hi everyone welcome to Professor long selectors in anatomy and physiology I'm Professor Bob long the series of videos that you're watching are intended for use by students who are enrolled in my human anatomy and physiology course at Del Mar College if anyone else finds these videos helpful by all means use them to your advantage I hope that they're helpful in understanding some of the more complex physiological processes and they help you understand some of the material but because every course is kind of designed specifically by an instructor with a specific goal in mind my class may not go exactly into all of the detail in some areas that some instructors do for example right now this specific video is intended for my human anatomy and physiology to course and we're doing a series on the sensory physiology this is the second video on the eyeball and if we did everything in the chapter on the eyeball we can do an entire semester on it so I'm going to trim some material out I'm going to try to focus on those concepts that I think are important for those students who are running into the allied health science programs in Del Mar which is an overwhelming majority of our students so anyway yes you know where the coronavirus set down so these videos are pretty crude I'm doing pretty quickly with my cell phone just to keep my students moving because I'm a I'm not an online guy but I'm having to do some online teaching so anyway now last in the last video we started covering the eyeball and I did a lot of external anatomy the eye that palpebrae the lacrimal structure the flow of tears through the eyeball you should know all of those structures you should know all that anatomy and physiology what we're gonna do now is we're gonna pick up on page 11 of my notes set so if you're in my class I hope you're on page 11 and the note set we're going to do the bottom half of the page now the way the eyeball is set up is it's set up with three layers of tissue we call the layers tunics some people refer to them as layers or coats or tunics the original anatomical terms that were used were the three tunics of the eye so I'm going to run into these and then we'll we'll start moving into some more complex physiology what I'm going to do is introduce the three tunics and then I'm going to go through each one of them and go through all the details I can of each specific later so that you guys can follow along in the notes set so let's get started the first of the three tunics of the is called the fibrous tunic now when you learn anatomy and physiology and once you get into science you should get to the point to where certain words make certain things pop into your head and medially you should be able to picture this stuff now the fibers tunic is mostly dense connective tissue you should start to think of collagen fibers elastic fibers and connective tissue anytime you see the term fibrous now it's a very tough thick later it's the outer layer of the eye we're gonna talk more about its detail in just a second the second major layer of the eye is called the vascular tunic now anytime you see vascular you should start thinking blood vessels the vascular tunic of the eye was originally named because it has a lot of blood vessels in it it's far more complex and has more structures in it than that a lot of muscle tissue and we'll talk about that when we get to it the third layer of the eye or the third tunic is called the neural tunic this is the layer that has the neurons in it it's mostly the retina but there's another layer of the eye that plays an important role or another later sub layer of the neural tunic so I'm going to go through each one of these layers in detail so I'm gonna erase these two so that we can focus on the fibers tunic at the moment the fibers tunic is mostly made up of two specific structures one of the structures of the fibers tubing is the sclera now from the last video as you know the sclera is really known as the white part of the eye so when you're looking at someone's eyeball all of the white part of the eyeball around the colored part and everything else is called the sclera and it is mostly dense connective tissue now the functions of the sclera is such okay it's filled with a lot of collagen and as you should have learned in part one collagen stuff stuff so the sclera provides shape and support to the eye you know even when you drain all the fluid out of the eyeball it doesn't completely collapse down on itself like an empty bag it still maintains its almost like a flat soccer ball it's not another percentage flattened and so it does give some shape and support for the eye and it also provides a strong point of attachment for the extraocular muscles so I'm gonna give you a little bit of a language lesson here the term extraocular means outside the eye okay another way to say this is the extrinsic eye muscles and you'll hear me use these two different terms extra ocular muscles or extrinsic eye muscles or extrinsic muscles of the eye extrinsic means outside of intrinsic means within or inside so you'll hear me use that term as well so that's pretty much what the sclera is it's dense connective tissue layer it provides some shape and support for the eye and it provides a really strong point of attachment for the extraocular muscles now in lab we're going over the four extra ocular muscles and you should know the superior rectus for example if we were looking at the eyeball from an anterior view again here's the right here's the nose so we'll draw the right