| 00:00 | So welcome back, Thio. The lecture on the visual system, and |
|
| 00:06 | talking about the projections that go from retina and the retinal circuit that we |
|
| 00:12 | . These projections, in the form the optic nerve, will cross over |
|
| 00:16 | the Chi Azman in the form of optic tract, will project into the |
|
| 00:20 | June uclick nucleus and the columnist, from there into the exhibit, a |
|
| 00:24 | with a primary visual cortex view one located and there will be more complex |
|
| 00:32 | . It's each stage the signal transmission hierarchically, more complex processing and the |
|
| 00:40 | of the visual cortex. Primary visual . Who will have the primal sketch |
|
| 00:45 | the visual view that will incorporate some as well as motion eso. We |
|
| 00:52 | discussed that from the visual cortex, divergence of these visual pathways, one |
|
| 00:57 | is associated with the parietal lobe through dorsal pathway through posterior parietal cortex and |
|
| 01:04 | other one into the ventral temporal which is inferior temporal cortex. |
|
| 01:10 | this information and finally emerging the complete and understanding of the visual information and |
|
| 01:18 | the sensor information gets incorporated with other , such as auditory and some out |
|
| 01:23 | sensory finally, will result in how process information, what emotional aspect of |
|
| 01:31 | information may be and what will Finally, the motor command out with |
|
| 01:36 | from the prefrontal cortex in the we discussed the details. Anatomy of |
|
| 01:43 | eye ball with the light will enter the pupil on the lens, well |
|
| 01:48 | onto the retina in the back of eye. And if we are processing |
|
| 01:54 | security vision in direct rays of phobia will contain the highest density of |
|
| 02:01 | photo receptors and will have the highest or the highest resolution. Aziz. |
|
| 02:07 | know cone photoreceptors are also chromatic. come in three colors and as we |
|
| 02:12 | that this light has to pass not through the cornea, enter through the |
|
| 02:19 | onto the eyeball through the eyeball, all the way back through the circuit |
|
| 02:24 | thio the photo receptors. Now this the direction of light from left to |
|
| 02:30 | , shown where the red arrow so coming through this direction will finally be |
|
| 02:38 | from the photon of light into an signal by the photo receptor cells, |
|
| 02:45 | photo receptor cells will communicate graded receptor to the bipolar ourselves, which will |
|
| 02:53 | communicate receptor graded potentials to the Cells in the ganglion cells will produce |
|
| 03:00 | potentials on the action. Potentials will transmitted through the optic nerve, an |
|
| 03:08 | tract, including the information from the and sending it on to the higher |
|
| 03:13 | and the foulness, an al GM the visual cortex. So horizontal cells |
|
| 03:20 | also responsible for controlling activation of the and also communication between the photoreceptors in |
|
| 03:28 | bipolar cells and the AM A crane are intertwined and in the synaptic communications |
|
| 03:35 | between the bipolar south and the retinal cells. If you are looking at |
|
| 03:42 | far point, your lens, as talked about, can adjust if that |
|
| 03:49 | of interest will move in closer towards . But you don't change your point |
|
| 03:55 | perception and point of view. What is your lens will adjust, and |
|
| 04:01 | the lens will think him as the will come closer to you. And |
|
| 04:06 | purpose of that thinning and thickening of lines is to make sure that the |
|
| 04:11 | of interest that you're focusing on is projected exactly and focused exactly in the |
|
| 04:18 | onto the retina. So in normal or 2020 vision and being a TRO |
|
| 04:25 | , this image will be correctly focused to the back off the retina, |
|
| 04:30 | it will be in focus. in the cases of hot high Perot |
|
| 04:35 | , the lens is shaped in such way that it is now focusing the |
|
| 04:42 | beyond the retinal cells and at the off the where the photo receptors are |
|
| 04:48 | the retinal circuit, that image will a pairing blurry. So in that |
|
| 04:52 | , if you use a con cave and it could be a contact lens |
|
| 04:59 | it can be glasses Glassland. So you do this, what you do |
|
| 05:05 | you essentially adjust the slide with respect the lands and with respect to the |
|
| 05:13 | of that image precisely onto the so that that image doesn't appear |
|
| 05:20 | And another way in which you could is you could do an adjustment to |
|
| 05:23 | lens itself through the laser surgery, , called LASIK, which can help |
|
| 05:31 | again that we shaped lens eso that fix the hyper o pia or my |
|
| 05:38 | . P. A problem In the of my opiates, images focus before |
|
| 05:44 | rotten again at the level of the , making this image appear, |
|
| 05:50 | blurry. And so, in this , if you have a con, |
|
| 05:59 | , cave lens, then you correct this projection, and you re focus |
|
| 06:07 | image exactly on the retina again, it fully into focus. So this |
|
| 06:15 | , you can adjust hyper opium, O Pia farsightedness and their side in |
|
| 06:21 | vision. Uh, in general, you look at the visual field of |
|
| 06:27 | one eye is seeing one eyes seeing degrees of the visual field. So |
|
| 06:35 | the whole surround this 360 degrees, I if you close one eye from |
|
| 06:48 | you are, no stops your thio the very peripheral here, the |
|
| 06:52 | you're seeing about you can move your away until you start seeing it, |
|
| 06:57 | then you can move your finger all way across until you stop seeing. |
|
| 07:01 | that's 115 degrees of space that you're with just one eye with the left |
|
| 07:07 | the right eye. And so, you know an object that is a |
|
| 07:12 | distance away. Imagine you're looking at dark sky and there's a bright spot |
|
| 07:19 | this bright spot of the movement, that moon is a known distance away |
|
| 07:24 | it will occupy approximately half a degree visual angle. So if you're looking |
|
| 07:33 | one eye and you see all of 150 degrees of the moon, it |
|
| 07:37 | out there. Of course, it how close or how far the moon |
|
| 07:40 | . But just imagine that the moon occupying half a degree of the visual |
|
| 07:47 | , and that will translate into exciting area on the retina that equals to |
|
| 07:54 | 140 micro meters in the amateur from you can think of each half a |
|
| 08:05 | at a certain distance would be occupying micro meter space and the retina, |
