Neurology | Optic Nerve | Cranial Nerve II: Visual Pathway and Lesions – Transcript

00:07hi Ninja nerds in this video we're going to talk about specifically the visual pathway so we're going to take how the light hits the retina and we're going to take it through the optic nerve and all the other different process if you guys have already watched our video on the photo transduction Cascade that's going to be very very important that you do that before we get into this visual pathway because we already talked about exactly how those light rays got converted into chemical changes and then electrical changes and how they went down the axons of the gangling cells which basically made up the optic nerve

00:34all right so now we're going to have two eyeballs right this is the we're going to say this is the left eyeball and this is the right eyeball okay now first things first what I want us to try to imagine here we're going to put a lot of different concepts together when you guys are looking you

00:59guys are like looking at anything around you we H our eyes are so amazing that they can pick up different types of visual Fields so for example this is the right visual field or the right eyes visual field and this is the left eyes visual field okay so what is this one right here this is the right eyes visual

01:25field and this one over here is the left eyes visual field okay now within the visual field you have two different components of this visual field we're going to say this is the nasal so since your you'd have your Honker right there pretend this is your nose Okay so pretend this structure here is your nose Okay since this is the nose these two structures

01:52that are near the nasal region this is the nasal component of the visual field all right so this is the nasal comp opponent of the visual field and then this one over here would be near the temple so this is the temporal component of the visual field and this over here is going to be the temporal component of the visual field okay now to make it easy though now that

02:20we know that this is what it is it's nasal and the temporals these words are going to get interchanged a lot so I do not want to confuse you guys so what I'm going to do is for this sake of it is I'm going to switch nasal and since this is the right visual field this is what gets confusing the right visual field has a left visual field and a right visual field okay so the right eye has a left visual field

02:47and a right visual field so we're going to say this is the left visual field and this is the right visual field okay so I just want to make it as simple as I possibly can here this whole right eye is going to have two Fields it's going to have the right visual field and left visual field same thing this left eye is going to have two visual Fields it's going to have

03:12a left visual field and a right visual field okay simple as that now we're going to be able to kind of do this a lot easier now so instead of using the words nasal and temporal but understand those words because it's going to be important in lesions okay let's say first off when we're looking out let's say that this part of the retina there's two parts of the retina so this is the right eye this

03:39part of the retina is closest to the temple or the right Temple right so we're going to call this part of the retina we're going to call this the temporal Hemi retina okay that's a temporal hemir retina now here's what gets really funky the

04:03temporal hemir retina is receiving light rays from the left visual field okay so from here this part here this left visual field is hitting this part of the retina okay so if light rays from the left visual field are hitting this part of the retina the temporal H retina but

04:28then the the what is this one this one is close to the actual nose so since it's close to the nose this is called the nasal right Hemi retina this is called the nasal hemir retina and this is called the temporal hemir retina the nasal hemir retina is receiving light from the right visual field so the nasal hem

04:55retina is getting hit with light from the right visual field all right so just to make sure we're clear left visual field hits the temporal hemir retina and the right visual field hits the nasal hemir retina sweet deal same thing would happen up here what would this one be this one right here would be the temporal hemir retina I'm going to put HR here and this right up here is going to

05:20be the nasal hemir retina okay and same thing nasal hemir retina is going to be receiving visual field from left visual field so it's going to be getting it from the left visual field and then the temporal hemir retina on the left eyeball is going to be receiving it from the right visual field okay now that we're done with that what happens with these fibers here's

05:47what I want you to remember anything from the right goes to the left anything with a left goes to the right that's it anything that's coming from the left okay well this temporal hemir retin this is on the right eyeball okay so this is the right eyeball it's picking up information from the left visual field well anything from the left has to go to the right oh so these should stay on the same side then so

06:14these fibers right here they should not go and cross over to the other side they should stay on the same side so they're going to come down the optic nerve and you know what happens the two optic nerves actually come together they come together and form this big old structure that you kind of see right here I'm actually not going to do it in brown here because I'm going to use this brown a lot I'm just going to say here that this point here where the two optic nerves are connected all of this part right here this whole thing is called

06:42the optic kiasma and the optic Asma is where the right optic nerve and the left optic nerve come together right near the pituitary gland so this is right near the pituitary gland okay now what happens here the fibers from the temporal hemiretina which is receiving it from the left visual field we said anything from the left visual field will go to the right eye okay so this is

