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 00:00:23,359 --> 00:00:24,900 PROFESSOR: This is the ninth session, 9 00:00:24,900 --> 00:00:29,200 but we have a little bit from the last session to finish. 10 00:00:29,200 --> 00:00:31,200 I want to say just a little more about 11 00:00:31,200 --> 00:00:32,660 the autonomic nervous system. 12 00:00:36,320 --> 00:00:39,160 And this is where we ended last time. 13 00:00:39,160 --> 00:00:46,840 And let's go back to when we talked 14 00:00:46,840 --> 00:00:52,840 about the early development of the spinal cord 15 00:00:52,840 --> 00:00:55,750 and the formation of the sympathetic ganglia. 16 00:00:55,750 --> 00:00:59,490 This was the picture we used. 17 00:00:59,490 --> 00:01:02,450 You see the thickening of the neural plate there, 18 00:01:02,450 --> 00:01:06,203 formation of the neural groove, and then the neural tube, 19 00:01:06,203 --> 00:01:10,740 formation of the dorsal root ganglia. 20 00:01:10,740 --> 00:01:12,820 But then, from those neural crest cells, 21 00:01:12,820 --> 00:01:15,690 we also have the formation-- some of these cells 22 00:01:15,690 --> 00:01:21,060 migrate and form the paravertibral ganglia, a series 23 00:01:21,060 --> 00:01:24,630 of interconnected ganglia alongside, 24 00:01:24,630 --> 00:01:28,050 just in front and to the side of the spinal cord. 25 00:01:28,050 --> 00:01:30,340 They're outside the vertebrae. 26 00:01:30,340 --> 00:01:34,490 In between the paravertibral ganglia and the neural tube 27 00:01:34,490 --> 00:01:36,410 there are the spinal vertebrae. 28 00:01:39,190 --> 00:01:46,230 And then there's also the prevertibral ganglia. 29 00:01:46,230 --> 00:01:52,550 One is the largest, cilia ganglion, innervating the gut. 30 00:01:52,550 --> 00:01:54,910 So we're going to talk about that innervation, 31 00:01:54,910 --> 00:01:57,135 sympathetic innervation pattern, first. 32 00:02:00,750 --> 00:02:03,200 The preganglionic motor neurons that 33 00:02:03,200 --> 00:02:07,600 innervate these three ganglia you see hear, 34 00:02:07,600 --> 00:02:14,030 sympathetic ganglia, are found from the first thoracic segment 35 00:02:14,030 --> 00:02:20,680 in the cord to about the second lumbar segment. 36 00:02:20,680 --> 00:02:24,190 And if you look at this series of sections 37 00:02:24,190 --> 00:02:28,600 that we saw before in slightly different colors, 38 00:02:28,600 --> 00:02:35,510 you'll see the little lateral horn in these three segments. 39 00:02:35,510 --> 00:02:38,480 This is L1 and to of the thoracic segments. 40 00:02:38,480 --> 00:02:42,390 There you see the little protrusion of the lateral horn. 41 00:02:42,390 --> 00:02:46,290 And if we take just a section-- this 42 00:02:46,290 --> 00:02:52,250 would be one of these sections-- there's the lateral horn, 43 00:02:52,250 --> 00:02:58,230 and I'm showing some of the preganglionic motor neurons. 44 00:02:58,230 --> 00:03:00,540 I will also show an axon descending 45 00:03:00,540 --> 00:03:02,550 from the brain that's connecting there 46 00:03:02,550 --> 00:03:06,980 directly to the lateral horn neurons. 47 00:03:06,980 --> 00:03:10,620 So these are preganglionic of the sympathetic system. 48 00:03:10,620 --> 00:03:13,190 So they're sending their axon out to a ganglia, 49 00:03:13,190 --> 00:03:15,020 either the paravertibral ganglion 50 00:03:15,020 --> 00:03:19,620 here at that level or a prevertibral ganglion, 51 00:03:19,620 --> 00:03:24,200 like this cilia ganglion, which I show here 52 00:03:24,200 --> 00:03:28,820 sending an axon to the smooth muscle of the gut. 53 00:03:28,820 --> 00:03:34,740 And notice that axons of the paravertibral ganglion cells 54 00:03:34,740 --> 00:03:37,730 send their axon back into the ventral root. 55 00:03:43,120 --> 00:03:46,130 These are the communicating nerves 56 00:03:46,130 --> 00:03:50,610 that connect the paravertibral ganglia, each of them, 57 00:03:50,610 --> 00:03:54,060 to the ventral roots. 58 00:03:54,060 --> 00:03:58,810 So the axon that goes back into the ventral root, 59 00:03:58,810 --> 00:04:01,325 besides to some of the intestinal tract, 60 00:04:01,325 --> 00:04:11,030 it's going to smooth muscles, glands, blood vessels, 61 00:04:11,030 --> 00:04:14,780 the arrector pili muscles, the muscles that make the hair 62 00:04:14,780 --> 00:04:20,050 fluff up, and sweat glands. 63 00:04:20,050 --> 00:04:26,330 And the upper thoracic, some of those nerves 64 00:04:26,330 --> 00:04:28,850 go to the cardiac muscles. 65 00:04:31,360 --> 00:04:36,350 This is a typical textbook illustration. 66 00:04:36,350 --> 00:04:40,350 This is one, I think, from the earlier Brodal volume. 67 00:04:40,350 --> 00:04:41,560 This is Per Brodal. 68 00:04:44,780 --> 00:04:48,040 And it shows the spinal cord. 69 00:04:48,040 --> 00:04:51,600 These would be lateral horn neurons 70 00:04:51,600 --> 00:04:55,030 sending their axons out to terminate. 71 00:04:55,030 --> 00:04:57,420 The paravertibral ganglia-- he just shows 72 00:04:57,420 --> 00:05:00,590 the chain of ganglia on one side. 73 00:05:00,590 --> 00:05:03,900 And then he shows a prevertibral ganglion here. 74 00:05:03,900 --> 00:05:05,850 There's also plexi. 75 00:05:05,850 --> 00:05:09,440 A plexus is just a tangle of nerve fibers. 76 00:05:09,440 --> 00:05:13,500 It may or may not have ganglion cells in it. 77 00:05:13,500 --> 00:05:15,510 The cilia ganglion, like you see here, 78 00:05:15,510 --> 00:05:22,380 has cells of the synthetic nervous system in it. 79 00:05:22,380 --> 00:05:28,290 And the axons of those cells then go out to the end organs. 80 00:05:28,290 --> 00:05:30,310 Now, for the parasympathetic, it's 81 00:05:30,310 --> 00:05:37,290 quite different in the nature of the innervation. 82 00:05:37,290 --> 00:05:41,440 Because now the preganglionic motor neurons 83 00:05:41,440 --> 00:05:43,510 are up in the brain. 84 00:05:43,510 --> 00:05:48,160 They're in the dorsal motor nucleus of the vagus nerve. 85 00:05:48,160 --> 00:05:50,810 They're in salivatory nuclei, very tiny nuclei 86 00:05:50,810 --> 00:05:53,780 in the upper hindbrain, the rostral hindbrain, 87 00:05:53,780 --> 00:05:56,530 or in a little part of the third nerve 88 00:05:56,530 --> 00:05:58,200 nucleus, the Edinger-Westphal nucleus, 89 00:05:58,200 --> 00:06:00,321 the nucleus that controls the pupus. 90 00:06:02,970 --> 00:06:09,200 OK, so now in the case of a parasympathetic system, 91 00:06:09,200 --> 00:06:15,180 the postsynaptic cell here, it gets the synapses 92 00:06:15,180 --> 00:06:19,190 from the brain, the axon coming from the brain. 93 00:06:19,190 --> 00:06:21,320 It's always near the end organ. 94 00:06:21,320 --> 00:06:26,550 So for the eye, it's just a ganglion behind the eye. 95 00:06:26,550 --> 00:06:29,720 And the axons go to the iris. 96 00:06:29,720 --> 00:06:35,090 With the gut, it's cells right in the wall of the gut. 97 00:06:35,090 --> 00:06:37,740 And as we will see, they form an entire nervous system 98 00:06:37,740 --> 00:06:40,130 by themselves. 99 00:06:40,130 --> 00:06:46,880 But there you see the axon of the postganglionic cell 100 00:06:46,880 --> 00:06:49,380 innervating the smooth muscle of the gut. 101 00:06:49,380 --> 00:06:52,990 And the same is true for pelvic organs here. 102 00:06:52,990 --> 00:06:55,920 This is, you can see, another way textbooks 103 00:06:55,920 --> 00:06:57,160 sometimes illustrate it here. 104 00:06:57,160 --> 00:07:00,850 They're showing three sections of the brain, midbrain, and two 105 00:07:00,850 --> 00:07:04,270 of the hindbrain, showing how the axons 106 00:07:04,270 --> 00:07:09,110 of the parasympathetic system go out to a ganglion. 107 00:07:09,110 --> 00:07:12,630 And they're just sketching some of those ganglia that 108 00:07:12,630 --> 00:07:14,790 are near the organs being innervated. 