VideoPoints

• ••• • •• • ••••• • •
BIOL 2301 Human Anatomy & Physiology I - BIOL2301_lecture21_1109
Help Tour
© Distribution of this video is restricted by its owner
Transcript ×
Auto highlight
Font-size
00:01 Courage morning y'all. So I'm There we go. All right.
00:13 today we have a lot of We're actually gonna spend probably 95% of
00:17 time in the eye today. Uh starting point though is going to be
00:21 gene generically with thema of century which is kind of a continuation of
00:26 we were talking about on Tuesday. what I was describing on Tuesday,
00:31 said, hey, remember when we're with these pathways, don't let all
00:34 names scare you, right. that's the big, the big takeaway
00:37 , don't let the name scare They're pretty simple. There's either going
00:41 be two neurons or three neurons in pathway. And the names of those
00:46 are pretty simple or the way we them is pretty simple. We call
00:49 12 and three, first order, or third order. All right.
00:53 so what we're looking at here is a generic term to say,
00:57 what is a somatosensory pathway? Somatosensory detection? That's what this is
01:03 All right. So somatosensory pathway is touch detection. And what are we
01:08 ? We're taking a signal from where receptor is located and we're taking it
01:12 to the somatosensory cortex so that we perceive that sense of touch or pain
01:19 temperature or whatever. So it's basically with that on the outside. So
01:24 are ascending pathways. All right. the first thing. So when I'm
01:29 with the sense of, of anything in anything that's sensor, it's always
01:33 to be ascending. All right. if we are below the neck,
01:39 should not be news to you. gonna use a spinal cord sensory
01:43 And if I'm above the neck, gonna be using a cranial nerve.
01:47 that sound familiar? So far? . I like seeing nodding heads this
01:52 in the morning. All right. , so far there's nothing new
01:55 Here's the new part, the two pathways. All right, I'm gonna
01:59 you the secret here. We're keeping simple because this is a freshman level
02:04 sophomore level class at college, When you go on to nursing
02:08 medical school, p A school whatever you get to learn the names
02:13 every single one of these stupid Yay. But remember all the pathways
02:18 named because of where they start and they go. All right. So
02:23 us, we have, and before even turn the slide over, I'm
02:26 to see if you can figure out the name means. We have the
02:29 column pathway and we have the antri pathway. All right, dorsal
02:35 Is there anything that we've talked about the spinal cord? That is a
02:40 ? I heard a yes. are you brave enough to tell me
02:45 it's the gray or let me, make it simple, multiple choice gray
02:49 white matter. OK. Gray? ? Let's vote gray. Why?
02:58 . Where are the tracks located? matter? OK. So when you
03:04 about a track, we're always talking being in the white matter. And
03:08 what we're looking at is we're looking one of the dorsal columns in the
03:13 ma or one of the columns of white matter. Remember we had three
03:16 , we called them fasi lati, ? Fasula, fasula. Remember those
03:21 had a dorsal ventral and a lateral . You gonna what now go back
03:27 look in the last unit you'll see like, oh OK. Yeah,
03:30 they are. So now let's take look at the names again. We
03:34 the dorsal column pathway. So which of the spinal cord would that be
03:39 white matter? The dorsal column? right. I'm gonna show you the
03:46 here. Actually, I don't think even have a picture. I'll make
03:48 easy for you. I'll draw How do we draw a spinal
03:54 One of these ugly looking things. we draw a little butterfly on the
04:01 so far. It look right. this area right here. What's this
04:08 the dorsal column. What is this down here? The ventral column?
04:14 this stuff over here? The lateral ? I'm not pointing at the
04:18 I'm pointing at the white matter. . So that's how you can look
04:21 it. All right. So now take a, take a name.
04:24 at the name again, dorsal Where is it gonna be located?
04:29 one top good? All right, lateral pathway. There's two names.
04:36 is it here? Is it Is it here? Yes. So
04:42 here, it's basically like uh the that's down here someplace. All
04:45 So that's all it is. in terms of what they're carrying is
04:49 carry different information. So one of things you can do is say once
04:53 learn the name, I know what carrying. So when I'm dealing with
04:55 dorsal columns, I'm dealing primarily with touch and proprioception from a position of
05:02 , of, of a limb or in space. When I'm dealing with
05:05 anti lateral pathway, I'm dealing primarily pain and temperature. All right.
05:10 , are those absolute no, but good enough for government work.
05:15 So uh gotta come back over here touch this stuff. So that's our
05:20 point. We already mentioned this. so we're just bringing it up
05:26 What are we dealing with when it to a somatosensory pathway? Three
05:31 First order, second order, third . All right. That's just how
05:34 name them. The first order neuron always a neuron that has the signal
05:40 in from the peripheral nervous system. cell body is located in that dorsal
05:44 ganglia. We always enter via the root, right? That's the
05:49 the outdoor is the ventral root, ? So that was why we kept
05:53 through that stupid cadence and you're why is he making me memorize this
05:56 stuff? It's because it keeps popping over and over and over again.
05:59 right. So we got the dorsal . There's our dorsal root ganglia would
06:02 where those cell bodies are located. then we come in and we enter
06:07 the spinal cord when we enter the cord, one of two things can
06:11 and it depends on which system you're at, you can come in and
06:15 travel up the spinal column. So would be, for example, in
06:19 dorsal column and then you're going to up here in the brain stem.
06:25 right. So that's one possibility. other possibility is you come in and
06:29 terminate in the gray matter of the cord. And that's where you're going
06:32 synapse with that second order neuron. notice up here, second order
06:37 second order neuron. All right. the second order neuron is gonna be
06:42 the central nervous system is the key to walk away from where I uh
06:46 synapse with it is gonna be depended which pathway I'm looking at. All
06:51 . So once I get that second neuron, what I'm gonna do is
06:55 am going to then project up to third order neuron. The third order
07:00 is located in the thalamus. All . So really, really simple.
07:05 order neurons, peripheral nervous system, order neurons are, are usually gonna
07:10 either the spinal cord or gonna originate the brain stem and they terminate at
07:14 thalamus. Third order neurons originate at thalamus and go on to the somatosensory
07:19 . And that's what they're trying to you. All right now in the
07:26 , what we see up here is see decussation. So you remember we
07:30 , oh, the left side of brain is primarily concerned with the right
07:32 of my body and vice versa. you remember us talking about that just
07:36 . All right. And so what is trying to show you is why
07:39 happens. OK. The information is in on one side, it's gonna
07:45 over at some point. All we're not concerned right now. When
07:49 it crossing over? But you can here here it's crossing over and now
07:53 on the opposite side. Here, stays on the same side. And
07:56 once you get that uh up here the brain stem, that's when you
08:00 over. It doesn't matter what did do? I crossed over? All
08:06 . This is the decussation. That's the term we use is decussate means
08:11 cross over anything else I see up . All right. So let's start
08:19 our dorsal column. All right. , it originally has, I
08:22 this is kind of the abbreviated It's like calling the medulla the medulla
08:25 of the medulla Langa, right? original name is the dorsal column,
08:31 mcal system. Oh my goodness. , what's it doing? It's telling
08:36 where you're starting and where you're All right. So do you remember
08:41 we looked at the medulla and the and the brain stem? And I
08:45 , hey, here we have these nuclei. I want you to learn
08:48 names right now because we're going to them later. And you all looked
08:51 me like a bunch of fish that just been caught and brought out of
08:54 water, right? And I don't worry about what they are just
08:59 , we're going to come to And then I mentioned another structure.
09:02 said, hey, there's this thing the medial meniscus and it's a generic
09:06 that is basically a tract of fibers up through it to these nuclei.
09:12 right. So now we're here on day where we're now applying that.
