Special Senses | Pupillary Light & Accommodation Reflex

I ninja nerds in this video we're going to talk about the pupillary light reflex an accomodation life is important because when doctors you guys ever watch a TV show you see these guys running in the doctors basically shining light into their eyes and looking to see what type of responses they have that's important because it actually happens in real life what doctors are really looking for is a certain time there's actually kind of a little thing to help you guys remember we'll talk about throughout the course of this video but I'm going to write it down now it's called perla okay and this is some of the things that the doctors are actually looking for whenever they're doing the people are your light responds with actually shining light to someone's eye so what they're looking for is they're looking to see that the pupils are equal round and reactive to light so round reactive to light and that they can perform accommodation okay so these are the things that the people are looking for these doctors are looking for the pupils to be equal round reactive to light and I'm going to go accommodation we'll talk about all these things mean all right so what we're going to try to do in this video is we're going to say let's pretend I'm going to take a light and I'm going to shine it into someone's eye and let's say that this case right here you see how this right here if we're going to save this the right eye and we're going to say this is the left eye what I'm going to do is is I'm going to shine a light into the person's left eye and I want to see how their pupils respond to that so let's go ahead and do that so let me pretend here for just a second then I'm shining some light onto this person's eye okay so here's my my light all right don't make fun of it I'm shining light into this person's eye okay now how does this all happen well if you guys have already seen our video on visual fields and their actual lesions you guys will understand exactly how this whole pathway is working so if you guys remember we actually take this is the left visual field and this is the right visual field right of the right eye sorry this is the right eye this is the left eye this right here is the left visual field of the left eye this right here is the right visual field of left eye left visual field of the right eye right visual field of the right line if you remember there were two different types of retina here there was the nasal Hemme retina which is going to be on this side closest to the nasal the nose right there and then you're going to have one closer to the temple sides and this is going to be the temporal hemming right knee okay so same thing over here well would you have over here over here you're going to have the nasal him here at knee and over here you're going to have a temporal Hemi right knee okay what did we say happened here we said that light from the right visual field of the right eye is going to hit the nasal hemorrhage knee over the right eye right and then we said that be left visual field of the right eye is going to hit the temporal Hemi reading so what is this one here Tim poor L Hemi right any of the right eye this one over here is the temporal Hemi right knee of the left eye and this is d nasal hemorrhage knee of left eye so same thing here hits the temporal Hemi right knee left visual field of the right eye then same thing over here left visual field of the left eye is going to hit the nasal hemorrhage knee of the left eye and then the right visual field of the left eye is going to hit the temporal Hemi retina of the left eye right that's all it is that they're actually having these visual fields that we're able to process then what did we say we said anything that is coming from the left visual field has to go to the right side of the brain anything from the right visual field has to go to the left side of the brain simple as that where is this coming from okay this is coming from the left visual field so it has to go to the right side of the brain so since this is already on the right side we're going to keep it that so it's going to be if C lateral alright same thing over here okay this is going to be the right visual field the right visual field of the left eye so if it's white it has to go to the left well since it's already on the Left let's keep this on the same side or it's you lateral then what did we say anything again from the left visual field has to go to the right eye so what's going to happen this one well this is on the left eye this is going to have to go to the right bring so over here it's going to cross at the optic chiasma and then come down and easier contralateral fibers okay coming from the left eye but picking up information from the what left visual field of the left eye same thing here this is going to be picking up processing information from the right visual field of the right eye but anything from the right visual field has to go where to the left side of the brain so this is going to have to cross over here and this would be the contralateral flowers and if you guys remember what did we say we labeled this right we said that this structure here was called B it was a specific nucleus a specific nucleus and we call that nucleus the lateral geniculate nucleus and there's two of them right these are basically