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BIOL 4315/6315 Neuroscience Mon Wed - Lecture 16 Eye II, Phototransduction, Receptive Fields, LGN
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00:02 this is no science lecture 16. gonna start talking about visual system to
00:08 visual system one. We will first up the eye anatomy and the circuitry
00:16 the retina and as we discussed there a certain anatomy to the eyeball whereas
00:22 certain flow of information as the light into the pupil and gets suggested by
00:30 lands to be projected on the back the eyeball. With Director is
00:36 The phobia is the zone that will the highest concentration of cone photoreceptors and
00:43 the highest security area, the highest ery But it also requires a lot
00:48 direct actual rays of light. So requires a lot of light and where
00:55 optic nerve exits out which is a of retinal ganglion cells that will put
01:02 axons into a bundle that is called nerve which is cranial nerves to this
01:10 is called optic disc because there's no receptors that are processing visual information which
01:17 also the blind spot area in each of the retinas. And this is
01:24 the optic nerve exit out of the . Now you recall the circuit in
01:30 retina is pretty complicated. The flow light is in this direction. So
01:38 the eyeball that will actually bypass retinal themselves bipolar cells and the photo transaction
01:45 that light signal into an electrical signal take place at the level of the
01:51 receptors. So the processing of information that the opposite direction. So after
01:57 photo receptors trance deus or transform this energy into electrical potential into synaptic
02:08 gets communicated to bipolar selves and gets to retinal ganglion cells. Retinal ganglion
02:15 are going to be the only output out of the retina. So the
02:19 will be the fibers of the saxons become the cranial nerve to off the
02:26 . And these interactions between the cone bipolar cells are regulated by the horizontal
02:34 . And interactions between bipolar cells and ganglion cells are regulated and influenced by
02:41 subtype of cell they're called. Um cells and we'll talk about them very
02:47 . So if you can imagine that in your lines, we talked about
02:52 hanging here, the suspense story ligaments you can actually cause the lens to
03:01 thicker or thinner. And if the is thinner it will help you focus
03:06 the points that are further away in . Uh And if the lance is
03:13 so the muscles would be relaxed these ligaments would be relaxed for it
03:19 become thicker. Then you're focusing on near point objects to the eye onto
03:27 retina. This basically focusing is called by the lens. So you have
03:36 ability without moving your head back and or moving your eyeballs. If you're
03:43 the same direction, you can adjust the focus whether it's far point,
03:48 airport focus. If you have regular shape then you have normal vision which
03:55 in metro pia. However, in instances the lens will not be focusing
04:04 image. So this image of the in normal vision will be focused perfectly
04:11 the anatomy of the eyeball and the onto the retina. But in some
04:17 it may get focused where the focus of the images actually would be beyond
04:24 the retina is, beyond where the receptors are. And so in order
04:31 correct for a propia, then you use this convex lens or convex glass
04:40 will basically help you refocus that image onto the onto the retina and vice
04:48 if your image is focused in front where the photo receptors so located it's
04:55 blurry. And then you would use concave lens of concave glass uh in
05:02 to adjust so that the image you're out projects again, we're supposed to
05:09 onto the retina. So basically farsightedness nearsightedness which a lot of people have
05:17 very common condition or even an older , you need reading glasses, two
05:22 to see things better. Um And obviously in modern optometry and modern optics
05:34 you can also have adjustment of the through LASIK surgery and that essentially reshapes
05:42 a way to learn so that it adjusted for refocusing the image onto the
05:50 . Now if you look at the and you have a knowledge of a
05:56 distance to the moon. Uh and also, if you close one eye
06:03 realize that you have about 150° So if you close one eye you
06:11 see 180, you don't see exactly , you see like 150° with one
06:18 and the nose stops you from seeing on the side. You're looking at
06:23 pencil. If it's up close it occupy 100 degrees of your field of
06:30 , Something right in your face, of the field of view. Uh
06:37 know objects that are far away like moon for example. You know the
06:43 to that object and you will know out of the 150° that moon at
06:49 certain distance will occupy only half a of visual angle when it has risen
06:56 the closer it is to the to to to the horizon of the bigger
07:01 may appear and that half a degree an angle. If you were living
07:07 the moon would activate about 100 and micro meters of space on the
07:14 So in order to perceive that bride in the sky, you would only
07:21 a portion of the retina. About and 40 micrometers of the retina.
07:24 can imagine it still involves dozens of that would be processing that information.
07:31 if the moon moved over here then would be a different part of the
07:37 processing the information on the moon depending that eye is pointing with with respect
07:46 the moon and so on. But you're actually focusing on and you're trying
07:51 focus on on the phobia because you be looking for a bright light.