09:17 right. So what we have here we're dealing with, remember, dorsal
09:22 with fine touch and proprioception. All , we're using myelinated a beta
09:28 So is that fast or slow, . That's what I want to hear
09:32 fast. How fast we don't It's just faster than slow. All
09:37 . So again, three neuron primary secondary tertiary. All right,
09:42 primary neurons enter in. So you see their cell bodies are located over
09:47 out in the peripheral nervous system. where the dorsal root gangling would
09:51 They enter into the central nervous system the spinal cord. They go through
09:55 dorsal column and they travel up to brain stem and in the brain
10:01 what they're going to do is they're to terminate in these two structures.
10:06 nucleus gryllus and the nucleus ciais, one is which, well, the
10:11 is for fibers coming from the lower , whereas the cis is for the
10:16 body. All right, let's just really quickly. What is the upper
10:21 ? What's the lower body? Ok. So keeps that order that
10:28 described and said, the nervous system highly ordered. All right. So
10:32 have the fasciculus and uh the uh fasciculus refers to the track itself.
10:38 the gricius is for the lower fasciculus is for or kotis is for
10:42 upper body. All right. So they're terminating, that's where the cell
10:47 of the second order neurons are. those are the nucleus chrysis and the
10:51 Ciotti. All right. So this would be lower, that would
10:55 upper body information. And then those are leaving from the brain stem,
11:01 cross over to the other side. you see that dec ace and the
11:06 that they're using is called the medial pathway. All right, that's what
11:12 just referred to. And it travels to the thalamus where it terminates on
11:17 third order neurons and the third order originate in the thalamus and then travel
11:21 to the somatosensory cortex. Again, artist screwed this up because they should
11:25 done one up to the upper one to the lower body to make
11:28 match. But it's an artist and doesn't know his biology. All
11:33 So in very, very simple just remember 123, right, the
11:40 for the dorsal are going to be up these tracks that go to very
11:45 locations to take information from the lower or the upper body. And then
11:51 travel through a specific track to the and from the thalamus to the mesentery
11:56 . All right. That's why I you to learn those names. That's
11:59 dorsal column, fine touch, pain, and temperature. On the
12:06 hand, are you going to use inter lateral system? Now, this
12:09 a little bit better because they show the actual structures down here of the
12:13 cord. So you can kind of what's going on again. How many
12:17 do we have? Three, first second or third order? All
12:23 Where are we going? We're going to cerebral cortex, what's involved the
12:27 ? All right. But here the that we're gonna use have special
12:32 they're called the spinal thalamic pathways or spinal thalamic tracts. And they have
12:37 specific names depending upon where you're So it could be the lateral spinal
12:40 track where anterior spinal thalamic tract. right. But again, the name
12:45 scare you. You should look at name and say what is it telling
12:48 about this pathway? It's using the cord and it's going to the
12:53 All right. And which side is on? It's either the anterior or
12:57 the lateral regions of the spinal That's all it is. So you
13:02 be scared by the big long All right. So we're primaries.
13:07 we're just gonna just kind of do side by side. So you can
13:10 here the primary is coming in. can see the cell body. Cell
13:14 is located in the dorsal root It comes into the dorsal horn of
13:18 gray matter. All right. Why gray matter? Why doesn't it just
13:22 in the white matter because we've got have a cell body there for that
13:27 order neuron. All right, gray represents cell bodies. That's why it's
13:32 there. All right, this is of a chicken and egg explanation.
13:36 right, the gray matter is cell . So that's why it's there.
13:43 we're gonna do is that we're gonna take that second order neuron and we're
13:46 to cross over in the spinal Notice it doesn't matter which tract.
13:51 right. And then what we do we pass out of the gray matter
13:54 we're now forming the tract of, interest. All right. So what
14:00 have is we have the anterior pathway so it's not a really good picture
14:04 it's trying to show you it's over down below and this one is trying
14:08 show you, oh look, it's out here over to the side,
14:10 the artist did a crappy job. you can just think, oh if
14:14 anterior, it's down here. If lateral, it's out here. All
14:19 . And what we're doing is we're on up. What is lateral,
14:22 is lower body, anterior is upper . At least they got those two
14:26 labeled in the right order. And where are we going? We
14:31 on the opposite side, we travel up and we go to the thalamus
14:37 look, he did it right. time you see that up here would
14:42 the legs and down here, that be your hands or your arms.
14:47 . So in the primary cort about century cortex, we go and that's
14:53 we're detecting or perceiving a sense of or a sense of temperature. That
15:00 all we need to do when it to these pathways. All right.
15:06 dorsal column versus spinal thalamic or an system, proprioception, fine touch versus
15:15 and pain. 1st, 2nd, order, what's the name of the
15:20 coming up? That's it pretty I spent a lot of time just
15:25 about that. Are there questions? . So in terms of both
15:38 what we're doing is remember the language the brain. This is actually really
15:41 good question. Why do I need these wires is kind of what you're
15:45 , right? Why do I need these systems? Sending signals? Can't
15:48 just send all the information up through same pathway? And the answer is
15:51 is because we're dealing with specific types signals so that the brain can understand
15:57 going around us. So my sense touch is distinct from my sense of
16:02 . My sense of temperature change is distinct from the pain and from the
16:06 of touch. And because the language the brain is simply action potentials,
16:12 need to have the signal coming down specific pathway so that my brain knows
16:16 type of signal it's actually receiving. so it's basically dividing up the information
16:22 a, in a specific way so you can perceive what's going on around
16:26 . That's why did I answer that ? Yeah. OK. Anyone
16:34 Yes, correct. So, remember was the purpose of the thalamus
16:42 in a very generic way it was sort information, right? And so
16:46 you're doing here, notice we're keeping really simple because we're just asking the
16:50 , how does it get up to place where we can perceive it?
16:53 remember the sense of pain is not stopping in the thalamus and then going
16:57 to the sma of century cortex, takes that information and sends it to
17:01 areas like to the limbic system. do I need to go to the
17:04 system? So that there is an aspect that I then associate with that
17:10 , for example, sadness, you , or maybe it goes to the
17:14 cortex as well. So what the of the thalamus is, is to
17:18 that information and say, OK, need to know where to send this
17:22 it doesn't say I need to know says I know where to send
17:24 I'm gonna send it up here. gonna send it over here. I'm
17:26 send it over here and then those parts of the brain are responsible for
17:30 the information in different ways so that gives you the broader context of that
17:37 or that sensation again. Good Anything else? No, no.
17:49 right. Let's go into the So what we're doing now is we're
17:54 transition away from touch, which is general sensation and we're moving into what
17:58 call the special sense, special senses slow down. My talking or I'll
18:03 slurring all over the place. All . And what we're gonna do is
18:07 gonna kind of pair these, these types of senses up into like
18:11 the eye stands out as being All right, the eye is responsible
18:16 detecting electromagnetic radiation and you have no structure in your body that detects electromagnetic
18:23 . All right, I'm gonna describe , but we're going to look at
18:26 ear which is a mechanoreceptor and it with the sense of hearing and the
18:30 of balance or equilibrium. And then we talk about the note, we
18:35 olfaction which is detecting chemicals and we the tongue which is gusta, which
18:39 detecting chemicals. So we have chemo . So we have electromagnetic receptors or
18:44 or light receptors is what we're going just refer to them as we have
18:48 receptors and we have chemo receptors that up our special senses. So let's
18:53 in on the, the one that of stands by itself. All
18:56 So this is our eye. The thing to do when you're dealing with
19:00 eye is start with a simple right? And so you just draw
19:03 out, it just circle and OK, here's my eye. And
19:06 you can see in this picture is it actually has three separate layers.
19:11 so what we're gonna do is we're to look at all three layers independently
19:14 see what each layer is responsible All right, but that's not all
19:18 gonna do. We're gonna actually also about how it protects itself.
