hey everyone welcome to professor long lectures anatomy and physiology professor long the series of videos that you're watching are designed for students taking my anatomy and physiology courses at Del Mar College in Corpus Christi Texas anyone else out there in YouTube land stumbles across these videos then you guys know that we're in the corona virus or Cova 19 shutdown and all of our face-to-face classes have been switched to online which is the reason I'm doing this series of videos to deliver the lectures to my students now if you find them helpful great if not oh well but they're designed for students taking my class to focus on the topics that I think are important for those people who are destined for the allied health science majors alright so this should be I believe the sixth lecture in the series of lectures on the sensory nervous system we've been talking about the general senses we talked about senses of olfaction and gustation we're going to begin the sensations and the sensory physiology of the eyeball and then we have to do hearing so we have probably three or four videos left if not more there's a lot of information for the sensory system and so we're going to do the best we can this first drawing in this first part of the lecture I'm going to do is really just going to be a lot of the anatomy of the eye when we understand the anatomy of the eye then we can start to go into the physiology and into the note set but for now you need to get some basic understanding of the anatomy of the eye this will help for the labs so I'm going to do two different pictures the first picture I'm going to do is going to show you an anterior view of the eyes that sits in the eyeball so one of the things you'll notice I'm going to draw the right eye so just for reference sake I'll put a nose over here one of the things that you'll see when we look at the anatomy of the eye as we have this little fold in the corner here and then the eyelids come up and down and meet over here okay I didn't draw this quite anatomically correct but give me a little a little bit of time and I'll get it right our eyelids the fleshy folds that surround the opening or the eyeball are called the eyelids or they're called palpebral there's a superior palpebral and an inferior tell me how Pedro for each time the area where the items need these little folds were they meet or referred to as a canvas this one is called the medial I'm sorry this one would be called the lateral canthus my bad I'm thinking of where I'm going wrong now where I'm at and then right here would be the medial canthus okay I'm gonna erase my label for the medial canthus because I'm gonna need to label another structure right there but it's right where the two eyeballs meet called the kantak folds or the medial and lateral canvass okay now we also have a superior and inferior kantak fold but I'm not going to label those we're not going to talk about them sitting behind your eyeball on your eyelids or the puppy brie would be the actual eyeball itself the eyeball itself has a white part of the eye which is called the sclera so when we talk about the sclera we're only talking about the white part of the eye man we're gonna go into the laters of the eyeball just a little bit now if I were to look at the eyeball from a sort of a lateral view or actually if I slice it in half and looked at it from a midsagittal view the eyeball would be shaped like this so we're gonna make this drawing again in just a little bit we're gonna make it more detailed where you can see all of what you need to see but the outer covering of the eye is going to come around like this and there will be an opening in it to which the optic nerve enters the eyeball okay this outer covering out here would be called the sclera the white part now the sclera is made out of a lot of dense connective tissue it's collagen fibers criss-crossing and multiple layers some running this way some running this way so learning in angles many layers of it which makes the sclera very thick and tough if it were all like that then no light would be able to enter the eyeball and one of the innovators of the iowa the retina is where we're gonna have the photoreceptors the cells that detect photons of light for vision so part of what we call the fibrous tunic and I'm just going to like this out I'm gonna discuss it now and while we're at it the fibrous tunic that the eye has what we call three major coats or laters or tunics okay the fibrous tunic is called the fibrous tunic because it's mostly dense connective tissue the sclera is a major player but near the front of the eye there's a part where the sclera the collagen fibers and the sclera instead of criticizing all strikes are lined up so perfectly that light can penetrate and this bulging section of the square that sticks out is called the cornea and where the two meet this little border where the clicked aspera and the cornea meet is called the limbus or the corneal luminous okay so the fibrous tunic contains the layer of dense connective tissue is very thick and tough called the sclera the function of the sclera is a point of attachment for the extraocular