07:57 receptors in the socket are the only sensitive cells. And ganglion sauce is
08:04 only output from the retina. The on bipolar cells. They don't produce
08:11 potentials to produce synaptic potentials. The ganglion cells are the only ones that
08:16 action potentials and communicate this action potentials the lateral ju Nicollet nucleus or LG
08:23 of the talons. So the retina often subdivided into these layers. The
08:30 nuclear layer out of flex A form nuclear inter plex, a form of
08:35 cell layer. So out of nuclear in the nuclei and the so Mazz
08:43 the cone and rod photoreceptors. Out plex, a form plex, a
08:50 of connectivity. These are the synopsis the bipolar cells and the photo
08:56 And you have the inner nuclear layer will contain the psalms and the nuclei
09:01 bipolar cells. And um a cream . Huh? And then you have
09:09 inner plexus form layer which will be connectivity here again between the democratic south
09:15 the bipolar cells and ganglion cells and ganglion cell layers of ganglion cell Selma's
09:21 form the optic nerve. There's another of the about the same thing that
09:29 just mentioned that the visualization of Uh you have certain differences morphological differences
09:38 the cones and rods. So cone , they really have different outer segments
09:46 rock. But receptors in rock photo , you have these free floating discs
09:53 these free floating discs would be literally like little organelles on their own number
10:01 discs that are formed inside the outer . And by that virtue, rock
10:08 can store a lot more of the pigment molecules that will be sensitive to
10:15 . So they are more sensitive to cones. They don't have these floating
10:22 uh member bonus discs. Instead they these shape like kind of imaginations in
10:30 outer membrane layer, so they don't as much of the surface area and
10:37 wouldn't be as sensitive as rod butter . So these are some of the
10:44 differences really. They have the inner which has the soma and the
10:51 and both have cinematic term synaptic terminals will synapse onto the bipolar cells.
11:00 um akron cells uh sorry, onto cells here and what you see very
11:08 is the outer segment is very Their function is also very different than
11:13 locations in the retina distribution across the varies between rod and cone photoreceptors.
11:21 the rods are highly sensitive to Their specialized night vision because of the
11:28 floating number nous discs and all that area that can store more off the
11:34 pigment and capture more light. So have high amplification of the light coming
11:42 and they can detect even a single of light. They are slow,
11:48 have low temporal resolution which means that slow to be activated, have slow
11:54 and long integration time and they are sensitive to scattered light or basically like
12:02 light or dusk light if you may system is lower acuity, so not
12:09 resolution, they're not present in central , it's dominated, thereby cones.
12:16 they have highly convergent retinal pathways. this shows that these retinal pathways,
12:24 best waves shown here, they will convergent retinal apocalypse as you can
12:30 Rock voter suppers will converge onto the bipolar selves. Now a good example
12:43 activation of Rockford receptors is walking into movie theater where you have ambient amount
12:50 light and you first don't see very , but then you take some time
12:57 it's long integration time. But after while you can discern people sitting in
13:04 chairs and then maybe seeing somebody's wearing colored clothing, darker color clothing and
13:09 find your friends or family sitting in the movie theater there are chromatic,
13:15 there's no color when you're looking at in the dark, there's really no
13:19 , there's, you can say there's scale things appear darker or lighter but
13:25 is really no color at night that can say, I can clearly see
13:29 is green or or or this is . So this is only one type
13:35 pigment that is being used by rods only one subtype of rod photoreceptors,
13:41 are lower sensitivity that specialized for day . They have less photo pigment,
13:48 lower amplification. However they are They have high temporal resolution and it
13:54 them very quickly to integrate the light and they are most sensitive to direct
13:59 reserve light to their dominating in the Code system is in high resolution high
14:06 system and they have dispersed, threatened . So there will be divergence from
14:12 photo receptors into the bipolar selves. three types of cones so cone see
14:20 there chromatic and they each have a pigment that is most sensitive to a
14:25 part of the visible light spectrum. this illustrates the number or the density
14:34 rods in red and cones and And this is the phobia area which
14:41 located in the center of the And it very clearly shows that the
14:47 photoreceptors the peak in the very Whereas phobia is and you can see
14:52 red line drop off for rod photoreceptors the phobia but rod photoreceptors are dominant
15:00 the periphery of the retina, so in the central retina and the periphery
15:04 the retina. So in the way high resolution, high acuity color vision
15:09 you have to focus and have a of lights in color and with high
15:15 But the night vision or rod You don't need much light, You
15:20 see color. And it's mostly peripheral that gets activated by these low levels
15:26 life. So the center is dominated the columns and nasal periphery. Nasal
15:33 of the retina is the nasal part the retina close to the nose and
15:37 temporal prefer is a part of the that is close to your temple.
15:42 its temporal retina, they are dominated rod photoreceptors. This is another view
15:50 the phobia. And what's really interesting that it's not only the concentration of
15:57 right in the phobia, right in central retina, but also the fact
16:03 the whole anatomy of the phobias bill it has like almost like a little
16:09 that allows for the race of life be captured and directed into that crater
16:16 bypass the other salsa would be obstructing passage of light because light is coming
16:28 this direction. So here you make special area where the light has almost
16:35 access and direct access to high densities cone photoreceptors. All right, blue
16:44 and red cold photo receptors. So you're seeing blue color, if there's
16:53 color out there, it's enough that just activate blue cones and 100%.
