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BIOL 4315 Neuroscience Tue Th 8.30-10am - NEURO Lecture 16 CNS III, Imaging, and RETINA
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00:01 according in progress. This is lecture of neuroscience. And when we left
00:08 last lecture was on the cranial So I have suggested that you should
00:18 several cranial nerves and you should be to identify the several cranial nerves that
00:25 highlighted. And now whether there's sensory or both and what functions they may
00:36 . So just just to remind you I had this pneumonic for you.
00:43 again is just an example of And if you recall the first
00:49 you have the first letter of this monitor or go to touch corresponding to
00:55 first letter of the cranial nerves. this is how you know what that
01:01 nerve what letter stands starts with Trow Klia T trigeminal V. The
01:09 opener. And then you want to which ones of these cranial nerves are
01:15 which ones of these nerves are motor which have both function sensory motor.
01:24 this is the second pneumonic. So much money. But so ask for
01:29 and promoter. B for balls. nerves that I pointed out to you
01:34 I want you to know that this is one or factory to optic
01:40 Popular motor. Five trigeminal eight vestibular and 10 vagus nerves. One is
01:51 It's # 12. It's because it's nerve and will study that individual
01:57 three is because it's an example of nerve where the name of the nerve
02:05 what function that nerve is responsible for motor. That's an easy one moving
02:12 killer the eye. And as examples example, number eight is the stimulus
02:20 also tells you that it's a nerve processes information from the stimulus apparatus and
02:27 cochlear. So it has two components from the stimulus Perata's and the second
02:33 from Cochlear. We just have to what platter or that one for
02:43 So we'll get we'll get the thalamus thalamus. You definitely need to know
02:50 thalamus is. It's a collection of nuclei responsible for different functions. We
02:56 GPL for sensory motor sensory okay we about L. G. N.
03:04 visual system. So you may want know some of these but we'll come
03:09 and know a lot more about the of L. G. N.
03:13 we study the visual system to hang this. But for cranial nerves it's
03:20 eight Mr. Bullock Oakland Town Because we encountered vagus nerve when we
03:27 the discovery of chemical neural transmission by Allawi And the difference is there the
03:33 that the cardiac muscle was inhibited by and that we later we learned that
03:39 skeletal muscles of neuro muscular junction from cord are excited by Seattle police.
03:45 that's why you want to know this . Now you want to be able
03:49 identify what is an optic nerve what an optic eye? ASM what is
03:53 optical track. Whereas the trigeminal nerve located. So there's good questions that
04:01 come from these diagrams that are based labeling and function. So I may
04:06 that this is this nerve and what does it perform. And if I'm
04:12 to the trigeminal nerve I may ask it sensory ziff motors in both.
04:17 so you should know the information about 123 456 nerves. Really not in
04:26 but the ones that you have to for this exam. Okay so this
04:32 the cranial nerves. And finally we're to talk about and remind ourselves a
04:37 bit about what we already know. mentioned that the spinal cord is subdivided
04:43 to the sacral lumber portions, thoracic and cervical portions. And so you
04:52 the cervical portions in the neck and have vertebra. So when you hear
05:01 talking about the injury happened at Two or L. Two. What
05:07 stands for is cervical vertebra. C is cervical vertebrae number one and there
05:14 be C. One C. Two . Three C. Four C.
05:18 C. Six C. Seven. there's seven cervical vertebra and in between
05:26 one of the vertebrae you have a nerve that comes out you know that
05:29 spinal nervous comprised of the sensory the dorsal root ganglion cells and also
05:34 motor component. So we'll review that 1/2. So in between each vertebra
05:42 one side you have a spinal nerve of course on the other side you
05:46 The spine owner of also thoracic for . T. one through t.
05:53 of thoracic vertebra. Okay so you T. One thoracic vertebra and then
06:01 . First thoracic nerve and T. . And then you have 12 thoracic
06:07 . This is the lumber. You L. one through L5. And
06:14 you have sacred this is s. here Now the spinal cord proper which
06:23 the spinal cord. That is just continuous structure. And set about
06:30 Two, L. Three. and L. two and L.
06:36 the spinal cord turns into what is car data, quanah caudate detail,
06:44 queen, a equestrian horses tail and it's no longer one continuous proper structure
06:55 rather bundles of fibers resemble the tail these fibers and innovating the lower extremities
07:07 . This is important also because in of cerebral spinal fluid infection or brain
07:16 such as meningitis uh such as covid definitive way to tell whether there is
07:25 infection and the brain is to take sample of the spinal cerebral spinal
07:33 And you would take that sample from spine and it's called a spinal
07:40 Where doctors would tap in. They tap through these meninges just like you
07:47 meninges surrounding the cns. We talked the dura, arachnoid pia mater.
