Special Senses | Pupillary Light and Accommodation Reflex

0:07hi Ninja nerds in this video we're going

0:09to talk about the pupilary light reflex

0:10and accommodation why is this important

0:12because when doctors you guys ever watch

0:14a TV show you see these guys running in

0:17the doctor's basically shining the light

0:18into their eyes and looking to see what

0:20type of responses they have that's

0:21important because that actually happens

0:23in real life what doctors are really

0:24looking for is a certain type you know

0:26there's actually kind of a little uh

0:28thing to help you guys remember we talk

0:30about it throughout the course of this

0:31video but I'm going to write it down now

0:33it's called

0:35Perla

0:37okay and this is some of the things that

0:39the doctors are actually looking for

0:41whenever they're doing the pupilary

0:42light response with actually shining a

0:44light into someone's eye so what they're

0:46looking for is they're looking to see

0:47that the

0:48pupils are

0:51equal

0:53round and reactive to light so

0:57round reactive to

1:01light and that they can perform

1:05accommodation okay so these are the

1:06things that the people are looking for

1:08these doctors they looking for the

1:08pupils to be equal round reactive to

1:10light and un able to go accommodation

1:13we'll talk about what all these things

1:15mean all right so what we're going to

1:17try to do in this video is we're going

1:19to say let's

1:20pretend I'm going to take a light and

1:23I'm going to shine into someone's eye

1:25and let's say that this case right here

1:26you see how this right here we're going

1:27to say this is the right eye

1:31and we're going to say this is the left

1:33eye what I'm going to do is is I'm going

1:35to shine a light into the person's left

1:38eye and I want to see how their pupils

1:41respond to that so let's go ahead and do

1:43that so let me pretend here for just a

1:46second that I'm shining some

1:49light onto this person's eye okay so

1:54here's

1:55my my light all right don't make fun of

1:58it I'm Shining light into this person's

2:01eye okay now how does this all happen

2:04well if you guys have already seen our

2:06video on visual fields and they're

2:08actual lesions you guys will understand

2:09exactly how this whole pathway is

2:11working so if you guys remember we

2:13actually take this is the left visual

2:15field and this is the right visual field

2:18right of the right eye I'm sorry this is

2:20the right eye this is the left eye this

2:22right here is the left visual field of

2:24the left eye this right here is the

2:26right visual field of the left eye left

2:28visual field of the right eye right

2:30visual field of the right eye if you

2:32remember there were two different types

2:34of retina here there was the nasal hemir

2:37retina which is going to be on this side

2:38closest to the nasal the nose right

2:40there and then you're going to have one

2:44closer to the temple side and this is

2:45going to be the temporal Hemy okay so

2:48same thing over here what would you have

2:50over here over here you're going to have

2:52the nasal hemir and over here you're

2:55going to have the temporal hiry okay

2:59what did we say happened here we said

3:01that light from the right visual field

3:03of the right eye is going to hit the

3:05nasal hemir Ry of the right eye right

3:09and then we said that the left visual

3:11field of the right eye is going to hit

3:14the temporal hemir so what is this one

3:17here temporal hemir rney of the right

3:19eye this one over here is the temporal

3:22hemir of the left eye and this is the

3:26nasal Hemy of left ey so same thing here

3:31hits the temporal hemony left visual

3:34field of the right eye then same thing

3:37over here left visual field of the left

3:40eye is going to hit the nasal Hemy of

3:44the left eye and then the right visual

3:47field of the left eye is going to hit

3:49the temporal Hemy of the left eye right

3:53that's all it is that they're actually

3:54having these visual fields that we're

3:56able to process then what did we say we

3:59said anything that is coming from the

4:01left visual field has to go to the right

4:03side of the brain anything from the

4:04right visual field has to go to the left

4:07side of the brain simple as that where

4:09is this coming from okay this is coming

4:11from the left visual field so it has to

4:12go to the right side of the brain so

4:15since this is already on the right side

4:16we're going to keep it that so it's

4:18going to be Ipsy lateral right same

4:21thing over here okay this is going to be

4:26the right visual field the right visual

4:28field of the left eye so if it's right

4:30it has to go to the left well since it's

4:31already on the left let's keep this on

4:34the same side or

4:36ipsilateral then what did we say

4:38anything again from the left visual

4:40field has to go to the right eye so

4:42what's going to happen to this one well

4:43this is on the left eye this is going to

4:45have to go to the right brain so over

4:47here it's going to cross at the optic

4:49Asma and then come down and is your

4:51Contra lateral fibers okay coming from

4:54the left eye but picking up information

4:57from the what left visual field of the

5:00left eye same thing here this is going

5:03to be picking up processing information

5:06from the right visual field of the right

5:08eye but anything from the right visual

5:11field has to go where to the left side

5:13of the brain so this is going to have to

5:15cross over here and this would be the

5:18contralateral fibers and if you guys

5:20remember what did we say we we labeled

5:23this right we said that this structure

5:24here was called the it was a specific

5:27nucleus a specific nucleus we call that

5:29nucleus the lateral geniculate nucleus

5:32and there's two of them right these are

5:34basically on the thalamus if you guys

5:35remember we said that here's your

5:37Thalamus which is in the D part of the

5:38dlon here's the thalamus there's a

5:41structure coming off of it called