109 00:07:14,790 --> 00:07:17,450 And then you have the same thing with the [INAUDIBLE] 110 00:07:17,450 --> 00:07:25,790 for the innervation of the organs of lumenation 111 00:07:25,790 --> 00:07:27,841 and the sexual organs. 112 00:07:27,841 --> 00:07:28,340 OK. 113 00:07:28,340 --> 00:07:32,450 So what about the neurotransmitters? 114 00:07:32,450 --> 00:07:34,825 How are the neurotransmitters different? 115 00:07:34,825 --> 00:07:38,750 Remember when we encountered this before? 116 00:07:38,750 --> 00:07:42,970 We talked about the discovery of Otto Loewi? 117 00:07:42,970 --> 00:07:46,200 What was his discovery? 118 00:07:46,200 --> 00:07:47,870 What was he studying the innervation of? 119 00:07:51,560 --> 00:07:54,240 The heart, exactly. 120 00:07:54,240 --> 00:07:58,100 And he found that it was a chemical released 121 00:07:58,100 --> 00:08:02,800 by the neurons that was causing the heart to speed up or slow 122 00:08:02,800 --> 00:08:09,170 down when the accelerator nerve or the decelerator nerve 123 00:08:09,170 --> 00:08:12,310 were activated. 124 00:08:12,310 --> 00:08:14,500 But Loewi didn't actually discovered 125 00:08:14,500 --> 00:08:17,025 the neurotransmitters of the autonomic innervation 126 00:08:17,025 --> 00:08:19,930 of the heart. 127 00:08:19,930 --> 00:08:22,020 What are the neurotransmitters? 128 00:08:25,520 --> 00:08:27,915 Acetylcholine for both. 129 00:08:30,730 --> 00:08:33,419 It actually is true for both if we're 130 00:08:33,419 --> 00:08:36,830 talking about the neurotransmitter 131 00:08:36,830 --> 00:08:42,559 release in the autonomic ganglia. 132 00:08:42,559 --> 00:08:45,200 It's always acetylcholine-- sympathetic and 133 00:08:45,200 --> 00:08:46,310 parasympathetic. 134 00:08:46,310 --> 00:08:52,200 But when the organ itself is innervated by the ganglion cell 135 00:08:52,200 --> 00:08:55,260 axon, then the neurotransmitters are different. 136 00:08:55,260 --> 00:08:59,090 So then what you were about to say is correct, 137 00:08:59,090 --> 00:09:00,410 they are different. 138 00:09:00,410 --> 00:09:03,975 Acetylcholine for the parasympathetic system 139 00:09:03,975 --> 00:09:08,620 in almost all cases and noradrenaline, or 140 00:09:08,620 --> 00:09:12,200 norepinephrine is the technical name, 141 00:09:12,200 --> 00:09:17,420 for-- that's the one that speeds the heart, norepinephrine. 142 00:09:17,420 --> 00:09:20,080 Norepinephrine or noradrenaline is very similar. 143 00:09:20,080 --> 00:09:23,816 Adrenaline is actually a trade name, but it's often used. 144 00:09:28,280 --> 00:09:30,860 The molecule is very similar to that of adrenaline, 145 00:09:30,860 --> 00:09:35,910 released by the adrenal glands. 146 00:09:35,910 --> 00:09:39,240 And they have similar effects on the postsynaptic side. 147 00:09:43,300 --> 00:09:46,859 So here I've just shown the innervation of the heart 148 00:09:46,859 --> 00:09:48,150 and the innervation of the gut. 149 00:09:48,150 --> 00:09:52,380 If you look at the gut here, I show acetylcholine 150 00:09:52,380 --> 00:09:55,960 being released in the cilia ganglion. 151 00:09:55,960 --> 00:09:57,965 And then the axon that innervates 152 00:09:57,965 --> 00:10:01,722 the gut is releasing norepinephrine, or is often 153 00:10:01,722 --> 00:10:06,290 just N-E in my abbreviations, or A-C-H for acetylcholine if it's 154 00:10:06,290 --> 00:10:07,540 parasympathetic. 155 00:10:07,540 --> 00:10:09,875 And notice the preganglionic cell 156 00:10:09,875 --> 00:10:15,380 for the-- you could be way down in the lower gut. 157 00:10:15,380 --> 00:10:17,802 But the parasympathetic axon originates here 158 00:10:17,802 --> 00:10:21,850 in the dorsal motor nucleus, the vagus nerve in the hindbrain. 159 00:10:21,850 --> 00:10:26,040 So the reason it's called the vagus nerve, 160 00:10:26,040 --> 00:10:27,480 it's a wandering nerve. 161 00:10:27,480 --> 00:10:29,082 It goes through a lot of the body, 162 00:10:29,082 --> 00:10:33,588 from all the way up here to all the way down to the body. 163 00:10:33,588 --> 00:10:39,115 So vagus means the wanderer, the vagus nerve, 164 00:10:39,115 --> 00:10:42,430 the 10th cranial nerve. 165 00:10:42,430 --> 00:10:44,800 So what about the enteric nervous system? 166 00:10:44,800 --> 00:10:48,130 I just mentioned it. 167 00:10:48,130 --> 00:10:52,300 Why do you think it's considered to be a separate system? 168 00:10:52,300 --> 00:10:59,960 It's it just the ganglionic neurons of the parasympathetic? 169 00:10:59,960 --> 00:11:03,930 It actually isn't quite that way. 170 00:11:03,930 --> 00:11:06,470 It is that, but it's much more. 171 00:11:06,470 --> 00:11:10,840 First of all, it's semi-autonomous. 172 00:11:10,840 --> 00:11:18,820 That means the neurons connect with each other and interact. 173 00:11:18,820 --> 00:11:21,970 Peristalsis in the gut is regulated by it. 174 00:11:21,970 --> 00:11:26,320 That will go on even if the gut loses its innervation 175 00:11:26,320 --> 00:11:28,770 in the brain. 176 00:11:28,770 --> 00:11:31,610 And there may be as many neurons in that system 177 00:11:31,610 --> 00:11:33,950 as in the entire spinal cord. 178 00:11:33,950 --> 00:11:37,220 This was all discovered in the last 20 years 179 00:11:37,220 --> 00:11:43,130 with advances in neuroanatomical methods. 180 00:11:43,130 --> 00:11:47,650 So most of these neurons are in the walls of the intestine. 181 00:11:47,650 --> 00:11:50,250 It's a network of multiple plexi. 182 00:11:50,250 --> 00:11:58,350 And here I list the different layers of the plexus, 183 00:11:58,350 --> 00:11:59,850 each containing neurons. 184 00:11:59,850 --> 00:12:01,890 It's innervated by the vagus nerve. 185 00:12:07,880 --> 00:12:10,330 It's similar to the cardiac ganglion, 186 00:12:10,330 --> 00:12:13,410 but we think the cardiac ganglion also 187 00:12:13,410 --> 00:12:17,540 has some interconnections within itself. 188 00:12:17,540 --> 00:12:19,330 So maybe the heart has a brain too, 189 00:12:19,330 --> 00:12:21,400 but the heart definitely has, and it's 190 00:12:21,400 --> 00:12:23,910 called the enteric nervous system. 191 00:12:23,910 --> 00:12:27,500 And I also point out here that various neurotransmitters 192 00:12:27,500 --> 00:12:30,890 are used in that system, various peptides, 193 00:12:30,890 --> 00:12:33,060 various neurotransmitters, not only acetylcholine. 194 00:12:37,280 --> 00:12:38,950 So that was a major discovery, very 195 00:12:38,950 --> 00:12:43,030 important in modern medicine, and of course opened up 196 00:12:43,030 --> 00:12:47,570 all kinds of new treatments with greater knowledge 197 00:12:47,570 --> 00:12:49,280 of the neurotransmitters there. 198 00:12:52,790 --> 00:12:55,580 I want to discuss just briefly the hierarchy 199 00:12:55,580 --> 00:13:00,230 of central control in the autonomic nervous system. 200 00:13:00,230 --> 00:13:02,910 And the best way to illustrate that 201 00:13:02,910 --> 00:13:05,885 is to talk about control of body temperature. 202 00:13:05,885 --> 00:13:10,810 We know body temperature is regulated 203 00:13:10,810 --> 00:13:13,582 by autonomic nervous system. 204 00:13:13,582 --> 00:13:17,910 And you could say in general for autonomic system, 205 00:13:17,910 --> 00:13:20,470 there's different levels of control, spinal level, 206 00:13:20,470 --> 00:13:24,310 hindbrain level, midbrain level, and forebrain level. 207 00:13:24,310 --> 00:13:26,455 Temperature regulation is the thing 208 00:13:26,455 --> 00:13:29,010 that's been studied most thoroughly 209 00:13:29,010 --> 00:13:31,745 by this woman, Evelyn Satinoff. 210 00:13:31,745 --> 00:13:34,360 She's written some very nice review papers. 