eyeball here's the pupil here's the iris and as you know from the last video we were looking at the eye from a lateral view at the front of the eye there's a structure that bulges out which would be called the cornea Quenya somewhat transparent so all of this out here all the way around would be sclera the optic nerve penetrates the sclera and enters into the eyeball but excuse you an idea so when we're looking through the cornea we can see the iris the colored part of your eye there are six extra ocular muscles that pull on the eyeball one that's attached here and runs almost straight back on we'll call the superior rectus the superior rectus when it contracts moves your eyeball to look in the superior direction there's one over here that's attached that runs kind of had an angle they all run towards the optic canal so to speak and this one would be called the medial rectus since the nose is over here this is the midline the medial rectus when it contracts pulls the eye across the midline of the eyeball here would be the lateral rectus so we can say that the medial rectus add up to your eye and brings it towards midline and in the lateral rectus abducts VI and then we have the inferior rectus the inferior rectus pulls your eye to make it look in the inferior direction so these four muscles the name of the muscle actually tells you which direction it moves the eye the medial rectus makes you look medially the lateral rectus will make the eyeball look out outward or laterally superior rectus moves your eyeballs up inferior rectus makes you look down at your toes if you did not move with your head now and later on we're gonna learn that in the centre of our field divisionist light comes in here really what's happening with our lens and the cornea is that they're going to try to focus the light a dot of light right on a structure called the fovea which is in the retina so when we look left or right one of the things that happens is this this is about the only way I know how to do this okay if I put a blue dot on the palm of my hand then when I'm looking straight at the camera light would be hitting there if I were focusing my eyes on that point but once I start to rotate it a little bit because of the way the eyeball is shaped I would actually have to rotate the eye a little bit in another direction in order for that fovea to be in the center of line of vision so when we look left and right we also have to slightly rotate the eyeballs so that we can keep the fovea in the center of the line of view because of that we also have two other muscle called obliques there's one that comes from underneath the eye we'll run a little bit posterior to this back here and attach this way that's the inferior oblique when it contracts it rotates your eyeball so that the top goes laterally and the bottom goes medially and then there's another muscle that comes up and loops through a little piece of connective tissue over here and attaches to your eyeball like this that one's called the superior rectus and when the superior rectus contracts it pulls through a little pulley or trulia and make sure eyeball rotate in this direction if we were looking at the right eyeball so one thing that I think is important for people to know is that there were three of your 12 cranial nerves which were dedicated for eyeball motion that must be really really important for vision and for survival and reproduction so one of the things that we know is the oculomotor nerve controls almost all the eyeball muscles so when you go over the cranial nerves cranial number 3 cranial nerve number 3 was called the oculomotor nerve oculomotor means moves the eyeball the way that you learned this is this so cranial nerve number 4 was called the trochlear nerve while trochlea means pulley and that's what this little loop of connective tissue is that this muscle loops through so the trochlear nerve actually controls the superior oblique and then cranial nerve number 6 this is called the abducens nerve the abducens nerve is going to add duct your eye to AB duct means to move away from midline so cranial nerve number 6 controls the lateral rectus cranial nerve number 4 controls the superior oblique and then cranial nerve number 3 controls the rest of the eye muscles it's kind of an easier way to know which eye muscles are controlled by which cranial nerves you should know that no cranial nerve three controls all the muscles of the eyeball except for the one that the trochlear can turn controls superior oblique and the abducens does the lateral rectus all right now all of those muscles are pulling on this connective tissue and so we want it to be really really strong now I'm going to erase all of this I hope you got that down and I need to do the last structure or the second structure which is part of the fibers to knit which is the cornea well like I said before in the last video if a photon of light hits the sclera it's reflected off it doesn't enter the eyeball the cells that are going to interpret the photons of light that are going to be triggered by them and send a signal to our brain so we can see are inside the eye in the layer of the neural tunic and the retina so when we are seeing something what we need is when the light hits the cornea it actually penetrates the cornea and enters into the front of the eyeball so that's what we're going to say is the function of the cornea so we erase this the second major structure of the fibers tunic it's called the cornea the cornea is said to be a translucent or transparent