in today's video with the help of the cadavers here in the lab we're going to take a look inside a real human eyeball as well as discuss how on Earth such a complex structure can even evolve in the first place it's going to be incredibly cool let's do this [Music] you are looking at a real human eye now the outermost layer of the eye is what's known as the fibrous layer or fibrous tunic and it's made up of the white which is more accurately known as the sclera as well as the cornea which we're going to be able to see much better from this cross-sectional view so I'm actually going to place this half to the side for now but as we're looking at this you can see that fibrous tunic there's the sclera the tough outer layer as it's connecting it's continuous with the cornea so this is the cornea that I'm poking with the probe here and then it's going to go back down and line up with the rest of the sclera and then they're going to go around and eventually in the back we meet the optic nerve so this is where all the neurons that are going to be heading towards the brain are going to be located now if we look at this red portion this red portion is what's known as the vascular tunic and it's just deep from superficial to deep right this is the outermost layer so this is the most superficial section of the eye because fibrous tunic then it goes vascular tunic which is where all the blood supply goes comes into the eye from and then the internal tunic is this film so if you look closely you're going to see this white film that's actually the internal tunic or the retina that's the that's the photoreceptive layer that all the rods and cones are going to be placed in although most of what you're seeing here would be just rods the cones are going to be more densely located in the back and what's known as the fovea although we won't be able to see that today but it's just cool to see that the eye is layered as most things are in within human anatomy but I'm going to go ahead and grab this other half again so we can see this structure here this is the lens now the lens actually broke a bit during the dissection process but that's okay but just know that this would be more solid this is just a crystalline network of proteins that will help further refract the light so what I can do is with my probe I can slide it between the cornea and this right here is actually the iris so if you look closely you might be able to see the iris which is actually two different muscles called the dilator and sphincter pupilly muscles and then there's a hole in the center of them called the pupil so when you see the black of the pupil you're actually looking into the eye and seeing the darkened pigment of the internal eye but in this space where my probe is there would be what's a humor called the aqueous humor and the aqueous humor helps provide nutrients to that cornea but light is going to go through that cornea be refracted through the aqueous humor go through the pupil which the dilator and sphincter pupilly muscles are going to be making wider or smaller depending on how much light needs to be let in and then the light is going to go towards this lens the lens will then refract it once again into this space now this space would normally be filled with another humor called the vitreous humor and the vitreous humor is going to be very jelly-like so upon the section you can like squeeze it out and that light is then going to go towards the back of the eye to that photoreceptive retina and again there's one small area that we can't really see in this dissection but it's called the fovea and the fovea is where all of the cones or at least the vast majority of your cones are going to be located in cones detect color the rest of the retina even though not all of the retina is actually visual are going to have rods in them and rods detect low light sensitivity so they're really kind of like black and white Vision more or less the retina is also going to have pigment cells in them and that's what gives a lot of the darkened aspect to the eye along with the vascular tunic and that's important because if the inside of the eye was bright like the the sclera light would just be bouncing around inside of the eye and it would be impossible to know where the light came from and you wouldn't see anything so you actually have to be able to absorb the light in order to see it when it act when it hits the proper photoreceptors but again all the rods and cones and all of the well it's not really the rods and cones they're going to be connecting to bipolar cells and ganglion cells and amicron cells but all the cells inside of the retina are then going to be sending their signals that are then going to go through that optic nerve and then just make their way to the optic chiasm and all the way to the back of the brain real quick I want to thank the sponsor today's video seed as long time viewers of this channel will know I am completely obsessed with the 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extremely easy to consume you just take a single capsule which is both your probiotic and Prebiotic twice daily and that's it it really doesn't get much easier than that if you're interested go ahead and click the link in the description below and use our code Anatomy for 25 off your first month's cds01 daily symbiotic plus free shipping I want to apologize right off the bat because I'm a terrible artist but what I'm attempting to show you here is the evolutionary progression from what's known as an eye spot all the way to what's known as a camera style eye which is what we have today so let's first Orient you as to what the colors are showing so you have a better understanding of what you're looking at but the Orange is what's known as a photoreceptive organelle and this photoreceptive organelle is able to detect the presence of light and it will then send a signal through the pink which is representing neurons or nerve fibers kind of depends on how you want to look at it and they're traveling through the black which is representing a microorganism at least at this point eventually this black is going to transition into the outer portion of an eyeball but at this very basic level you're essentially looking at a microorganism that has the ability to detect the presence of light and that's about it right but that's actually very useful because if you're able to determine that there is light or isn't light this is the beginnings of a circadian rhythm right this is what is throughout all of the animal kingdom and it's and it's extremely essential to a wide variety of bodily processes but this is still very basic right all you're able to say is do we have light or do we not