19:22 uh, and how we, that these structures allow the eye to
19:27 light and so on and so forth how it takes light and sends it
19:31 exactly where it needs to be. , your eye sits in the orbit
19:35 the skull. You should know that surrounded by fat, which basically protects
19:40 and holds it in place. Um you look at these three layers,
19:44 have the fibrous or the outer which is gonna be the two structures
19:48 the sclera and the cornea. The is the white part of your
19:52 The cornea is the front part that allow light into their eye underlying that
19:57 can see here is this red part for purpose because we refer to it
20:02 the vascular tunic. This is where the blood vessels of the eye are
20:06 . They are the ones that provide nutrients in both directions, but we
20:09 have a couple of other structures. that would be the choroid. The
20:12 structures include the iris, the ciliary . And we're going to go into
20:15 detail about each of these, all . And then finally, on the
20:19 , this is the layer we're going spend our time talking about because this
20:23 the layer that actually does the light . All right, we refer to
20:27 as the nervous tunic because it is from nervous tissue. It's really interesting
20:32 it actually develops because it's basically a that's built inside out. It's
20:37 All right. But what we're gonna focusing on is we're gonna be focusing
20:40 the retina and the uh the cells the retina basically converge and form what
20:45 called the optic nerve. So, are we actually detecting? All
20:53 visible light is a form of electromagnetic . So you've probably seen this someplace
20:59 , right? Where it's like, , uh these are different wavelengths of
21:04 and within that we have all sorts things. So like here's a radio
21:07 , infrared ultraviolet x rays, gamma , all sorts of fun stuff.
21:11 in the midst of all that, is a very, very small band
21:15 electromagnetic radiation that stimulates the receptors in eyes and allows us to perceive the
21:22 around us. That's what we refer as being visible light. All right
21:26 , you do not need to, gonna see these numbers over and over
21:29 . You do not need to memorize . I'm not gonna ever ask you
21:32 is the wavelength of light. And other thing I want to point out
21:36 you here is that when we think wavelength typically, we think of a
21:40 which looks like a sine wave or co sine wave. If you remember
21:45 no light energy is really interesting. energy is interesting. It actually has
21:51 wave forms that work together. So a magnetic field and electrical field and
21:55 very complicated and scary. And if go onto uh Wikipedia, you can
22:00 pull up this picture and it's actually a movable image. And so you'll
22:05 to watch it for a while and these waves are doing things in sync
22:09 it's very, very complicated, but going to just keep it simple.
22:13 right. But the reason I mentioned is because when you think of sound
22:17 , they're like waves, you normally about like, you know, if
22:20 snap a rope, you can create wavelength. All right now to the
22:25 of a wave, you do need understand wavelength and amplitude wavelength is the
22:29 between two peaks or really the same along a wave. We just usually
22:34 to it as the peak it And this is the important part
22:38 All right, that's being carried by photon. All right. So when
22:42 looking at this, what you're saying is that there is an energy change
22:47 those wavelengths change. All right. second thing is amplitude, the amplitude
22:54 to the height. So basically the would be from the trough to the
22:58 of the nearby wave. So that and what that refers to is the
23:04 . All right. So I could uh shine a red light at
23:09 right? That would be specific but I could make it a bright
23:14 light or I could make it a red light. So that dimness or
23:18 brightness is the energy is, is the intensity, right? It's not
23:24 energy, even though it feels like have to put more energy to make
23:26 brighter. So there are two different . So that's one of the key
23:30 here. All right. So the level of, of processing here
23:36 or discussion here has to do with we protect the eye. The eye
23:40 an important structure um uh in that engage in our environment primarily through
23:49 All right. And this is not say for those people who lack sight
23:53 you can't engage, there are ways get engage other than sight. But
23:57 a species, as an organism, eyes are front forward. We are
24:02 , we are ST are critters that with our environment by looking at it
24:08 on and catching the things we want eat and so on and so
24:11 All right. So losing eyes is . So we have some structures that
24:16 us to protect our eyes. All . First off, we have
24:21 Well, that's a protective structure. , it's actually your sweat band.
24:25 right. So if you've ever looked somebody and I encourage you to go
24:28 in the mirror and go look at eyebrow and look at its shape.
24:31 right, it has this kind of shape. Some of them are more
24:35 than others. Right. Again, a genetic thing. But that,
24:39 shape of that eye or that eyebrow when that sweat is dripping down your
24:45 , it hits that eyebrow and that ridge and what it does is it
24:49 the water either away from the uh laterally or immediately towards your nose
24:55 that it doesn't drip directly into your . That's kind of cool. All
25:00 . So we have sweatbands. Second are your eyelashes now, your
25:05 right? We are going to be from the margin of your eyelids.
25:09 , I encourage you go look in mirror, get up nice and close
25:11 see how they're just jammed in the of these pr All right. And
25:17 they do is they prevent objects from in and touching your eyeballs. All
25:23 . Now, there is a right? All you gotta do and
25:27 know, yes, some of you go, I could touch my
25:29 Yes, I know you can. you fight really hard and hold your
25:32 open you. But if, as come towards your eye, if you
25:36 that, that, that uh you know, or touch the uh
25:41 that has a fiber in it, nerve fiber that creates a reflex to
25:45 you to close your eye eyelids. right. And yes, I know
25:49 could do it. You could if , if you try really hard,
25:52 you're gonna have to fight it for while. All right, it's a
25:55 reflex. All right. So what does, it just basically prevents
25:58 materials from getting into your eyes. it also serves as a fan.
26:02 you can imagine there's dust and all of horrible things in the environment that
26:06 just floating around. And if they near the eye, you know,
26:09 just kind of floating, they may touch the eyelash to make their eyes
26:12 . But every time you blink, you're doing is you're brushing the air
26:17 front of you, which pushes that away. So that's why we have
26:22 . All right, then your eye , these are the pal breath.
26:27 So that's a fun word to Uh they are the movable structures that
26:32 and protect, they're like shades, basically protect and cover the front of
26:36 eyes. Now, there is a core uh inside uh their skin on
26:41 outside. You have a special structure the conjunctiva that uh lines the inner
26:47 . There are glands associated with it are producing um uh a wax that
26:54 of keeps things uh basically your tears the surface of the eye. Um
27:00 those are called the tarsal glands. And in essence, what you've done
27:05 you are basically opening and closing a that basically just is a protective like
27:10 , if I close my eye, can sit there and do this all
27:13 long and I can't hurt my But if I open my eye and
27:16 my eye the same way, not good, right? Um The space
27:23 referred to as the palpable fissure, ? Just the space and then
27:30 um there's just a fun word. just gonna say it. Now,
27:32 gonna deal with it in a So this portion right here where the
27:35 Palle ray come together right here near nose that's called the coronal. So
27:41 lacrimal coronal fun word coronal, that's . All right. And basically,
27:49 where all the goo and the nasty would wake up in the morning and
27:51 , yuck, I got stuff But actually, it's an important structure
27:54 terms of how tears are removed from surface of the eye. All
27:59 So that was really outer structures. I mentioned the conjunctiva. So here
28:04 the conjunctiva. It starts on the of the palpable uh pal pal pra
28:10 we have names for the two sides it. The conjunctiva has the palpable
28:16 and then it has the side that the ocular side. All right.
28:22 , the way that the conjunctiva works that your eye sits in this
28:27 And if you wanted to, if didn't exist, you could just take
28:30 finger and run it behind your Can you do that? No conjunctiva
28:35 in the way. And so it creates the barrier from the external surface
28:39 your body to the internal side of body. All right. That's,
28:44 why it exists now. It is tight like saran wrap and it doesn't
28:49 the cornea, right. So you can imagine here's my cornea right
28:54 in the front. That's that bump that you see right here and it
28:59 attached to the surface of the sclera it's loose like a skirt. And
29:05 why it's loose is so that you then move your eye around,
29:09 If it was tight, I couldn't my eye in any direction. So
29:13 needs to be loose to allow that happen. All right. Now,
29:16 , there's a lot of vasculature in conjunctiva. All right. And what
29:21 doing is providing nutrients to the cells the sclera behind it, right?