07:54 the doctors would essentially go right below spinal cord proper by puncturing through the
08:04 that we talked about and sampling a bit of the cerebral spinal fluid that
08:11 present in the spinal canal at the of the spinal cord. So and
08:16 reason why it's done at that level because you can put a relatively soft
08:24 in between the horses scale fibers without through the proper titian. So you
08:34 sample cerebrospinal fluid. You would know there is a bacterial infection, if
08:38 is a viral infection and that would that you have a viral or bacterial
08:44 in the C. N. Now there um common way or common
08:53 that targets this area is also And you may have heard the epidural
09:04 anesthesia versus subdural sub is below api's dural anesthesia. And that is common
09:13 the child delivery. And the point is you want to anesthetist and you
09:20 to inject and tap into in between cottage requirement fibers below and numb the
09:28 or the mother that is delivering a from the contractions to pay in the
09:34 pain. So a lot of times it has an effect of numbing the
09:39 and women cannot often move their legs they're giving birth to. So it
09:45 on the sensitivity of everyone the sensitivity anesthesia and percent potentially the procedure how
09:54 is performed by the anesthesiologists in the . So this is the spinal nerve
10:01 a single spinal nerve as a collection both the sensor and the motor
10:06 It was this root ganglion dorsal root . So this bulge here is formed
10:13 you have collections of DRG soma is . I remember the dorsal root ganglion
10:19 have that peripheral axon that goes into periphery. And then from the soma
10:25 it sends the central axon into the part of the spinal cord. Then
10:31 that inside spinal cord property had inter and then the output. The motor
10:37 of the spinal nerve is the motor fibers that are running into the muscles
10:43 joints. Yeah, so this is spinal cord. And if you look
10:50 this portion here that is a darker . This is the gray matter of
10:55 spinal cord which means it contains the of neurons. And you can see
11:02 this gray matter of the spinal cord sort of a butterfly shape. Or
11:09 would say maybe it's texas longhorn You know either way you look at
11:15 but it has a dorsal horn and has the ventral horn. So dorsal
11:19 is where the inputs will be coming and contacting the cells. And then
11:26 the ventral horn you can see the will be coming out. These are
11:30 motor neurons. And then you have is called dorsal columns here and all
11:37 the surrounding white matter dorsal column, column, ventral columns. They contain
11:44 and descending fibers through the spinal So remember all of the information.
11:49 going to come in from the body the spinal cord. It has to
11:53 and then form the cortex. Of there's reflexive behavior that we talked about
11:58 the level of, let's say reflex . But inevitably that's still makes you
12:05 of that reflective behavior which is sending communicating information to the top. You
12:11 all of the sense of information, you have a motor output command.
12:15 if it's a motor optic command that your tongue and muscles and you're speaking
12:19 is your brain stem moving, you nerves, moving your tongue, chewing
12:25 of these things you're doing if you're your hands and playing tennis, this
12:30 everything spinal cord from down here, fibers. So there's a lot of
12:37 and descending fibers running in. And should know that the major ascending sensory
12:44 which is ascending a sensor information was . His motor commands and sensor
12:52 Touch pain on the phase temperature. you can see that this is dorsal
13:01 which is a major sending phablets. there is another one that is called
13:06 thalamic tract. So what does that you most of the things in
13:12 They say what they are spinal That means it goes from spine,
13:18 spinal cord into thalamus. It was Arabella. This goes from spine to
13:27 . So descending motor pathways, their pathways. Because their motor commands that
13:33 coming from the motor cortex from the ganglia from those regions that initiate and
13:40 to execute them out of commands. are the descending pathways, collateral pathway
13:47 venture medial pathway. And you can that cortical spinal, that means it
13:51 from cortex to spine, Rubira spinal a different area to spine. Medullary
13:58 spinal track. You don't have to all of the details. But the
14:02 is that the name's kind of tell where the tracks are going to and
14:08 . So for the exam you need know the dorsal column nuclei is the
14:13 ascending pathways here but know that lateral ventral medial pathways are the major descending
14:22 . Okay, but not the details rubber, Aspinall versus cortical spinal and
14:26 on. It's a little bit too detail. Now this becomes very important
14:30 you pursue a graduate degree or you a medical degree in nursing degree or
14:36 some instances um dental degree, Anything do with rehabilitation with damage to the
14:43 or spinal cord and such because you see that if you sustain the damage
14:48 the to the ventral or to the part of the spinal cord on the
14:56 school exam you would be asked a . This person has sensation but doesn't
15:03 motor function which portion of the spinal was injured. It still has
15:10 That means the sensory the sending pathways functioning. There's no motor, that
15:16 that the descending pathways are not And those questions get very specific.
