Transcript for:
Physio: Neurology and Visual System Notes (19)

all right uh good morning everyone let me know if you can hear me okay I think this is where we stopped off at but let me know if that's not the case County thank you Katherine confirms sounds good all right so we were um getting through our neurology introduction we were discussing some of the sort of sensory nerves that we talked about within the skin that can detect things like pressure and touch and heat and cold all that kind of good stuff here um the next thing I wanted to talk about was the how we get the signals from peripheral tissues actually into the brain itself and so the two most common sort of sensory Pathways we're going to run into um include this medial lisal pathway and then also the anterolateral system and so they will serve sort of different functions as we get into it as we're going to see here so um and again these are going to be these aeren signals these are signals coming from the periphery into the actual brain itself and so the first of which is that dorsal column this is that Lum a medial limus pathway here and so we're going to see these will synapse a little bit differently in terms of which where they're going to be synapsing at within the actual scene as itself and so we'll get into that as we'll look at the pictures here in just a second um the big differences here between the two will include on the dorsal column here this medial lisal pathway is that these are good for um very fast transmission of signals they also will have very good ability to detect like where the signals are coming from so this kind of high spatial orientation you can see there in terms of like where the actual signals are coming from so that's useful because it can detect specifically where on the body the signals are coming from that's good the an lateral pathway here we're going to see it's a little bit slower um and these are going to be good for detecting things like pain um temperature you know things like other crew kind of tactial Sensations that we'll get into um so slower transmission although I mean 40 meters a seconds is not slow by any means but slower than we'll see with the medial lisal pathway as we get into it so what we'll see here is that when we are looking at this medial litical pathway um if we're looking at touch that has like a high degree of localization so if you're thinking about like being able to detect you sensation coming from like the fingertips for example you can detect very specifically where those are coming from and so there's a high degree of um specificity and where that's coming from from actually locationally speaking I'm also find there's a lot of fine gradation of intensity so again fingertips are nice to think about here because again you have very fine degrees of intensity can sort of detect there in terms of like pressure and things like that um we'll also find that things like you know positional you know Sensations from the joints can be detected through here as well which is good because it's very a fast sort of pathway here so that way the brain can sort of detect that and be able to move against that very quickly and the andr lateral system here you're going to get more of the pain um tickle itches come from the system here sexual Sensations uh come from the system as well as we'll see and so for that medial lisal pathway here we can see that the initial Sensations may be coming from peripheral tissues like say the in this case here the foot or the fingers here um once you get up into the medula this is where this is going to then cross over so that's a pretty common thing you're going to run into with sensory Pathways is that signals coming in from say the right side of the body eventually going to cross over onto the left side of the brain where they cross over is going to be dictated based off of the nervous system pathway you're dealing with in this case here the medial lisal pathway is going to happen in the medula when you see this crossover that occurs once that crossover happens then you're going to see the signal gets transmitted up into the thalamus we talked about the thalamus being kind of the processing center for many you know effer signals Um this can then be transmitted into the sort of smat of sensory cortex and where that transmits is going to be based off where the signal is coming from in the body itself we'll talk about that you can see there's sort of a layout of where the different sensory signals are going to be kind of um sent to based off of which portion of the B is coming from and I'll give you a picture what that looks like here in just just a moment so the first place this is these signals are sent to is the samato sensory uh area one has really good localization for the most part but depending on the number of nerves that are sent or I guess the number of nerves are sort of um I don't know I guess like designated for each part of the body um can change and so this will give you more or less sensitivity so what I mean by that is is if you're looking at this sort of breakdown of parts of the body they're going to be in the smat sensor area one um if you can notice is that the larger areas typically have more neurons sort of like dedicated to it and so place like you know the face you notice here there's a lot more nerves because it's a much larger area places like the hands you know your head and neck you probably don't need a lot of like very distinct sensory information coming from there because it's not as important as like your hands or your face for example and so um as a result of that you'll have differing degrees of sensitivity dedicated to those areas and that's useful from a survival sort of standpoint um useful for you know being able to to do fine motor control of things like You're know your face and your hands and and whatnot as we'll get into so I kind of gets into looking at the degrees of Sensation that we can get from these different areas here and so uh for example in this left picture here what you can notice is is if you say you have a single point of stimulation here the degree of stimulation of this nerve will dictate how much of a sort of stimulus that we can get and what you can see is there's a sort of a recruitment process that happens here to where if I just have sort of a weak signal coming in you know maybe only record recruit a certain number of neurons here we get sort of a kind of a weak stimulus here but then as I recruit more and more neurons so I'm sending a bigger signal indicating a bigger sensation I'm trying to detect there you can start to recruit more of these sort of internal neurons here that get the bigger signal versus all the way where we get this very strong sort of stimulus here so that's important because that allows us to to distinguish between light touch versus heavier sort of Sensations that can happen there similarly what you going to run into is that you may have different points on the body being stimulated here which may start to recruit similar sets of neurons and so this gets into being able to detect find differences in points of contact or points of um say inputs from the neurons itself and so let's say we have two adjacent points that are strongly stimulated here if you notice each Red Wave here are the specific points of the body being stimulated here but because they recruit similar neurons here you're going to see that this Blue Wave is what's ultimately is what's detected so why is that important well because if we were to look at for instance here this this 2o touch threshold so you see this little device here they have different points on the plastic here which will be separated by a certain number of millimeters and so your ability to detect those two different points will be dictated based off of the sort of sensory intervation that happens here so places like the first finger here if you notice it can detect differences within 2 mm meaning there's a high degree of difference here within this sort of different interation meaning that you can detect those differences very easily because there is a lot of this sort of like lateral inhibition that happens here to the point where I can see these two red points very distinctly which is good in the fingers because you want have that high degree of sensation for dexterity purposes and whatnot um as opposed to if we were to get into places like say the abdomen or the back we don't really need that high degree of sensitivity we just need to know okay there's pressure here there's some kind of point you know putting pressure on certain aspects of the thigh or the back whatever the case may be um I don't really need to know so much about the difference in the fine action between the different points there so because of that because we have much finer interation of places like the fingers you can detect those differences very easily versus in other places like the back of the thigh it's much much more difficult you need a much bigger difference in those Sensations meaning actual difference in the points in terms of like distance to be able to detect okay that feels like two points instead of just one and you can practice this on yourself or your friend if you wanted to to kind of get a sense for what that feels like on the other hand we have the anro lateral pathway here and so what we can see is that um instead of crossing over in the magula here we're going to notice in the spinal column the crossing over happens pretty early and so you can see here whether it's the finger or the toes as the case may be it I wouldn't advise putting a flame against your skin but um that just goes to show you that this is having to do with pain it's having to do with temperature sensation um tickles or itches or sexual stimulations are all going to be happening through this an lateral pathway here and so we'll see the premier neurons synaps in the dorsal horn and then they cross over to this contralateral side so crossing over from say right to left or left to right whatever the case may be um and then traveling up and through the brain here and so they'll synapse in the thalamus and then they'll have other Sensory neurons that are going to be terminating that Century cortex um after the crossing over process here it'll be pretty similar to what we saw that medial lisal pathway um note here this is also slower um you know 40 m a second versus several hundred as we saw before but still slower in in general sense here when it comes to pain Pain's a very important sensation to be aware of so that we can address that and and you know if we put a a hand on the stove for examp example we feel pain we need to be able to react to that very quickly here and so there's two main types of pain sensation we can run into there's fast pain and slow pain fast pain is usually felt within say a tenth of a second or so after the stimulus is applied so this is where we get our kind of like sharp or pricking or acute pain um this is more so seen in those kind of very acute cases where like I would cut myself or I stepped on something or whatever the case may this is not usually the type of pain that gets felt in like there like kind of deep type of tissues slow pain on the other hand or so takes more than like a second or so to be really felt and kind of will slowly increase and this can happen over the course of like seconds and minutes as the case may be and so here you get more of this kind of like dull kind of like throbbing chronic pain here um and this can be felt both more you know sort of peripherally but also in this kind of deep sort of tissue here and so in each case here we're going to see this pain is going to be sensing or being sensed from the free nerve endings and this can happen from a number of different cases here so it could be mechanical sort of issues like maybe like a crush type of injury um thermal sort of causes maybe I suck my hand into a freezer that's very cold chemical causes maybe um you know someone's exposed to you know a strong acid or