|
| 08:12 | the 140 micrometers of space will contain off photo receptors that collectively make what |
|
| 08:21 | call receptive fields. And there's receptive for this information outside for this luminescent |
|
| 08:30 | . Outside, this process by the and the retina really perceives mostly the |
|
| 08:37 | and luminescence that is observing in the world. So two very important points |
|
| 08:47 | this whole circuit is the photo. , by their own way, are |
|
| 08:52 | only way south in the circuit that life sensitive that are responsible for photo |
|
| 09:00 | reduction and that the ganglion cells in action potentials is the only output from |
|
| 09:07 | retina. So although the visual it's transducer and synaptic, Aly and |
|
| 09:14 | chemically processed through multiple interactions of multiple , ganglion cells is the only output |
|
| 09:25 | the ganglion. Cell axles form the nerve exiting out of the reckless and |
|
| 09:32 | right away is quite often divided into . The outer nuclear layer, which |
|
| 09:37 | contain the nuclei off the photo is the most outer layer. It's |
|
| 09:41 | most outer on the eyeball, if may, the outer plexi form |
|
| 09:48 | which is the connections between the photo cells from bipolar cells, as well |
|
| 09:53 | the horizontal south synapses, the inner layer which will contain the so Hamas |
|
| 10:01 | the nuclei off the horizontal bipolar and , a Quran cells all in this |
|
| 10:08 | , the inner blocks of form which will have the synapses, the |
|
| 10:12 | between bipolar south, the ganglion cells well as the AM a cretin cells |
|
| 10:18 | the ganglion cell there, which is ganglion cells on there. So HMAS |
|
| 10:25 | out the output here further, that forms the optic nervous no longer a |
|
| 10:32 | in the retina. So this is view of this llama organization in the |
|
| 10:40 | where you have the ganglion cell the inter plex reform. So you |
|
| 10:46 | either go from the outer outer is the outer outside, Off the |
|
| 10:52 | the high ball or inner is from inside ganglion inter plex to form inner |
|
| 10:58 | outer plex to form out of Then you have layer photo receptor outer |
|
| 11:04 | and this is where photo transaction happens then you have the pigmented pigmentation and |
|
| 11:11 | him out to the epithelium here in back. So if you want |
|
| 11:16 | observe something with the highest security and the most color. Then you want |
|
| 11:21 | focus these direct actual rays of life onto the phobia. The photo |
|
| 11:29 | They have the canonical morphology between Yet they have some morphological differences as |
|
| 11:38 | . Rod and come photoreceptors. They have the out of segments in this |
|
| 11:43 | . Segments contain member Enis disks and member in his disks half photo photo |
|
| 11:51 | . So the difference is that in photoreceptors, this out of segment discs |
|
| 12:00 | free floating, and they have an membrane that allows them to be free |
|
| 12:07 | inside the outer membrane off the outer , thereby increasing the surface area where |
|
| 12:18 | Pigment Road Dobson could be stored. so, in the come from the |
|
| 12:27 | and this outer segment, the member discs they're not free floating. |
|
| 12:33 | the photo pigment is stored along the that has multiple imaginations along the way |
|
| 12:41 | , increasing the surface area for the photo receptor. Then we have the |
|
| 12:48 | segments, which will also include the bodies, the Selma's and then the |
|
| 12:53 | terminals. So the synaptic terminals from receptor cells into the bipolar ourselves. |
|
| 13:05 | outer segments are responsible for photo and you can see that you have |
|
| 13:14 | lot mawr, the surface area. you have a free floating disc versus |
|
| 13:18 | you have imagination of these member nous protections into the South, and this |
|
| 13:25 | the inner segment, these air the terminals. The inner segment is a |
|
| 13:29 | . Synthetic machinery off the cell and synaptic terminal is the contact of the |
|
| 13:35 | cells, the bipolar cells and the cells. These air the major differences |
|
| 13:44 | rods and cones and their respective neural . Systems so rods our high sensitivity |
|
| 13:58 | receptors. They have high sensitivity to and their specialized for night vision. |
|
| 14:04 | have more photo pigment and capture more . Roz Air High amplification and a |
|
| 14:11 | photon detection is possible with the rod . Because it is a it |
|
| 14:16 | It is low. It is high . At the same time, it |
|
| 14:20 | low temporal resolution, which means that rods to resolve the signal, it |
|
| 14:29 | happen slowly. It will have slow on long integration time, that long |
|
| 14:35 | time of low levels of light. it, at the same time is |
|
| 14:41 | sensitive to these low levels or scattered of light rod system is low accumulated |
|
| 14:50 | , then it's not present in So rod system is not really being |
|
| 14:55 | for high resolution or high security, it has highly conversion retinal pathways. |
|
| 15:03 | you look at the circuit in the , Ron System is a dramatic. |
|
| 15:09 | has only one type of rod pigment for the receptors are, on the |
|
| 15:16 | hand, lower sensitivity and their specialized day vision. They have last photo |
|
| 15:23 | and are capable are not much capable amplifications that have lower amplification of |
|
| 15:31 | um, signal, but fast. has high temporal resolution. It has |
|
| 15:37 | fast response of short integration time and most sensitive to direct actual race. |
|
| 15:45 | if you want to resolve something with color and if you want to resolve |
|
| 15:51 | with a lot of detail, you to make sure that you have sufficient |
|
| 15:55 | amount of light on hitting the object reflecting back directly axel rays of light |
|
| 16:04 | your phobia region. Con system is high security system, concentrated in the |
|
| 16:11 | a phobia and has the virgin and retinal pathways and khan systems chromatic. |
|
| 16:19 | you have three types of cones, with a distinct pigment that is most |
|
| 16:24 | to a different wavelength off the visible spectrum. So when you think about |
|
| 16:33 | system, you can think about it your grace scale system, lighter and |
|
| 16:41 | , and your cone system as your system that has three different types, |
|
| 16:49 | cones and combination of activation of these different kinds of cones can produce a |
|
| 16:55 | of Hughes and colors that you can , um, on a daily |
|
