 The visual system is very, very important from the point of view of nature as well as from the point of view of the sand. So just a quick overview of what we had left off, especially for those who had missed. The visual system, the visual pathway starts from the retina. Optic nerve, I'm not good at the details, you'll have to read up on your own those are missed out. Optic hyacinth, optic tract. You can see the optic tract is winding around the cerebral piranha. This is the cerebral piranha of the mid-brain, this is the cerebral piranha of the mid-brain. Optic tract. Next, lateral geniculate body, LGV, you'll never forget that, lateral geniculate body. This is the lateral geniculate body, the thalamus. And yesterday we had said that it's six layers. From the lateral geniculate body the synapse will occur and the whole layer of neurons will start. So LGV is where the ganglion cell acts on synapse. And I told you yesterday that visual system has got four order of neurons. So the fourth order of neurons is starting from the LGV. I hope this point is clear to everybody. And the portion which starts from the LGV and reaches the occipital cortex, that segment is called the optic visual or the calcarine radiation. And that's a little tricky and we have left it off here. So this is the visual of the optic radiation. This is quite tricky. So let's take off where we had, let's go back to the LGV, optic radiation, optic radiation. Now, before I start the optic radiation, yesterday I said something very significant about the optic tract. Who will remind me what I have said? Especially somebody here asked me a question also and that gentleman is missing. We have said that each optic tract receives fibres from that side of all the retina. I have yet said that means the right optic tract will receive fibres from the right half of the right retina and the right half of the left retina. Likewise, the left optic tract will receive fibres from the left half of the left retina and the left half of the right retina. I hope this point was clear to everybody because I need to build up on that. So that each optic tract receives fibres from that half of both retina. Are we clear? We have simplified the whole sentence. So the same principle holds for the LGV also. Because all the fibres with an optic tract are synapsing and 90% of the fibres with an optic tract are synapsing in the LGV. So LGV also receives fibres from the same half of both retina. Yes. Now let's continue with the next order of neuron from the LGV. Let's say the red one here or the blue one here. The next order of neurons we're just starting from the LGV, one which we're calling an optic radiation now. They are also serving the same thing. Yes. They are serving the same half of both the retina. Yes or no? I get this from you. So this whole double layer which is shown in red here or blue here. The left one is receiving fibres from the left half of the left retina and the left half of the right retina and white squares are clear. Now we are going to square the picture a little bit. Not because I want to do it, but because this is how it is. What he has done is he has shown the optic radiation by two lines on this side also and this side also. Actually it is just to simplify matters. The whole optic radiation is divided into two distinct bundles. He has shown it just by two lines. Here is the actual bundle, shown diagrammatically here. Let's take a good look at that, digest that point. Optic radiation is not one fibre, it's millions of fibres spreading out like that. It's called radiation. So it is divided into two bundles. What is a medial group? Look at these set of fibres which are coming from the NGV. These fibres. These are the medial bundles of optic radiation. That is shown in a single line here and a single line here. Actually it's a bundle of millions of fibres. And this bundle is a little lateral to that. Just doing a little bit of weird loop here. That is a lateral bundle. I need you to look at that. So the whole optic radiation gets physiologically, anatomically and functionally divided into two bundles. They are all spread out equally, but for descriptive purposes they are divided into a lateral bundle and a medial bundle. Clear this much? Now I need something from you. If the whole optic radiation is serving the same half of both the retinae. Once you divide this optic radiation into two equal bundles. Let's say 1 million fibres in the medial bundle and 1 million fibres in the lateral bundle. What will this serve? Which part of the retina will it serve? Let's take the left optic radiation. That is shown in red. Wonderful. Exactly. Because now what happens is the optic radiation is divided into two halves. That means now each component of the retina is serving one fourth of the retina, yes or no? It will get this point. I want this from you. Each component, each bundle of the optic radiation, medial and lateral, will serve one fourth of each retina, corresponding retina. Are we clear this much? Because the whole optic radiation is serving half of each retina. So when you divide half of half what happens? You may want to correct. I need you to understand this very clearly because I am going to start with the medical provisions right now. So before I start discussing the optic radiation to you. The medial bundle shown here is serving one fourth of the same retina on both the sides. And the lateral bundle is serving one fourth of the same retina on the retina on the same side. And by same thing for this side also, the medial bundle is serving one fourth of the retina on the corresponding side. Both the eyes and the lateral bundle is being the same thing. Now comes the question, which one will serve the upper portion of the retina or which one will serve the lower portion? And I am going to come to that right now. Do you understand that each component of the optic radiation serves one fourth of each retina? Do you understand this much? Absolutely, no ambiguity. Okay, now let's take the medial component. The medial component is a simpler one. That's why we are starting with it