15:22 damage of the spinal cord was done detected at C3 in this specific
15:30 And they would say the most lateral of the ventral medial pathway. And
15:37 be like, and you're like my med medulla, that's what it stands
15:43 . So it's something to do with brainstem function. Medulla, vital body
15:49 . Okay, so again, those can get very specific but if you
15:56 at this map and the structures that can actually derive what is going on
16:03 knowing where damage has happened, whether happened on the ventral side, whether
16:07 happened ventral medial side, whether it on the dorsal side of the spinal
16:11 and you will have problems with sensory motor outputs and different outputs from the
16:17 the cortex or from cerebellum and so . So for the exam now they're
16:23 dorsal column descending mode apocalypses, major paco, and ventral medial part.
16:30 have autonomic nervous system of course, peripheral nervous system that comes out that
16:35 don't spend much time talking about in course. But what we will talk
16:41 is imaging and imaging the brain And most of the time when you
16:47 thinking about clinical imaging, you're thinking static images. That's something like X
16:54 . So if you had a injured which I havent injured knee in the
16:59 right now and it's causing all sorts problems for the whole family. Just
17:04 knee, not problems, but My wife hasn't injured me and she
17:10 drive very well. So I'm in of everything for pick ups and drop
17:15 . So, but you will do X ray on your knee and they
17:19 say, oh well what will X show you there's damage to the
17:24 There's maybe a torn tendon, something hard and soft tissue, but it's
17:34 functional. Doesn't tell you the activity the knee doesn't measure the activity in
17:40 knee. Just as that something changed rays. Typically actually would do a
17:45 office. So in the, in old days, I don't know if
17:50 experience those old days, but you to put a lead thing on you
17:54 cover yourself. Going to a separate was a big box. That was
18:00 X ray. And it would take , you know, move to pictures
18:05 pictures. And then, so that about like 15, 20 years ago
18:12 they would actually print the pictures and would look at it. Now you
18:16 to the dentist office, you just your jaw and this thing rotates and
18:22 multiple x ray pictures, puts a dimensional picture of that X ray and
18:27 all of your teeth right away within . So it's great. So it's
18:33 for hard tissue for bone breakage of bones, you can detect things like
18:39 cancer with X rays. Um but most of the cases you would want
18:46 go into something that is called computer . Ct scans you hear about cT
18:53 . Ct scans are really sophisticated X that are multidimensional and they have different
18:58 of cT scans Can have up to planes through which they image across the
19:07 structure of one focus structure in the . We can detect swelling abnormalities
19:14 Um carcinogenic growth and things like Mhm. M. R.
19:20 Is a different technique. It's magnetic resonance imaging. There's no X ray
19:28 and you're really getting more detail. the resolution of C. T.
19:36 . F. M. R. is still approximately one cubic centimeter.
19:44 you cannot visualize single cells. 10 is a single cell dynamics. And
19:52 of these techniques including M. RI and X ray will show you changes
19:57 are static changes. There is a there there is a damage in that
20:01 of the brain. There is blood . But in order to see what's
20:08 to the function of the brain, have to use techniques that are positive
20:13 emission tomography, Pet and FMRI or magnetic resonance imaging. And with all
20:21 these imaging techniques when you're measuring When neurons get active neurons sucked a
20:31 of oxygen. They demand a lot oxygen. They suck a lot of
20:37 and glucose. This is the main of food from neurons and so the
20:45 regions that get engaged and are they will be sequestering these resources.
20:51 oxygen resources, hemoglobin molecules that are . They will sequester the glucose and
21:00 nutrients going to those areas of the that are very active in a very
21:05 areas of the brain would also start because neurons that are very active would
21:11 start swelling because of the activity and in the ionic and local fluid
21:18 So what functional imaging does it allows to really track the regional blood flow
21:27 brain metabolism. MRI or magnetic resonance is based on hydrogen atom has one
21:37 . It can bounce between high energy low energy state. The frequency at
21:44 this proton absorbs energy basically bounces between and high energy state is called resonant
21:51 . So that's the resonance part of are in the M. R.
21:57 . And then the person sits in coil and there's radio waves that are
22:03 by protons that are collected by this coil. So M. R.
22:09 . S. Has a big magnet you will hear things like two
22:13 Three T 70. What does that ? Have you heard of Tesla?
22:18 the strength of the magnet is a powerful magnets and you need to have
22:25 environment special rooms for M. I. S. And F.
22:29 . R. S. So they be located and lower portions of the
22:35 because it doesn't need much vibration or the basement. Ah If you walk
22:43 in front of very powerful magnet like a spoon in your hand, the
22:47 is gonna fly and stick to that if it has a lot of
22:51 So this things that need to be around this and then your body or
22:57 slides into that magnet that it has high sensitivity to these changes. So
23:05 . M. R. I. we talk about F. M.