| 17:04 | even right now. An example. , if the rod system is, |
|
| 17:10 | walk into the movie theater and when walk in from the bright lights, |
|
| 17:17 | walking through the concession stands up. movie theater advertisements lit hallways, and |
|
| 17:26 | your cone system is fully activated. seeing everything in colors. You're seeing |
|
| 17:31 | blinking because there's direct axel lights from ads on the walls and from the |
|
| 17:37 | in the bathroom. You're seeing all detail all the color, and then |
|
| 17:42 | walk into the movie theater and for a second or two is almost all |
|
| 17:49 | dark to the point where you get for a second. I can't see |
|
| 17:54 | . Then one or two seconds you start seeing, especially if the |
|
| 17:59 | is dark in the movie theater. start seeing you start seeing the |
|
| 18:05 | You start seeing lighter a parent's off that the audience is wearing. You |
|
| 18:14 | seeing darker seeds to start seeing darker who start discerning people from the |
|
| 18:25 | and then this way you kind of yourself. And so it takes time |
|
| 18:32 | this night vision system to kick When it does, it's quite |
|
| 18:38 | And after a while of sitting in theater, the system would just pretty |
|
| 18:42 | where Now you can start seeing quite bit of detail around you. |
|
| 18:48 | Then you walk out and you want . Look at some details, some |
|
| 18:55 | , some color and discern something of detail. You walk out into bright |
|
| 19:00 | and again you have the reactivation off cone system and your eyeballs and everything |
|
| 19:07 | focused around the phobia. And if basically took this retina and you stretch |
|
| 19:16 | it across 0 90 degrees, 70 here with the gap of about 10 |
|
| 19:23 | , and this gap is a blind and you look at the dominant photo |
|
| 19:29 | that are expressed. Zero would represent central retina, and the central retina |
|
| 19:34 | dominated by cone photoreceptors. Your recep person phobia. You can see |
|
| 19:40 | high number of them in blue, the Y axis here is the number |
|
| 19:49 | photo receptors and use you can see you go away from the center, |
|
| 19:53 | have some cone photoreceptors but the pewter . And it's very small amount of |
|
| 19:59 | photoreceptors going into the poor for as to rod photoreceptors that are really not |
|
| 20:07 | in the central area. It is here, right a little bit before |
|
| 20:11 | blind spot. But it is about speaks about 10 degrees away in each |
|
| 20:17 | from the center. So the central is dominated by cones, this blue |
|
| 20:23 | and the periphery surrounding of the center the periphery is dominating by rod photoreceptors |
|
| 20:31 | temporal per refer. In the Matt refers Thio the side of the |
|
| 20:36 | closer to the temple and nasal for refers to the side of the |
|
| 20:41 | That's closer to the nose, so can see that you have electro micro |
|
| 20:46 | off these cone and rod photoreceptors in in the retina. Now, this |
|
| 20:52 | another representation off this morphological arrangement that would see in the faux V. |
|
| 20:59 | particular, you have this massive, , indentation in the actual structure off |
|
| 21:09 | retina and the back in the so that all of the direct axel |
|
| 21:14 | of light could focus directly on to Cohn dominated photo receptor system here in |
|
| 21:21 | phobia for high acuity, the faster vision. Um, so now the |
|
| 21:31 | photoreceptors chromatic cone photoreceptors are blue, and red, but we're not seeing |
|
| 21:41 | three colors. We see a lot colors, and we know that there |
|
| 21:44 | , ah, visible wavelength of life we perceive from 400 to 700 nanometers |
|
| 21:52 | 400. We have ultraviolet and about . We have infrared wave lines, |
|
| 22:01 | in order to see blue color, we're seeing is blue color can be |
|
| 22:07 | by activating primarily blue cone photoreceptors with wavelength of light of about 444 130 |
|
| 22:19 | . Thio perceived green color that is there in the outside world, you |
|
| 22:26 | have a combination off red, blue green, and that will be producing |
|
| 22:30 | green color that's in the high 400 range. 474 180 nanometer range. |
|
| 22:39 | color. What we see in the world is yellow. Actually, if |
|
| 22:43 | look outside some of the trees that changing a little bit of the colors |
|
| 22:49 | the fall here all the most of nature here is evergreen, but if |
|
| 22:55 | find yellow oranges combinations off activation of and red, about 550 nanometers |
|
| 23:03 | And again, if you had a out there, that wasn't, |
|
| 23:07 | 650 nanometers. And you would know since in the red spectrum it's between |
|
| 23:13 | between 606 100 700. You have transition between oranges and into deep dark |
|
| 23:21 | Rad's, and so what you see the table below is the color perceived |
|
| 23:29 | blue is 100% activation of blue Parlor color perceived. This green is |
|
| 23:37 | off red cones, 67% activation of cones in 36% activation of glucose, |
|
| 23:45 | yellow is created by 83% bread, activation of green cones and 0% activation |
|
| 23:54 | blue comes. So now you can that if you shifted a light if |
|
| 23:58 | light out in the world changed, say from yellow sunlight Thio, orange |
|
| 24:05 | . That means that that line that perceiving instead of activating now 83% in |
|
| 24:13 | of red and green counts, it shift now. MAWR forward Activating War |
|
| 24:18 | the Red counts closer to 600 nanometers it's going to be a pairing wars |
|
| 24:24 | orange like color. So when the changes from outside world, when the |
|
| 24:31 | in the least changes it turns now you to perceive that color orange, |
|
| 24:37 | will be activating a lesser number of counts and a greater number of red |
|
| 24:41 | until the high wavelengths of light will purely be producing. Use different variations |
|
| 24:49 | red light mixing colored lights, and mixing of red, green and blue |
|
| 24:56 | causes equal activation of the three types cars and the perception of white |
|
| 25:02 | If you have three types of lights you activate them equally 4, 35 |
|
| 25:08 | and 5 60 way lines here that shown optimally 100% to get wide |
|
| 25:15 | If you activate here, 555 145 you're now getting the yellow light, |
|
| 25:25 | , and so this is what it . On the outside world, there |
|
| 25:29 | different wavelengths of light. The wavelengths light are changing, and they're changing |
|
| 25:35 | varying degrees. Activation of these three types of the current photo receptors and |
