:42:03,000 --> 00:42:03,945 Spinal cord. 670 00:42:03,945 --> 00:42:06,020 Some of them go to motor neurons. 671 00:42:06,020 --> 00:42:08,850 Corpus striatum doesn't do that. 672 00:42:08,850 --> 00:42:10,960 Pathways from corpus striatum don't make it 673 00:42:10,960 --> 00:42:11,768 past the midbrain. 674 00:42:16,240 --> 00:42:21,360 And the neocortex is involved in both of those systems. 675 00:42:21,360 --> 00:42:25,510 I separated somatic and limbic here, 676 00:42:25,510 --> 00:42:27,890 but here's the way I summarize it. 677 00:42:27,890 --> 00:42:29,357 Here's the somatic on the left. 678 00:42:29,357 --> 00:42:30,690 There's the limbic on the right. 679 00:42:35,460 --> 00:42:39,280 So you see here, the limbic system connections are shorter. 680 00:42:39,280 --> 00:42:41,540 They don't make it past the brain stem. 681 00:42:41,540 --> 00:42:43,560 In fact, I could have been even more specific. 682 00:42:43,560 --> 00:42:47,140 I'd say they don't make it past the midbrain. 683 00:42:47,140 --> 00:42:53,460 Whereas the neocortex goes into the spinal cord. 684 00:43:00,949 --> 00:43:02,990 The other difference, of course, is the neocortex 685 00:43:02,990 --> 00:43:05,600 is related to limbic structures as much 686 00:43:05,600 --> 00:43:07,710 as to somatic structures. 687 00:43:07,710 --> 00:43:09,626 And what about the striatum? 688 00:43:09,626 --> 00:43:12,280 Well, here, I've been a little unfair 689 00:43:12,280 --> 00:43:16,170 because I've just lumped the limbic parts of the striatum 690 00:43:16,170 --> 00:43:18,005 and called them limbic structures, 691 00:43:18,005 --> 00:43:20,380 just to simplify the diagram. 692 00:43:20,380 --> 00:43:22,492 The better diagrams is this one. 693 00:43:22,492 --> 00:43:26,280 It looks more complex because limbic system structures 694 00:43:26,280 --> 00:43:27,090 are shorter. 695 00:43:27,090 --> 00:43:30,300 So you're going to have more of them. 696 00:43:30,300 --> 00:43:33,710 Strongly connected to hypothalamus, strongly 697 00:43:33,710 --> 00:43:35,850 connected to other limbic structures that 698 00:43:35,850 --> 00:43:36,660 aren't striatal. 699 00:43:42,240 --> 00:43:44,075 Most of the connections that are large 700 00:43:44,075 --> 00:43:46,735 are going in and out of the hypothalamus, 701 00:43:46,735 --> 00:43:49,490 but there are a few that go into the brain stem, 702 00:43:49,490 --> 00:43:51,680 especially to those structures in the midbrain. 703 00:43:51,680 --> 00:43:57,380 That's how now to define the limbic midbrain structures. 704 00:43:57,380 --> 00:44:00,400 He made lesions in the limbic endbrain structures 705 00:44:00,400 --> 00:44:03,505 like the amygdala and hippocampus. 706 00:44:03,505 --> 00:44:08,180 And he said, the fibers not only go to the hypothalamus, 707 00:44:08,180 --> 00:44:13,170 they go beyond the hypothalamus into these medial midbrain 708 00:44:13,170 --> 00:44:15,130 structures, the central gray area 709 00:44:15,130 --> 00:44:16,870 and the ventral tegmental area. 710 00:44:16,870 --> 00:44:19,480 So that's how we define them. 711 00:44:19,480 --> 00:44:22,030 All right. 712 00:44:22,030 --> 00:44:24,310 So this is for your review. 713 00:44:24,310 --> 00:44:26,930 Read them, and make sure you understand 714 00:44:26,930 --> 00:44:28,620 these various things. 715 00:44:28,620 --> 00:44:34,000 Just listing major things we've gone through in the class. 716 00:44:34,000 --> 00:44:36,850 It's a good review when you're preparing 717 00:44:36,850 --> 00:44:40,495 for your midterm, which unfortunately occurs all 718 00:44:40,495 --> 00:44:42,280 too soon. 719 00:44:42,280 --> 00:44:44,710 So that's why I put these in here. 720 00:44:44,710 --> 00:44:46,060 It's a good point to review. 721 00:44:48,930 --> 00:44:50,875 What we're going to do next time, 722 00:44:50,875 --> 00:44:53,923 we will start by talking about segmentation. 723 00:44:56,460 --> 00:45:00,190 That's what a neuromere is. 724 00:45:00,190 --> 00:45:02,300 So what would a prosomere be? 725 00:45:04,950 --> 00:45:09,640 Remember, in the hindbrain what neuromeres were called? 726 00:45:09,640 --> 00:45:12,670 Rhombomeres, right. 727 00:45:12,670 --> 00:45:17,730 The midbrain only has one or two, the mesomere. 728 00:45:17,730 --> 00:45:21,450 There is an isthmic segment too. 729 00:45:21,450 --> 00:45:24,074 Some people would say that's midbrain. 730 00:45:24,074 --> 00:45:25,490 Other people would say, well, it's 731 00:45:25,490 --> 00:45:27,810 between the midbrain and the hindbrain. 732 00:45:27,810 --> 00:45:28,980 I would say it's midbrain. 