on thalamus if you guys remember we said that here's your thalamus which is in the diet part of the diencephalon here's the thalamus there's a structure coming off of it called the lateral geniculate nucleus we're just zooming in on it so we're basically zooming in on that latter geniculate nucleus and it's layered it has one two three four five six same thing over here one two three four five six we said if see lateral fibres are going to go 2 2 3 and 5 if see lateral fibres go 2 2 3 and 5 so how where's it going to go them so these are the FC lateral fibres these blue fibers here so they're going to go to 2 3 & 5 contralateral fibers go to 1 4 6 so this is going to go to 1 4 6 then we set out of that the information from this can come out of the Leggett lateral geniculate nucleus a good chunk of it right can come out and it can go through it's called the superior retinal fibres are the baram's which is going through the parietal lobe that's why it's the superior retinal fibers so same thing over here and again this is coming through the parietal lobe to where the calcarine fissure is of the occipital lobe superior retinal fibers or the baram's loop and then there's also going to be the ones that are coming from the inferior portion which is coming through the temporal lobe or Myers loops which are again going to the occipital lobe or the striate cortex where the visual processing is going to occur where basically the sensation of whatever you see is turned into perception it's made real now that's what normally happens to make you consciously aware of what you're seeing but here's the thing we're not looking at that we're trying to look at how our pupils responding so this is going to occur at the brainstem level it's a reflex we can become made consciously aware that there's light shine into our eyes we wouldn't know how the pupils are responding so what happens here some of these fibers that are coming from the ladder is niculae nucleus some of them come into a special level within the brainstem specifically at the level of the midbrain the level of the midbrain now in the back of the midbrain at this level you're going to have a structure here which is called the superior colliculus and again with the structure here be called superior colliculus you're at the level of the superior colliculus there's a nucleus just anterior to that let's make this nucleus let's make it this nice pink color here so here's this nice little pink nucleus right here and this nucleus is really special it's called the pre tactile nucleus and obviously you have two of them right protect all nucleus so again you can do this the white protect all nucleus is the left protect all nucleus what happens is these fibers that are coming in here that are coming from the one four and six and the ones that are coming from the two three and five some of them are they're going to come into the midbrain and what happens is some of the fibers might go to the superior colliculus why would some of these fibers go to the superior colliculus because if you know the superior colliculus action controls your reflexive head and eye movements response to a visual symbol so if I see someone walking by I'm going to move my head on my eyes with responsive that's the function of the superior colliculus so some of these fibers can actually go to the superior colliculus but a good chunk of these fibers are actually going to what's called the pre tactile nucleus some of them are going to be pre Tecton nucleus now here's what's really really cool you remember that this was actually this little canal here was called the cerebral duct is where the cerebrospinal fluid is correct above it is the third ventricle below it it's the fourth ventricle and on the sides of it you had the somatic motor fibers of the third nerve nucleus right and then what do we say just to be super super particular if you want to be what was the structure around the cerebral aqueduct it was called the periaqueductal gray matter and then what we're here on the sides this is actually going to be the edinger less full nucleus I'm going to put W adding your Westfall okay and if you want nucleus I'll put in so adding your Westfall nucleus so same thing over here I'm not going to show all the fibers coming in here through each limb and I'm just going to say they're coming in here and then some of these fibers can go to the superior colas okay but most of the fibers are going to go where are going to come here to the pre tectal nucleus which is in the brainstem of the midbrain right and again it's going to sign apps onto the protecta nucleus now here's what's really really cool okay which I that I shine the light in let's kind of follow that because I want to show you something really really interesting okay I shined the light on the left eye let's follow the light from the nasal Hemi ready if I follow this one it's coming this way okay so it's crossing over to the other side these are the contralateral fibers it's coming this way I'll go into lateral geniculate nucleus Oh some of these fibers are going to the superior colliculus I'm going to the protect on the nucleus okay cool so I know that the fibers that are picking up the information from the left visual field of the left eye are taking it to the right side of the brain to the pretax of nucleus okay then I know that from the temporal