base for example could be caused for for chemical pain there a lot of of times chemical pains um can be brought about by the inflammatory response and so if you were to for instance stub your toe and then you end up seeing that you have an inflammatory response where you end having a lot of release of things like histamine or serotonin that can also cause a chemical sensation of pain there um and what you're going to find is is that these receptors don't really adapt so much so as we talked about previously we mentioned how like you know the feeling of clothes on your skin that's not very useful sensory information and so your brain starts to discard that very quickly and meaning you adapt to it quite quickly um pain on the other hand is something you really don't want to adapt to because you're in pain so obviously something probably bad is happening to you so there's sort of like a survival response that says like okay well we should get away from this um we don't want to adapt to this very quickly because Pain's not a good response we w't get away from that um and in fact you may actually find some cases where these pain signals may become actually more sensitive over time this is like over the course of like months and years um and so there's a term called hyper Alesia in which the pain sensing fibers become more sensitive to pain meaning it's more easy for them to be triggered than it would be sort of a baseline so you can run into that especially like chronic pain patients you run into and so what we'll find is there two different Pathways that will happen here um as these signals are going to be transmitted from the peripheral tissues through the spinal column and into the brain itself um we'll notice here that these kind of fast pain fibers are going to be transmitted more specifically to those SM sensory areas much more quickly so that allows for a quick response of something like you know how my hands on a stove stove is hot all me retract from that very quickly so that's good that we want that those kind of fast pain receptors there slow pain fibers on their hand are going to be traveling more sort to the thalamus um again these are going to be happening over the course of like minutes to days and weeks and years and things like that um and so those are not going to elicit the same sort of like kind of quick responses as we're going to see and we'll talk a little bit about motor responses to pain a little bit later in the different PowerPoints we get into it so the fast pain signals are transmitted via this neop spin spinothalamic tract here which you can see and again we're going to see there's very good localization of pain because this will coordinate with our kind of tactile receptors meaning if I put put my hand on a stove the brain's going to know pretty quickly where that Pain's coming from to be able to react to that very quickly to be able to remove that sensation or remove my hand whenever the pain might be there and so this is usually regulated through the actions of glutamate which is an excitatory neurotransmitter we've talked about previously being you know major mainly going to be excitatory in nature there um on the other hand though the slow pain sensation is going to be through this paleo spinal tract here um this one you're going to find there's less ability to localize this and this comes a lot with um a visceral pain like you know pain from like the organs itself where we're not really able to determine where specifically it's coming from like how can I determine if my sple in pain or not like you can't really tell but we'll talk about localization how that kind of works in just a bit um notice here the nerves are going to be releasing glutamate similar to the neop spinothalamic tract um we also have the presence of substance p whenever I hear substance P I think substance pain um because usually this is going to be related to that um and so substance p is going to be important for helping to kind of sensitize these nerves to be able to feel pain more acutely um substance P if you're not aware um there's a drug we'll talk about get the pharmacology stuff when uh it comes to capsacin so you can use capsacin on your skin to treat things like osteoarthritis and whatnot and that actually causes releases substance p in caps if you don't know that's what causes Peppers to be spicy and so initially you might think oh it sounds bad because you know peppers are spicy peppers cause pain um what's NE about caps actually causes a depletion of substance P because you're releasing too much of it eventually leading to basically desensitization so people can use capsacin topically for treatment of things of osteoarthritis to actually help to reduce overall pain sensation by depleting substance speed so kind of an interesting way we can to modify the system here to deal with things like pain for example now it's important that we have our own ways to deal with pain without having to rely on things like medications here so we do have an analgesia system sort of built in to ourselves and so we're going to see that these signals are going to be transmitted from the peripheral tissues into the spinal column and then into the brain itself um however there are some mediating factors we're going to run into so there's some things that we're going to intervene here to be a able to modify the signals that ultimately get sent up into the brain itself and so what we can see here is that serotonin plays a big role here because this can actually stimulate the release of things called enlin and en keins are some of the sort of natural opioid like substances that our brain our brains produce and so um if you've ever heard of someone like running a marathon and get the runner's high the runner's high is thought to be produced by things like cins and dorphin whatnot um that are being released from the CNS in order to deal with the pain signals that are coming in cuz I don't know if you've ever run long distance but it's not a very comfortable thing to do right it's not it's not fun it's it's painful you got to run through the pain right so your brain is releasing these different sort of neurotransmitters in order to deal with that sensation here so we have things like beta endorphins and en keins and dorphin um basically these are the brain's own opioids so similar to how you could use morphine or heroin to deal with pain these neurotransmitters do the same thing and basically what they're doing is they're releasing these neurotransmitters onto receptors within this Pathway to be able to basically turn down the signal so much and so I don't have a lot of experience with opioids I think um when I got my wisdom te taken out when I was a teen they gave me a pretty weak one called daret which is propox ofine which is now off the market because it's was it's a very bad drug um but one of my professors in Pharmacy pharmacy school described opioids as being like yeah you know you're in pain like he can still tell but it's just like you I'm okay with it it's fine it basically turns down that signal so to speak and so this is the natural sort of substances that can do that without relying on external pharmacology and so you're suppressing the signals that are getting to the brain itself so that way you're just turning down the volume on the pain you're experiencing there are cases where we have what we call referred pain and so this is where we're going to see pain occurring in certain tissues that is remote from the tissue that's actually causing the pain what I mean by that so as you can see here in this picture you can see there's visceral nerve fibers and then skin nerve fibers and these signals can be sort of mixed up to where the brain can't really tell the difference between one versus another and so this is where we run into cases where let's say someone's having a heart attack they're complaining about their having you know say Arm numbness that their shoulder and their left arm that's not really a a shoulder problem it's a heart problem and so it's a type of referred pain the patients may experience and again I'm not having to memorize every single one of these here but just gives you an idea of saying hey you know if the patient is having pain being experience say on the you know say right upper quadrant here maybe that's a liver or gallbladder problem maybe it's not the actual tissue itself that's painful it could be referring back to one of these other visceral sort of organs so that can be in some ways how patients will present with pain um that could be more indicative of a more internal sort of issue as opposed to just a more peripheral or topical time of problem you running into there uh then we have thermal sensation here we're going to see these are regulated by both we have cold receptors warm receptors and then pain receptors too because we know that when we're at the extremes of temperature that we can have pain associated with that and so whether very very cold Sensations or very very hot as we run into and it's interesting too because we're going to find that the density of these receptors will vary depending on on the tissue that we're dealing with so for example um we're going to find one that we are typically more sensitive to cold than we am to warm temperatures so we have about 3 to 10 times more cold receptors than warm receptors although I'll tell you we on this time of year my warm receptors are very much more stimulated than the cold ones but I digress um and you'll find depending on the tissues here you're going to find for example here on the lips or the finger we have way more cold receptors here than if we were to say on the trunk it self which is good if we're like you know having food coming and we need to detect the temperature if we're touching something want to detect the temperature there and here we're going to find that we will have some adaptation but it's usually pretty slow as compared to other types of sensation like touch for example or pressure um and it's not completely you we don't adapt to it completely here and so what's interesting here too is not so much that we have it's more so we have a bigger response to changes in temperature than we are just the static temperature itself so I like to think about the example of going from if you ever go on a vacation and you go to a hotel and they have a hot tub and they have the pool I'll say it's non-heated pool so going from that sensation of say sitting in the hot tub for 10 15 minutes very hot temperature and then jumping into a cold pool which Maybe not cold so to speak but is say room temperature um you're going to feel that much more than if you had just gone to the pool by itself because there is a greater change in temperature and so your body's going to be feeling that much more acutely so that's the thing we're going to respond much more to than just the actual Baseline temperature of the thing itself um and of course at the extremes we'll start to see pain receptors start to get involved as well when we start get into either burning hot Sensations or freezing cold Sensations what not um indicating hey there's kind of thermal injury happening here let's retract our limbs or get away from the situation the case may be so uh that does it for this particular section I'm going to move on to the next one let me if you have questions no I don't want to get feedback to Microsoft all right no questions so far let's move on let's talk about Vision I was reading through this last night and I was having to re acquaint myself with the topic and whatnot and um the eyes are amazing it's incredible that we have Vision the way that we do um so complex so so interesting but let's let's let's get into it first of which um as we get into the specific sensory receptors um it'll be important to kind of know which nerves are associated with which sensation um so I'll go through these more specifically as we get into it um some of these cranial nerves will be more sensory in nature so for example cranial nerve one