muscles so that when they pull it doesn't rip the tissue that's why we have some strong connective tissue there it also provides some shape and support for the eyeball and makes it very tough the cornea is a transparent portion of the of the sclera that allows light to enter the front of the eye if you're going to try to follow me I've already skipped a little bit of page 11 we're going to come back to this in just a moment but we're doing the bottom of page 11 the fibrous tunic is mostly sclera it's a dense layer of connective tissue or layer of dense connective tissue that provides shape and support for the eye and as a point of attachment for the what we call the extrinsic or extraocular muscles of the eye and in the cornea is a transparent portion of the or translucent portion of the fibrous tunic that allows photons of light to enter the front of the eye if a photon of light were shot at the eyeball and hit the square it would bounce off but when it hits the cornea and penetrates and enters the eye so that's the function of the cornea to let light enter into the front of the eye I'm not going to draw the cornea on here now the next layer of the eyeball is going to be called the avascular tunic every time you hear certain words that anatomy and physiology your brain should immediately jump to other things when you hear the term vascular you start to think of blood vessels so the vascular tuning is going to have a lot of blood vessels in it some of those blood vessels are going to penetrate the eye through the optic nerve and then fan out on the inside here and the network or complex layer of blood vessels that layer of blood vessels is called a colloid coat under the choroid tunic and that's part of the vascular tunic of the eye there's more structures that are part of the vascular to excuse me so the choroid coat is really as blood vessels and those blood vessels allow blood flow into the eye to bring to deliver nutrients and ions and things for all the neurons inside the eye and feed them all those nutrients and ions they dump their waste into it and then that fluid is going to be reabsorbed and taken back out of the eyeball so it allows blood flow to the eye to supply the eye with nutrients and ions and wash away waste know the other parts of the vascular tunic are several fold now before I I'm trying to do two things at once here because in order for you to understand what we're looking at here I kind of need this drawing one of the structures that sparked the vascular tunic is this large muscular structure called a ciliary muscle the semi-arid muscle hangs down inside the eye and sticks up from the bottom actually it's a ring shaped muscle we're looking at a round muscle like this but we've cut it in half we've sliced it and we're seeing it from this view so we're seeing the top part and the bottom part but it's really part of around the muscle I'm gonna redraw this and re label it in a little bit but that sumi airy muscle is going to contain or hold onto these tiny little ligaments these little pieces of connective tissue and they're going to suspend the lens those little pieces of connective tissue called suspensory ligaments they suspend the lens and in this structure would be the lens inside the eye and the ciliary muscle controls the shape of the lens so we can focus at different distances I'm going to go over all that stuff with you in in just a moment I'm trying to get to this structure there's another structure that's part of the vascular tunic and by the way the simiiariy muscle the suspensory ligaments and the lands are collectively known as the ciliary body okay there's another structure that hangs off of that that's a muscular structure that hangs down like this and that structure is called the iris and that's what I'm trying to get to the iris has a hole in it called the pupil and as light enters the front of the eye any photons of light that hit the iris are blocked from entering into the eye so as light enters the cornea if it passes through the pupil it will be focused back on to the retina so the iris is a muscular structure that's going to regulate the amount of light that enters into the back of the eyeball because too much folks too many photons of light too bright of a light will blind you you can't see well they're too bright or too dark of a light this muscle is going to control the size of the pupil to control how much light is entering the eyeball now the reason I do all that is because I'm not going to drop the cornea we're going to look right through the cornea now we're gonna see the structure that provides your eye color which is called the iris as a ring shaped structure if you have blue eyes it's the blue part of your eyes if you have brown eyes it's the brown part of the eye and there'll be some little lines running out from the iris this way all the way around it and the hole in the middle of the iris I'm going to put the little letter P here that's called the pupil okay the pupil is a hole in the iris and that's eye into the back of the light into the back of the eyeball the iris has muscles that can constrict or dilate regulating that light so