Hemi right knee which is picking up information from the right visual field left eye it's taking this information and taking it down the ipsilateral fibers which are going into the actual brain stem and going where some of the fibers are go to the superior colliculus and some of these fibers are go to the protecto nucleus on the left side oh wow this is interesting so left pre Technol nucleus is innervated and right protective nucleus is innervated you know what else is even special the pre tactile nucleus is so intelligent that it can actually cross so if you give fibers that can go to the editor Westfall nucleus on the right side and the editor Westfall nucleus on the left side that's a beautiful thing so again what would happen with this one here it would give information to the editor Westfall nucleus on the left side and it would also give fibers over here to the editor Westfall nucleus on the right side the pretext a nucleus is so amazing that it can actually respond to that right and it can cross these fibers over so it has bilateral control of the right an aggressive own nucleus and laughs Annika Westfall nucleus that's amazing now from here what will happen okay so we shine the light into the eye we stimulated oh we stimulated a special special cell you guys remember from the physiology video that we actually did on the phototransduction cascade there was different parts there was actually one layer two layer three layers we're not going to draw more but there was the photoreceptors which were the rods and cones then there was the bipolar neurons okay and then there was the one right after that which was the ganglion cells these ganglion cells are very very interesting little buggers remember we talked about pigments that were within the rods and the cones like rhodopsin and hopson's for the cones well guess what gangland cells have another type of pigment it's called melanopsin melanopsin and what happens is whenever we shine light into a person's eyes we can activate these ganglion cells which are consisting of the melanopsin that pigment and is melanopsin is activated it can actually send it can actually trigger this cascade down these actual neurons the actual axons of the ganglion cell vacations that makes up the optic nerve okay so really when I'm shining a light into the eye which is the main one that's getting activated the ganglion cells during the pupillary light reflex and they send these action potentials down through MC lateral and contralateral fibers okay activate what protected nucleus protected nucleus can cross to both sides or does bilateral control activates the editor Westphal nucleus it's the edinger Westphal nucleus is activated he's a parasympathetic fiber he's going to move with the oculomotor nerve right and when he moves you guys know a little bit here he'll come to a ganglia and again both sides so this is the right one this one over here would be v laughs one and again what is that ganglia called or that group of cell bodies located within the pns that ganglia is called a ciliary ganglion now what happens so again these actually post ganglionic parasympathetic fibers that are coming out here they're actually going to be a component of something very important you know they're actually a part of what's called the short ciliary nerves because you know with the short ciliary nerves are going to be sympathetic fibers and fibers from the trigeminal nerve but moving with it and what happens is it pierces through the sclera and through it's called the pericardial space and it gives supply to the ciliary muscle and it gives supply to a specific muscle within the pupil that we'll talk about called the sphincter pupil a so again what happened here it pierces through the sclera moves through the pericardial space and gives supply to the ciliary muscle and it gives supply to thee thank their people eh now how would that respond what would be the person's response okay let's look at the response to the silly err is how that's affected so first thing we're going to do is we're going to look at see how the silly Aris is affected and then we're going to look and see how the pupil is affected by this parasympathetic and then we'll compare it with sympathetic okay so silly airs first so here we go this was our short ciliary nerve it's coming in here piercing through and it's going to give supply to the ciliary muscle right there this big chunk of muscle now here's what confuses some students here right here is the end of these ciliary muscle when the ciliary muscle so whenever these parasympathetic fibers come over here and innervate the ciliary muscle they're going to act on what's called m3 receptors muscarinic type 3 receptors which is going to increase the calcium levels inside of the ciliary muscle now when it does that it's going to stimulate the CLE areas muscle to contract when it contracts it's going to pull so down here at this fixed edge on your right right down here what's going to happen is it's going to pull that part upwards so as it pulls this upwards this part stays stable here this stays stable right here this part moves and it moves upwards as it moves upwards okay like imagine here imagine this is the fixed point here and imagine this is that point down here when this muscle contracts it pulls the thumb in toward the pointer finger so as it pulls it this