is all Factory that's a sensory receptor so we can smell things we'll talk about that believe in the next PowerPoint um on the other hand we may have some that are going to be more somatic in nature meaning that they're going to be causing movement so like cranial nerve 3 for example causes a lot of movement of the eye for example and so we'll T touch on these as we kind of go through I'm sure in your Anatomy course you're getting more acquainted with these more specifically in terms of which cral nerves are involved with which specific actions here in the body um I'll kind of touch on these individually as we kind of go through the different Sensations whatnot as we as we touch upon them so um other ones here we can see for sure that some of these are going to be involved with um specific things like you know Salvation for example some CR nerves involved with these in terms of like their their sematic actions here um we're going to find that for example see here where am I the Vegas nerve is really respon responsible for things like you know our autonomic nervous system like the parasympathetic actions we'll get into all these as we kind of go through the individuals here um and so generally the function is what I'm looking more for not necessarily um memorizing all these in terms of like which specific body parts are going to be affecting but generally what each of the nerves are going to be responsible for as we get into it so let's talk about the eye the eye itself is a pretty complicated sense organ here um we're going to find that it is um made up of several different kind of individual components which allow us for the sense of vision that we normally have here so we're going to get into those as we go through here and you can see the different sort of portions see there locations composition and the general function here we're going to talk about some of the major portions we go through and generally what their functions are this is just for your kind of reference as you can go back to when you're getting into your your studying sort of purposes here so generally speaking when we're talking about the internal anatomy of the eye itself I'm not going to get so specific when it comes to Anatomy necessarily but I'm talking about the kind of the general flow of things as we're looking at like you know light being taken in how that gets sensed and all that um so what we're going to notice here initially we're going to have what consider sort of be the interior portion of the eye itself well then have the post posterior portion posterior cavity and when we're looking at the anterior cavity we can see it gets broken up into both the posterior and anterior sort of chamber here so interior chamber see first then you get the posterior chamber and so this is the entire interior cavity I'll get into the specifics here just a little bit to cond delate which each of these portions are doing here um and then we get into the vitory sort of chamber here which is the posterior cavity um namely we're going to see the retina is going to be located towards the back of the eye here the phobia is really important because this is where we mainly are going to be focusing light and mainly focusing our vision for the most part um and we get into places like you know your optic nerve and the blood supply and all that coming through here as well so what we're going to see is as we detect light so as photons sort of enter the eye itself we're going to notice that there's a focusing of the light itself um through the pupil and through the lens onto this focal Point that's going to be what we call the phobia and this is where we're going to find the highest concentration of our cones um which are going to be part of the light sensing organs that we have so we'll talk about rods and cones their different actions here in just a little bit um but generally speaking here we're going to see that mostly we're going to find Focus onto the fobia itself which is going to be allowing us to be able to like read a book for example here you'll notice that you know you'll have a general Central Focus point for your vision where everything is very clear and you know kind of in your perfect if you're kind of aware of it if you're thinking about it kind of notice say yeah some of the details are lost I'm losing focus on the periphery here versus the thing I'm actually looking at has the greatest Clarity the greatest sort of resolution or Focus here um it has to do with how the light is going to be Focus onto that fobia that focal point for our General Vision here we'll talk about near sidedness and far sidedness in just a little bit how that sort of differs as we get into it and so if we were to look at um let's say we're doing a fun fundoscopic examination of the eye itself um here we're going to notice that the cranial nerve or cranial two excuse me um is going to be what's innervating the eyes itself and so you can see here there's this optic cup along with this sort of disc here um and so this is where all the veins and arteries along with the optic nerve are going to be coming in we'll also note this is also our blind spot because there's no rods and cones here to really detect any sort of light and so if we're driving a car for example we have a blind spot because there's a certain area of the eye where we're not really getting any Activision and so maybe there's a car in the way that we don't see that we then sideswipe which I I hope you don't do but what we're going to see here is that as you will have this inovation and supplying blood flow to the eye itself you'll notice here they have the fobia and then the immacula itself and so this is where you're going to see the greatest concentration of your cones the cones being the kind of light sensing color sensing sort of portions of the eye itself um this is where the light is going to be attempted to focus on because this is where you have the greatest resolution you have the greatest ability to detect actual you know um detail in the actual Vision you have there to be able to read off PowerPoint slide or to um look at a pretty painting whatever the case may be so the goal here is to focus the light on this area here because this is where the highest percentage of our receptors that are available to be able to detect that light and so when it comes to Vision um we are only able to see just a tiny sliver of available electromagnetic energy out there in the world um so there's the visible light spectrum which will kind of travel from certain wavelengths here um above which you get infrared light and ultraviolet light which we cannot really see um I guess unless you have like a super power which I'm I'm not VAR went having but we basically can see within this visible light sort of spectrum here and if you notice it generally follows the the royi Biv sort of delineation of the spectrum of color of the rainbow so to speak um and so how we detect these different wavelengths of light we'll discuss more detail based off the type of cones and whatnot we have available in the eye itself so what we're going to see here is that light so this is the visual pathway so how does light actually travel through the eye to actually get into being detected by these light sensitive receptors so first of which we're going to see here is the light passes through the cornea into the anterior chamber of the anterior cavity of the eye this will be a little confusing because we're talking about anterior posterior a lot but basically it's going to travel into the anterior chamber of this initial anterior cavity here once it's there the light is then going to be passing through the pupil into the poster ior chamber of the Interior cavity to the lens so lens here is very important because this is what's going to help us to be able to focus the light onto that fobia onto that area where we have the highest degree of resolution of the light we're receiving there and well then once we are through that interior cavity the light then passes through the lens into the posterior cavity of the eye itself so this is where we're traveling through the vitous humor of the eye itself and then finally hting the back of the eye we're getting the right now itself that's where your rods and cones are going to be available or present where they can be interacted with um and so at the very back we'll notice there's this pigmented chid layer the fact this pigmented is really important because we want it to be dark to be able to absorb a lot of light we'll talk about more details on that here in just a little bit and so what we can see here is that as we have light being projected into the eye itself is that we will find that the pathway can be sort of dictated based off like one where the location of the item is so we trying to read a book it's very up close or we trying to look at something that's very far away um we're going to find that the lens can accommodate to that to try to be able to focus that image onto that phobia as best as it can and so depending on the degree of accommodation of the lens we have available how pliable it is that can really dictate how well we are able to then Focus that picture onto the eye the right itself and so you can see here as well that different things are able to depending on the medium that we're in things will transmit light a little bit different but ultimately what we're going to see is this kind of focusing through the lens onto the back of the retina itself to actually get the image transmitted to the brain we'll talk about that transmission through the optic nerve here in just a a little bit interestingly we can find as well and I'll get into this is what we're going to see is that the lens is going to be sort of supported by these suspensory suspensory I guess I should say uh ligaments here and there's going to be these ciliary muscles that are located here and So based off of how contracted or how relaxed these sary muscles are you can find there's either a push pushing or pulling on the lens um that allows it to become either more sort of um flat or more curved and that will be useful to help to focus this light depending if we're looking at something very close up or very far away we'll go into more details what that looks like here in just a little bit another picture what this sort of visual pathway looks like as we see light coming through the anterior cavity is located the very front of the eye versus the posterior cavity which is mostly like the aquous humor lights can be traveling through in the we get into the actual light sensing cells and rods and cones and all that I can do it just a little bit and again the goal is to try to focus light onto the fobia because what we're going to find is this is where we get the highest degree of the color sensing the cones we talk about rods and cones rods are good for like black and white type of vision the cones are good for color vision and so we're going to find is we have the highest degree concentration of those cones in the fobia here because this where we're trying to focus most of that light to get most of the detail there you'll find there's some differences that can happen you through aging or you just natural um changes in the eye shape and things like that that cause some problems we'll in just a little bit once you get into the actual back of the eye so we're in the posterior chamber here um what we're going to find is is that light's going to be coming from this direction in particular it's going be traveling here to the pigmented layer of the back of the eye this is where the retina is and so it's interesting here because what you notice is light's coming in this direction we'll see that the light sensing organs like the rods and the cones are going to be located back towards the pigmented layer but then the signal gets transmitted sort of retrograde to a degree back to these gangling cells to then travel through the optic nerve to be detected by the brain and so what that's going to look like is and one thing I