17:00 is the light absorption or percentage of activation of blue cones and you will
17:05 blue color. Alright, so only cone subtype is activated to see blue
17:13 . But what if you want to green color? Where you have green
17:19 receptors with green color is actually a of activating green photo receptors, Blue
17:29 receptors and red photo receptors To come with this green colour. So to
17:37 green, red cones will be that 31% of red cones will be
17:43 , 67% of green cones will be and 36% of blue cones will be
17:52 to produce that you that color of . How about yellow? You don't
18:01 yellow codes? So what do you on the palette when you mix colors
18:07 get yellow, green and red And get yellow and to see yellow color
18:16 in the world you have activation of of red cone and 83% of the
18:24 cones are activated. And how many do we see? We see a
18:30 of colors, but we don't see many colors as chicken. They have
18:38 Hughes, they can perceive more hues humans actually, which is kind of
18:43 . So the chicken's world is actually colorful. Hopefully if it's free range
18:49 somewhere on a happy farms. So and how many of us are arguing
18:58 what color we're seeing? No, , no, no, this is
19:03 blue gray, no, no, know like, no, no,
19:07 , this is teal or whatever names , you know for different colors and
19:11 . So many arguments that this is . No, this is really dark
19:16 , it's black. So how do get these? How do you get
19:20 arguments? How do you get you know that don't perceive certain
19:23 Well you may be missing a certain of cone and you may not be
19:29 to activate the red cones and you lose the spectrum of colors that would
19:36 otherwise produced. Now you're on the , Your artist palette is now reduced
19:42 blue and green. You can get many colors from that and some artists
19:47 would have an interpretation of the world limited colors. You know,
19:52 it's very interesting because it's a completely interpretation of what we would be seeing
19:58 you have all three types of How about your cones are located slightly
20:04 . They're distributed in the right How about you have a slightly different
20:08 of these counts that are expressed in of us and that would be,
20:13 of us will have just about the plus minus of each, but that
20:17 minus is hey, I'm seeing this now, I'm seeing this color potentially
20:22 the stimulus is the same. So interpret it differently because you may have
20:27 different wiring or you may have a subset of cones or different densities and
20:34 levels of these different cones. But that's what you do with with these
20:41 . Is that you're doing color So you can mix red and green
20:48 you get yellow, you mix green and blue, you get
20:53 blue and red. You get uh and violet. Here you're getting another
21:02 . Okay. And of course if talking about wavelengths, then the peak
21:10 blue activation on the blue color is nanometers. Green is 530 nanometers.
21:18 the wavelength out there. That 530 wavelength will actually activate uh here for
21:29 , the green and the red to certain extent and produce of color that
21:33 light green or yellow. Okay. 560 is the wavelength to get the
21:41 color. And this is also part the microscopy world. The reason why
21:48 are capable of using sometimes two or different color dyes. Like fluorescent dyes
21:54 or four is because you can put optical filters in your microscope that only
22:00 you to see between 424 140. you know that that filter is only
22:08 let in that wavelength and that you're going to be looking at the blue
22:13 . And then you switch the filter the microscope and now you're only looking
22:17 the wavelength of 5 20 to 5 . So you're just looking at the
22:21 color and it's like a carousel in microscope. You may have five or
22:25 different built in filters so you can image the same cell that has been
22:31 with three or four antibodies at different . And that's how you'll be able
22:38 pick up this. There's there's different of light in the same song.
22:42 , so this is more or less what we want to learn in the
22:48 this first section of uh of the system. And I'm pushing it on
22:57 . Here we go. And now gonna move into how this uh life
23:02 converted into an electrical signal. I'm , I'm sitting down a little bit
23:06 today. You guys don't mind? neurotransmitters is what we've learned about.
23:13 we learned about metal tropic signaling. we said that when neurotransmitter binds to
23:18 protein coupled receptors it initiates downstream It can um false for a light
23:26 defaults for aly nearby channels through the pathway, it can activate uh enzymes
23:33 secondary messengers it can cause calcium induced release and so on and so
23:39 So how does the light convert the ? So the light actually activates?
23:45 have this photo pigment molecule and it the light now instead of the
23:53 that will change confirmation of this retinal . And by changing the confirmation that
24:02 done. Either have the jeep Rodion , either active or inactive.
24:09 And it turns out that in this you will actually in order to to
24:15 to make a change here to generate change to transducer signal signal. You're
24:21 reduce secondary messenger, you're gonna reduce of ions. So what let's talk
24:31 this actually we can come back to uh slide in a second. So
24:36 have options here. Okay, these your uh audience that are sensitive and
24:42 have a retinol and it's an active its trans configuration. And then the
24:48 activates this molecule to CIS configuration. when this G podium, which is
24:57 Doosan is inactive, the cells are of sodium because there's a lot of
25:06 GMP which is cyclic GMP gated sodium and the cyclic GMP is keeping the
25:15 channel open. So in the in absence of light or in the dark
25:22 is a lot of sodium influx ng the south. So the number in
25:27 in the dark is actually deep polarized the dark. These photos after numbering
25:36 are approximately minus 30 million bowls. is something what we learned is different
25:42 the pastor said. That presses minus minutes activated minus 35. Now it's
25:47 the opposite. It's d polarized There's a lot of influx of sodium
25:54 you turn on the light, you the influx of sodium because you reduce
26:00 cycling GMP into GMP and that is because you actually activate the G protein
26:08 that G protein complex activates fossil diastolic . And the fox pedestrians chews up
26:17 GMP and spits out GMP. And the absence of C. GMP,
26:25 C. GMP gated sodium channels are . So you need C. GMP
26:31 keep these channels open. You have lot of it in the dark.