211 00:13:34,360 --> 00:13:39,080 I think I cite a major review she wrote in the book 212 00:13:39,080 --> 00:13:42,350 as a suggested reading. 213 00:13:42,350 --> 00:13:46,440 So what does this mean, that there's these multiple levels? 214 00:13:46,440 --> 00:13:51,320 It means that if you have an animal in which the spinal cord 215 00:13:51,320 --> 00:13:54,820 has been disconnected from the brain-- 216 00:13:54,820 --> 00:13:58,270 so the brain can influence only the head region, 217 00:13:58,270 --> 00:14:01,280 no longer influences the body-- you still 218 00:14:01,280 --> 00:14:05,330 have temperature regulation of the body. 219 00:14:05,330 --> 00:14:10,250 But it's not nearly as good as the temperature regulation 220 00:14:10,250 --> 00:14:12,840 is if the animal is intact. 221 00:14:12,840 --> 00:14:16,995 If you leave the hindbrain connected but not the midbrain 222 00:14:16,995 --> 00:14:20,410 and the forebrain, then the regulation improves. 223 00:14:20,410 --> 00:14:23,230 But it's still not normal. 224 00:14:23,230 --> 00:14:25,600 The midbrain adds a little more, but only 225 00:14:25,600 --> 00:14:29,780 if you have the hypothalamus in the diencephalon, 226 00:14:29,780 --> 00:14:35,496 the tweenbrain do you get really normal endothermic regulation 227 00:14:35,496 --> 00:14:36,731 in warmblooded animals. 228 00:14:40,462 --> 00:14:42,420 Of course, all of this would be quite different 229 00:14:42,420 --> 00:14:46,570 if we're dealing with the poikilothermic animals, 230 00:14:46,570 --> 00:14:52,030 the animals that lose body temperature as regulated only 231 00:14:52,030 --> 00:14:55,580 by their behavior and not by internal mechanisms. 232 00:14:58,045 --> 00:15:00,461 And I'm not going to go through the supplementary figures. 233 00:15:05,820 --> 00:15:09,542 So now, let's get into the hindbrain. 234 00:15:09,542 --> 00:15:11,500 And we'll talk a little bit about segmentation. 235 00:15:15,530 --> 00:15:16,980 Oh, wait a minute. 236 00:15:16,980 --> 00:15:28,865 Before that, I want to have that little intermission 237 00:15:28,865 --> 00:15:32,040 in the book, where it's important to talk 238 00:15:32,040 --> 00:15:35,850 at some point about the meninges and the glial cells. 239 00:15:35,850 --> 00:15:38,060 So let's just do that first here. 240 00:15:42,740 --> 00:15:44,380 Remember how the whole nervous system 241 00:15:44,380 --> 00:15:46,780 forms around the ventricle. 242 00:15:46,780 --> 00:15:50,920 It's the walls of the tube. 243 00:15:50,920 --> 00:15:57,120 The cerebral spinal fluid that is inside that ventricle 244 00:15:57,120 --> 00:16:01,670 is pretty important because it has nutrients 245 00:16:01,670 --> 00:16:04,629 that it bathes with all the cells, especially 246 00:16:04,629 --> 00:16:05,795 the ones near the ventricle. 247 00:16:08,570 --> 00:16:10,780 It's important for that. 248 00:16:10,780 --> 00:16:14,820 It's important in regulation of fluid balance. 249 00:16:14,820 --> 00:16:18,680 There are very specific brain regions involved in that. 250 00:16:18,680 --> 00:16:21,270 We'll be talking about that. 251 00:16:21,270 --> 00:16:23,360 It's also a communication medium. 252 00:16:23,360 --> 00:16:26,550 This has not been studied all that much, 253 00:16:26,550 --> 00:16:30,640 but there are neurons that secrete substances 254 00:16:30,640 --> 00:16:33,850 into the cerebrospinal fluid. 255 00:16:33,850 --> 00:16:38,960 And because that fluid then [INAUDIBLE] 256 00:16:38,960 --> 00:16:42,030 through the ventricular system and through the penetration 257 00:16:42,030 --> 00:16:46,950 of that fluid into the intercellular 258 00:16:46,950 --> 00:16:52,350 space in the brain, there could be changes in the brain, 259 00:16:52,350 --> 00:16:58,510 because there are some regions where even fairly 260 00:16:58,510 --> 00:17:01,370 large molecules can get into the brain in that fluid. 261 00:17:05,109 --> 00:17:08,619 So let's take a look at how that fluid is made. 262 00:17:08,619 --> 00:17:11,859 These are questions we want to answer. 263 00:17:11,859 --> 00:17:15,720 What cells make the cerebrospinal fluid? 264 00:17:15,720 --> 00:17:19,160 Originally it was just the fluid, the embryonic fluid. 265 00:17:19,160 --> 00:17:22,502 And then the neural tube closed, so now it's all inside. 266 00:17:22,502 --> 00:17:24,835 So the only way you're going to replenish that fluid now 267 00:17:24,835 --> 00:17:27,630 is if you have cells secreting it. 268 00:17:30,810 --> 00:17:35,251 But you have to keep in mind the cerebrospinal fluid isn't just 269 00:17:35,251 --> 00:17:36,000 in the ventricles. 270 00:17:36,000 --> 00:17:38,160 It's also outside the brain. 271 00:17:38,160 --> 00:17:41,130 How does it get out? 272 00:17:41,130 --> 00:17:44,355 It's around the outside, outside the pia. 273 00:17:48,130 --> 00:17:52,385 We say it's in the subarachnoid space surrounding the brain, 274 00:17:52,385 --> 00:17:56,150 so if you wanted to see what that means 275 00:17:56,150 --> 00:17:58,524 and how it gets there. 276 00:17:58,524 --> 00:18:00,315 And then a term for a part of the ventricle 277 00:18:00,315 --> 00:18:01,860 is the aqueduct of Sylvius. 278 00:18:01,860 --> 00:18:04,780 We'll define that too. 279 00:18:04,780 --> 00:18:10,300 First of all, can somebody tell me what cells make it? 280 00:18:10,300 --> 00:18:12,660 What are the choroid plexus cells? 281 00:18:12,660 --> 00:18:14,390 That's exactly right. 282 00:18:14,390 --> 00:18:17,300 What are they? 283 00:18:17,300 --> 00:18:18,480 They're ependymal cells. 284 00:18:18,480 --> 00:18:19,700 What are ependymal cells? 285 00:18:24,580 --> 00:18:28,850 They're cells that line the ventricle. 286 00:18:28,850 --> 00:18:31,940 The ependymal cells are those cells 287 00:18:31,940 --> 00:18:36,600 at the very inner edge of the central nervous system. 288 00:18:36,600 --> 00:18:52,840 So in this picture, I show here places 289 00:18:52,840 --> 00:18:56,150 where that lining, the ependymal cells, which are 290 00:18:56,150 --> 00:18:58,110 all along the ventrical here. 291 00:19:00,900 --> 00:19:06,450 When the wall of the neural tube is thin there, 292 00:19:06,450 --> 00:19:11,590 some of those cells become-- they proliferate. 293 00:19:11,590 --> 00:19:14,630 So they proliferate so much that when 294 00:19:14,630 --> 00:19:18,020 you're doing a dissection in the adult brain 295 00:19:18,020 --> 00:19:20,990 and you enter the ventricle, you'll sometimes 296 00:19:20,990 --> 00:19:23,830 find them as clumps of red stuff. 297 00:19:23,830 --> 00:19:25,300 You don't realize what they are. 298 00:19:25,300 --> 00:19:26,720 But here's what they are. 299 00:19:26,720 --> 00:19:29,030 They're these cells that have proliferated. 300 00:19:29,030 --> 00:19:32,860 So the length of this membrane has gotten much longer, 301 00:19:32,860 --> 00:19:37,500 and it sort of corrugates like that. 302 00:19:37,500 --> 00:19:41,270 They are secreting cerebrospinal fluid 303 00:19:41,270 --> 00:19:44,090 into the lateral ventricles. 304 00:19:44,090 --> 00:19:46,990 And they secrete so much that it flows out 305 00:19:46,990 --> 00:19:50,340 of the lateral ventricles, as you see here with the arrows, 306 00:19:50,340 --> 00:19:53,250 and into the third ventricle, where there 307 00:19:53,250 --> 00:19:56,390 is more choroid plexus at the roof. 308 00:19:56,390 --> 00:20:02,700 But the third ventricle is a narrow ventricle 309 00:20:02,700 --> 00:20:08,070 that goes all the way down and all the way to the top. 310 00:20:08,070 --> 00:20:10,320 So there's not very much choroid plexus there. 311 00:20:10,320 --> 00:20:13,840 Most of the fluid is made here in the lateral ventricles. 