1 00:00:02,300 --> 00:00:06,370 - [Instructor] So this laboratory will cover an overview 2 00:00:06,370 --> 00:00:08,010 of the nervous system, 3 00:00:08,010 --> 00:00:10,000 both the central nervous system 4 00:00:10,000 --> 00:00:12,780 and peripheral nervous system. 5 00:00:12,780 --> 00:00:15,370 Before we begin looking at the brains, 6 00:00:15,370 --> 00:00:19,940 I want to take a few seconds to talk to you about 7 00:00:19,940 --> 00:00:22,610 how we have this wonderful opportunity 8 00:00:22,610 --> 00:00:24,510 for you to see the brains. 9 00:00:24,510 --> 00:00:25,860 And this is due to the fact 10 00:00:25,860 --> 00:00:30,860 that local Vermonters have given selflessly of themselves, 11 00:00:30,940 --> 00:00:34,660 not only them, but their family members, 12 00:00:34,660 --> 00:00:37,870 to make the decision to donate their body 13 00:00:37,870 --> 00:00:41,390 to the Department of Neurological Science's 14 00:00:41,390 --> 00:00:43,653 Anatomical Donor Program. 15 00:00:45,670 --> 00:00:50,630 They gave their brains with the intent of teaching others. 16 00:00:50,630 --> 00:00:55,630 So we want to use respect when we examine these specimens. 17 00:00:56,440 --> 00:00:59,860 So the first specimen we're going to look at shows you 18 00:00:59,860 --> 00:01:04,860 an example of how the brain sits within your body. 19 00:01:05,000 --> 00:01:07,460 This is a sagittal cut, 20 00:01:07,460 --> 00:01:11,520 a midsagittal cut right down the brain. 21 00:01:11,520 --> 00:01:14,280 You can see the skull is here. 22 00:01:14,280 --> 00:01:17,820 We have a thin membrane 23 00:01:17,820 --> 00:01:20,000 called the dural septa. 24 00:01:20,000 --> 00:01:24,867 Specifically, this dural septa is called the falx cerebri. 25 00:01:25,780 --> 00:01:28,859 It separates the two hemispheres, 26 00:01:28,859 --> 00:01:31,810 cerebri coming from cerebrum. 27 00:01:31,810 --> 00:01:35,530 And what this membrane does is prevents your brain 28 00:01:35,530 --> 00:01:39,740 from moving side to side or laterally. 29 00:01:39,740 --> 00:01:42,410 There's another membrane that you can't see here, 30 00:01:42,410 --> 00:01:44,530 but we'll see in another specimen 31 00:01:44,530 --> 00:01:47,060 called the tentorium cerebellum, 32 00:01:47,060 --> 00:01:50,860 cerebellum because this is the cerebellum. 33 00:01:50,860 --> 00:01:55,730 This membrane actually continues down horizontally here, 34 00:01:55,730 --> 00:01:58,320 and what it does is prevents the brain 35 00:01:58,320 --> 00:02:01,593 from moving around too much up and down. 36 00:02:03,050 --> 00:02:06,680 The central nervous system consists of the brain 37 00:02:07,790 --> 00:02:09,123 and spinal cord. 38 00:02:10,390 --> 00:02:14,430 The five components of the brain are 39 00:02:14,430 --> 00:02:15,973 the cerebrum, 40 00:02:17,010 --> 00:02:18,713 the diencephalon, 41 00:02:19,830 --> 00:02:21,323 the brain stem, 42 00:02:22,370 --> 00:02:23,513 cerebellum, 43 00:02:24,710 --> 00:02:25,993 and spinal cord. 44 00:02:26,970 --> 00:02:29,920 So one of the things I want to impress upon you is 45 00:02:29,920 --> 00:02:32,423 how small the spinal cord is. 46 00:02:33,470 --> 00:02:37,310 And this is the largest part of the spinal cord, 47 00:02:37,310 --> 00:02:39,200 from here to here. 48 00:02:39,200 --> 00:02:41,400 We'll see it in another specimen. 49 00:02:41,400 --> 00:02:45,460 This enlargement is called the cervical enlargement. 50 00:02:45,460 --> 00:02:48,100 The cervical enlargement is large 51 00:02:48,100 --> 00:02:51,510 because this will contain the spinal nerves 52 00:02:51,510 --> 00:02:55,660 that are going out to innervate your upper extremity. 53 00:02:55,660 --> 00:02:57,670 And when we look at the spinal cord, 54 00:02:57,670 --> 00:03:00,860 we will talk about the dorsal 55 00:03:00,860 --> 00:03:04,960 and the ventral components of the spinal cord. 56 00:03:04,960 --> 00:03:09,170 The dorsal spinal cord is on the back of the body. 57 00:03:09,170 --> 00:03:13,340 The ventral spinal cord is underneath, 58 00:03:13,340 --> 00:03:15,760 ventral, close to the viscera, 59 00:03:15,760 --> 00:03:17,480 close to the guts here. 60 00:03:17,480 --> 00:03:22,480 So what we're seeing here are the dorsal roots 61 00:03:22,480 --> 00:03:25,600 of the spinal nerves that are coming in, 62 00:03:25,600 --> 00:03:29,360 bringing sensory information into the spinal cord. 63 00:03:29,360 --> 00:03:33,410 Now, what you can't see down here is another enlargement 64 00:03:33,410 --> 00:03:35,430 in the lumbar region, 65 00:03:35,430 --> 00:03:38,400 and this is going to go to innervate the muscles 66 00:03:38,400 --> 00:03:41,470 of your lower extremities. 67 00:03:41,470 --> 00:03:44,620 Now, your spinal cord actually ends 68 00:03:44,620 --> 00:03:47,053 in the lumbar vertebrae. 69 00:03:47,920 --> 00:03:51,350 So what you have to appreciate 70 00:03:54,580 --> 00:03:56,280 is that the spinal cord 71 00:04:01,210 --> 00:04:05,490 at the end is essentially nothing more 72 00:04:05,490 --> 00:04:10,490 than a bunch of really long nerve roots. 73 00:04:10,620 --> 00:04:13,200 And this looks like a horse's tail, 74 00:04:13,200 --> 00:04:16,620 and that's why this area of the spinal cord 75 00:04:16,620 --> 00:04:20,840 below the ending is called the cauda equina. 76 00:04:20,840 --> 00:04:25,040 We'll see this in a closeup shot in another specimen. 77 00:04:25,040 --> 00:04:29,640 So this is another sagittal cut of the brain. 78 00:04:29,640 --> 00:04:33,180 And I think what I want to have you appreciate, 79 00:04:33,180 --> 00:04:36,740 how little space there is between the brain 80 00:04:36,740 --> 00:04:39,040 and this membrane 81 00:04:39,040 --> 00:04:41,093 called the dura membrane. 82 00:04:41,930 --> 00:04:45,930 There are three meninges that cover the brain, 83 00:04:45,930 --> 00:04:49,670 the relatively thick dura mater, 84 00:04:49,670 --> 00:04:53,170 right underneath it the arachnoid matter. 85 00:04:53,170 --> 00:04:57,170 There is space underneath the arachnoid mater 86 00:04:57,170 --> 00:05:00,410 called the subarachnoid space. 87 00:05:00,410 --> 00:05:04,720 This space is filled with cerebrospinal fluid. 