26:34 once you activate the retinol you don't C. GMP. And the sodium
26:39 closed And you actually have in the . Because the sodium channels close,
26:47 now have a decrease in the membrane . So it goes in the dark
26:52 -30 In the light to -16 little and hyper polarizes and then it goes
27:00 again to about -30 little balls. cones require more energy to get
27:08 More light rods gets saturated by bright . So rods are very sensitive.
27:16 is this concept of receptive fields that going to discuss for the next several
27:24 and it's probably gonna be a lot information that uh is very useful but
27:31 might be a little bit confusing at same time. And the way that
27:36 like to introduce receptive feels is uh about your body and different nerves that
27:49 connected into your hand and different nerves are connected into your legs and your
27:57 . And so if somebody tap you the shoulder, what is this area
28:04 . This is the receptive field My neurons here, my door,
28:09 gangly and then this muscle and joint the skin will will say it's the
28:16 , right? Somebody tapped me here say, hey somebody stopping me on
28:23 your left side here. Somebody's tapping on the back. Right, You
28:28 feel it. So there's an area south of process information from our
28:36 The cells of process information and send information into spinal. And it's not
28:42 style, right? It's a lot South cells are small. We have
28:47 lot of nerve endings. So it's lot of south. So now if
28:52 apply this concept of you have a on your body that communicates certain information
28:58 the spinal cord, that's the receptive . But we'll talk about receptive field
29:03 is when we talk about somatic sensory . Actually discuss this within the context
29:08 somatosensory system. But for now, is receptive fields? This area of
29:13 retina that when stimulated with light changes south member in bhutan trunk area,
29:21 the retina. So whenever you're looking that dot that moon in the far
29:26 is not one photo receptor that is . It's 100 and 40 micro meters
29:32 space, brady is 140 micrometers that activated or diameter. Sorry. So
29:40 a lot of cells. It's a of cones. So it will be
29:45 lot of cones that will be in . That will be perceiving that one
29:52 that accounts for just half a angle visual space. So you have these
29:58 fields. And so the nature build that at the level of the retina
30:05 fields or collections of photo receptors. these photoreceptors have what is called on
30:14 bipolar receptive field properties. So the that you can actually envision this is
30:23 there are the center surround, just it's shown here. There's a center
30:30 that center there's going to be collection the photo receptors and the surround there's
30:36 be like a donut. Outside area the donut is another set of photo
30:44 and also what is all this. is your circuit. This is the
30:50 you recognize built it is how we the visual information. And it turns
30:58 that at the level of the retina have these concentric, they're called on
31:03 off. Or you can call them with the middle, on and
31:07 This is the receptive field. This how retina perceives light and in many
31:15 it can be activated. The center these photo receptors when the center receives
31:24 most light when the center is When the center is activated, then
31:30 produce a lot of action potentials So this is light on stimulus.
31:37 is called an on center ganglion cells the level of bipolar cells and ganglion
31:43 . You have these on off receptive properties. It means that the bipolar
31:49 and ganglion cells are hooked into these , clumps of photo receptors, doughnut
31:56 shape that are responsible for receptive fuel . So the inside of the inside
32:03 stimulated produces a lot of light. have an on center ganglion cell but
32:11 can see that if the light is most of the light is shown on
32:17 periphery, on the outside of the . You don't produce as many action
32:26 from that entire receptive field. Okay it's like a receptive field is like
32:32 collection of cells. And how you this collection of cells is how they're
32:38 to respond. They can produce now the action potential is produced. They
32:45 not produced by photo receptors. Okay give me a second. Thank
33:01 . They're not produced by photoreceptors. what cells produce action potentials? What's
33:10 only output from the retina retinal ganglion ? So you're recording this information.
33:18 recording these action potentials from retinal ganglion And that means that retinal ganglion cells
33:29 a photo receptors they received the widened communicate that information to bipolar cells.
33:36 cells have similar structure. They will on off concentric receptive field properties right
33:43 ganglion cells will have on off center field properties. You can record action
33:49 so you shine the light in the of a long, you've got a
33:53 of action potentials in the retinal ganglion you shine the line around onto the
34:00 of the donut you can see you get as many action potentials for off
34:07 . Then there are cells retinal ganglion will be connected to clumps of these
34:13 and at the center of the photo is activated. Like here it will
34:20 the opposite. It will actually produce least number of actual credentials. And
34:28 the periphery is activated it will produce most action potentials. And if this
34:36 of cells, there's no variance in in this. Across whatever dot you're
34:44 whatever dot you're looking remember that dot has a bright side and the darker
34:49 around it. Right? So whatever you're looking here, if you illuminate
34:55 evenly the center and the surround there not much change in the action potential
35:03 from before the light stimulus. During after light stimulus. Even illumination.
35:13 the same code before illumination. It's dark. It's even during illumination.