5:44the lateral geniculate nucleus we're

5:46just zooming in on it so we're basically

5:48zooming in on that lateral geniculate

5:50nucleus and it's layered it has one 2 3

5:544 5 6 same thing over here 1 2 3 4 five

6:00six we

6:02said ipsilateral fibers are going to go

6:05to 2 three and five ipsilateral fibers

6:09go to 2 3 and five so where is it going

6:11to go then so these are the ipsilateral

6:13fibers these blue fibers here so they're

6:15going to go to 2 3 and five

6:18controlateral fibers go to 1 4 6 so this

6:23is going to go to 1 4 6 then we said out

6:28of that the information from this can

6:32come out of the later geniculate nucleus

6:34a good chunk of it right can come out

6:36and it can go through it's called The

6:38Superior retinal fibers of the baram's

6:40loop which is going through the parial

6:42lobe that's why it's the superior

6:43retinal fibers so same thing over here

6:47and again this is coming through the

6:48parietal lobe to where the calcarine

6:50fisser is of the occipital lobe Superior

6:53retinal fibers or The baram's Loop and

6:55then there's also going to be the ones

6:56that are coming from the inferior port

6:59portion which is coming through the

7:00temporal lobe or Myers Loops which are

7:03again going to the occipital lobe or the

7:05striate cortex where the visual

7:08processing is going to occur where

7:10basically the sensation of whatever you

7:12see is turned into perception It's Made

7:15Real now that's what normally happens to

7:18make you consciously aware of what

7:20you're seeing but here's the thing we're

7:22not looking at that we're trying to look

7:24at how are our pupils responding so this

7:27is going to occur at the brain stem

7:28level it's a reflex we can become made

7:31consciously aware that there's light

7:32shine into our eyes but we want to know

7:34how the pupils are responding so what

7:36happens here some of these fibers that

7:38are coming from the later geniculate

7:39nucleus some of them come into a special

7:42level within the brain stem specifically

7:45at the level of

7:47the

7:49midbrain at the level of the midbrain

7:52now in the back of the midbrain at this

7:55level you're going to have a structure

7:57here which is called the super Superior

8:00calculus and again what would this

8:01structure here be called Superior

8:03calculus you're at the level of the

8:05superior calculus there's a nucleus just

8:09anterior to that let's make this nucleus

8:13let's make it this nice pink color here

8:16so here is this nice little pink nucleus

8:18right here and this nucleus is really

8:21special it's called the preal nucleus

8:24and obviously you have two of them right

8:26pretectal nucleus so again you could say

8:28this the right PR pral nucleus is the

8:30left pretectal nucleus what happens is

8:32these fibers that are coming in here

8:35that are coming from the 14 and six and

8:38the ones that are coming from the 2

8:40three and

8:41five sign up again they're going to

8:45come into the

8:47midbrain and what happens is some of the

8:50fibers might go to the Super calculus

8:53why would some of these fibers go to the

8:55superior calculus because if you know

8:57the superior calculus actually controls

8:59your reflexive head and eye movements

9:02response to a visual stimulus so if I

9:04see someone walking by I'm GNA move my

9:06head on my eyes with response to that

9:08that's the function of the superior

9:10calculus so some of these fibers can

9:12actually go to the superior calculus but

9:15a good chunk of these fibers are

9:17actually going to What's called the

9:19pretectal nucleus some of them are going

9:22to the pretectal nucleus now here's

9:24what's really really cool you remember

9:27that this was actually this little Canal

9:29here what called the cerebral Aqueduct

9:31this is where the cerebral spinal fluid

9:33is Right Above It is the third ventricle

9:35below it is the fourth

9:36ventricle and then on the sides of it

9:39you had the samatam motor fibers of the

9:41third nerve

9:42nucleus right and then what did we say

9:45just to be super super particular if you

9:47want to be what was the structure around

9:49the cerebral Aqueduct it was called the

9:52per aqueductal gray

9:54matter and then what we're here on the

9:56sides this is actually going to be the

10:00Edinger Westfall nucleus I'm going to

10:03put ew Edinger Westfall okay and if you

10:06want nucleus I'll put n so Edinger

10:08Westfall nucleus so same thing over here

10:10I'm not going to show all the fibers

10:12coming in here through each lamina I'm

10:13just going to say they're coming in here

10:15and then some of these fibers can go to

10:17the superior

10:19calculus okay but most of the fibers are

10:21going to go where are going to come here

10:25to the pretectal nucleus which is in the

10:29brain stem of the midbrain right and

10:31again it's going to syapse onto the

10:32pretectal nucleus now here's what's

10:34really really cool okay which eye did I

10:38Shine the Light in let's kind of Follow

10:40that because I want to show you

10:41something really really

10:42interesting okay I shine the light on

10:45the left eye let's follow the the light

10:48from the nasal Hemet if I follow this

10:50one it's coming this way okay so it's

10:53crossing over to the other side these

10:55are the contralateral fibers it's coming

10:57this way oh it's going into later

10:59inculate nucleus oh some of these fibers

11:01are going to the Super calculus some are

11:03going to the pretao nucleus Okay cool so

11:06I know that the fibers that are picking

11:07up information from the left visual

11:09field of the left eye are taking it to

11:12the right side of the brain to the

11:13pretectal nucleus okay then I know that

11:16from the temporal Hemy which is picking

11:18up information from the right visual

11:19field of left eye it's taking this

11:22information and taking it down the

11:23ipsilateral fibers which are going into

11:26the actual brain stem and going where

11:29some of the fibers will go to the

