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BIOL 4315 & 6315 Neuroscience Mon-Wed 1-2.30 PM - Neuroscience Lecture 16 Visual System II
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00:00 Recording in progress. This is uh Visual System two lecture. And we
00:11 the last lecture by talking about the in the retina or the retinal
00:18 And in particular, we highlight that there are three major cell types that
00:26 and send that visual information. The is where photo transduction takes place.
00:35 cells that are connected to photo receptors will communicate synaptic potentials to the gang
00:41 . The gang cells that will form optic nerve, the axons will produce
00:46 actions and the the output from the and the processing of information that we
00:54 and kind of a in the processing direction which is photoreceptors bipolar cells or
01:03 cells is influenced and controlled. In by these two other subtypes of
01:09 the horizontal and the rene cells And again, the only output from
01:16 retina is optic nerve which is retinal and cell axons. So now this
01:27 another presentation of the retina is subdivided layers which is the outer nuclear layer
01:35 where you have uh the photoreceptors. outer plexiform layer is nuclear because you'll
01:43 their cell here with the nuclei they out of plexiform layer. These are
01:49 synaptic connections between photoreceptors, bipolar cells well as the horizontal cells in our
01:56 layer which contain the cell, most the nuclei horizonal bipolar and a cells
02:01 this area. Here, then you the inter plexiform layer, plexus,
02:07 connections there again with bipolar cells, gang cells, then amari cells
02:14 Then you have the ganglion cell layer is the gang cells to put their
02:19 to form the optic nerve cranial nerve . Just another illustration of these
02:26 the gang layer which is in. this is the photoreceptors outer layer.
02:32 is the outer nuclear layer where you have the sous plexiform internuclear sous of
02:38 nuclei, inter flexi form connections. then cell cell layer finally. And
02:46 is all in the back of the where we have the retina. There
02:50 clear differences between photoreceptors. And one those differences is in their structure,
02:56 only in their function and structure is correlated to function. Uh One of
03:02 stark differences between the cone and the receptors is the in the outer segments
03:08 the photoreceptors. And you can see clearly that rock photo receptors contain numberous
03:15 that are free floating discs. And they have so much of these discs
03:20 so much of the membrane, a of surface area of the membrane,
03:25 store a lot of photo pigments, lot of light sensitive molecules are being
03:32 here. It makes them more sensitive , cones. On the other
03:36 the outer segments have a different They don't have these preload disks.
03:42 , they have these indentations or imaginations the outer membrane itself of the outer
03:50 . And that doesn't give them as of the photo pigment, doesn't give
03:54 as much of the area to store photo pigment. Um But that virtue
03:59 them less sensitive that rod than rod cells in our direction and realize.
04:10 this is a sort of an inside . Uh These are free floating discs
04:16 here you have the poles in the membrane and the free floating discs provide
04:23 a lot more of the surface This is where the photo transduction and
04:29 outer segments is where the photo transduction place. This is where the light
04:34 activate light sensitive molecules and it will into an electrochemical signaling inner layers where
04:41 have biosyn machinery because that's the that's the nucleus of the cell and
04:48 the plexiform layer. So the synaptic are the contacts of the synapses between
04:54 cells. So bipolar cells direct mian and so on. The functional differences
05:02 such that rods are highly sensitive to . They're specialized for night vision.