35:20 all light across. It's all even . Okay, so the retina is
35:32 at these on and off on central cell. Off center ganglion cell,
35:38 action potentials when you have activation in in the surrounding. When you have
35:44 dark spot in the center, if have the dark spot in the
35:49 it also makes the surround lighter. you'll also have the activation most of
35:53 activation of these off center ganglion Okay, there's a circuit of
36:02 two bipolar selves into the retinal ganglion . But in general This is the
36:11 one. And retina is basically a of these. On off center surround
36:48 field properties. Okay? That you're in all of these will have their
36:56 on and off center and some of will have overlapping receptive fields.
37:02 so this is what retina is The retina is distinguishing the outside
37:09 Basically. If you were to connect to the computer and the computer had
37:15 ability to see what retina is capable processing of this electromagnetic signal that's coming
37:22 . It's capable of photo transducer singing . It's capable of producing action potentials
37:27 it produces action potentials and that action pattern is dependent on these circular center
37:35 receptive field properties in the retina photo . So basically retina is like a
37:44 of luminescence, right? Because we're talking about a number of action
37:50 lighter, brighter, darker spot, spot, light spot. So it's
37:58 luminous, it's obviously detecting the color . But it's not that color processing
38:08 is buried within these receptive field properties . So this circuit that we talked
38:18 . I believe it actually repeats in following lecture too. And it may
38:22 a little bit confusing, but this you that for example, if you
38:26 a cone that is a center cone you have a light on that
38:33 It discusses several important things and there several important take home messages from the
38:40 . So first of all, the take home message is is as always
38:44 want to know what kind of neurotransmitters cells use. So photo receptors use
38:51 as a neurotransmitter, bipolar cells use as a neurotransmitter. Retinal ganglion cells
38:59 glutamate, a neurotransmitter. What does tell you? These are all excitatory
39:06 . They release excitatory neurotransmitter. But question is what about the post synaptic
39:15 ? Remember that the response of the depends on the post synaptic receptors that
39:20 expresses. We saw an example of acetylcholine having d polarizing effect masculinity.
39:28 receptors in the cns having a hyper effect. The opposing effects on the
39:34 of the membrane. So yeah So since these photoreceptors are polarized until
39:43 receive like this I mean they're constantly neurotransmitters until they're re polarized and then
39:50 stop. Yeah there's a certain steady of release of the neurotransmitter. But
39:55 when they're releasing this neurotransmitter the downstream are not always activated because downstream what
40:04 have is you have bipolar cells and turns out that they're bipolar cells that
40:11 medical tropic leader members sectors and then iron a tropic apple kinase receptors where
40:20 talked about. So this is classical you release glutamate and apple kinda is
40:26 to de polarize the cell. This deep polarized it's also going to be
40:32 with stuff. So in this case plus and the serpent it means that
40:39 is signed, conserving synapse that means if I release glutamate this is d
40:46 The level is glutamate. This is polarized. This release glutamate and this
40:50 d polarized assigned conservative. However what in the light? He actually hyper
41:00 in the what? Right. So is no blood. So in the
41:09 this is hyper polarized, this is same sign conservative. So what is
41:14 happen to this is gonna be hyper . This is not going to release
41:19 a sign conservative. It's also gonna hyper polarized. So if there is
41:24 light in the center under this photo that's connected to the tropics cell,
41:31 cell is going to be hyper It's not going to react to the
41:37 and it's very likely off center ganglion which means it's going to react to
41:42 photo receptor that's going to be in periphery and off center zone.
41:50 good presence of light, there's no . This was hyper polarized and if
41:59 dark there is good in it, dark, there is a little bit
42:05 this is d polarized in the I am a tropic but this is
42:12 burning synapse and this is a matter a tropical do something with the advice
42:17 amp it d polarizes tropic and hyper hyper polarizes the cell in the
42:27 The cell is hyper in the The cell is d polarized with this
42:31 is hyper polarized, the cell is control arising in the light. This
42:37 becomes hyper polarized because there's no glutamate no activation of literal tropic receptor.
