VideoPoints

• ••• • •• • ••••• • •
BIOL 4315/6315 Neuroscience Tue Th - NEURO Lecture 16 _ 1_ Eye II, Phototansduction, Receptive fields, LGN
Help Tour
© Distribution of this video is restricted by its owner
Transcript ×
Auto highlight
Font-size
00:02 This is lecture 16 of neuroscience and will cover I. Two which will
00:09 the retinal circuits. We will cover photo transaction that happens in the photo
00:16 process by which the light electromagnetic radiation converted into the electrical potential for receptor
00:30 . And then we will move on talk about the central visual pathways which
00:37 output from the retina into the lateral of the thalamus and from there into
00:43 primary visual cortex in the occipital Okay. Within the circuit, as
00:48 understood when the light comes in the is all the way in the back
00:53 the eyeball. And phobia will contain concentrations of codes which will have highest
01:01 vision in that area or highest resolution . And it's centrally located right in
01:07 middle of the lengths so that the is concentrated on the phobia and you
01:13 the optic nerve that will exit out . You have the optic disc where
01:17 have a blind spot because the place the retinal ganglion cell fibers form an
01:24 nerve and exit out this area will have photoreceptors that process visual information.
01:31 you'll have a blind spot there. now once it hits the retina,
01:39 light, as you notice the light coming in this direction and it actually
01:45 to pass through this thicket of cells order to excite the photo receptors in
01:53 back. You have rod photoreceptors, subtype of rod photoreceptors and three subtypes
02:00 , red and blue of cone Those photoreceptors synapse onto the bipolar cells
02:11 bipolar cells still have only receptor So graded potential synaptic potentials in this
02:19 and then they synapse onto the retinal cells. And retinal ganglion cells are
02:25 to be the only subtype of the only output that comes out of
02:30 retina and also retinal ganglion cells in processing of information in this direction.
02:39 only cells that are producing action potentials photoreceptors, receptor potentials bipolar cells not
02:47 . And then retinal ganglion cells will action potentials and this action potential information
02:53 be communicated through the optic nerve fibers is cranial nerve to remember to the
02:58 . G. N. There is significant control by horizontal cells of connectivity
03:05 the photoreceptors and the bipolar cells and amma queen cells of the synaptic connectivity
03:12 the bipolar cells and the retinal ganglion So typically as we talked about lens
03:22 is suspended here by the ligaments which can contract and can relax and if
03:29 contract the lens becomes thicker and if relax okay if they relax the lens
03:40 thicker, if they contract the lens thinner they actually stretch on the
03:44 Okay this ligaments that are holding Okay so if the ligaments contract is
03:51 a muscle it becomes shorter so if becomes shorter the lens becomes longer.
03:56 . If if if this is if is relaxed it allows for the lines
04:02 plump up and have a more rounded . And this is how you can
04:07 in a different distances without walking up a person, you just need to
04:13 your eyeballs a little bit and then you don't even need to move your
04:18 , you just refocus into the different even along the same uh point of
04:25 . So this changing of the lens accommodate for the image to be perfectly
04:32 on the retina, basically perfectly presented the area of the retina to the
04:36 separate. Uh This is called accommodation the lens normal vision. If you
04:42 normal vision you have normal accommodation, shape of the lens and the projected
04:48 will be directed and focused onto the onto the retina. If you have
04:54 propia the lens shape as such that your images focused beyond where the photoreceptors
05:06 be wanting to receive that image where would be projected just like with a
05:11 , you can refocus the projector, can it can focus behind or in
05:16 if you move the screen so now projecting it behind. So you can
05:22 it by um providing a concave glass concave lens. And that will help
05:31 lens to refocus the image on where supposed to be onto the photoreceptors in
05:39 retina. In myopia, this image be projected by the lens in front
05:46 the photoreceptors. Also giving a blurry and to fix that, you will
05:54 a con cave lens here. Okay this will accommodate in front and instead
06:03 the lens that will accommodate the image the retina properly. So basically
06:10 if you have farsightedness of shortsightedness can remedied by glasses by lenses and also
06:21 LASIK which is the surgery that can the shape of the, of the
06:28 essentially. Now if you close one with you will realize is that your
06:36 of view if you have 360°, around your field of view with one eye
06:41 about 150° if you know for example the moon is at when it has
