WEBVTT 00:00:00.000 --> 00:00:02.580 align:middle line:84% The following content is provided under a Creative 00:00:02.580 --> 00:00:04.090 align:middle line:90% Commons license. 00:00:04.090 --> 00:00:06.430 align:middle line:84% Your support will help MIT OpenCourseWare 00:00:06.430 --> 00:00:10.800 align:middle line:84% continue to offer high-quality educational resources for free. 00:00:10.800 --> 00:00:13.410 align:middle line:84% To make a donation or view additional materials 00:00:13.410 --> 00:00:17.310 align:middle line:84% from hundreds of MIT courses, visit MIT OpenCourseWare 00:00:17.310 --> 00:00:17.935 align:middle line:90% at ocw.mit.edu. 00:00:17.935 --> 00:00:22.160 align:middle line:90% 00:00:22.160 --> 00:00:27.040 align:middle line:84% PROFESSOR: We have a few more slides from last time 00:00:27.040 --> 00:00:30.710 align:middle line:84% to finish up because of the problems 00:00:30.710 --> 00:00:32.680 align:middle line:90% I had with the computer. 00:00:32.680 --> 00:00:35.720 align:middle line:84% We have a class Wednesday with a quiz. 00:00:35.720 --> 00:00:41.880 align:middle line:84% And Friday, as most of you know, it's a student holiday. 00:00:41.880 --> 00:00:46.460 align:middle line:84% I would encourage all of you to go to the career fair-- 00:00:46.460 --> 00:00:49.670 align:middle line:84% especially if you've not been to one before. 00:00:49.670 --> 00:00:53.640 align:middle line:84% Even if you fully expect to go to medical school or something 00:00:53.640 --> 00:00:55.000 align:middle line:90% like that-- you never know. 00:00:55.000 --> 00:00:56.920 align:middle line:84% You should know what's out there. 00:00:56.920 --> 00:01:02.820 align:middle line:90% 00:01:02.820 --> 00:01:05.940 align:middle line:84% All right we started talking about the ethology of geese 00:01:05.940 --> 00:01:11.390 align:middle line:84% last time, and we saw a video where 00:01:11.390 --> 00:01:13.380 align:middle line:84% you could see Konrad Lorenz and some 00:01:13.380 --> 00:01:18.500 align:middle line:84% of his early work discovering imprinting. 00:01:18.500 --> 00:01:22.590 align:middle line:84% They showed the work he'd done with geese. 00:01:22.590 --> 00:01:25.850 align:middle line:84% And then later, work on social behavior of geese 00:01:25.850 --> 00:01:30.090 align:middle line:84% and the role of early experience and learning. 00:01:30.090 --> 00:01:37.112 align:middle line:90% 00:01:37.112 --> 00:01:41.010 align:middle line:84% What was the answer to this question-- 00:01:41.010 --> 00:01:45.980 align:middle line:84% "Is the response of geese to an aerial predator innate?" 00:01:45.980 --> 00:01:51.725 align:middle line:84% In the video you saw this bird shape-- 00:01:51.725 --> 00:01:53.800 align:middle line:84% it was actually made to look quite a bit 00:01:53.800 --> 00:01:56.330 align:middle line:84% like a bird in that video, but you 00:01:56.330 --> 00:02:00.010 align:middle line:84% can use a silhouette-- that they glided above the birds. 00:02:00.010 --> 00:02:03.610 align:middle line:84% And the birds showed a mobbing reaction. 00:02:03.610 --> 00:02:07.100 align:middle line:84% They forget about their individual squabbles 00:02:07.100 --> 00:02:09.509 align:middle line:84% and whatever they had been doing, 00:02:09.509 --> 00:02:12.720 align:middle line:84% and they all pretty much do the same thing. 00:02:12.720 --> 00:02:17.070 align:middle line:84% And they protect their young and so forth. 00:02:17.070 --> 00:02:19.050 align:middle line:90% Is that an innate response? 00:02:19.050 --> 00:02:20.110 align:middle line:90% What did we see? 00:02:20.110 --> 00:02:23.780 align:middle line:90% 00:02:23.780 --> 00:02:28.360 align:middle line:84% Did they have an innate response to the shape of a hawk as 00:02:28.360 --> 00:02:29.455 align:middle line:90% opposed to a goose? 00:02:29.455 --> 00:02:33.930 align:middle line:90% 00:02:33.930 --> 00:02:37.835 align:middle line:84% Hawk shapes-- short neck, longer tail. 00:02:37.835 --> 00:02:40.130 align:middle line:84% The goose shape-- the duck shape-- 00:02:40.130 --> 00:02:43.740 align:middle line:90% long neck, shorter tail. 00:02:43.740 --> 00:02:49.340 align:middle line:84% So they make a very different silhouette when it's moving. 00:02:49.340 --> 00:02:53.290 align:middle line:90% Is that an innate response? 00:02:53.290 --> 00:02:55.220 align:middle line:84% There's still some claims in the literature 00:02:55.220 --> 00:02:59.000 align:middle line:84% that in perhaps some birds it is innate. 00:02:59.000 --> 00:03:02.060 align:middle line:84% And it's clear there are some innate responses made 00:03:02.060 --> 00:03:06.360 align:middle line:90% to overhead movement. 00:03:06.360 --> 00:03:09.190 align:middle line:84% But the precise shape they're responding to 00:03:09.190 --> 00:03:13.060 align:middle line:90% is probably not innate. 00:03:13.060 --> 00:03:16.040 align:middle line:84% That doesn't mean that birds don't have many innate 00:03:16.040 --> 00:03:19.880 align:middle line:84% responses to specific visual configurations, 00:03:19.880 --> 00:03:23.630 align:middle line:90% because they certainly do. 00:03:23.630 --> 00:03:27.260 align:middle line:84% Migrating birds, for example, can respond 00:03:27.260 --> 00:03:30.600 align:middle line:90% to the patterns of the stars. 00:03:30.600 --> 00:03:35.290 align:middle line:84% But in this case they're responding 00:03:35.290 --> 00:03:39.540 align:middle line:84% to slow, overhead movement, and the species 00:03:39.540 --> 00:03:42.480 align:middle line:84% may differ a little bit into the details of the movement they 00:03:42.480 --> 00:03:44.940 align:middle line:90% respond best to. 00:03:44.940 --> 00:03:48.580 align:middle line:84% But that doesn't mean it doesn't change with experience. 00:03:48.580 --> 00:03:49.600 align:middle line:90% They do. 00:03:49.600 --> 00:03:52.080 align:middle line:84% Depending on their experience, they can change. 00:03:52.080 --> 00:03:55.570 align:middle line:90% 00:03:55.570 --> 00:03:57.916 align:middle line:90% So that was this discussion. 00:03:57.916 --> 00:04:01.560 align:middle line:90% 00:04:01.560 --> 00:04:03.770 align:middle line:84% And this is the paper that did that-- 00:04:03.770 --> 00:04:08.500 align:middle line:84% a very nice analysis of the whole hawk/goose story-- 00:04:08.500 --> 00:04:14.080 align:middle line:84% because of some of the early work of Tinbergen and Lorenz, 00:04:14.080 --> 00:04:19.470 align:middle line:84% some of which they did together before World War II, where they 00:04:19.470 --> 00:04:21.779 align:middle line:84% met and spent the summer together working 00:04:21.779 --> 00:04:23.020 align:middle line:90% on this and other problems. 00:04:23.020 --> 00:04:32.960 align:middle line:90% 00:04:32.960 --> 00:04:37.540 align:middle line:84% Let's talk a little bit about human instincts, 00:04:37.540 --> 00:04:38.840 align:middle line:90% or fixed-action patterns. 00:04:38.840 --> 00:04:41.810 align:middle line:90% 00:04:41.810 --> 00:04:44.100 align:middle line:84% We know that yawning can be considered 00:04:44.100 --> 00:04:47.340 align:middle line:90% a human fixed-action pattern. 00:04:47.340 --> 00:04:49.720 align:middle line:84% Tends to be triggered by the yawning in other people, 00:04:49.720 --> 00:04:53.820 align:middle line:84% and it seems to have some kind of social meaning. 00:04:53.820 --> 00:04:56.915 align:middle line:84% It doesn't only mean that you feel tired. 00:04:56.915 --> 00:05:01.160 align:middle line:84% In fact, it has other meanings as well. 00:05:01.160 --> 00:05:03.000 align:middle line:84% And there's still some things about it 00:05:03.000 --> 00:05:04.530 align:middle line:90% we don't fully understand. 00:05:04.530 --> 00:05:10.180 align:middle line:90% But we do know it's inbuilt. 00:05:10.180 --> 00:05:14.020 align:middle line:90% These are their other examples. 00:05:14.020 --> 00:05:17.390 align:middle line:84% First of all, expressions of emotion. 00:05:17.390 --> 00:05:22.300 align:middle line:84% That was the work, remember, of Irenaus Eibl-Eibesfeld, 00:05:22.300 --> 00:05:26.710 align:middle line:84% where he studied emotional expressions 00:05:26.710 --> 00:05:29.310 align:middle line:90% in blind and deaf people. 00:05:29.310 --> 00:05:31.590 align:middle line:84% People born blind and deaf, found 00:05:31.590 --> 00:05:35.000 align:middle line:84% that they were the same as in normally 00:05:35.000 --> 00:05:37.380 align:middle line:90% sighted and hearing people. 00:05:37.380 --> 00:05:39.580 align:middle line:84% And he also studied across cultures. 00:05:39.580 --> 00:05:43.680 align:middle line:84% He went to cultures that had never seen Western expressions 00:05:43.680 --> 00:05:45.100 align:middle line:90% at all. 00:05:45.100 --> 00:05:52.140 align:middle line:84% And people in those cultures made all the very same types 00:05:52.140 --> 00:05:58.380 align:middle line:84% of expressions that you see in what we call 00:05:58.380 --> 00:05:59.560 align:middle line:90% the more developed cultures. 00:05:59.560 --> 00:06:03.210 align:middle line:90% 00:06:03.210 --> 00:06:06.100 align:middle line:90% Walking is an instinct. 00:06:06.100 --> 00:06:09.280 align:middle line:84% But don't we teach our children to walk? 00:06:09.280 --> 00:06:12.150 align:middle line:90% We always say that. 00:06:12.150 --> 00:06:18.940 align:middle line:84% "Oh, I've been teaching my child to walk, and he finally did it. 00:06:18.940 --> 00:06:22.730 align:middle line:84% He was a little bit slow to learn." 00:06:22.730 --> 00:06:26.280 align:middle line:84% Is this an accurate way of talking? 00:06:26.280 --> 00:06:26.780 align:middle line:90% Somebody? 00:06:26.780 --> 00:06:30.430 align:middle line:90% 00:06:30.430 --> 00:06:31.660 align:middle line:90% No. 00:06:31.660 --> 00:06:34.800 align:middle line:84% Because walking is instinctive behavior. 00:06:34.800 --> 00:06:42.040 align:middle line:84% The child starts walking because his nervous system has reached 00:06:42.040 --> 00:06:44.730 align:middle line:84% the state of maturity where the circuits underlying 00:06:44.730 --> 00:06:46.210 align:middle line:90% walking are mature enough. 