07:09going to cross I mean it's not going to cross it's going to stay on the same side so it's going to come down the right optic nerve where the optic Asma is it's not going to cross it's going to stay on the same side and it's going to move down this structure right here which is called the optic tract and we're going to stop right there okay so what is this structure right here this long tube likee structure here this whole tube like structure here is called the optic tract so this would be the right optic tract what do you think this one

07:36is this is the left optic tract and this is the optic Asma okay now let's follow this nasal hemor retina well the nasal hemor retina is receiving information from the right visual field well anything from the right goes to the left so this has got a cross so these fibers from the nasal hemir retina it's going to come through the optic nerve the right optic nerve

08:02and it's going to cross at the optic Asma and go over here to the opposite side it's going to come over to what optic tract it's going to come over here to the left optic tract and it's going to come right to there and that's what we'll stop at that point okay now that we understand this this should be a lot easier now let's do this one nasal Hema is receiving what it's getting hit from the left visual field well if it's receiving information from the left

08:30visual field anything from the left has to go to the right oh okay well this is on the left that means it has to cross over here so it'll come down the left optic nerve but then instead of going on the same side it's going to cross over it's going to become contralateral right and these fibers are going to come over here and they're going to move all the way over here on this side and come right there okay so all the things that are

08:58coming from the left visual ual field on the left nasal hemir Rey is going to be coming from the left visual field is going to be taking that information on the right optic tract and into this area that we're going to talk about in a second let's keep going temporal Hemy it's going to be receiving information from the right visual field right of the left eye so it's going to be receiving from the right visual field when anything from the right goes to the left we're already on the left side of the eye let's just keep it ipsilateral so these fibers here

09:26are going to come down the left optic nerve it's not going to cross at the optic chasma it's going to stay on the same side and move down the left optic tract and into this area right here okay so these are your fibers that are crossing and these are the ipsilateral fibers so what are these fibers right here called these fiber here that are staying on the same side are your ipsilateral fibers these are the ipsilateral fibers and these fibers here that are

09:54crossing are called your contralateral fibers Mantra lateral fibers okay all right sweet deal now that we know that let's keep it bring let's keep bringing it to where we're going to go next so we already went from these Hemes from the visual fields we followed it down their optic nerves the optic Chasm we followed it down the optic tract we see the ipsilateral fibers and we know the contralateral fibers sweet deal what happens is from

10:20this optic tract it's going to come to a special area in the thalamus I'm actually zooming in on the specific nucleus on that Thalamus but let's say pretend here that I have I draw kind of like a little view of the thalamus it has kind of like this like piece like symbol a little bit and it kind of looks like this and what happens is it has a special nucleus coming off of it right it has a special

10:46nucleus coming off of it like this it's called the lateral geniculate nucleus what I'm doing is I'm taking the lateral geniculate nucleus and just zooming in on it okay so this right here is the thalamus but a special nucleus of the thalamus is called the lateral geniculate nucleus I'm taking the lateral geniculate nucleus and zooming in on it okay so that we're clear so this is a latog geniculate

11:09nucleus it has a total of six layers six layers so we'll layer this one 2 3 4 five six and then same thing over here one 2 3 4 five six why am I telling you this

11:32because any Ipsy lateral fibers go to two three and five layers so ipsilateral fibers within the lateral geniculate nucleus are going to go to layers two layers three and layers five so what does that leave for the Contra lateral the Contra lateral is left with going to 1 four and six so then the contralateral fibers will go to 1 4 and six

12:01okay so now it comes into this area right so I'm going to kind of make these different because obviously the same color but look here from this one this is the contralateral so this one is the controlateral fiber the contralateral Fiber goes to what 1 four and six so if I were to do it let's actually just make it a different color from this point so that we're not confusing this so now I'm going to come from this contralateral fiber it's going to be maroon it's going

12:25to give connections to four it's going to give connections to six and it's going to give connections to one then the Ipsy lateral fibers are going to go to two 3 and five okay and the same thing is going to happen over here let's say that I just for the sake of it I I do the same thing over here the ipsilateral fibers and the Contra lateral fibers over here so this one

12:52right here is the Contra lateral I'm going to keep the contralateral maroon contralateral goes to what it goes to six it goes goes to four and it goes to one Ipsy lateral fibers are going to go to two three and five now from this they're going to come out of the latog geniculate nucleus so these fibers are going to be coming out of the latog geniculate nucleus so they