to note here as well is this pigmented layer is really important because it contains a lot of melanin so what you want is is a lot of dark coloration in the back here because that helps to absorb more light as opposed to just like reflecting it back through the rest of the Chamber of the eye um so for example if you have someone who has albinism albino person uh they lack the production of melanin and so what happens in those situations there is they don't have this nice dark background here and so when they get exposed to like a high degree of light like they go into a bright room or something or they wake up for example um from dark to light um they can have a lot of refraction of this light through the back of the the retina leading to high sensitivity to that light because they're just being bombarded with it and so that can be a problem for them when it comes to vision for most individuals though they have a nice and degree of melanin which pigments this background layer here which absorbs a lot of light so that way you don't see a lot of reflection reflection of light on throughout the rest of the C cavity and so rods and the cones can absorb their stuff we'll talk about the process there in just a minute and then they're going to be transmitted through these other cells we'll talk about in more detail eventually traveling to the optic nerve itself note as well is that depending on where you're at within the retina you may find a different sort of U makeup of the different types of receptors that are available so for example on this picture to the left here what you'll notice is is that on the left side this is going to be more sort of like the peripheral sort of retina you'll see a lot more rods being available which you can kind of rods versus a cone based of the picture here um which is good rods are going to be good for like black versus white sort of discrimination so um night vision for example is going to be largely based off of of your rods um cones are good for color discrimination but what you'll see is that um in the peripheral vision you're going to see a lot more rods being present here versus if you're on the right side of the picture this is closer to the fobia which is going to be more so made up of mostly cones this is where you get the greatest resolution of your picture in terms of like the color and we to make out actually specifically you're looking at your actual actual focus of the picture itself so we'll come back to this we'll talk about these different receptors and different cells and whatnot but that's kind of the general sort of flow of the light in terms of the visual pathway you're going to see there all right so the pupil and Iris excuse me um so we're going to see the iros here is this pigmented epithelium we can see that increases or decreases the diameter of the pupil itself and this is through cranial nerve number three the ocular motor nerve makes sense basically affecting the eye here um and what we can find here is that we can see that we can either get constriction of it and so this will be done by contraction of the circular muscles so the circular muscles itself will constrict which will cause the close of that which will cause meiosis that is mediated through the parasympathetic stimulation so if you're in a rest and digest State you're probably not really looking out for threats or danger so you can utilize the parasympathetic nervous system to cause constriction of the circular muscle causing closure of the pil itself so less light comes in so generally your visual input of photons is not going to be as great on the other hand though if we were to have sympathetic inovation so you get that fight ORF flight response you're worried you're looking out for danger you're going to see dilation so you're going to see my diasis that happen here so instead of contraction of the circular muscles like you would see with the parasympathetic interation here you're going to see contraction of the radial muscles so I kind of think about the circular muscles kind of like closing I can see kind of closing on the circle there versus the radial muscles are pulling it apart my hands are visible there but you can see the radial muscles you're pulling that apart and that's going to be through the sympathetic interation which will cause myasis interesting point just to go off on a tangent for a moment um there are medications that can affect the people's themselves and that's one of the things we look for when we have someone like a drug overdose for example we can look at the pupils and that can give us a clue potentially into what substance the person might have might have taken um so for example if someone has overdosed on something that is anti- parasympathetic so they to overdose on something like a inh hisam like benad that has anti-cholinergic properties that will actually cause the opposite here of the parasympathetic stimulation will actually cause myiasis so they may come in with very big saucer looking pupils and that could give us a clue in terms of what the person might have actually done um and interestingly if you've ever heard of the term the belladon alkaloids it's a series of chemicals um that are coming from a certain classification of plants um including you know substances like atropine and and zamine things like that um but they call them belladon alkaloids because of the fact that they actually um were used back in the day back in I don't know what specific times but back in the day they're used to be some physical beauty that was associated with having big saucer looking pupils and so they would have concoctions of compounds they would use in the eye itself to actually cause myiasis to cause the pupils to dilate and that was thought to be a sign of beauty and so they called them belladon because belladon means beautiful woman in Italian and so they would put these chemicals into the eye to try to induce this my Dr they thought it was attractive I imagine those people were probably pretty sensitive to light cuz all these extra photons are coming in here um probably couldn't see very well but um at the time it was thought to be L of beauty um I imagine if I went on a date with somebody uh and they showed up with big huge saucer looking pupils that assume they're on drugs or doing something uh I don't know if I'd continue with that date or not maybe ask them for whatever they were using who knows anyway so depending on the amount of light that is going to be present here we're going to find that the pupils will respond to this and so for example in dim light what we're going to see is that the ey is not getting enough sort of Sensation from the photons coming in and so what this going to cause is some dilation of the eye itself and so we're going to see activation of these radial muscles that will help to open up the pupil to cause my diasis on the other hand though if we're in very bright light so if I were to go say from inside to outside one of the responses you would end up seeing is it will find this kind of post Gonic parasympathetic axon gets activated here and so we'll see the circular muscles will contract that will then cause constriction of the pupil to cause meiosis and again these are going to be sort of adaptive responses to either low light situations bright light situations depending on how we need to respond to that obviously I mentioned drugs can involve this as well but generally speaking this is the normal sort of function in terms of how the peoples will change I mentioned the cranial nerve three will help to control the sort of pupillary reflex here so in bright light you should expect to see restriction so this will be the parasympathetic reflex so those circular muscles will help to contract and then in we have dim light we're going to see the sympathetic activation happens here and so here you're going to have contraction of the radial sort of muscles here so in both cases whether we're in low light or highlight we're going to see that we're having contraction of the muscles but which muscles are going to be important here because in the low light situations we're going to see that we have contraction of the radial muscles that help pull the people open but in a low light situation highlight situation should say um we're going to have constriction that radial musle here to try and limit the number of photons entering into the brain stem or entering into the ey itself I should say other things we'll see here is a lens is helpful for allowing us to focus the light more specifically and so we're going to see here this composed layers of living cells are normally completely clear so unless you have like cataracts or something it should be completely clear here avascular mean there's no blood vessels to kind of get in the way and con RCT or obstruct the vision here and it'll be attached to muscles called the ciliary muscles or the ciliary body here so this is really important because this allows us to be able to stretch or relax the lens and will allow it to achieve more of a flat versus sort of a globular sort of shape here and this allows us to focus the light onto the back of the retina onto the fobia itself here and so how we can constrict or relax this is going to be through these zules which are these kind of dispensory ligaments we're going to see here theary body is going to have the muscles Z actually attaches to the lens itself that allows us to either relax or constrict this just another picture what this sort of looks like here again you can see the zonals are going to be going all throughout the lens itself so if we were to have contraction or relaxation of the muscle we can see this kind of confirmational change I'll show you what that looks like here in just more detail in a second so um the Aquis humor not to be humorous here but the Aquis humor um is important because this is what actually transmits a lot of the um so the nutrients and oxygen things like that through the eye itself and so we're going to see the Aquis humor gets fills the anterior and posterior Chambers in the cavity of the eye itself the anterior cavity particular and so this this kind of clear sort of like watery type of liquid here that gets secreted from the ilary body itself and so this is what even though we don't have a vascular Supply going to like say the lens for example it is able to provide those nutrients and nourishment to those areas itself and so it's important um we'll see then that it needs to go somewhere it needs to be able to be released and so this is through the canal of schlim which is another one of my favorite organs to say the canal of schlim wonderful um and then it gets eventually drained back into the blood supply so this is really critical here too because one of the I conditions we'll talk about when we get into discussing Opthalmic medications is a condition called glaucoma which glaucoma is a condition where you have elevated intraocular pressures so the pressure is too high and so there's two main types you're run into there's closed angle glaucoma and there's open angle glaucoma closed angle is much more of like a an acute surgical sort of issue because you have a direct blockage of flow of the aquous humor to relie to go out of the ice the pressure buil quickly very painful usually a surgical sort of issue but the more Insidious type is this open angle glaucoma where you have people that either produce too much aquous humor or they can't get rid of it so in those cases we then require medications to actually help out with that in order to be able to either decrease how much aquous humor are producing or to get rid of it more easily um to help reduce eventual degradation of vision for the person um so that's one of the big problems you're run into with glaucoma is that people will eventually develop blindness because that high pressure in the eye is not very well tolerated the high pressure on the optic nerve will eventually lead to blindness and so just little little side note there and so you can see