|
| 25:42 | us toe perceive all of these beautiful in the in the outside world, |
|
| 25:47 | that is very much here, likened Painter's palette, where one would take |
|
| 25:54 | and mix them together and mixing two three colors together. We'll give you |
|
| 26:00 | yet completely different color, like in case, a white one. It's |
|
| 26:05 | little pause here for a second, let's look at how photo transaction takes |
|
| 26:12 | in the retina. Well, we're well familiar with is the diagram here |
|
| 26:18 | the left, where you have a chemical neurotransmitter binding Tuju pretty and coupled |
|
| 26:25 | that receptor activities you protein and And that complex can have an effect |
|
| 26:31 | that connected the secondary messenger and can the opening or closing off the ion |
|
| 26:37 | , increasing or decreasing ionic conduct Ince's ionic through other ion channels, and |
|
| 26:44 | the shortcut route you remember. The protein complex itself can does not have |
|
| 26:51 | always have in the factor enzyme that also directly affect the nearby Ionic |
|
| 26:58 | In the visual system in foot of deduction, it's not the chemical that's |
|
| 27:05 | from the outside world when it's coming of light. And when that light |
|
| 27:13 | photo pigment molecule, it activates a Rodin, and that G protein actually |
|
| 27:21 | a channel. So it's measurable Tropic and this Medical Tropic signaling in the |
|
| 27:31 | photo transaction of life perception is Thio sodium conduct Insists and sodium |
|
| 27:39 | What is different than from what you already in the scores is that in |
|
| 27:47 | rest, addressed or in the photo receptors are deep polarized. At |
|
| 27:55 | 30 million bowls. There is a of cycling GMP unsightly GMP keeps the |
|
| 28:01 | channel open, and this constant flux sodium channel D polarizes plasma membranes and |
|
| 28:08 | the resting membrane potential around minus 30 bowls. Remember, these are not |
|
| 28:13 | cells that produce action potential. So not worried here of crossing the threshold |
|
| 28:18 | action potential. These air receptor cells they produced graded receptor potentials when the |
|
| 28:27 | is on the photo receptors. What is with the slide here depicted in |
|
| 28:36 | , the photo receptors will actually hyper in the presence of life. And |
|
| 28:43 | when you switch the light off, the photo receptors will come back through |
|
| 28:49 | sodium signaling and rebuild the polarized membrane . So the light will control the |
|
| 28:56 | of sodium. And by controlling the of sodium, it will cause the |
|
| 29:01 | polarization. This is shown here in detail where you have the option, |
|
| 29:08 | , from SIS, with activation of turning into Trans and the G. |
|
| 29:17 | , um transducer inactivation. It's an here, but one. The light |
|
| 29:22 | and when it's inactive, there is of cycle GMP, and they're |
|
| 29:29 | GMP keeps sodium channel open. It's cycling GMP gated sodium channel. |
|
| 29:37 | So this is measurable Tropic activation. through G protein coupled receptor row |
|
| 29:44 | in this case, and in the , this channel sodium channel. It's |
|
| 29:52 | by cycling GMP. So when the hits and you activate the G protein |
|
| 30:01 | him, you acted a bus for strays and that bus for Dia stories |
|
| 30:08 | cycle GMP into GMP. And in absence of cycling GMP, the sodium |
|
| 30:15 | is closed. So when the lights , activation through this G protein complex |
|
| 30:23 | reduction of cycling GMP and causes reduction sodium influx, thereby causing hyper polarization |
|
| 30:32 | the line is heading onto these Sorry. Now we're gonna talk about |
|
| 30:46 | fields and what a receptive field. I discussed with you just a little |
|
| 30:52 | ago. How half a degree of fuel, the view that they're looking |
|
| 30:58 | the moon and the far distance will a radius of about 140. My |
|
| 31:03 | is a space, and so you see that different lights out there different |
|
| 31:11 | of lights at the level of the will activate different numbers or different groups |
|
| 31:17 | these photoreceptors. And these photoreceptors in retina are organized into these on off |
|
| 31:25 | fields. Mhm on off where there a center and there is a |
|
| 31:33 | There's a center of the receptive field the surround of the receptive field. |
|
| 31:38 | the center of the receptive field usually a very different response from the surround |
|
| 31:43 | the receptive field cells and vice Okay. And those cells, |
|
| 31:51 | from the receptive fields and the photoreceptors connected to bipolar cells indirectly, they |
|
| 32:00 | modulated by the horizontal cells and from cells. That information is communicated them |
|
| 32:07 | gangrene themselves. Yeah, so you see again this communication between bipolar cells |
|
| 32:14 | and the photo receptor output. Synaptic is very much intertwined and modulated by |
|
| 32:22 | horizontal Selves. So how do these fields work? And we're recording action |
|
| 32:31 | in this case from the ganglion So we're recording What's the output coming |
|
| 32:36 | ? And we're shining different, light different size of light across visual |
|
| 32:46 | so you can focus strain across in visual field and you can now test |
|
| 32:52 | perception of these different receptive fields in retina. So the on center ganglion |
|
| 33:00 | will produce the most action potentials. the center, when the cones in |
|
| 33:05 | center are activated and they're on, will produce the most action potentials. |
|
| 33:13 | this is the light here in But if you project that same life |
|
| 33:18 | the surrounding area, in the surrounding to the center, then you get |
|
| 33:23 | least action potential. You reduce the of actual potential studies produced, and |
|
| 33:30 | you have a diffuse elimination across the area that you are perceiving, then |
|
| 33:38 | not changing the number of action potentials much because that tells you that that |
|
| 33:45 | of the visual feel that you're looking is pretty much uniformly across. There |
|
| 33:50 | not much change of luminescence. And this is what retina encodes. If |
|
| 33:55 | took the retina out and you connected retina to the computer and serve |
|
| 34:00 | retina, what do you see? will tell you. I see the |
|
| 34:06 | as on off, some to surround of light in luminescence and different varied |
|
| 34:17 | off amplitude. That's what I I don't see much of the detail |