23:08 . I. And this is sort a this is a pet scan image
23:13 you would also have a coil like in FmRI FmR. I measures the
23:19 of oxy hemoglobin which is oxygenated, versus de oxy human little bit.
23:26 where there is a lot of neuronal . There is more of deoxyribonucleic Logan
23:32 those neurons are sucking the oxygen on molecule with positron emission tomography is a
23:43 labeled solution that is injected. It's positively charged ions in the blood stream
23:52 bind electrons and electromagnetic radiation in the of photon. And what you're detecting
24:01 the pet scans is glucose consumption. you're looking at two deoxyribonucleic O.
24:07 two D. G. And again there is a lot of activity,
24:12 going to be a higher demand for . So are you really imaging neuronal
24:21 when you're imaging using imaging with pet and FmRI you're not you're not recording
24:28 activity here. You are recording changes oxygen and the blood flow of that
24:35 . You're recording changes in the supply glucose and nutrients. How close is
24:42 correlated to brain activity really close? and of course it's not real
24:48 But these are very fast machines these . The resolution of even F.
24:53 . R. I. And T. Um Multidimensional cts are trying
24:59 go to about 100 micrometers resolution. now we're talking about potentially little clumps
25:05 cells that now the ultimate for neuroscience to be able to use these non
25:12 techniques. This is an advantage. Pat, you're getting something injected.
25:17 not it's a little bit invasive but not invasive. Nobody has to open
25:21 skull. Nobody has to look into brain by doing a massive surgery.
25:27 these are non invasive techniques. The as they're slow in the sense that
25:32 don't see real time activity. You that activity on the computer. You
25:37 to discard the delays between if you presenting a stimulation to a subject in
25:42 camera or if a subject is having normal brain activity. So it takes
25:48 to process that information. And when reconstruct what what's happening in real
25:53 So it's not completely real time. it's very fast. Yeah, but
25:59 resolution. And I say the ultimate to have these noninvasive techniques that will
26:07 able these techniques. Noninvasive techniques and you're seeing, like uh this is
26:17 control and this is stimulation on the , this is control. And if
26:21 subtract the two maps public activity you the difference and that difference shows you
26:28 difference between the unstinting elated and stimulated . And so you see these maps
26:34 these maps don't have much resolution but not invasive. The ultimate is to
26:39 able to go down to the resolution a single cell, maybe potentially the
26:44 of a single synapse while still having of this additional information at a circuit
26:51 and at a gross anatomical structural How to accomplish that. I think
26:58 may be more sensitive tools and it's to be up to young generation to
27:06 guys to figure these things out. concludes our section on the cns,
27:16 parts and functions and a little bit the functional imaging. Now we're going
27:22 start talking about the visual system and is introduction to the visual system,
27:31 german to Rome Just out, it's very interesting term when you think about
27:41 but Gaston, this configuration reform or you make a complete picture of the
27:49 world um Gustav metaphorically could be used understanding of the outside world, not
27:57 just visualizing complete picture of the outside is a combination of multiple sensory inputs
28:05 how we process, how we associate sensory inputs. Um what we see
28:13 example represents properties of objects and also organization of our brain structures and the
28:23 that our brain is organized And you a certain side of architecture in the
28:29 will also organize the sensations or perceptions the motor out that that we're capable
28:34 doing. Mm hmm. three dimensional that we see quite often Formed from
28:44 Dimensions. So if you were to at this image you would say,
29:08 obviously this is a cube. But reality it's not it's not a three
29:15 structure. It's a flat board and dots on the flat board. It's
29:21 these three dimensional representations a lot of from two dimensions we've learned because we
29:29 an association and a comparison. But that the cube is going to be
29:34 cube if we can if we came touched it and so we will prove
29:39 to us. And if we came we couldn't touch the Cuban. 39
29:44 then we would try to adjust on we're understanding the outside world as we're
29:49 . We have the plasticity and probably that that Cube is actually flat.