00:06:46.210 --> 00:06:49.140 align:middle line:84% They're spinal circuits, primarily. 00:06:49.140 --> 00:06:50.780 align:middle line:90% Also hindbrain. 00:06:50.780 --> 00:06:51.970 align:middle line:90% That's what you need. 00:06:51.970 --> 00:06:54.170 align:middle line:84% You need the balance of a vestibular system 00:06:54.170 --> 00:06:56.705 align:middle line:84% and so forth, which is a hindbrain sense. 00:06:56.705 --> 00:07:01.750 align:middle line:90% 00:07:01.750 --> 00:07:04.710 align:middle line:90% But it's instinctive movement. 00:07:04.710 --> 00:07:08.180 align:middle line:84% Then I said that eye blinks and swallowing are actually 00:07:08.180 --> 00:07:11.060 align:middle line:84% fixed-action patterns, so they're normally 00:07:11.060 --> 00:07:13.560 align:middle line:90% called reflexes. 00:07:13.560 --> 00:07:18.840 align:middle line:84% So why would they be called fixed-action patterns and not 00:07:18.840 --> 00:07:20.690 align:middle line:90% reflexes? 00:07:20.690 --> 00:07:24.190 align:middle line:84% What do they need to be a fixed-action pattern and not 00:07:24.190 --> 00:07:27.160 align:middle line:90% a reflex? 00:07:27.160 --> 00:07:31.388 align:middle line:84% That could be on the quiz on Wednesday. 00:07:31.388 --> 00:07:32.680 align:middle line:90% There's got to be a difference. 00:07:32.680 --> 00:07:33.677 align:middle line:90% Yes? 00:07:33.677 --> 00:07:35.094 align:middle line:84% AUDIENCE: Fixed-action pattern has 00:07:35.094 --> 00:07:37.130 align:middle line:90% some type of motivations to it. 00:07:37.130 --> 00:07:39.310 align:middle line:84% PROFESSOR: OK, there's some motivation 00:07:39.310 --> 00:07:42.010 align:middle line:90% which builds up over time. 00:07:42.010 --> 00:07:46.360 align:middle line:84% So the longer you go without an eye blink 00:07:46.360 --> 00:07:50.130 align:middle line:84% or without swallowing, the more likely you are to do it. 00:07:50.130 --> 00:07:54.810 align:middle line:84% And it's difficult to go too long 00:07:54.810 --> 00:07:57.140 align:middle line:90% without blinking your eyes. 00:07:57.140 --> 00:07:59.148 align:middle line:84% I mean, there's a clear function to that. 00:07:59.148 --> 00:08:00.565 align:middle line:84% You need to lubricate the corneas. 00:08:00.565 --> 00:08:04.230 align:middle line:90% 00:08:04.230 --> 00:08:08.450 align:middle line:84% And we can stare at each other and see who blinks first, 00:08:08.450 --> 00:08:12.360 align:middle line:84% but in fact the motivation to blink-- 00:08:12.360 --> 00:08:14.460 align:middle line:84% the motivation goes up and up and up 00:08:14.460 --> 00:08:17.640 align:middle line:84% until the threshold for eliciting 00:08:17.640 --> 00:08:21.940 align:middle line:84% that response becomes very low, and almost anything 00:08:21.940 --> 00:08:24.810 align:middle line:90% can cause it. 00:08:24.810 --> 00:08:28.250 align:middle line:84% Of course we blink our eyes to protect our corneas not just 00:08:28.250 --> 00:08:32.490 align:middle line:84% from drying, but from other things too. 00:08:32.490 --> 00:08:35.510 align:middle line:84% If you puff air on it, that's the one 00:08:35.510 --> 00:08:38.724 align:middle line:84% that's normally called a reflex any touch of the cornea 00:08:38.724 --> 00:08:40.890 align:middle line:90% will elicit. 00:08:40.890 --> 00:08:43.070 align:middle line:84% But it also fits all the characteristics 00:08:43.070 --> 00:08:49.000 align:middle line:84% of an instinctive movement, a fixed-action pattern 00:08:49.000 --> 00:08:52.730 align:middle line:84% It doesn't normally respond to a sensory trigger, 00:08:52.730 --> 00:08:55.470 align:middle line:84% but it will occur with almost no trigger-- 00:08:55.470 --> 00:08:57.770 align:middle line:90% with very little trigger-- 00:08:57.770 --> 00:08:59.120 align:middle line:90% after enough time passed. 00:08:59.120 --> 00:09:01.550 align:middle line:84% And the same is true for swallowing. 00:09:01.550 --> 00:09:05.942 align:middle line:84% We don't swallow as often as we blink our eyes, 00:09:05.942 --> 00:09:09.090 align:middle line:84% but it still has many of the characteristics 00:09:09.090 --> 00:09:13.050 align:middle line:90% of a fixed-action pattern. 00:09:13.050 --> 00:09:17.580 align:middle line:84% And that we discussed a little bit here. 00:09:17.580 --> 00:09:22.520 align:middle line:84% So now let's go to another term common in ethology-- 00:09:22.520 --> 00:09:26.390 align:middle line:84% the concept of a supernormal stimulus. 00:09:26.390 --> 00:09:29.910 align:middle line:84% We say such a stimulus acts as a releaser 00:09:29.910 --> 00:09:31.315 align:middle line:90% of a fixed-action pattern. 00:09:31.315 --> 00:09:35.600 align:middle line:90% 00:09:35.600 --> 00:09:38.560 align:middle line:84% And I'm asking here for a fixed-action pattern in herring 00:09:38.560 --> 00:09:42.300 align:middle line:84% gull chicks, but you can think of other kinds 00:09:42.300 --> 00:09:44.295 align:middle line:84% of supernormal stimuli for other animals. 00:09:44.295 --> 00:09:47.090 align:middle line:90% 00:09:47.090 --> 00:09:50.430 align:middle line:84% So in the case of herring gulls, they 00:09:50.430 --> 00:09:53.830 align:middle line:84% have this conspicuous red orange spot-- 00:09:53.830 --> 00:09:58.350 align:middle line:84% pretty conspicuous-- you can see it there in the gull. 00:09:58.350 --> 00:10:00.226 align:middle line:90% That orange spot. 00:10:00.226 --> 00:10:01.805 align:middle line:90% It's seen better from below. 00:10:01.805 --> 00:10:06.020 align:middle line:90% 00:10:06.020 --> 00:10:13.860 align:middle line:84% And gull chicks respond to that spot when their parent is 00:10:13.860 --> 00:10:16.070 align:middle line:90% over them and moving. 00:10:16.070 --> 00:10:19.710 align:middle line:90% 00:10:19.710 --> 00:10:24.360 align:middle line:84% You can get an even stronger gaping response 00:10:24.360 --> 00:10:31.530 align:middle line:84% just by painting an orange spot on a yellow pencil 00:10:31.530 --> 00:10:32.630 align:middle line:90% and moving it a lot. 00:10:32.630 --> 00:10:34.340 align:middle line:90% You can get a stronger response. 00:10:34.340 --> 00:10:37.850 align:middle line:84% You can make it a supernormal stimulus 00:10:37.850 --> 00:10:40.295 align:middle line:84% by making it more prominent, by more movement. 00:10:40.295 --> 00:10:42.840 align:middle line:90% 00:10:42.840 --> 00:10:45.390 align:middle line:84% You can have perhaps greater contrast. 00:10:45.390 --> 00:10:48.240 align:middle line:84% But you can elicit that response even more. 00:10:48.240 --> 00:10:50.970 align:middle line:84% When you create a stronger response 00:10:50.970 --> 00:10:54.730 align:middle line:84% than normal with a slightly different stimulus, 00:10:54.730 --> 00:10:59.250 align:middle line:84% then we call it a supernormal stimulus. 00:10:59.250 --> 00:11:03.120 align:middle line:84% Another early discovery by ethologists 00:11:03.120 --> 00:11:07.010 align:middle line:84% was the supernormal stimulus in gulls 00:11:07.010 --> 00:11:10.740 align:middle line:84% to an egg that's rolled away from the nest, 00:11:10.740 --> 00:11:14.190 align:middle line:84% like a herring gull-- they nest on shore. 00:11:14.190 --> 00:11:18.660 align:middle line:84% An egg that rolls away from the other eggs, the bird 00:11:18.660 --> 00:11:22.830 align:middle line:84% reaches out and hooks his beak around it, 00:11:22.830 --> 00:11:26.590 align:middle line:84% and pulls it back into the nest by rolling it back in the nest. 00:11:26.590 --> 00:11:31.560 align:middle line:84% And if you make an egg larger than normal, 00:11:31.560 --> 00:11:36.800 align:middle line:84% he responds more strongly, shows more vigorous egg rolling. 00:11:36.800 --> 00:11:38.545 align:middle line:84% Serves as a supernormal stimulus. 00:11:38.545 --> 00:11:41.930 align:middle line:90% 00:11:41.930 --> 00:11:46.590 align:middle line:84% So then I want some examples in humans. 00:11:46.590 --> 00:11:50.270 align:middle line:84% Can you think of any supernormal stimuli in humans? 00:11:50.270 --> 00:11:54.870 align:middle line:84% We actually use them, yes, in advertising 00:11:54.870 --> 00:11:57.040 align:middle line:90% and social behavior. 00:11:57.040 --> 00:11:59.790 align:middle line:90% Let's start with foods. 00:11:59.790 --> 00:12:05.910 align:middle line:84% Foods that are especially sweet and high in fats 00:12:05.910 --> 00:12:07.910 align:middle line:90% serve as supernormal stimuli. 00:12:07.910 --> 00:12:11.220 align:middle line:84% We have an instinctive preference 00:12:11.220 --> 00:12:13.290 align:middle line:90% for sweeter and fatter foods. 00:12:13.290 --> 00:12:17.870 align:middle line:90% 00:12:17.870 --> 00:12:21.280 align:middle line:90% At least most of us do. 00:12:21.280 --> 00:12:23.620 align:middle line:84% And I put in here beware of restaurants, 00:12:23.620 --> 00:12:26.430 align:middle line:84% because there's a simple reason why 00:12:26.430 --> 00:12:28.650 align:middle line:90% I say beware in restaurants. 00:12:28.650 --> 00:12:32.310 align:middle line:84% The restaurant owner is in business. 00:12:32.310 --> 00:12:33.990 align:middle line:90% He wants to sell more food. 00:12:33.990 --> 00:12:38.690 align:middle line:84% He wants to sell food that attracts people. 00:12:38.690 --> 00:12:40.680 align:middle line:84% And the same is true of supermarkets. 00:12:40.680 --> 00:12:42.650 align:middle line:84% I say beware of supermarkets, too. 00:12:42.650 --> 00:12:44.480 align:middle line:90% I always read the label. 00:12:44.480 --> 00:12:50.185 align:middle line:84% For example, when I buy a jam, I read all these different jams 00:12:50.185 --> 00:12:52.020 align:middle line:90% that are lined up on the shelf. 00:12:52.020 --> 00:12:55.290 align:middle line:90% I read calories per tablespoon. 