11:30superior calculus and some of these

11:31fibers will go to the pretectal nucleus

11:34on the left side oh wow so this is

11:36interesting so left pretectal nucleus is

11:38interated and right pretectal nucleus is

11:41interated but you know what else is even

11:42special the pretectal nucleus is so

11:45intelligent that it can actually cross

11:49so it can give fibers that can go to the

11:50Edinger Westfall nucleus on the right

11:52side and the edigar westall nucleus on

11:54the left side so that's a beautiful

11:56thing so again what would happen with

11:57this one here it would give information

12:00to the Edinger Westfall nucleus on the

12:02left side and it would also give fibers

12:04over here to the Edinger Westfall

12:05nucleus on the right side the pretext of

12:09the nucleus is so amazing that it can

12:11actually respond to that right and it

12:12can cross these fibers over so it has

12:15bilateral control of the right endinger

12:17Westfall nucleus and left endinger

12:19Westfall nucleus that's amazing now from

12:23here what will happen Okay so we shine

12:26the light into the eye we stimulated

12:29oh we stimulated a special special cell

12:33you guys remember from the uh physiology

12:37video that we actually did on the photo

12:38transduction Cascade there was different

12:40parts there was actually one layer two

12:43layer three layers we're not going to

12:45draw them all but there was the photo

12:49receptors which were the rods and cones

12:52then there was the bipolar

12:55neurons okay and then there was the one

12:58right after that was which was the

12:59gangon

13:01cells these ganglion cells are very very

13:05interesting little buggers remember we

13:07talked about pigments that were within

13:09the uh rods and the cones like ropson

13:12and then photopsin for the cones well

13:15guess what Gangland cells have another

13:16type of pigment it's

13:19called

13:21melanopsin melanopsin and what happens

13:24is whenever we shine light into a

13:26person's eyes we can activate these

13:29gangon cells which are consisting of the

13:31melanopsin that pigment and if

13:34melanopsin is activated it can actually

13:37send it can actually trigger this

13:40Cascade down these actual neurons the

13:43actual axons of the Gangland cells which

13:45basically makes up the optic nerve okay

13:48so really when I'm shining a light into

13:50the eye which is the main one that's

13:52getting

13:53activated the Gangland cells during the

13:55pupilary light reflex and they send

13:57these Action potentials down through

13:59ipsilateral and contralateral fibers

14:02okay activate what pretectal nucleus

14:04pretectal nucleus can cross to both Sid

14:06so it has bilateral control activates

14:09the Edinger Westfall

14:11nucleus if the Edinger Westfall nucleus

14:14is activated he's a parasympathetic

14:15fiber he's going to move with the ocular

14:17motor nerve right and when he moves you

14:20guys know a little bit here he'll come

14:23to a ganglia and again both sides so

14:25this is the right one this one over here

14:27would be the

14:30left one and again what is that ganglia

14:33called or that group of cell bodies

14:34located within the pns that ganglia is

14:37called a

14:39ciliary gangon now what happens so again

14:43these actual postganglionic

14:44parasympathetic fibers that are coming

14:45out here they're actually going to be a

14:47component of something very important

14:48you know they're actually part of What's

14:49called the short ciliary nerves because

14:53you know with the short ciliary nerves

14:54there's going to be sympathetic fibers

14:55and fibers from the trigeminal nerve

14:57that moving with it and what happens is

14:59it pierces through the

15:01Scara and through What's called the

15:03peric coral space and it gives supply to

15:06the ciliaris muscle and it gives Supply

15:10to a specific muscle within the pupil

15:12that we'll talk about called the

15:13sphincter pupila so again what happens

15:16here it pierces through the Scara moves

15:18through the peric coral space and gives

15:20supply to the celarus muscle and it

15:24gives supply to the sphincter

15:26pupila now how would that respond what

15:29would be the person's response okay

15:33let's look at the response to the

15:35ciliaris how that's affected so first

15:37thing we're going to do is we're going

15:38to look at see how the ciliaris is

15:41affected and then we're going to look

15:43and see how the pupil is affected by

15:45this parasympathetic and then we'll

15:46compare it with sympathetic okay so

15:49cair's first so here we go this was our

15:53short ciliary nerve it's coming in here

15:56piercing through and it's going to going

15:58to give supply to the ciliaris muscle

16:00right there this big chunk of muscle now

16:04here's what confuses some students

16:07here right

16:09here is the end of the ciliary muscle

16:13when the ciliary muscle so whenever

16:15these parasympathetic fibers come over

16:17here and inate the CIS muscle they're

16:19going to act on what's called M3

16:21receptors muscarinic type 3 receptors

16:24which is going to increase the calcium

16:25levels inside of the celarus muscle now

16:28when it does that it's going to

16:30stimulate the ceris muscle to contract

16:33when it contracts it's going to pull so

16:36down here at this fixed Edge down here

16:37right right down here what's going to

16:40happen is it's going to pull that part

16:42upwards so as it pulls this upwards this

16:45part stays stable right here this stays

16:48stable right here this part moves and it

16:51moves upwards as it moves upwards okay

16:55like imagine here imagine this is the

16:57fix point here and imagine this is that

17:00point down here when this muscle

17:01contracts it pulls the thumb in towards

17:04the pointer finger so as it pulls it

17:07this muscle shortens as it shortens

17:10something really interesting happens you

17:12see these little blue things that were

17:13connected to the lens here they get

17:16really really loose what are these blue