88 00:05:04,720 --> 00:05:07,900 So the brain actually floats 89 00:05:07,900 --> 00:05:10,270 within cerebrospinal fluid. 90 00:05:10,270 --> 00:05:11,740 And that's why, again, 91 00:05:11,740 --> 00:05:15,760 we need these two membranes, called dural septa, 92 00:05:15,760 --> 00:05:17,960 to help separate the brain. 93 00:05:17,960 --> 00:05:21,220 This, as we saw in the previous specimen, 94 00:05:21,220 --> 00:05:23,987 is called the falx cerebri. 95 00:05:26,490 --> 00:05:31,180 One dural septa that you couldn't see on the last specimen 96 00:05:31,180 --> 00:05:36,040 was this membrane right here, the tentorium cerebellum. 97 00:05:36,040 --> 00:05:37,520 This is the cerebellum. 98 00:05:37,520 --> 00:05:39,470 So the five parts of the brain, 99 00:05:39,470 --> 00:05:41,773 again, are the cerebrum, 100 00:05:42,620 --> 00:05:44,650 the diencephalon, 101 00:05:44,650 --> 00:05:46,300 the brain stem, 102 00:05:46,300 --> 00:05:47,520 the cerebellum, 103 00:05:47,520 --> 00:05:51,893 and what you can't appreciate here is the spinal cord. 104 00:05:54,150 --> 00:05:56,770 Now we're looking at the nervous system 105 00:05:56,770 --> 00:05:59,630 from a different perspective, 106 00:05:59,630 --> 00:06:01,873 outside of the body. 107 00:06:02,730 --> 00:06:07,730 This dissection represents a Herculean effort 108 00:06:08,020 --> 00:06:11,950 by Bruce Fonda, an anatomist here in the department, 109 00:06:11,950 --> 00:06:16,700 who painstakingly not only took the brain out of the skull 110 00:06:16,700 --> 00:06:20,810 and the spinal cord out of individual vertebrae 111 00:06:20,810 --> 00:06:25,110 but actually followed out the major nerves 112 00:06:25,110 --> 00:06:27,623 of the arm and the leg. 113 00:06:28,770 --> 00:06:32,130 So again, I want to focus on the concept 114 00:06:32,130 --> 00:06:34,490 of dorsal and ventral. 115 00:06:34,490 --> 00:06:38,243 Since this person is laying on their back, 116 00:06:40,500 --> 00:06:42,870 the side of the spinal cord that we're seeing here 117 00:06:42,870 --> 00:06:45,180 is the ventral spinal cord. 118 00:06:45,180 --> 00:06:49,020 So this would contain the ventral roots 119 00:06:49,020 --> 00:06:53,370 or the motor neurons that are going out to muscles 120 00:06:53,370 --> 00:06:55,990 to cause muscle contraction. 121 00:06:55,990 --> 00:06:59,460 The nervous system contains the cerebrum, 122 00:06:59,460 --> 00:07:03,880 the diencephalon in this case we can't see, 123 00:07:03,880 --> 00:07:07,333 the diencephalon you have to see from inside, 124 00:07:08,300 --> 00:07:09,433 the brain stem, 125 00:07:10,300 --> 00:07:12,110 the cerebellum, 126 00:07:12,110 --> 00:07:13,970 and the spinal cord. 127 00:07:13,970 --> 00:07:17,030 Now, one of the things that you hopefully can appreciate 128 00:07:17,030 --> 00:07:19,620 here on the brain stem 129 00:07:19,620 --> 00:07:22,760 is that this is the vascular tree 130 00:07:22,760 --> 00:07:26,710 that's going to provide the blood supply 131 00:07:26,710 --> 00:07:29,123 to the brain stem and the brain. 132 00:07:30,190 --> 00:07:33,450 Another thing I want you to appreciate from the ventral 133 00:07:33,450 --> 00:07:37,930 or underside of the brain are these nerves. 134 00:07:37,930 --> 00:07:41,990 These nerves are called cranial nerves. 135 00:07:41,990 --> 00:07:45,390 The cranial nerves are similar 136 00:07:45,390 --> 00:07:47,480 to the spinal nerves. 137 00:07:47,480 --> 00:07:50,830 Cranial nerves contain sensory, 138 00:07:50,830 --> 00:07:54,130 motor, and autonomic innervation, 139 00:07:54,130 --> 00:07:58,583 but this information is only going to the head and neck. 140 00:07:59,850 --> 00:08:03,240 Spinal nerves, like the cranial nerves, 141 00:08:03,240 --> 00:08:07,360 are receiving sensory information from the body, 142 00:08:07,360 --> 00:08:10,370 sending motor information to the body, 143 00:08:10,370 --> 00:08:13,200 and in two regions of the spinal cord, 144 00:08:13,200 --> 00:08:15,340 in the thoracic region 145 00:08:15,340 --> 00:08:17,160 and in the sacral region, 146 00:08:17,160 --> 00:08:22,160 it also has what we call autonomic innervation. 147 00:08:22,160 --> 00:08:25,170 Autonomic innervation for the thorax 148 00:08:25,170 --> 00:08:27,020 is going to the viscera, 149 00:08:27,020 --> 00:08:31,260 the heart, the lungs, the GI tract. 150 00:08:31,260 --> 00:08:33,960 In the sacral region of the spinal cord, 151 00:08:33,960 --> 00:08:37,140 the autonomic innervation is largely going 152 00:08:37,140 --> 00:08:41,163 to the bladder, bowel, and your reproductive structures. 153 00:08:42,020 --> 00:08:44,760 Now, and if you zoom in carefully here, 154 00:08:44,760 --> 00:08:47,430 you can see that there are some spinal nerves 155 00:08:47,430 --> 00:08:50,840 that come straight out as individual units. 156 00:08:50,840 --> 00:08:53,800 However, in several regions 157 00:08:53,800 --> 00:08:55,633 of the spinal cord, 158 00:08:56,750 --> 00:09:01,250 individual nerves join together with other nerves 159 00:09:01,250 --> 00:09:03,500 to form the superhighway 160 00:09:03,500 --> 00:09:05,460 that are called plexus, 161 00:09:05,460 --> 00:09:08,830 plexuses or plexi plurally. 162 00:09:08,830 --> 00:09:10,230 So what this is 163 00:09:10,230 --> 00:09:14,360 is the accumulation of individual nerves, 164 00:09:14,360 --> 00:09:18,363 and we have three major plexi. 165 00:09:19,410 --> 00:09:21,160 Technically, there are four. 166 00:09:21,160 --> 00:09:24,110 You have the cervical plexus, 167 00:09:24,110 --> 00:09:26,530 the brachial plexus, 168 00:09:26,530 --> 00:09:28,370 the lumbar plexus, 169 00:09:28,370 --> 00:09:30,070 and the sacral plexus. 170 00:09:30,070 --> 00:09:32,330 And quite often the lumbar 171 00:09:32,330 --> 00:09:36,120 and sacral plexus are merged together 172 00:09:36,120 --> 00:09:39,950 into the lumbosacral plexus. 173 00:09:39,950 --> 00:09:43,940 And the biggest nerve of the lumbosacral plexus 174 00:09:43,940 --> 00:09:46,530 is the sciatic nerve. 