first. The medial component is the single eye here. It actually refers to this whole millions of fibres going medial. The medial component is because it's situated more medial, that's all. The medial component. This carries fibres from the upper quadrant of both the retina. So this bundle, this is the left optic radiation medial component, right? This is receiving fibres from the left upper quadrant of the left retina and the left upper quadrant of the right retina, are we there? Yes. So this is receiving fibres from the upper quadrant of both the retinas, same side. So much so far, so good. The medial component, it goes straight back through the parietal lobe which I have shown in the next picture, the medial component. It goes straight back from the LGB through the parietal lobe, mind you, you are saying parietal lobe is not on the cortex, it is deep inside, it's white matter. It goes straight back through the parietal lobe and reaches the occipital lobe. Now go back to the chapter on occipital lobe. We have said that the occipital lobe is divided by a calcarine sulcus, yes? Which divides the occipital lobe into a superior and an inferior bank. What name did we give the superior bank? The Curious Guides. And the inferior bank we named it as? Lameball Guides, wonderful. So this medial bundle, it goes straight back through the parietal lobe, the medial bundle goes straight back through the parietal lobe and ends in the Curious Guiders. So now tell me, each Curious Guiders serves which, what will be the retina, we have already done this in the cortex chapter. Lower. Gotcha, gotcha. I've got the retina, not the visual retina. Each Curious Guiders serves the upper quadrants of each retina on the same side, yes? Because it is receiving the medial bundle. You see, this is what is called retinotopic projection. Everything is going systematically. This is very important to understand. So this is the medial bundle. Now let's take the lateral bundle, the lateral component. This is a little more tricky. The lateral bundle, it is shown diagrammatically here. It is shown as this. The lateral bundle goes, does not go straight back. Instead, it makes a forward bend towards the temporal lobe. In fact, into the temporal lobe, of course, deep inside the temporal lobe, you can see it's making a forward bend into the temporal lobe. The fibers from the LGBT are going into the temporal lobe. They enter the temporal lobe, get deep inside, and then they move back. They travel through the temporal lobe, deep inside. Temporal lobe, as you know, is already lower down. This is the temporal lobe. So the fibers go towards the temporal lobe and then they come back. The previous one went through the parietal lobe. This one goes through the temporal lobe. And where will it reach? It reaches the lateral lobe. This forward bend is called, it makes a curve. It's called the mayor's loop. So now let me give you a nice sweep into the memory. The lateral bundle receives fibers from the lower quadrants of the same size of both retinae, forms the mayor's loop, and goes to the lingual diners, all L, L, L, L. The lateral bundle receives fibers from the lower quadrant, forms the mayor's loop, and goes to the lower bank, another L, which is the lingual diners. This is all marked in red, blue, blue here for you. So each lingual diners serves which quadrant of retinae? If you understand it, everything's going to be plain as daylight. Each lingual diners serves the lower quadrants of both the retinae. Yes? Now I'm going to do something more which you have already answered. I'm going to show you the projection of each retina of the visual peak, which I'm going to do in the next slide. But right now I need you to understand this. So this portion, this whole optic radiation together travels in a portion of the white matter, which is known as the retrolenticular part of the internal capsule. Let me go back a few slides to show you which is this retrol. This is a picture of the internal capsule, natural in genome Australian. This is the quartet nucleus, this is the thalamus, this is the lentiform nucleus. How do you know about this? You all know this. You can see the lateral geniculate body. The fibers are going like this. This is behind the lenticular nucleus, that's what it's called, the retrolenticular part of the internal capsule. And they travel by the optic radiation, and they reach the skewness and the lingual fibers. The optic radiation in the parietal lobe and in the temporal lobe is supplied by NCA. When it reaches the occipital lobe, it is supplied by PCA. So optic radiation has again got dual supply. So because optic radiation, lesions and strokes are very common. So these are the few second points about the optic radiation. Now let's go and do, this is an actual dissection of the visual pathway, and you can see in an actual dissection also it looks pretty much the same. Can you see these mares loop fibers? The mares loop fibers going and going back, and this is the medial bundle, this is the lateral bundle. So this is an actual dissection. They would have spent maybe many weeks and months to do this dissection. So we have finished with the visual pathway. So I'm going to again quickly summarize retina, optic nerve, optic plasma, optic tract. Agility, optic radiation, medial bundle, lateral bundle. Give us guidance. We have to know every step of the pathway, because we have lesions at every level. Now let me show you the projection of the retina. This will be the visual field. First let me define a few terms for you. Many of these things you may know already. This visual field is defined as the sum total of the universe that we see with both our eyes open. So when we have both our eyes open, I can see this much. When I'm looking straight, this is what's impending on my visual field. There's a certain portion of the visual field where both the eyes visually overlap. So that portion is shown in this hatched area here. That is the binocular visual field. There's a little bit on this side and a little bit on this side. Those are the monocular visual fields of each eye