312 00:20:13,840 --> 00:20:18,825 And it flows then caudally through this narrowed ventricle 313 00:20:18,825 --> 00:20:23,130 in the midbrain, where it gets a special name, the aqueduct 314 00:20:23,130 --> 00:20:27,230 of Sylvius, because Sylvius described it. 315 00:20:27,230 --> 00:20:31,620 And then, when it gets to the fourth ventricle, which 316 00:20:31,620 --> 00:20:39,650 is much bigger-- remember the fourth ventricle widens out-- 317 00:20:39,650 --> 00:20:45,500 there are little openings to the outside, lateral apertures 318 00:20:45,500 --> 00:20:48,502 and one midline aperture. 319 00:20:48,502 --> 00:20:52,480 The lateral apertures, for those history buffs, 320 00:20:52,480 --> 00:21:00,360 are named for Luschka, because Luschka named them-- sorry, 321 00:21:00,360 --> 00:21:02,070 discovered them. 322 00:21:02,070 --> 00:21:04,470 And other people named it after him. 323 00:21:04,470 --> 00:21:06,470 And then there's one right on the midline that's 324 00:21:06,470 --> 00:21:12,110 named after [INAUDIBLE], because he described them. 325 00:21:12,110 --> 00:21:13,810 So that's how the fluid gets out. 326 00:21:13,810 --> 00:21:16,735 Now, it also goes all the way down. 327 00:21:16,735 --> 00:21:21,278 It forms the cerebrospinal fluid of the cord also. 328 00:21:21,278 --> 00:21:23,491 AUDIENCE: [INAUDIBLE]. 329 00:21:23,491 --> 00:21:24,740 PROFESSOR: There are openings. 330 00:21:24,740 --> 00:21:29,145 It flows right out into the subarachnoid space. 331 00:21:29,145 --> 00:21:34,640 So let's look at that, where it's flowing to. 332 00:21:34,640 --> 00:21:38,250 This is just what I said. 333 00:21:38,250 --> 00:21:41,390 So now I want the layers of the meninges that 334 00:21:41,390 --> 00:21:44,660 surround the brain and spinal cord. 335 00:21:44,660 --> 00:21:46,865 And then I want a little more detail. 336 00:21:46,865 --> 00:21:49,736 I want to know what the pial-glial membrane is. 337 00:21:49,736 --> 00:21:51,710 What are the cells that make it? 338 00:21:51,710 --> 00:21:54,030 But first of all, you should all know the meninges. 339 00:21:56,590 --> 00:22:04,590 Dura, which means tough mother, right. 340 00:22:04,590 --> 00:22:07,440 Dura mater-- it's not matter. 341 00:22:07,440 --> 00:22:12,560 It's not dura matter, it's dura mater, the tough mother. 342 00:22:12,560 --> 00:22:16,742 And then the innermost one, what's that? 343 00:22:19,520 --> 00:22:21,450 The soft mother, right. 344 00:22:21,450 --> 00:22:24,150 Pia mother, the gentle mother. 345 00:22:24,150 --> 00:22:27,750 It's very thin, it's transparent. 346 00:22:27,750 --> 00:22:29,790 When you do a brain dissection, people 347 00:22:29,790 --> 00:22:33,080 will say, oh, make sure you remove all the meninges. 348 00:22:33,080 --> 00:22:34,800 Make sure you remove the pia. 349 00:22:34,800 --> 00:22:35,930 How can you remove the pia? 350 00:22:35,930 --> 00:22:37,900 You can't even see it. 351 00:22:37,900 --> 00:22:38,735 It's so thin. 352 00:22:38,735 --> 00:22:41,180 It's people that don't know they're anatomy very well that 353 00:22:41,180 --> 00:22:42,350 ask you to do that. 354 00:22:42,350 --> 00:22:43,880 What they're really asking you to do 355 00:22:43,880 --> 00:22:47,720 is to pull out the arachnoid. 356 00:22:47,720 --> 00:22:52,400 The arachnoid, what is the word arachnoid mean? 357 00:22:52,400 --> 00:22:54,080 Spider. 358 00:22:54,080 --> 00:22:57,360 It's like a spider's web. 359 00:22:57,360 --> 00:23:02,910 So I love this figure from Brodal. 360 00:23:02,910 --> 00:23:07,670 I made a new version of it for the book. 361 00:23:07,670 --> 00:23:10,240 He shows a little piece of it here 362 00:23:10,240 --> 00:23:12,690 and a little piece of the brain all the way down 363 00:23:12,690 --> 00:23:15,100 to the ventrical underneath. 364 00:23:15,100 --> 00:23:18,385 So at the top you have the thick one. 365 00:23:18,385 --> 00:23:22,100 It's like canvas in monkeys and humans. 366 00:23:22,100 --> 00:23:23,595 In the rat, it's pretty thin. 367 00:23:23,595 --> 00:23:24,830 You see right through it. 368 00:23:24,830 --> 00:23:26,330 You don't see it very readily. 369 00:23:26,330 --> 00:23:28,980 But when you do surgery, you become aware of it, 370 00:23:28,980 --> 00:23:31,670 because it is tougher than the other layers. 371 00:23:31,670 --> 00:23:33,560 That's the dura. 372 00:23:33,560 --> 00:23:41,190 And right below it is the cells of the arachnoid tissue. 373 00:23:41,190 --> 00:23:43,860 And notice that the arachnoid cells have extensions 374 00:23:43,860 --> 00:23:48,580 that go right down and attach to the pia. 375 00:23:48,580 --> 00:23:51,295 It's those attachments that make it look like a spider. 376 00:23:53,900 --> 00:23:57,305 And the arachnoid goes right down 377 00:23:57,305 --> 00:24:00,120 in between the hemispheres, for example, 378 00:24:00,120 --> 00:24:03,370 where the dura does not. 379 00:24:03,370 --> 00:24:06,530 There is dura between the hemispheres and the cerebellum. 380 00:24:06,530 --> 00:24:11,210 It goes in there and makes dissections difficult, 381 00:24:11,210 --> 00:24:13,560 because the dura is so tough. 382 00:24:13,560 --> 00:24:16,580 And note here, the blood vessel is 383 00:24:16,580 --> 00:24:24,050 encased by those cells of the pia mater, the gentle mother. 384 00:24:24,050 --> 00:24:29,020 They surround the blood vessels, even when the blood vessel here 385 00:24:29,020 --> 00:24:36,180 has penetration into the brain, the pial cells follow it down, 386 00:24:36,180 --> 00:24:39,245 but not when it becomes a capillary. 387 00:24:39,245 --> 00:24:41,150 They disappear. 388 00:24:41,150 --> 00:24:48,500 But that blood vessel never contacts the brain cell, 389 00:24:48,500 --> 00:24:52,550 because of these glial cells. 390 00:24:52,550 --> 00:24:55,230 This is a picture of an astrocyte, 391 00:24:55,230 --> 00:25:00,030 and you see the astrocytic endfeet, abutting the pia here, 392 00:25:00,030 --> 00:25:06,060 so we call that the pial-glial membrane at the surface. 393 00:25:06,060 --> 00:25:11,860 It's not pial cells contacting the brain cells, the dendrites. 394 00:25:11,860 --> 00:25:17,650 It's contacting the endfeet of glial cells and the astrocytes. 395 00:25:17,650 --> 00:25:23,260 And similarly, the astrocytes abut the blood vessels. 396 00:25:23,260 --> 00:25:30,590 So the astrocytes are critical in the oxygenation of the brain 397 00:25:30,590 --> 00:25:32,450 and the nutrition of the brain. 398 00:25:32,450 --> 00:25:38,950 Access to glucose and oxygen has to involve these astrocytes. 399 00:25:42,350 --> 00:25:44,050 Now, there are other glia. 400 00:25:44,050 --> 00:25:46,830 I point out here, there are oligodendrocytes. 401 00:25:46,830 --> 00:25:49,700 We talked about how the oligodendrocytes make myelin. 402 00:25:49,700 --> 00:25:55,260 They also forms these little satellites around neurons. 403 00:25:55,260 --> 00:25:58,460 And for any of you that want to study it, 404 00:25:58,460 --> 00:26:03,010 you can take a magnifying glass and study the picture. 405 00:26:03,010 --> 00:26:07,970 You can actually make out all those things here. 406 00:26:07,970 --> 00:26:12,000 You can see pial cells, collagen fibers, smooth muscle-- 407 00:26:12,000 --> 00:26:13,250 very thin. 408 00:26:13,250 --> 00:26:16,020 And note here, you have a blood vessel. 409 00:26:22,710 --> 00:26:25,610 And there's the nucleus, the blood vessel. 410 00:26:25,610 --> 00:26:26,970 There's smooth muscle. 411 00:26:34,290 --> 00:26:40,000 And I want to quickly get on with this. 412 00:26:40,000 --> 00:26:49,780 I want to go-- it looks like I didn't open. 413 00:26:49,780 --> 00:26:51,114 Yeah, OK. 414 00:26:51,114 --> 00:26:53,530 This is all we're left with. 415 00:26:53,530 --> 00:26:55,350 All right. 416 00:26:55,350 --> 00:26:58,840 So now we can get to the hindbrain. 