here this canal is Slim this is where eventually the fluid should be eventually draining out through to eventually get back into the blood supply uh to be recycled there but the C BL sary body is what's actually producing the the aqua humor itself and just another picture here kind of showing you the general process where you see the cellary body here's going to be actually forming the aquous humor here notice there's going to be General sort of like flow and transmission of the fluid through the vitous humor itself versus when actually get gets expelled it's going be through this canal schim to eventually be sent back to the blood supply there so all right so let's talk about light refraction itself when the light's going to be passing from one medium to another it's going to bend and so the lens is the main thing that's going to help us to actually Bend this light to be able to get it to where it needs to be which is on the phobia in the highest degree of resolution of vision itself and so as you can see here we're going to be going from the pupil light travels and going through the lens and then onto the actual phobia Central of that immacula we talked about fob where we're going to see that highest concentration of cones um and interestingly we're going to find that when light travels through here is that the picture actually gets morphed um so we're going to find that we actually see there's a flipping of the picture both up to down and left to right luckily our brain is smart enough to be able to translate that image into what we normally see um however the eyes are not that's not what the eyes are actually actually sensing there and so if we were to look at light refraction here we see the image is flipped upside down and right to left in the process here and so you can see depending on where the light's coming from it will be able to ref on a different portion of the eye itself and so I think B is really helpful kind of showing you to see okay well how's this actual picture being morphed here and so that's important because how the lens is able to focus this light or its ability to do so can really dictate how well the person's vision is going to be how can they focus that Vision to be able to actually see the image itself as clear as possible so has to do lens accommodation so accommodation think about like accommodations like your hotel room but the accommodation be able the ability to to react to whatever you're trying to focus on to be able to accommodate or be able to adapt to that and so combination of the ability of the lens to keep an object focused on the retina as the distance between the eye and the object moves so how do we for looking at something like a distant duck as in the picture here um how do we accommodate the lens to keep that picture focused on the fobia as best we can and so so what we're going to find is that we can change this so if we were to have contraction of the sary muscle so as you can see in the right side of the picture here you're going to see that these ligaments that hold the lens in place are going to relax because the muscle is now contracted that distance here and so it's going to be allowing for relaxation of the suspensory ligaments thus the lens is able to thicken and basically kind of rounds itself so this is good because it helps us to be able to focus on close or near things so as you can see on the right if we're looking at a butterfly that's 25 cm away it's very specific um you would able to see be able to see that there's contraction of that Cy muscle that allows us for very close sort of focusing of the lens um by allowing it to sort of Round Up on the other hand if we are in a situation where we're trying to look at something very far away we're going to see there's relax ation of the sary muscle that'll pull on the suspensory ligaments that causes the lens to form a more sort of flat shape or thin and flat shape there and this allows us to be able to focus on things that are distant or far away so keep that in mind because it's a little confusing because here you're noticing the C muscle if we want to look at something close up it'll contract to allow for these ligaments to relax to cause a more conical shape for the lens so we can look at something close up or if we're looking at something far away the muscle relaxes to cause the lens to pull apart because those ligaments are more taut to be able to look at something that's far away just be aware of those as we go through here and so our ability to resolve these images and be able to look at something um can be measured right so if we're looking at our near point of vision is the minimum distance from the eyes an object can be brought into to focus okay and then how well we can sharpen that Vision how well we can resolve it here or we can distinguish say two different letters that are maybe close together for example here we can do that using our snellin eye chart and so for example here this is something you'd have say on a wall and the person would stand 20 ft away and you'd have them be able to read off the letters as you go through here and so if they're at a point where they could read the eighth line here that would indicate okay you're at 20 ft away and you're able to read all the letters at 20 ft away that's 2020 Vision because you're at 20 ft and you can read the stuff that's 20 ft away right versus if you are have poor resolution you may find that you're in situations where you're able only able to read the letters that you should be able to read it say 70 ft away so if you're at 20 ft and you're only a to read to Oz you might say oh you have 2070 Vision because I shouldn't be expected to read that at 70 ft away but I can only read it 20 ft away so that's where we get our kind of 2020 type of vision those kind measurements from I have a question here uh could you explain the lens accommodation more specifically the contraction relaxation again thanks absolutely let's look back at that okay so if we're looking at this picture here these two pictures so if we are trying to look at something far away we're going to try to focus that distant image onto the fobia right or that part of the retina that's going to be and we receptors here in just a little bit but the highest degree of detail here um what we're going to find is is that when you're trying to look at something far away the sary muscles are going to relax when these relax that will put tension on the ligaments here on the lens that tension causes a stretching of the lens which causes it to become more flat okay becomes thin and it flattens so that allows you to be able to focus that image that light onto the fobia there for a farway object on the other hand though if we're trying to look at something very close up like if I'm trying to read a PowerPoint on the computer screen in front of me which you'll see here is is that the actual CER muscles relax should misspoke the C muscles will contract so when these contract that actually allows for sort of they the sort of shorten themselves and so as a result of that you're actually going to find that the ligaments are relaxed so the ligaments become more loose and that causes the lens to develop this more thicker round kind of shape and so that helps us to focus on things are much closer up and so it sounds counterintuitive because you're like wait a second the muscles are relaxing which causes the thing to actually condense itself it's a little counterintuitive keep just keep these in mind so when we have sary muscle contraction that causes the lens to round up because these ligaments here are going to be more relaxed on the other hand we have relax cular muscles here laments are going to be more taut th causing the lens to pull apart that's better for far Vision okay that does not explain things and what you can kind I think this picture does a better job kind of illustrating the point where you can see here that when we have the sary muscle which is relaxed you can see here that it's kind of pulling the lens more totly through the action of the ligaments here versus when the muscle is contracted it is able to be thicker thus it causes those uh ligaments to loosen and thus the lens is going to become more sort of globular circular kind of shaped here versus the kind of thin flat kind of shape so let me know if that doesn't explain the answer or explain your question there so then we get into our ability to actually see things right so myopia is the process where we see nearsightedness occurring here and so this is where distant images are brought to a point to focus in front of the retina so if you notice here you have someone who is trying to focus the light and this is sometimes due to somebody having an elongated eyeball so you have people have big feet small feet some people have longer eyeballs some people have shorter eyeballs not a qualitative kind of thing but just it happens and so what you can see here with myopia you're having a difficult time sort of focusing on Those Distant images because the IM is not being focused on the actual back of the retina itself and so in those cases there what we can do is use a concave lens which will help to sort of refract the light a bit further back to eventually hit the actual retina itself and so in those cases someone with nearsightedness they'll need a concave lens in order to correct their myopia or their nearsightedness some question um yeah so the lens will almost become a magnifying glass uh to convex yes I would say so yeah so um as you're sort of modifying the the shape of the lens based off the amount of light coming in based off of what you're trying to focus on more specifically um yeah you'll see it kind of form more of a convex versus not quite concave I would say um but trying to focus the light in different ways to try to hit that retina as best it can and again there's that communication between um the vision the brain is detecting talk about that in more detail in a second um versus you know how that response will happen in terms of like either sympathetic parasympathetic actions and whatnot to try to focus a little bit greater so that way the once the brain detect okay we have a clear image here then then we're good to go so yeah I think so all right uh if you have hyperopia which is a term referring to far sidedness this a situation where the distant images are actually being brought into Focus behind the eyeball so behind the retina itself and so this is usually due to someone having more of a short eyeball as opposed to a long one like we saw myopia um here using more of a convex lens as you can see here this will help to kind of shorten the focus point the focal point onto the retina itself so depending on the person's condition depending on their particular eyesight we he we can use different shaped lenses in order to be able to accommodate for their specific um issues there um and then there's people that are kind of both problems so stigmatism and so this is where there may be an asymmetry with the the cornea or the lens curvatures itself and so you get these different focal points you can see here there's multiple points which the brain is trying to receive that and it can just be quite difficult and so here instead of using either convex or concave lens here we can use what we call cylindrical lens to help try to Res resolve that a little bit easier so there's a better picture of that here in just a second all right so if you were to have imop which is normal vision here there's no correction that's needed if they were have myopia or near sidedness usually the eyeball is too long meaning you're focusing the point before you hit the retina itself using a concave lens will help to refocus that you have hyperopia or far sidedness notice here the picture is being resolved further back from the retina itself so we can use a concave lens to help correct that and then if we have something like a stigmatism where everything is kind of going off here we use a cilindrical lens um this will have to