29:55 we've learned that it's three dimensional this of these sensations into a stable pattern
30:01 gestalt that is constant despite variation. the information received. The brain makes
30:08 assumptions about what is to be seen the world, expectations that seems to
30:13 in part from experience. And apart built in neural wiring. So we
30:19 a certain wiring, finite abilities and wiring and then we're presented with different
30:25 on the outside world. So we to group things together. This is
30:35 pattern that you would call an ambiguous . It's just dots. It just
30:40 like kind of a square of And this if you look here on
30:47 on the left and where I want ask you on the left here on
30:54 top, what are you seeing? common answer would be I'm seeing columns
31:01 blue or black dots and columns of dots. And if I asked
31:07 what are you seeing here at the last year will say, well I'm
31:10 rose of yellow dots and rows of dots, but that's because we group
31:21 based on similarity. In reality. the author wanted to represent us as
31:28 alternating blue, yellow, blue, , blue, yellow. But the
31:34 impression that you got is that these evil rose for columns. This is
31:41 principle. What are you seeing here the right here you're seeing again,
31:49 seeing columns on the bottom here. seeing roast and that's because these dots
31:57 are close to each other by We think that they belong to the
32:03 . Call him here. In reality user or the creator of this may
32:09 wanted you to have two dots that further away, two dots that are
32:14 , two dots that are further two dots that are closer. We
32:20 . Yeah. So what if you the two proximity and uh the
32:26 So will one win? Great I think the color would probably win
32:34 it would have more contrast. But if you take that color away and
32:38 something different like a shade and then proximity with one another and that depends
32:44 on the on the size of the to. So it's a very good
32:49 which is more powerful. Uh And think that depends, it depends on
32:55 things how big the object is, color, the brightness maybe of the
33:00 which is going to be more I would vote for similarity but don't
33:13 me on that if there is some study and he said oh no we
33:18 the wrong one. So let's see these illusions. Like if you actually
33:25 these lines and you didn't have these lines, you would think that the
33:29 line is shorter and bottom line is because of the of the edges year
33:37 pointing and this makes the arrow seem the same line but they're the same
33:43 there. Misreadings are illusions of visual by the brain also listed how the
33:50 applies certain assumptions about the digital world the sensor information we received. So
33:57 other words, when we see things proximity or we think we see
34:01 we think that this is a longer . We have to look at additional
34:05 such as well. Are you being by other visual cues that make this
34:11 seem longer rather than shorter? What you got rid of these other additional
34:16 cues and looked at just the line , then you would realize it's the
34:20 line. But we go about our and we see things and we
34:24 oh, you know, like how times have you been on the court
34:29 people have called out and others in to rest? The third one,
34:36 think it was both they call the one you get on the phone,
34:40 know, slow replay. But if don't have that slope, we don't
34:46 that little replay and three people telling exactly what we're looking at or what
34:51 stepped on or what is ahead or bus size and so on. Mm
34:57 . So well, we just assume and luckily we have this constant understanding
35:03 example, that we know that there's people sitting in the hallway and one
35:08 sitting further away that that person is not a tiny tiny person, but
35:16 a person that is a distance further . So if you were to bring
35:20 person, it wouldn't be this you know, little like mhm fairy
35:26 character and that's information that we've learned if we didn't learn that, then
35:34 would see, oh it's an elf don't hold, you know, but
35:38 know that because of the distance and know how things get smaller that you
35:42 that this door is probably the same as the door in the back.
35:47 it's tiny. It looks tiny. you've learned these things also when you
35:54 things and you see things and you forget them. So these are some
35:57 simple illusions. But this is a or two faces. And this is
36:03 green frog or yellow fish. And illusions are illusions until you realize that
36:11 illusions. And once you've learned that , you recollected very quickly, you're
36:16 longer confused whether it's fish or you can see both. There's the
36:21 of the frog here, frog This is a fish. So looks
36:29 it's redfish and bullfrog from such a a basin on Itunes east. So
36:41 do we perceive light? You have of light electromagnetic radiation. A certain
36:50 that we perceive amplitude and frequency are . So how strong is the source
36:58 light is the amplitude? What color the light is the frequency of that
37:06 line? So our visible spectrum is 400 to 700 nm is the wavelength
37:14 we process on this low end, have ultraviolet rays and then you have
37:22 rays here and then on this high you have infrared race radar broadcast bands
37:30 c circuits, things like that. Roy G bev. it's something that
37:37 a good abbreviation backwards from red, , yellow, green G. Business
37:47 indigo, violent, violent Roy G . So you can go backwards or
37:53 can go from longest to shortest wave . So you can have a weak
37:59 spot like a flashlight. So the , if you go and buy a
38:04 for camping or fishing or work, will see lumens for the intensity of
38:13 essentially the same as an amplitude of wave line. You can have white
38:18 that's very dim and I have white on the same wavelength, the same
38:23 same frequency, the same wavelength, much higher amplitude. And this is
38:28 to be a lot more lumens and see it from much further away.
38:34 light travels a lot of times the gets reflected from the objects that we're
38:40 . Light gets absorbed by darker colors light gets rare fracked ID. We're
38:49 when it passes through two different such as between air and water.