05:09 will contain a lot more of the pigment because they have these brief loading
05:13 and a lot of surface area to that photo pigment, they capture more
05:20 . Uh It's a classical uh example rod activation is what you would call
05:28 dusk or night vision that we When you walk into a movie
05:35 you lose the bright lights. And the screen is not Flasher or bright
05:42 , the room is dark and at everything is dark and everything looks the
05:47 . But as your eyes and as photo receptors accommodate to this low light
05:56 or dark room, you start discerning , you can start seeing slightly different
06:02 shades from slightly lighter shades. So can start noticing the rows in the
06:07 theater, lighter t shirts of the sitting there. And so it's a
06:13 that has high amplification, a single detection, which means that you don't
06:18 a lot of light and you can in the dark with rods, but
06:24 have low temporal resolution, which means a slow response. It takes a
06:30 time for you to adjust to that vision and to integrate these changes so
06:35 your rods can start picking up the in the dark. So it takes
06:41 and they're more sensitive to scattered Scattered light is nondirect light. So
06:46 to dim dim light, it's low . So you cannot resolve a lot
06:53 uh detail and that is true even your uh eyes and your rock photoreceptor
07:02 and kick in to low levels of you will still not be able to
07:06 as much detail as you would when were to activate the cone photoreceptor
07:13 which requires direct axial rays of So it's low acuity and it's not
07:19 in phobia. Me phobia is this , very central region in the
07:23 And that's right in the line of light coming into the pupil into the
07:29 and uh pupil and hitting the back the retina and the phobia. And
07:34 highly converged on retinal pathways. That that they converge to form these retinal
07:41 and the rods converge and then they're . So it's only one rod pigment
07:47 best way that I can discern between and achromatic. Well, think about
07:53 as grayscale. So if you just rods, your world would be like
07:58 scale like a power point gray And then so you would see darker
08:02 lighter shades just like you would in movie theater, but you would not
08:07 colors and you see colors. We cone system, which is lower sensitivity
08:14 is specialized for day vision and it's sensitivity because it doesn't store as much
08:19 the photo pigment. It's lower amplification , but it's fast. So it
08:26 high temporal resolution, fast response response short integration time. And it's most
08:34 when you have direct axial rays of that are hitting on the object that
08:40 focusing. Another example is here in dimly lit restaurant, you can see
08:48 menu, but you can see it's better if you put your phone flashlight
08:53 it and you can see everything and not because you're not seeing, but
08:58 you actually need these direct active rays light to engage with comb photoreceptors that
09:04 high acuity. So they're responsible for good spatial resolution. This is where
09:12 focus the cones and the phobia on that you are doing or on the
09:16 scale, especially they have dispersed retinal . There are three types of color
09:23 , each with a distinct pigment that most sensitive to a different part of
09:28 visible light spectrum. OK. It like a kind of a mouthful but
09:34 look at what we just talked So this shows the location of the
09:39 retina right here and this is going the temporal perier near the temple,
09:45 this is going into the nasal So each eye has a nasal to
09:50 nose and temporal to the temple So retina sitting in the back of
09:56 eye like this, it's not Yeah, it's just like the shape
10:01 the eyeball. So the back of eyeball is the retina and it's like
10:06 , uh the very center of it contain and be very highly populated by
10:12 cone photoreceptors. So they will peak the area of the phobia and the
10:17 retina and the rod photoreceptors will be more expressed on the peripheral region.
10:25 there's a central region, central region and then the peripheral regions, let's
10:31 the inner versus the outer ring of retina with the peripheral regions and also
10:38 . In this case, it's right, mostly uh and that will
10:43 dominated by rods. So it's different . There's this really cool feature in
10:52 retina is this crater physical crater that for the light in the Phobia to
11:01 gathered sort of like when you pour , all the water goes down into
11:04 tunnel. So the light gets directed through this very specialized crater in the
11:11 of the retina that collects the light directs all of the axial rays of
11:17 , direct axel rays of light onto cone photoreceptors. And because you can
11:22 that there is this kind of of formation, the light doesn't have to
11:28 through gang cell bipolar cells because the is passing through electromagnetic uh uh radiation
11:36 to 700 nanometers passing through here and it activates. But in this
11:41 it goes directly in the photo. that's what makes it also a faster
11:48 . And this anatomical feature allows for most exposure to direct axial rays of
11:53 to the cones that are located in phobia. So we have blue and
11:58 what that means is that we have types of cones from the previous
12:03 And each cone is tuned to a wavelength of light. So blue
12:10 green cones and red cones. But you look on the outside world,
12:16 see a lot more color than three , green, right and blue,
12:24 see black, we see white, see yellow, we see this whole
12:29 where you live from red to to . How does that happen if we
12:36 have three types of cones? How we get all of these different colors
12:41 all of these different hues? And perceive a lot of color. Um
12:47 some other animals are better at receiving colors. So for example, chickens
12:55 uh better color perception. So chicken's is actually a very colorful world,
12:59 more colorful than ours what we But so let's say if there is