actually it's somewhat opaque to be translucent means it really lets all the light through and it does it does refract some of the light a little bit but we refer to it as a translucent later or poor part of sorry it's the translucent part of the fibrous tunic that allows light or we can say photons of light to enter the front of the eyeball okay those are the two major structures of the fibrous tunic and by the way don't forget about the conjunctiva which covers the cornea and a little bit of the sclera so now I'm going to erase some of this we're going to move into the second layer of the eye which is called the vascular tunic and as we do the vascular tunic there's a lot of structures and there's a lot going on so follow up okay when it comes to the second major tunic of the eye we're going to talk about the vascular tunic so the major structures of the vascular tunic one of them is called the choroid current the choroid later also called the choroid plexus now before I go into all of this there's a concept that I want to repeat to all of you guys and get across to you now normally I have such a big board in class and I have a drawing of the eyeball to the side and we just keep adding notes I'm gonna redraw this and we're gonna see all the anatomy come together but I want to explain the choroid plexus of the necessity for it so the example that I like to use for my classes is this imagine if you decided to move off the grid to get away from the rest of the world so probably what you're going to do is if you're going to start to build a little Casa somewhere you're gonna do it somewhere near water we have to have water in order to survive but not only do we need water to survive we also can make waste in the water and if the rivers flowing in this direction then you can go get water you can make coffee with it you can do all the things you need to do and if you make waste into the water it wash away also other animals fish little crabs and things dear other animals need to come to use the water as well which provides you a source of food and nutrition now over time what if someone else besides saying I want to live off the grid too and so other people start moving in oh and by the way you get a partner in life and all these people start moving in and moving downstream building little houses well that's no big deal because if you've got to go to the restroom it all gets washed down to them well what happens if people start moving upstream from you and these people start not only utilizing all the supplies but also start making waste in there you go out to get a bucket of water to make some coffee in the morning and your neighbors reading the newspaper sitting on the river making waste well some people would wait long enough and let it wash away I know it's no big deal some people would say oh no I will never ever ever ever drink from that River again how gross one of the things we don't realize is what if the river goes around and around and around and so everything you take out of it and dump into it isn't gonna circulate back to you well the river represents your blood our blood is filled with water and ions and nutrients that we need to sustain life we take stuff from it and we don't stuff in it the people represent the cells of your body eventually if we continue to dump waste into the river it becomes contaminated or you've heard this term sepsis where it goes septic if you know what a septic tank is that's where everything goes when you flush the toilet at a farm well we don't want our blood to become septic it would start to poison ourselves and we would all start to get sick and die that's what happens we don't clean our blood now fortunately mother nature puts up organs here what is called the liver and we have a couple of kidneys that clean our blood and filter but on occasion some of the wastes of some cells even though it's in trace amounts will get into an area before we can go and filter and clean it now one of the things I like to remind my students is this our cells have a range of conditions in which they operate called homeostasis and for some cells those ranges are very narrow everything must be perfect the subs are big wet sore weenies oxygen and glucose calcium and sodium and potassium and everything's not just right those cells start freaking out and dropping like flies some cells have very wide ranges of homeostatic conditions they can take big fluctuations and things I like to think of it this way the biggest wimps and the human body are neurons so neurons can't handle even a little bit of toxin and trash from other cells being dumped in so what happens if one of these two cells says I can't handle that and I'm gonna move back to the city unless you do something what you have to do then is you've got to actually siphon off some of the fluid run it through a special filtration membrane and then what you get out would have been cerebrospinal fluid and this filtration membrane is a special series of blood vessels in the brain that we called the choroid plexus so essentially the choroid plexus filters your blood to flow marieville spinal fluid a really pure and clean solution that has lots of nutrients and ions and valuable stuff for the neurons and then as they dump their waste back into it it gets reabsorbed back into our bloodstream well the red light inside the eye is neurons mm-hmm it's got to have the same kind of filtration membrane so the choroid plexus or the colloid coat of the eye basically supplies oxygen nutrients and ions