38:56 it actually gets refracted when it enters light from air into this acquitted solution
39:04 the eyeball where you have the iris surrounded by sklar ara in the very
39:12 of it is the pupil. That's the information is going to entrust through
39:17 pupil and the cornea surrounding it. have that extra ocular muscles. So
39:23 you're talking about ocular Motor nerve, movement of these muscles that are attached
39:29 the eyeball is going to move the . Mhm. And in the back
39:35 the eyeball you have the optic So the retina will be located in
39:39 very back of the eyeball. In before we get into the specifics of
39:44 retinal circuit the L. G. . And the cortex this is the
39:49 of the visual system. What visual is. This is a very good
39:55 of a major sensory system and human to which we dedicate a lot of
40:02 power and we rely on vision a . It starts out in the retina
40:08 the retina it goes into the thalamus the lateral manipulate nucleus of the
40:14 You will learn that algae. Is a six layer structure and from
40:18 lateral nucleus nucleus of the columnist. information goes into the primary Visual Cortical
40:26 D. one or Broad Mons Area . And if you recall we have
40:31 primary secondary tertiary co ordinary preliminary processing . And then we have what we
40:36 association areas. Association areas is we're sensory modalities. Get bound together.
40:46 a binding of vision, hearing, sensation, smell that evokes according reaction
40:55 reaction in the brain or the motor . So this is a primary visual
41:00 area and we'll understand everything in the up until the V. One and
41:06 understand how the one creates a primal of the outside world in the next
41:12 of hours. So if you follow the next couple of hours you'll actually
41:17 how the circuit and the cells create images that you're seeing to the point
41:24 the primal sketch of this world that should be able to understand. Now
41:28 area V one as we talked there's a hierarchically more complex processing in
41:36 V. Two and V. And you can see that the visual
41:40 actually split into the ventral inferior temporal targeting inferior temporal cortex and into the
41:51 parietal pathway which is targeting posterior parietal . And you have a code
41:57 It says that one pathway is concerned processing color, that's a color
42:06 And this pathway color pathway is related the temporal lobe and processing in the
42:13 lobe. There's also auditory information in temple of and that's why you have
42:20 mixing of senses and some individuals and they hear music they see color.
42:27 we'll talk about that. It's called . We're all in some degree sin
42:31 actually because we learn by association including association. So you also in this
42:39 pathway that is going into the dorsal , whether you're processing here, you
42:43 processing motion, you're processing depth, processing form. So you you see
42:52 at each junction that processing gets more . Is this the only pathway that
42:58 form? No, the temporal pathway form. So there's your redundant.
43:03 if you lost understanding of form within larger context of the visual or censor
43:10 from one path where you still have of form through the other path
43:16 It's potentially not as essential. You survive without color but without pattern not
43:26 much. Okay. Conor is will you the chair is black,
43:31 green or white, but it's a . You see the form form be
43:36 whether it's a chair or step forward . So that's the form information will
43:46 into the pupil. You have this here for draining of the tears.
43:51 have this clara lack amal glands that the tears. You have this uh
43:58 right here. Okay, so the comes in through the pupil enters and
44:03 have this lens and this lenses suspended this by the suspense serie ligaments and
44:11 has the sillier bodies. And basically ligaments can pull on the lens and
44:18 it thinner or it can relax, can pull make it thinner or it
44:25 relax. And actually the lens will up. And as your lens becomes
44:30 or thicker you're refocusing on different whatever of interest you're looking at this light
44:40 going through passed through the acquis environment . So in the front here you
44:46 the acu Aquarius humor which is a of the nutrients and one of the
44:52 in glaucoma is actually upset in the of these Aquarius humor nutrients. And
44:58 here you have the vitreous humor. vitreous humor which is gel like
45:04 It gives more the shape to the that we know. You have innovation
45:09 the blood vessels through the eyeball and the back of the eyeball you have
45:14 retina and the retina will put out fibers in the form of the optic
45:21 that legs it out from one eye where it exits out here you will
45:25 a blind spot because there's no photo processing here at the blind spot,
45:32 in the light and the line with pupil. You have the phobia right
45:38 in the back of the retina. phobia is a special location that has
45:45 indentation and this indentation focuses in the onto the phobia. You can see
45:53 there's a certain circuit and then particularly photo receptors that will transducer. This
46:01 from photons of light into electrochemical signals located on the very back of the
46:07 and that there is actually a circuit cells, ganglion cells, bipolar cells
46:12 the slide bypasses through the circuit before activates photoreceptors. Retina is a part
46:20 the cns. Remember when we talked the developing of the nervous system,
46:24 said look at this optic stock and the cut that becomes the retina.
46:29 phobia is a region where you will the highest security division or the highest
46:35 vision. So let's talk a little about the circuit. This is the
46:40 of light in red and this is direction of retinal digital information processing.