13:04 blue light out there, this electromagnetic within this nanometer range of blue light
13:13 that blue light is shining on your . So then blue live will activate
13:18 cone photo in this 420 40 nanometer in. And for you to perceive
13:26 color which is blue color, it's activation of the blue cones to perceive
13:33 color. What about green color? view of green color? So there's
13:40 green color, right? It falls about 480 here nanometers of wavelength and
13:49 turns out that it actually activates a bit of the red. So red
13:53 are a little bit reactive to this of light. And so do the
13:57 cones. And so the green which is different proportions. So in
14:02 case, the red cone and the cone was only activated to its 36%
14:09 activation and the green cone was activated 67%. But if you were to
14:17 a little bit of red on like a painter's palette, a little
14:21 of blue and more of green and mix those three colors together, you
14:27 actually get this green color that you be perceiving. So now yellow,
14:34 , you don't have yellow cones and . In this case, is about
14:40 60 nanometer range. Yellow turns out 83% of red and green cones and
14:50 blue columns. And again, if were uh painting with paints and you
14:55 click green and red in equal proportions you mix them, you would perceive
15:02 close to yellow color. So this how we're able to discern different
15:09 Uh And uh somebody had a question me in the other class actually and
15:16 , how come men and women don't all colors? And I wasn't sure
15:23 it was a right way to ask question or if that is really something
15:28 has been measured and studied or if just anecdotal, um people in general
15:34 agree on colors all the time. Somebody will say no, this
15:40 you know, super dark, navy , somebody will know this is
15:43 you know, it's like, why that? Well, what if you
15:47 missing an expression of certain photoreceptor? if you're missing uh blue cones you're
15:53 born and your genetic code doesn't allow to uh to express the blue
16:00 So you don't have the perception of blue colors, right? And your
16:05 is very different and there are famous that are color blind or they're missing
16:10 certain particular use. It doesn't mean they don't see in color but everything
16:14 look red, red, yellow and and and green, the whole
16:20 And imagine if a painter painted a building, but you know, there's
16:27 and red representation in that. So may have slightly different levels of expression
16:34 those photoreceptors. We're slight variants of other anyways. So might be that
16:42 of our photoreceptors cones are more Maybe the blue ones in my system
16:49 more sensitive. So, biased things with the blue collar a little
16:53 but in your system, maybe the ones are stronger. So you bias
16:57 though with the red color and this where maybe the disagreements could come.
17:01 that's not also, you know, about potential other anatomical features of the
17:07 and penetration of the light through the eyeball and so on. We just
17:12 on that. Now we perform color if you mix green, red and
17:20 , you get white, you get shades of blue, different shades of
17:25 , violet indigo, but it's all by these three chromatic colors.
17:35 So this actually concludes the first section we were supposed to discuss about the
17:44 OK. So, so here in in this section, now we start
17:51 about receptive fields. So we missed couple of slides here on the
17:57 So please review these. We just photo transduction. I somehow forgot to
18:03 the recording button but please review this transduction on how it happens. Hm
18:11 then let's talk about receptive fields. what is the receptive field car of
18:21 retina that once stimulated with light changes cell's membrane potential? Remember we said
18:28 retina is big and if you have moon a dot in space that you're
18:35 at, it's gonna occupy a certain of retina that's gonna be processing that
18:41 for the moon who said it was for the moon a half a degree
18:45 visual angle who said something, 100 micrometers and numbers are not really that
18:50 , but so a small patch of retina is looking at the moon and
18:54 that patch, 100 micrometers, let's there's a lot of photoreceptors, collections
19:01 photo receptors. So those photo receptors are receiving the information, this is
19:07 this is the area of the retina within that area, there's gonna be
19:10 perception and that perception is gonna come by receptive fields created by ganglion cells
19:18 are really created by collections of So, photoreceptors will get activated by
19:23 of life, not just one s of these photoreceptors. Eventually, they're
19:30 affect the signaling by polar cells. eventually they're gonna affect the signaling into
19:37 retinal ganglion cells. And because of connectivity here, now when you talk
19:44 receptive fields, the easiest way for in this stage to understand receptive field
19:52 you have a receptive field on your here and a certain size receptive
19:59 receptive fields here for touching, this not for vision. So you have
20:05 fields here in the retina who will responsible for processing the light information,
20:12 and light information. And the way we're gonna try to understand this is
20:17 I don't want you to get a . I just want you to understand
20:20 features of the system uh and be to answer the exam questions. And
20:26 later in your future careers, you pursue a lot more of the information
20:31 schematics and modeling of this. In simple terms, if I were to
20:37 the retina out of the eye and it to the computer. So I
20:43 the retina out of the whole visual , it's not connected to thalamus,
20:47 not connected to cortex, it connected the computer retina. And I said
20:51 retina. Oh retina. Oh What you see? Right. I want
20:57 know how much of that visual information takes place in the retina. I
21:02 that my visual cortex, the primary cortex will construct the the whole gestal
21:10 and view that we're looking at. ? So I want to know.