muscle shortens as assurance something really interesting happens you see these little blue things that were connected to the lens here they get really really loose what are these blue things here called they're called your suspensory ligaments or your silly Arizonians now originally they were a little tight but whenever the ciliary muscle contracts these become really relaxed when they become relaxed they don't pull in the lens as much and now because of that the lens starts bulging and becoming really very globular if it becomes very globular this plays a role in what's called near vision okay so what is the response here with the ciliary first thing ciliary contracts okay then zonals relaxed lens bulges and why is that important I'll talk about in a little bit more detail but it actually affects the light rays that are being refracted into the actual eye onto the retina so when the light rays are coming in here because it's now globular it brings this actual lens closer to what the actual object okay so it actually is going to it decrease what's called the focal length okay but it helps what's called the near point of vision okay so that's how it's affecting it now for the pupil which I love this one same thing here the short ciliary earth is going to come up and it's going to supply the pupil but looking at it from this view doesn't do it justice so now what I'm doing is I'm taking the iris and I'm looking at from the anterior view so you're getting an anterior view of the iris and right here is the pupil hole so this is where the light is actually entering okay now the iris has muscles that are circular wrapping around it these muscles that are wrapping around are very circular there are very specific type they're called it's called the sphincter pupil a and what happens is these think their pupil they have what's called muscarinic receptors on them they have muscarinic receptors on them and three receptors what happens is the short ciliary nerves come in here and act on the muscarinic receptors the type 3 receptors and cause them to contract when it contracts it causes this actual muscle to squeeze like a sphincter and as it starts squeezing like a sphincter it makes the pupil hole smaller and small Moeller and smaller so by squeezing it imagine me trying to wring out like a rag that's what it's doing to it and it's making the pupil really really small so add this muscle start trying to contract it makes the pupil smaller and that is called constriction of the pupil okay so for the pupil what is it doing to the pupil it's actually constricting pupil okay through the sphincter pupil a why is that important because let's imagine here's normal pupil whole but then the parasympathetic comes into play and it makes this pupil even smaller so that space there is now going to be eating smaller look how much smaller it is holy crap it's a small temple right so now that the pupil holds a lot smaller look how much light can get in very little light so because very little light rays can get in here that is very very important because again what it does is it focuses the light on a specific point in the eye which is called the fovea centralis trying to focus the light onto the fovea centralis within the macula okay macula lutea so again pupil constricts to focus the light onto the retina okay specifically the phobias and trials where the cones are and again when the lens bulges for the near point of vision now let's see the sympathetic affects this oh but I didn't explain something here the pupils constricted but what was really interesting what was the most interesting part about this I shined light into the left eye but which nerves got activated both short ciliary nerves were activated that means that both of my pupils constricted but I only shined light into the left eye why did both my pupils constrict because of this cross connection okay because it is cross connection here with the protecto nucleus that's why both of them are going to become activated and constrict the pupil also because remember the nasal Hemi right divers went on to the other side and these Apes alatar attending temporal Hemi right knee fibres went to the same side so there's a lot of cross connection there now whenever I shine light into the left eye in the left pupil constricts this is called a direct response if I shine light into the left eye and the right people constricts that's called a consensual response this is what you should be seeing normally when you do this type of test as pupillary light reflex okay so normally when you shine the light into the left eye you can even do it you could shine it in either their left eye here and block their face if you want make sure that they have a direct response which is on the same side and then make sure that you shine that eye onto that left eye and they have a response onto the other side the right eye okay that's the consensual response alright sweet deal so we talked about direct response consensual response and how the parasympathetic is affecting this actual ciliary and the pupil now I want to take a brief look at how the sympathetic is effecting look at this more in the autonomic nervous system but I do you guys remember talked about it many times if a cross-section of spinal cord here cross-section with spinal cord on the outer parts here you're going to have let's do this