respectively. So this is the monocular portion, this is the monocular portion. If you want to take each visual field separately, you'll find that one visual field is like this and one visual field is like this. What they've done is they've just separated them. An actual charting. This is what we do. We chart the visual field of each eye separately. So we chart the visual field of each eye separately. This is the visual field of the right eye. This is the visual field of the left eye. Here we do not cross our hands. So this is the one of the things we notice when we look at each monocular visual field. This is the binocular, but when we chart it, we chart each monocular visual field. What is the first thing we notice when we look at each monocular visual field? First of all, we notice that it is not a perfect circle. This is the temporal half of visual field. I'm not talking about the right eye now. The temporal portion of visual field is much more extensive than the nasal portion. Yes? I'm talking of the visual field. The temporal visual field is more extensive than the nasal. Why? Because the lateral orbital margin is more recessed. Here the medial orbital margin is more projecting by the virtue of the nose. That is the reason. Can anybody tell me why phylogenically the temporal visual field is more developmentally evolutionary wise? Just take an answer. No cross. When we go to Ramapithecus and Osteopithecus, yes, predators like the velocity vector always comes from the sides. Do you remember? Jurassic Park. They never come from the front, predators. Nature gave us a wider visual field on the temporal side. You can see the movement. This is the map of business. Look at the exact geometric center. What do you see here? Exact geometric center. This is the macular visual field. That is the area of maximum visual activity. When we look at an object clear straight, this is the macular visual field. This is the geometric center. It is not strictly geometric center but it is the geometric center of eye. We take a vertical line through that and we take a horizontal line through similarly on this side. That is how we divide the visual field into four quadrants as you can see there. What quadrant will you name this as? Visual field. Superior nasal, upper nasal, wonderful. What quadrant will you name this as? Lower temporal quadrant on the left visual field. What will you name this as? Lower temporal visual, temporal quadrant of the right visual field. So on and so forth. This is how we will divide. Let's continue with our story. If you look just 15, suppose I am the person and this is my visual field. Right eye, this is my visual field of my left eye. So this is my macular visual field. If I just look 15 degrees to the temporal side, if I just look 15 degrees to the temporal side, can you see a black dot here? What do you think that is? Wonderful. Wonderful. That is the physiological light spot. I am going to use that word spotom on just after this portion of the chapter. Spotom means a blind spot. And this represents the area where there is no rods and cones. So this is the place where we have a blind spot. Why is the blind spot the temporal part of the visual field? Can anybody tell me based on yesterday what we saw? I told you about the fundus yesterday. Why is the black spot the temporal part of the visual field? Okay, you are right, but let's not answer my question. When we describe the retina, remember we said that the physiological blind spot or the optic vis is situated nasal to the macular? Yes or no? If we say it is situated nasal to the macular, so if something is situated nasal to the macular, its prediction of the visual field is going to be diametrically opposite in step one. The reason is because the light from the world crosses like a pinhole camera at our people. So anything from the right goes to the left and vice versa. Anything from the temporal goes to the nasal and vice versa. And that is what I am going to tell you next in the next slide. So because the optic disk is situated nasal to the macular, its visual field representation will be in the temporal part of the visual field. Are we clear about this? So this is the optic disk, the blind spot. It is approximately 50 degrees from the center. 50 degrees temporal to the center. Okay. So now that we have understood the fundamental essentials, these are some of the things which again we will be repeating in FCM, in the second FCM, not in today's world. Now let me show you how the eye is represented, how the visual field is represented in each retina and how it continues through the optic track, optic radiation and so on and so forth. Take a look at this picture. This is the right eye, this is the left eye. Look at the color coding, orange, orange, blue, blue. He has done it with a specific purpose. This is the visual field. This portion is the binocular. This is the monocular of one side. This is the monocular of one side. Are we clear about this much? Look at the light rays crossing in the pupil. Look at the light rays crossing in the pupil. Light rays from the left, they are crossing and they're falling in the right half of this retina and they're falling in the right half of this retina. Yes? Likewise, the light rays from the blue portion, which is on the right side, is crossing at the pupil and falling on the left half of this retina and the left half of this retina. Yes? This is the pinhole effect. When there's a pinhole like the pupil, the light rays cross. I have a clear opposite. The same principle applies to the supine field quadrant also. Light rays from the top will go to the lower part of the retina and light rays from below will go to the upper part of the retina. This point also has to be remembered. So here he's showing only the right left. Now, when we were talking about the retina, we said that the optic nerve in the hyacinth, the nasal fibres cross. Yes? If you see carefully, you'll see that this is the nasal fibre blue from this retina. Yes? And from this retina, this is the orange. Can you see they're crossing? Why is this crossing done? It is again