21:14 does retina see what the cortex Remember we talk that this is a
21:19 organ, it receives information, it it and it sends it to higher
21:25 . And the point of these systems a sensory system like a visual system
21:28 that at each station, the processing that information is getting more complex.
21:34 that means that the sensory organ, retina is not going to produce what
21:39 seeing at the primary visual cortex. gonna have to involve these other structures
21:43 and and and circus in the thalamus in the cortex in order to have
21:49 view. So it turns out when photo receptors in the retina are exposed
21:56 light. The question is what are most reactive to? And you would
22:01 to know in that case, the cells that produce action potentials are retinal
22:06 cells. So you could flash the on photoreceptors, you can record synaptic
22:11 in photoreceptors, bipolar cells. But you want to know the output and
22:15 action potential, so you have to from retinal ganglion cells. And so
22:21 turns out that the way retina is in the way retina sees the outside
22:33 is by these concentric center surround receptive . And I usually draw smaller
22:45 but I'm gonna populate it with receptive . Some of them are overlapping because
22:52 of the cells photoreceptors is going to overlapping by different flashes of life.
23:02 this is what if I were to the computer to threaten the hair retina
23:19 convey the world to me as a of luminescence with center surround receptive field
23:30 where the whole outside world is perceived these darker and lighter luminescent shade.
23:43 let's say a piece of the retina activated here by some stimulus, it
23:47 activate collections of those photoreceptors and they're activated by round beams of light.
23:56 if I took a a AAA stick light, I wouldn't get as much
24:02 on as the retinal retinal gang So receptive field is also what are
24:07 cells re receiving? What are they to? And it turns out retinal
24:12 cells perceive these round concentric center surround luminescence properties which means darker and lighter
24:24 . Mm. So in some the retinal ganglion cells, these are
24:31 action potential trials. In some retinal gang cells will produce the most
24:36 potential tras if you shine the light the very center of this collection of
24:42 centers around photoreceptors, it's called an center ganglion cell. Because when the
24:50 is shown in the very center of photoreceptors. The rental gang cell produces
24:56 most action potentials. If the light is activating the surround, that cell
25:04 produce the least action potentials. So that means that these ganglion cells
25:11 are connected to the photoreceptors above are reacting to the center, but
25:16 they're reacting to the center, they're reacting to the surround. So retinal
25:20 cells below connected photoreceptors, these are central cells that means that the beam
25:26 light should be on the center. it's off on the surround, it
25:31 decrease the number of actual potentials. if the beam of light, whatever
25:37 moon, that star in the distance equally illuminate the center and the surround
25:43 code of action potentials in as far frequency does not change. So this
25:50 to you that what retina is perceiving the code right, more action potentials
25:56 or no change in action potentials. code here in action potential is what
26:01 really perceiving. It's perceiving the contrast the luminescence brighter or lighter. And
26:07 there is no difference between the surround center, there is no difference in
26:12 output of action potentials that tells you there's even illumination in that part of
26:17 visual field for the retina. And there are off center cells, off
26:25 gangrene cells and off center gang cells most active when the surround light is
26:35 shone on the surround of the photoreceptors produces the most action potentials. When
26:42 center is being activated, it produces least action potentials. If there is
26:47 illumination across all of the photoreceptors in receptive field, there is no change
26:52 the firing rates. So retinal gang cell firing rates essentially encode the difference
27:00 luminescence between the center and surround If you were to detect, depict
27:06 picture of the outside world, you have to deal with this kind of
27:11 . You'd have to put whatever you imagine a person, a stick or
27:16 by using the properties of the receptive in the retina. And they would
27:21 allow you to discern the center surround luminescence properties of the outside world.