17:18things here called they're called your

17:20suspensory ligaments or your ciliary

17:23zonals now originally they were a little

17:25tight but whenever the ciliaris muscle

17:27contracts these become really relaxed

17:31when they become relaxed they don't pull

17:33on the lens as much and now because of

17:36that the lens starts bulging and becomes

17:41really very globular if it becomes very

17:44globular this plays a role in what's

17:46called near Vision okay so what is the

17:50response here with the ciliaris first

17:53thing

17:55ciliaris

17:56contracts okay

17:59then

18:01zonals

18:02relax lens

18:06bulges and why is that important we'll

18:09talk about in a little bit more detail

18:10but it actually affects the light rays

18:12that are being refracted into the actual

18:14eye onto the retina so when the light

18:16rays are coming in here because it's now

18:18globular it brings this actual lens

18:21closer to what's the actual object okay

18:25so it actually is going to it decreases

18:27What's called the focal length Okay but

18:30it helps with What's called the

18:32near

18:34point of

18:36vision okay so that's how it's affecting

18:39it now for the pupil which I love this

18:42one same thing here the short ciliary

18:45nerve is going to come up and it's going

18:47to supply the pupil but looking at it

18:49from this view doesn't do it justice so

18:50now what I'm doing is I'm taking the

18:52iris and I'm looking at from the

18:54anterior view so you're getting an

18:55anterior view of the iris and right here

18:57is the pup hole so this is where the

18:59light is actually entering okay now the

19:03iris has muscles that are circular

19:06wrapping around it these muscles that

19:09are wrapping around and are very

19:10circular they're a very specific type

19:12they're called it's called the

19:16sphincter

19:19pupila and what happens is these

19:21sphincter pupila have what's called

19:22muscarinic receptors on them they have

19:25muscarinic receptors on them M3

19:27receptors

19:28what happens is the short ciliary nerves

19:31come in here and act on The muscarinic

19:35receptors the type three receptors and

19:37cause them to contract when it contracts

19:40it causes this actual muscle to squeeze

19:44like a sphincter and as it starts

19:47squeezing like a sphincter it makes the

19:49pupil hole smaller and smaller and

19:52smaller so by squeezing it imagine me

19:55trying to ring out like a rag that's

19:57what it's doing to it and it's making

19:59the pupil really really small so as this

20:03muscle starts trying to

20:05contract it makes the pupil smaller and

20:07that is called constriction of the pupil

20:11okay so for the pupil what is it doing

20:14to the pupil it's

20:16actually constricting

20:20pupil okay through the sphincter pupila

20:23why is that important because let's

20:26imagine here's normal pupil hole but

20:29then the parasympathetic comes into play

20:32and it makes this

20:34pupil even smaller so that space there

20:37is now going to be even smaller look how

20:38much smaller it is holy crap that's a

20:41small pupil right so now that the pupil

20:43hle is a lot smaller look how much light

20:46can get in very little light so because

20:50very little light rays can get in here

20:52that is very very important because

20:54again what it does is it focuses the

20:57light on a specific point in the eye

21:00which is called the fobia centralis

21:04trying to focus the light onto the fobus

21:06andalus within the

21:07macula okay immacula

21:10ludia so again pupil constricts to focus

21:13the light onto the retina okay

21:15specifically the phobia andalus where

21:17the cones are and again when the lens

21:19bulges it's for the near point of vision

21:21now let's see how the sympathetic

21:23affects

21:24this oh but I didn't explain something

21:27here

21:28the pupil's constricted but what was

21:31really interesting what was the most

21:33interesting part about this I shined

21:35light into the left eye but which nerves

21:38got activated both short ciliary nerves

21:42were activated that means that both of

21:44my pupils constricted but I only shined

21:47light into the left eye why did both my

21:50pupils constrict because of this cross

21:53connection okay because of this cross

21:55connection here with the pretectal

21:56nucleus that's why both of them are

21:59going to become activated and constrict

22:02the pupil also because remember the

22:04nasal Hemy fibers went on to the other

22:06side and these ipsilateral T temporal

22:09hemir fibers went to the same side so

22:11there's a lot of cross connection there

22:13now whenever I shine light into the left

22:16eye and the left pupil constricts this

22:19is called a direct

22:25response if I shine light into the left

22:28in the right pupil constricts that's

22:31called a consensual response this is

22:34what you should be seeing

22:38normally when you do this type of test

22:40this pupilary light reflex okay so

22:42normally when you shine the light into

22:43the left eye you could even do it you

22:45could shine it into their their left eye

22:47here and block their face if you want

22:50make sure that they have a direct

22:51response which is on the same side and

22:53then make sure that you shine that eye

22:54into that left eye and they have a

22:55response onto the other side the right

22:57eye

22:58okay that's the consensual response all

23:01right sweet deal so we talked about

23:02direct response consensual response and

23:04how the parasympathetic is affecting

23:06this actual ciliaris in the pupil now I

23:09want to take a brief look at how the

23:10sympathetic is affecting it we'll look

23:12at this more in the autonomic nervous

23:13system but if you guys remember talked

23:16about it many times we have a

23:18cross-section of spinal cord here

23:20cross-section of a spinal cord on the

23:22outer

23:23parts here you're going to have let's do

23:27this bad boy here and this no let's do

23:30it in this actual purple here this

23:34purple's boss all right on the lateral