not random. It is done with a very specific purpose. Once the nasal fibres cross and they go to the optic tract, the temporal fibres don't cross. Yes? So the temporal fibres, which is shown in blue here, remains on the same side and the temporal fibres from here, which is shown in orange, did not cross. So the nasal fibres crossed. The temporal fibres did not cross. Once they read the optic tract, now do you see the color coding has become uniform? The left optic tract now is carrying only the blue fibres and the right optic tract is carrying only the orange fibres. Did you notice that? So what does it mean? It means that the left optic tract, which I said at the beginning of this class, receives fibres from the left half of the left retina and the left half of the right retina. I think that's exactly what we said, right? Likewise, the right optic tract, it receives fibres from the right half of the right retina and the right half of the left retina. Makes sense? Now project the optic tract to the visual field. Project the optic tract to the visual field. First you have understood which tract, each tract receives fibres from which part? If the left optic tract, blue, receives fibres from the left half of the retina, what is the visual field of the left half of each retina? Right, right of each, yes? So let's point down to the next simple level. Each optic tract serves the opposite half of the visual field of both eyes, yes? Are we clear? Same thing applies to the right side. Look at the orange. Orange is receiving fibres from the right, right half of both retina. So right half of both retina receives, serves which visual field? The left half of both the visual fields. So each right optic tract serves the left half of the visual field of both the eyes. So far so good? Because I'm going to exactly build up on the same field when I start with the illegal portion. Let's continue now from the optic tract of the LGB. Same thing works. LGB also receives fibres from the same half of both the retina. So therefore, each LGB is serving the opposite half of the visual fields of both the eyes, yes? Yes, because each optic tract serves the LGB. Then from the LGB, we have the optic radiation. Suppose I would consider the optic radiation as a whole bundle, without dividing it to medium and lateral. Each optic radiation as shown by this will serve which part of the visual field? Just extrapolate and tell me. Each optic radiation, it serves the opposite half of the visual field of both the eyes, yes or no? So left optic radiation has a whole, let's say 2 million fibres, whatever number you want to go. It's serving the right half of the visual fields of both the eyes, which is receiving fibres from the left half of the retina, which is serving the opposite half of the visual field. Did we get this point absolutely clear? Once you have understood it, there's nothing to read any further. Now you can go straight to the regular part. Now what we did, we took the optic radiation, because we are serious, we broke it up into 2 bundles, into a medial bundle and a lateral bundle. And what did we say about the medial bundle carrying? We said the medial bundle was carrying fibres from the upper quadrant of the same side retina of both the eyes, yes? So if the medial bundle is carrying fibres from the upper quadrant of the same side of both the retina, which visual field will it serve? So make it more precise. It will serve the opposite side, lower quadrants of both the visual fields. Are we clear? And what did we say about the lateral bundle? The medial loop, it received fibres from the same side, lower quadrant of each retina, yes? So which visual field will it serve? Upper temporal quadrant, upper quadrant of the opposite side of both the visual fields. Clear? Let's continue now. The visual optic radiation ended in the occipital cortex. Let's consider the whole occipital cortex, irrespective of cuneous gyrus and lingual gyrus. Each occipital cortex serves which visual field? We mentioned this in the occipital cortex chapter. I just narrowed it down straight to the simplest form when we were talking about the occipital cortex. We said each occipital cortex serves the opposite half of the visual fields of both the eyes. Now you can extrapolate it in terms of the visual pathway. Now again we will break it down. Because the medial bundle goes to the cuneous gyrus and the lateral bundle goes to the lingual gyrus. So each cuneous gyrus serves which part of the visual field? Opposite? Lower quadrant of both the visual fields. And each lingual gyrus serves the upper quadrant of the visual fields of both the eye. Are we clear? Absolutely about this. Once you've understood this, you are good to go. This is a wonderful diagram called optic k-link where he has given in a color-coded fashion the visual field in a three-dimensional imaginary way and he has given multiple color-coded lines how each part of the visual field projects to each part of the retina and how the fibres cross and all the NGV, blah, blah, blah, and each of the visual cortex. I mean, if you want to look at it, you'll find that it's a little enhanced but I think all of you have really understood it. This is something we need to understand. You can use yourself but don't spend too much time. Now let's come to the last part of this chapter and then we'll start the clinicals. So we have finished with the visual part and its direction, the visual field, et cetera. Now the remaining part of this chapter is equally, if not more important, the various visual reflexes. I think we have been talking about visual reflexes right in the slide called chapter level. Now we are going to go to the depths of several reflexes out of which three of them we will go in detail and the other two we will mention in passing. Before that, you have to have a very thorough understanding of the autonomic supply of the eye. That's why I put this picture, this picture, this picture here. So we will cover it again in CN3. In simple terms, what is the sympathetic supply of the eye ratio? Sympathetic supply? Is all this analogy