and it removes waste and carbon dioxide back into the bloodstream that's the major function of the choroid code which is a large part of the vascular tunic so now that we have this concept down I hope you understand that concept because every where in the body that we have neurons we have special filtration structures a coral-red plexus so to speak so I'm gonna erase all this and we're going to continue on with the other structures of the vascular tunic I'm gonna do some of this and then I'm gonna stop because when these videos get too long guys it's 6 3 forever to load them into YouTube and I'm trying to beat the deadline of the first day of class so when we go through the choroid code there's the second major structure or through the vascular tunic I should say it's called the ciliary body now anytime you see body and ANP that means there are several structures that function together and the ciliary body is made up of three basic structures are three major structures there's the ciliary muscle the ciliary muscle is a muscle that controls the shape of the limbs for what we call accommodation sorry or focusing when we have to focus the shape of the lens our lens is rather elastic it's made up of some elastic fibers that that are called lens fibers that allow the lens to be to change shape the muscle is going to pull on the ends of it or relax and allow the lens to be pulled into a flatter shape or when it muscle relaxants actually the muscle contracts it becomes rounded we'll talk about the details of that so that's what the ciliary muscle does attach to the ciliary muscle some structures called suspensory ligaments the suspensory ligaments simply suspend the lens for a combination or they just suspend the lens we're just going to leave it at that for now and I'll draw this and show it to you in just a second and then we have the lens itself the lens can change shape to focus at different distances and I'm going to explain all this and then we'll wrap up this part of the video ok so the similary Russell is going to contract and relax it's going to change the shape of the lens what suspends the lens or attaches it to that muscle of suspensory ligaments and then the lens itself since it's made out of a lot of lens fibers which are very elastic in nature can change shape to refract or bend light there's one other structure that's a major player and really to but one of them is the lack of the structure in the vascular tunic there is the iris so one of the things we say about the iris is is that it is the big more pigmented part of the vascular tunic oops and spell that very well it's the pigmented part of the vascular tunic and its major function is it can regulate the amount of light entering the posterior cavity of the eye and I'm gonna explain what this is in a minute okay so the structure called the iris as the part of your eye that has pigment or color to it that gives you your eye color and it's really a muscular structure that can regulate the amount of light that enters the posterior cavity of the eye within the iris is a hole called the pupil so for the pupil it's simply just a hole in the iris that allows light through so for you to see what I'm talking about I'm gonna draw this stuff out so we're finishing up with page 11 going to be moving on to page 12 and I'm going to talk about all of these structures okay so let me erase all of this I hope you got the notes down and let me explain a few more things and let's look at it visually so we can actually see what we're talking about so as you guys know the fibrous tunic will arch around to the cords of the back of the eye like this I didn't draw a very neat version of it but you get the idea there's a little border between the sclera and the cornea called the corneal limbus or the limbus of the eye and then the fibrous tunic comes around this way kind of a little bit inferior to the midline is where the optic nerve comes into the eyeball okay so this is your fibrous tunic sclera and cornea we've done that entering into the eyeball through the optic nerve or some blood vessels and some of those blood vessels run just deep to the sclera this layer of blood vessels is what we're going to call the choroid coat or the colloid plexus of the eye it's going to deliver blood to the idol now when we get close to the front of the eye there's two major muscular structures one of those muscular structures is what we call the ciliary muscle I hope that color shows up I'm going to switch colors so that you can see a little bit better I'm not sure how well orange shows up on the camera I don't actually get to watch all of my videos so there's a muscular structure that hangs down in here and this structure is the ciliary muscle now as I stated in the last video briefly the ciliary muscle is actually a ring shaped muscle like this okay it's got some fibers going around like this and the ciliary muscle if I cut it in half well before I finish let me show you this there's some little tiny hairlike structures then go all the way around the edges of the ciliary muscle called suspensory ligaments and then they're going to attach the lens here so as the ciliary muscle constricts and dilates it's going to change the shape of the lens because these little suspensory ligaments are suspending the lens so there'll be some little connective tissue pieces here and then the lens will be suspended like this so this is our ciliary body the ciliary muscle the suspensory ligaments and the lens and when the muscle contracts and relaxes and will