27:31 there's there, there, there, , there is color because of
27:37 There's no color perception though, until process that information into the eye centers
27:44 the cortex. The receptor field is receptor area. In this case,
27:51 receptor area and it's not one a lot of photoreceptor area which when
27:58 results in a response of a particular neuron. In this case, dorsal
28:04 cell as measured by the frequency of action potentials. This is another illustration
28:15 this and you can again think of as on center gang and cell is
28:22 activated here off center gang cell, produces the least action potentials in the
28:29 activation, dark spot. Again, is another example where dark spot.
28:35 it's on center light, that dark will actually inhibit all of these on
28:42 cells but can activate the off center . Why? Because the surround becomes
28:50 . So it's almost like shining the but not instead you're exposing it in
28:54 dark hair in the very something. now you have center only activation or
29:03 center cells and then you have in two. So you can see that
29:07 center cells are firing a lot on activation T one to T two time
29:13 , there's no activity in the off cells. And then you spread even
29:19 across all of those photoreceptors. And happens is the number of action potentials
29:24 the frequency becomes the same in the and the surround and it's, when
29:29 the same, it tells you it's same darkness or the same lightness all
29:33 that clump of the photo pretty And then there's this whole circuit and
29:43 this kind of a uh complicated diagram sounds that, that, that,
29:47 is shown here uh is the circuitry is responsible for producing these signals that
29:57 seeing in the off center and on gangle cells. And the circuit is
30:02 that just bothers students so much when show it to them. But there
30:08 certain things that you should just First of all, in the dark
30:12 receptors are depolarized, right? It's opposite in the light, they're hyper
30:20 . Everybody got that. So dark light currents depolarize in the dark
30:28 one, then we have release of . So, neurotransmission chemical that gets
30:36 by other sufferers is glutamate and it released on bipolar cells. And it
30:42 out that there are two types of cells. There are bipolar cells that
30:49 a ionotropic glut and there are bipolar that express not a tropic with an
30:58 . And so we now have light dark. This is the stimulus
31:03 This is the cone is being illuminated the light. So if it's being
31:09 , then this cell is going to hyper polarized, right, sitting in
31:13 line. OK. If it's hyper , it's not going to release
31:20 It's not releasing glutamate. This cell known to be also hyperpolarize because it's
31:28 per second. So when this is , this is depolarized. When this
31:33 hyper polarized, there's no glutamate, is hyper polarized. So we call
31:37 synapsis sine conserving here plus is not . It's sine conserving. It means
31:43 if this is depolarized, this is , this is hyperpolarize, this is
31:47 . This is what sine conserving synapse it is dependent on glutamate and this
31:52 signaling. And if this cell is polarized there, there is no glutamate
31:58 again. And this gang is not do anything. OK. So the
32:04 cells you only have an A in MD a all of the ionotropic glutamate
32:10 that the gang cells. Now what the opposite on the other side?
32:18 what about the metabotropic stuff? So , remember that a lot of times
32:23 may be depolarizing and metabotropic physiologically may causing a different effect on the membrane
32:32 deeper and couple of cascades, it hyperpolarize. And so that is the
32:37 , the glutamate gets released when glutamate released, this is a sign inverting
32:44 . That means that if this is , glutamate is released, this is
32:48 sign inverting. That means this is be hyper polarized because glutamate like the
32:53 complex, it will hyperpolarize the However, this is now in the
33:00 , right? This is sitting in light. So it is hyper
33:05 So there is no glutamate being So this is the opposite converting.