an attribute for you? So it produces the pleural dilatation, medriasis. Sympathetic supply comes from the superior cervical ganglion. We will mention this again in detail when we come to the autonomic nervous system. Superior cervical ganglion supplies the dilator of your blade in the iris and causes dilatation. Superior cervical in axonal, alpha-1 receptors, you don't know that yet. Parasympathetic. Where does it come from? You will know this. CN3, okay. Remember, an eddinger with small nucleus in the midbrain, which we said of the parasympathetic component of CN3, eddinger with small nucleus is shown here. Eddinger with small nucleus gives the parasympathetic component, which is coming out with CN3. CN3 is coming from the front of the midbrain. Remember the two red arrows in your exam? It's coming out from the front of the... It's traveling with the CN3. It synapses in the c-ganglion. Post-ganglionic fibres then go and supply the sphincter pupae. Sphincter pupae is the inner one. The dilator pupae is the outer one. It supplies muscarinic receptors. What's this? Puberty constriction for myosis. Are we clear? Parasympathetic. Puberty constriction. Sympathetic. Puberty dilatation. Constriction is called myosis. Dilatation is called matriasis. So this is in simple terms. The sympathetic and parasympathetic... All the visual effects will be dependent on these two concepts. Okay, now let's go to the nuts and bolts. The ones shown in blue are the ones which we need to go in great detail. Let's just name them first and then we'll take one by one. The pupillary or the light reflex. The coagulation of the near response. The corneal or the blink reflex. And the pupillary skin reflex. These are the ones we will take next. So let's start with the first one. The pupillary or the light reflex. First, what are the components of this reflex? What is this reflex? Because you will be doing this in XK and you will be asked questions on this. It's the most frequently tested procedure in any patient who comes to you. When I shine a torch like in any one eye, the pupils on that side constrict and the pupil of the opposite eye also constrict. The constriction of the pupil of the same side is called direct clear right light reflex and the constriction of the pupil of the opposite side is called consensual light reflex. Are we clear? In the exact trust, believe me, when they write this word, when the doctor showed a light, there was no consensual response, but there was a direct response. So you have to understand. That means the opposite side did not react, but this side reacted. That's what they're trying to say. So these are the components of the light reflex. Also called the pupillary reflex of the light reflex. Now let's take a look at the pathway. It is called the retinome mesenchyslite pathway. We will make it simple. This may look a little dense for you. I'm going to make it simple. This picture relates to this. Okay, let me apologize for this slide. I've added one picture, which is not very early. I know you were going to write to jump at me because I realized that I need to tell you something. So I just clicked it a little bit just this morning. That's how we thought of it. So the initial part of the pathway is the same. Retina, optic nerve, optic plasma, optic tract. So for some reason, yesterday when I was talking about optic tract, I said 90% of the fibres go to the LGVS. I said a small percent of fibres do not go to the LGVS. I moved somewhere else, remember? I said that. I said one of them, where they go, is pre-technical nucleus. Another one, we said three other places. We will not talk about that. Some of the fibres do not go to the LGVS. They instead branch off to the pre-technical nucleus. And where was the pre-technical nucleus located? You will read the brainstorm. It is located in the mid-grade just adjacent to the superior colliculus. So this is the superior colliculus. So superior colliculus nucleus just adjacent to that is the pre-technical nucleus. And that is shown diagrammatically here. That is shown diagrammatically here. So they instead, from the optic tract, they branch off. They go to the pre-technical nucleus. It is shown in a very diagrammatic fashion here. CN2 going to the pre-technical nucleus. Here this happens. This tract, this portion is called the retino mesenchilic tract. Because it is going from retina to the mesenchilic tract. And this segment, which goes to the pre-technical nucleus, this segment is the superior brachium. The brachium of the superior colliculus, which you mentioned in the brainstorm. This is the reason why you have to keep going back and forth between brainstorms because we are using these terms which are not new to you. But you must refresh your memory, what I mean. So there is the pre-technical nucleus. Now something happens in the pre-technical nucleus. The pre-technical nucleus sends criss-crossing fibres to both the sides, Edinger-Vespaul nucleus. Just now my good Edinger-Vespaul nucleus is the parasympathetic nucleus of CN3. So this pre-technical nucleus, this is easier to understand. That is why I am using this picture. The same thing is shown there also. Each pre-technical nucleus sends to this side, parasympathetic, and sends to the same side. The opposite side also sends here and here. So at one place, the fibres are crossing. Yes or no? And you have to know that. The place where the fibres are crossing. That is called, anybody? Posterior Commissure. That is the reason I put this picture because I wanted to show you the posterior commissure. It was covered when we were doing the white matter of the cerebral cortex. Remember? This is the posterior commissure. It is located under the pedial gland. Is it ring a bell? The posterior commissure is located just under the pedial gland just above the superior migraines. That is the reason I put this picture. So this is the posterior commissure. Diagrammatically, this is the posterior commissure actually. So the crossing fibres crossing the posterior commissure. Why do they have to cross? Let me say just now that if I have to shine a torsion