when we look at the front of the eye we're really seeing sort of several parts of these two layers again I'm gonna go back over these layers and we're gonna write out all the details in a little bit but I wanted to give you some of this basic anatomy we have the sclera the cornea which we're looking through to see the iris of the pupil at the front of the eye we have the superior inferior palpebral the lateral and the medial canthus where they meet now over by the media this there will be a gritty squishy little pink organ like looking Dean then you'll see here and that structure can well we'll talk about its functions a little bit later but for now I want to focus on the eyeball itself now one of the things that happens and one of the reasons I'm drawing all of this is to give you this anatomy so we can talk about tears we're gonna jump around a little bit of the note set but I'll get to that in just a moment just follow along usually sitting superior and a little lateral to the eye and deep to the skin but up here by the ended is a gland called a lacrimal gland Lac Lima in in Latin and lagrima and many Spanish languages Portuguese and Spanish and stuff can mean tear so the lacrimal gland really is the tear gland coming out of the lacrimal gland there'd be some little channels called lacrimal ducts and those little lacrimal ducts would eventually run through the eyelid or behind it and release tears onto the surface of the eye now we are secreting tears 24 hours a day seven days a week we just don't realize it and what happens is as we're making and secreting the tears when we blink that wipes the tears over the surface of the eye one of the functions of tears is to keep the surface of the eyeball moist if you blow air across your eyes if you help your eyes open and a fan your eyeballs would dry out and start to itch and be uncomfortable so we moisten our eyeballs by blinking and wiping tears over them a second function of Tears is that tears can wash away any debris or irritants if something starts irritating your eye you will hyper secrete tears and they'll start to wash away all that trash and debris so now a third function of tears as tears contain an enzyme called lysozyme life so two lice means to digest or break and xym means it's an enzyme lysozyme is an enzyme that is in tears that has antimicrobial properties it can help bring down or digest and kill certain bacteria and some viruses our eyeball by the way is a huge Avenue for viruses and bacteria have you ever seen someone sneeze under a blacklight we will blow this mist of microscopic droplets all over the place upwards to ten to twenty five feet around our body so if someone sneezes at the mall and you're walking through it you might get a microscopic droplet that has some virus or bacteria and pick up an infection that's why we tend to wear face shields and surgery and things so anyway it's also why you should cover your nose and things when you sneeze so that you're not spreading viruses like the corona virus anyway sorry so now when when tears are being secreted the reason we don't we're not aware of them as they get whipped over by the top Hebrew to the medial canthus and it's our structure over here called the the latest lacrimal sir lacrimal lake I forget what that actual term is but it isn't it if we look very carefully at the eyelids under a microscope you'll see two tiny little pores like someone punctured the island those openings are called a lacrimal punctum punto would be plural and the tears are going to run over the eyeball and drain through the lacrimal punctum now if you look at the models in lab what you'll notice is there are these slight little truck shirt that sits over here underneath our skin that will have a hole or opening in the bottom that will drain into our nasal cavities these little channels happen to be called lacrimal canals and some books will use the term lacrimal canaliculi which means little canals and as the tears drain through these canals and collected in this large structure called the mackerel sac and then through a little tube called the nasolacrimal duct into our nasal passageways which by the way if you look in my notes set on one of the pages I believe it's page 12 I think it says list the structures in correct order through which tears would flow and let me see excuse me I got it I had an interruption there and it threw me off a little bit I apologize yeah it's on page 11 lists the structures in order that tears would flow through well first is lacrimal gland second is the lacrimal ducts third would be the lacrimal punctum fourth would be the lacrimal canals fifth would be the mackerel sack six would be the nasolacrimal duct and then we reabsorb the tears into our nasal passages because of the enzymes and other things present in tears the salts and what you rotate your nose so when we secrete too many tears it can sometimes irritate the nose and then your nose starts to run your the mucus trying to flesh things out now we're not aware of the tears usually because we are secreting them at the exact same rate that we reabsorb them when we become either very emotional or something as