23:37gry horn or the intermediate lateral

23:40grey horn of the spinal cord you have

23:43these

23:44preganglionic sympathetic fibers so

23:47preganglionic sympathetic fibers here

23:49the actual cell bodies of them they're

23:52going to come out here right when they

23:55come out here they can actually go to a

23:57specific ific ganglia okay where a group

24:00of cell bodies are located right within

24:02the pns that ganglia that they're going

24:05to go

24:06to is actually called a

24:10superior

24:13cervical

24:17gangon now what happens is from this the

24:21post ganglionic fibers are going to come

24:22out when the postganglionic fibers come

24:25out they're going to wrap around this

24:26artery here you guys are like probably

24:29like w what the heck is that artery this

24:31artery is called the internal cored

24:33artery it's called the internal cored

24:38artery it's a branch off of the common

24:39cored artery now these postganglionic

24:43sympathetic fibers form like a nice

24:44little plexus they actually kind of call

24:46it the cored plexus right here okay it's

24:48kind of like a sympathetic plexus coming

24:50off the cored now as it's coming

24:54upwards towards this region it actually

24:56moves through

24:58the super orbital Fisher with the

25:00trigeminal nerve like the Opthalmic

25:02division when it comes out it actually

25:06becomes a part of that short ciliary

25:09nerve so some of the fibers here can

25:11actually cross

25:13over and communicate with the short

25:16ciliary nerve and go in with the short

25:18ciliary nerves which is the

25:20parasympathetic and the trial nerve

25:22fibers and Supply the ciliaris and

25:25the pupil right the mus of the pupil it

25:29also can go just with the trigeminal

25:31nerve and Pierce the Scara and again go

25:35and Supply the pupil and the ciliaris

25:39muscle this is a part of What's called

25:41the long ciliary

25:43nerves so the sympathetic fibrous can

25:45actually become a part of the uh short

25:47ciliary nerves and it can become a part

25:50of the long ciliary nerves if it's in

25:51the long C nerves it's only moving with

25:53trigeminal which is a part of cranial

25:56nerve five

25:59a branch of the cranial nerve 5 right

26:00we're not going to talk about that

26:03now and then if it's a short ciliar

26:05nerves it'll be moving with the

26:08parasympathetic fibers the trial nerve

26:10branch and the sympathetic branch

26:15okay all right sweet deal so we did that

26:18now how does the sympathetic affect the

26:22actual ciliaris and the pupil

26:25okay so if you guys look from this view

26:29now let's say that this is actually

26:31going to be the sympathetic fibers

26:33they're piercing through the scare and

26:34they're going to supply the ciliaris and

26:36they're going to supply the pupil okay

26:40now what happens here when it goes to

26:43the pupil I'm sorry to the ciliaris

26:46muscle it's going to relax the ciliaris

26:49muscle so it's going to relax the

26:52ciliaris muscle now if the C ciliaris

26:56muscle relaxes this part over here goes

26:59back so now this part over here that was

27:02actually really really tense before

27:04really really tense because it was

27:05pulling from this Edge because before we

27:07were pulling from this Edge we were

27:10pulling it this way now what's going to

27:12happen is it's going to start relaxing

27:14and it's going to start going back to

27:15its normal position as it starts trying

27:17to go back to its normal position what

27:20happens to these ciliary zonals now well

27:22now they'll be pulled in that direction

27:25as they're pulled in that direction they

27:27start becoming very very tight and as

27:30they start becoming really really tight

27:32they start pulling on the lens and when

27:35they start pulling on the lens guess

27:36what it does to the lens it makes the

27:39lens really

27:41flat so now if you flatten the lens what

27:44is that good

27:45for holy crap if I flatten the lens

27:49that's going to take this lens farther

27:51away from that focal length or the

27:53object that I'm trying to look at so now

27:55because that it's going to affect the

27:57actual light rays that are actually

27:59going to be refracted onto the fobia

28:02okay so it's going to be more for far

28:04Vision or distance Vision on top of

28:08that it's going to come over here and

28:11it's going to

28:13activate this actual muscles within the

28:15iris but this is what's really really

28:18weird it'll activate these muscles

28:19within the iris let's come down here for

28:21a second to see exactly how these

28:22sympathetic fibers are arranged I'm

28:24sorry these muscle fibers are

28:25arranged these muscle fibers over here

28:27for the iris are arranged in like radial

28:29like spokes okay they're radiating

28:32outwards in like spokes within a tire

28:34wheel right what happens is Imagine them

28:39all being at this point right here a lot

28:41of the fibers are connecting to this one

28:43point right there on the iris right on

28:46the pupil hole what happens is when the

28:50sympathetic nervous system comes over

28:52here when these actual sympathetic

28:54fibers sympathetic nervous system fibers

28:56come over here and activate these actual

28:59radial muscles or you want to know what

29:02it's actually really called the radial

29:03muscles it's called the dilator

29:07pupula it's called the dilator pupila

29:10when it activates these muscles these

29:13muscles pull from that point there

29:17outwards they pull from that Central

29:19Point there outwards and they're trying

29:22to yank the pupil hole wide right so

29:26imagine I'm trying to take like a a

29:29structure right here and I'm trying to

29:31pull it apart that's what these muscles

29:34are doing they're trying to pull the

29:36pupil hole out

29:38wide if they try to do that what's that

29:41for that's for dilation of the pupils

29:44okay so how is this sympathetic

29:46affecting here how are these sympathetic

29:48nervous system fibers affecting they're

29:50causing the

29:53ciliaris to