in your right eye, both your eyes should constrict. So to get this consensual response, you need to cross all the fibres. Make sense? Once the fibres are synapsed in the, from the prejective to the eddinger vespal, the post, the pre-ganionic fibres, from the paracenter to the gluteus, they travel with CN3, as we mentioned just a little while back, and they connect to the ciliary gangion, which I showed you in the previous, the synapse to the ciliary gangion, and the short ciliary nerves. Short ciliary nerves carry the post-ganionic fibres through the sphincter replay of both eyes. So therefore, in a nutshell, afferent is CN2 and efferent is bilateral CN3. I need you to understand this point. This is a brainstem reflex. Unlike the spinal reflex, this is the brainstem reflex, and the best way to do it is, we will make hydrometric representation. So there also. Afferent is CN2, and efferent is bilateral CN3. Why am I saying this? Safety of life to this side also. If I shine a torchlight here, afferent will be CN2, bilateral CN3. Because in the clinical portion of this chapter, we are going to create agents. I'm telling you now itself, if I shine a torchlight in this eye, and I find that the person's, this eye is not responding, this is responding. That's what I mean by saying that when you shine a torchlight, in almost right eye, there was no consensual response. That's all I'll say. I won't say anything more. Where is the relation? I'll say it. I shine a torchlight in the right eye, and there was no consensual response. That's all I'll say. Where is the relation? A, B, C, D, D. Just look at that formula. I shine a torchlight in the right eye, there was no consensual response. That means there's a CN3 paralysis on the left side. I showed a torchlight on the right side, and there was only a consensual response. CN3 on the same side. I shine a torchlight on the right eye, and there was no direct or consensual response. Same side, CN2. Make sense? You see? You apply this formula, things become like, you know, clear and great daylight. This is how you will be given questions. And that's exactly what you do most. It's not a theoretical situation. This is what we do. So this is the futile light reflex, that is consensual at this point here. Now, let's go back. What happens in the penial gland enlarges? I'm repeating something which you know already. When this penial gland enlarges, what does it do? It compresses on the posterior commission. When it compresses on the posterior commission, which is this here, what does it do? It knocks off the futile light reflex of both the sides. Remember, we had Ardell Robertson Pupil? Where a commutation reaction was present, which I'm going to mention in the next slide, but there was no ERP, a commutation reaction present. Pupillary reaction absent. Now, do you know how it works? Because it consists and knocked out the posterior commission. Therefore, there was no futile light reaction. Are we here on either side? Make sense? Let's take the exact physiological opposite. Did we consider something called cortical blindness when we were doing the occipital cortex? We call it ankle syndrome, top of the basilar syndrome. What did we say about cortical blindness? We said that the person is blind. He cannot see, but he confibrillates, but he's not aware that he's blind. He's blind, but he's not aware. However, if you shine a torchlight, you find that people are reacting. So it's an exact opposite situation. Yes or no? What happens? Because he is due to the reacting because his retinome isn't your flake pathway. His retinome isn't your flake pathway. He's intact. Therefore, this futile reaction is present. But his occipital cortex is not functioning. Therefore, he cannot see. Make sense? Because the retinome isn't your flake pathway. It did not go to the occipital cortex. From the optic trachea branched off into the mid-brain. If we understand this, you'll understand the basis of why we are talking about these things. So even if a person has got occipital infarction, so-called cortical blindness, he may not be able to see yet surprisingly when you shine a torchlight, you find all these people are intact. That indicates that his retinome isn't your flake pathway is fine. The occipital cortex may have gone. Did you understand this? And that is what is mentioned here. So try to understand the ramifications. All of these are understanding. Now let's come to the next reflex. The combination reflex, which is also equally important because then you'll be doing this in your FCM and it'll be just in your own sense. What are the components of this combination reflex? Three components. It's all mentioned here. It's also about the neural response. When I'm looking at an object at a distance which is coming closer and closer to my face, what, five or seven, eight centimeters or 10 centimeters, or you try to look at the tip of your nose. This is for the final sake of it. What are the three things which happen to your eyes? Two things you can see from outside. One thing you cannot see from outside. But three things happen. Both eyes converge. Wonderful. Next. Both the pupils constrict. Wonderful. Next component. That's a third thing which happens because you can't see what it happens. Yes, yes, yes. Wonderful. The lens increases its curvature and increases its refractive index. Why does it have to do that? Because now the object is very close. If it does not increase its refractive index, the light will fall behind my head. So you want to converge the light rays even more, right? How do you make it converge? Go back to your physics. Why increase the refractive index of the lens? Primarily, both are... So that the light rays will converge more and follow my retina. But this you can't see from outside, but it happens. Something you will have to make it happen. So these are the three components of the conditional response or the near response. Clear? Now let's look at the pathway. This pathway is called... The previous pathway we call it retino-mesant Catholic. Remember? This pathway is called the occipitomisant Catholic. So