417 00:26:58,840 --> 00:27:02,060 We have enough time, I think, to introduce the hindbrain 418 00:27:02,060 --> 00:27:04,680 and talk about segmentation of the hindbrain. 419 00:27:04,680 --> 00:27:06,880 And I particularly want you to learn 420 00:27:06,880 --> 00:27:10,680 about the differences between hindbrain and spinal cord. 421 00:27:10,680 --> 00:27:14,080 I call the hindbrain a glamorized spinal cord-- very 422 00:27:14,080 --> 00:27:18,092 similar in organization to the spinal cord, 423 00:27:18,092 --> 00:27:20,050 but you have to learn what the similarities are 424 00:27:20,050 --> 00:27:23,600 and what the differences are. 425 00:27:23,600 --> 00:27:25,330 So these, remember, are the names 426 00:27:25,330 --> 00:27:30,840 for the encephalon, which is the Greek word for brain. 427 00:27:30,840 --> 00:27:34,300 Hindbrain, the rhombencephalon, the mesencephalon, 428 00:27:34,300 --> 00:27:39,023 the prosencephalon, consisting of the diencephalon 429 00:27:39,023 --> 00:27:40,317 and the telencephalon. 430 00:27:43,341 --> 00:27:43,840 OK. 431 00:27:43,840 --> 00:27:51,110 So, first of all, when that neural tube 432 00:27:51,110 --> 00:27:53,910 forms at the brain level, it does 433 00:27:53,910 --> 00:27:58,390 something that is not true down in the core. 434 00:27:58,390 --> 00:28:00,370 It develops flexures. 435 00:28:00,370 --> 00:28:03,030 Now, what are the flexures of the neural tube? 436 00:28:03,030 --> 00:28:04,280 These are from the Nauta book. 437 00:28:07,800 --> 00:28:12,010 Very early, you get these sharp bends. 438 00:28:12,010 --> 00:28:16,490 At the cervical level, this is the cervical flexure here. 439 00:28:16,490 --> 00:28:22,400 And there's the mesencephalic flexure. 440 00:28:22,400 --> 00:28:27,493 So they're both concave downward. 441 00:28:33,070 --> 00:28:36,000 Convexity is at the dorsal surface. 442 00:28:36,000 --> 00:28:39,360 And then in between those two flexures, 443 00:28:39,360 --> 00:28:40,940 you get the pontine flexure forming, 444 00:28:40,940 --> 00:28:45,210 and that forms in the opposite direction. 445 00:28:45,210 --> 00:28:47,320 And it's when that pontine flexure 446 00:28:47,320 --> 00:28:51,490 forms that the roof plate widens. 447 00:28:51,490 --> 00:28:57,015 It's like taking a pea pod that splits when you bend it. 448 00:28:57,015 --> 00:28:59,230 So it widens out. 449 00:29:05,060 --> 00:29:08,210 Now, we know about the origin of the term rhombencephalon 450 00:29:08,210 --> 00:29:09,910 because of this rounded shape. 451 00:29:09,910 --> 00:29:12,440 We've mentioned that before. 452 00:29:12,440 --> 00:29:14,030 But there's another question I want 453 00:29:14,030 --> 00:29:17,360 to ask about that, because this landmark, the obex, 454 00:29:17,360 --> 00:29:20,330 is commonly used in neuroanatomy. 455 00:29:20,330 --> 00:29:24,282 The radiologists use it too. 456 00:29:24,282 --> 00:29:25,740 If you're in medical school, you're 457 00:29:25,740 --> 00:29:28,735 learning a little bit about radiology of the brain. 458 00:29:28,735 --> 00:29:31,370 You'll learn this. 459 00:29:31,370 --> 00:29:33,710 This is what they mean by the obex-- this point 460 00:29:33,710 --> 00:29:39,770 right here at the caudal end of that rhombic shape, 461 00:29:39,770 --> 00:29:43,880 where the widened roof plate is no longer widened. 462 00:29:43,880 --> 00:29:46,070 That is what the obex is. 463 00:29:46,070 --> 00:29:48,270 It's an important area because it's 464 00:29:48,270 --> 00:29:51,880 an area where there's a weakening of the blood brain 465 00:29:51,880 --> 00:29:54,820 barrier. 466 00:29:54,820 --> 00:29:59,820 And it's very important for getting rid of toxins, 467 00:29:59,820 --> 00:30:01,835 it can elicit vomiting and so forth, 468 00:30:01,835 --> 00:30:04,150 when there's something bad in the blood. 469 00:30:04,150 --> 00:30:05,800 OK. 470 00:30:05,800 --> 00:30:12,340 So these are now some topics that we'll be going through. 471 00:30:12,340 --> 00:30:15,397 We won't get to all of them today. 472 00:30:15,397 --> 00:30:17,480 We're going to compare the structural organization 473 00:30:17,480 --> 00:30:20,690 to spinal cord, talk about basic functions and cell groupings. 474 00:30:25,330 --> 00:30:29,060 So first of all, how is the hindbrain embryologically 475 00:30:29,060 --> 00:30:33,040 very similar to the spinal cord? 476 00:30:33,040 --> 00:30:36,665 We want to compare and contrast the columns 477 00:30:36,665 --> 00:30:40,640 of secondary sensory cells and motor neurons 478 00:30:40,640 --> 00:30:44,520 of the hindbrain and spinal cord. 479 00:30:44,520 --> 00:30:50,030 If I asked you in just a very few words what 480 00:30:50,030 --> 00:30:52,989 is the difference between hindbrain and spinal cord, 481 00:30:52,989 --> 00:30:53,780 what would you say? 482 00:31:01,130 --> 00:31:03,110 I mean, what are the secondary sensory neurons 483 00:31:03,110 --> 00:31:04,220 of the hindbrain? 484 00:31:04,220 --> 00:31:09,940 What are hindbrain senses, like auditory, vestibular? 485 00:31:09,940 --> 00:31:14,060 They form clumps of cells, nuclei. 486 00:31:14,060 --> 00:31:15,827 That's not true in the spinal cord. 487 00:31:19,630 --> 00:31:22,065 In the spinal cell, there's a continuous column 488 00:31:22,065 --> 00:31:24,740 of secondary sensory cells, but that's probably 489 00:31:24,740 --> 00:31:27,350 because the inputs don't come in through a single nerve. 490 00:31:27,350 --> 00:31:28,900 They come in through multiple nerves. 491 00:31:31,470 --> 00:31:36,080 The dorsal roots of those nerves have a distribution 492 00:31:36,080 --> 00:31:39,316 that-- it always overlaps with the adjoining root. 493 00:31:39,316 --> 00:31:45,290 So there's a continuous group of secondary sensory neurons. 494 00:31:45,290 --> 00:31:48,440 So let's look at that glamorized spinal cord. 495 00:31:48,440 --> 00:31:50,210 There's differences in the roots too. 496 00:31:50,210 --> 00:31:52,160 I mentioned this before. 497 00:31:52,160 --> 00:31:57,160 We have the spinal roots with a [INAUDIBLE] 498 00:31:57,160 --> 00:32:03,740 of roots, sensory in the back, dorsally. 499 00:32:03,740 --> 00:32:07,920 Motor in the front, ventrally. 500 00:32:07,920 --> 00:32:12,450 But in the hindbrain, you have mixed nerves also. 501 00:32:12,450 --> 00:32:14,930 There are nerves just like dorsal roots. 502 00:32:14,930 --> 00:32:17,370 There are nerves like ventral roots. 503 00:32:17,370 --> 00:32:18,870 But there's also mixed nerves, where 504 00:32:18,870 --> 00:32:20,360 you have sensory and motor. 505 00:32:24,180 --> 00:32:29,130 So in the book, I used colors for this, 506 00:32:29,130 --> 00:32:32,135 separating secondary sensory nuclei 507 00:32:32,135 --> 00:32:34,910 at their cell groups in the inner plate 508 00:32:34,910 --> 00:32:37,822 and similarly for the motor neurons. 509 00:32:37,822 --> 00:32:41,340 In the spinal cord, they're pretty continuous, 510 00:32:41,340 --> 00:32:44,000 unless we're dealing with the enlargements 511 00:32:44,000 --> 00:32:46,745 where there's extra goops of motor neurons innervating 512 00:32:46,745 --> 00:32:50,940 the muscles of the arms or the legs and the feet and hands. 513 00:32:55,190 --> 00:32:57,380 So let's look at that. 514 00:32:57,380 --> 00:32:59,990 The picture of the embryonic spinal cord 515 00:32:59,990 --> 00:33:03,770 at the top-- embryonic hindbrain at the bottom, where 516 00:33:03,770 --> 00:33:06,120 the neurotube is thicker. 517 00:33:06,120 --> 00:33:10,040 You have the widening of the roof plate. 518 00:33:10,040 --> 00:33:13,645 But there, the secondary sensory cells form a column. 519 00:33:16,330 --> 00:33:21,380 They're always in that region, whereas here, they're 520 00:33:21,380 --> 00:33:22,470 in these separate columns. 