175 00:09:46,530 --> 00:09:49,410 This is what gives you, if you sit on your wallet, 176 00:09:49,410 --> 00:09:52,910 this is what gives you the pain sensation 177 00:09:52,910 --> 00:09:56,120 radiating down your leg. 178 00:09:56,120 --> 00:09:58,420 Now what we're going to do is go 179 00:09:58,420 --> 00:10:02,130 and look at the anatomy in greater detail 180 00:10:02,130 --> 00:10:04,943 of the brain and the spinal cord. 181 00:10:07,120 --> 00:10:10,870 So we'll start working our way up the nervous system, 182 00:10:10,870 --> 00:10:13,890 starting with the spinal cord. 183 00:10:13,890 --> 00:10:17,053 This is where we'll bring in sensory information. 184 00:10:18,090 --> 00:10:19,660 When you look at the spinal cord, 185 00:10:19,660 --> 00:10:21,990 you could see, just like the brain, 186 00:10:21,990 --> 00:10:25,253 the spinal cord is surrounded by dura mater, 187 00:10:26,380 --> 00:10:28,540 arachnoid mater, 188 00:10:28,540 --> 00:10:32,660 a subarachnoid space that's filled with cerebrospinal fluid, 189 00:10:32,660 --> 00:10:35,680 and then the third meninge that we can't see, 190 00:10:35,680 --> 00:10:39,660 either here in the spinal cord or in the cerebrum, 191 00:10:39,660 --> 00:10:40,750 is the pia mater. 192 00:10:40,750 --> 00:10:44,470 And the Pia mater is just a single cell layer thick 193 00:10:44,470 --> 00:10:45,883 that surrounds the brain. 194 00:10:46,870 --> 00:10:50,550 Now, you really can't tell from orientation here 195 00:10:50,550 --> 00:10:54,320 without it being in the body 196 00:10:54,320 --> 00:10:57,070 which is dorsal sensory 197 00:10:57,070 --> 00:11:00,050 and which is ventral motor. 198 00:11:00,050 --> 00:11:03,270 The one thing that you can appreciate here 199 00:11:03,270 --> 00:11:05,200 is these little balls 200 00:11:05,200 --> 00:11:08,150 that are sitting adjacent to the spinal cord. 201 00:11:08,150 --> 00:11:11,340 These balls are actually the collection 202 00:11:11,340 --> 00:11:15,870 of nerve cell bodies of sensory neurons. 203 00:11:15,870 --> 00:11:19,610 These are called the dorsal root ganglia. 204 00:11:19,610 --> 00:11:22,710 There are no synapses 205 00:11:22,710 --> 00:11:25,760 in the dorsal root ganglia. 206 00:11:25,760 --> 00:11:29,910 The dorsal root ganglia only represents 207 00:11:29,910 --> 00:11:34,520 the cell body, the soma, or perikaryon, 208 00:11:34,520 --> 00:11:36,720 three terminology that you should be able 209 00:11:36,720 --> 00:11:38,740 to use interchangeably 210 00:11:38,740 --> 00:11:41,400 that represent the sensory neurons 211 00:11:41,400 --> 00:11:43,733 entering into the spinal cord. 212 00:11:45,480 --> 00:11:47,330 In order for you to see which is dorsal 213 00:11:47,330 --> 00:11:48,750 and which is ventral, 214 00:11:48,750 --> 00:11:51,470 what you'd have to do is you'd have to look 215 00:11:51,470 --> 00:11:54,540 at a cross section of the spinal cord. 216 00:11:54,540 --> 00:11:58,460 So here we have a cross section of the spinal cord, 217 00:11:58,460 --> 00:12:02,440 and you can tell which is dorsal 218 00:12:02,440 --> 00:12:04,000 and which is ventral 219 00:12:04,000 --> 00:12:07,270 by the shape of the gray matter. 220 00:12:07,270 --> 00:12:10,950 The spinal cord has a central gray matter 221 00:12:10,950 --> 00:12:13,870 surrounded by white matter. 222 00:12:13,870 --> 00:12:16,850 The white matter represents the axons 223 00:12:16,850 --> 00:12:20,310 of sensory neurons going up 224 00:12:20,310 --> 00:12:21,930 to the cerebrum 225 00:12:21,930 --> 00:12:24,500 and the axons of motor neurons 226 00:12:24,500 --> 00:12:26,843 from the cerebrum coming down. 227 00:12:27,990 --> 00:12:31,890 This is the dorsal side of the spinal cord. 228 00:12:31,890 --> 00:12:34,890 This is called the dorsal root entry zone, 229 00:12:34,890 --> 00:12:38,353 and you can see it's contiguous with the outside. 230 00:12:39,290 --> 00:12:43,870 Generally, the ventral root doesn't go all the way down. 231 00:12:43,870 --> 00:12:47,370 There's a little bit of white matter that sits around here. 232 00:12:47,370 --> 00:12:51,910 So the dorsal root is going to have sensory information 233 00:12:51,910 --> 00:12:54,250 and the ventral horn here. 234 00:12:54,250 --> 00:12:56,480 So this is the dorsal 235 00:12:57,580 --> 00:12:59,640 horn of the gray matter 236 00:12:59,640 --> 00:13:03,410 and the ventral horn of the gray matter. 237 00:13:03,410 --> 00:13:07,310 This is where the sensory neurons 238 00:13:07,310 --> 00:13:09,930 that came in through 239 00:13:09,930 --> 00:13:14,130 the dorsal root of the spinal nerve 240 00:13:14,130 --> 00:13:16,370 are going to synapse. 241 00:13:16,370 --> 00:13:18,860 They'll then have motor neurons 242 00:13:18,860 --> 00:13:22,690 that will then exit the ventral root. 243 00:13:22,690 --> 00:13:26,690 When the dorsal root of the spinal nerve 244 00:13:26,690 --> 00:13:31,520 and the ventral root of the spinal nerve come together, 245 00:13:31,520 --> 00:13:35,260 you have what's called the spinal nerve. 246 00:13:35,260 --> 00:13:38,360 And again, in certain areas of the spinal cord, 247 00:13:38,360 --> 00:13:41,840 in the thoracic region and in the sacral region, 248 00:13:41,840 --> 00:13:46,840 in addition to having sensory afferents 249 00:13:46,910 --> 00:13:49,140 and motor efferents, 250 00:13:49,140 --> 00:13:52,230 you will also have autonomic nerves 251 00:13:52,230 --> 00:13:55,030 that are going to innervate the viscera. 252 00:13:55,030 --> 00:13:58,760 Now, one of the things that you might not have appreciated 253 00:13:58,760 --> 00:14:01,930 is when you look at how the spinal cord sits 254 00:14:01,930 --> 00:14:03,990 within the vertebral column 255 00:14:03,990 --> 00:14:07,280 and how the spinal nerves exit, 256 00:14:07,280 --> 00:14:10,200 you can see that the spinal nerves exit 257 00:14:10,200 --> 00:14:13,510 through a relatively small space. 258 00:14:13,510 --> 00:14:17,020 So if you have a crush here 259 00:14:17,020 --> 00:14:20,700 that damages or compresses the spinal root, 260 00:14:20,700 --> 00:14:22,240 you're going to take out 261 00:14:22,240 --> 00:14:26,510 not only the sensory information coming in 262 00:14:26,510 --> 00:14:29,530 but the motor information coming out. 263 00:14:29,530 --> 00:14:33,950 Finally, if we look here at the very end of the spinal cord, 264 00:14:33,950 --> 00:14:36,110 something that we also couldn't appreciate 265 00:14:36,110 --> 00:14:38,650 in the other two specimens that we looked at 266 00:14:38,650 --> 00:14:41,420 was that the spinal cord ends 267 00:14:41,420 --> 00:14:46,007 in a rather tapered structure called the conus medullaris 268 00:14:46,860 --> 00:14:49,270 and that all the nerves that are coming out 269 00:14:49,270 --> 00:14:53,230 after that are called the cauda equina. 