you already get something. This pathway involves something from the occipital cortex to the mid-brain. And that's why I show you in the form of a simple line diagram. So let's take a little more. Again, I'm trying to make it very simple. The first part of the pathway is the same as the visual pathway. That means everything. Retina, optic nerve, optic chiasma, full optic tract, lgb, optic radiation, occipital cortex. So this pathway is called the occipitomisant Catholic. The occipital cortex. Full. Same. So no repetition. The next part of the pathway. From the occipital cortex, fibres go to the frontal eye field. Does it ring a bell? Where was the frontal eye field? Frontal eye field goes in. Don't they radiate a little from the virus? Yes. Remember? The one which is responsible for turning both eyes to the opposite side. So fibres from the occipital they go to the frontal eye field on the same side of the frontal eye field on the same side. The story is not over yet. From the frontal eye field, fibres descend down through the internal capsule, through the middle. And that is what is shown here. And shown here. This is the corticotectal path. Cortics to the tecton, tecton is mid-brain. To be aware of this. From the mid-brain, it goes to the special nucleus in the motor nucleus of CN3. We have named it. But we are doing the free step. We call it the convergent center for the nucleus of earlier. Do we remember? So it goes to the convergent center for the nucleus of earlier. And what does this do? It activates the medial rectus of both the eyes. So both the eyes are convergent. Makes sense? The first problem is over. So it goes to the convergent center, nucleus of earlier. The medial convergences. Convergences done. But everything is happening in seven agency, but we are describing it separately. What are the other two components which were remaining? Fibers go to the edgier-vescal nucleus just like the previous. And goes to CN3. And goes to the constrictor nucleus. Same. One more component is remaining. Which one was that? Fibers also from the edgier-vescal nucleus go to another muscle. Celiadase muscle. It goes to the celiadase muscle. And once the celiadase muscle contracts, we need these components. So you've got all three components. We discuss this separately, but they all happen simultaneously. Convergence, sphincter pupillain, constriction of the peoples, and celiadase muscle. So our portion of the edgier-vescal nucleus supplies the sphincter pupillain, lower portion of the edgier-vescal nucleus applies to the celiadase muscle. You've got all the components. So this is the oxypitome-miscephalic pathway. In the clinical portion of the chapter, we will see a series of conditions which are known as light, near dissociation. Right now I'm just going to define it for you, but I'm going to use the storm-day draw. But before I describe it for you, you tell me what do you understand that this behavior is called? Light, near dissociation. Light, near dissociation. Does it mean something? Something has been dissociated from something. This, okay, let me define it for you. I'm going to use it very quickly. There are many components of this idea. Light, near dissociation means the person has got accommodation near response, but person does not have light response. That means there is a dissociation. Person's eye is responding to accommodation, but the person's eye is not responding to light, and you already know what's the condition. Argyle draw-persons. Argyle draw-persons pupill is one example of light, near dissociation. Where eye is responding to the accommodation, but is not responding to the light. We will see a series of these conditions. All of them are collectively clubbed under this heading called light, near dissociation. You see, these terms are all dependent on these pathways. So this is the second important reflex that we need to let me complete this. Just a few more slides and we'll take our break. The corneal or the plate reflex. Again, this is the break-step reflex. And again, it was the same principle which I mentioned there. First, what are the components of the reflex? Who shall I use? Like in a picture, I'll use you. The light near response, the corneal of the plate reflex is either, actually it is mentioned in your FCM lab, but we mention it to tell you not to do it. With the risk of corneal, the other person will look up inside and from the lateral aspect, you touch. Just lightly touch the corneal. You're not asked to do it because you will produce corneal abrasion. Even if you try to do it, that side I will blink and the opposite I will also blink. So this is also a reflex. Same side I will blink and the opposite I will also essentially protect your fingers. So let's look at the pathway. It's not as complicated, but again there will be some crossing over of fibers because both sides. Afrent. Afrent. C and V1. Afrent going through C and V1. Which nucleus? This question was one of those which I identified many of you. Spinal nucleus of trigeminal. You touched a tube of cold water on the face. Which nucleus was the question and 25%? Spinal nucleus of trigeminal receives pain, temperature and light touch from the cornea. Spinal nucleus of trigeminal. In the video also I said you must know all the names of the nucleus of trigeminal. So it goes to the spinal nucleus of trigeminal which is shown here. It's a long nucleus. Goes to the spinal nucleus of trigeminal. Upper portion receives lightness from the cornea. The lower portion receives pain and temperature from the face. From the spinal nucleus of trigeminal by means of internal shell fibers, axons, which go through the medial longitudinal fasciculus. This is shown just by means of one line here. It is shown here a little more extensively. It goes through both the sides. CN7 motor nucleus. CN5 spinal nucleus of trigeminal is in the bonds. And both the motor nuclei of CN7 are in the bonds. And that is why he has shown the crystal in the bonds here. Remember they make very little bonds. They go through both the same CN7. CN7, it turns, senses motor fibers out. So