29:26 nutrients to the cells in uh on the palpable side, on the
29:29 side. So when it becomes you get vasodilation, when you get
29:35 , that means blood moves close to surface and it gets all red.
29:39 that's when you have that pinkish reddish , right? It's not necessarily pink
29:44 . I'm just trying to avoid that , but that's what that when you
29:48 red bloodshot eyes, that's the blood in the conjunctiva. So, conjunctivitis
29:54 an infection of that structure. Notice on the surface, also highly
30:00 So that's why you say you poke in the eye and it hurts.
30:02 , that's what, what you're feeling nerves that have been touched there.
30:12 when we think of tears, we of here, don't we like my
30:18 form here and then they come rolling . But your tear ducts are located
30:23 , but your tear gland is located out here. OK. So on
30:29 superior side and lateral side of the , this is your lacrimal gland.
30:35 is constantly producing tears. All it's releasing this material which we call
30:40 . We're not even going to describe tears are. It's water plus a
30:43 bunch of other stuff. One of , I guess I'm describing it,
30:46 of the things that's in tears is some salts, but one of the
30:51 components of tears is immunoglobulin A IG and so what you can imagine is
30:57 that's watering on your body is where wanna live, right? And so
31:02 first line of defense against bacteria infecting eye is just soaking that surface of
31:08 eye with immunoglobulin, which is will up to bacteria. And so then
31:14 macrophages and other things as well recognize and kill it. So the lac
31:19 produces most of the IG A in body or releases most of the IG
31:23 in your body. All right there's other things there, there's like
31:28 . Um this is a uh an that specifically looks at bacteria and
31:32 makes them tear apart, rip So that's what lysozyme is. Um
31:37 made to be released on the lateral and then tears float over the surface
31:44 then they move towards the lacrimal Uh excuse me, the lacrimal
31:48 Now, here at the coronal is we're going to open up into the
31:53 duct. So the lacrimal duct is in the nasal cavity. And so
31:57 we see here is we have to fluid on the surface of our eye
32:02 into this uh lacrimal uh duct. so we have and again, go
32:07 in the mirror and you'll see you can go look and be
32:10 oh I have these two little Those are the lachrymal puncta. They
32:14 little tiny holes into these little tiny duct jewels that open up into the
32:20 region of the lacrimal duct, which called the lacrimal sac. And then
32:25 roll down through that and then empty into the nasal cavity. All
32:29 Now, generally speaking, we don't so much that we have to sit
32:33 and sniffle all the time, But have you noticed when you have
32:36 good cry? You know what, , you know what I'm talking
32:39 The good cry. Ladies know what talking about, guys don't cry,
32:43 ? We just, we we bottle up and hold it in till,
32:46 we have to break something. Um, but when you have that
32:50 cry, what do you do? right over and over because you're producing
32:55 much water, so much fluid that just rolling into that nasal cavity.
33:00 that's why you're doing all the All right. Plus you're producing so
33:04 water that it overcome the sebu that tarsal glands are producing on the edges
33:09 your eyelids. So the water actually over the edges, but normally you
33:14 produce enough here. So that's why just stays on of your eye.
33:21 . So there you go. Laal , scary picture. Not just because
33:27 eyes are staring at you. but the reason it is a scary
33:31 because there's a lot of names of and here's the good news. You
33:34 need to know the names of All right. I've never asked about
33:37 are the names of the, the or the extrinsic muscles of the
33:40 What I wanna do here is I show you where the extrinsic muscles of
33:43 eye are located. They're attached to sclera of the eye. And what
33:49 extrinsic muscles of the eye do is you to turn your eyes without turning
33:53 head right. So you can look down left, right, you
33:57 um, because these muscles are attached the eye and are pulling on the
34:02 externally. All right. So if have extrinsic muscles, do you think
34:07 have intrinsic muscles as well? What you think? Yeah. OK.
34:12 , the sclera? All right. when you look at somebody and see
34:16 whites of their eyes, that's the and then the portion that sits on
34:20 front, the bump, right where pupils and your uh pupils are located
34:25 where your iris is located that would underneath the cornea. All right.
34:30 if we go back to the picture , you can see this is the
34:34 and then everything else on the surface sclera come. So, speaking
34:43 let's walk through the tunics. Now again, there's gonna feel like
34:48 lots of information here, but it should be pretty straightforward. All
34:51 . So sclera is a structure that all the material of the eye
34:57 All right. So, uh if were to divide the eye up into
35:00 parts, you'd say the sclera is posterior portion and then the cornea is
35:05 anterior portion. All right, of tunic. All right, we call
35:10 the fibrous tunic. It's actually a very, very dense material. It
35:15 from the dura matter. So the extends around the optic optic nerve and
35:21 it forms the structure that is All right. And so it's what
35:26 the shape of the eye. Uh here taking the A and P
35:31 Are you guys getting to this Ok. So you also get to
35:36 that conjunctiva where it's kind of attached a little tiny skirt. You don't
35:40 the whole thing, it's just like clip around it. And so you
35:43 like a little mini skirt of the . All right. Anyway, so
35:49 are you doing? You're providing the , you're protecting the eye. So
35:52 really rough and tough. So it's to penetrate through it. Uh And
35:56 I mentioned, it's the attachment point the extrinsic eye muscles. All
36:01 the cornea, on the other is a uh transparent structure. The
36:08 that make this up are still they just happen to be transparent.
36:12 don't have blood vessels there because that infer interfere with the uh passage of
36:17 through it. So instead nutrients are be delivered by the fluids that are
36:22 on either side of the cornea. we're going to talk about the fluid
36:26 the inside in just a moment, going to be called the aqueous
36:29 But on the surface, that would the tears. So nut uh tears
36:33 nutrients to the surface of the specifically the cornea. All right.
36:41 So why is it transparent? I'm just gonna point it out
36:46 So see that little divot that I'm . All right, that's where our
36:52 uh uh our strongest. Uh It's our sense of sight, but basically
36:59 the most of the receptors for the of ser are gonna be located.
37:02 get to it in just a I don't wanna confuse. All
37:05 But what we want to do is want to take a light that's coming
37:08 and we wanna allow it to pass back here to that point. All
37:13 . So the first thing that we're have to have is a structure that
37:16 gonna help focus that light, that . That's the first thing that the
37:20 does. All right, it helps bend the light as it passes into
37:26 structure of the eye. All And this is a process called refraction
37:31 into the next layer. So we three layers, we have the fibrous
37:35 , then we have the vascular So the name should tell you kind
37:38 generically what it does. It provides uh blood vessels so that nutrients can
37:44 delivered to the structures of the sclera also to provide nutrients to the stuff
37:49 the inside where we're gonna see the tissue. All right. So this
37:53 where a lot of the blood vessels gonna be located and that's what we're
37:58 in this particular case. All This is also where we have the
38:02 muscles of the eye, all So the intrinsic muscles of the eye
38:07 the muscles that are called the ciliary and it includes the iris. All
38:14 . So what do we have the majority of the vascular tunic is
38:20 choroid, all right. And so choroid is the thing that's providing the
38:24 to the retina and to the inside the sclera as you move anteriorly.
38:31 you can see here this kind of structure. All right. This is
38:35 is referred to as the ciliary All right. And so we have
38:40 muscles, the ce ciliary muscles are to a series of ligaments. Those
38:44 are attached to the lens of the . All right. And then the
38:49 thing that we have is we have ciliary processes which are just not well
38:53 here. They're not like easy to , but the ciliary processes are the
38:57 that are responsible for producing that aqueous that's found in this region, the
39:04 cavity of the eye. So we're come back to just a second,
39:08 that's where it's made from. All . So it's made it floats uh
39:12 into this space, it goes around iris and then it's gonna sit in
39:19 anterior cavity and it exit out these tiny gaps, these little tiny
39:23 They're my favorite structures in the entire because they had the most stupidest name
39:27 . They're called the canal of slim after the guy who discovered it.