33:11 this is depolarized. Now this is polarized, this is depolarized.
33:16 It's inverted and then this releases glutamate this is depolarized. Also this is
33:22 , so that means that this off cell is gonna be connected to some
33:30 photo or soft person is gonna be . One of them surround is being
33:38 . OK. Now, for the and why I am asking you not
33:43 get yourself a headache over these diagrams because I'm asking you to remember a
33:50 dark and light currents depolarization Hypo B asking you to remember it's all
33:57 So this is all excited or inert . So if you have all excited
34:01 inert letter, how do you depolarize certain cells? It's because there's a
34:06 in bipolar cells. Some a some that, if they are ample,
34:14 sign can show them if they are , there's, and that's all,
34:21 all I would like for you to is that there are, it's all
34:26 or neurotransmitter, but we can get and inhibition by activating tropic excitation,
34:34 tropic, we get inhibition in these and they're later connected to the either
34:39 or off center cells. So if if it is hard for you to
34:44 that in within, like how does really relate to all of these clumps
34:48 and off surround? How would this would then be activated? Exactly.
34:53 neuroscience too. Uh For now, think it's important to just know these
35:02 that I've discussed, whether it's hyper polarizing, whether it's science
35:07 whether it's sign inverting. And in , understanding that there is this unique
35:14 of activation of the threaten us just way it is. You know,
35:18 didn't build this system, somebody else . And the system is most reactive
35:23 centers around beams of light. And see that Eliana also most reactive sal
35:31 L G M lateral geniculate nucleus of thalamus, which processes visual information also
35:37 mostly reactive to round beams of light surround me. And you'll see that
35:42 the time you get through the it gets a little bit more
35:47 So what I always tell students is if you could take this, these
35:54 shapes and represent an outside world, a stick figure, using these two
36:06 , you can make them really but it's a lot of work.
36:10 then an art it's called point to you ever seen paintings that are just
36:15 , point, point, point, , point, point, point point
36:17 then everything goes together, trees, , whatever else is in the
36:22 So it's like point to. So just like center surround, that's what
36:26 have. But it's kind of a to draw uh something, an object
36:31 something like that just using these, not impossible, but it's difficult and
36:36 what retina sees. That's what retina . Now, I'm gonna throw in
36:43 thing here and these are horizontal they're inhibiter cells. So they're
36:50 And what happens is that this is conserving synapse. So when this cone
36:55 depolarized, right? This is the horizontal cell and then it's gonna feed
37:04 on the code and it's gonna inhibit Chrome. So you basically have sign
37:14 and then this is depolarized sign This is gonna get hyperpolarize, gonna
37:20 . But in, but in what I'd like for you to think
37:23 this is a negative feedback circuit. a lot of excitation, a lot
37:28 excitation, negative feedback has tone it right. So this is where the
37:36 sauce and the Amain sauce command, allow for spatial segmentation or spatial spread
37:45 the visual activation across the retina. other words, they can tune,
37:51 you tune sharpen the luminescence by having inhibitory activities. And in general,
37:59 have the control by horizontal cells here complicates the circuit a little bit.
38:07 glutamate horizontal cells of Gaba horizontal cells gap junctions, remember gap junctions are
38:14 junctions. Horizontal cells, broad area retinal illumination and it's controlling the
38:23 controlling glutamate releases from cones through this feedback mechanism. So this is what
38:32 in the retina, the signal gets into an electrochemical signal. Eventually it
38:40 action potentials that gets produced by re in cells. And that information is
38:45 communicated upwards into the thalamus and into primary visual cord. OK. So
38:53 for photo transduction, you should know light, the dark current, the
38:59 that the cyclic GMP regulates sodium. it's a G protein coupled mechanism by
39:04 it is being regulated to the Uh You should know that it's sign
39:10 versus sign converting and that you have receptive field properties that are center surrounded
39:16 level of direct and the main take messages from this lecture and this lecture
39:23 actually short. So now the final on the visual system is is
39:35 it has some of the reviews in . Um Wait a second.