521 00:33:25,320 --> 00:33:30,520 Except when I picture them, I generally 522 00:33:30,520 --> 00:33:31,960 show different colors. 523 00:33:31,960 --> 00:33:38,404 I show, for example-- I'll then use red for this, 524 00:33:38,404 --> 00:33:39,570 because it's viscerosensory. 525 00:33:44,450 --> 00:33:48,470 And I'll use green here for the special century, and usually 526 00:33:48,470 --> 00:33:51,730 another color, green, for general sensory. 527 00:33:51,730 --> 00:33:55,435 Often the somatic senses are called general sensory 528 00:33:55,435 --> 00:33:59,040 because they cover the whole body surface quite generally, 529 00:33:59,040 --> 00:34:01,530 where as the special senses are more localized in the head 530 00:34:01,530 --> 00:34:03,590 region. 531 00:34:03,590 --> 00:34:06,740 And then similarly for the motor neurons. 532 00:34:06,740 --> 00:34:09,290 We have the visceral motor neurons here. 533 00:34:12,409 --> 00:34:16,250 And then we have somatic motor neurons, 534 00:34:16,250 --> 00:34:18,845 like the motor neurons innervating 535 00:34:18,845 --> 00:34:23,560 the eye muscles, or the tongue. 536 00:34:23,560 --> 00:34:25,330 They're in that position. 537 00:34:25,330 --> 00:34:32,190 And then we have the branchial motor column here 538 00:34:32,190 --> 00:34:35,874 that are very much like the somatic motor column, 539 00:34:35,874 --> 00:34:39,330 but you can see, they form a separate column of cells 540 00:34:39,330 --> 00:34:41,659 and they have a different type of embryonic origin. 541 00:34:50,199 --> 00:34:53,830 So let's go to functions a little bit. 542 00:34:53,830 --> 00:34:56,239 Hindbrain is known to be an essential controller 543 00:34:56,239 --> 00:34:57,210 of vital functions. 544 00:34:57,210 --> 00:35:00,930 And what vital functions are we talking about? 545 00:35:00,930 --> 00:35:04,815 Why is it that if you suffer much of a lesion or a stroke 546 00:35:04,815 --> 00:35:08,490 at the hindbrain, you're likely to die? 547 00:35:08,490 --> 00:35:11,690 What are the vital functions being affected? 548 00:35:11,690 --> 00:35:13,250 What is the most vital? 549 00:35:17,810 --> 00:35:22,440 Probably not heart or blood pressure control, 550 00:35:22,440 --> 00:35:25,850 even though that's important in the hindbrain. 551 00:35:25,850 --> 00:35:29,664 But remember, the heart has its own ganglion, 552 00:35:29,664 --> 00:35:32,250 and it has spinal innervation. 553 00:35:32,250 --> 00:35:36,920 And even without that, the heart will keep beating. 554 00:35:36,920 --> 00:35:39,430 Breathing, exactly. 555 00:35:39,430 --> 00:35:42,185 You can't breathe without circuits in the hindbrain. 556 00:35:44,830 --> 00:35:48,120 Those circuits even reach the midbrain. 557 00:35:48,120 --> 00:35:52,780 So all the way down from lower midbrain all the way down 558 00:35:52,780 --> 00:35:57,050 to the fourth cervical level, critical for breathing control. 559 00:35:57,050 --> 00:35:57,550 OK. 560 00:36:00,330 --> 00:36:02,455 What are the other routine maintenance functions 561 00:36:02,455 --> 00:36:03,690 of the hindbrain? 562 00:36:03,690 --> 00:36:06,310 There's actually a lot of them. 563 00:36:06,310 --> 00:36:09,650 But what are some of the things that-- remember, 564 00:36:09,650 --> 00:36:12,820 what we called routine maintenance functions before? 565 00:36:12,820 --> 00:36:15,470 They're always reflex-type functions, or at least 566 00:36:15,470 --> 00:36:17,940 automatic. 567 00:36:17,940 --> 00:36:19,811 They can be programmed movements too. 568 00:36:19,811 --> 00:36:20,310 Yes? 569 00:36:23,842 --> 00:36:26,814 You have to speak loudly, or I can't-- 570 00:36:26,814 --> 00:36:27,730 AUDIENCE: [INAUDIBLE]. 571 00:36:30,284 --> 00:36:30,950 PROFESSOR: Yeah. 572 00:36:30,950 --> 00:36:32,440 Yeah, exactly. 573 00:36:32,440 --> 00:36:34,250 The vestibular reflexes. 574 00:36:34,250 --> 00:36:35,450 We don't think about them. 575 00:36:35,450 --> 00:36:37,050 They're pretty automatic. 576 00:36:37,050 --> 00:36:40,060 They keep us upright. 577 00:36:40,060 --> 00:36:41,835 And they're happening all the time. 578 00:36:41,835 --> 00:36:44,422 They're part of that mantle we're always wearing, 579 00:36:44,422 --> 00:36:45,380 the mantle of relexing. 580 00:36:48,040 --> 00:36:50,160 That's a routine maintenance function. 581 00:36:50,160 --> 00:36:54,360 But there's other things too, things that bother us, 582 00:36:54,360 --> 00:36:56,300 something in the air that makes you sneeze. 583 00:36:56,300 --> 00:36:57,810 You just sneeze. 584 00:36:57,810 --> 00:37:01,140 It's a reflex, and you have trouble controlling it. 585 00:37:01,140 --> 00:37:03,035 Although, yes, we have descending connections 586 00:37:03,035 --> 00:37:05,570 from the forebrain and we can try to suppress it, 587 00:37:05,570 --> 00:37:08,920 but it's almost impossible to completely suppress. 588 00:37:08,920 --> 00:37:11,820 What's another one like that? 589 00:37:11,820 --> 00:37:14,270 Eye blink. 590 00:37:14,270 --> 00:37:17,690 The eyes blink all the time. 591 00:37:17,690 --> 00:37:19,740 You can voluntarily blink the eyes 592 00:37:19,740 --> 00:37:21,380 and you start thinking about it. 593 00:37:21,380 --> 00:37:23,990 You won't be paying attention for a while. 594 00:37:23,990 --> 00:37:26,530 But it's a fixed action pattern. 595 00:37:26,530 --> 00:37:30,290 It's being generated all the time. 596 00:37:30,290 --> 00:37:32,590 It's very important for lubricating the cornea. 597 00:37:32,590 --> 00:37:33,439 Yes? 598 00:37:33,439 --> 00:37:34,355 AUDIENCE: [INAUDIBLE]. 599 00:37:41,790 --> 00:37:43,980 PROFESSOR: Oh, there are. 600 00:37:43,980 --> 00:37:45,680 It's also a reflex. 601 00:37:45,680 --> 00:37:46,590 You can trigger it. 602 00:37:46,590 --> 00:37:50,740 But what you're really doing is you're tremendously 603 00:37:50,740 --> 00:37:54,940 increasing the input into the control of that fixed action 604 00:37:54,940 --> 00:37:55,990 pattern. 605 00:37:55,990 --> 00:37:59,880 You've greatly increased the likelihood that you will blink. 606 00:37:59,880 --> 00:38:02,970 But yes, it does respond to sensory input. 607 00:38:02,970 --> 00:38:05,585 In a very powerful way, that's true of almost every drive, 608 00:38:05,585 --> 00:38:08,120 every motivation. 609 00:38:08,120 --> 00:38:11,180 We have a very strong motivation to blink our eyes. 610 00:38:11,180 --> 00:38:14,340 That's what a staring contest is all about. 611 00:38:14,340 --> 00:38:16,460 Can you resist? 612 00:38:16,460 --> 00:38:17,950 How long can you resist? 613 00:38:17,950 --> 00:38:22,230 Can you resist longer than your friend? 614 00:38:22,230 --> 00:38:25,840 OK, well, how is the hindbrain involved 615 00:38:25,840 --> 00:38:29,270 in higher functions like speech? 616 00:38:29,270 --> 00:38:30,230 Well, wait a minute. 617 00:38:30,230 --> 00:38:33,090 Hindbrain is lower level, right? 618 00:38:33,090 --> 00:38:36,200 Well, it's involved in speech. 619 00:38:36,200 --> 00:38:36,700 Why? 620 00:38:39,640 --> 00:38:43,450 What do we need in order to speak? 621 00:38:43,450 --> 00:38:46,900 Respiration, important. 622 00:38:46,900 --> 00:38:53,850 Control of tongue and jaws and lips, all 623 00:38:53,850 --> 00:38:56,230 controlled by the hindbrain. 624 00:38:56,230 --> 00:38:59,823 Several different cranial nerves, as you will see. 625 00:39:03,680 --> 00:39:08,910 What's the critical role of the hindbrain in feeding behavior? 626 00:39:08,910 --> 00:39:12,470 We can't eat with this hindbrain. 627 00:39:12,470 --> 00:39:14,420 Swallowing. 628 00:39:14,420 --> 00:39:17,300 It's a very complex reflex. 629 00:39:17,300 --> 00:39:19,260 It's a fixed action pattern. 