correct that so a little more difficult but we can fix those people there and there's presbyopia which I feel like I'm experiencing more and more as I slowly approach 40 um here we're losing accommodation of the lens with age itself so you're going to be noticing as people get older um they have a reduced flexibility of the lens itself you're going to notice um there's sort of this like kind of forward movement of the zonular fiber attachment here and basically the lens cannot thicken um to increase that refraction in your object so this is why people often times as they get older require corrective lenses in order to U be able to resolve those images on the back of the retina as best they can there and then there's things like cataracts that can develop here so here we notice um that either through issues like you know changes and proteins in the eye itself like UV damage um age trauma you know hereditary sort of issues here um you can have the lens actually being clouded um which eventually can be removed if you have cataract surgery for example here um to help restore vision for the individual so just some examples how things can kind of go wrong there all right so if we're looking at the retina thr up thos scope let's say we're doing our fundoscopic exam here um what you can notice is you notice the optic nerve which is going to be where all the blood vessels and the optic nerve rection coming into the eye itself you notice the fobia this is we get the greatest resolution where the light should be focused in order to get our vision here um and so interestingly too because we have this optic nerve coming here there's a lack of things like rods and cones in this area so if you're to consider what your blind spot is this is actually it where the actual optic nerve itself is coming into the eye and so let's talk about the actual actual chemical process of how we respond to light here and so how we detect light in in the brain itself and so what we're going to see here is as light enters in through the eyee um we're going to notice here there's a pigmented epithelium that is going to be at the back of the eye itself and this is very dark has a lot of melanin and that's good because we want it to be able to absorb light instead of just you know reflecting it every which way we'll then have our photo receptors which are going to be made up of our cones and rods we'll talk about the differences here just a little bit we'll then have our horizontal cells bipolar cells of the Amrine cells and then finally the gangan cells which are going to communicate to the optic nerve itself or cranial nerve number two so interestingly you're going to see that light is going to be traveling in this direction the actual light detecting cells are here and then the signal is going to transmit back this direction and eventually head towards the optic nerve itself so it's kind of like a forward you know two steps forward one step back kind of process we going to see and so another picture what this looks like so you noce see the direction of Lights heading in through the eye we're going to see here it hits the back of the eye we have that pigmented epithelium here the rods and cones are going to reside we'll talk about the chemical process for how we actually detect light itself and then you're going to hit these horizontal cells notice horizontal meaning it's going to be able to send signals left and right so to speak le in this orientation here have our bipolar cells which are going to be transmitting signals to these Amur and gangion cells and then finally the ganglion uh ganglion cells are going to transmit it to the optic nerve itself where it can transmit to the brain we'll talk about the different process there as we get into it all right so let's talk about the rods and cones uh the rods are allowing us to detect black and white Vision especially in low light and so the reason why these are able to function are through the process or the chemical named ropson um I was reading through the textbook last night just refreshed myself on some of this and they call redops and visual purple which I thought was a very kind of I don't know cool kind of name there um but interestingly red option actually absorbs green light the best meaning green things are easier to see at nighttime than you would see other colors which is why if you ever watch TV um watch you know cop shows or military shows when they have night vision goggles everything shows up green because that's the easiest color to detect at very low light levels and so rods are good for black and white vision good for low light vision um and they require vitamin A vitamin is really necessary for All Vision as we're going to see here in just a little bit um the cones are going to be better for actually detecting different color so we're going to see there's things like blue cones and green cones and red cones um that will detect different lights rods are going to be kind of in between that where they're just really detecting green the best however it's mostly kind of like black and white type of vision and so you can see the general sort of function here where you can or see the general form of it we're going to have these kind of outward segments here which is going to be mostly containing the ropion and I'll talk about the chemical process here in just a little bit um here we're going to see there's also these inner segments here we have like a mitochondria that are producing energy and whatnot and the actual nucleus itself which will be located further in in this kind of outer limiting sort of membrane so the normal process you're going to see here and so sensing light is a little bit different than a lot of your other types sensory organs cuz mostly when you're looking at things like touch or if you're looking at smell or you know hearing you're going to see that a lot of those signals are transmitted via depolarization lights in one exception where you're going to actually see that sensing light causes hyperpolarization so this is the one case where you see the opposite which is why that occurs why we develop that way I don't know but that's a general process here so what the normal looks like right is that in normally what you're going to see here is that you have a chemical around called cyclic GMP cgmp and what that does is it keeps these little sodium channels open and so what you notice is as you go through here you're going to see that there is a natural flow of ions maintaining the resting membrane potential which is instead of like a normal neuron which is like you know say -70 let's say this is like -4 molts for example and so you notice if the sodium potassium pumps work working here you're losing some potassium you're bringing in some sodium um things are just kind of flowing things are just kind of chilling until there's light detected so this is the dark State here if you notice here dark the sodium channels are open okay so what's going to happen here is you have this buildup of a compound called ropson once light is detected in one of these rods ropson starts to go through this sort of breakdown process and eventually develops what we call Meta ropson 2 this is what they consider sort of to be the active form here once this gets formed here what you're going to see is is that we start to break down this cyclic GMP how does that occur well it occurs because ropson through its breakdown products forms this G protein transducin which helps to activate this phosphodiesterase phosphodiesterase will start to breakdown cycle GMP once this is gone sodium channels close which you can see in this picture here let me move that sodium channels close which then will trigger a hyperpolarization of the cone the R I should say because we're blocking the positives from coming in this causes a hyperpolarization that then starts the signal Pathway to go to the brain that says hey we're reacting to light so that is odd because most other sensory organs are triggered by depolarizations this is triggered light is detected through hyperpolarization so kind of keep that in mind it's a little strange but again redops and detects light it breaks down starts to activate this G protein which activates this phoso dasas this breaks down cyc GMP less of that cause the sodium channel to close thus we get our detection of light because now the cell is hyperpolarized couple other points vitamin A we mentioned vitamin is necessary for vision how does that occur well if you look here you can see that we have this all trans retinal versus retinol I'm sure some of you if you're interested in skin care you've probably heard of retinol before right um so vitamin A otherwise know is all trans retinol um you will find that it can be interconverted into retinal retinal is necessary because this is what actually gets converted into ropson so you'll see scopin plus this retinal comes together to form ropson and so there's an interesting interplay here because what you'll find is is that in situations where you have very low light situations so say you're like in the in in the dark in the middle of the night you're getting up to go to the bathroom you have a lot of adoption available because the eyes are like I'm ready for light wherever it's going to come from ready to see stuff so you have a lot of that built up versus if you like go out to the beach and you're outside for sever hours you don't need to detect there's this kind of accommodation effect that happens there where you're like okay I'm getting bombarded with photons I don't need as much of this Sur to be able to see stuff and so you'll find that instead of producing a lot of ropin you'll keep it stored in this state of vitamin A so you have these vitamin A stores that are ready to go and so that's again another reason why if you go in from a very light situation um very bright situation outside to walking inside it takes you a little bit of time to be able to adjust to that lower light situation because of the fact that you are now having to produce more of that redops and to be able to detect that light in the first place so just know vitamine is necessary in order for you to be able to see in the first place because it helps to form this ropson that is able to then react to light um interestingly there's a couple other things to note here as well um for for example there is a drug called isot troan acutane that we use for treating acne it works by interfering with vitamin A one of the problems you can run into Vision disturbances because people can't see as well because their vitamin A is all screwed up uh another case here uh there's a drug called cenil or Viagra that we use to treat erectile dysfunction how does that treat erectile dysfunction well it works as a phoso dester inhibitor that causes increased blood flow to go to the penis to cause an erection well it also can interfere with this phosph eye itself and interestingly actually causes something called cyanopsia actually causes the vision to become more blue that can be a side effect of that medication there so little interesting points here you can see through this pathway it's a little complicated but hopefully it kind of make some sense in terms of how I described it there um in terms of the visual pathway here as I mentioned light's going to be coming in this direction hitting that pigmented layer which is going to be absorbing a lot of light though which allows for the rods and cones to be able to not being bombarded with a lot of reflected light from from the background there um notice here on the left side of this picture as I mentioned this is more for your peripheral vision where you see a lot more rods versus cones on the right side of this particular picture you're going to see a lot more of the cones being available in the fobia where you're going to see the most kind of resolution of the picture itself um notice here I'm not going to get super in depth on the details in terms of the other cells in particular but just note that we'll have horizontal