270 00:14:53,230 --> 00:14:54,730 But the other thing that I want 271 00:14:54,730 --> 00:14:58,990 to point out is this structure right here. 272 00:14:58,990 --> 00:15:01,630 This is a connective tissue structure 273 00:15:01,630 --> 00:15:04,810 called the filum terminale. 274 00:15:04,810 --> 00:15:08,210 It is the terminal end of the spinal cord, 275 00:15:08,210 --> 00:15:12,570 and it's a piece of connective tissue that attaches 276 00:15:13,550 --> 00:15:15,840 to the dura. 277 00:15:15,840 --> 00:15:19,010 And just like you had dural septa 278 00:15:20,070 --> 00:15:23,080 that helped support the brain 279 00:15:23,080 --> 00:15:26,420 and prevent it from moving inside of the skull, 280 00:15:26,420 --> 00:15:30,440 the purpose of this filum terminale 281 00:15:30,440 --> 00:15:33,540 is to attach the spinal cord to the dura. 282 00:15:33,540 --> 00:15:38,010 Because it likewise is floating in cerebrospinal fluid, 283 00:15:38,010 --> 00:15:41,803 and you don't want it to be jostled around too much. 284 00:15:42,980 --> 00:15:44,860 Now what we'll do is we'll move up 285 00:15:44,860 --> 00:15:48,293 and focus exclusively on the brain. 286 00:15:50,440 --> 00:15:55,440 So we saw how the brain fits inside of the skull. 287 00:15:55,470 --> 00:15:59,020 And now that we've seen the brain outside of the skull, 288 00:15:59,020 --> 00:16:04,020 you can see how really thin that dural membrane is. 289 00:16:04,040 --> 00:16:06,160 Remember, underneath the dura is going 290 00:16:06,160 --> 00:16:09,860 to be another layer called the arachnoid matter. 291 00:16:09,860 --> 00:16:12,330 And underneath the arachnoid matter, 292 00:16:12,330 --> 00:16:16,910 we're going to see our superficial blood vessels. 293 00:16:16,910 --> 00:16:18,480 So when the specimen, 294 00:16:18,480 --> 00:16:21,480 looked at the specimen that was lying on its back, 295 00:16:21,480 --> 00:16:24,580 we saw that there are blood vessels that run 296 00:16:24,580 --> 00:16:27,100 underneath the brain, 297 00:16:27,100 --> 00:16:29,410 primarily around the brain stem. 298 00:16:29,410 --> 00:16:31,570 But you can also see that there are lots 299 00:16:31,570 --> 00:16:35,660 of blood vessels here throughout the entire brain. 300 00:16:35,660 --> 00:16:37,480 And we'll have another lab devoted 301 00:16:37,480 --> 00:16:39,453 exclusively to blood supply. 302 00:16:40,550 --> 00:16:43,010 So unlike the body that has 303 00:16:43,010 --> 00:16:45,560 what's called the lymphatic system, 304 00:16:45,560 --> 00:16:46,820 you know that you're sick 305 00:16:47,926 --> 00:16:50,690 when your lymph nodes swell. 306 00:16:50,690 --> 00:16:52,240 All right. 307 00:16:52,240 --> 00:16:55,240 Unlike the brain that doesn't have a lymphatic system, 308 00:16:55,240 --> 00:17:00,240 we have to have another system in addition to blood supply, 309 00:17:00,330 --> 00:17:04,040 to provide nutrients to the brain and remove waste. 310 00:17:04,040 --> 00:17:06,560 And that happens to be the ventricular system 311 00:17:06,560 --> 00:17:08,960 and cerebrospinal fluid. 312 00:17:08,960 --> 00:17:12,030 Well, once the cerebrospinal fluid has circulated 313 00:17:12,030 --> 00:17:15,350 throughout not only the outside of the brain 314 00:17:15,350 --> 00:17:18,010 but we'll see later within the brain 315 00:17:18,010 --> 00:17:20,080 in structures called ventricles, 316 00:17:20,080 --> 00:17:22,600 all the waste products have to be taken back 317 00:17:22,600 --> 00:17:24,900 into the venous circulation, 318 00:17:24,900 --> 00:17:26,930 the unoxygenated blood 319 00:17:26,930 --> 00:17:29,220 that's going to be going back to the heart. 320 00:17:29,220 --> 00:17:32,200 And one of the ways it does that is through 321 00:17:34,800 --> 00:17:36,910 these blood vessels here. 322 00:17:36,910 --> 00:17:40,490 These blood vessels are veins 323 00:17:40,490 --> 00:17:41,570 that are taking 324 00:17:42,920 --> 00:17:46,090 unoxygenated, waste-filled blood 325 00:17:46,090 --> 00:17:49,770 from the brain and returning it to the heart. 326 00:17:49,770 --> 00:17:51,020 Now unfortunately, you could see 327 00:17:51,020 --> 00:17:53,730 that there's a little bit of space here 328 00:17:53,730 --> 00:17:56,330 before the veins connect 329 00:17:56,330 --> 00:18:00,290 with the structure here called the sinus. 330 00:18:00,290 --> 00:18:02,910 The sinus is a blood-filled cavity 331 00:18:02,910 --> 00:18:06,090 that contains unoxygenated venous blood 332 00:18:06,090 --> 00:18:08,100 going back to the heart. 333 00:18:08,100 --> 00:18:11,050 We also said that the brain is sitting 334 00:18:11,050 --> 00:18:13,670 inside of cerebrospinal fluid. 335 00:18:13,670 --> 00:18:16,990 So if the brain moves too much, 336 00:18:16,990 --> 00:18:21,710 it's possible that you could tear, damage those vessels, 337 00:18:21,710 --> 00:18:25,680 and what you would have is a sub, 338 00:18:25,680 --> 00:18:29,150 under, dural hematoma. 339 00:18:29,150 --> 00:18:32,220 And in the next specimen, we'll show what happens 340 00:18:32,220 --> 00:18:35,203 when you have a subdural hematoma. 341 00:18:37,974 --> 00:18:40,660 So this is an example of a brain 342 00:18:40,660 --> 00:18:44,530 that experienced a subdural hematoma, 343 00:18:44,530 --> 00:18:48,670 and what you can see is that the blood is filling in 344 00:18:48,670 --> 00:18:51,393 all the crevices of the brain. 345 00:18:52,990 --> 00:18:55,810 While this looks extremely bad, 346 00:18:55,810 --> 00:18:59,610 in reality this is not as bad as another type 347 00:18:59,610 --> 00:19:03,950 of hematoma called an epidural hematoma, 348 00:19:03,950 --> 00:19:07,010 epi being outside of the dura. 349 00:19:07,010 --> 00:19:10,220 Because at least here we've got two benefits. 