630 00:39:19,260 --> 00:39:23,130 We call it a reflex, but it's actually a fixed action pattern 631 00:39:23,130 --> 00:39:25,585 that can be-- the probability of triggering 632 00:39:25,585 --> 00:39:30,980 it goes way up with certain stimuli, the stimuli 633 00:39:30,980 --> 00:39:33,580 in the back of the tongue. 634 00:39:33,580 --> 00:39:36,530 But we do swallow automatically and periodically 635 00:39:36,530 --> 00:39:41,900 all the time to keep our throats lubricated. 636 00:39:41,900 --> 00:39:44,515 But what else do we need in the hindbrain for feeding? 637 00:39:47,090 --> 00:39:54,450 Control of the jaw-- jaw opening, jaw closing. 638 00:39:54,450 --> 00:39:57,990 There's a special nucleus that's part of the fifth nerve that's 639 00:39:57,990 --> 00:39:59,010 not just sensory. 640 00:39:59,010 --> 00:40:01,470 It's not just the trigeminal nerve. 641 00:40:01,470 --> 00:40:05,920 It's also the masticatory nerve, the motor complement 642 00:40:05,920 --> 00:40:07,230 of the fifth cranial nerve. 643 00:40:07,230 --> 00:40:08,056 Yes? 644 00:40:08,056 --> 00:40:08,972 AUDIENCE: [INAUDIBLE]. 645 00:40:14,870 --> 00:40:17,540 PROFESSOR: That's always an interesting question, 646 00:40:17,540 --> 00:40:19,570 because a lot of it seems to be-- 647 00:40:19,570 --> 00:40:21,770 we do it pretty automatically. 648 00:40:21,770 --> 00:40:24,130 But you can become quite conscious of it 649 00:40:24,130 --> 00:40:29,500 also, just like for eye-blink or jaw opening. 650 00:40:29,500 --> 00:40:30,310 We'll do it. 651 00:40:30,310 --> 00:40:34,408 Even an unconscious person will show some of these movements. 652 00:40:34,408 --> 00:40:35,324 AUDIENCE: [INAUDIBLE]. 653 00:40:42,942 --> 00:40:44,900 PROFESSOR: When you're doing other things, yes. 654 00:40:44,900 --> 00:40:47,970 But some other things can inhibit that. 655 00:40:47,970 --> 00:40:51,155 And that's even true of things in the gut, 656 00:40:51,155 --> 00:40:53,810 if it has an enteric nervous system controlling them. 657 00:40:53,810 --> 00:40:56,760 But some of them can be inhibited. 658 00:40:56,760 --> 00:40:58,810 But mostly that's automatic too. 659 00:40:58,810 --> 00:41:00,680 It's when the sympathetic nervous system 660 00:41:00,680 --> 00:41:01,566 is highly activated. 661 00:41:01,566 --> 00:41:02,990 It inhibits their system. 662 00:41:02,990 --> 00:41:03,547 Yes? 663 00:41:03,547 --> 00:41:04,463 AUDIENCE: [INAUDIBLE]. 664 00:41:10,216 --> 00:41:11,340 PROFESSOR: Visual saccades. 665 00:41:11,340 --> 00:41:13,130 Yeah, that's a very good question. 666 00:41:15,880 --> 00:41:21,110 It's called a visual reflex because they 667 00:41:21,110 --> 00:41:22,720 are being generated all the time, 668 00:41:22,720 --> 00:41:25,362 but strongly influenced by the attentional mechanisms 669 00:41:25,362 --> 00:41:26,070 of our neocortex. 670 00:41:29,600 --> 00:41:30,100 All right. 671 00:41:30,100 --> 00:41:36,960 So this just summarized most of what I just said. 672 00:41:36,960 --> 00:41:39,520 I didn't mention here the widespread modulation 673 00:41:39,520 --> 00:41:44,392 of brain activity in sleep and waking, arousal effects. 674 00:41:44,392 --> 00:41:49,550 But let's just see that a little bit 675 00:41:49,550 --> 00:41:51,190 from the neuroanatomical side. 676 00:41:51,190 --> 00:41:57,550 First of all, neuron types-- Nauta and his collaborator, 677 00:41:57,550 --> 00:42:05,900 Ramon-Moliner made a nice contribution to this field 678 00:42:05,900 --> 00:42:09,660 when they wrote an article called "The Isodendritic 679 00:42:09,660 --> 00:42:11,400 Core of the Brain Stem." 680 00:42:11,400 --> 00:42:16,870 They were talking about two types of neural shapes 681 00:42:16,870 --> 00:42:21,190 that you keep seeing throughout the brain stem, 682 00:42:21,190 --> 00:42:23,510 especially in the hindbrain. 683 00:42:23,510 --> 00:42:25,990 What are the two types they're talking about? 684 00:42:29,810 --> 00:42:32,750 What they called isodendritic is something 685 00:42:32,750 --> 00:42:36,035 that looks like a motor neuron-- long dendrites. 686 00:42:41,950 --> 00:42:45,600 There's the nucleus, there's an axon, 687 00:42:45,600 --> 00:42:47,940 and here are the dendritic branches. 688 00:42:47,940 --> 00:42:53,656 This is isodendritic, very much like a motor neuron. 689 00:42:53,656 --> 00:42:56,600 I won't try to draw the whole thing. 690 00:42:56,600 --> 00:42:59,780 A lot of the reticular formation cells are like that. 691 00:42:59,780 --> 00:43:01,240 They just look like motor neurons. 692 00:43:01,240 --> 00:43:03,600 Though some of them are-- the dendrites 693 00:43:03,600 --> 00:43:06,300 are mostly in a plane. 694 00:43:06,300 --> 00:43:07,200 That's isodendritic. 695 00:43:13,280 --> 00:43:16,700 Then they talked about idiodendritic. 696 00:43:16,700 --> 00:43:18,780 Let's draw an idiodendritic cell. 697 00:43:18,780 --> 00:43:21,030 Here is the nucleus. 698 00:43:21,030 --> 00:43:25,390 And here's a dendrite that instead of this motor 699 00:43:25,390 --> 00:43:31,860 neuron-like stellate shape, it's much more specific. 700 00:43:31,860 --> 00:43:35,640 And idiodendritic cells look very different. 701 00:43:35,640 --> 00:43:38,200 For example, it may be like this. 702 00:43:38,200 --> 00:43:41,660 It may terminate in specific layers. 703 00:43:41,660 --> 00:43:45,380 There's many idiodendritic cells in the retina like that. 704 00:43:45,380 --> 00:43:48,470 They did get different kinds of input in different layers. 705 00:43:48,470 --> 00:43:53,390 Other idiodendritic cells have other, but not necessarily 706 00:43:53,390 --> 00:43:56,930 laminar, in the way they terminate. 707 00:43:56,930 --> 00:44:00,820 Cortical pyramidal cells we can call idiodendritic. 708 00:44:00,820 --> 00:44:02,970 They're specialized. 709 00:44:02,970 --> 00:44:06,380 Some interneurons, they're given names 710 00:44:06,380 --> 00:44:09,754 according to these very particular shapes they have. 711 00:44:09,754 --> 00:44:10,795 They're not isodendritic. 712 00:44:14,240 --> 00:44:21,700 In addition, the Scheidels, who were great anatomists using 713 00:44:21,700 --> 00:44:25,800 the Golgi method here in America-- much of their career 714 00:44:25,800 --> 00:44:31,050 was spent in Los Angeles-- they described in addition segments 715 00:44:31,050 --> 00:44:33,410 in the neuropil. 716 00:44:33,410 --> 00:44:37,320 And they described axons with very wide distribution. 717 00:44:37,320 --> 00:44:42,030 So here is a little diagram of these little disc-like 718 00:44:42,030 --> 00:44:43,470 segments. 719 00:44:43,470 --> 00:44:45,320 Here's what they found. 720 00:44:45,320 --> 00:44:48,300 Here are the isodendritic neurons 721 00:44:48,300 --> 00:44:51,354 that are renticular formation, just a few of them. 722 00:44:51,354 --> 00:44:53,805 But note, their dendrites, they found, 723 00:44:53,805 --> 00:45:03,200 are always within or mostly within these little plates. 724 00:45:03,200 --> 00:45:06,760 And the axons from the cortex-- here's 725 00:45:06,760 --> 00:45:09,800 a few pyramidal tract axons-- note 726 00:45:09,800 --> 00:45:12,450 that they leave at right angles, and they go up 727 00:45:12,450 --> 00:45:17,112 into those segments, so you can diagram it. 728 00:45:17,112 --> 00:45:20,590 If this is pyramidal tract down here, 729 00:45:20,590 --> 00:45:27,370 the axons go up and terminate within those little segments. 730 00:45:32,680 --> 00:45:34,970 And that's what you're seeing in that picture. 731 00:45:37,970 --> 00:45:41,742 Note here that the cells in the hypoglossal nucleus, 732 00:45:41,742 --> 00:45:45,450 the 12th cranial nerve nucleus, they're 733 00:45:45,450 --> 00:45:48,240 not in these segments at all. 734 00:45:48,240 --> 00:45:50,902 So they look very different in the Golgi state. 