cells which are able to send signals sort of laterally to be able to have an inhibitory sort of effect here so if we're trying to focus on one particular spot of vision uh we may try to inhibit other points of um light they're not necessary for our particular Focus itself um and then that will transmit to our bipolar cells which will then transmit to both Amrine and the ganglionic cells gangion cells are important because that then transmits the optic nerve itself okay I mentioned there are three types of cones that are available we have our blue cone green cone and then our red cone um and so we're going to see here the rods are kind of in between green and blue mostly on the green side of things in particular but mostly a black and white type of vision here and so depending on the signal coming in and depending on the degree that each of these cones are stimulated the brain has the ability to decode this so for example if I were to just see a blue light itself you may notice that 97% of your blue cones are stimulated but really not a lot of your green or red cones are stimulated thus my brain would decode that signal as being okay this is a blue light that I'm seeing versus if I was looking at something like a red cone and I was seeing just a pure red light you might just see 99% of those red cones being activated but no blue and then maybe very little green okay so depending on the ratio you'll get these different lights so let's go instead of just saying blue or red let's look at something like a yellow light right so yellow light may get like say 83 83% of these green and red cones activated but very little blue So based off the ratios your brain can kind of decode that to be like okay that's a yellow light versus green versus you know Orange versus Violet for example and again kind of going for Roy G Biv kind of uh VIs visible light sort of spectrum that we see there and there are cases where you have color blindness where people cannot see colors here um with this loss of color perception and a lot of this can be dictated based off of the loss of a specific type of cone the most common would either be loss of red or green cones um so if you have a loss of red cones this would be called a protopia versus green cones is deuteranopia and then if you have lots of blue cones called tritanopia although this is more rare than the other two there um and inter L this is something that gets transmitted from mother to son usually as you're going to see um because this is an XL sort of condition you're going to find that the father is not able to transmit this because if it's a boy they're transmitting the Y chromosome on the other hand if it's a girl they're transmitting X chromosome so they can't really transmit that so much there um so in the case here you're going to find that the mothers are going to be more likely to be affecting the sons um versus producing like carriers for example there um so for example my father he is uh has deuteranopia so he has difficulty Discerning red versus kind of greenish and bluish type of colors there um and so I as far as I know have no issue with color perception although maybe that could be the case I just don't know it who who knows um monochromacy would be if you have tailor or two types of cones again that's pretty pretty rare to that and just give you an idea what that might look like if you're trying to compare um the different colors here and again this can be make it difficult to just discern the differences between one color versus another so like you know if you have normal vision you could probably tell pretty easily this is like kind of a more redish color versus more orangish versus you have protopia it's very difficult to discern the difference between the two so just some examples there and we have tests to be able to detect this so for example this is the ishihara color test here where if you have normal vision you would see that this here it says um 43 and this one here says 79 I'm just kidding no um 74 and 42 just proving my my color Discerning abilities um and so here this can detect certain types of color blindness based off of what either whe they can detect the numbers at all or whether they can detect certain numbers here um so for example they can see the four only versus the two only May indicate different types of color blindness so just something to note there and as I mentioned the vision is best at the fobia centralis so this is when the port called the macula ludia and this gives us the greatest density of cones and also the greatest association with ganglionic cells and so what you can find is is that in peripheral parts of the vision you may find that multiple rods and cones may be attached to say a single gangion here we're going to find in the fobia that we have much more kind of like almost a onet to one kind of Association here and so this works best when you have good light conditions you're going to get the most detail here likely what you're probably sitting at right now um however you may find there's over stimulation you can run into issues where having a lot of bright light can cause pain issues to happen there like I'm looking at a light right now to try to keep my face somewhat um in in lighted but uh it is not fun to look at because it is bright and so you'll see those neurons in the right now gather at the optic disc so this is your blind spot this is where you're not going to be able to have any active rods and cones here and so this is considered to be the blind spot also exiting as cranial nerve number two and where your blood vessels are coming in and out as well and so looking at the visual pathway this is important because we want to be able to understand how it's going to be transmitting signals into the brain itself so we mentioned light's going to be passing through the cornea going through the anterior chamber of the anterior cavity mentioned then going through the pupil into the posterior chamber of the anterior cavity it's the lens itself then we get to the posterior cavity of the eye itself so then traveling through the aquous humor to the retina then we hit the pigmented cells we the rods and cones horizontal cells bipolar cells Amrine cells and then finally get to the ganglionic cells which go to the optic nerve so kind of keep that pathway in mind in terms of the general flow of things where does it go from there though once we get into the actual optic nerve how do things get transmitted so that's what we're going to talk about now so here we're talking about the visual fields and so this is something that can be a little bit complicated um for a lot of students and so just try to keep this straight as we go through and again ask questions if you have questions um as we get through here so we're looking at the visual Fields so this is the part of the external World being projected onto our red nuts right or maybe we're in a simulation like in The Matrix who can say but let's say we're in the normal World we're seeing this kind of external World being projected on to the right now so let's look at the right eye first we're looking at the right eye itself because of the flipping of light that occurs as light passes through the lens we're going to find that light coming from the left visual field is going to be transmitted onto the right side or the lateral aspect of the retina okay light from the right side gets transmitted onto the more medial or the nasal aspect of the retina itself so keep this flipping in mind this is important how the light gets transmitted to the brain itself okay so light from the left visual field gets transmitted onto the right or the lateral aspect of the retina light from the right visual field gets transmitt to the left or medial aspect of the retina look at the left eye the left eye here we can see that light from the left visual field gets trans to the medial aspect so the opposite medial aspect of the retina light from the right visual field gets transmitted to the lateral or the left aspect of the retina okay why does that matter who cares we care because that dictates where it going to go to in the brain so if we're looking at something we need to understand where those signals are going at into the brain again we need to be able to take two points of input from the vision from our two eyeballs to to get this binocular sort of feel this binocular vision that we have here that we like unless you have only one eye which case less important but regardless and so what we're going to see here is that that light signal gets transmitted and that these signals need to be incorporated to be able to get your typical type of vision you'd expect to see and so we're going to see how this travels it's going to travel back to oipal lobe um into our sort of visual sort of Cortex talk about here more detail so from the optic nerve see you have the optic kaym this is where we're going to see a splitting of the visual Fields okay so that means is is that light hitting the left aspect of the retina on either eye gets transmitted to the left occipital cortex but that light is coming from the right visual field so that's where it gets a little confusing so the right visual field if you notice here is projecting onto the left aspect of the retina on both eyes that then transmits and so if you notice the left aspect of the retina on the left eye gets transmitted along Its Right portion of the or on the correct portion of the the brain there for the medial aspect of the right eye which is getting that right visual field if you notice here the opticis it crosses over so everything being transmitted onto the left portion of the visual field or the left portion of the eyes on the retinas gets transmitted over to the left portion of the brain even though it's coming from the right visual field the opposite is true as well so everything coming from the left visual field that gets projected onto the right aspects of the retinas and both thids gets transmitted over to the right globe of the occipital cortex so keep that in mind so if I said you know light from the left visual field onto the right eye where does that go if I know it's the left visual field I know it projects onto the right portion of the retina I know that's going to go into the right eye is going to go to the right occipital Lo okay so keep those Pathways in mind when you're looking at that stuff and once you're in the occipital lobe here you're going to see this where the primary sort of visual cortex is going be located it will then sort of transmit itself through different portions of the brain here where it can go to communicating with Thea sensory as pathway you can communicate with other portions like the um language centers and talking to the memory Pathways all kinds of other stuff and we'll see here as we get into it so um this picture also does a good example of or does a good job of illustrating where the signals are coming from so as I mentioned here everything being projected onto the left aspect of the retina here is traveling to the left aspect of the brain vice versa here once in the occipital pathway here know the primary visual cortex here and then we're going to again this is where the macula mainly gets focused your primary focus of your vision is located right here the other aspects if you're looking at your kind of peripheral vision is going to be projected Le in less Focus but is going to be dictated I guess sends by other portions of the brain itself once you get into the secondary visual cortexes is where it can do things like dealing with u making 3D positions or noticing motion or the form of something um so where get into looking at things like visual details and colors and all that kind of stuff so the main sensory portion here is going to be terminating here in the actual primary visual cortex and then everything else gets sent out from there to try to then incorporate that into okay what am I even looking at can I what am I even you know what is this thing is this is a sphere is it a cone is it