350 00:19:10,220 --> 00:19:14,370 Number one, this is low-pressure venous blood. 351 00:19:14,370 --> 00:19:16,540 This is unlike arterial blood, 352 00:19:16,540 --> 00:19:19,680 high pressure coming out of your aorta, 353 00:19:19,680 --> 00:19:21,763 taking blood to the brain. 354 00:19:22,670 --> 00:19:26,760 Second benefit is because it's under the dura, 355 00:19:26,760 --> 00:19:30,880 it can fill in all the spaces here, 356 00:19:30,880 --> 00:19:35,300 and it really doesn't cause too many neurologic deficits 357 00:19:35,300 --> 00:19:39,450 until all the spaces here become filled. 358 00:19:39,450 --> 00:19:42,600 And then the brain can't hold any more volume. 359 00:19:42,600 --> 00:19:44,260 And what ends up happening, 360 00:19:44,260 --> 00:19:47,120 the brain ends up pressing down 361 00:19:47,120 --> 00:19:51,740 through the tentorium cerebellum here, 362 00:19:51,740 --> 00:19:54,000 'cause we said the tentorium cerebellum, 363 00:19:54,000 --> 00:19:58,560 and it pushes down on this region of the brain stem. 364 00:19:58,560 --> 00:19:59,820 This region of the brain stem 365 00:19:59,820 --> 00:20:02,450 is called the medulla oblongata, 366 00:20:02,450 --> 00:20:04,590 and what it is responsible for is 367 00:20:04,590 --> 00:20:08,120 for regulating your heartbeat and breathing. 368 00:20:08,120 --> 00:20:11,330 And if you don't stop the bleeding in the brain here, 369 00:20:11,330 --> 00:20:14,720 you will end up with a herniation and die. 370 00:20:14,720 --> 00:20:19,223 And this is what likely happened to this patient. 371 00:20:21,410 --> 00:20:24,250 Now that we've covered the spinal cord, 372 00:20:24,250 --> 00:20:26,640 we'll spend the majority of our time discussing 373 00:20:26,640 --> 00:20:31,550 the four remaining divisions of the central nervous system, 374 00:20:31,550 --> 00:20:35,060 the cerebrum, which is the largest part, 375 00:20:35,060 --> 00:20:36,180 as we said earlier, 376 00:20:36,180 --> 00:20:39,763 the diencephalon cannot be seen from the outside, 377 00:20:41,090 --> 00:20:43,423 the cerebellum, shown here, 378 00:20:44,370 --> 00:20:46,930 and the brain stem, 379 00:20:46,930 --> 00:20:47,763 shown here. 380 00:20:48,950 --> 00:20:52,420 So first, let's focus on the cerebrum. 381 00:20:52,420 --> 00:20:56,100 One of the first things that I hope you can appreciate is 382 00:20:56,100 --> 00:20:58,320 that the cerebrum is divided 383 00:20:58,320 --> 00:21:01,920 into a left and a right hemisphere 384 00:21:01,920 --> 00:21:04,770 and that they are divided here 385 00:21:04,770 --> 00:21:07,360 by this long, deep depression 386 00:21:07,360 --> 00:21:09,950 called the longitudinal 387 00:21:09,950 --> 00:21:13,363 or interhemispheric fissure. 388 00:21:14,640 --> 00:21:16,200 So the first concept that I want 389 00:21:16,200 --> 00:21:19,190 to talk about at the cerebrum is that 390 00:21:19,190 --> 00:21:24,190 the left hemisphere controls the right side of the body 391 00:21:24,560 --> 00:21:29,560 and the right hemisphere controls the left side of the body. 392 00:21:29,880 --> 00:21:34,640 So when you put your right hand on something, 393 00:21:34,640 --> 00:21:37,480 all of that information is going to be perceived 394 00:21:37,480 --> 00:21:39,163 by the left hemisphere. 395 00:21:41,790 --> 00:21:45,360 If I turn the cerebrum this way, 396 00:21:45,360 --> 00:21:48,600 you can see that the cerebrum 397 00:21:48,600 --> 00:21:51,860 has these depressions 398 00:21:51,860 --> 00:21:53,520 and ridges. 399 00:21:53,520 --> 00:21:55,560 The depressions, 400 00:21:55,560 --> 00:21:59,210 a single depression is called a sulcus, 401 00:21:59,210 --> 00:22:02,163 multiple depressions are called sulci. 402 00:22:04,850 --> 00:22:08,160 The ridge is called a gyrus, 403 00:22:08,160 --> 00:22:10,760 or multiple are called gyri. 404 00:22:12,070 --> 00:22:16,850 And these depressions and ridges actually mean something. 405 00:22:16,850 --> 00:22:21,440 They contain functionally relative information. 406 00:22:21,440 --> 00:22:25,450 So if we look at the major depression, 407 00:22:25,450 --> 00:22:28,033 this major depression right here, 408 00:22:28,910 --> 00:22:33,240 this depression is called the central sulcus. 409 00:22:33,240 --> 00:22:36,500 And the central sulcus is what divides 410 00:22:37,530 --> 00:22:42,370 the frontal lobe from the parietal lobe. 411 00:22:42,370 --> 00:22:46,380 So now we can talk about the lobes of the brain. 412 00:22:46,380 --> 00:22:48,950 We have four major lobes, 413 00:22:48,950 --> 00:22:50,820 the frontal, 414 00:22:50,820 --> 00:22:52,870 the parietal, 415 00:22:52,870 --> 00:22:54,650 the occipital, 416 00:22:54,650 --> 00:22:57,610 and down here the temporal low. 417 00:22:57,610 --> 00:23:01,263 And we also have another fissure here. 418 00:23:02,460 --> 00:23:04,560 A deep depression is a fissure. 419 00:23:04,560 --> 00:23:07,510 And this is called the Sylvian fissure 420 00:23:07,510 --> 00:23:09,730 or the lateral fissure. 421 00:23:09,730 --> 00:23:11,700 And what the lateral fissure 422 00:23:11,700 --> 00:23:13,630 or Sylvian fissure does 423 00:23:13,630 --> 00:23:16,850 is separate the frontal 424 00:23:16,850 --> 00:23:20,500 and parietal lobes from the temporal lobe. 425 00:23:20,500 --> 00:23:23,900 Now, notice the shape of the temporal lobe 426 00:23:23,900 --> 00:23:26,040 because the shape of the temporal lobe 427 00:23:26,040 --> 00:23:30,600 will be a great landmark for you to be able to determine 428 00:23:30,600 --> 00:23:33,780 whether you're looking at the right hemisphere 429 00:23:33,780 --> 00:23:37,750 or if you're looking at the left hemisphere. 430 00:23:37,750 --> 00:23:41,300 Even if I took off the cerebellum and brain stem 431 00:23:41,300 --> 00:23:45,510 and you had no opportunity to use the cerebellum 432 00:23:45,510 --> 00:23:48,330 as a landmark for what's the back of the brain 433 00:23:48,330 --> 00:23:49,880 and the front of the brain, 434 00:23:49,880 --> 00:23:52,800 you should be able to look at the shape 435 00:23:52,800 --> 00:23:55,930 and pointiness of the temporal lobe 436 00:23:55,930 --> 00:23:58,063 to see that this is a left hemisphere. 