allow the lens to change shape the other muscular structure that comes off of that is going to be this structure that hangs down like this called the iris and again the iris is also a ring shaped muscle or around muscle but there's actually two layers of muscle here one of the mut layers of muscle goes around this way we call this from the pupillary oops constrictor muscles when this muscle which is actually called an annular muscle will write some of this out and talk about it later but it's an angular muscle the term on guru means ring like the end and this finger the annular fingers were your ring finger or the you know the anal sphincter this is a sphincter type muscle when it comes when it could contracts it actually is going to squeeze down and make this the size in here much smaller the hole in the middle would be the pupil so if the pupillary constrictor muscle contracts the pupil get smaller there's another muscle in the iris where the fibers actually run outwardly I'm going to use a different color so you can see this the fibers are going to run out like this and these are the actual lines that you see because this muscle sits in front of the people re constrictor and the muscle fibers that are running outward are actually going to pull in this direction they're going to pull outwardly and that represents what we call the pupillary dilator muscle that is actually described as a radial muscle when we talk about radial muscles what we mean is the radial muscle fibers will radiate out in a ring like rays of sunshine and the other muscles are ring shaped muscles so when the pupillary constrictor muscle contracts the people actually get smaller when the pupillary dilator muscle contracts it dilates or increases the size of the pupil so if we took a good look at this in this sense when light enters the front of the eye let's say a photon of light enters the cornea if it hits the iris that light cannot enter into the back of the eye where the retina is the only light that's going to be allowed into the eyeball has now which penetrates the pupil itself and hits the lens so some of the light gets blocked here the only amount of light that enters the back of the eye called the posterior cavity back here is going to be that light that passes through the pupil if I increase the size of the pupil then when I dilate my pupil and it gets larger you can see that a dilated pupil would allow all of the light that was previously blocked into the eye so that's gonna be really important because as you know if it's too bright you can't see it's almost blinding if it's too dark you can't see much detail so we had to have just the right amount of light and reflexively these two muscles are always adjusting the size of the pupil to regulate the amount of light entering the back of the eye okay so um one of the things I do want to mention at this point because that's the next thing and the note set now that we know the anatomy and we see it let me erase all this and I'll redraw much more pretty and neatly okay now that we can kind of start to visualize the anatomy here we can start to understand the words that were writing and the words in the textbook and they'll start to make more sense so I'm going to put a few details about the pupillary dye later and the people are a constrictor muscles down and I want you to know this information okay because it's really important for your understanding of a lot of things so now if I'm gonna draw redraw the pupillary constrictor muscle well let's say the pupil is that big and the pupillary constrictor muscle goes around like this we're not drawing the iris now I'm actually going into this muscle or the muscles inside the iris itself when that muscle contracts the size of the pupil actually gets smaller the iris doesn't change size but the the muscle contracts making the pupils smaller so for the pupillary dilator muscle I'm sorry people are constricting it can decrease the size of the pupil in two scenarios in a in a dark room I'm sorry in a bright room getting ahead of myself when it's too bright or under parasympathetic stimulation our people are in constrictor muscle will decrease the size of the pupil if it's too bright or if you're under parasympathetic stimulation I don't like and my 10min ship is kind of poor right there but as you guys should know parasympathetic is resting digest if you're trying to take a nap or go to sleep you want less light in the eyeball that helps you fall asleep so you should know that the pupil area constrictor can decrease the size of the pupil when you are in a bright room or under parasympathetic stimulation now I'm gonna erase all that for the pupillary dilator muscle let's say the pupil is this size the people are a dilator muscle its fibers are run outwardly and when you look at the models you'll see within the pupil all these lines running out you're actually seeing the the muscle fibers of the people are you dilate or muscle when that muscle contracts the fibers are actually going to pull out in this direction the way that they're attached inside and so what it's going to do is it will increase the size of the pupil as the fibers pull it outwardly why do we want to do that it will increase the size of the pupil then your two under two conditions in a dark room if there's not enough photons of light hitting the retina to trigger a visual transduction and you can't see you're going to try to let more light in or under Paris super that I'm sorry under sympathetic stimulation when someone is excited