00:12:55.290 --> 00:12:58.160 align:middle line:90% 50 every one. 00:12:58.160 --> 00:13:01.250 align:middle line:84% And then you read the details and you find out why. 00:13:01.250 --> 00:13:05.680 align:middle line:84% They've added high fructose corn syrup to it-- 00:13:05.680 --> 00:13:09.080 align:middle line:84% one of the most common ingredients 00:13:09.080 --> 00:13:12.550 align:middle line:84% in the American supermarket is high fructose corn syrup. 00:13:12.550 --> 00:13:13.350 align:middle line:90% Why? 00:13:13.350 --> 00:13:14.450 align:middle line:90% Because it's sweet. 00:13:14.450 --> 00:13:19.340 align:middle line:84% Because people like it better when it's sweet. 00:13:19.340 --> 00:13:22.640 align:middle line:84% And because I'm diabetic, I don't want the 50 calories. 00:13:22.640 --> 00:13:24.020 align:middle line:90% I want it to be natural. 00:13:24.020 --> 00:13:26.180 align:middle line:84% I don't want artificial sweetener either. 00:13:26.180 --> 00:13:29.000 align:middle line:90% 00:13:29.000 --> 00:13:32.130 align:middle line:84% So I prefer to make the jam myself, or find 00:13:32.130 --> 00:13:34.425 align:middle line:90% one that doesn't add that. 00:13:34.425 --> 00:13:38.150 align:middle line:84% They even will say "all natural" on it sometimes, 00:13:38.150 --> 00:13:39.722 align:middle line:90% and they'll still add sugar. 00:13:39.722 --> 00:13:41.180 align:middle line:84% They'll say, well, sugar's natural. 00:13:41.180 --> 00:13:43.820 align:middle line:90% 00:13:43.820 --> 00:13:47.960 align:middle line:84% Anyway, it's because it's instinctive 00:13:47.960 --> 00:13:50.490 align:middle line:84% that it's used to make more money. 00:13:50.490 --> 00:13:54.070 align:middle line:90% 00:13:54.070 --> 00:13:57.890 align:middle line:84% Think of the stimuli in sexual attraction. 00:13:57.890 --> 00:14:00.290 align:middle line:84% We call it the "poster effect" in advertising. 00:14:00.290 --> 00:14:03.180 align:middle line:90% 00:14:03.180 --> 00:14:07.240 align:middle line:84% When they advertise cars or other products, 00:14:07.240 --> 00:14:11.320 align:middle line:84% they often use a beautiful woman in the ad. 00:14:11.320 --> 00:14:12.110 align:middle line:90% Why? 00:14:12.110 --> 00:14:13.995 align:middle line:90% Just to attract attention. 00:14:13.995 --> 00:14:17.730 align:middle line:90% They're trying to sell it. 00:14:17.730 --> 00:14:19.787 align:middle line:84% They put them on posters even if they 00:14:19.787 --> 00:14:21.245 align:middle line:84% have nothing to do with the product 00:14:21.245 --> 00:14:22.703 align:middle line:84% that they're actually advertising-- 00:14:22.703 --> 00:14:25.520 align:middle line:90% 00:14:25.520 --> 00:14:26.670 align:middle line:90% with a beautiful smile. 00:14:26.670 --> 00:14:29.520 align:middle line:84% That helps, too, because we have an instinctive response 00:14:29.520 --> 00:14:31.510 align:middle line:90% to that. 00:14:31.510 --> 00:14:34.980 align:middle line:84% What about enhancements of appearance? 00:14:34.980 --> 00:14:39.893 align:middle line:84% How has male appearance been enhanced in men? 00:14:39.893 --> 00:14:41.560 align:middle line:84% Of course, we exaggerate shoulder width. 00:14:41.560 --> 00:14:45.080 align:middle line:84% We create suits, we put shoulder pads in. 00:14:45.080 --> 00:14:47.130 align:middle line:84% I mean, men already have broader shoulders 00:14:47.130 --> 00:14:52.490 align:middle line:84% than women on average, but to enhance 00:14:52.490 --> 00:14:53.930 align:middle line:90% that we add shoulder pads. 00:14:53.930 --> 00:14:59.440 align:middle line:90% 00:14:59.440 --> 00:15:03.570 align:middle line:84% In medieval costumes, it was common to enhance 00:15:03.570 --> 00:15:07.550 align:middle line:84% the penis area by putting this cowl-- often 00:15:07.550 --> 00:15:09.160 align:middle line:90% in a different color. 00:15:09.160 --> 00:15:11.340 align:middle line:84% And you see it in Shakespearean plays 00:15:11.340 --> 00:15:15.750 align:middle line:90% if they have period customs. 00:15:15.750 --> 00:15:20.730 align:middle line:84% In primitive tribes you often see-- 00:15:20.730 --> 00:15:23.730 align:middle line:84% for example, many of them use this-- sometimes 00:15:23.730 --> 00:15:28.110 align:middle line:84% the only clothing they wear is a penis sheath if they're males. 00:15:28.110 --> 00:15:31.850 align:middle line:90% Enhance the whole appearance-- 00:15:31.850 --> 00:15:34.460 align:middle line:90% usually of an erect penis. 00:15:34.460 --> 00:15:39.170 align:middle line:84% But it's just part of the costume. 00:15:39.170 --> 00:15:40.590 align:middle line:90% So another enhancement. 00:15:40.590 --> 00:15:44.270 align:middle line:84% It's creating a kind of supernormal stimulus. 00:15:44.270 --> 00:15:47.540 align:middle line:84% Female, it's even easier to think of these things. 00:15:47.540 --> 00:15:51.840 align:middle line:84% The waist-to-hip ratio-- men have a natural response 00:15:51.840 --> 00:15:55.195 align:middle line:84% to young women with a certain waist-to-hip ratio. 00:15:55.195 --> 00:15:57.230 align:middle line:84% We'll talk about that when we talk 00:15:57.230 --> 00:15:59.365 align:middle line:90% about research in sociobiology. 00:15:59.365 --> 00:16:02.100 align:middle line:90% 00:16:02.100 --> 00:16:05.780 align:middle line:84% But girdles and bustles were invented in order 00:16:05.780 --> 00:16:08.060 align:middle line:90% to enhance that. 00:16:08.060 --> 00:16:09.700 align:middle line:90% Of course, breast prominence-- 00:16:09.700 --> 00:16:13.770 align:middle line:84% that's still pretty common, especially in young girls-- 00:16:13.770 --> 00:16:15.640 align:middle line:90% you see it in high school. 00:16:15.640 --> 00:16:21.870 align:middle line:84% But it occurs almost everywhere in women of different ages. 00:16:21.870 --> 00:16:23.000 align:middle line:90% Think of other aspects-- 00:16:23.000 --> 00:16:24.710 align:middle line:90% lip color. 00:16:24.710 --> 00:16:27.575 align:middle line:90% Why is lip color enhanced? 00:16:27.575 --> 00:16:28.930 align:middle line:90% Why do women wear lipstick-- 00:16:28.930 --> 00:16:32.950 align:middle line:84% and in fact they enlarge the lips sometimes. 00:16:32.950 --> 00:16:34.310 align:middle line:90% What is that related to? 00:16:34.310 --> 00:16:36.980 align:middle line:90% 00:16:36.980 --> 00:16:38.740 align:middle line:90% You don't know? 00:16:38.740 --> 00:16:39.970 align:middle line:90% You do it, right? 00:16:39.970 --> 00:16:41.350 align:middle line:90% Some of you do. 00:16:41.350 --> 00:16:44.570 align:middle line:90% You know why? 00:16:44.570 --> 00:16:46.160 align:middle line:84% You know, you don't have to know why. 00:16:46.160 --> 00:16:50.170 align:middle line:84% When it comes to instincts, you don't have to know why. 00:16:50.170 --> 00:16:51.670 align:middle line:90% It's built-in. 00:16:51.670 --> 00:16:54.800 align:middle line:84% You don't have to know where it came from. 00:16:54.800 --> 00:16:58.170 align:middle line:84% Well, in sexual arousal, lips become redder and larger. 00:16:58.170 --> 00:17:01.280 align:middle line:90% 00:17:01.280 --> 00:17:03.750 align:middle line:90% So it elicits this response-- 00:17:03.750 --> 00:17:05.520 align:middle line:84% especially from the opposite sex. 00:17:05.520 --> 00:17:11.619 align:middle line:90% 00:17:11.619 --> 00:17:16.950 align:middle line:84% Why would shoulder size be enhanced in women? 00:17:16.950 --> 00:17:20.300 align:middle line:84% I can think of one possibility that would 00:17:20.300 --> 00:17:21.635 align:middle line:90% fit what we've been saying. 00:17:21.635 --> 00:17:29.160 align:middle line:84% And one is simply that the hourglass shape is not 00:17:29.160 --> 00:17:31.220 align:middle line:84% just waist-to-hip ratio, but it's 00:17:31.220 --> 00:17:35.025 align:middle line:84% the whole enhancement of a narrow waist by make 00:17:35.025 --> 00:17:36.430 align:middle line:90% the shoulders a little wider. 00:17:36.430 --> 00:17:38.890 align:middle line:84% But I think there's other reasons in modern culture. 00:17:38.890 --> 00:17:42.090 align:middle line:84% In fact, it's become much more common in modern culture 00:17:42.090 --> 00:17:46.780 align:middle line:90% than it was many years ago. 00:17:46.780 --> 00:17:51.740 align:middle line:84% And that is that women want to de-feminize 00:17:51.740 --> 00:17:53.340 align:middle line:90% their appearance somewhat. 00:17:53.340 --> 00:17:56.990 align:middle line:90% They want to be more like men. 00:17:56.990 --> 00:17:58.600 align:middle line:84% Now we don't think of it that way 00:17:58.600 --> 00:18:00.880 align:middle line:84% so much, but certainly when women first 00:18:00.880 --> 00:18:04.860 align:middle line:84% began to enter the business world a lot more. 00:18:04.860 --> 00:18:09.580 align:middle line:84% When did women really enter the world of business 00:18:09.580 --> 00:18:12.570 align:middle line:90% and the world of labor? 00:18:12.570 --> 00:18:17.550 align:middle line:84% During the wars, when all the men were going off to war. 00:18:17.550 --> 00:18:21.860 align:middle line:84% The economy would have fallen apart. 00:18:21.860 --> 00:18:27.910 align:middle line:84% So older men that were not going to the war, they needed help. 00:18:27.910 --> 00:18:33.540 align:middle line:84% So women came in and took over a lot of those jobs. 00:18:33.540 --> 00:18:38.960 align:middle line:84% But now, of course, women are at every level in business-- 00:18:38.960 --> 00:18:41.620 align:middle line:90% including right up to the top. 00:18:41.620 --> 00:18:45.990 align:middle line:84% But it's still fairly common for a business woman 00:18:45.990 --> 00:18:50.760 align:middle line:84% to wear suits that look like male suits. 00:18:50.760 --> 00:18:54.020 align:middle line:84% All right, well, anyway that's a somewhat separate reason 00:18:54.020 --> 00:18:56.295 align:middle line:84% that has nothing to do with supernormal stimuli. 00:18:56.295 --> 00:18:58.153 align:middle line:84% It has to do with kind of imitation. 