437 00:23:59,820 --> 00:24:02,390 So if we focus in more 438 00:24:02,390 --> 00:24:04,730 on the various sulci, 439 00:24:04,730 --> 00:24:07,460 we can say that if this 440 00:24:07,460 --> 00:24:10,100 on the left hemisphere 441 00:24:10,100 --> 00:24:12,713 is the central sulcus, 442 00:24:13,840 --> 00:24:18,070 then the bump right in front of the central sulcus, 443 00:24:18,070 --> 00:24:22,810 we call the precentral gyrus, 444 00:24:22,810 --> 00:24:24,723 pre because it's before. 445 00:24:25,590 --> 00:24:29,703 And this gyrus contains the motor information. 446 00:24:30,730 --> 00:24:34,150 It doesn't contain alpha motor neurons 447 00:24:34,150 --> 00:24:36,900 that are innervating your skeletal muscle. 448 00:24:36,900 --> 00:24:41,840 These motor neurons up here we call upper motor neurons. 449 00:24:41,840 --> 00:24:44,160 These are the command neurons. 450 00:24:44,160 --> 00:24:47,640 These are the neurons that are going to tell your muscles 451 00:24:47,640 --> 00:24:50,513 in your arm and your legs to move. 452 00:24:52,060 --> 00:24:54,730 They're the high command center. 453 00:24:54,730 --> 00:24:59,310 Right in front of the precentral gyrus, 454 00:24:59,310 --> 00:25:02,140 you have a triangular region right here 455 00:25:02,140 --> 00:25:04,910 called the premotor cortex, 456 00:25:04,910 --> 00:25:07,970 and the purpose of the premotor cortex is 457 00:25:07,970 --> 00:25:10,500 to plan motor activities. 458 00:25:10,500 --> 00:25:13,300 Really doesn't execute the motor activities. 459 00:25:13,300 --> 00:25:15,320 It makes a plan 460 00:25:15,320 --> 00:25:17,780 and tells that plan 461 00:25:17,780 --> 00:25:21,410 to the precentral gyrus. 462 00:25:21,410 --> 00:25:23,910 And that plan then gets commanded 463 00:25:23,910 --> 00:25:28,260 to the alpha motor neurons in your spinal cord 464 00:25:28,260 --> 00:25:31,090 that then go and innervate the muscle. 465 00:25:31,090 --> 00:25:33,400 Believe it or not, there is a map 466 00:25:33,400 --> 00:25:37,090 of your body within this gyrus. 467 00:25:37,090 --> 00:25:38,860 Where the motor neurons that are going 468 00:25:38,860 --> 00:25:42,610 to be controlling your feet and legs 469 00:25:42,610 --> 00:25:46,200 are deep here in the interhemispheric fissure, 470 00:25:46,200 --> 00:25:48,760 your arms and body 471 00:25:48,760 --> 00:25:51,053 and face are out here. 472 00:25:52,340 --> 00:25:54,300 In addition, within the frontal lobe, 473 00:25:54,300 --> 00:25:57,860 you have another region right about here 474 00:25:57,860 --> 00:26:00,770 that's called Broca's area. 475 00:26:00,770 --> 00:26:05,770 And Broca's area is for the motor component of speech, 476 00:26:06,050 --> 00:26:08,230 not moving your tongue, 477 00:26:08,230 --> 00:26:11,990 but your ability to express your thoughts. 478 00:26:11,990 --> 00:26:13,240 It is motor. 479 00:26:13,240 --> 00:26:15,060 Now, what's interesting is 480 00:26:15,060 --> 00:26:19,460 that Broca's area is located very, very close 481 00:26:19,460 --> 00:26:23,390 to the tongue and mouth region of your motor map. 482 00:26:23,390 --> 00:26:27,230 But again, I want to make sure that you understand 483 00:26:27,230 --> 00:26:31,380 that if you have an aphasia, the inability to speak, 484 00:26:31,380 --> 00:26:34,750 it has nothing to do with the inability 485 00:26:34,750 --> 00:26:37,120 to move your tongues and lips. 486 00:26:37,120 --> 00:26:40,913 It's your inability to express yourself. 487 00:26:41,750 --> 00:26:46,350 So this is the motor component of the frontal lobe. 488 00:26:46,350 --> 00:26:49,910 The vast majority of the frontal lobe here 489 00:26:49,910 --> 00:26:53,530 is called the prefrontal cortex. 490 00:26:53,530 --> 00:26:58,530 And the purpose of the prefrontal cortex is limbic, 491 00:26:59,390 --> 00:27:02,760 limbic functions like your personality, 492 00:27:02,760 --> 00:27:05,323 storage of long-term memories, 493 00:27:06,500 --> 00:27:09,060 deciding what is right and wrong, 494 00:27:09,060 --> 00:27:11,870 regret, motivation, 495 00:27:11,870 --> 00:27:15,790 all these things that define you as being you. 496 00:27:15,790 --> 00:27:20,020 So when I hold this person's prefrontal cortex, 497 00:27:20,020 --> 00:27:24,950 this is all the experiences that that person ever had 498 00:27:24,950 --> 00:27:27,793 being stored here in the prefrontal lobe. 499 00:27:28,970 --> 00:27:33,970 If we go back behind the central sulcus, 500 00:27:34,270 --> 00:27:38,430 the gyrus that is right behind the central sulcus 501 00:27:38,430 --> 00:27:42,700 is called the postcentral gyrus. 502 00:27:42,700 --> 00:27:45,880 And the purpose of the postcentral gyrus 503 00:27:45,880 --> 00:27:48,660 is somatosensory information, 504 00:27:48,660 --> 00:27:53,350 soma coming from the root body. 505 00:27:53,350 --> 00:27:56,740 Right, so this is body information. 506 00:27:56,740 --> 00:28:00,020 This is where the sensory information 507 00:28:00,020 --> 00:28:03,470 from your right side of your body will end up 508 00:28:03,470 --> 00:28:05,730 since this is a left hemisphere. 509 00:28:05,730 --> 00:28:09,010 And just like I said there is a map, 510 00:28:09,010 --> 00:28:10,740 a homunculus, 511 00:28:10,740 --> 00:28:13,087 for motor information, 512 00:28:13,087 --> 00:28:16,768 there is a map in the postcentral gyrus 513 00:28:16,768 --> 00:28:19,268 for somatosensory information. 514 00:28:21,010 --> 00:28:25,470 Basically the entire parietal lobe is exclusively 515 00:28:25,470 --> 00:28:28,150 for somatosensory information. 516 00:28:28,150 --> 00:28:32,540 Similarly, if we look back here to the occipital lobe, 517 00:28:32,540 --> 00:28:36,740 the occipital lobe is purely for visual information. 518 00:28:36,740 --> 00:28:38,540 So I joke when I go out 519 00:28:38,540 --> 00:28:42,410 and do elementary school lessons on the brain, 520 00:28:42,410 --> 00:28:46,543 that, yes, you indeed have eyes at the back of your brain. 