733 00:45:28,980 --> 00:45:30,012 It's caudal midbrain. 734 00:45:33,950 --> 00:45:37,570 But then, when you go forward, prosomeres. 735 00:45:37,570 --> 00:45:47,870 Remember, prosencephalon-- it means the endbrain 736 00:45:47,870 --> 00:45:53,850 and tweenbrain together, both prosencephalic, forebrain. 737 00:45:53,850 --> 00:45:55,710 So they're the forebrain segments. 738 00:45:59,420 --> 00:46:02,430 The segments of the diencephalon were initially 739 00:46:02,430 --> 00:46:05,260 defined just structurally. 740 00:46:05,260 --> 00:46:08,400 You can make them out in careful studies, 741 00:46:08,400 --> 00:46:10,780 especially with fiber connections, 742 00:46:10,780 --> 00:46:13,120 in early development. 743 00:46:13,120 --> 00:46:17,460 And you see, epithalamus, thalamus, subthalamus, 744 00:46:17,460 --> 00:46:19,460 and hypothalamus. 745 00:46:19,460 --> 00:46:23,020 The structural studies initially just indicated those four. 746 00:46:23,020 --> 00:46:27,980 And interesting enough, they're caudal to rostral. 747 00:46:27,980 --> 00:46:31,280 We think of them as dorsal to ventral, 748 00:46:31,280 --> 00:46:32,720 but that's just because of the way 749 00:46:32,720 --> 00:46:37,060 the neuraxis bends around during development. 750 00:46:37,060 --> 00:46:39,900 So anyway, we'll talk about this the beginning 751 00:46:39,900 --> 00:46:40,650 of the last class. 752 00:46:40,650 --> 00:46:43,250 This shows those divisions as they've 753 00:46:43,250 --> 00:46:47,660 been made largely from gene expression data. 754 00:46:47,660 --> 00:46:51,050 But you can see the interpretation has changed. 755 00:46:51,050 --> 00:46:53,185 It's changed from this at the top 756 00:46:53,185 --> 00:46:56,700 to this down here, because the gene expression 757 00:46:56,700 --> 00:47:00,560 data are pretty complex. 758 00:47:00,560 --> 00:47:03,095 And people get slightly different results, 759 00:47:03,095 --> 00:47:04,965 and they put more emphasis sometimes 760 00:47:04,965 --> 00:47:07,370 on one gene versus another. 761 00:47:07,370 --> 00:47:10,240 So it's changed a bit, and it's the most argument-- 762 00:47:10,240 --> 00:47:13,170 they used to think that the entire endbrain here developed 763 00:47:13,170 --> 00:47:15,390 out of just one or two neuromeres. 764 00:47:15,390 --> 00:47:18,915 With the tweenbrain now, that's not so accepted. 765 00:47:21,850 --> 00:47:26,240 It appears to develop quite largely separately. 766 00:47:26,240 --> 00:47:28,449 So we'll go through that. 767 00:47:28,449 --> 00:47:29,990 And then we'll talk a little bit more 768 00:47:29,990 --> 00:47:34,102 about the meaning of that gene expression data. 769 00:47:34,102 --> 00:47:36,390 So we'll come back to these questions. 770 00:47:36,390 --> 00:47:38,300 I won't go through these in class 771 00:47:38,300 --> 00:47:43,330 unless you can't figure them out. 772 00:47:43,330 --> 00:47:49,260 You please bring it up or post questions of the forum. 773 00:47:49,260 --> 00:47:52,790 And also, if you think because of the changes I'd like to make 774 00:47:52,790 --> 00:47:56,580 I'm going to give you a quiz at the beginning of every class. 775 00:47:56,580 --> 00:48:00,270 If it's a question on the reading for that day, 776 00:48:00,270 --> 00:48:02,800 I will try to make it a fairly easy question 777 00:48:02,800 --> 00:48:04,530 that you'll be able to answer if you've 778 00:48:04,530 --> 00:48:07,109 read the chapter carefully, but I 779 00:48:07,109 --> 00:48:08,650 won't expect you to get every detail. 780 00:48:11,340 --> 00:48:13,110 And sometimes I will be including 781 00:48:13,110 --> 00:48:15,970 a question on the previous class, 782 00:48:15,970 --> 00:48:19,310 just like today, the little practice quiz you had today. 783 00:48:19,310 --> 00:48:21,219 So we won't take a full 10 minutes 784 00:48:21,219 --> 00:48:23,635 at all-- just a few minutes at the beginning of the class, 785 00:48:23,635 --> 00:48:26,580 and then I'll go ahead with the discussion. 786 00:48:26,580 --> 00:48:28,610 But if you have any issues about this 787 00:48:28,610 --> 00:48:31,450 or you can make suggestions about what kind of worksheets 788 00:48:31,450 --> 00:48:35,200 you would like, just post it for me on the forum, 789 00:48:35,200 --> 00:48:38,570 and I will listen, and Caitlin will listen. 790 00:48:38,570 --> 00:48:40,070 We'll try to come up with something. 791 00:48:40,070 --> 00:48:43,966 We can bring you worksheets that you can work on. 792 00:48:43,966 --> 00:48:45,340 You suggested this the other day, 793 00:48:45,340 --> 00:48:48,070 and I think it's a good idea.