|
| 34:23 | kind of discern on understand what faces . I do not really received the |
|
| 34:31 | . I just know that things air darker or lighter. And there might |
|
| 34:36 | a pattern that's related to motion of object that's changing in the circular, |
|
| 34:42 | fields across the retina. But this all I see is a retina. |
|
| 34:47 | if you want to see the whole , you gotta ask L G M |
|
| 34:51 | the primary visual cortex on. They'll you how that happens, but I |
|
| 34:56 | tell you how that happens on the , as opposed to the left, |
|
| 35:00 | you have a non center ganglion It's just the same logic, but |
|
| 35:05 | here the least action potentials for the on an action potential activity is produced |
|
| 35:12 | activating the center. That means that the light from this particular object on |
|
| 35:16 | outside falls on the piece of the that has an off center receptive field |
|
| 35:21 | that will have number of cones in center that will be off when the |
|
| 35:29 | is activating them, it will turn the ganglion cells when the light is |
|
| 35:35 | them and when the light is activating surrounded. So these air off center |
|
| 35:40 | themselves that are most responsive to the that falls in the surround of the |
|
| 35:46 | fields of the council will produce the actual potentials. So the receptive field |
|
| 35:53 | a receptor cell area, which one results in a responsible particular sensory |
|
| 36:01 | and we're looking at activation of cone . We're looking at activation of the |
|
| 36:09 | of these photoreceptors of form receptive Some of these receptive fields on center |
|
| 36:16 | cells. They make ganglion cells fire when the light is shown in the |
|
| 36:22 | and others can excited mawr. When patterns of light activate the surround off |
|
| 36:30 | central area of these receptive fields and cones. And so you can also |
|
| 36:36 | that by activating different on and off ganglion cells that are connected to join |
|
| 36:44 | connected. You have divergent and convergent here, through bipolar cells, were |
|
| 36:50 | to get retinal ganglion cells. Now control the luminescence and the output through |
|
| 36:58 | cells. The input, the light coming in the photo receptors and the |
|
| 37:03 | of the action potentials and the encoding the action potentials. Depending on the |
|
| 37:08 | fields that are activated across Raton and all that luminescence in the visual |
|
| 37:17 | you will produce a certain frequency in certain pattern out of that from the |
|
| 37:23 | potentials coming out of the retina that link is very specific and specially, |
|
| 37:29 | , encoded map through the retinal ganglion through the Lado Jinich. You it |
|
| 37:35 | who was all the way into the . Texas is another representation off |
|
| 37:40 | uh, if you haven't off center cell, you can actually have a |
|
| 37:45 | spot in the center and the dark in the center. It will actually |
|
| 37:50 | the most activity as well. Center surround again. You can see a |
|
| 37:58 | where you have activation of justice, in the center cell and you have |
|
| 38:03 | lot of action potentials. And then t two between t two t |
|
| 38:08 | you activate a larger area, you the surround, and you can see |
|
| 38:13 | the frequency of action potential number decreases that tells you that all of a |
|
| 38:19 | luminescence across the receptive field has gotten . Okay, so that number of |
|
| 38:26 | potentials is including luminescence and contrast. you make or difference in luminescence across |
|
| 38:34 | receptive fields across the receptive fields air and made off combinations off these cold |
|
| 38:45 | rock voters afters. And so the of the matter is, we have |
|
| 38:52 | remember a couple of things. We to remember that these, uh, |
|
| 38:57 | photo receptor cells so photo receptor cells linked to bipolar cells. So we |
|
| 39:01 | two types of bipolar cells, one of bipolar. Sal will express medical |
|
| 39:07 | glutamate receptors and another one I on tropic ample kind interceptors. And this |
|
| 39:14 | very significant because if you recall, response of the pot synaptic response of |
|
| 39:19 | cell depends not on the neurotransmitter glutamate comes pre cinematically, but on the |
|
| 39:29 | synaptic receptors that air dominating the cells dominating those patches and synapses for these |
|
| 39:35 | cells. So in bipolar cells, you have release of glutamate, that |
|
| 39:43 | ample keenan receptors what it is going do to this by all ourself from |
|
| 39:49 | from the photo receptor, this glue will excite by Paul herself. So |
|
| 39:55 | positive sign here stands for sign concerning , excitation, excitation and release of |
|
| 40:03 | . And the photo receptor means excitation deep polarization off the cell here through |
|
| 40:11 | hamper kind of receptors. But that be in the dark. It |
|
| 40:16 | Talk about the dark in the You're releasing glutamate, your d polarizing |
|
| 40:21 | cell in the light. What This Conus sitting here in the |
|
| 40:26 | What happens in the life in the ? You hyper polarized yourself when you |
|
| 40:32 | polarized the cell. What happens to glutamate transmission? You reduce Lumi transmission |
|
| 40:38 | you reduce with the transmission and the , so you hyper polarized the |
|
| 40:44 | What happens to the bipolar cell that off center? It's hyper polarized as |
|
| 40:50 | , so bipolar cells it is hyper it's not going to be releasing gluten |
|
| 40:55 | again. Classes here indicates signed concerning minus, on the other hand, |
|
| 41:02 | a sign inverting synapse. What that is glutamate. Unlike through an a |
|
| 41:07 | signaling excitation or deep polarization equals deep or hyper polarization, and the light |
|
| 41:14 | hyper polarization. This is just the medical. Tropic glutamate receptors will produce |
|
| 41:20 | different person attic response in these on bipolar Selves. And if this Sal |
|
| 41:27 | is in the like, what happens the life? There is a reduction |
|
| 41:31 | glutamate release, and because glutamate is polarizing for these cells, if there |
|
| 41:38 | in reduction of legitimate release, that that glue tomate is going to dipole |
|
| 41:45 | . And this on Santa Cell is to be deep polarized in this presence |
|
| 41:50 | life because it has glutamate receptors that otherwise inhibited. But now there is |
|
| 41:56 | good. Only while the hamper kind in the presence of light, there |
|