the more we will raise the muscle of both the sides and cause a good thing. So again, let's look at the same principle. And again, we will be asked questions. So let me just change this to CN5, CN7, CN7. What are your big reflexes? Affrent is CN5. Affrent is both like CN7. Now, again, answer my question. I tried to touch his left cornea. And there was no consensual response. What is the, where is the side of the region? I'm giving you all the questions which are asked in the shelf, in the DNA and blocks. I touched his left cornea and there was no consensual response. CN7 on the right side is gone. I touched his left cornea and there was no direct or consensual response. CN5 on the left side. So you see I'm going to give multiple options. CN5 on the left, CN5 on the right, CN5 on the right, CN7 on the left, CN7 on the right. When you look at those options, you get autopsied. Don't even look at the options. Just read the question. Think of the answer. Go straight to the answer and take it and get out. That is how you do it. Just read the question. Think of the answer. Go straight to the answer and take it and get out. That is how you answer. When you know the stuff and you look at the options, because I'm a tricky guy. You know that, isn't it? So go straight to the answer. So this is how you answer the questions. And it's all mentioned there. This is also a very useful reflex which is done in unconscious patients. You want to see whether the person is unconscious and you want to determine whether there's any lesion of the brainstem or not. Because patients are not able to tell you if it's an unconscious. So this test is done here. And you find this responding. That means this brainstem is in there. Because this is happening in the brainstem. So this is the clinical use of this. So these brainstem reflexes are used. Mind you, these brainstem reflexes are different from spinal reflexes. Spinal reflexes are monosynaptic reflexes. Only one synapse. Here there are two synapses. First it goes to one nucleus. Then it goes to another nucleus. So there's an afferent nucleus. There's an efferent nucleus. Are we clear? So there's an afferent nucleus, which is in this case, spinal nucleus, and there's an efferent nucleus, which is the CN7 motor nucleus. The previous one also. There was an afferent nucleus. The pre-technal nucleus. And the efferent nucleus was the eddy nervous spinal nucleus. Okay, you're asking something. Yes? What did you say? Okay, so... Yes, if there's no direct line, that means the CN5 didn't even take the afferent. Right? And if there's no direct response, but there's a consensual response, what's the answer? If there's an eye-touch, there was no direct response, but there was a consensual response. What does it mean? CN7. CN7. That makes sense. So if you look at this formula, things become much easier. Okay. Serious spinal reflex. I'm not going to do the details now, but it's an important reflex. All I'll tell you is that the serous spinal reflex is, suppose somebody wears a new shirt, and what do you do to that person? You pinch the person's back here, isn't it? You pinch. When you do that, what happens to the person? This person is very sensitive, by the way. He's very sensitive. So it looks like you're already being the victim of it. So when you pinch somebody painfully, the pupil's dying. This is called the pupillary skin reflex. Next time you go to try it out, you can go home and try it out with each other. That is called the pupillary skin reflex. It's also called the serous spinal reflex. I'm not going to do the details now because I'm going to describe this whole thing in much more detail in the autonomic nervous system chapter. As part of the Horner syndrome. In Horner syndrome, we will describe the full pathway. That's why I'm not going to describe it now. But I told you what is the reflex. And in Horner syndrome, this reflex is gone. So this is the director's response. Finally, the last one. The various body reflexes. I've just broken them up into different components, but I'm just going to name them. The first one is the visual body reflex. What is an example of a visual body reflex? Somebody gives you? That was a visual body reflex. When you see something, you give a response. Because she saw something and she responded, isn't it? It can also be something very benign. Like you're holding a newspaper. That's supposed to have a visual body reflex. So these are some examples. What is the afferent? Afferent is the retinotectal tract. To the superior molecules, not to the pre-tectal nucleus. And the efferent is retinotectal tract and the efferent is tectospinal and tectobarbore. Retinotectal tract to the superior molecules. Go back to superior molecules. What did we say it is concerned with? Visual body reflex and spinal reflex. So retinotectal, retinotectal and tectospinal and tectobarbore. It goes to many muscles. It goes to muscles in the body. It goes to muscles in the head. That's why we call it tectospinal and tectobarbore. So which part of the body are moving? Next one. Spinal visual reflexes. You get something... Oh my God, this is a cockroach there. So something tickled you and you jumped. So that was your spinal visual reflex. Something stimulated you. So the first part of the performance was the spinal tectospinal tract. Which we already seen. Just in passing. And the efferent component is the tectospinal tract. Spinal tectospinal. And the third component is the audio visual reflex. You hear a sound, you turn that way. So fibers from the optic tract go to the meteorological body. And fibers from the peak period and superior college will stay connected to each other. So called lightning and thunder reflex. So this is the audio visual. So these are all the lesser important ones. We just rename the names of the reflexes. Now we take a break. And in the same game, we start with the clinical portion of the chapter. And you'll find that they're going to go exactly the same way. First part of the chapter will be all the visual fluctuations. And the next part of the chapter will be the visual reflex. Yes.