39:32 an unfortunate name. And if your name is slim, I apologize.
39:38 don't think I have any slims All right. But that's what it's
39:40 . You don't need another canal I'm not gonna ask you about the
39:42 of slim. Just like saying It's fun. It's a fun
39:46 All right. The last structure is iris. All right. When you
39:51 in somebody's eyes and you say you the most beautiful eyes I've ever
39:55 What you're talking about is you're usually about those irises, those color of
40:00 eyes, right? So it is muscle, it is a pigmented muscle
40:05 it is a type of smooth All right. So we're gonna talk
40:10 this in just a moment and what job is is to regulate how much
40:15 is actually passing into the eye. right. So here we have the
40:22 . Now when we talk about the , we usually refer to the
40:25 Your pupils are beautiful. No, are your irises that are beautiful.
40:29 you look in the pupil, you nothing but black. You see the
40:32 of everyone's soul. I'm just All right. What you're looking at
40:42 is when you're looking through the what you're actually seeing is the inside
40:47 their eye. But it's like looking a dark closet that absorbs light because
40:52 inside of your eye actually has epithelium is pigmented. So when light goes
40:57 , it doesn't come back out, where the blackness comes from. All
41:03 . But I'm looking at people who wearing glasses you go to the eye
41:07 , they make you put your chin the stupid thing and then what they
41:10 is they shine a horribly bright light your eye and you're like, they're
41:14 , don't blink and you're like, , I can't help it. But
41:17 they're doing is they're actually shining a in there and they're looking uh at
41:21 structures that the lights are actually But when we just have gene generic
41:26 going in, it actually doesn't bounce , it just gets absorbed. All
41:31 . So the pupil, the that's the hole through which light is
41:36 passing between the muscles that make up um iris. There are two muscles
41:42 make up the iris itself. All , there are two types of smooth
41:46 . One is a sphincter muscle, is a dilator muscle, the sphincter
41:50 , whenever you hear sphincter, you think immediately it's a structure that is
41:54 . And so when it contracts, makes the space inside that muscle
42:01 So the sphincter pupil makes the pupil . All right. Now, when
42:07 relaxes, it doesn't have what you in skeletal muscle, it doesn't have
42:11 tin. So it doesn't just spring to the other shape. You need
42:14 muscle to cause the uh that's large . And that's what the second muscle
42:20 for. All right. So these the dilator pupil, these are radial
42:24 and so they're basically radiating from that . And so when they contract,
42:29 they do is they pull the other away and they make the pupil
42:33 Now they're controlled through the autonomic nervous . The sphincter pupil is parasympathetic,
42:40 dilator pupil is sympathetic. How do remember this? All right. When
42:46 have my flight or flight response, of the thing, one of the
42:49 . So you think that flight or , my heart rate goes up,
42:54 ? You know, when you're scared rate goes up, right? My
42:58 rate goes up, I start sweating . And the other thing that happens
43:03 I'm looking for a path of My eyes dilate and lets allows more
43:08 in so I can see more clearly me. That's how I remember
43:16 So sympathetic dilator makes the pupil larger , makes a pupil smaller,
43:24 not radial, excuse me, circumferential circular. Now, a structure that
43:33 part of the vascular layer but is with it is the lens. All
43:39 . This is this transparent structure to the sill muscles via those ligaments are
43:46 . All right. These are called suspensa ligaments. All right. And
43:49 we can do is we use this to bend light so that we can
43:54 things that are near versus those things are far. In other words,
43:58 adjust our lens able to focus in things depending upon how close or how
44:03 they are. All right. this is going to be a little
44:07 weird in terms of how I'm going describe it. So you got to
44:09 about how this muscle is shaped. right. So you can see the
44:14 layer and so you can think of , I have this round structure and
44:17 muscles are wrapped around the round So when they contract, what they
44:23 is they move towards each other, ? So that muscle is gonna move
44:26 this direction and when those muscles uh they fall backwards, you kind
44:31 see that. So think about the structure. If I'm, if I'm
44:36 , which way am I gonna I'm gonna go this way,
44:38 I'm gonna come around this way and I relax, uh I go back
44:42 way and they're attached to ligaments. if I have this ligament and I
44:48 this direction, the ligament becomes All right. Does that kind of
44:55 sense? In other words, if holding under a rope and I go
44:59 way, do you see how the gets smaller? But if I go
45:02 other direction, the ligament gets right? So that's what's going on
45:06 you're actually contracting and relaxing these types muscles. So when I'm looking at
45:13 close by what I'm focusing near what is, is I am contracting the
45:20 , I'm working hard, right? about when you're studying and reading.
45:24 you working hard? Everyone nod your and say, of course I am
45:27 that's just who I am. Does that happen? Have you noticed
45:30 you read you kind of get a over time? It's not because you're
45:34 your brows because your eyes are working hard and those muscles are in a
45:39 of constant contraction, but the ligaments getting loose because you, the muscle
45:45 forward and when those liens are what happens is that when the ligaments
45:49 loose, then the lens itself is doing what it's bulging outward.
45:56 So that bottom thing right there is you what near vision is going
46:01 Muscles are contracted, the ligaments are , the lens kind of relaxes
46:06 It bulges because it's like, nothing's pulling on me. But when
46:10 look far off, I'm gonna relax muscle itself. So the muscle falls
46:16 and when that muscle falls backwards, pulls on the ligament, the ligament
46:21 tight, it pulls on the lens so this fat lens now gets thin
46:26 so I can see far. All . Well, that's kind of
46:32 How do I remember this? Not . Ok. How do I remember
46:35 ? Think about how you feel at end of the day, right?
46:39 tired, you go sit down in chair, you put your headphones on
46:43 your earbuds in and what do you ? Your eyes unfocused and you're off
46:51 with that three mile stare that's how remember when I have that three mile
46:57 , I'm usually tired and relaxed. the muscles themselves are relaxed.
47:03 but what I'm doing is while my muscle to relax, I'm tightening
47:07 ligaments and pulling on the lens so can see far and that's what the
47:12 picture is showing you. So, so that you can see, see
47:18 tight the ligaments are in the little . See how loose they are if
47:22 all loosey goosey. So that's how can remember far vision, relaxed
47:29 near vision, tight muscles. And , I think about what I'm reading
47:33 how tired my eyes get because they're so hard. All right.
47:39 this process and you can go between two things very, very quickly.
47:43 mean, look at your paper, at me, look at your
47:44 look at me see how quickly your focus actually just to give you a
47:49 is your eyes are actually scanning around . Uh I think it's uh it
47:55 your, your field of vision something 30,000 times per second. So you're
48:00 gonna go, you're just scanning things the time, but we're talking
48:04 So if you move to this, that's referred to as accommodation, your
48:08 to go from long to near that's so far, everybody's with me,
48:17 ? Yes. No, kind of . All right. So let's just
48:22 with a fraction real quick. This the physics lesson of the day.
48:25 refraction simply is the uh changing the of light as it moves through an
48:30 a substance. And so what happens the light bends and so the,
48:36 perception of something that we're looking at like it bends as well. So
48:39 you've ever looked at something like a , I, they always put pencils
48:42 water. I don't come on, mean, put a straw in the
48:46 . No one sucks on a pencil the water, right? Um But
48:50 you can see here, this look when you pass through, this
48:52 what light would do. But when we're talking about refraction, you
48:55 see there's a bending and so that reflected in what we see. And
48:58 you can see here, we see bending of an object. All
49:02 It's not that the object is is that the light itself as it's
49:06 , is bending as it passes through substance. All right. And so
49:11 is important because we're going to take of this to then focus like to
49:17 we want it in the back of eye. All right. Now,
49:21 lens that allows this to happen has have a specific shape. All
49:26 there's two different ways that you can a lens, you can create a
49:29 lens. This is what concave looks . And so the focal point of
49:33 concave lens actually sits in front of lens. And what it does is
49:37 causes light to move away from the point. All right, now,
49:41 can use something that's concave and you actually focus light rays on it.