735 00:45:50,902 --> 00:45:53,120 Now, here's the other thing they described 736 00:45:53,120 --> 00:45:55,050 that was so important. 737 00:45:55,050 --> 00:45:56,260 Here is one neuron. 738 00:45:56,260 --> 00:46:00,010 This entire picture is of one neuron. 739 00:46:00,010 --> 00:46:03,160 It goes from the cervical spinal cord 740 00:46:03,160 --> 00:46:06,925 to the rostral end of the thalamus, the diencephalon. 741 00:46:06,925 --> 00:46:09,910 And this is one thick section where 742 00:46:09,910 --> 00:46:17,140 they could follow the axon from this cell in the hindbrain-- it 743 00:46:17,140 --> 00:46:22,970 was a lower pontine cell or upper medulla oblongata. 744 00:46:22,970 --> 00:46:25,780 Here's the axon, and it bifurcates. 745 00:46:25,780 --> 00:46:27,515 Here's the descending branch where 746 00:46:27,515 --> 00:46:30,360 it distributes various collaterals. 747 00:46:30,360 --> 00:46:32,260 And look at the ascending branch. 748 00:46:32,260 --> 00:46:35,710 Collaterals in the particular formation of the hindbrain, 749 00:46:35,710 --> 00:46:39,375 the midbrain where it has some extensive arbors 750 00:46:39,375 --> 00:46:42,510 in the central gray matter of the midbrain. 751 00:46:42,510 --> 00:46:46,590 And then it goes into the older parts of the thalamus. 752 00:46:46,590 --> 00:46:48,910 Widespread distribution, there's even 753 00:46:48,910 --> 00:46:52,660 a branch that goes into the hypothalamus. 754 00:46:52,660 --> 00:46:56,530 So with the number of neurons in the hindbrain like that, 755 00:46:56,530 --> 00:47:00,910 you can be sure that the activity of some of these cells 756 00:47:00,910 --> 00:47:03,910 is affecting the whole state of the hindbrain. 757 00:47:07,120 --> 00:47:10,050 Now, a little bit about segmentation, 758 00:47:10,050 --> 00:47:12,030 how these segments arrive. 759 00:47:12,030 --> 00:47:14,610 you might want to know, where does that term come from, 760 00:47:14,610 --> 00:47:16,530 the branchial motor column? 761 00:47:16,530 --> 00:47:21,590 Well, in the embryo, there are what we call branchial arches. 762 00:47:21,590 --> 00:47:24,660 Branchial arches in aquatic vertebrates 763 00:47:24,660 --> 00:47:25,750 can form the gill arches. 764 00:47:28,530 --> 00:47:33,340 But we still have that in our embryonic development. 765 00:47:33,340 --> 00:47:36,740 Here are the embryonic branchial arches. 766 00:47:36,740 --> 00:47:40,510 And each arch is innervated by a certain segment 767 00:47:40,510 --> 00:47:43,840 of the hindbrain. 768 00:47:43,840 --> 00:47:49,741 They're innervated by cranial nerve five, seven, nine, 769 00:47:49,741 --> 00:47:53,550 and 10, innervate these branchial arch tissues. 770 00:48:00,320 --> 00:48:02,570 The nucleus ambiguous is the nucleus 771 00:48:02,570 --> 00:48:05,192 that controls swallowing and vocalization. 772 00:48:05,192 --> 00:48:08,200 It goes out through the ninth and 10th nerve. 773 00:48:08,200 --> 00:48:09,116 AUDIENCE: [INAUDIBLE]. 774 00:48:16,590 --> 00:48:18,110 PROFESSOR: Yes, the branchial arches 775 00:48:18,110 --> 00:48:19,860 are present throughout the vertebrates. 776 00:48:19,860 --> 00:48:25,260 But they develop later in the embryo into different things. 777 00:48:25,260 --> 00:48:29,240 So the branchial arches in humans here form the jaws. 778 00:48:29,240 --> 00:48:34,360 The auditory ossicles, the bones, the hyoid bone, 779 00:48:34,360 --> 00:48:36,890 and the pharyngeal skeleton, including the thyroid 780 00:48:36,890 --> 00:48:38,970 cartilage. 781 00:48:38,970 --> 00:48:44,740 These are all branchial arch tissues in humans. 782 00:48:44,740 --> 00:48:50,780 So we know that the mesoderm below the head 783 00:48:50,780 --> 00:48:54,450 also segments, especially for muscles. 784 00:48:54,450 --> 00:48:56,340 These are the somites. 785 00:48:56,340 --> 00:49:00,135 Muscles form this segmented appearance. 786 00:49:00,135 --> 00:49:05,922 And early in development of the embryo, you can see them. 787 00:49:05,922 --> 00:49:15,320 And we know now that these segments have different gene 788 00:49:15,320 --> 00:49:16,610 expression. 789 00:49:16,610 --> 00:49:18,530 And these gene expression studies 790 00:49:18,530 --> 00:49:20,800 have been carried forward into the brain where 791 00:49:20,800 --> 00:49:22,905 you keep seeing segments. 792 00:49:26,090 --> 00:49:30,050 This is one major type of gene, the homeobox gene, 793 00:49:30,050 --> 00:49:38,880 named for the sequence of genes in there, 794 00:49:38,880 --> 00:49:43,030 the sequence that these genes show that's similar, 795 00:49:43,030 --> 00:49:45,315 one to the other, but then they have differences too, 796 00:49:45,315 --> 00:49:47,340 so they're different homeobox genes. 797 00:49:47,340 --> 00:49:51,740 They are transcription factors that are expressed differently 798 00:49:51,740 --> 00:49:53,714 in different segmental levels. 799 00:49:53,714 --> 00:49:54,880 And these are just examples. 800 00:49:57,590 --> 00:50:00,370 They've been highly studied in drosophila. 801 00:50:00,370 --> 00:50:05,760 And here they've colored the fly and shown the expression 802 00:50:05,760 --> 00:50:11,140 of different homeobox genes in different segments of the body. 803 00:50:11,140 --> 00:50:13,510 And if they look at the chromosome that 804 00:50:13,510 --> 00:50:17,990 has those genes, they see that the genes expressed 805 00:50:17,990 --> 00:50:20,760 rostrally are at one end of the chromosome, 806 00:50:20,760 --> 00:50:23,033 the ones expressed caudally are at the other end 807 00:50:23,033 --> 00:50:25,680 of the chromosome, and so forth in between. 808 00:50:25,680 --> 00:50:30,090 The same is true of all the vertebrates. 809 00:50:30,090 --> 00:50:32,740 But when you get to an animal like the mouse, 810 00:50:32,740 --> 00:50:35,880 you have at least four different chromosomes 811 00:50:35,880 --> 00:50:39,706 that have what we call paralogous groups-- that is, 812 00:50:39,706 --> 00:50:44,670 they're related to the homeobox genes in the fruit fly, 813 00:50:44,670 --> 00:50:47,120 but they're found in more than one chromosome. 814 00:50:47,120 --> 00:50:49,830 But still, if they're expressed rostrally in the body, 815 00:50:49,830 --> 00:50:52,104 they're at one end of the chromosome. 816 00:50:52,104 --> 00:50:53,853 If they're expressed caudally, they're 817 00:50:53,853 --> 00:50:56,800 at the other end of the chromosome. 818 00:50:56,800 --> 00:50:59,260 This is just examples and actual photographs 819 00:50:59,260 --> 00:51:01,240 of the mouse embryos showing [INAUDIBLE]. 820 00:51:01,240 --> 00:51:05,970 Actually, they're immunostaining using antibodies 821 00:51:05,970 --> 00:51:10,240 that are specific for the protein products of the Hox 822 00:51:10,240 --> 00:51:12,110 genes that they're showing. 823 00:51:12,110 --> 00:51:13,970 So this is Hox B1. 824 00:51:13,970 --> 00:51:17,120 You see it's expressed in one little region in the brain, 825 00:51:17,120 --> 00:51:21,050 and then more caudally it's also expressed. 826 00:51:21,050 --> 00:51:27,530 Here, it starts its expression more caudally than this one. 827 00:51:27,530 --> 00:51:30,280 This is B4. 828 00:51:30,280 --> 00:51:31,680 This one even more caudally. 829 00:51:31,680 --> 00:51:33,410 And again, there they are. 830 00:51:33,410 --> 00:51:37,140 There's their positions on the chromosome. 831 00:51:37,140 --> 00:51:41,410 And this just shows expression along the anterior posterior 832 00:51:41,410 --> 00:51:46,509 axis, how the rostral limit is very clearly defined. 833 00:51:46,509 --> 00:51:48,300 We'll say a little bit more about Hox genes 834 00:51:48,300 --> 00:51:51,040 right at the beginning of the next class.