bad boy here and this now let's do it in this actual purple here it's purple balls all right on the lateral gray horn or the intermediate lateral gray Horn of the spinal cord you have these pre ganglionic sympathetic fibers so pre ganglionic sympathetic fibers here the actual cell bodies of them they're going to come out here all right when they come out here they can actually go to a specific ganglia okay we're a group of cell bodies are located right within the pns that ganglia that they're going to go to is actually called a superior cervical gangly on now what happens is from this the postganglionic fibers are going to come out when the postganglionic fibers come out they're going to wrap around this artery here whoa you guys are like a pile of wool what the heck is that artery this artery is called the internal carotid artery it's called E internal carotid artery it's a branch off of the common carotid artery now these postganglionic sympathetic fibers form like a nice little plexus they actually kind of called the carotid plexus right here okay it sounded like a sympathetic plexus coming off the carotid now added coming upwards towards this region and actually moves through the superior little finisher with a trigeminal nerve like the ophthalmic division when it comes out it actually becomes a part of that short ciliary nerve so some of the fibers here can actually cross over and communicate with the short ciliary nerve and go in with the short ciliary nerves which is the parasympathetic and the trigeminal nerve fibers and supply these silly airs and the pupil right the muscle of the pupil it also can go just with the trigeminal nerve in Pierce the sclera and again go and supply the pupil and the ciliary muscle this is a part of what's called a long ciliary nerves so the sympathetic fibers can actually become a part of the short ciliary nerves and it can become a part of the long ciliary nerves if it's in the long ciliary nerves it's only moving with trigeminal which is a part of cranial nerve five a branch of the crane under five right we're not going to talk about that now and then if it's a short ciliary nerves it'll be moving with the parasympathetic fibers the trigeminal nerve branch and the sympathetic branch okay all right sweet deal so we did that now how does the sympathetic affect the actual silly errors in the pupil okay so if you guys look from this view now let's say that this is actually going to be the sympathetic fibers they're piercing through the scolaire and they're going to supply the silly eros and they're going to supply the pupil okay now what happens here when it goes to the pupil I'm sorry to the ciliary muscle it's going to relax the ciliary muscle so it's going to relax the ciliary muscle now if the searly ciliary muscle relaxes this part over here goes back so now this part over here that was actually really really tense before really really tense because it was pulling from this edge because before we were pulling from this as we were pulling it this way now what's going to happen is it's going to start relaxing it's going to start going back to its normal position as it starts trying to go back to its normal position what happens to these ciliary zonals now well now they'll be pulled in that direction as they're pulled in that direction they start becoming very very tight and as they start becoming really really tight they start pulling on the lens and when they start pulling on the lid guess what does to the lens it makes the lens really flat so now if you flatten the lens what is that good for holy crap if I flatten the lens that's going to take this lens farther away from that focal length or the object that I'm trying to look at so now because that's going to affect the actual light rays that are actually gonna be refracted onto the fovea okay so it's going to be more for far vision or distance vision on top of that it's going to come over here and it's going to activate this actual muscles within the iris but this is what's really really weird it'll activate these muscles of the iris let's come down here for a second to see exactly how these sympathetic fibers are arranged I'm sorry these muscle fibers are arranged these muscle fibers over here for the iris are arranged and like radial like spokes because they're radiating outwards and like spokes within a tire wheel right what happens is imagine them all being at this point right here a lot of the fibers are connecting to this one point right there on the iris right on the pupil hole what happens is when the sympathetic nervous system comes over here when these actual sympathetic fibers sympathetic nervous system fibers come over here and activate these actual radial muscles or no no it's actually really called the radial muscles it's called the dilator pupil a it's called the dilator peoplein when it activates these muscles these muscles pull from that point they're outwards they pull from that central point they're outwards and they're trying to yank the pupil whole wide right so imagine I'm trying to take out like a structure right here and I'm trying to pull it apart that's what these muscles are doing they're trying to pull the pupil hole out wide if they try to do that what's that for that's for dilation of the pupils okay so how is the sympathetic effecting here how are these sympathetic nervous system