49:45 if you can get a concave you can cook with a concave mirror
49:48 can create. In fact, some the um um uh solar uh uh
49:55 that we have basically take light, them off mirrors to a focal point
49:59 that you can get most energy focused a specific location. All right.
50:03 that's, that would be concave or . And we don't like that.
50:06 not helpful for us. What we is we want to focus our light
50:10 the end of our eye. And the focal point sits behind the
50:14 So we're going to use a convex and this is just showing you how
50:18 reflecting or excuse me, how we're that light to the focal point.
50:27 what is causing all these different Well, we have different materials in
50:33 eyes. And so we have two areas that have this fluid or goo
50:39 sits in our eyes. All And so they're gonna be located in
50:43 uh these cavities. So we have is referred to as the anterior cavity
50:48 we have what is referred to as posterior cavity, the posterior cavity would
50:52 uh the majority of the eyes, me see if I have a better
50:55 on the next slide. Yeah, just go to the next slide real
50:58 . So this would be the posterior over here. This right here is
51:02 anterior cavity. So you can see cavity, posterior cavity would be all
51:06 stuff. All right. So posterior simple, it's filled with this goo
51:13 substance that doesn't really change over the of your life. You don't always
51:17 it. It's kind of made very slowly. Um Have you ever
51:20 that you have, like every now then you'll see like something in your
51:24 of vision and you'll like, kind focus on it, you'll see it
51:26 of float you. I don't know you call, we always call them
51:28 , right? But if you're like , you can kinda see it
51:31 oh, look, there's this thing looks like a thread. Now,
51:33 gonna look at it and it's then it starts doing this as you're
51:36 to focus in on it. Have noticed that? Yeah. OK.
51:40 , those are actually dead cells that sitting in the vitreous humor,
51:44 And so light rays are actually hitting and we're, and refracting and so
51:49 have the perception of them because they're including the light actually getting to,
51:54 know, to the retina. All . But anyway, so the vous
51:58 it's there, it basically helps to the eye. Um, it has
52:03 nutrient uh structure, you know, it's primarily to maintain the shape and
52:07 kind of gelatinous and doesn't do much . So that's what you'd find down
52:12 . The anterior chamber or sorry, anterior cavity is filled with the aqueous
52:17 . It's what's made by the ciliary . Remember, we said the ciliary
52:21 are here where the ciliary muscles are . And so it contains nutrients and
52:26 and its job is to provide the to the cells of the cornea,
52:31 cells of the lens and other And what we see here is there's
52:36 a division of the anterior cavity. I'm making my uh v or excuse
52:40 aqueous humor. And it's here that over the posterior or the anterior portion
52:45 the lens in what is called the chamber. And then it floats out
52:49 the anterior chamber which sits in front the iris and then it will then
52:54 out via the canals of sle and , you don't even know the
53:00 All right. Again, lots of on a slide take home is I'm
53:08 light. That's all you need to . All right. And again,
53:12 need to know this. But what that is a structure through which light
53:15 is gonna bend it. So you to think in terms of, all
53:18 , if I'm getting my light back to the phobia, then what I've
53:23 to do is every time light passes something it's bending to some degree.
53:29 the cornea bends the light, the humor bends the light, the lens
53:33 the light. The vitreous humor bends light and it's the, the culmination
53:38 all this bending that brings the light to a point to this focal
53:44 The lens is the thing that's doing most work because what can I do
53:47 the lens? I can change its . Can I change anything about the
53:53 ? No. Can I change anything the aqueous humor? No. Can
53:56 change anything about the vitreous humor? they are basically constants. So we're
54:00 talking about when I am trying to light, I'm going to change the
54:05 of that lens. All right. so the focal point is called the
54:12 cis. This is where your best is located. All right.
54:16 I'm gonna challenge you for something. want you to see this just right
54:19 . So you can understand, I you to focus on something on your
54:21 or your notes or something and Is it crystal clear to you?
54:25 right, keep your eyes on And I want you to kind of
54:29 without moving your eyes to the things the thing you're focusing on and are
54:34 blurry? Like as you move away over here? Do you notice that
54:38 blurriness out on the periphery and what want to do is you don't like
54:42 blurriness. So what do you You move your eye, right?
54:46 when you're looking at things, the that is directly in front of you
54:51 where light is coming in straight for most part. All right. And
54:57 this is where our clearest vision is it's going directly back to that bull's
55:02 . But on the edges of that eye, your vision is not so
55:06 . So if you see movement or you see something that seems kind of
55:10 or out of place to you, do you do if you move your
55:13 or move your eyes so that you're at that thing straight on? All
55:18 . So yes, you can detect . But your clearest vision bovio central
55:27 layer is the retina. All Now we're gonna, I I want
55:32 to focus in on this picture before start saying here's your eye, which
55:36 is light coming in, it's coming through the cornea through the lens back
55:43 the phobias andis. OK. When looking at the retina, what you
55:49 is, is light is passing through layers of cells to get to the
55:55 that we're interested in. OK. these are gonna be the cells that
56:00 most interested in. And then the last layer of the retina is
56:05 pigmented layer of cells. So we break down the retina into two
56:11 We have the pigmented epithelium. All . So here's this, here's your
56:17 light is passing through and we're talking this layer first. So if you're
56:22 from outside to in, you'd go sclera to choroid. And the first
56:27 you'd see would be that pigmented This is what is absorbing the light
56:32 how is it absorbing the light? , it has a bunch of melanin
56:36 located in that structure. So when comes in, it gets absorbed by
56:40 melanin pigment, that's why the inside your eye is so black. All
56:45 . Now, this is a good . It's not a bad thing because
56:47 know, you can imagine my my sclera is not particularly light
56:53 Is it if I put a flashlight the outside of my sclera light would
56:57 through, right? And that could with my vision. So, having
57:01 pigmented layer of cells basically prevents light passing through errantly through the sclera.
57:08 only allows light to pass through the and ultimately through the iris and then
57:15 the winds. All right. So is the furthest light layer from the
57:21 , but it is the nearest layer the outside. Does that kind of
57:25 sense? Right. And then you the neural layer and these are all
57:30 cells that are arranged to pick up and then send the signal on up
57:36 the visual cortex. All right. its job is to take light energy
57:42 convert it into action potentials. That the whole function of the neural
57:48 So when we look at the neural , again, look at the lighthouse
57:52 through what we're gonna do is we're from the outside inward, we're going
57:57 this side to that side. So cells of interest, the things that
58:01 want to talk about are called the cells. There are two types of
58:05 . All right, they're called the and the cones. Why do we
58:08 them rods and cones? They're shaped rods and cones. All right.
58:13 easy. All right, their job to receive the light wave, the
58:17 energy converted into a greater potential, greater potential results in the production of
58:22 chemical signal that we're going to use to determine whether or not light or
58:27 whether or not it's light or In other words, where it's basically
58:30 when light hits this portion of the , that's what you're perceiving. The
58:35 layer of cells are called bipolar They're bipolar cells because they have 12
58:42 . Hence, bipolar very, very names. All right. Now,
58:48 job is to take the signal being by the photoreceptor cell and to begin
58:55 the uh what you are perceiving. right. So this is where
58:59 I think it's kind of interesting and me, we could spend eight lectures
59:04 the eye and still not even scratch surface. But the idea here is
59:09 you are processing visual input even before leaves the eye. All right,
59:16 , that's the idea. The next cells are called the ganglion cells.
59:23 produce action potentials. And what they is they send that information outward.
59:28 their axons become the optic nerve. when you're looking at the optic
59:34 you're looking at the axon sum of the ganglion cells inside your eye.