00:18:58.153 --> 00:19:01.280 align:middle line:90% 00:19:01.280 --> 00:19:04.600 align:middle line:84% Then Scott in your textbook, he's 00:19:04.600 --> 00:19:06.290 align:middle line:84% talking about controlling behavior-- 00:19:06.290 --> 00:19:08.570 align:middle line:90% the role of the nervous system. 00:19:08.570 --> 00:19:11.800 align:middle line:84% And I would like you to at least know 00:19:11.800 --> 00:19:15.100 align:middle line:84% simple definitions of neurons and nervous systems 00:19:15.100 --> 00:19:18.370 align:middle line:84% so we can talk more easily about it. 00:19:18.370 --> 00:19:20.570 align:middle line:84% So I'm asking you for definitions 00:19:20.570 --> 00:19:26.080 align:middle line:84% of a primary sensory neuron, a secondary sensory neuron, 00:19:26.080 --> 00:19:28.210 align:middle line:90% a motor neuron, an interneuron. 00:19:28.210 --> 00:19:30.940 align:middle line:90% How do we define those things? 00:19:30.940 --> 00:19:31.810 align:middle line:90% You should all know. 00:19:31.810 --> 00:19:34.808 align:middle line:90% You've all had 901. 00:19:34.808 --> 00:19:36.280 align:middle line:90% Or you're taking it now. 00:19:36.280 --> 00:19:39.110 align:middle line:90% 00:19:39.110 --> 00:19:41.730 align:middle line:84% But maybe you didn't learn it, because they're not always 00:19:41.730 --> 00:19:47.520 align:middle line:84% so attentive to neuroanatomical details as I am. 00:19:47.520 --> 00:19:50.610 align:middle line:84% So let me give you some definitions. 00:19:50.610 --> 00:19:53.740 align:middle line:84% A primary sensory neuron is a neuron 00:19:53.740 --> 00:19:58.380 align:middle line:84% with a cell body outside the brain or spinal cord-- 00:19:58.380 --> 00:20:01.500 align:middle line:84% the central nervous system is brain and spinal cord-- 00:20:01.500 --> 00:20:04.940 align:middle line:84% the peripheral nervous system are outside. 00:20:04.940 --> 00:20:06.775 align:middle line:84% Peripheral nervous system are the nerves 00:20:06.775 --> 00:20:08.160 align:middle line:90% going to our skin and muscle. 00:20:08.160 --> 00:20:11.550 align:middle line:90% 00:20:11.550 --> 00:20:15.980 align:middle line:84% So the primary sensory neuron has the cell body outside. 00:20:15.980 --> 00:20:20.510 align:middle line:84% In primitive animals, it's in the surface epithelium. 00:20:20.510 --> 00:20:24.610 align:middle line:84% In us, it's in a ganglion near the central nervous system 00:20:24.610 --> 00:20:27.180 align:middle line:84% with a peripheral axon going out to the periphery. 00:20:27.180 --> 00:20:30.320 align:middle line:90% 00:20:30.320 --> 00:20:32.300 align:middle line:84% We have them in a little bit different shape 00:20:32.300 --> 00:20:35.315 align:middle line:84% for the skin of the body and for, say, the auditory 00:20:35.315 --> 00:20:38.310 align:middle line:90% or the olfactory system. 00:20:38.310 --> 00:20:41.185 align:middle line:84% But all these systems have a primary sensory neuron. 00:20:41.185 --> 00:20:42.780 align:middle line:84% What is a secondary sensory neuron? 00:20:42.780 --> 00:20:46.620 align:middle line:84% Well, the neuron that those neurons 00:20:46.620 --> 00:20:52.870 align:middle line:84% synapse with, or contact and transmit their activity to. 00:20:52.870 --> 00:20:54.330 align:middle line:90% They're in the central system. 00:20:54.330 --> 00:20:56.920 align:middle line:90% But they're the ones contacted. 00:20:56.920 --> 00:21:00.100 align:middle line:84% So we talk about the cochlear nuclei, for example. 00:21:00.100 --> 00:21:02.480 align:middle line:84% They get input from the auditory nerve. 00:21:02.480 --> 00:21:06.090 align:middle line:90% 00:21:06.090 --> 00:21:08.040 align:middle line:84% The trigeminal nuclei in the hindbrain 00:21:08.040 --> 00:21:10.220 align:middle line:84% getting input from the skin of the face. 00:21:10.220 --> 00:21:13.550 align:middle line:90% 00:21:13.550 --> 00:21:16.940 align:middle line:90% What's a motor neuron? 00:21:16.940 --> 00:21:20.450 align:middle line:90% Where is its cell body? 00:21:20.450 --> 00:21:26.117 align:middle line:84% Where's the cell body of a neuron innervating a muscle? 00:21:26.117 --> 00:21:27.492 align:middle line:84% AUDIENCE: I was going to say it's 00:21:27.492 --> 00:21:28.880 align:middle line:90% right on top of the muscle. 00:21:28.880 --> 00:21:29.960 align:middle line:90% PROFESSOR: No, it isn't. 00:21:29.960 --> 00:21:32.680 align:middle line:84% It's in the central nervous system. 00:21:32.680 --> 00:21:34.950 align:middle line:84% Any neuron in the central nervous system 00:21:34.950 --> 00:21:38.300 align:middle line:84% with a nerve fiber and axon leaving 00:21:38.300 --> 00:21:44.920 align:middle line:84% the central nervous system is a motor neuron. 00:21:44.920 --> 00:21:46.640 align:middle line:84% If it's an alpha motor neuron, it's 00:21:46.640 --> 00:21:49.570 align:middle line:84% contacting a striated muscle cell. 00:21:49.570 --> 00:21:52.020 align:middle line:90% So most of them are like that. 00:21:52.020 --> 00:21:54.900 align:middle line:84% But then there are also neurons like that that 00:21:54.900 --> 00:21:56.990 align:middle line:90% contact a cell in a ganglion. 00:21:56.990 --> 00:22:00.890 align:middle line:84% These are the autonomic nervous system cells. 00:22:00.890 --> 00:22:03.613 align:middle line:84% There you have a preganglonic motor neuron and then 00:22:03.613 --> 00:22:04.780 align:middle line:90% the ganglionic motor neuron. 00:22:04.780 --> 00:22:08.550 align:middle line:90% 00:22:08.550 --> 00:22:10.590 align:middle line:90% What are all the other neurons? 00:22:10.590 --> 00:22:13.250 align:middle line:84% We have the primary sensory, secondary sensory, 00:22:13.250 --> 00:22:14.420 align:middle line:90% and motor neuron. 00:22:14.420 --> 00:22:18.310 align:middle line:84% What are those enormous numbers of neurons in between? 00:22:18.310 --> 00:22:22.160 align:middle line:84% The general term is they're interneurons. 00:22:22.160 --> 00:22:25.620 align:middle line:84% But in the field of neuroanatomy, 00:22:25.620 --> 00:22:31.990 align:middle line:84% usually the interneuron is a short axon cell. 00:22:31.990 --> 00:22:35.950 align:middle line:84% But really, all the long axon cells and the short axon 00:22:35.950 --> 00:22:39.600 align:middle line:90% neurons are all interneurons. 00:22:39.600 --> 00:22:42.650 align:middle line:84% This is just a diagram that summarizes all those things 00:22:42.650 --> 00:22:45.600 align:middle line:90% I just told you. 00:22:45.600 --> 00:22:49.063 align:middle line:84% Some of you learn best if I describe it all verbally. 00:22:49.063 --> 00:22:50.730 align:middle line:84% Some of you have more trouble with that, 00:22:50.730 --> 00:22:52.938 align:middle line:84% but you see a picture like that and it's all obvious. 00:22:52.938 --> 00:22:56.272 align:middle line:90% 00:22:56.272 --> 00:22:59.310 align:middle line:84% In the left screen, the color's a lot better, 00:22:59.310 --> 00:23:04.820 align:middle line:84% because I used green to describe some of those cells 00:23:04.820 --> 00:23:07.290 align:middle line:84% where I've got pointers going to them. 00:23:07.290 --> 00:23:09.390 align:middle line:84% So there's the primary sensory neuron. 00:23:09.390 --> 00:23:12.390 align:middle line:84% You see where the cell body is there? 00:23:12.390 --> 00:23:14.280 align:middle line:84% Everything within those two lines 00:23:14.280 --> 00:23:18.510 align:middle line:84% is the central nervous system, like the spinal cord. 00:23:18.510 --> 00:23:20.242 align:middle line:84% But it could be in the brain, too. 00:23:20.242 --> 00:23:21.950 align:middle line:84% And there's the motor neuron with an axon 00:23:21.950 --> 00:23:23.150 align:middle line:90% going to a muscle cell. 00:23:23.150 --> 00:23:26.380 align:middle line:90% 00:23:26.380 --> 00:23:28.240 align:middle line:84% So I colored the motor neurons in. 00:23:28.240 --> 00:23:30.310 align:middle line:84% I've colored the primary sensory neuron. 00:23:30.310 --> 00:23:34.670 align:middle line:84% Secondary sensory neurons-- well in the book 00:23:34.670 --> 00:23:37.210 align:middle line:84% I'm writing I colored them green in the initial diagram, 00:23:37.210 --> 00:23:40.040 align:middle line:84% but I didn't color them green, here. 00:23:40.040 --> 00:23:41.300 align:middle line:90% All right. 00:23:41.300 --> 00:23:43.470 align:middle line:84% So one of the major specialization 00:23:43.470 --> 00:23:50.680 align:middle line:84% of neurons that govern how we sense, how we move, 00:23:50.680 --> 00:23:54.000 align:middle line:90% how we think-- everything. 00:23:54.000 --> 00:23:58.200 align:middle line:84% How are those cells different from other cells? 00:23:58.200 --> 00:24:01.030 align:middle line:84% How are they different from liver cells and kidney cells, 00:24:01.030 --> 00:24:02.740 align:middle line:90% and skin cells, and so forth? 00:24:02.740 --> 00:24:03.320 align:middle line:90% Yes. 00:24:03.320 --> 00:24:06.000 align:middle line:84% AUDIENCE: There are [INAUDIBLE] that transmit [INAUDIBLE]?? 00:24:06.000 --> 00:24:06.583 align:middle line:90% PROFESSOR: OK. 00:24:06.583 --> 00:24:08.030 align:middle line:90% That's a big one. 00:24:08.030 --> 00:24:10.510 align:middle line:84% That's a specialization of a neuron. 00:24:10.510 --> 00:24:13.410 align:middle line:84% They can transmit what we call action potentials 00:24:13.410 --> 00:24:17.000 align:middle line:84% over long distances down axons, because the axon is 00:24:17.000 --> 00:24:23.310 align:middle line:84% a specialized property of the neuron membrane-- 00:24:23.310 --> 00:24:26.030 align:middle line:90% of the axon. 00:24:26.030 --> 00:24:27.720 align:middle line:84% They have many processes that don't 00:24:27.720 --> 00:24:33.360 align:middle line:84% transmit action potentials, but they still respond to input. 00:24:33.360 --> 00:24:36.400 align:middle line:84% So the general property here is this first one. 00:24:36.400 --> 00:24:37.880 align:middle line:90% We call it irritability. 