red blue what the case may be is all dictated through those other accessory Pathways here last thing I want to talk about here is going to be actual eye movement so how do we actually dictate how the eye moves itself because part of part of this is going to be under voluntary control part of this may be under more involuntary controls we're going to see here um dictate based off of Are We voluntarily kind of fixating on something versus we're just trying to maintain fixation here and so we're going to see there are six main eye muscles that're going to help to um move the eye around in order to focus on things we want to focus on so we see the superior rectus muscle inferior rectus muscle lateral medial Superior oblique and then inferior oblique here and then finally the eyelid gets controlled by this Le levator palpa superioris which that's just great name right there and so you want to know the general functions of these muscles here and how they're going to be moving the eye itself so we're going to look at some more details on that as we get into it um in terms of muscle innervations what we're going to see here is that for the majority cranial nerve number three does the most of these the majority of these so um everything except for lateral erectus which is going to be through cranial nerve six and then the superior oblique which is cranial nerve four those are the only exceptions so I was watching a video yesterday it's like a med school kind of Trainer video on this um and they said lr6 so4 and so that means lateral erectus six is the cral nerve that inates it and then s so4 which is superior oblique is uh cral nerve four and then everything else is the cral nerve number three so if you know that you're good to go from that standpoint and so generally speaking here we're going to find um and kind of just go through the more specific or interations that you can see um and so looking at the general function of what these muscles are going to do okay again I love this picture here I don't know where I found it but I was just like man that lady's got some great eyeshadow going on got some great makeup going on here but regardless what you're going to find is a superior rectus is be moving the eye upwards and laterally so as you can see in this picture here inferior rectus moves the eye downward and laterally medial rectus will adduct the eye meaning it's going to move the eye closer towards the medial aspect meaning the nose the lateral rectus will abduct the eye so moving it away we laterally and then the two that are weird are the obliques because you would expect based off of just the picture here you would expect the obliques to move the eye let's say for instance the inferior oblique to move the eye down and Superior oblique to move it uh the eye up not the case instead Superior oblique moves the eye downward and more mediately and the inferior moves the eye upwards immediately so those are the weird ones just know those are a little bit different in terms of what their fun function is otherwise the name of the muscle should kind of clue you into what the's doing itself so and then it's interesting too because we need to as I mentioned a lot of the in sensory input that comes into the eyes is thrown away as garbage data because we're not seeing new information the brain loves new information way we can focus on new things and focus on dangers and whatever the case may be um and so we have this process called the ptic movement of the eye itself and so again we can have voluntary fixation where we choose to focus on one particular thing here and then we have this involuntary fixation which allows us to once we fixed on something to kind of maintain that fixation here but in order to maintain new inputs eyes has all these kind of random jumps and movements here and so if you notice on this picture right here is you see the voluntary movement um to a fixation sites by the solid line but then the dotted line is all the other kind of CTIC movements that happen here to kind of keep reframing the picture in order to keep new information coming in cuz again with our skin like we don't need to feel our shirt on us but with vision it changes so rapidly we want to keep things nice and fresh and so from that standpoint here uh it's important that we are able to have this process and if you notice here if you look um you can see the interation where you have things like the involuntary fixation area which is going to be mediated through the cortex of the occipital lobe versus more frontal cortex is where you see the voluntary fixation where have become more conscious control of that and then you see cran numers three four and six which are going to be able to regulating the movement the eye itself in order to keep that psychotic movement in order to keep us kind of fixated on the thing we want to kind of focus on there so anyway that'll do it for this section what I'm going to do now is answer any questions you have and then we're going to come back at 10: uh so I'll have a separate stream there uh we'll come back at 10 and we'll do our hearing smell and taste I believe are the three other senses we're going to talk about there any questions I can answer at this moment a question here uh could you clarify the thermal sensation regarding the receptors adapting slowly again from lecture 18 slide 55 yeah let me pull that up all right um so someone had a question about thermal sensation regarding the receptors adapting slowly yeah so that is more to do with um if you were to compare like your sense of touch versus sense of temperature right um so you know like the clothes against your skin you feel that as soon as you put your shirt on but you don't keep feeling it after a while because those nerves get adapted to that sensation the brain discards a lot of that data on the other hand though the body will try to um will adapt more slowly to changes in temperature um to where because it's more of like a survival sort of instinct and especially when it comes to cold receptors because I think most people probably consider cold to be the more dangerous temperature uh versus hot within reason um and so you become less well adapted to that cold because you want those signals coming to the brain that says hey you're too cold put on a jacket or whatever the case may be and so because that is more slowly adapting um that allows you to keep those Sensations going to say hey you need to go change your environment or change your clothing what the case may be um and similarly have those pain Sensations associated with that too where if you get at those extremes of temperature it says hey you need to like immediately do something about this because this hurts get away from this as as fast as you can so it's good that we have that kind of slow adaptation that occurs to change in temperature but let me know if that does not answer your question uh for color blindness since has passed from mother to Sun with a color blind trait end with the sun to only pass through one generation at most um so from that standpoint you will still find um that girls can be carriers and so while the sun is not able to transmit that to their son they could still transmit that to their daughter because it's xlink so you may find that the the father who is color blind will transmit their X chromosome which carries that trait to their daughter often times what you'll find is is that the mother who is unlikely to have the color blind trait on either of her A's will transmit something that is the normal X trait for that um so from that standpoint you're mainly are producing more carriers although it was funny cuz I asked my daughter last night I said oh can you read these ishara tests I didn't say isara but say can you read tell me what numbers there are and you could tell she was kind of Faking it I was like come on you're not color blind you tell what numbers these are and she's looking at she's like nope I think it's uh looks like a butterfly I was like go on just cuz you want to be different um but anyway so yeah so would not necessarily stop with the sun they could potentially pass it on to their daughters as the case may be so the direction of light would be from the gangan cell to the pigmented epithelium whereas the transmission or whereas the direction a signal transmission be from the P pigmented epithelium to the gangling cells yeah let me pull that back up so I'm looking at this picture here so the lights transmitting in this direction the ganglionic cells the am all these cells don't have anything to do with the light transmission at this point right so the lights coming in this direction here hits that pigment pigmented epithelium um where it'll absorb that light and then whatever's left over is going to be interacting with the rods and cones to interact with that ropion that we talked about and again the function of the rods and cones are very similar to one another it's just the individual proteins um between the cones versus the rods a little different but I don't want to get in the Weeds on that um so the signal transmission is from the light down here to the rods and cones and then once that signal gets transmitted it's going to be going up through these horizontal cells bipolar cells AMR cells G cells all the good stuff Y what other questions can I answer at this moment I explain again the secondary visual areas and the degrees of change in primary visual cortex 5719 yeah so um basically what we're referring to there is is that the signal from the eyes itself is being transmitted PowerPoint cursor you canot see that what's going on anyway so from the eyes itself you're going to see that signal gets transmitted back to the occipital lobe and so you'll notice in that Primary Vision cortex that's where like the fobia signals are coming in so that's where you get the sharpest type of vision and then you're going to notice here as well as you get these kind of degrees of changing um the degrees of of vision here so like for instance um seeing out in your very peripheral vision notice here there's not as much signal as you would see like in versus the immaculate itself um so you get some detail but not a whole lot right um from there you'll then be able to send out those signals from the eyes itself into these other processing areas so for example in these secondary visual areas um you're able to then take okay I'm getting vision from the left and the right let's form that together to make this binocular vision okay what can I determine in terms of what's the 3D Shape of this thing um you know how fast is this car coming at me in traffic how fast um you know is what color is this apple that I'm about to eat what are the casid may be um a lot of that's going to be processed through those secondary visual areas that then get transmitted elsewhere um so there's a lot of interconnections we're going to get into in a bit later whereas for instance you know how do I read a something on text from a book how do I convert that into language well I've got to be able to see the text itself send that back to that occipital lobe to then send over to my language areas to say oh yeah I see these characters this means the word banana and then I need to be able to convert that to be like okay what the heck is a banana oh yeah you you know through the language centers you're then able to interact with your memory centers and all that to be like oh yeah this word says banana a banana is a yellow fruit that blah blah you know so there's a lot of incorporation with other areas than the brain here it's to help it work all in in tandem with one another so hopeful that answers your question okay so I'm going to go um get some water and whatnot so I will come back on to the next stream at 10:00 uh and then we'll talk about our smell and vision I think we'll probably end a little early on that one so we should be good to go from that standpoint um I I will see you in just a bit if you have questions fre to post them up I I'll be back at 10 o'clock bye