59:41 , there are two other layers of in here that are less important for
59:45 to know they're what are referred to the horizontal cells and the amacrine
59:49 they help in the processing of All right. So what they're doing
59:54 they're modulating signals to help you perceive it is that you're perceiving. All
60:00 . So they're modulating signals. So horizontals are modulating between photoreceptors and
60:05 Amrine cells modulate between bipolar and ganglion . There are a couple of other
60:15 that are found in the eye. mentioning them briefly. All right.
60:18 we have something called a photosensitive ganglionic . All right. So they're a
60:23 of ganglion cell, but they don't a role in vision. All
60:28 they play a role or, or a unique role in the
60:31 And when I was looking at this , I was like, oh,
60:33 , I kind of forgot some of . All right. So the first
60:36 that it does and this is the that's, we're most familiar with
60:38 It helps to, uh, reset circadian clock to help you understand what
60:44 of day it is. So, just had a time change. Do
60:47 feel like it's like 630? And just feel like it's nine o'clock right
60:52 ? Right? Because it's so Right. That's a function of these
60:55 . They're basically telling you it's so . It should be this time of
60:59 for you. And you're like, , but it's not, I've,
61:02 , it's, it, it can't , it's not possible or maybe it's
61:05 opposite. I can't believe how early is. All right. So that's
61:08 first thing that it does. All . The second thing that it does
61:12 helps to regulate your pupil size. do I know how much light is
61:16 in my eyes? Well, these detect the presence of light themselves.
61:21 , they're not dependent on photoreceptor they're doing their own detecting and they
61:25 a signal back up to the regions the brain that are responsible for regulating
61:30 wide the pupil opens up. So the second thing that they do.
61:34 the last thing that they do is , your internal clock is regulated by
61:37 whole bunch of molecules. One which is called melatonin is one of
61:42 molecules that are regulated. And so send signal to the penile gland to
61:46 this is how much melatonin you should releasing. So part of the reason
61:51 dark outside and you feel so tired because these cells are going, it's
61:55 , it's time for bed. Here's that melatonin in you, but it's
61:58 o'clock. All right. The other are the uh retinal pigmented epithelial
62:05 So, these were the, this that picture I'm showing you here.
62:08 those are your rods and cones up . There's that pigmented epithelium. So
62:12 job is not solely to absorb One of the unique features because it
62:17 light. You can use this as dark room to help create things.
62:23 we're gonna learn here about a molecule are, it's not listed up
62:27 A molecule that you're gonna need. we're gonna talk about this on Tuesday
62:30 be able to see it's called All right. A L, not
62:34 , it's not the alcohol, it's A L which is whatever and what
62:38 is. It's basically this molecule right . Divided in half. Vitamin
62:43 All right. So if you go just look up a picture of vitamin
62:46 , you'll see that it's this long with these two little uh cyclic rings
62:50 the end. And if you cut exactly in half, you get two
62:53 molecules and it's this retinol molecule that eye uses to actually detect light.
62:59 so what happens is is when you the shape of the retinol molecule,
63:03 , that's a function of the energy being absorbed by the light,
63:07 blah, blah blah. We'll get that later. All right. But
63:10 order to see light again, you to reshape the retinol molecule back into
63:15 original shape. All right. So light it changes shape and I extend
63:21 to a dark space and I reshape and then I put it back so
63:24 it can then be re changed and a cycle in there that allows that
63:28 happen. All right, I know kind of talking about something that we
63:32 really described yet. Let's talk about . If you do know, have
63:35 ever gone to a movie theater? and dark and you go to a
63:38 and then you walk out of the and it's like crazy bright. You
63:42 see anything, right? That brightness you're like, I can't see
63:47 What you're doing is you're bleaching your , that's the term that they
63:50 It's called bleaching your receptors. You're providing so much light that you basically
63:55 absorbing all the light and you're changing the retinol. And so it takes
63:59 little bit of time for that retinol be recharged. All right.
64:04 the pigmented epithelial cells are responsible for them and re and getting them back
64:09 the original shape so that you can now, how much time does it
64:12 for your eyes to get used to brightness couple of minutes. 3 to
64:16 minutes. Yeah. And then the is true. With dark going into
64:20 dark space. It takes a long for your eyes to adjust the dark
64:22 10 to 20 minutes because different cells doing different things. But it's the
64:26 sort of thing. It's recharging retinol or resetting them. This is what
64:31 does. All right. I'm gonna here for a second. Are there
64:41 questions so far? These are, , we're notice how, what we're
64:45 is we're working our way inward and working our way downward to the structures
64:49 interest. The cells of interest are photoreceptor cells that that doesn't mean we're
64:53 ignore bipolar cells. It doesn't mean gonna ignore ganglion cells. But when
64:57 look at a structure and you what is it doing in this
65:00 what's the eye doing? It's basically me to see it's detecting light.
65:04 want to focus on the thing that's light, right? And so that's
65:07 we're gonna talk about the photoreceptor All right. These are the rods
65:10 the coats, rods. You only one type of rod, you can
65:16 structurally what they look like. They this rodlike shape. Um Up here
65:20 this, this little squiggly line, they're trying to show you is that
65:23 , this rod structure is filled with bunch of pancake like structures. They
65:29 look like a series of pancakes that been stacked on each o each
65:32 And it's in these little tiny membranous , these little pancakes where the structures
65:38 allow you to detect light are actually . All right contrast that to the
65:43 cell. What happens with the cone ? Again, the artist of crappy
65:47 is that the membrane uh the uh cell, the plas membrane of the
65:51 actually fold folds on itself multiple So it's basically like, I'm just
65:56 keep folding and folding and folding. structurally, they're very different, but
66:00 do the same thing, they detect , but we only have one of
66:04 and what it does is it detects um that we would normally consider light
66:10 we would have at low intensity All right. In other words,
66:14 allows us to see primarily in the . So if you get up in
66:18 middle of the night, you don't to turn on a light,
66:20 What do you do? You just of walk around, you can kind
66:22 vaguely see where things are. Those your uh rods allowing you to
66:28 All right. So they have what would call a high sensitivity to
66:33 A just a photon by itself can , activate one of these cells.
66:37 that also means that there's a lot photons, you basically over bleach
66:41 they stop working. And so that's you have the cones come into
66:44 So cones, there are three All right. These three types give
66:50 to what is our day or color ? All right. So, like
66:55 now, your vision is primarily dominated the cones working and the rods themselves
67:01 kind of turned off. Rods are located if you take your retina and
67:06 think about your retina being like right? So you can see I
67:09 see in my eye, right? be going through my retina doesn't go
67:14 the way around. It's just back in the back. So if I
67:17 my retina and flatten it out, the stuff on the edges is primarily
67:24 . And then as I move towards phobias andis, I change the rods
67:29 start replacing them with cones so that phobias inis is 100% cone. All
67:35 . Which is why your vision is keen at the pho centrals. All
67:43 . What else do I have up ? Oh, in terms of
67:45 you have about 100 million rods located the retina of a single eye,
67:51 have about 3 to 5 million um located in a single retina. But
67:58 they're localized and specific, that's, OK. Um This statement I'm going
68:08 get to here is a little bit uh complex and it's gonna have to
68:15 with the acuity as well. All . So the way I want you
68:19 think about this is when you think convergence. What you're saying is we
68:23 things moving towards a particular location, right, or, or, or
68:30 . So the way that you can that the statement says up there high
68:33 of convergence, low degree of So you can imagine like this for
68:38 ganglion cell, each ganglion cell, when we're talking about high convergence would
68:43 many bipolar cells associated with it. so I'm just going to make up
68:49 number. So let's say I have ganglion cell, one ganglion cell,
68:52 would have 10 bipolar cells. And for each bipolar cell, I would
68:57 10 rods. So you can imagine convergence is if I stimulate any of
69:03 rods. So any of those hundreds , I'm going to stimulate that ganglion
69:08 . All right. So that would a high degree of convergence. Lots
69:12 different cells result in the stimulation of one cell down there at the
69:16 All right, doesn't matter if the is sitting over here or if the
69:21 is sitting over there right there. focal field or that receptive field is
69:27 upon that one ganglion. So high we expect where we're gonna have lots
69:34 lots of cells. Low convergence. the other hand, is the
69:38 I would have a ganglion cell. on that ganglion cell, I have
69:42 bipolar cell. And again, these extremes, right? And then on
69:46 bipolar cell, I have one photoreceptor . So the only thing that's gonna
69:51 that ganglion cell is if light hits one or that one photoreceptor cell.