39:49 It has some of the slides that like these kind of slides, for
39:54 that I call, I call them review slide, a reminder slide.
39:57 I've just talked about for the last , 20 minutes, use these to
40:03 notes so use these and if you summarize everything for Reus put cone under
40:11 , put three colors. So you that they are colored, put further
40:17 , put photo transduction, put in and GP. And you know that
40:23 know, you can take really good and then we can put phobia
40:28 you know IQ division. Uh Here can take a lot of notes or
40:33 can just kind of point out the important things that some uh cells are
40:39 reactive, other cells are surround But in general, you have this
40:44 of a representation of the level of rep. Hm. So one more
40:52 , the same circuit. So usually this a couple of times and the
40:57 that come out that comes out of retina. So you have these on
41:01 retinal gang cells based on receptive field based on their reactivity to light.
41:08 outputs from retina can also be subdivided on the anatomy. So in the
41:14 , you have two dominant types of that are called M for magna and
41:18 for parva. And you also have cells that are not as dominant not
41:23 populous, they're called non MP subtypes cells. So the parvo cells have
41:31 receptive fields and parvo cells were So their small cells and you can
41:37 their processes that ST of their processes is also smaller compared to large cells
41:43 have very widely spatially spread out Thereby, the small cell will be
41:51 and be processing small receptive fields. means that they will process information from
41:58 cones or raw photo receptors that they're to. They're slower conductance,
42:05 it's usually slower conductance, uh higher , they're less sensitive to low
42:14 OK. This is distinction based on and also some physiological features, but
42:19 is not on the receptive fields. can have a power cell that's on
42:24 parasol, that's off san. We're talking about the anatomical range, uh
42:31 differences in anatomical range. And as as the processes that can cover much
42:36 the spatial uh area in the retina magna large, faster conducting cells,
42:43 sensitive to low contrast, the non cells are very interesting and they don't
42:52 of a fit in either this parvo magno group and they are concerned with
42:59 information processing. So now we're gonna the retina, this is a sensory
43:06 . Uh it's a part of the nervous system and we're gonna go up
43:12 what happens in the higher processing the higher processing areas, we'll come
43:18 to the slide in a little bit projection. So out of the
43:24 80-90% of the things that come out the retina. So retinal ganglion
43:29 80-90% of retinal Gambian cell axons go lateral geniculate nucleus which is Gina lateral
43:36 nucleus. 10% of the outputs from eyes will go to tectum lumber,
43:44 and tina is superior in interior In this case, the projections are
43:49 into the superior colliculus. Super Colliculus responsible for the eye movements. Static
44:01 movements are the movements of the eye we constantly do in a jump like
44:08 when we refocus on different objects as come further closer, nearer or move
44:14 and state. Yeah. So, eye movements, if anybody has a
44:21 , cats are really awesome and eye , it's one of the best models
44:25 study the movements because they'll be sitting and their eyes will be bouncing back
44:32 forth with eyeballs like that because they're refocusing. So that's the cat.