521 00:28:47,640 --> 00:28:51,340 The fourth lobe down here is the temporal lobe, 522 00:28:51,340 --> 00:28:55,280 and we'll see that there are two very important components 523 00:28:55,280 --> 00:28:58,090 of the limbic system here in the temporal lobe. 524 00:28:58,090 --> 00:29:01,460 You have the amygdala deep down within here 525 00:29:01,460 --> 00:29:03,550 that's involved in emotion, 526 00:29:03,550 --> 00:29:05,400 and you have the hippocampus, 527 00:29:05,400 --> 00:29:09,310 which is involved in learning and memory. 528 00:29:09,310 --> 00:29:13,460 Another important component of the temporal lobe, 529 00:29:13,460 --> 00:29:16,430 right about here, right where your ears would sit, 530 00:29:16,430 --> 00:29:21,430 is this is where the primary auditory cortex is located. 531 00:29:21,800 --> 00:29:26,090 Interestingly, right here within the parietal 532 00:29:26,090 --> 00:29:28,600 and a little bit of the temporal lobe 533 00:29:28,600 --> 00:29:32,750 is another language area called Wernicke's area. 534 00:29:32,750 --> 00:29:36,570 Wernicke's area, interestingly, 535 00:29:36,570 --> 00:29:39,770 is near the primary auditory cortex,, 536 00:29:39,770 --> 00:29:44,770 but individuals that have Wernicke's aphasia are not deaf. 537 00:29:44,960 --> 00:29:47,760 They just can't comprehend 538 00:29:47,760 --> 00:29:50,520 or understand speech. 539 00:29:50,520 --> 00:29:52,430 They'll be able to speak fine. 540 00:29:52,430 --> 00:29:54,670 They might misuse words. 541 00:29:54,670 --> 00:29:56,810 But the bottom line is here 542 00:29:56,810 --> 00:29:59,320 that this is a sensory 543 00:29:59,320 --> 00:30:01,970 or receptive aphasia, 544 00:30:01,970 --> 00:30:06,320 whereas Broca's aphasia is an expressive 545 00:30:06,320 --> 00:30:10,483 or motor aphasia because they can't express themselves. 546 00:30:13,250 --> 00:30:15,750 Other component of the cerebrum, 547 00:30:15,750 --> 00:30:18,253 now we're looking at the underside, 548 00:30:19,750 --> 00:30:22,073 is we can see here, 549 00:30:23,130 --> 00:30:25,190 the temporal lobes, 550 00:30:25,190 --> 00:30:28,010 and you can see the brain stem. 551 00:30:28,010 --> 00:30:30,830 There are three components to the brain stem, 552 00:30:30,830 --> 00:30:31,963 the midbrain, 553 00:30:33,020 --> 00:30:36,800 this big, bulgy part here, the pons, 554 00:30:36,800 --> 00:30:39,670 and this smaller part here that will be contiguous 555 00:30:39,670 --> 00:30:42,930 with the spinal cord, the medulla. 556 00:30:42,930 --> 00:30:45,390 And we'll have an entire laboratory 557 00:30:45,390 --> 00:30:47,963 devoted to the brain stem. 558 00:30:48,870 --> 00:30:52,040 The last component is the cerebellum. 559 00:30:52,040 --> 00:30:53,700 And just like the cerebrum 560 00:30:53,700 --> 00:30:56,410 has a left and a right hemisphere, 561 00:30:56,410 --> 00:30:58,310 you can see that the cerebellum 562 00:30:58,310 --> 00:31:01,270 has a left and a right hemisphere. 563 00:31:01,270 --> 00:31:03,210 Now, what's important to understand here 564 00:31:03,210 --> 00:31:05,420 about the cerebellum is that the purpose 565 00:31:05,420 --> 00:31:09,920 of the cerebellum is balance and coordination. 566 00:31:09,920 --> 00:31:11,700 So you make a motor plan, 567 00:31:11,700 --> 00:31:14,840 and you decide you want to do something. 568 00:31:14,840 --> 00:31:17,430 That information, do something, 569 00:31:17,430 --> 00:31:20,100 is not only going to go to the motor neurons 570 00:31:20,100 --> 00:31:24,220 in your spinal cord so that you actually do what you want. 571 00:31:24,220 --> 00:31:28,720 That information will also go here to the cerebellum. 572 00:31:28,720 --> 00:31:32,910 So as you start to do whatever it is you want, 573 00:31:32,910 --> 00:31:36,390 sensory information will be coming into the cerebellum. 574 00:31:36,390 --> 00:31:40,670 And the purpose of the cerebellum is to compare 575 00:31:40,670 --> 00:31:44,370 what you want to do, what the motor plan is 576 00:31:44,370 --> 00:31:46,790 with what you are actually doing. 577 00:31:46,790 --> 00:31:50,070 And if you're not executing a good motor plan, 578 00:31:50,070 --> 00:31:53,363 then it's the purpose of the cerebellum to fix that. 579 00:31:54,340 --> 00:31:57,820 An important concept about the cerebellum 580 00:31:57,820 --> 00:32:00,930 is that if you have cerebellum damage, 581 00:32:00,930 --> 00:32:03,910 you will see a neurologic deficit 582 00:32:03,910 --> 00:32:07,760 on the side that you have the damage 583 00:32:07,760 --> 00:32:11,600 because the cerebellum is unable to fix 584 00:32:11,600 --> 00:32:14,550 what you are doing wrong. 585 00:32:14,550 --> 00:32:17,540 Whereas if you have damage to the cerebrum, 586 00:32:17,540 --> 00:32:21,560 a stroke on the left hemisphere will give rise 587 00:32:21,560 --> 00:32:24,460 to neurologic damages on the right, 588 00:32:24,460 --> 00:32:28,450 and a stroke in the right hemisphere will give rise 589 00:32:28,450 --> 00:32:32,470 to neurologic damages on the left. 590 00:32:32,470 --> 00:32:35,930 Now what we want to do is cut the brain in half 591 00:32:35,930 --> 00:32:37,740 because the one thing we can't see 592 00:32:37,740 --> 00:32:40,793 from the outside is the diencephalon. 593 00:32:42,210 --> 00:32:46,430 So now what we're looking at is a midsagittal cut 594 00:32:47,610 --> 00:32:48,483 of the brain. 595 00:32:49,460 --> 00:32:52,900 I'll flip the brain over for a second 596 00:32:52,900 --> 00:32:54,840 and ask you to decide 597 00:32:54,840 --> 00:32:58,410 whether I'm holding a right hemisphere 598 00:32:58,410 --> 00:32:59,853 or a left hemisphere. 599 00:33:08,160 --> 00:33:11,320 This is the right hemisphere. 600 00:33:11,320 --> 00:33:14,880 Notice the shape of the temporal lobe 601 00:33:14,880 --> 00:33:18,523 and the fact that we have the cerebellum here at the back. 602 00:33:19,440 --> 00:33:23,430 If I flip it over, another way that you can tell 603 00:33:23,430 --> 00:33:26,880 that it's a right hemisphere is the shape 604 00:33:26,880 --> 00:33:29,423 of this structure right here. 605 00:33:30,300 --> 00:33:32,880 I said earlier that the left hemisphere controls 606 00:33:32,880 --> 00:33:34,680 the right side of the body 607 00:33:34,680 --> 00:33:36,380 and the right hemisphere controls 608 00:33:36,380 --> 00:33:37,920 the left side of the body. 609 00:33:37,920 --> 00:33:40,830 So we must have some structure 610 00:33:40,830 --> 00:33:42,940 that allows the left hemisphere 611 00:33:42,940 --> 00:33:45,480 and the right hemisphere to communicate, 612 00:33:45,480 --> 00:33:48,433 and that happens to be the corpus callosum. 