46:46 the light is going to come through eyeball is going to go through the
46:52 of these cells here and then it's to activate the photo receptors in the
46:58 of the retina have cone and rod . There are three types of cone
47:06 blue, red and green. You miss that on the labeling exam in
47:11 diagram and there's only one type of photo receptor and their acrobatic. These
47:19 receptors will transducer and energy of live an electrochemical signal that electrochemical signal is
47:27 to get communicated to these blue cells bipolar ourselves. And the bipolar cells
47:34 synapse and contacted by the retinal ganglion . Retinal ganglion cells. Their axons
47:42 form the fibers of the optic nerve is cranial nerve to the optic
47:49 So the only output from the retina coming out of these retinal ganglion
47:55 The only action potentials in the circuit get produced get produced by retinal ganglion
48:02 photo receptors or receptor cells therefore they produce receptor potentials Grated receptor potential.
48:11 we're going to be communicated to this cells also integrated fashion. And only
48:17 Reynolds ganglion cells are excited enough that produce action potentials. Yeah. So
48:29 can see that this these ligaments that the lands they can thicken it or
48:35 can thin it out. So you see that if for example it's
48:40 it can focus on a point that's away. But if the lens thickens
48:45 that means that it has to focus the point. Ah That is
48:52 Sorry I have to make sure it's something um painful. Uh Now there
49:00 dysfunctions in the in the lens and is a good exam question. Hi
49:06 versus myopia. In metro pia is vision When you focus a flower you're
49:12 at and the lens is the proper and it focuses right on the
49:17 right on the photo receptors and high . That image is focused behind the
49:25 . So in the retina is looking an image it sees it blurry.
49:31 the correction is to have this kong slams. Okay and in myopia the
49:43 focused before the photo receptors before the . And this is a concave lends
49:53 being used in order to adjust So this is what's in your
49:56 If you're short sighted or far you will have one of these adjustments
50:02 the glasses that will refocus the image onto the back of the eyeball onto
50:09 retina. These are the glasses or uh okay alliances that you can put
50:19 your eyes. So when we're looking one eye you can close one
50:29 the amount that you're seeing is about and 50 degrees. So there's 360
50:35 . Space, One eye sees about And if you look at the moon
50:44 you knew the distance to the moon you would know that this moon from
50:54 150° occupies half a degree of visual . The visual angle Moon is
51:03 So out of 150 you're seeing half that moon. You know the distance
51:09 the moon. You can actually calculate you know the overall size of the
51:16 . It can calculate how much of retinal space will get activated by half
51:22 degree angle That moon and there's about microm of space. That means that
51:30 going to be 140 micrometers of space the retina dedicated to looking at that
51:37 . That's what can they do But what when you're not able
51:44 I'm ridiculous. That's a good I don't know the good treatment for
51:51 myopia. Yeah, that's a good . But this is how you would
51:56 how much of the retinol space is by a particular image. Okay,
52:05 if that moon was much closer was bigger, it would occupy let's say
52:12 And there's 3°, would be three times times two. So two Important points
52:22 information that is processed the light information processed by photo receptors is the only
52:29 sensitive cells and the only output is ganglion cells. But in between there's
52:37 regulation of this flow of information from bipolar cells, ganglion cells by two
52:43 of cells of horizontal cells and the a queen cells. And so there's
52:48 control of the circuit and this is retinol circuit information going in exciting photo
52:55 connecting onto bipolar cells. And then have the horizontal cells that will be
53:00 these sent out the connections the ganglion layer and the back is referred to
53:06 ganglion cell. There the inter plex form layers the connections between ganglion
53:11 these horizontal cells and bipolar cells. this is the synaptic connections inner nuclear
53:19 . Uh the so Mazz of the um akron cells and mostly bipolar cells
53:25 of plucks the form layers, the between bipolar cells and between cells and
53:30 retinal ganglion cells and outer nuclear As the selma's off the photo receptors
53:38 the layer of photo receptor out of is where the photo transaction actually takes
53:44 . And finally here you have the epithelium. The differences between cone and
53:52 photoreceptors. So rod photoreceptors will have freely floating discs that have their own
54:01 and cone photoreceptors. The outer segments have these membranes indentations rather than free
54:08 discs. So these free floating discs the outer segments are going to be
54:17 with photo pigment and it's going to these rod photo receptor is very sensitive
54:23 light because they can store a lot pigment, they have a lot more
54:27 the surface area with these free floating . So the outer segment is where
54:33 photo transaction takes place. The inner which is the selma and all of
54:38 organ al machinery by synthetic machinery of cell and the synaptic terminal is this
54:45 a form layers where the photo receptor will be contacting bipolar cells and retinal
54:54 cells. These are the main differences rods and cones. Rods are high
55:01 to light. Their specialist for night , they have a lot more photo
55:05 on the street floating discs and capture light. They have high amplification.