| 42:02 | no glutamate, so they will get polarized. They will hyper polarized bipolar |
|
| 42:08 | center cells, the synapses between bipolar and the ganglion cells assigned conservative since |
|
| 42:20 | recall that, and that's the reason it is because at the level of |
|
| 42:24 | ganglion cells you don't have in the medical, tropical, intimate receptors. |
|
| 42:30 | you have all I on a tropic kind and an MBA receptors there. |
|
| 42:38 | again, glutamate is excited. for the bipolar self, would have |
|
| 42:43 | kinda interceptor. So if there is polarization here, there's deep polarization |
|
| 42:48 | But in the presence of life, hyper polarization, and therefore there's a |
|
| 42:53 | polarization here, and there is now popularization or reduction of off center |
|
| 42:59 | Cell activation. Uh huh. So the sign inverting synapse in the presence |
|
| 43:07 | glutamate, the cells I proposal and the doctor cells hyper apologized. |
|
| 43:12 | in the presence of light is in diagram, you cut off, glue |
|
| 43:16 | , and you do polarize on center self, and then you dip polarize |
|
| 43:22 | central ganglion self, and this is the ganglion cells. No. |
|
| 43:27 | they're receiving information from the on or bipolar cells because they're not communicating to |
|
| 43:35 | photo receptors. It's these photoreceptors. groups of these photoreceptors then make up |
|
| 43:43 | receptive fields and then get modulated by bipolar cells through the synapses and through |
|
| 43:50 | receptors, glutamate signaling finally then affecting output on on and off ganglion cells |
|
| 44:00 | the retina into the lateral Jean Nicolas of the Calamos. And it actually |
|
| 44:07 | even more complex. Horizontal cells are cells. So whenever there is in |
|
| 44:15 | dark a lot of glutamate that's being on the south or D polarized, |
|
| 44:20 | will also active in horizontal south and cells are inhibitory. Horizontal cells will |
|
| 44:29 | . With Jabba these photo receptor they will hyper polarized them. So |
|
| 44:35 | is a negative feedback circuit between the in the horizontal cells that will also |
|
| 44:43 | the communication between the photos after south the my poll ourselves. Uh |
|
| 44:50 | So cones will release glutamate. Horizontal will release Gabba, and horizontal cells |
|
| 44:59 | gonna be interconnected with each other. gap junctions as well. Bipolar cells |
|
| 45:06 | also releasing glutamate. Cohn horizontal synapses assigned conserving so deep polarization and the |
|
| 45:16 | will dipaula rise the horizontal cell. then the horizontal cell will release |
|
| 45:23 | and it will cause hyper polarization. cells, because they're interconnected through yob |
|
| 45:32 | and they communicate laterally with photoreceptors are responsible for integrating broad areas of retinal |
|
| 45:46 | . Integrating broad areas for these Co joining them, maybe drawing some |
|
| 45:54 | of a comparative activity levels and communicating across the retinal circus. Very primary |
|
| 46:03 | circuits, horizontal cells again released Gabon and by that virtually control of convoluted |
|
| 46:11 | release. So the cells get deep too much and too much glue to |
|
| 46:16 | horizontal south. You can and hyper them. I gather release in the |
|
| 46:21 | feedback like fashion. So it is complex circuit, and it is not |
|
| 46:29 | to understand it the very first But it is important to understand these |
|
| 46:35 | concepts that you have groups of collections of what we call on and |
|
| 46:41 | recep tress that produce these on and center surround the center can beyond the |
|
| 46:47 | can be off the surround can beyond surround can be off. And so |
|
| 46:52 | have these round luminescence patterns on and center surround like receptive field properties. |
|
| 47:02 | what the readiness perceiving on the outside is. This by Is this luminescence |
|
| 47:09 | off center surround receptive fields and the that it can control the information out |
|
| 47:19 | it can control the information out, by being connected to different types of |
|
| 47:25 | cells and by being connected to thunder that are located even in the center |
|
| 47:31 | the surround dictating and then the number action potential. So we'll be coming |
|
| 47:36 | different ganglion cells and a very specifically connected thio specific spatial areas off the |
|
| 47:46 | . And then you introduce another layer complexity to control by horizontal cells. |
|
| 47:51 | don't even not really discussing AM a cells here, the negative feedback |
|
| 47:56 | also controlling the circuit, modulating the and activity after receptor cells? Can |
|
| 48:05 | ? So as we reviewed the retina the circuit in the retina? Number |
|
| 48:13 | , as we understood that further transaction two visual number System number three will |
|
| 48:21 | the central processing of what happens when information enters into photo receptors after it |
|
| 48:27 | transducer into an electrochemical signals. After signal gets communicated through the interconnected circuit |
|
| 48:35 | the retina and gets out, put finally, by the retinal ganglion cells |
|
| 48:43 | and off retinal ganglion cells in the off the frequency and the pattern of |
|
| 48:49 | potentials again at the level of the encoding information and outside visual world as |
|
| 48:59 | off center surround patterns off luminescence. what readily seen. So for us |
|
| 49:08 | understand how the whole picture of the forms, we have to understand what |
|
| 49:13 | subsequently in the lateral Jinich Hewlett What happens in the cortex of one |
|
| 49:18 | of a structure and function we have the way in this visual system for |
|
| 49:24 | to complete the primal sketch off the of the visual field? The |
|
| 49:32 | which will contain a lot of will be binocular will have color. |
|
| 49:37 | will have motion, so we will these circuits again. But the idea |
|
| 49:43 | is that information from the photo receptors communicated to bipolar cells. Depending on |
|
| 49:50 | type of the glutamate receptors that they . The response is going to be |
|
| 49:56 | , thereby influencing the output from the from the ganglion cells, which can |
|
| 50:01 | on center off center ganglion cells, on the circuit through which they're connected |
|
| 50:06 | the photo receptors and the modulation recall off the hammock ran off the |
|
| 50:12 | cells. We don't get to talk immigrants cells here in the sense of |
|