42:43 it's the opposite. So the cell D polarized and this is not a
42:47 of conserving because of the level of retinal ganglion cells, the only half
42:52 tropical intimate receptors. I'm in the . B. A. And therefore
42:58 is D polarized. This is also to be polarized. So this is
43:03 it's a little bit tricky. It exactly answer your question but there is
43:07 to be basically if light on or in the presence of the absence of
43:13 if you have both circuits that could either activated or inactivated hyper polarizing or
43:20 . Polarizing. And uh and this an important thing to know about the
43:27 because a lot of you get confused you think that I'm gonna start asking
43:33 detailed questions but I think it's fair ask from the slide what neurotransmitter these
43:40 express? Easy. Okay if this bond style and the tropical intimate with
43:48 , what does it do easy? know what it does glutamate excites and
43:53 deep polarization through Ireland tropic and kindly if that same gluten, advanced,
43:58 tropic receptors. It's the opposite effect the drop. You're seeing this and
44:07 you're seeing that at the level of gang themselves. You have on the
44:12 receptors and now you're seeing that synopsis have on the tropic receptive society and
44:19 deep polarization polarization. The ones that medical tropical silent burning equalization here is
44:27 polarization. Hyper polarization here needs deep . And there isn't that much more
44:35 I cannot ask you about the properties there is some of the fields except
44:39 there are collections of these on off surround cells with the retina processes this
44:47 really. The changes in luminous. you may in this pattern this is
44:53 pattern, this is actual geometrical pattern your retina will see. It will
44:58 this bright and dark spots across the . Now there is another type of
45:09 that we talk about. These are cells and we also have um a
45:15 cells. And what's interesting again is reason why I want to show it
45:20 you is because we talked about some these things. So horizontal salsa inhibitor
45:26 will release Gaba. So there's another of control for you. That's why
45:31 cannot really answer that question straightforward because photo receptor releases glutamate. It may
45:39 that I am a tropic sell on south. But it will also be
45:44 exciting horizontal cell and this horizontal cell have a negative feedback and it will
45:52 inhibit that photo was something. This negative feedback in conditions. Okay so
46:00 excited inhibition and that inhibition inhibited It's like you come to talk to
46:06 that person doesn't want to talk to both and we apply it or an
46:10 if you talk to somebody who will there's well so now you have this
46:18 of control here by the inhibitory cells those inhibitory cells. That means that
46:23 somehow can shape the sensitivity and the to luminescence and sharpness in the edges
46:31 the receptive fields because they can inhibit where they inhibit activity, they can
46:36 in more within certain receptive fields, cells release glutamate. Uh The other
46:43 thing, horizontal cells have gap junctions them. So remember these are electrical
46:49 , we started them at the very of this section. Horizontal south can
46:54 because of the gap junctions. If is illuminated and they're excited they can
47:00 that information broad area of illumination. can sculpt it also. Uh And
47:07 can sculpt the activation of the cones releasing Gabba on them and inhibiting the
47:14 of life coming in to these So here you have inhibitors synapses by
47:22 cells that we're discussing here and here have this negative feedback loop. So
47:28 oh excitation horizontal cells that means I'm inhibit here and now there's an addition
47:35 the self. So that's why your is very good but it's difficult to
47:42 it because it involves multiple uh first tropic medical tropic to bipolar selves and
47:51 involves self inhibition of the activated Okay so now we're gonna move on
48:03 our next slide presentation, which is is mine? Here we go.
48:29 gonna start moving into the central regions from the retina and the retina perceives
48:42 world in these concentric on and off of cone and rod photo sappers depending
48:51 the area that you're located in the . You have the circuit. So
48:58 is receptive potentials, synaptic potentials, cells, action potential Charles. And
49:06 put out the retina the circuit We can review the next lecture but
49:14 you can remember that there is bipolar that have Tampa Kane versus metabolic tropical
49:20 . They will react differently to that . If you can remember that in
49:26 light the cells get high to They do the opposite with stimulation of
49:31 we learned in other south. Then should be able to just know most
49:37 the things you need to know about circuit for the exam. Uh And
49:42 there is a inhibition. There's another of control in the circuit by the
49:48 cells such as horizontal cells. Now we look at the ganglion cells that
49:54 out of the retina there are on retinal ganglion south as we described based
50:00 the receptive field properties. But there's anatomical and functional distinctions of these axons
50:07 retinal ganglion cells located in the Some of them are magna or
50:13 Type. Some of them are parvo P. Type and some of them
50:18 cannot be placed within even the magno the part of a subtype of retinal
50:24 cells. So they're referred to as Mp type. Sometimes they're referred to
50:30 intermediary cells and also as Kanye cellular are all the same type of cell
50:37 has three names parvo is small. have small receptive fields. So smaller
50:45 will be having less synapses and they hook into less of the photo receptor
50:52 . Coming right. This areas will smaller. So they'll have smaller receptive
50:58 which means that some of the information into retinal ganglion cells will be smaller
51:04 and other information will be larger concentric around fields. They have slower conductors
51:12 they're small. They're less sensitive to contrast mm Retinal ganglion cell. So
51:20 or large. They are fast. have more sensitivity to light. They
51:26 larger receptive fields because they will have synaptic ability to look into the photo
51:33 above them, sending that information. from the retina uh in the retina
51:40 now we're just seeing so far this pattern, the center surround the circular
51:48 areas slightly different in size. By time we get to the central visual
51:56 we can see a lot of different interpret a lot of different patterns.
52:01 have the color. We have the . We have the depth perception and
52:06 of these other good things. And we'll see how we can actually
52:11 I'm gonna come back and talk about slides and a little bit we'll see
52:15 we can construct what we call a image of the outside world.