00:24:37.880 --> 00:24:43.330 align:middle line:84% They respond to stimulation, and the response spreads. 00:24:43.330 --> 00:24:46.110 align:middle line:90% 00:24:46.110 --> 00:24:47.960 align:middle line:84% Even if it's not an action potential, 00:24:47.960 --> 00:24:50.860 align:middle line:90% you still get that spread. 00:24:50.860 --> 00:24:54.240 align:middle line:84% Well, if you could record from cells in a leaf, 00:24:54.240 --> 00:24:58.080 align:middle line:84% and you might find potentials across the membrane, 00:24:58.080 --> 00:25:00.900 align:middle line:84% and it might respond to stimulation and spread. 00:25:00.900 --> 00:25:04.140 align:middle line:84% But they're rarely like action potentials. 00:25:04.140 --> 00:25:11.350 align:middle line:90% 00:25:11.350 --> 00:25:15.160 align:middle line:84% So we call the response to a stimulus either mechanical 00:25:15.160 --> 00:25:21.110 align:middle line:84% or chemical that's being irritable or responsive 00:25:21.110 --> 00:25:24.170 align:middle line:84% to the outside world outside the cell. 00:25:24.170 --> 00:25:29.190 align:middle line:84% Conduction is that spread of potential 00:25:29.190 --> 00:25:34.240 align:middle line:84% where they have that extra specialization in the axon. 00:25:34.240 --> 00:25:37.350 align:middle line:84% It begins at a little place right near the cell body 00:25:37.350 --> 00:25:41.530 align:middle line:84% usually, near the beginning of the axon-- the axon hillock-- 00:25:41.530 --> 00:25:45.230 align:middle line:84% and the action that's where the action potential is initiated. 00:25:45.230 --> 00:25:47.490 align:middle line:84% How is it different from the other potentials? 00:25:47.490 --> 00:25:54.690 align:middle line:84% Well, once it's triggered, it goes all the way down the axon. 00:25:54.690 --> 00:25:56.800 align:middle line:84% Unless something unusual happens to block it, 00:25:56.800 --> 00:25:59.780 align:middle line:84% it goes all the way down to the axon endings. 00:25:59.780 --> 00:26:08.730 align:middle line:84% And there it can transmit its response to other cells 00:26:08.730 --> 00:26:11.820 align:middle line:84% at these contacts with other cells. 00:26:11.820 --> 00:26:15.220 align:middle line:90% We call those contacts synapses. 00:26:15.220 --> 00:26:17.780 align:middle line:84% Most of them are chemical synapses. 00:26:17.780 --> 00:26:20.610 align:middle line:84% And they cause a release of a chemical substance-- 00:26:20.610 --> 00:26:23.810 align:middle line:84% a neurotransmitter that affects the next cell. 00:26:23.810 --> 00:26:26.920 align:middle line:84% So these are the major specializations 00:26:26.920 --> 00:26:31.650 align:middle line:84% of nerve cells compared with any other cells in the body. 00:26:31.650 --> 00:26:34.360 align:middle line:90% 00:26:34.360 --> 00:26:39.050 align:middle line:84% So let's talk about some of the things 00:26:39.050 --> 00:26:42.590 align:middle line:90% these nervous system cells do. 00:26:42.590 --> 00:26:47.020 align:middle line:84% We'll talk about an example used by Scott in his book. 00:26:47.020 --> 00:26:48.920 align:middle line:84% He talks about the wandering spider. 00:26:48.920 --> 00:26:51.830 align:middle line:84% It's a spider that doesn't make a web, 00:26:51.830 --> 00:26:56.590 align:middle line:90% but it still hunts insect prey. 00:26:56.590 --> 00:26:58.990 align:middle line:84% How does it catch them without a web? 00:26:58.990 --> 00:27:03.090 align:middle line:90% 00:27:03.090 --> 00:27:06.790 align:middle line:84% It's got a lot of eyes, so you would 00:27:06.790 --> 00:27:09.760 align:middle line:90% think it's using its eyes. 00:27:09.760 --> 00:27:12.640 align:middle line:84% But you can blind them or block their eyes-- 00:27:12.640 --> 00:27:15.273 align:middle line:84% you can temporarily blind them just by covering their eyes 00:27:15.273 --> 00:27:15.940 align:middle line:90% with something-- 00:27:15.940 --> 00:27:19.330 align:middle line:90% 00:27:19.330 --> 00:27:22.230 align:middle line:90% and they still catch flies. 00:27:22.230 --> 00:27:25.140 align:middle line:90% How do they do it? 00:27:25.140 --> 00:27:26.033 align:middle line:90% Yes? 00:27:26.033 --> 00:27:29.320 align:middle line:84% AUDIENCE: Well, they have a lot of hairs on their legs. 00:27:29.320 --> 00:27:30.699 align:middle line:90% PROFESSOR: Little hairs, right? 00:27:30.699 --> 00:27:31.324 align:middle line:90% AUDIENCE: Yeah. 00:27:31.324 --> 00:27:39.620 align:middle line:84% They can detect small motions [INAUDIBLE] disturbances. 00:27:39.620 --> 00:27:43.100 align:middle line:84% PROFESSOR: Yeah, you're describing 00:27:43.100 --> 00:27:47.480 align:middle line:84% a pattern of disturbance in the air around a moving insect. 00:27:47.480 --> 00:27:49.830 align:middle line:90% Exactly. 00:27:49.830 --> 00:27:57.300 align:middle line:84% And this little spider has these little sensory hairs. 00:27:57.300 --> 00:28:00.960 align:middle line:84% Very interesting, because each hair, when it bends, 00:28:00.960 --> 00:28:04.430 align:middle line:84% there are at least four afferent sensory neurons-- 00:28:04.430 --> 00:28:07.760 align:middle line:84% they're called afferents-- sensory processes 00:28:07.760 --> 00:28:10.960 align:middle line:90% attached to that hair. 00:28:10.960 --> 00:28:14.260 align:middle line:84% So when the hair bends one way, one cell responds the most. 00:28:14.260 --> 00:28:16.700 align:middle line:84% It bends another way-- the opposite way-- another cell 00:28:16.700 --> 00:28:17.920 align:middle line:90% responds, and so forth. 00:28:17.920 --> 00:28:19.390 align:middle line:90% So in four different directions. 00:28:19.390 --> 00:28:24.330 align:middle line:84% And depending on its response, that one hair, 00:28:24.330 --> 00:28:30.170 align:middle line:84% you can tell basically where the direction of air current 00:28:30.170 --> 00:28:33.120 align:middle line:90% stimulating the hair. 00:28:33.120 --> 00:28:37.030 align:middle line:84% And it seems to be born with the ability 00:28:37.030 --> 00:28:42.730 align:middle line:84% to use the pattern of responses in all those hairs covering 00:28:42.730 --> 00:28:43.770 align:middle line:90% its body. 00:28:43.770 --> 00:28:47.630 align:middle line:84% And there's lots of them-- over 100. 00:28:47.630 --> 00:28:55.670 align:middle line:84% And it can actually leap into the air and grab insects. 00:28:55.670 --> 00:28:58.960 align:middle line:84% Up to 20 centimeters away they can detect things. 00:28:58.960 --> 00:29:01.120 align:middle line:84% And it can leap several centimeters. 00:29:01.120 --> 00:29:05.640 align:middle line:84% So it can tell when the insect's approaching, 00:29:05.640 --> 00:29:06.650 align:middle line:90% when it gets close-- 00:29:06.650 --> 00:29:12.913 align:middle line:84% it sort of times its leap when it's close enough, 00:29:12.913 --> 00:29:14.080 align:middle line:90% and it can catch the insect. 00:29:14.080 --> 00:29:17.130 align:middle line:90% 00:29:17.130 --> 00:29:18.040 align:middle line:90% Very interesting. 00:29:18.040 --> 00:29:19.570 align:middle line:90% He's got a nice description. 00:29:19.570 --> 00:29:21.550 align:middle line:84% There's a box covering two pages, there. 00:29:21.550 --> 00:29:24.450 align:middle line:84% And they even have some neurophysiological results 00:29:24.450 --> 00:29:28.260 align:middle line:84% where they're recording from some 00:29:28.260 --> 00:29:30.930 align:middle line:84% of the neurons responsive to those hairs. 00:29:30.930 --> 00:29:34.834 align:middle line:90% 00:29:34.834 --> 00:29:37.500 align:middle line:84% And of course, other kinds of spiders 00:29:37.500 --> 00:29:39.420 align:middle line:84% have other kinds of specializations. 00:29:39.420 --> 00:29:42.050 align:middle line:84% Usually they're responding to vibrations in the web 00:29:42.050 --> 00:29:44.830 align:middle line:84% when something is caught in their web. 00:29:44.830 --> 00:29:46.955 align:middle line:84% But these webless spiders have other means. 00:29:46.955 --> 00:29:52.570 align:middle line:90% 00:29:52.570 --> 00:29:56.820 align:middle line:84% So let's talk a little bit about the toad. 00:29:56.820 --> 00:30:00.850 align:middle line:84% Frogs and toads have a very specialized system 00:30:00.850 --> 00:30:02.480 align:middle line:90% for catching prey. 00:30:02.480 --> 00:30:06.580 align:middle line:84% They also catch insects, like that spider. 00:30:06.580 --> 00:30:09.845 align:middle line:84% But here the specializations are in its visual system. 00:30:09.845 --> 00:30:13.890 align:middle line:90% 00:30:13.890 --> 00:30:16.850 align:middle line:84% There are cells in the retina that 00:30:16.850 --> 00:30:20.100 align:middle line:84% are specifically tuned to respond 00:30:20.100 --> 00:30:25.520 align:middle line:90% to small, usually darker-- 00:30:25.520 --> 00:30:27.440 align:middle line:84% the little stimulus in the visual field 00:30:27.440 --> 00:30:29.040 align:middle line:84% darker than the rest of the field, 00:30:29.040 --> 00:30:33.310 align:middle line:84% like a fly or another small insect. 00:30:33.310 --> 00:30:36.850 align:middle line:84% And these cells respond best when 00:30:36.850 --> 00:30:39.900 align:middle line:90% a fly-like stimulus is moving. 00:30:39.900 --> 00:30:43.740 align:middle line:84% So just a little spot will stimulate those cells, 00:30:43.740 --> 00:30:44.980 align:middle line:90% as long as it's moving. 00:30:44.980 --> 00:30:48.320 align:middle line:90% 00:30:48.320 --> 00:30:50.400 align:middle line:90% Now those are in the retina. 00:30:50.400 --> 00:30:56.290 align:middle line:84% The retina's not enough to cause the frog to catch him. 00:30:56.290 --> 00:30:58.380 align:middle line:90% Where does the information go? 00:30:58.380 --> 00:31:00.710 align:middle line:84% Well, it goes down the optic nerve 00:31:00.710 --> 00:31:03.790 align:middle line:84% and to the opposite side of the roof of the midbrain, 00:31:03.790 --> 00:31:06.970 align:middle line:84% to the optic node of the midbrain. 