29:55relax zonals

29:59tighten then

30:02what not only that but after the zonal

30:04tighten what happens the

30:06lens

30:08flattens if it flattens that's for

30:11distance

30:13Vision far distance vision and then it's

30:16also going to act on the what the

30:20pupils and it's going to cause the

30:21pupils to

30:23dilate oh real quick what do you call it

30:27me write up here on the top up

30:29here if the pupils

30:33dilate or if the pupils constrict they

30:35give it another name they call the

30:38dilation they call it midias midias and

30:42they call the constriction

30:45meosis okay so if the meiosis is

30:47constriction of the pupil dilation is

30:49midias

30:51okay now why are why are the peoples

30:54dilating why are the peoples dilating

30:55that's another question

30:57if the pupils dilate I'm not going to go

30:59over there for a second I'm going to

31:00imagine this imagine the pupils were

31:02like this right like this very little

31:05light was coming in through this area

31:07very little light rays could come in

31:08they were trying to focus it onto a

31:09central spot well now if it's a

31:12sympathetic situation a fight ORF flight

31:15situation you want to be able to see

31:17things from far away you want your eyes

31:19to be Keen right you want to be able to

31:20see as much as

31:22possible so like if you're running away

31:24from a dog you want to see all the

31:25multiple possibilities of where could

31:27run okay so because of that we're going

31:30to make this pupil bigger so that more

31:32light rays can come into the eye and

31:34focus on different parts of the retino

31:36right so that's going to be the

31:37importance for distance Vision it's

31:39dilating the pupils and again celarus

31:42relax zonal tighten lens flattens and

31:44that's going to be again for distance

31:46Vision all right sweet

31:48deal so we've talked about the

31:52sympathetic supply to the actual eye and

31:53we talked about the parasympathetic

31:55Supply Supply and we've talked about the

31:57pupilary light reflex obviously in any

32:00situation in which this is damaged the

32:03actual uh parasympathetic fibers the

32:05sympathetic fibers are damaged it could

32:07definitely have some type of problem on

32:09the actual pupilary light responses and

32:12the ciliary light responses specifically

32:14the accommodation that's why whenever

32:15you're shining the light and you don't

32:17see the direct and potential response it

32:19could mean that maybe there is something

32:20wrong but it might not mean that okay

32:22that's when you have to Warrant more

32:24tests all right all right sweet deal so

32:27that covers that part now let's talk

32:29about something else before we uh

32:31continue to keep going forward I want to

32:33talk about something that helps to keep

32:35our eyes lubricated constantly okay so I

32:38wanted to throw this in in here real

32:39quick I want to talk real briefly about

32:42lacation or the production of

32:44Tears okay laal fluid this is important

32:48not only for crying unfortunately but

32:49also it's very important because it

32:52keeps the actual cornea nice and

32:53lubricated and picks up any waste

32:55product so how does this all

32:58work okay let's say here and we're going

33:01to number it we're going to go piece by

33:02piece here let's say first step you see

33:05this structure right here this is the

33:06lacrimal gland so you have a bunch of

33:09lacrimal glands here and they're located

33:11on the lateral side of the eye so let's

33:13say that this is the nose so let's say

33:14that this is the nose side that's

33:16actually the nasal cavity right there

33:17and let's say over here is the actual

33:19temporal side or the zygomatic side

33:22right now on this side the lateral side

33:26these acal glands are going to be

33:27situated you know there's a nerve it's

33:29called the seventh cranial nerve or

33:31facial nerve right so cranial nerve

33:34seven innervates this right from the

33:36terop palatin ganglia so from the terop

33:39palatin ganglia they're actually going

33:40to have these fibers coming out

33:44anyway it's going to come here and

33:47release certain chemicals that causes

33:48the production of lacrimal fluid what's

33:50going to happen to that lacrimal fluid

33:52the lacrimal fluid is going to come out

33:55onto the cornea here and it's going to

33:57move across the cornea and other parts

34:00of the eye medially CU you know over

34:04here you're going to have a little thing

34:06here this little Edge part here this

34:08little V part there that's actually

34:10called the lateral commissioner so it's

34:11called the lateral commissioner over

34:13here this would be the medial commission

34:16don't get that confused though with the

34:18space between the superior palra and the

34:21inferior palra that's called the palpo

34:23Fisher so really this space right here

34:25is called the pal alal Fisher so lateral

34:29commiss and medial commiss and then

34:32again pal Fisher is the space so now

34:35lacrimal glands make fluid so lacrimal

34:38fluid is

34:40produced then where does it

34:43go

34:46moves

34:48lateral to medial sweet all right now

34:52where does it go from here you know

34:56there's like a little there's actually a

34:57little fleshy part here called the corle

35:00the lacrimal corle right

35:02there what happens is this lacrm fluid

35:07goes up through a tiny little hole here

35:10on the sides on the bottom part here and

35:12on the top part so up on the top part

35:14and the bottom part there's this tiny

35:15little holes okay these tiny little

35:18holes here are called the

35:23lacal

35:25Puna so it moves through the laaa then

35:29from the lacopa the little

35:31hole it goes into through these canals

35:35these tiny little canals and then into

35:37this big old sack

35:39here okay so again where's it going it's

35:42going from this Paco punto which is the

35:44hole through these little tiny canals

35:47into this big old

35:49sack and then we go into the next