55:10 are sensitive to single photon detection but are slow, they have low temporal
55:17 . They have slow response or long time of visual information. They are
55:23 sensitive to scattered light. So the system is a low acuity system,
55:29 not really present info via, it highly convergent retinol pathways and it's a
55:36 . So it's only one type of voter receptor. Night vision. Rod
55:42 a good example. Rod photoreceptors get when you walk into a dark
55:48 A good example is when when you into a movie theater or dark room
55:54 has people sitting in it, it about one second to accommodate yourself to
56:01 that low light information to start seeing of people on chairs. If you
56:06 another few seconds you may start seeing color people darker color and somebody waving
56:12 you recognize your friend is there. this is really low acuity, you
56:18 see much resolution but you are very to it. But it takes the
56:23 to integrate that information to adjust. little levels of life cones have lower
56:30 . They specialize for division, they less photo pigments so they need more
56:35 , they have lower amplification, they high temporal resolution. So they are
56:39 fast uh and short integration time. more sensitive to direct or axel rays
56:47 light. It's a high security system in the phobia and it has dispersed
56:53 taxiways and it's chromatic. So there three types of cones that each have
57:00 distinct pigment that is most sensitive to parts of the visible spectrum. So
57:08 you look in this phobia region right , you have a little crater
57:12 an indentation that is going to be . The light. The light coming
57:17 through the pupil is going to be in the direct actual rays of
57:21 So whenever you focus your eyeball and your pupil for the highest security vision
57:28 you need the most light. When you can see the small things
57:31 turn on the light and you concentrate and you see it, it's high
57:36 vision as you can see that there's high density of cone photoreceptors and this
57:42 here allows for the rays of light be directly funneled to the photo
57:49 The ones that are surrounding the area be funneled through the circuit of the
57:56 cells, retinal ganglion cells so you need more light in the periphery here
58:03 the central phobia region to activate So again, this shows that cones
58:10 shown in blue and cones have the density in these very central regions of
58:17 retina. And rods. As you see, rods will have higher densities
58:23 rod photoreceptors on the periphery. Outside this phobia that we're discussing, did
58:31 have a question for the previous the size of the, are they
58:38 to scale? Um I don't know this is drawn to scale. It's
58:45 for illustrative purposes. Uh In I don't have a good answer for
58:50 . What's the approximate size of the ? We should probably look it
58:54 It's several 100 micrometers across or what basically you're trying to see what percentage
58:59 the retina is a phobia? The region maybe. So I don't have
59:04 good answer for that. I could it up, but again, if
59:11 looked in the center of the you would see a lot of the
59:18 photoreceptors and is dominated by cone If you looked in the periphery,
59:24 would see that as you have some photoreceptors but it is very much dominated
59:29 rods. Right? So what does tell you? That tells you that
59:34 you want something very high acuity you to focus in. But peripheral is
59:40 sensitive to low levels of light and actually, our periphery helps us detect
59:47 lot of things in motion in the . You get activated quite often first
59:53 you refocus your pupil into that motion coming from the periphery. Um These
60:01 different photo receptor activations by different So you have the blue, the
60:10 and the red counts and what it you that blue light Roy G biv
60:18 be blue is on the lower end spectrum, be somewhere around 440 nm
60:27 wave lines. And if you have blue light that blue light is gonna
60:33 blue cones, it's going to activate too. Almost 100 You have here
60:42 of blue cones that are 100% in wavelength of light. What if there
60:47 a wavelength of light coming in at 480 nanometers, which is close to
60:56 was supposed to green. So there's green light. How do we perceive
61:00 light? We perceive green light because going to be 31% activation. Blue
61:12 , sorry of Fred 36% of blue here and the highest activation of green
61:21 67% of combination color mixing of 67 light. If you put it on
61:27 palate, 36 of blue and 31% red and you mix the three
61:35 you would get green. Yellow Is about 550 nm in length. It
61:44 83% of red And 83% of So again, if you were to
61:51 the red and green and mix them , you would get the yellow
61:58 So you have three types of accounts the Hughes the different hues that you're
62:03 . The combination of these different Because we don't just see Roy G
62:09 . You don't see red. How red iterations of red? Do you
62:13 many? And there's light red, red, there's light orange, dark
62:19 and so on. And it's actually was very disappointed a few years ago
62:24 learn that chickens see a lot more than humans. Chicken world is a
62:29 more colorful than human world. But way that we see color is basically
62:36 principle of color mixing the stimuli that coming at us in different wavelengths will
62:43 to a very degree percentage the The blue for the green. Uh
62:50 receptors comes and differential activation and different will give you a slightly different
62:56 Dark green, light green, neon and so on. Mhm. So
63:06 actually concludes
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