52:25 at the level of the visual some color and some motion. Uh
52:37 of retinal ganglion cell outputs go into lateral nucleus about 10% to 15% or
52:47 Goes to a tact um which is curriculum. Remember we have corporate Quadra
52:53 as superior curriculums and empirical Oculus. 10% goes to superior curriculum and superior
53:01 will be processing psychotic eye movements, eye movements. Are these jump like
53:07 that we do with our eyes? almost reflexive. There's no smooth pursuit
53:13 we're capable of, meaning that if seeing something moving, you're gonna have
53:19 move your eyeball to trace motion in field of view and to move your
53:26 . You don't move it smoothly like . But rather you do it in
53:30 jump like movements. These are called eye movements. I always say that
53:36 any of you have cats or love , you can watch cats and cats
53:42 really good at having these almost like eyes back and forth. These are
53:48 eye movements. And cats are some the best models for studying the psychotic
53:53 movements. 123% of retinol outputs go the super cat asthmatic nucleus which is
54:02 circadian rhythm. Uh Master controller. right, so we have inputs coming
54:12 the eye. Some of them are cross over through the sky as you
54:16 the stock of the pituitary gland. it crosses over kayaks and it becomes
54:21 tract and it goes into the lateral . So the field of view that
54:28 looking at is divided into the hemi . We have the left visual honey
54:35 and the right visual honey field. a fixation point is right in the
54:41 , right in the center of your , you're looking right ahead of
54:44 Then you can divide these fields into and right. This portion of the
54:50 here you're fixating this whole portion of field here is referred to as binocular
54:56 field. So the information that you with this one, I can also
55:03 a lot of it can be pursued another eye so that when the two
55:07 overlap and processing information is called the visual field. And then you have
55:14 right visual field that is only going get processed by the right eye.
55:18 left visual field is going to get by the left eye. So your
55:24 are like cops like this sitting in back of the eyeball. And this
55:30 of the retina is going to be over there at the center of the
55:34 is going to be looking over there this part of the retina is gonna
55:37 looking over there. The same with this will be looking over there,
55:42 will be looking over here. And so what you can see with
55:46 periphery. These eyes, you cannot more because this nose gets in the
55:53 . So if you were to get of the nose you would actually see
55:57 in that direction. Uh Now you certain fibers that are crossing over.
56:08 you can see that the nasal component the retina closer to the kayaks and
56:14 to the nose is the component that going to cross over contra laterally.
56:21 we can see that the temporal component . The red temporal component is gonna
56:28 . It's a lateral it's not going cross over. So from the retina
56:34 Kai as um you have the optic , the optic track projects into the
56:40 and left lateral nuclear nuclei. And nuclei on each side will project into
56:46 area. 17 occipital lobes, just visual cortex. So let's talk a
56:53 bit about some of the visual deficits one might have. If there's a
57:02 areas that can get damaged along this of the optic nerve tie asthma optic
57:10 without damage to the lateral nucleus or cortex and so on. So if
57:17 were to lose one eye or have nerve cut or impact that damaged uh
57:28 the case may be. If you to lose one eye, it's an
57:33 of you closing one eye and you see how much of the visual field
57:38 lost, you actually just lost this here and everything else. The binocular
57:46 is still preserved because it's looking by right eye and the periphery on the
57:52 is preserved. So you only would peripheral vision on one side. If
57:59 had transaction of the optic nerve, black represents the loss of the visual
58:05 that you wouldn't be able to proceed the cut is at the level of
58:11 optic tract. Now you have optic that's comprised of the fibers that crossover
58:21 fibers. So these nasal area is to be damaged here from this retina
58:29 then the temporal fibers from this And the temporal fibers number. We're
58:35 over there because it's a cup, looking over. Their temporal goes to
58:39 temple is looking over there. So loss would be tremendous. It would
58:45 half in this case the the whole right visual hemi field would be
58:55 So let's stop the tract. You lose perception of the right hemi field
59:05 . Now, what if the damage to the optic chasm damage happens to
59:11 optic eye? As you're looking at fibers that are crossing over, You're
59:16 at nasal fibers that are crossing over the chi asim where nasal fibers looking
59:23 nasal fibers are looking in the periphery looking in the periphery. So you
59:29 have loss of peripheral vision on both . If you had to cut throughout
59:35 track. But you would preserve the binocular zone, he would have a
59:41 vision preserved here in the binocular Uh there's a pituitary giants that have
59:51 pituitary gland and that blind can start onto the optic chasm. So famous
60:00 , like when I talk about giants really very big. People like Andre
60:04 giant and some other characters that made into the movies. But typically they
60:13 some issues like growth, hormonal body growth issues because their pituitary
60:19 so they grow too large. And pituitary gland is very big and pituitary
60:26 can start pushing on the chi as it pushes on the kayaks and it
60:30 cause the loss of the peripheral And this loss of the peripheral vision
60:35 also referred to as a tunnel So it would be the same as
60:39 just closed. You're you formed a around your face that would be a
60:47 to the optic chasm. So, your book, I think there's even
60:52 explanation about how uh Goliath may have a pituitary giant and had a tunnel
61:03 and the famous biblical battle of David Goliath where David won against the
61:11 the neuroscientist interpretation as a Goliath was 30 giant. He had tunnel vision
61:18 David managed to run up and hit with a stone slightly from the peripheral
61:24 where he couldn't see David approaching him that's how the battle was warned between
61:31 Israelites and Philistines in this biblical So it's a neuroscientist explanation of basically
61:41 vision and and pituitary giants through the to the optic eye. ASM projections
61:49 the retina going to the lateral nucleus lateral nucleus nucleus. This is a
61:55 stain of LG on very clearly demonstrates a six layered structure 123456 and the
62:06 two layers. So medial collateral uh magna layers one and two. Then
62:18 have part of a 3456. It that magnolia Harris will receive inputs from
62:27 cellular retinal ganglion styles. And each . G. N. Will receive
62:34 layer from each eye. Powerful layers information from the parvo retinal game.