35:50destination okay so from lacrimal

35:54Puna to the lacrimal

35:58canaliculi which are little

36:00canals then

36:04lacrimal Sac then from the lacrimal

36:08Sac it goes through this structure here

36:11so it's called the nasal lacrimal duct

36:13and from this nasal lacrimal duct it

36:15empties into the nasal cavity but

36:18specifically where in the nasal can

36:19cavity okay in the nasal C if looking at

36:23an anterior view so this would be the

36:24vulmer here so if I separate here vomer

36:27from this part down and then

36:28perpendicular plate from this part on

36:30the above right from the atho bone this

36:33part here is called the superior nasal

36:35cone middle nasal cone and then this one

36:38right here is called the inferior nasal

36:40cone in between them is the superior

36:42meatus middle meatus and inferior meatus

36:45little

36:46grooves this nasol lacrimal duct empties

36:50in through the inferus of the nasal

36:52Canal okay or the nasal cavity so

36:56lacrimal Sac to

36:58what nasol lacrimal

37:03duct and then from

37:06there

37:09empties at

37:11level of

37:14inferior

37:16meatus of nasal

37:19cavity all right sweet stinking

37:23deal holy frick Knuckles we've done a

37:25lot so far all right let's hang in there

37:27we're almost done okay so we've done the

37:30pupilary light reflex with the

37:31sympathetic parasympathetic and we

37:33covered

37:34lacrimation last thing I wanted to throw

37:36in here was I wanted to talk just a tiny

37:38little bit about light rays a little bit

37:41more I wanted to go a little bit more

37:42onto that and talk about exactly how

37:44that light is being focused onto the

37:46retina all right so now let's go ahead

37:48just I think it'd be good to get a nice

37:50recap okay of whatever happened with the

37:52parasympathetic and the sympathetic on

37:54the eyeball just so that you guys

37:55exactly know

37:57how it's all affected all right so let's

37:58go ahead and do that so again we said

37:59that the we were going to make this

38:01parasympathetic that was actually blue

38:02over there so let's write over here

38:05par

38:07sympathetic and then below down here

38:09let's say that this is for the

38:10sympathetic and then we're going to talk

38:11about myopia and hyperopia okay so right

38:14here is going to be

38:17sympathetic all

38:19right so now if you guys remember what

38:23did we say happened within the

38:24parasympathetic first things first we

38:26said that the

38:29ciliaris

38:31contracted okay when the ciliaris

38:34contracted it pulled upwards which made

38:36the ciliary zonals really loose so the

38:40zonals or the suspensory ligaments

38:42became loose so they loosen up a little

38:45bit right then when they loosen what

38:47happened to the lens they weren't

38:48pulling on the lens as much so the lens

38:50became globular looks exactly the same

38:53let me fix that a little bit let me make

38:55it a little bit more globular here all

38:58right now that sucker is Beefy all right

39:00so now we got a beefy old lens right so

39:03this lens is going

39:05to

39:07bulge now when the lens bulges

39:11right we said that this was going to

39:13affect the light rays okay it's going to

39:15affect the light rays that are coming in

39:17here then what else do we say happens so

39:20it's the lens bulging is actually going

39:21to do what it's going to bring the lens

39:24closer like like the focal length it's

39:26going to shrink the focal length and

39:27bring the image closer bring the lens

39:30closer to the object that we're trying

39:31to focus on okay so lens bulging helps

39:34with our

39:35near point of

39:39vision and then we said the

39:43pupils would constrict

39:47why okay it's to

39:49prevent diverging Rays from getting in

39:53so to prevent diverging light rays from

39:56getting in okay and to focus the actual

40:00light on the phobia so if we constrict

40:03the pupil it'll help to allow for the

40:05light rays that are coming in here no

40:08diverging light rays pretty much all

40:11parallel to actually come in and focus

40:13on to a specific point in the retina all

40:17right now what about the sympathetic the

40:21sympathetic we said that the

40:22actual ciliaris relaxed

40:29then when the celarus relax what

40:31happened to the zonals the

40:32zonals

40:35tighten right because remember it went

40:37back down to this position as it went

40:39back down to this position what happened

40:40to the zonals they become tight as the

40:43zonal become tight what happens to the

40:45lens the lens

40:48flattens as the lens

40:51flattens look what

40:55happens you

40:58decrease okay now as the lens flattens

41:01now remember the object was out here you

41:03actually increase that distance the

41:05focal length between the the lens and

41:07that object right so now it's going to

41:10be more for far Vision or distance

41:13Vision so this is more for distance

41:19Vision another thing is we said that the

41:22pupil what happened to the pupil the

41:25pupil

41:28dilates if the pupil dilates this soccer

41:31gets freaking big then what's going to

41:34happen more light rays can come in and

41:36focus more of that light on different

41:38parts of the retina so now the light

41:39rays that are coming in here we have

41:42more light rays coming in and if there's

41:44more light rays coming in we can focus

41:46more of these light rays on a larger

41:48part of the retina right we can focus on

41:50now a larger part of the

41:51retina okay so this is more for your

41:53flight or fight okay or you can see this

41:56dilation response you know when else

41:58You' see this dilation response when

42:00you're actually uh going from like a a

42:02certain type of room maybe when you're

42:03going from a a light room into a dark

42:06room because when you go from a light

42:07room into a dark room your actual pupils

42:09will dilate when you go from a what this

42:13was going from a light to a dark this

42:14would be going from a dark to a light

42:16room the peoples will constrict all

42:19right all right sweet deal now let's do