00:31:06.970 --> 00:31:08.490 align:middle line:90% Or the optic tectum-- 00:31:08.490 --> 00:31:10.680 align:middle line:90% tectum just means "roof"-- 00:31:10.680 --> 00:31:14.493 align:middle line:84% the roof of the midbrain on the opposite side gets that input. 00:31:14.493 --> 00:31:18.620 align:middle line:90% 00:31:18.620 --> 00:31:21.810 align:middle line:84% And what do we know about the way 00:31:21.810 --> 00:31:29.360 align:middle line:84% the retina maps, senses fibers to the midbrain tectum? 00:31:29.360 --> 00:31:32.020 align:middle line:84% Well, we know it forms an organized map. 00:31:32.020 --> 00:31:35.020 align:middle line:84% So one part of the retina projects the one part 00:31:35.020 --> 00:31:36.640 align:middle line:90% of that optic lobe. 00:31:36.640 --> 00:31:39.100 align:middle line:84% Another part of the retina projects to another part. 00:31:39.100 --> 00:31:43.570 align:middle line:84% So it forms a map to the retina in the brain. 00:31:43.570 --> 00:31:47.580 align:middle line:84% We have that in our midbrain, too-- 00:31:47.580 --> 00:31:51.300 align:middle line:84% as well as other parts of our visual system. 00:31:51.300 --> 00:31:55.162 align:middle line:84% But in the frog, the dominant part by far-- 00:31:55.162 --> 00:31:59.130 align:middle line:84% and the only really important part for this prey catching-- 00:31:59.130 --> 00:32:00.210 align:middle line:90% is there in the midbrain. 00:32:00.210 --> 00:32:09.340 align:middle line:90% 00:32:09.340 --> 00:32:12.990 align:middle line:84% So what else do frogs and toads eat besides flies? 00:32:12.990 --> 00:32:18.890 align:middle line:90% 00:32:18.890 --> 00:32:23.172 align:middle line:84% Don't you ever have pet frogs and toads? 00:32:23.172 --> 00:32:23.840 align:middle line:90% AUDIENCE: Worms? 00:32:23.840 --> 00:32:24.620 align:middle line:90% PROFESSOR: Worms. 00:32:24.620 --> 00:32:25.120 align:middle line:90% Right. 00:32:25.120 --> 00:32:28.440 align:middle line:84% They love worms as much as they love flies. 00:32:28.440 --> 00:32:30.490 align:middle line:90% What characterizes a worm? 00:32:30.490 --> 00:32:36.350 align:middle line:84% Well, it's got to be moving and longer than it is wide. 00:32:36.350 --> 00:32:40.470 align:middle line:84% So if you make artificial stimuli and show them 00:32:40.470 --> 00:32:42.680 align:middle line:84% to the frog-- and this has been done by, say, 00:32:42.680 --> 00:32:46.400 align:middle line:84% placing the frog or the toad in the center of a turntable, 00:32:46.400 --> 00:32:48.190 align:middle line:84% and you put the stimuli on the platter, 00:32:48.190 --> 00:32:51.890 align:middle line:84% and you rotate it around, and you can put little black 00:32:51.890 --> 00:32:52.710 align:middle line:90% spots-- 00:32:52.710 --> 00:32:55.550 align:middle line:84% and you'll see that the frog keeps making these orienting 00:32:55.550 --> 00:32:58.050 align:middle line:90% movements towards it. 00:32:58.050 --> 00:33:01.750 align:middle line:84% Well, if you put in the elongated worm-like object, 00:33:01.750 --> 00:33:03.730 align:middle line:90% he does the same thing. 00:33:03.730 --> 00:33:06.460 align:middle line:84% And if you make it longer and longer, 00:33:06.460 --> 00:33:07.840 align:middle line:90% he responds more and more. 00:33:07.840 --> 00:33:11.320 align:middle line:90% 00:33:11.320 --> 00:33:12.820 align:middle line:90% What if you do the opposite? 00:33:12.820 --> 00:33:14.650 align:middle line:90% You make it wider and wider? 00:33:14.650 --> 00:33:17.512 align:middle line:90% 00:33:17.512 --> 00:33:21.680 align:middle line:90% He responds less and less. 00:33:21.680 --> 00:33:26.250 align:middle line:84% And if you start, say, with a square object, when it's little 00:33:26.250 --> 00:33:28.090 align:middle line:90% he does respond more and more. 00:33:28.090 --> 00:33:29.750 align:middle line:84% But then it reaches a certain size 00:33:29.750 --> 00:33:32.400 align:middle line:84% and it rapidly responds less and less. 00:33:32.400 --> 00:33:36.590 align:middle line:84% And it gets really big, and his whole response changes. 00:33:36.590 --> 00:33:38.580 align:middle line:90% He starts crouching. 00:33:38.580 --> 00:33:40.860 align:middle line:84% It starts being dangerous to him. 00:33:40.860 --> 00:33:42.710 align:middle line:84% These are all built-in responses-- 00:33:42.710 --> 00:33:45.800 align:middle line:84% innate responses-- of frogs and toads. 00:33:45.800 --> 00:33:55.810 align:middle line:90% 00:33:55.810 --> 00:33:57.960 align:middle line:84% So we've already talked about where 00:33:57.960 --> 00:34:00.555 align:middle line:84% in the central nervous system of a toad-- 00:34:00.555 --> 00:34:04.870 align:middle line:84% and then we could say the same thing about frogs-- 00:34:04.870 --> 00:34:07.790 align:middle line:84% that input from the retina is going. 00:34:07.790 --> 00:34:11.210 align:middle line:84% So here I'm asking, where in the central nervous system 00:34:11.210 --> 00:34:13.620 align:middle line:84% of a toad could electrical stimulus 00:34:13.620 --> 00:34:17.000 align:middle line:84% elicit a prey-catching, fixed-action pattern? 00:34:17.000 --> 00:34:20.090 align:middle line:84% Well, you could put an electrode in there. 00:34:20.090 --> 00:34:24.184 align:middle line:84% You anesthetize the frog, and implant the electrode. 00:34:24.184 --> 00:34:26.800 align:middle line:84% Let him wake up, recover from the surgery. 00:34:26.800 --> 00:34:30.510 align:middle line:84% Now just a little electrical stimulus in one part 00:34:30.510 --> 00:34:32.050 align:middle line:90% of that tectum-- 00:34:32.050 --> 00:34:37.290 align:middle line:84% that midbrain surface-- will elicit those turning movements 00:34:37.290 --> 00:34:39.570 align:middle line:90% that we were just talking about. 00:34:39.570 --> 00:34:41.804 align:middle line:84% So they can be elicited electrically. 00:34:41.804 --> 00:34:45.340 align:middle line:90% 00:34:45.340 --> 00:34:48.030 align:middle line:84% The only problem is when you elicit them electrically, 00:34:48.030 --> 00:34:49.489 align:middle line:90% he never follows through. 00:34:49.489 --> 00:34:51.030 align:middle line:90% What does a normal frog do? 00:34:51.030 --> 00:34:52.449 align:middle line:90% He's following the worm. 00:34:52.449 --> 00:34:57.750 align:middle line:90% 00:34:57.750 --> 00:35:01.290 align:middle line:90% Then what does he do to get it? 00:35:01.290 --> 00:35:02.735 align:middle line:90% Flips his tongue out. 00:35:02.735 --> 00:35:07.980 align:middle line:84% His tongue comes out like a dart. 00:35:07.980 --> 00:35:10.610 align:middle line:84% And the tongue is sticky at the end. 00:35:10.610 --> 00:35:13.360 align:middle line:90% So, splat! 00:35:13.360 --> 00:35:16.280 align:middle line:90% He gets it, pulls it back. 00:35:16.280 --> 00:35:17.630 align:middle line:90% Same for a fly. 00:35:17.630 --> 00:35:24.120 align:middle line:84% For the fly, he's tuned to wait until the fly alights. 00:35:24.120 --> 00:35:26.830 align:middle line:84% If it wasn't moving he will never try to get it. 00:35:26.830 --> 00:35:31.430 align:middle line:84% But if it was moving and stops, see the frog will just 00:35:31.430 --> 00:35:33.000 align:middle line:90% sit there and watch it move. 00:35:33.000 --> 00:35:36.690 align:middle line:84% But if it alights, then he'll get the prey-catching 00:35:36.690 --> 00:35:37.230 align:middle line:90% response-- 00:35:37.230 --> 00:35:38.930 align:middle line:90% if it's within range. 00:35:38.930 --> 00:35:42.700 align:middle line:84% He does have enough depth vision to know whether it's 00:35:42.700 --> 00:35:45.170 align:middle line:90% within range of his tongue. 00:35:45.170 --> 00:35:46.960 align:middle line:84% When you stimulate it electrically, 00:35:46.960 --> 00:35:49.770 align:middle line:90% you never get the tongue flick. 00:35:49.770 --> 00:35:50.270 align:middle line:90% Why? 00:35:50.270 --> 00:35:52.930 align:middle line:90% 00:35:52.930 --> 00:35:54.270 align:middle line:90% Give me a reason. 00:35:54.270 --> 00:35:57.760 align:middle line:90% I can stimulate repeatedly. 00:35:57.760 --> 00:36:00.460 align:middle line:84% I can stimulate the turning movements. 00:36:00.460 --> 00:36:03.220 align:middle line:84% He keeps reorienting to different positions 00:36:03.220 --> 00:36:06.320 align:middle line:84% in the field every time I stimulate them. 00:36:06.320 --> 00:36:09.680 align:middle line:84% Why does he never flip his tongue? 00:36:09.680 --> 00:36:13.380 align:middle line:90% Isn't that all built-in? 00:36:13.380 --> 00:36:16.820 align:middle line:84% Isn't it part of the same fixed-action pattern? 00:36:16.820 --> 00:36:18.760 align:middle line:90% Well normally, yes. 00:36:18.760 --> 00:36:20.580 align:middle line:84% Because normally, of course, just think. 00:36:20.580 --> 00:36:23.850 align:middle line:90% 00:36:23.850 --> 00:36:25.485 align:middle line:84% This is a frog without an electrode. 00:36:25.485 --> 00:36:28.050 align:middle line:90% He turns. 00:36:28.050 --> 00:36:32.600 align:middle line:84% That stimulus is moving across his tectum. 00:36:32.600 --> 00:36:37.280 align:middle line:84% He always brings it so the stimulus is in front of him. 00:36:37.280 --> 00:36:39.440 align:middle line:90% So he's aligned. 00:36:39.440 --> 00:36:41.410 align:middle line:84% So he can make the tongue flick response. 00:36:41.410 --> 00:36:45.490 align:middle line:84% Now it's always up in the front of the tectum. 00:36:45.490 --> 00:36:49.000 align:middle line:84% That's the part of the tectum which, if you stimulate, 00:36:49.000 --> 00:36:52.680 align:middle line:84% you can also get the tongue flick. 00:36:52.680 --> 00:36:55.290 align:middle line:84% But with just one electrode in the middle of the tectum, 00:36:55.290 --> 00:36:57.860 align:middle line:84% you'll never get it, because we can't 00:36:57.860 --> 00:36:59.600 align:middle line:90% imitate with a fixed electrode. 