| 50:17 | yeah, barging neurotransmitter and inhibiting the receptors for being persistently and too much |
|
| 50:25 | polarized. In addition, Thio classifications the retinal ganglion cells based on the |
|
| 50:34 | fields such as on and off retinal cells. There is also declassification of |
|
| 50:40 | ganglion cells based on anatomical and some the functional properties. Such a |
|
| 50:49 | M and P type and non MP M stands for Magno P stands for |
|
| 50:56 | and non MP type or intermediary fibers just that that we will discuss in |
|
| 51:03 | following lecture. The parvo cells are cells that have small, receptive fields |
|
| 51:10 | small processes that conduct information slower unless less sensitive to low contrast of |
|
| 51:18 | The Magno cells retinal cells are thes a ganglion, cells faster, |
|
| 51:25 | south, so they're more sensitive to contrast. And so we have these |
|
| 51:32 | of the information leading us thio. , the central processing of visual |
|
| 51:40 | Let's see what you're seeing here. a lot of batteries in here. |
|
| 51:46 | a black and white checkered pattern. a center here. There's almost, |
|
| 51:52 | raise off son like structure in the center. It seems that maybe this |
|
| 51:58 | a vortex. But once you study one of these circles close. So |
|
| 52:03 | realize that each one of these circles , uh, independent. It's not |
|
| 52:10 | to another circle, but your perception you this three dimensional, illusion off |
|
| 52:17 | vortex. It helps you imagine a , and all of us are seeing |
|
| 52:23 | same thing. And the reason why seeing the same thing. The longer |
|
| 52:28 | look at it, the more similarities will recognize. As we discuss this |
|
| 52:34 | , it's because off the perception that have, and also because off the |
|
| 52:41 | system structure the structure from the retina thalamus l g m all the way |
|
| 52:48 | the cortex that has spatial and temporal of this visual information the terms of |
|
| 52:57 | dimensional objects into three dimensional perceptions that us to agree that this is a |
|
| 53:06 | complex pattern and that nobody is saying that I'm on Lee seeing triangles everywhere |
|
| 53:13 | . Well, you may be seeing triangles, but that's not the only |
|
| 53:16 | will you be seeing. Maybe you I'm only seeing triangles. I'm not |
|
| 53:20 | these diamonds there. It's only But most of it, you |
|
| 53:23 | I see this diamond shape and looks the circle is maybe made of the |
|
| 53:27 | lines that are intertwined white and black , making one circle. We have |
|
| 53:33 | certain structure along these anatomical pathways that us to seethe. Same are |
|
| 53:41 | very, very close to the same . And again, as we discussed |
|
| 53:44 | longer, look at this image It will be the same we're |
|
| 53:49 | So it's not like there's some universal information, but the perception of the |
|
| 53:55 | information is similar. It's encoded and reproduced by the circuits. And there's |
|
| 54:03 | structure, very complex, of precise that allow us to reproduce these visual |
|
| 54:09 | along the way. And let's talk where the information will come back to |
|
| 54:14 | previous slides, where the information goes the retina from the retina. 80 |
|
| 54:20 | 90% of the projections go into the jean Nicolas nucleus. So you will |
|
| 54:25 | that you have optic nerve optic Part of the optic nerve will cross |
|
| 54:31 | through the optic eye as, that will form the optic tract after |
|
| 54:36 | crosses through the chi as um, that track will project into the lateral |
|
| 54:40 | nucleus. So 80 to 90% of of the retinal output nothing goes back |
|
| 54:47 | retina. By the way, all the visual information exits out of the |
|
| 54:52 | . 80 90% of it goes to l. G M. Lateral nuclear |
|
| 54:56 | subsequently sends that information to the primary cortex for precise visual image and visual |
|
| 55:06 | . Formation 10% off the output. 10% of all of the fibers from |
|
| 55:13 | eyes end up going to text him to superior curricula. So part of |
|
| 55:20 | corporate Quadri Gemini Superior, Caligula which processes psychotic fast eye movement. |
|
| 55:29 | located in brain stem brain stem, older than Al gm L. Gina's |
|
| 55:38 | the neocortex. Why would you need and superior curricula? Us. Because |
|
| 55:46 | want to move your eyes. You Thio? You're responsible Tech team is |
|
| 55:52 | for this almost reflexive like behavior off eye movements S a C c |
|
| 56:01 | D I. C c. Caddick movements. He's very quick. Jump |
|
| 56:06 | movements as we're doing smooth pursuit. again, This is that the level |
|
| 56:12 | the brainstem we have toe learn how move our eyes, then quickly, |
|
| 56:20 | , and we adjust to life and move and it's almost reflexive. So |
|
| 56:24 | you move your eyes and then you that you're looking at something first you |
|
| 56:28 | your eyes and you say, I'm looking at a glass and it's |
|
| 56:32 | , and it's, uh I'm looking a can, and it says it's |
|
| 56:35 | water now to see the details. first thing when you move your |
|
| 56:38 | you just you can. Then you , oh, sparkling water lime |
|
| 56:43 | Now you're engaging L. G M the cortex. But for this |
|
| 56:47 | if something is moving, a lot it is that the level of the |
|
| 56:51 | stem for the psychotic eye movement for control of the psychotic eye movements 123% |
|
| 56:58 | the output from the rattling goes to super charismatic nuclear's super charismatic nucleus, |
|
| 57:06 | above the chi as um, would on the other side, security to |
|
| 57:09 | chi as um is responsible for circadian . Those are your dire colonel, |
|
| 57:16 | day nine rhythms and what super charismatic does It encodes different transcription factors that |
|
| 57:23 | you wake up when the light is and stay away when the light is |
|
| 57:28 | and as the light changes and the gets darker, the expression off the |
|
| 57:36 | factors changes, and therefore you are adjusting your body and you're adjusting your |
|
| 57:44 | clock. Remember, super charismatic nucleus the master body clock. It regulates |
|
| 57:50 | wake and sleep. You're tired. your circadian cycles, your wake and |
|
| 57:55 | cycles, and so small information of light from the retina, whether it's |
|
| 58:01 | outside or dark, goes into the charismatically includes and influences influences the pattern |
|
| 58:09 | this transcription factors, thereby influencing our rhythms. It's very difficult to go |
|