42:22another thing and let's talk about last

42:24thing here let's talk about two

42:26different types of uh situations that

42:28can happen in people's eyes happens to

42:31me

42:32myopia and let's talk about another one

42:35called

42:36hyperopia there actually is another one

42:38called Old person's eye or presbyopia

42:41and it's just as you get older the

42:43vision starts being affected and if you

42:45notice you ever notice certain older

42:47people I'm not trying to make fun of

42:48anyone but they have to hold the book

42:50all the way out here because their near

42:52vision is affected that's what can

42:53happen you can actually develop

42:54presbyopia which can affect the ciliary

42:56zonals and the the lens can actually

42:58start accumulating a lot of crystallin

43:00proteins so it can affect the refraction

43:02again they have to hold images really

43:04really far away so they can see it

43:05clearly all right anyway myopia myopia

43:10is basically when the old eyeball here

43:14is too

43:15long it's too

43:18long okay and hopia is usually the

43:22eyeball is too

43:24short so what happens is for this person

43:28if the eyeball is too long imagine here

43:31I have the light rays coming here okay

43:33here's these light rays coming in

43:35through the pupil as it comes in through

43:38the pupil the lens is going to try to

43:42focus these light

43:44rays it's going to have like a focal

43:46point

43:47right and the part where they a lot of

43:50these light rays cross and then they can

43:52kind of come out like this okay this

43:55point right right here that focal point

43:58right there that's where the image is

44:00formed now that's not good you want to

44:02know why because the retina is right

44:06here the retina is right here and it's

44:09not formed on the retina it's formed in

44:12front of the retina when an image is

44:14formed in front of the retina that's

44:15going to affect what type of vision it's

44:17going to affect the far Vision distance

44:20Vision so people with myopia they are

44:23nearsighted in other words they can see

44:25things nearby

44:26but they can't see worth a darn things

44:28very far away so this

44:30is

44:34nearsighted okay so they can see near

44:38can't see

44:40far okay so they have a hard time with

44:43distance Vision how would you change

44:45that okay well the problem is that this

44:47is converging too early well give them

44:50some type of glasses or uh certain types

44:52of contacts a lens that will diverge

44:55those light rays what do you give them

44:59give them a concave lens so give them

45:02some type of lens like

45:07this if you give them a lens like this

45:10when the light rays are coming in it'll

45:12actually spread these light rays out so

45:14as the light rays are coming in here it

45:17can help to spread some of these light

45:19rays out a little bit and if the light

45:22Ray are spread out a little bit that

45:25when they actually come in to the eye

45:27they're not going to be focused on that

45:29point anymore they're going to be

45:30focused a little bit farther away now so

45:33now the light rays as they're coming

45:35back here because we diverged it with

45:38that concave lens as we diverge it now

45:43these light rays will actually form

45:45where they'll form perfectly onto the

45:49redon let's just assume for this case

45:51here that the retina is going to be

45:53right here okay it's not but just assume

45:56okay so again that focal point right

45:59there that it hits that focal point is

46:02going to be hitting the retina how do we

46:03fix it we gave him a

46:06concave lens because the concave lens is

46:10going to do what to the light rays it's

46:12going to be a

46:14Divergent lens meaning it kind of

46:17spreads the light rays outward as you

46:19spread the light rays outward whenever

46:21it converges onto that focal point there

46:23it's going to converge a little bit more

46:25farther back

46:27with hyperopia the eyeball is too short

46:30so now look as the light rays are coming

46:33in and they're being focused

46:37here onto this person's

46:40retina it's being focused onto the

46:44retina farther

46:46back so it's being focused a lot

46:50farther back here and as it's being

46:53focused a lot farther back it's getting

46:55formed the image is starting to form

46:57behind the retina so where's the retina

46:58here the retina is going to be in this

47:01case we're just going to draw it like

47:02this in red it's right here the image

47:04though that focal point is forming right

47:06here behind the retina so because of

47:09that how do we fix that we got to give

47:11them a lens that will actually converge

47:13the light rays before they're coming in

47:15how do you do that you give them

47:17opposite of a concave lens you give them

47:19a convex lens if you give them a convex

47:24lens what the convex lens will do is is

47:27it'll have these light rays that are

47:29coming

47:30in it will converge

47:33them okay so it'll converge these light

47:35rays even more as these light rays are

47:37more

47:38converged they have more

47:41convergence they'll actually

47:43form a little bit more

47:47anteriorly okay so they'll form a little

47:49bit more anteriorly and they'll form

47:51perfectly on to that nice old retina so

47:55their focal point will now be on the

47:56retina okay and the purpose of the

47:59convex lens is it's going to be a

48:01converging

48:02lens converging

48:05lens so it's going to bring the light

48:07rays in closer so that the image forms

48:09anterior to I'm sorry a little bit more

48:11anterior on the retina

48:15okay Nur we covered so much information

48:17in this video I really thank you guys

48:19for sticking in there with me and

48:20hanging in there I hope you guys enjoyed

48:22it I hope you guys really did understand

48:24it and and I hope you learned a lot if

48:26you guys did like the video please hit

48:28the like button comment down in the

48:29comment section and please subscribe as

48:31always Engineers until next time