fibers effecting they're causing the ciliary to relax zonules tighten then what not only that but after the zone is tighten what happened to lens flattens if it flattens that for distance vision far distance vision and then it's also going to act on me what the pupils and it's going to cause the pupils to dilate Oh real quick what do you call it right up here on the top up here if the pupils dilate or if the pupils constrict they give it another name they call the dilation they call it mid reassess major ASIS and they call the constriction meiosis okay so if these meiosis constriction the pupil dilation is major ASIS okay now why are why are the people's dilating why are the people's dilating that's another question if the pupils dilate I'm not going to go over there for a second I might imagine this imagine the pupils were like this right like this very little light was coming in through this area very little light rays could come in then we're trying to focus it onto a central spot well now if it's a sympathetic situation a fight or flight situation you want to be able to see things from far away you want your eyes to be keen right you want to be able to see as much as possible so like if you're running away from a dog you want to see all the multiple possibilities of where you can run okay so because of that we're going to make this pupil bigger so that more light rays can come into the eye and focus on different parts of the red now right so that's going to be the importance for distance vision sky leaving the pupils and again ciliary as relaxing as tightened lens flattens and that's going to be again for distance vision all right sweet deal so we've talked about the sympathetic supply to the actual eye and we talked about the parasympathetic fly supply and we talked about the pupillary light reflex obviously in any situation in which this is damaged the actual comparison pathetic fibers the sympathetic fibers are damaged it could definitely have some type of problem on the actual pupillary light responses and the ciliary light responses specifically to do the accomodation that's why whenever you're shining a light and you don't see the directing potential response it could mean that maybe there is something wrong but it might not mean that okay that's when you have to warm more tests all right all right sweet deal so that covers that part now let's talk about something else before we continue to keep going forward I want to talk about something that helps to keep our eyes lubricated constantly okay I want to throw this in here real quick I want to talk real briefly about lacrimation or the production of tears okay lacrimal fluid this is important not only for crying unfortunately but also it's very important because it keeps the actual cornea nice and lubricated and picks up any waste product so how did this all work okay let's say here we're going to number it we're going to go piece by piece here let's say first step you see the structure right here this is the lacrimal gland so you have a bunch of lacrimal glands here and they're located on the lateral side of the eye so let's say that this is the nose so let's say that this is the nose side that's actually the nasal cavity right there and I'll say over here is the actual temporal side of the zygomatic side right now on this side the lateral side these lacrimal glands are going to be situated you know there's a nerve it's called the seventh cranial nerve or facial nerve right so cranial nerve saben innervate this right from the tear go palatine ganglia so from the tear go palatine ganglia you're actually going to have these fibers coming out anyway it's going to come here and release certain chemicals that causes the production of lacrimal fluid what's going to happen that I lack the fluid the lacrimal fluid is going to come out onto the cornea here and it's going to move across the cornea in other parts of the eye immediately because you know over here you're going to have a little thing here this little edge part here this little v part there that's actually called the lateral commissioner so it's called the lateral commissioner over here this would be the medial commissioner don't get that confused though with this space between the superior palpebral and the inferior pabre that's called the palpebral fissure so really this space right here is called the palpebral fissure so lateral commissure and medial commissure and then again palpebral fissure is the space so now lacrimal glands make fluid so lacrimal fluid is produced then where does it go moves lateral to medial sweep alright now where does it go from here you know there's like a little there's actually a little fleshy part here called the core uncle the lacrimal uncle right there what happens is this Lakmal fluid goes up through a tiny little hole here on the sides on the bottom part here and on the top part soap on the top part and the bottom part there's tiny little holes okay these tiny little holes here are called the lacrimal punctum so moves through the lacrimal punctum then from the lacrimal punctum a little hole it goes into through these canals do tiny little canals and then into this big old sack here okay so again where is it going it's going from these polaco punko which is the hole through these little tiny canals into this big old sack then we're going to the next