62:43 Kanye cellular as I mentioned was also NPC cells and you can see that
62:51 between these very dense bands of lateral nucleus layers. You also have this
62:58 cells in between and ventral to each . Those are the non NPR the
63:04 cellular subtypes of cells. We believe their function is different from M.
63:11 P. Types of south and we their function is started to color
63:17 Uh what you have essentially is you redundancy and parallel processing because you have
63:24 larissa. N. L. M. LG. N layers.
63:28 ocular so the cells in each layer information from only one eye at the
63:37 of L. G. M. field properties are similar to retina.
63:47 on is still processing these centers around of the outside world. In this
63:56 and off receptive field properties pattern 80% projections into lateral Jinich Hewlett nucleus of
64:06 origin. Don't confuse this with this to 90% of output from L.
64:16 . M. Goes to the from goes to the L. G.
64:21 . The retina communicates to algae on all of the outputs go into the
64:29 G. M. However, algae is a beast of its own.
64:34 turns out that it receives a lot inputs from cortex then from the L
64:40 . M. So 80% of projections come into L. G.
64:46 They're coming from cortex and that's why we see with. L.
64:50 M is influenced by how we feel cortical projections into L. G.
64:54 . Already talked about follows an G. N. Having the ability
64:58 get the signal to modulate the turn tune and turn up the signal
65:04 the level of L G. Now, L G M is receiving
65:08 signal from the cortex and that cortex from association area. I'm not association
65:15 is telling you I'm in a really mood right now. I'm not really
65:20 in looking at this or perceive it a different way because I'm cranky so
65:26 L. G. And I'm not to focus on this. I'm going
65:29 focus on my camel t. All . So cortex informs algae on it
65:37 modulate even more how that information from outside world is being taken in and
65:44 the focus of that information is and the perception is being directed. That's
65:49 I said. What we see is Belgian is is how we feel.
65:55 So did you say that 80% of productions from the redneck bowl into the
66:00 . G. Is right? But 50% of all the ones that come
66:04 the L. G. N. . From the cortex this is
66:08 G. N. This is 20% the L. G. M.
66:15 is right now 80 - 90% of in rattle and go sell GM.
66:24 it only comprises a portion of the that algae on receives and algae on
66:29 most of its inputs going into G. On from cortex. Yeah
66:41 that's a good way maybe to And maybe I should make a little
66:44 like this on the slides. Uh you have six layers. You have
66:53 layers as you can see it's a and blue. So this is the
66:58 retina that stays up bilateral temporal and is 235 contra lateral. That crossover
67:08 contact 146. So you have bilateral 235 contra lateral layers. 146.
67:16 means those are the L. N. Layers that are receiving information
67:20 the contra lateral I. One magno which is one and then two part
67:26 a four and six for blue is which is two and two parvo which
67:32 three and five. So each on side of the L. G.
67:37 . Three layers from one I three are from the other eye. Out
67:42 these three layers from one I one magno to a parvo on the other
67:47 the same thing three layers from one three layers from the other one is
67:52 from one eye to a parvo. is magnum from one eye to a
67:58 . So that organization you have the lateral and multilateral label gear contra iptc
68:05 contra contra. See I I see see From 1 - six or you
68:12 devise a Fox Bonnie pneumonic. Um kidding. It's easy to remember.
68:23 I see I see that's how I to remember. So contrary iptc iptc
68:30 contra and now I know 123456 non same as overlying principle layer ventral to
68:39 principal layer. Those are the konya L. G. M subtypes of
68:44 . So these are the six Now these six layers from the
68:48 G. M are going to project the area 17. In the primary
68:53 cortex this is the primary sensor information area and you can see that area
69:01 in macaque monkey is much larger relative the size of its brain? As
69:07 to humans? Where area 17? primary this primal sketch of what I
69:16 , not how I feel about not how to interpret this all of
69:20 . This is what I see and occupies more of the brain space and
69:26 that occupies little brain space of what see. I need to see what
69:29 see. The rest of what I with what I see is the interpretation
69:33 what I see and that's a lot area in the brain that will be
69:38 to that interpretation. You have a topic map point by point representation from
69:45 outside world. From the retina. point on the retina is looking there
69:51 that point in the retina will communicate to a specific point in the
69:55 G L G. M will communicate information specific point in the primary visual
70:01 that is referred to as retina topic . The point in the retina has
70:05 point in the visual field looking at parts of the visual field. It's
70:10 retina topic map and from LG on projections go into neocortex and this is
70:18 we're gonna end today. Just remind that neocortex is a six layer structure
70:24 then we come back we're going to the precise connectivity in this visual cortex
70:31 we're going to understand how from this and off concentric circle like receptive field
70:37 in the retina and L. M. How do we get to
70:41 primal sketch in the primary visual So what are the south? What
70:46 the the functionality of the South that us to create this? What is
70:52 anatomy behind the connectivity that allows us create this primal sketch on the primary
70:58 ? Okay so that's for Wednesday. see everyone in class on Wednesday and
71:03 will be our last lecture before our review which is next week. Okay
71:10 come on.
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