have light that's why this next design is really really cool and I'll show you what the green means in a second but what's actually happening here is that photoreceptive organelle has now become what's known as a eye cup and this is going to actually help determine the direction that light is coming from and that's what the green is representing so let's say like a photon comes from this direction and hits this aspect of that photoreceptive organelle well then obviously you can determine that the light came from that direction and so all that's what all these other green lines are showing you but it's important to understand that this is a very broad understanding this is not very precise it's more like the light is coming from that direction or from that direction it's not like it's coming from there or there instead that's when we get to this one as you can see here the uh you know the outer aspect of the organism has created a really small aperture all right so we're really starting to get into this camera style eye and as you can see as that Photon now comes in here if it's able to make its way through this tiny Gap and hit this aspect of that photoreceptive layer which you know you might be able to consider this a retina at this point so I'll come back that in just a second but if you're able to hit this specific aspect you have a lot better of an understanding of where that light is actually coming from now the reason why I say like it's hard to know if this is a retina is because you know understanding the exact transition points from one structure to another is it's it's a very difficult thing to do inside of evolutionary biology in fact it's hard to even say when does this become an eye like we know it's an I spot but some say the eye cup can actually be considered the first I because you're able to to determine spatial information While others say no you need more complex structures to really be you know considered an eye so I mean it's just up for debate but regardless this is what's known as a pinhole by creating the pinhole we have much more Precision so we went from an eye spot to an eye cup to a pinhole and then we transition to this and what you'll notice is there is this dark blue line that is coming across this is the beginnings of a cornea the cornea is a refractory piece of tissue that is going to help bend light to get to specific areas on that retina but it's also important to understand that it's now also closed off the outer aspect of this I guess I at this point so if we quickly go back to here when there's no cornea you have to understand that this organism is in the water at this point which means this hollow cavity here is really a water filled cavity but by closing it off with a cornea now the body can create or the organism can create something called humor humor is a jelly-like substance that is going to assist in just how light is you know being transmitted and going throughout this photoreceptive structure so we're going to see that you actually have different kinds of humor in our eye but from there this is where we develop what's known as a lens and the lens is what's in Red so that again that dark blue is representing a basic cornea but now we have a lens this is another refractory piece of tissue and as you can see I've drawn some light that's coming in from this direction and what will happen is it is being bent by the cornea and the lens and being directed to a specific area in the back of the retina this is going to be extremely important especially when you consider just the diversity of rods and cones and just how there's really precise areas for vision but it's really cool to see that what's happening is now it's like cool we are going to bend a light you know it's not it's not just that we want light coming from directions we want to get light to a very specific spot really really cool but what you also can't see because again I'm a terrible artist is what's also in here is going to be the beginnings of what's known as the iris iris is a muscular tissue that's able to dilate and constrict and there's a hole in the center of the iris which is what we call a pupil by dilating it can let more light in by constricting it closes off more light so again now we're getting to very precise aperture here and when we go back to this one like here I mean this aperture this opening is really just created by the organism itself right the wall of the organism well I mean it's important to understand that this organism there they move they're fluid so it's not like this is set in stone but still it's pretty much going to be essentially the same size but now with an iris you're able to control how much light is getting in and out and then you bend it through the lens and the cornea and then last we get to our type of I which is known as a camera style and again you can actually start saying this is a camera style I but this is just a you know a better camera um so what's happened is the cornea is now much smaller so what's happening is you can see the corneum very broad here but now it's getting smaller it's also getting thicker it's going to actually have its own humor inside of it but then the lens has also become more ovular I'm not sure I did a great job representing this but here it's more circular now the lens is more oval shaped and again this is going to help just the Precision of refracting that light to get it to the back of the retina so you can see that the progression actually from an eye spot to a camera style lens is very logical and rational now some say that this is not possible through the evolutionary process that it's just too complex but what's fascinating is that scientists through the study of say like genetics proteinomics uh just overall microbiology studying cranial fossils of many different organisms have discovered that this entire process can happen in as little as 500 000 years which geologically Speaking is the blink of an eye so really really cool I often tell my students you'd be surprised with what nature can do when there are environmental pressures accompanying mutations thanks for watching everybody there are a ton of different topics we can discuss with the eyes so be sure to let us know in the comments below what you'd like to hear from us maybe it's amblyopia myopia retinal attachment nearsightedness farsightedness cataracts the list goes on and on so again just let us know what you'd be interested in seeing be sure to click the link in the description below and begin your seed Journey today and as always be sure to like obviously comment as we just discussed And subscribe if you feel so inclined and I'll see in the next video [Music] foreign [Music] [Music]