| 58:17 | sleep during the day, and it's to stay away at night, and |
|
| 58:23 | have to adjust that rhythm if you're to, for example, worked this |
|
| 58:27 | shift overnight shift. It takes a time to adjust that rhythm, and |
|
| 58:32 | fact, our circadian clock so pretty strongly ingrained. Uh, you |
|
| 58:39 | jet lag when you travel long distances your circadian rhythms, your circadian |
|
| 58:44 | is resetting and you might be jet . That means that you're lagging behind |
|
| 58:50 | jet. The jet crossed all through of these time zones from United States |
|
| 58:57 | Africa. But now you're in and you're feeling like you are still |
|
| 59:04 | a different time zone. So Africa be about 8 to 10 hours ahead |
|
| 59:10 | time. The east of us. when it's New York time, it |
|
| 59:16 | be eight or 10 p.m. And everybody going to sleep in Africa, and |
|
| 59:20 | just awoken. So you have to for these clock to just especially if |
|
| 59:27 | cross over time zones and you have wait for that clock to adjust. |
|
| 59:32 | it can impact your productivity. And impacts a lot of people's productivity that |
|
| 59:37 | at night, even with long term that are night shifts most of the |
|
| 59:46 | industrial accidents and the factories and, example, Chernobyl nuclear plant explosion in |
|
| 59:55 | former Soviet Union in Ukraine that waas night, many different accidents happened at |
|
| 60:02 | , partly because of the human partly because of the super charismatic nucleus |
|
| 60:07 | this encoding for us to react not today in light, but also to |
|
| 60:12 | societal cues off mawr activity or less , more people on the phone, |
|
| 60:17 | the screen or less people on the on the screen use cycles on dso |
|
| 60:23 | . So when we look at that that is being sent, this is |
|
| 60:28 | field of view that is perceived by eyes and it can be subdivided if |
|
| 60:34 | fixating right in the center or the of view. You're fixating on object |
|
| 60:39 | in the center. You have the visual, honey field, and you |
|
| 60:43 | the right visual. Help me field left visual. Having field is shown |
|
| 60:47 | on the left, and you can the right is on the right and |
|
| 60:50 | can see the projection. Send Go from the eye here until the |
|
| 60:54 | Jinich Hewlett nucleus and into the primary cortex in the pivotal oh, where |
|
| 60:59 | will finally form the primal sketch off outside world off the visual outside |
|
| 61:09 | So the fibers that of temple fibers close to the temples they do not |
|
| 61:16 | over. That means that they stayed lateral on the same side but nasal |
|
| 61:21 | . So the retina itself is divided nasal and retinal. Okay, So |
|
| 61:27 | fibers and on this side of the spot closer to the knows they're going |
|
| 61:32 | cross over through the chi as well laterally, and they will end up |
|
| 61:37 | the other side from the left to on the contra lateral side, hand |
|
| 61:41 | right l g m and so you see that optic nerve is comprised and |
|
| 61:48 | information on lee from one eye. optic nerve carries the information from this |
|
| 61:55 | from the temporal nasal retina. then half of these fibers and nasal |
|
| 62:01 | crossover anatomically through the chi as, And now that if you look at |
|
| 62:07 | optic track optic tract in blue or tract and red will contain information from |
|
| 62:16 | eyes. So optic nerve has information just one. I am one |
|
| 62:23 | but optic tract will have information from own temporal retina. It's still laterally |
|
| 62:30 | contra lateral nasal retina forming the optic . That information is then going to |
|
| 62:37 | into the lateral you Nicollet nucleus from sides of the colonists and then project |
|
| 62:44 | the primary visual cortex. And so will understand how the information from both |
|
| 62:50 | gets co joined again into the court and form a binocular field of |
|
| 62:56 | Now two eyes when they're looking in visual field. The center zone |
|
| 63:02 | the center geographic geometrical uh, object can be perceived and viewed by both |
|
| 63:13 | . Mhm. So however you can that the periphery on the left, |
|
| 63:19 | additional area of the field of view Onley perceived by the left eye. |
|
| 63:26 | because retinas are like cops there like here. So this this part of |
|
| 63:33 | retina will be staring over there. by this virtue, this close nasal |
|
| 63:40 | will be looking at the most peripheral of you here. Okay. |
|
| 63:47 | If you looked at this nasal retina the right on Lee, this nasal |
|
| 63:52 | will be perceiving this peripheral field of and you'll understand it'll that that are |
|
| 63:57 | when we review a subsequent slide on damage Thio optic nerve and loss of |
|
| 64:05 | in different fields of you. But now, it's important to understand. |
|
| 64:10 | nerve carries information from why my optic will have FC on contra lateral |
|
| 64:17 | The temporal stays of still lateral that fibers crossover contra laterally. The two |
|
| 64:25 | can see this binocular visual field, then each one of the eyes, |
|
| 64:30 | right can see its own right The left concedes some left periphery. |
|
| 64:35 | would you do that? Because you this thing called nose in the |
|
| 64:41 | Okay. So it wouldn't make sense the right eye to try to see |
|
| 64:45 | in the periphery here on the left right eye. And the formation of |
|
| 64:49 | cop makes you see what's on the here the most likewise nasal having written |
|
| 64:58 | will allow you to see the information is on the periphery here on the |
|
| 65:03 | . And if you look in the , if you try to look that |
|
| 65:07 | with the direction to the left just close your eye and you realize |
|
| 65:11 | it stops with your nose. That's it stops right here, looking from |
|
| 65:17 | to right. And you won't be to see the periphery off this. |
|
| 65:21 | this is sort of the central binocular field also referred to as the central |
|
| 65:28 | off the visual information on the outside . So we will end the lecture |
|
| 65:34 | here, But when we come we'll actually review some of this material |
|
| 65:38 | then review how different lesions either to nerve or tracked or chi as, |
|
| 65:43 | can affect what loss of visual field view a subject are patiently suffer. |
|
| 65:52 | , so I'm gonna stop the Onda, check the chat. If |
|
| 65:57 | is any questions and I will see next lecture will stop the recording. |
|
| 66:05 | talking about the central visual |
|