irritating the eye or damages the eye we can hyper secrete tears and will secrete them faster than these little tiny drains can can drain them and the tears will run over the edge of the pulpy bring down your face so I wanted to talk about the structures of tear formation where we secrete tears or where we absorb them and their flow through here now I'm gonna do another drawing in just a moment but I'm going to stop this video for now and I'm gonna go through all the level up I'll stop the video in a moment but I'm gonna go through some other structures and some other things in the note set and then we'll get into the coats of the eye and get into their great detail so if you're following along in my notes that when it comes to vision on page 11 there's a few definitions number one you need to review the anatomy the eye we've done some of it here we'll do some more in just a moment there's some definitions you need to know when a chalazion is you need to know what a sty is and it asks you to define lysozyme now one of the structures that asks about is what is the palpebral and the ocular conjunctiva so think about this okay I'm gonna erase this drawing and I'm gonna redraw without all the extra stuff on it real quick because I want to show you something really interesting as your eyeball comes down towards the front and the cornea bulges out so this would be part of your sclera and your cornea at the front of the eye your eyelids would be sitting here like this there's some eyelashes sticking off now there's a very thin membrane that coats the visible outer surface of the eye and it sits right on the sclera and the cornea it is a single layer of squamous epithelium it's simple squamous epithelium that layer is called the ocular conjunctiva or some people say conjunctiva conjunctiva the ocular conjunctiva that exact same membrane is going to fold back and my up against two and eventually blend into the epithelium on the back of the eyelid but since it's on the back of the eyelid and we call that the palpebral conjunctiva is a single layer of squamous epithelium and the ocular conjunctiva actually coats or covers the visible outer surface in the eye so if you're trying to put a contact lens in and you touch the surface of your eyeball you're not physically touching the cornea directly you're touching the ocular conjunctiva on the surface of the eye that would be like me putting saran wrap over a window I wouldn't be touching the glass I'd be touching the saran wrap now a couple of things number one if you do wear contacts and one gets stuck up in your eyelid people start to panic and think oh my god it's going to get behind my eyeball and damage my brain well it can't that contact lens gets stuck up here and it can't go back behind your so the conjunctiva covers the entire outer surface of the eye and the back of the eyelids and it's almost like a barrier to prevent physical debris and things from getting back into the eye when they help when the conjunctiva gets irritated it gets inflamed as you know itis is inflammation so we can develop what's called conjunctivitis pink conjunctivitis is just inflammation a redness and swelling of the conjunctiva and because we have these blood vessels on the surface of the eye start to dilate the red against the white sclera starts to look like a pinkish color so another term for conjunctivitis is pinkeye one of the things I like to address by the way and people get wrong is not all pinkeye is contagious if the pink eye or conjunctivitis is caused by physical damage like you scratch your eyeball or some sand gets in it that's not contagious it will get inflamed it will get conjunctivitis let's do the physical damage like an abrasion if it's due the bacteria if someone doesn't wash their hands and there's bacteria or a virus on their hands if someone goes to the restroom doesn't wash their hands they touch something you touch that then you scratch your eyeball you might transfer some bacterial or viral material under the surface the eye and it gets inflamed conjunctivitis that's due to the presence of pathogens is contagious if you touch your eye it's going to cause someone else to get it if they touch that same thing okay so know that about conjunctivitis know when it is and when it is not contagious okay and then we listed the structures in order through which tears would flow so that's going to get us through the initial portion of some of the anatomy of the eye and some interesting stuff I'll ask you about the order of the flow of tears I'll ask you about some of the layers of the eyeball but I hope that helps you get oriented I'm gonna stop this video here I'm sorry for the interruption I hope I can edit it out but if you see this gap my son went for a run and he came in and was knocking on the doors I apologize I'm gonna try to edit that out so if you see a stop in the video and fix it back up it's because I figured out how to do some editing some trimming of the video I've been working on that trying to get smarter anyway thanks for watching I hope you learned something I hope you have as much fun as I did I'll see you on the flip side of the next video