613 00:33:49,350 --> 00:33:51,010 Another way that you can tell 614 00:33:51,010 --> 00:33:54,020 that this is the right hemisphere 615 00:33:54,020 --> 00:33:59,020 is look at the shape of the pons and the cerebellum. 616 00:33:59,320 --> 00:34:01,560 And when you look at the pons and the cerebellum, 617 00:34:01,560 --> 00:34:04,020 you can see this space here. 618 00:34:04,020 --> 00:34:07,070 So this is now one structure that we can see 619 00:34:07,070 --> 00:34:09,750 that we weren't able to see before, 620 00:34:09,750 --> 00:34:12,760 and that happens to be the ventricular system. 621 00:34:12,760 --> 00:34:16,740 The ventricular system represents a series 622 00:34:20,160 --> 00:34:23,030 of fluid-filled structures. 623 00:34:23,030 --> 00:34:26,030 So this mold 624 00:34:26,030 --> 00:34:27,920 is actually plastic, 625 00:34:27,920 --> 00:34:31,703 but what it's showing is the shape of the ventricles. 626 00:34:32,780 --> 00:34:36,180 This is really cerebrospinal fluid, 627 00:34:36,180 --> 00:34:40,990 and this would sit in the brain just like this. 628 00:34:40,990 --> 00:34:43,743 So if I push on this, 629 00:34:44,640 --> 00:34:48,110 you might see some cerebrospinal fluid 630 00:34:48,110 --> 00:34:50,517 coming out of this hole here. 631 00:34:50,517 --> 00:34:55,220 And the reason why is you have two lateral ventricles. 632 00:34:55,220 --> 00:34:57,187 You have one in the left hemisphere 633 00:34:57,187 --> 00:34:59,460 and one in the right hemisphere. 634 00:34:59,460 --> 00:35:02,270 And what they do is they drain 635 00:35:02,270 --> 00:35:05,140 by this small hole here 636 00:35:05,140 --> 00:35:07,940 into the third ventricle. 637 00:35:07,940 --> 00:35:09,680 The third ventricle 638 00:35:09,680 --> 00:35:13,103 is this space shown right here. 639 00:35:14,290 --> 00:35:17,890 The third ventricle is the perfect landmark 640 00:35:17,890 --> 00:35:19,840 for the diencephalon. 641 00:35:19,840 --> 00:35:21,610 So this space, 642 00:35:21,610 --> 00:35:25,090 this neural tissue right here, 643 00:35:25,090 --> 00:35:26,513 is the diencephalon. 644 00:35:27,360 --> 00:35:30,940 From the third ventricle, the cerebrospinal fluid drains 645 00:35:30,940 --> 00:35:35,050 through a very small canal here 646 00:35:35,050 --> 00:35:38,340 called the cerebral aqueduct. 647 00:35:38,340 --> 00:35:40,330 From the cerebral aqueduct, 648 00:35:40,330 --> 00:35:43,150 it drains into the fourth ventricle. 649 00:35:43,150 --> 00:35:44,600 From the fourth ventricle, 650 00:35:44,600 --> 00:35:46,770 it goes out through 651 00:35:47,710 --> 00:35:50,090 the subarachnoid space, 652 00:35:50,090 --> 00:35:52,130 all the way around the brain, 653 00:35:52,130 --> 00:35:54,490 and, as we saw earlier, 654 00:35:54,490 --> 00:35:57,060 to a dural sinus 655 00:35:57,060 --> 00:35:59,960 and back into your general circulation. 656 00:35:59,960 --> 00:36:03,890 So now the question is we have cerebrospinal fluid, 657 00:36:03,890 --> 00:36:06,770 where does the cerebrospinal fluid come from? 658 00:36:06,770 --> 00:36:09,430 And the cerebrospinal fluid is made 659 00:36:09,430 --> 00:36:14,160 from this tissue called choroid plexus. 660 00:36:14,160 --> 00:36:17,950 So the choroid plexus is blood vessels 661 00:36:17,950 --> 00:36:21,950 and specialized cells that withdraw substances 662 00:36:21,950 --> 00:36:26,140 from the blood and put it into the cerebrospinal fluid 663 00:36:26,140 --> 00:36:27,543 to deliver to the brain. 664 00:36:29,300 --> 00:36:32,030 So the diencephalon here 665 00:36:32,920 --> 00:36:36,060 has three major parts. 666 00:36:36,060 --> 00:36:38,323 It has the thalamus. 667 00:36:40,000 --> 00:36:43,910 The thalamus is considered a sensory relay. 668 00:36:43,910 --> 00:36:47,790 All sensory information and motor information is going 669 00:36:47,790 --> 00:36:50,823 to end up going through the thalamus. 670 00:36:51,950 --> 00:36:53,470 Under the thalamus, 671 00:36:53,470 --> 00:36:57,170 this small triangular piece of tissue here 672 00:36:57,170 --> 00:36:59,970 is called the hypothalamus, 673 00:36:59,970 --> 00:37:02,600 hypo for being under. 674 00:37:02,600 --> 00:37:04,230 The one thing that I want you to think 675 00:37:04,230 --> 00:37:08,240 about the hypothalamus is homeostasis, 676 00:37:08,240 --> 00:37:11,040 homeostasis or thermostat. 677 00:37:11,040 --> 00:37:15,540 This is going to regulate all of your autonomic function, 678 00:37:15,540 --> 00:37:16,670 how much sleep, 679 00:37:16,670 --> 00:37:19,850 whether you're thirsty, whether you're hungry, 680 00:37:19,850 --> 00:37:23,040 all the functions that you don't have to think about, 681 00:37:23,040 --> 00:37:26,100 whether you're hot or cold. 682 00:37:26,100 --> 00:37:29,513 Think of it as homeostasis or a thermostat. 683 00:37:30,510 --> 00:37:35,510 The third component is actually a gland located right here. 684 00:37:36,290 --> 00:37:39,200 This is called the pineal gland. 685 00:37:39,200 --> 00:37:41,830 We'll talk about the pineal gland later, 686 00:37:41,830 --> 00:37:46,070 but the purpose of the pineal gland is to make melatonin. 687 00:37:46,070 --> 00:37:49,240 And because of its connections with the hypothalamus, 688 00:37:49,240 --> 00:37:52,440 it regulates what are called circadian rhythms, 689 00:37:52,440 --> 00:37:56,170 circa diem, about a day. 690 00:37:56,170 --> 00:37:59,100 Most important one is sleep 691 00:37:59,100 --> 00:38:02,930 because this gland makes melatonin, 692 00:38:02,930 --> 00:38:07,513 and melatonin is responsible for maintaining sleep. 693 00:38:08,400 --> 00:38:10,380 The other thing I think you can appreciate 694 00:38:10,380 --> 00:38:15,380 in this sagittal view is the three parts of the brain stem, 695 00:38:15,680 --> 00:38:16,653 the midbrain, 696 00:38:17,490 --> 00:38:20,330 this huge, bulgy pons, 697 00:38:20,330 --> 00:38:22,193 and then the medulla.