destination okay so from lack of a puncta to the lacrimal can now lick you lie with your little canals then lacrimal sac then from the lacrimal sac it goes through this structure here this is called the nasolacrimal duct and from this nasolacrimal duct it empties into the nasal cavity but specifically we're in the nasal canal cavity okay in the nasal cavity filled in an anterior view so this would be the vomer here so if I step right here boomer from this part down and then perpendicular plate from this part on the Bob right from the ethmoid bone this part here is called the superior nasal conchae middle nasal conchae and then this one right here is called the inferior nasal conchae in between them is the superior meatus middle meatus and in fear me this little grooves this nasolacrimal duct empties in through the infuriated of the nasal canal okay are the nasal cavity so lacrimal sac - what nasolacrimal duct and then from there empties at level of inferior me ATIS of nasal cavity all right sweet stinking deal holy Frick knuckles we've done a lot so far all right let's hang in there we're almost done okay so we've done the people area light reflex with pathetic parasympathetic and we covered lacrimation last thing I wanted to throw in here was I wanted to talk just a tiny little bit about light rays a little bit more I wanted to go a little bit more onto that and talk about exactly how that light is being focused on to the retina all right so now let's go ahead just I think it'd be good to get a nice recap okay of whatever happened with the parasympathetic and the sympathetic on the eyeball just so that you guys exactly know how it's all affected okay so let's go ahead and do that so again we said that the we were going to make this parasympathetic that was actually blue over there so let's right over here para sympathetic and then below down here lifted this is for the sympathetic and we're gonna talk about myopia and hyperopia okay so right here is going to be sympathetic all right so now if you guys remember what do we say happen within the parasympathetic first things first we said that the silly eros contracted okay when the ciliary is contracted it pulled upwards which made the silly areas o'neill's really loose so the zone eul's when the suspensory ligaments became loose so they loosen up a little bit right then when they loosen what happened to the lens they weren't pulling on the lens as much so the lens became globular looks exactly the same let me fix that a little bit let me make it a little bit more globular here all right now that suckers beefy all right so now we've got a beefy old lens right so this lens is going to bulge now when the lens bulges right we said that this was going to affect the light rays okay it's going to affect the light rays that are coming in here then what else did we say happens so is the lens bulging is actually going to do what it's going to bring the lens closer like in like the focal length it's going to shrink the focal length and bring the image closer bring the lens closer to the object that we're trying to focus on because the lens bulging helps with our near point of vision and then we said the pupils would constrict why okay it's to prevent diverging rays from getting in so to prevent diverging light rays from getting in okay and to focus the actual light on the fovea so if we constrict the pupil it'll help to allow for the light rays that are coming in here no diverging light rays pretty much all parallel to actually come in and focus on to a specific point in the retina all right now what about the sympathetic the sympathetic we said that the actual silly eros relaxed then when the ciliary is relaxed what happened to the zonals the zonules tighten right because remember it went back down to this position as we went back down to this position what happened to the zone eels they become tight as the zones become tight what happens to the lens the lens flattens as the lens flattens look what happens you decrease okay now the length flattens now remember the object was out here you actually increase that distance the focal length between the lens and that object right so now it's going to be more for far vision or distance vision so this is more for distance vision another thing is we said that the pupil what happened to the pupil the pupil dilates if the pupil dilates this soccer gets fragged and big and what's going to happen more light rays can come in and focus more of that light on different parts of the retina so now the light rays that are coming in here we have more light rays coming in and if there's more light rays coming in we can focus more of these light rays on a larger part of the retina all right we can focus um now a larger part of the right now I guess is more for your flight or fight okay or you can see this dilation response you know what else you see this dilation response when you're actually going from like a certain type of room maybe when you're going from a a light room into a dark room because when you go from a light room into a dark room your actual pupils will dilate when you go from a what this was going from a light to a dark this would be going from a dark to a light room the people will constrict all right all right sweet deal now let's do another thing and let's talk about lasting here let's talk about two different types