00:36:59.600 --> 00:37:06.080 align:middle line:84% We can't imitate the whole normal stimulus sequence. 00:37:06.080 --> 00:37:08.280 align:middle line:84% Then here I say, what would change if an electrode 00:37:08.280 --> 00:37:11.100 align:middle line:90% were moved a short distance? 00:37:11.100 --> 00:37:13.400 align:middle line:84% Well, he would just change the position 00:37:13.400 --> 00:37:15.287 align:middle line:90% he's orienting towards. 00:37:15.287 --> 00:37:17.120 align:middle line:84% So you put it way in the back of the tectum, 00:37:17.120 --> 00:37:20.603 align:middle line:84% he would make these bigger orienting moves. 00:37:20.603 --> 00:37:22.020 align:middle line:84% If you put it closer to the front, 00:37:22.020 --> 00:37:25.250 align:middle line:84% he makes short orienting movements. 00:37:25.250 --> 00:37:29.975 align:middle line:84% If you place it closer to the midline, he orients upward. 00:37:29.975 --> 00:37:32.300 align:middle line:84% If you place it further out laterally, 00:37:32.300 --> 00:37:37.030 align:middle line:84% he orients to the side and downward. 00:37:37.030 --> 00:37:41.470 align:middle line:84% Well, the map we have of the retina in our midbrain 00:37:41.470 --> 00:37:44.960 align:middle line:84% is the same as the map in the frog. 00:37:44.960 --> 00:37:49.250 align:middle line:84% It's conserved across all the vertebrates. 00:37:49.250 --> 00:37:54.570 align:middle line:84% The relative size of structures changes a lot, 00:37:54.570 --> 00:37:57.400 align:middle line:84% but the existence of these structures 00:37:57.400 --> 00:37:59.670 align:middle line:84% is the same throughout the vertebrates. 00:37:59.670 --> 00:38:03.510 align:middle line:84% And that's true for all the structures of the spinal cord 00:38:03.510 --> 00:38:06.115 align:middle line:84% and brain stem that control these fixed-action patterns. 00:38:06.115 --> 00:38:09.010 align:middle line:90% 00:38:09.010 --> 00:38:10.600 align:middle line:90% Another concept here. 00:38:10.600 --> 00:38:13.155 align:middle line:84% We talked about what a motor neuron is. 00:38:13.155 --> 00:38:14.930 align:middle line:84% If the motor neuron's stimulated, 00:38:14.930 --> 00:38:16.610 align:middle line:90% you get a muscle twitch. 00:38:16.610 --> 00:38:19.161 align:middle line:90% 00:38:19.161 --> 00:38:21.740 align:middle line:84% If a group of motor neurons are stimulated, 00:38:21.740 --> 00:38:23.910 align:middle line:90% you can get more movement. 00:38:23.910 --> 00:38:27.710 align:middle line:84% And if I stimulate all the motor neurons in the cord, 00:38:27.710 --> 00:38:30.810 align:middle line:84% I can get suddenly rigidity if I'm stimulating, 00:38:30.810 --> 00:38:33.205 align:middle line:84% say, in the motor neurons controlling my hand. 00:38:33.205 --> 00:38:35.290 align:middle line:84% But if I'm stimulating just one group of them 00:38:35.290 --> 00:38:37.155 align:middle line:90% I can get flexion of the hand. 00:38:37.155 --> 00:38:40.460 align:middle line:84% I stimulate another group, I can get-- 00:38:40.460 --> 00:38:43.980 align:middle line:84% this would be extension, this would be flexion. 00:38:43.980 --> 00:38:46.060 align:middle line:90% So I could elicit grasping. 00:38:46.060 --> 00:38:50.450 align:middle line:90% What about a command neuron? 00:38:50.450 --> 00:38:53.170 align:middle line:84% It has a different meaning, also very 00:38:53.170 --> 00:38:57.430 align:middle line:84% important in studying the control of these movements 00:38:57.430 --> 00:38:59.660 align:middle line:90% in fixed-action patterns. 00:38:59.660 --> 00:39:01.383 align:middle line:90% What is a command neuron? 00:39:01.383 --> 00:39:05.820 align:middle line:90% 00:39:05.820 --> 00:39:12.250 align:middle line:84% It's a term used in neuroethology 00:39:12.250 --> 00:39:16.000 align:middle line:84% to describe a neuron that you can identify. 00:39:16.000 --> 00:39:16.950 align:middle line:90% Usually it's a neuron. 00:39:16.950 --> 00:39:21.230 align:middle line:84% You can identify the same neuron in one member of the species 00:39:21.230 --> 00:39:22.237 align:middle line:90% to another. 00:39:22.237 --> 00:39:24.320 align:middle line:84% Sometimes they even have different color pigments. 00:39:24.320 --> 00:39:28.030 align:middle line:90% 00:39:28.030 --> 00:39:31.220 align:middle line:84% It's a neuron where if you stimulate that one 00:39:31.220 --> 00:39:35.120 align:middle line:84% neuron you stimulate a whole pattern of movement. 00:39:35.120 --> 00:39:38.760 align:middle line:84% You get a behavior from one neuron. 00:39:38.760 --> 00:39:42.630 align:middle line:84% You stimulate a command neuron in a crayfish, you can elicit, 00:39:42.630 --> 00:39:44.570 align:middle line:84% if you're in the right place, you 00:39:44.570 --> 00:39:46.300 align:middle line:84% stimulate the right command neuron, 00:39:46.300 --> 00:39:48.390 align:middle line:84% you can get a tail-flip response. 00:39:48.390 --> 00:39:52.375 align:middle line:84% The animal will escape as if escaping from a predator. 00:39:52.375 --> 00:39:56.460 align:middle line:90% 00:39:56.460 --> 00:40:01.500 align:middle line:84% Mammals and vertebrates in general-- 00:40:01.500 --> 00:40:04.720 align:middle line:84% it's harder to find the command neuron. 00:40:04.720 --> 00:40:06.765 align:middle line:84% There are a few very large neurons 00:40:06.765 --> 00:40:11.373 align:middle line:84% that you can identify, say, across fish and amphibians. 00:40:11.373 --> 00:40:14.212 align:middle line:90% 00:40:14.212 --> 00:40:16.660 align:middle line:84% There's very giant cells in the hindbrain 00:40:16.660 --> 00:40:19.760 align:middle line:84% they call the Mauthner cells that can elicit rapid escape 00:40:19.760 --> 00:40:21.580 align:middle line:90% responses. 00:40:21.580 --> 00:40:23.220 align:middle line:90% They're like command neurons. 00:40:23.220 --> 00:40:25.820 align:middle line:84% But otherwise, usually these are insects 00:40:25.820 --> 00:40:27.155 align:middle line:90% and other invertebrates. 00:40:27.155 --> 00:40:33.130 align:middle line:90% 00:40:33.130 --> 00:40:33.630 align:middle line:90% All right. 00:40:33.630 --> 00:40:36.270 align:middle line:84% That's the difference between a command neuron and a motor 00:40:36.270 --> 00:40:36.770 align:middle line:90% neuron. 00:40:36.770 --> 00:40:40.170 align:middle line:84% In a vertebrate you have groups of neurons 00:40:40.170 --> 00:40:44.190 align:middle line:84% though that act as command groups of neurons, which 00:40:44.190 --> 00:40:50.290 align:middle line:84% when stimulated can elicit a whole sequence of movements-- 00:40:50.290 --> 00:40:54.100 align:middle line:84% for example, in the caudal part of the midbrain. 00:40:54.100 --> 00:40:56.160 align:middle line:90% Below the optic tectum-- 00:40:56.160 --> 00:40:58.450 align:middle line:84% below in fact the auditory tectum-- 00:40:58.450 --> 00:41:00.490 align:middle line:90% it's in the caudal midbrain-- 00:41:00.490 --> 00:41:04.650 align:middle line:84% there's an area there which, when activated, 00:41:04.650 --> 00:41:07.560 align:middle line:90% elicits locomotion. 00:41:07.560 --> 00:41:11.241 align:middle line:84% You get the right place and you stimulate 00:41:11.241 --> 00:41:15.780 align:middle line:84% with enough activation, you can get rapid running movements. 00:41:15.780 --> 00:41:19.160 align:middle line:84% There are similar groups of neurons 00:41:19.160 --> 00:41:23.890 align:middle line:84% further forward in an area we call the subthalamus. 00:41:23.890 --> 00:41:26.590 align:middle line:84% Parts of the subthalamus get direct visual input 00:41:26.590 --> 00:41:29.800 align:middle line:90% from the retina. 00:41:29.800 --> 00:41:35.630 align:middle line:84% And more immediately, they can activate these neurons 00:41:35.630 --> 00:41:38.950 align:middle line:84% that seem to connect directly to that midbrain center, 00:41:38.950 --> 00:41:43.360 align:middle line:84% because they also elicit rapid running movements usually 00:41:43.360 --> 00:41:45.240 align:middle line:90% involved in escape behavior. 00:41:45.240 --> 00:41:48.310 align:middle line:84% That's a kind of command neuron group. 00:41:48.310 --> 00:41:51.380 align:middle line:84% It's just that we can't identify the single neuron. 00:41:51.380 --> 00:41:53.890 align:middle line:84% So if I say "command neuron," I'm 00:41:53.890 --> 00:42:00.080 align:middle line:84% almost always talking about invertebrate animals 00:42:00.080 --> 00:42:04.850 align:middle line:84% where we can actually identify the same cell from animal 00:42:04.850 --> 00:42:05.500 align:middle line:90% to animal. 00:42:05.500 --> 00:42:08.770 align:middle line:90% 00:42:08.770 --> 00:42:13.660 align:middle line:84% So let's talk about the giant axon. 00:42:13.660 --> 00:42:16.645 align:middle line:84% What is the main advantage of the giant axon 00:42:16.645 --> 00:42:20.150 align:middle line:84% in the triggering of an escape response? 00:42:20.150 --> 00:42:23.820 align:middle line:90% You see giant axons in squid. 00:42:23.820 --> 00:42:28.810 align:middle line:84% It was the discovery of giant axons in squid 00:42:28.810 --> 00:42:35.220 align:middle line:84% that led to the detailed physiology of the action 00:42:35.220 --> 00:42:38.480 align:middle line:90% potential for the first time. 00:42:38.480 --> 00:42:46.070 align:middle line:84% Because this was before microelectrodes were perfected. 00:42:46.070 --> 00:42:49.960 align:middle line:84% They could get a tiny wire inside that giant axon. 00:42:49.960 --> 00:42:55.070 align:middle line:84% They were up to one millimeter in diameter in a squid. 00:42:55.070 --> 00:42:59.260 align:middle line:84% So it enabled detailed study of the physiology of the action 00:42:59.260 --> 00:43:02.475 align:middle line:90% potential in the giant axon. 00:43:02.475 --> 00:43:06.110 align:middle line:84% But why would the squid have giant axons? 00:43:06.110 --> 00:43:07.970 align:middle line:90% They use a lot of energy. 