69:56 . Now again, I want you think about the dark. When you
69:59 in the dark, you go into dark space or a dark room,
70:03 ? Let's say you go into your , it's dark and you see there's
70:06 lump in the corner. Can you the details of the lump? It
70:10 be the laundry that you haven't bothered ? It could be a serial
70:15 right? You don't know, but can at least see the lump.
70:18 right. So the rods allow you see things generically, right? This
70:24 of like, oh, it doesn't if the lights coming and hitting this
70:28 or it's hitting that rod or this , at least I detect light and
70:31 gives me a sense of what I'm at. Whereas in the light and
70:38 dealing with cones that light either hits cone or it doesn't. And it
70:42 me a really, really sharp right? So when I have high
70:49 , I have low acuity. Does make sense? So I can't clearly
70:55 things. But when I have high low convergence, I'm gonna have very
71:01 acuity. All right. Now I'm that now we're gonna see a slide
71:07 that helps us kind of visualize So this, this is looking at
71:12 retina, you're looking in the eye can kind of see. So the
71:15 , if you're looking straight into the right through the down through the pupil
71:19 the, you know, past the , this is what you'd see and
71:22 in the back. That would be region called the maculata inside the
71:26 The maculata is like the fovea If you're familiar with dart boards,
71:30 bull's eye has two circles, you have the full bull's eye and
71:33 have the double bull's eye. So single bull's eye would, that would
71:36 the maculata, the double bull's eye the center, center, the
71:40 very center. That would be the . What this graph is showing you
71:45 the dis distribution of rods and cones this picture up here. So here
71:51 is saying this is the pus The blue line represents the number of
71:56 . The green line represents the number cones, all right. And this
72:00 a uh this is a density and you can see way out here on
72:03 edge. What am I? I'm mostly rods, very few
72:08 right? As I move closer and , what do I get? I
72:11 more and more cones and less relatively speaking. And then finally,
72:17 I got nothing but cones. So can see in terms of their distribution
72:23 are found primarily in the periphery. are found primarily in the fus inis
72:29 my cl cleanest vision is all in terms of that adaptation. This
72:37 of what am I looking at? said that rods are sensitive to
72:42 They work really well in the but they are bleached out in the
72:45 . So what they do is they rise to sco topic uh uh
72:51 So when it's dark, you can things but you can't see things clearly
72:57 the light when you've bleached out, your rods and your cones have taken
73:02 . And again, this is a . So you just have to imagine
73:04 is what my eyes are doing. can see things much more clearly because
73:11 their activity. They are less sensitive . So you need more light to
73:15 them is what we're saying, this a process of dark adaptation of using
73:21 ro rods to see. I'm gonna back uh to the uh the rods
73:29 the cones here for a second. I wanna just mention this, this
73:32 what I want you to know about cells. This is a very complex
73:34 . So I wanna skip over something . A bipolar cell creates graded
73:41 They're stimulated by the photoreceptor cells. they're downstream and then we skip over
73:46 middle stuff here and they're gonna synapse the gla ganglion cells. This I
73:52 is a little bit too complicated. throws things off and makes things
73:57 So just ignore that for right now terms of the receptive field. Here's
74:02 convergence, right. Here's our ganglion , here's our cone cone to bipolar
74:09 ganglion. So only when this thing stimulated, am I gonna be able
74:14 detect light and send that signal up the optic or the visual cortex?
74:19 , it doesn't matter if I activate cell or that cell or this
74:22 any one of these cells can stimulate ganglion cell. So this is why
74:26 get that vague sense of light from particular area. This is why imagery
74:32 here is fuzzy. Yeah, I see stuff and I can see movement
74:35 , but I can't clearly see what is. I'm looking at if I
74:40 to see what that is, I my head so that now light is
74:44 these, you're getting that uh low and this is that acuity that I
74:50 describing. Now, I apologize for technology here. What we're looking at
75:00 are three different images trying to describe . Screens. All right, that's
75:05 the picture is from. All but I think this is a good
75:08 to kind of see this. All , you guys are probably now a
75:11 that hasn't ever had to deal with Def. All right. Standard De
75:16 what I grew up with. I grew up with black and white
75:19 . There were actual TV shows that still black and white in reruns,
75:25 like Nick at night. Like just reruns when I was a kid.
75:29 was the saddest thing when you came the show that was black and
75:32 right? But all the TV S Standard Def. Standard definition is a
75:37 that we describe the number of lines the bottom of the screen to the
75:41 of the screen. Standard definition is P. You ever heard that
75:45 Right? 480 P. You're gonna worse, right? But that would
75:50 standard definition. So this is an in Standard Def. Can you detect
75:54 said in that picture? Sure you . What's that? That's mount,
75:59 that? Some house or building of sort? And then back there,
76:04 that town or village, something like ? So you can see what it
76:08 you can perceive and you can fill the blanks on your own of what
76:11 is. OK. Now here this the difference between Standard Def and High
76:17 . High Def. Despite what the people are telling you is not 720
76:22 , it's 1080 P. All That is the true definition and then
76:27 , oh, that requires more So we're gonna go ahead and redefine
76:30 as 720. And so some TV and channels will go oh well,
76:34 is High Def but they're pumping 720 ripping you off and we hate these
76:40 . OK? But what it is says number of lines from the top
76:43 the bottom is now 1080. So is 2.5 times what you have
76:49 Right. So look at what having lines, does, does this is
76:53 picture clear than that over there? you see the village now? Can
76:58 see the mountain in the background? . Right. When this happened,
77:01 was like a miracle for those of who enjoy television. It's like,
77:05 remember going to the store for the time and seeing a 85 inch or
77:09 inch television. That's how big they . 65 inch and watching a football
77:13 . I was like, it's like at the game. It wasn't like
77:17 at the game. But relative to , it was all right. And
77:21 finally we now have four K, K is 2100 and 60 P.
77:28 , is it really 21? 60 ? No, it should be
77:32 But again, the marketers got they actually have screens that have 4000
77:36 . They now have screens that have lines. But, but you can't
77:40 them now because they want you to the money on the technology that they
77:43 to get to there. Right. look how clear this is relative to
77:48 . All right, this is what is. The more concentrated my,
77:54 cones are. That means they're very close together just like these are
78:01 , very close together and they provide to what it is that I'm looking
78:07 when I'm doing have a lack of when I have a high degree of
78:11 , what this is saying. So the way that you can think about
78:14 , if this is my line, can have lots and lots of lines
78:19 I can get really clear images. here I have very thick lines because
78:24 doesn't matter if the light hits here here, this cell is gonna be
78:27 . So I'm getting this type of . So that's why the imagery on
78:31 periphery is blurry. Why your imagery in the center is clear because coming
78:41 , we have lots of lots of which are showing low convergence versus out
78:48 where we have lots of rods which high convergence. OK. That's what
78:54 take home is there. So you larger receptive fields. When you have
79:03 convergence, you get reduced acuity as result, vice versa. For the
79:08 . Last slide. Uh Yeah, last slide. Um This is what
79:13 gonna say about this slide. It's , very complex. Don't need to
79:17 this. I won't ask you. . So very complex. All
79:24 When we come back, we're going ask the question, how does the
79:27 and the cone turn that light signal an actual graded potential? And how
79:32 we perceive that light red? We're to get to it. So basically
79:40 just think it's a molecule
-
+