44:39 thing uh way to think about the movement is that we don't have a
44:44 visual pursuit of objects. In other , if the car is moving across
44:49 the distance to that car may stay , it's not like it's gonna be
44:56 , your eyes are going very smoothly it like in a kind of a
45:01 of cool zoom camera that goes like instead as the car moves across your
45:07 are gonna go focus, focus, , focus, focus, focus,
45:11 , focus to that car. These sy animals, OK? And they're
45:15 by tech. So that visual input is not as important for processing the
45:21 information telling you that it's a red or something like that, but rather
45:26 the object across the space. Uh to 3 projections out of the retina
45:38 through the super cosmetic nucleus. Super nucleus is responsible for circadian rhythms or
45:47 body, day, night rhythms, cycle, diurnal rhythms. Um And
45:57 you can see the projections from the come out, they form optic nerve
46:03 the s when they cross over, become optic tract and project this is
46:08 the uh inferior view of the brain project it into the high order
46:15 So the whole visual field, if look at the visual field, We
46:22 about how one eye sees about 150 of the 360 surround. But if
46:34 close one eye and you close another , you have this binocular zone and
46:41 can see quite a bit in this zone, which means that this is
46:46 zone, this is the information of visual field that can be seen by
46:51 eyes. The eyes and the retina shaped like this right. So this
46:59 of the retina is going to be over there. The reason why you
47:04 see with the right eye as far with the left eye is because you
47:07 this thing called the nose, middle the retina tries to look and it
47:12 cut off by, by the So this is your limitation and then
47:17 open the other eye and you can that periphery. So this eye will
47:23 the periphery on the right, this will have the peripheral on the left
47:29 both eyes will have this binocular overlapping . Actually, I have to show
47:35 something really cool. Give me a . Uh it's a, it's a
47:39 that I recently. Uh so we this binocular zone. You can see
47:47 certain fibers cross over the fibers that over are the nasal fibers. So
47:53 this is a nasal and it crosses this is a nasal and blue on
47:57 other side and that crosses over the tract after the Chism will contain information
48:04 both eyes, optic nerve here before chasm still carries information from just one
48:11 . And this is a fixation point in the very middle of the
48:14 You have this large binocular and you the peripheral which is gonna be monocular
48:20 one high by the other. So happens is it gonna be the last
48:25 for the day? And what happens you have damage along these retinal
48:32 If you have a damage to just optic nerve on one side in
48:38 you now have the loss of the field. So if you lose one
48:45 or if you cut an optic nerve if there's a damage, trauma,
48:52 , cancer's growth, whatever, but is gone. It's the same as
48:56 one eye, you just lost periphery on that one side. Uh So
49:03 when you think about this visual this is a good exercise to
49:07 Ok. Well, you can do certain other exercises like for example,
49:12 you now have a transaction of the tract optic track contains fibers from both
49:22 . It contains nasal fibers that cross and temporal fibers of the same
49:30 Nasal fibers on this side, I off the track nasal fibers that cross
49:36 . Remember nasal is looking over there use this also it's not flat,
49:41 cups. So when you put a , this point is looking there center
49:45 looking there, this point is looking right. OK. So if you
49:51 the nasal crossing over where is nasal over there? So you're gonna lose
49:56 periphery on that side. OK. the nasal crossing over temporal on this
50:05 which stays the same is processing information this side. Temporal is from this
50:13 . Uh Therefore, you're gonna lose of the field of view on the
50:19 side. Nasal fibers crossing over you those you lost the periphery and now
50:29 staying on the same side. Temporal looking toward the center again, cannot
50:35 the periphery that the right eye can but loses the center and can still
50:40 the fibers that are not damaged. nasal fibers that cross over will process
50:45 information on the other side of the if you have a damage or transaction
50:50 the optics and this is the So now you have damaged nasal crossing
50:59 and nasal crossing over if the damage to the optics. So if nasal
51:05 over here, you lost peripheral view this side, nasal crossing over
51:11 you lost peripheral view on this Therefore, you have what is called
51:16 vision. So uh sometimes uh pituitary which is right next to the optic
51:27 could be larger pituitary gland and gets , starts pushing on the optics and
51:35 may have tunnel vision. In in people that are giants, they're
51:41 often pituitary giants. So real like like fairy tale giants, but like
51:49 giants like Andre the giant, like actor uh or some other giants,
51:57 typically have tunnel vision because a lot times their growth is dependent on the
52:04 gland. It's un gorged. So larger structure. It starts pushing on
52:09 optic cosm and starts causing a loss the peripheral he view. Ah So
52:18 can start thinking about it. And I have students that come up after
52:22 class and say, I I understand going on with my, you
52:26 optic nerve or something like that or understand what my ophthalmologist told me and
52:32 part of the field of view that me missing. Uh So you can
52:37 thinking about the connectivity here. when we come back, we will
52:41 up into the lateral nucleus nucleus and the way into the primary visual cortex
52:47 we will construct the primal sketch of outside lone. So I will see
52:52 back on Monday, appreciate everyone waiting me for a few minutes and uh
52:59 a good rest of the
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