of situations that can happen in people's eyes happens to me myopia let's talk about another one called hyperopia there actually is another one called old person's height or presbyopia and it's just as you get older the vision starts being affected and if you know you ever notice certain older people I'm not trying to make fun of anyone but they have to hold the book all the way out here because they're near vision is affected that's what can happen you can actually develop presbyopia which can affect the ciliary zonules and the the lens can actually start accumulating a lot of crystalline proteins so it can affect the refraction again they have to hold and which is really really far away so they can see it clearly are anyway myopia myopia is basically when the old eyeball here is too long it's too long okay and hyperopia is usually the eyeball is too short so what happens is for this person if the eyeball is too long imagine here I have the light rays coming here okay here's these light rays coming in through the pupil as it comes in through the pupil the lens is going to try to focus these light rays it's going to have like a focal point right and the part where they a lot of these light rays cross and then they cannot kind of come out like this okay this point right here that focal point right there that's where the image is formed that's not good don't know why because the retinas right here the retinas right here and it's not formed on the retina it's formed in front of the retina when an image is formed in front of the retina that's going to affect what type of vision it's going to affect the far vision distance vision so people with myopia they are nearsighted in other words they can see things nearby but they can't see worth a darn things very far away so this is nearsighted okay so they can see near can't see far okay so they have a hard time with distance vision how would you change that okay well the problem is that this is converging too early we'll give them some type of glasses or certain types of contacts a lens that will diverge those light rays what do you give them give them a concave lens so give them some type of lens like this if you give them a lens like this when the light rays are coming in it'll actually spread these light rays out so as the light rays are coming in here it can help to spread some of these light rays out a little bit and if the light rays are spread out a little bit that when they actually come in to the eye they're not going to be focused on that point anymore they're going to be focused a little bit farther away now so now the light rays as they're coming back here because we diverged it with that concave lens as we diverge it now these light rays will actually form where the form perfectly onto the red dime let's just assume for this case here that the red is going to be right here okay it's not but just assume okay so again that focal point right there that it hits that focal point is going to be hitting the red now how do we fix it we gave them a concave lens because the concave lens is going to do what to the light rays it's going to be a divergent lenz meaning you can spread the light rays outward as you spread the light rays outward whenever it converges on to that focal point there it's going to converge a little bit more farther back with hyperopia the eyeball is too short so now look at the light rays are coming in and they're being focused here on to this person's retina it's being focused on to the retina farther back so it's being focused a lot farther back here and as it's being focused a lot farther back it's getting formed the image is starting to form behind the retina so where's the retina here the retina is going to be in this case we're just going to draw like this in red it's right here the image though that focal point is forming right here behind the retina so because of that how do we fix that we got to give them a lens that will actually converge the light rays before they're coming in how do you do that you give them opposite of a concave lens you give them a convex lens if you give them a convex lens what the convex lens will do is is it'll have these light rays that are coming in it will converge them okay so it will converge these light rays even more as these light rays are more converged they have more convergence they'll actually form a little bit more anteriorly okay so they'll form a little bit more anteriorly and they'll form perfectly on to that nice old retina so their focal point will now be on the retina okay and the purpose of the convex lens is it's going to be a converging lens converging lens so it's going to bring the light rays in closer so that the image forms and tear to them sorry a little bit more anterior on the retina okay mister as we covered so much information in this video I really thank you guys for sticking in there with me and hanging in there I hope you guys enjoyed it I hope you guys really did understand it and and I hope you learned a lot if you guys did like the video please hit the like button comment down the comment section and please subscribe as always engineering until next time

Channel: Ninja Nerd

Views: 141,675

Rating: 4.9701571 out of 5

Keywords: special senses, pupillary light and accommodation reflex

Id: -_kmchtMVd8

Length: 48min 33sec (2913 seconds)

Published: Sat Jul 29 2017