00:43:07.970 --> 00:43:10.555 align:middle line:84% If all their axons were like that, 00:43:10.555 --> 00:43:14.470 align:middle line:90% they'd be gigantic animals. 00:43:14.470 --> 00:43:18.330 align:middle line:84% Some of them are pretty large, but they're not gigantic. 00:43:18.330 --> 00:43:20.506 align:middle line:84% And some of them are small, too, but all of them 00:43:20.506 --> 00:43:21.840 align:middle line:90% have these giant axons. 00:43:21.840 --> 00:43:24.210 align:middle line:90% Why? 00:43:24.210 --> 00:43:31.142 align:middle line:84% What's the advantage of making an axon larger in diameter? 00:43:31.142 --> 00:43:32.850 align:middle line:84% AUDIENCE: They have more rapid responses? 00:43:32.850 --> 00:43:35.090 align:middle line:84% PROFESSOR: Yeah, one word-- speed. 00:43:35.090 --> 00:43:36.155 align:middle line:90% Rapid conduction. 00:43:36.155 --> 00:43:40.360 align:middle line:90% 00:43:40.360 --> 00:43:44.650 align:middle line:90% That's why giant axons evolved. 00:43:44.650 --> 00:43:48.330 align:middle line:84% Because axonal conduction speed depends 00:43:48.330 --> 00:43:54.670 align:middle line:84% first of all on the diameter of the axon. 00:43:54.670 --> 00:43:57.415 align:middle line:84% So you get faster conduction of the action potential. 00:43:57.415 --> 00:44:00.890 align:middle line:90% 00:44:00.890 --> 00:44:03.560 align:middle line:84% Well, we have rapid conduction too, 00:44:03.560 --> 00:44:05.690 align:middle line:90% and we don't have giant axons. 00:44:05.690 --> 00:44:08.230 align:middle line:84% We do have some axons larger than others, 00:44:08.230 --> 00:44:10.860 align:middle line:84% and they do conduct more rapidly, 00:44:10.860 --> 00:44:14.700 align:middle line:84% but they're nowhere near the size of the squid. 00:44:14.700 --> 00:44:19.920 align:middle line:84% And yet we get conduction that's just as fast as in the squid-- 00:44:19.920 --> 00:44:21.770 align:middle line:90% probably faster. 00:44:21.770 --> 00:44:26.360 align:middle line:84% I can't remember the exact speed of conduction in a giant axon, 00:44:26.360 --> 00:44:31.330 align:middle line:84% but I know the long axons down to our spinal cord 00:44:31.330 --> 00:44:34.350 align:middle line:90% are very rapidly conducting. 00:44:34.350 --> 00:44:39.293 align:middle line:84% The reason is the evolution of the myelin sheath. 00:44:39.293 --> 00:44:42.240 align:middle line:90% 00:44:42.240 --> 00:44:48.300 align:middle line:84% Myelin is when the axon is wrapped round and round 00:44:48.300 --> 00:44:52.550 align:middle line:84% by the membrane of a glial cell that sort of insulates 00:44:52.550 --> 00:44:58.150 align:middle line:84% the axon from the ionic potentials that normally 00:44:58.150 --> 00:45:00.810 align:middle line:84% are involved in the action potential. 00:45:00.810 --> 00:45:03.590 align:middle line:84% Well, if you insulated the whole axon like that, 00:45:03.590 --> 00:45:07.930 align:middle line:84% you wouldn't get any action potentials at all. 00:45:07.930 --> 00:45:11.700 align:middle line:84% So this is why it gets-- first of all, 00:45:11.700 --> 00:45:17.085 align:middle line:84% deal with the rate of spread of current down an axon. 00:45:17.085 --> 00:45:21.570 align:middle line:84% For all you engineers, this should make sense to you. 00:45:21.570 --> 00:45:24.930 align:middle line:84% If you're not engineers, well, be patient. 00:45:24.930 --> 00:45:28.820 align:middle line:84% You've studied basic physics and math. 00:45:28.820 --> 00:45:31.930 align:middle line:84% The rate of passive spread of current 00:45:31.930 --> 00:45:38.110 align:middle line:84% down the center of an axon is proportional to the reciprocal 00:45:38.110 --> 00:45:38.875 align:middle line:90% of this product. 00:45:38.875 --> 00:45:46.390 align:middle line:90% 00:45:46.390 --> 00:45:50.030 align:middle line:84% The resistance of the axon down the cylinder 00:45:50.030 --> 00:45:55.260 align:middle line:84% can be measured, and the capacitance of the membrane. 00:45:55.260 --> 00:45:59.680 align:middle line:84% You can increase the capacitance with myelin. 00:45:59.680 --> 00:46:02.780 align:middle line:84% You can decrease the resistance simply 00:46:02.780 --> 00:46:04.615 align:middle line:84% by making the axon bigger around. 00:46:04.615 --> 00:46:09.210 align:middle line:90% 00:46:09.210 --> 00:46:13.850 align:middle line:84% I point out down here that the resistance decreases 00:46:13.850 --> 00:46:17.760 align:middle line:84% in proportion to the square of the diameter of the axon, 00:46:17.760 --> 00:46:22.860 align:middle line:84% and the capacitance increases in proportion to the diameter. 00:46:22.860 --> 00:46:25.510 align:middle line:84% So then how does the action potential move? 00:46:25.510 --> 00:46:31.100 align:middle line:84% We know that the myelin makes that passive conduction 00:46:31.100 --> 00:46:34.000 align:middle line:84% the passive spread of current-- the kind of spread 00:46:34.000 --> 00:46:37.240 align:middle line:84% you get in the cell body where you touch the cell in one 00:46:37.240 --> 00:46:39.730 align:middle line:84% place-- you stimulate it in one place-- it does spread 00:46:39.730 --> 00:46:42.270 align:middle line:90% to the rest of the cell. 00:46:42.270 --> 00:46:44.130 align:middle line:84% But not if it's not an action potential. 00:46:44.130 --> 00:46:45.640 align:middle line:90% In fact, it gets detrimental. 00:46:45.640 --> 00:46:48.660 align:middle line:84% It gets weaker the further you get from where you stimulate. 00:46:48.660 --> 00:46:52.420 align:middle line:84% The same is true in all those little processes of the cell 00:46:52.420 --> 00:46:53.990 align:middle line:90% we called dendrites. 00:46:53.990 --> 00:46:54.865 align:middle line:90% It spreads passively. 00:46:54.865 --> 00:47:00.290 align:middle line:90% 00:47:00.290 --> 00:47:03.240 align:middle line:90% Here's a greatly enlarged axon-- 00:47:03.240 --> 00:47:05.120 align:middle line:90% this long cylinder. 00:47:05.120 --> 00:47:07.790 align:middle line:90% That's the axon membrane. 00:47:07.790 --> 00:47:10.400 align:middle line:90% The way the myelin forms is-- 00:47:10.400 --> 00:47:14.475 align:middle line:90% 00:47:14.475 --> 00:47:17.515 align:middle line:84% let's say this is a peripheral axon in our leg. 00:47:17.515 --> 00:47:21.370 align:middle line:90% 00:47:21.370 --> 00:47:24.800 align:middle line:84% We'll draw the cell body forming that. 00:47:24.800 --> 00:47:26.670 align:middle line:90% Here's the nucleus. 00:47:26.670 --> 00:47:30.790 align:middle line:84% That cell, its membrane is wrapped 00:47:30.790 --> 00:47:33.800 align:middle line:84% round and round and around this portion of the axon. 00:47:33.800 --> 00:47:36.750 align:middle line:90% This is a cross-section. 00:47:36.750 --> 00:47:39.670 align:middle line:84% And then there's another cell wrapping its membrane here. 00:47:39.670 --> 00:47:42.350 align:middle line:84% Another one here wrapping its membrane. 00:47:42.350 --> 00:47:43.892 align:middle line:84% These cells are called Schwann cells. 00:47:43.892 --> 00:47:44.933 align:middle line:90% They're in the periphery. 00:47:44.933 --> 00:47:47.310 align:middle line:84% If this was in the central nervous system, in the brain, 00:47:47.310 --> 00:47:50.180 align:middle line:84% say, where we also have a lot of myelin, 00:47:50.180 --> 00:47:51.760 align:middle line:90% same in the spinal cord-- 00:47:51.760 --> 00:47:55.560 align:middle line:84% then there would be a cell up here forming myelin, 00:47:55.560 --> 00:48:02.840 align:middle line:90% and like this. 00:48:02.840 --> 00:48:14.680 align:middle line:84% And it would have these branches spreading down and wrapping 00:48:14.680 --> 00:48:21.270 align:middle line:84% the membrane round and round and around the axon. 00:48:21.270 --> 00:48:23.395 align:middle line:84% So the same cell here can myelinate 00:48:23.395 --> 00:48:27.350 align:middle line:90% a whole bunch of axons. 00:48:27.350 --> 00:48:29.395 align:middle line:84% That's an [INAUDIBLE] site in the brain. 00:48:29.395 --> 00:48:31.570 align:middle line:84% So the same thing is accomplished. 00:48:31.570 --> 00:48:36.470 align:middle line:84% These cells are insulating the axon. 00:48:36.470 --> 00:48:40.210 align:middle line:90% So how does that help? 00:48:40.210 --> 00:48:48.830 align:middle line:84% If the action potential, say, is triggered here, 00:48:48.830 --> 00:48:54.890 align:middle line:84% we know that this depolarization of the membrane 00:48:54.890 --> 00:48:59.330 align:middle line:90% spreads very fast down the axon. 00:48:59.330 --> 00:49:01.900 align:middle line:90% 00:49:01.900 --> 00:49:05.390 align:middle line:84% No action potential until you get to the next node 00:49:05.390 --> 00:49:07.780 align:middle line:90% here, where there's no myelin. 00:49:07.780 --> 00:49:10.620 align:middle line:84% It triggers an action potential there. 00:49:10.620 --> 00:49:15.470 align:middle line:84% Then that spreads decrementally down to the next node. 00:49:15.470 --> 00:49:19.660 align:middle line:84% The spread is extremely rapid with a large diameter 00:49:19.660 --> 00:49:21.930 align:middle line:90% and with the insulated membrane. 00:49:21.930 --> 00:49:24.230 align:middle line:84% It keeps triggering the action potential in node 00:49:24.230 --> 00:49:25.560 align:middle line:90% after node after node-- 00:49:25.560 --> 00:49:28.150 align:middle line:84% that's called saltatory conduction-- 00:49:28.150 --> 00:49:30.100 align:middle line:90% jumping conduction. 00:49:30.100 --> 00:49:33.000 align:middle line:90% And it just goes b-r-r-a-p! 00:49:33.000 --> 00:49:36.090 align:middle line:84% And it goes very, very fast without making 00:49:36.090 --> 00:49:38.680 align:middle line:90% the axon so gigantic. 00:49:38.680 --> 00:49:41.770 align:middle line:90% So that's how it happens. 00:49:41.770 --> 00:49:45.660 align:middle line:90% And that's the end of the class. 00:49:45.660 --> 00:49:51.450 align:middle line:84% And we'll talk about motivational states next time. 00:49:51.450 --> 00:50:03.638 align:middle line:90%