06:51 at a far distant point and you the distance to that moon. That
06:57 which would be a small dot in sky would occupy half a degree of
07:02 angle. All right. So 1 of the entire space that you can
07:10 the dock that wide dot which is moon. And to process that
07:17 you would excite about 100 40 Micro of retinol space. And the moon
07:25 not only a dot. Sometimes you actually see the landmasses and uh and
07:32 appears like the oceans or the or craters. And you can see the
07:37 , the shade differences in the Uh but it would be 100 and
07:43 micrometers of retina that gets excited by half a degree of visual angle by
07:52 moon at a certain distance. And how does reading the process of
08:00 Of course the photo receptors will be for photo transaction. And the ganglion
08:09 will be the only output from this circuits. Retinal ganglion cells will be
08:16 only output into the latter with There's also descriptions of these circuits and
08:25 layers in your book and other books these are essentially the same. But
08:31 image can be used. You have layer of photo receptors where they have
08:38 outer segments of the photo receptors. have the outer nuclear layer which is
08:43 selma's and the nuclei of the photo . You have the outer plexus form
08:50 which is the synopsis. The plexus the connectivity between photoreceptors bipolar cells and
08:59 cells. And then you have inner layer which are the so Mazz of
09:07 horizontal cells and the bipolar cells. also the um Akron sells nuclear with
09:12 soma as you have the inter plex form layer which is the connectivity between
09:18 synapses here bipolar cells, retinal ganglion and in cells as they control the
09:25 interactions and the ganglion cell there which the ganglion south and the output that
09:31 out is off the nerve to optic a cranial nerve. To the biggest
09:37 in the morphology of the photo receptors that cone photoreceptors have these member nous
09:47 which increase the surface area and allow a certain amount storage of photo
09:53 Uh They're called Member nous disks containing pigments but these member nous discs in
10:00 out the segments are free floating discs they have their own free floating kind
10:07 this rectangular disk like shape the membranes provides for a lot more surface area
10:13 a lot more ability to store food pigment and therefore makes rod cells more
10:21 to light. This is just another that um overall they're similar types of
10:28 but the stark difference in these two of photoreceptors is really noted in their
10:35 segments and the disks. Outer photo . This is where the photo transaction
10:42 take place in er is where you bio synthetic machinery of the selma and
10:47 nucleus of the cell and synaptic Of course of the contact points with
10:53 cells and the horizontal cells. Now two types of photoreceptors have different functions
11:03 because they can store more photo they're highly sensitive to light. Their
11:08 for low light or night vision or vision, more photo pigment more capturing
11:18 the light. They have high amplification essentially in these outer segments that are
11:25 of detecting single photons. They're slow they can pick up those single photons
11:32 for them to pick up those level of light. They have low temporal
11:37 . They will have slow response because integration time will be long. However
11:42 are also more sensitive to scattered light scattered light basically are not direct actual
11:48 of light which usually to used to something or to look at something in
11:55 detail. These are scattered, low of life, pardon me? Rock
12:03 is low acuity, it's not present the central phobia. They have highly
12:09 retinal pathways. So if you look this diagram it will show you that
12:13 pathways from rods are converging onto the cells from rods and the last feature
12:21 that their acrobatic, there's one type motor pigment and the best comparison or
12:28 for night on vision. And using analogy of when you walk into a
12:33 room or a movie theater that has a lot of light but you cannot
12:38 everybody's face, you recognize them and first it seems really really dark and
12:43 a few seconds later you start distinguishing steps and the chairs and the people
12:49 in the chairs and then another second two later you see some darker and
12:54 color floating people are wearing and then know you you wave and you find
12:58 friends and such. So um this basically what with the rod photoreceptors would
13:07 , they don't need much light, very sensitive but it takes time to
13:12 accommodate to that low level of light integrate that information in the rods and
13:20 . They're low sensitivity which means that daylight vision they require a lot of
13:26 . They have less potent pigment the amplification, their high temporal resolution systems
13:33 they're fast response and short integration More sensitive to direct their actual rays
13:39 light cone system is high acuity concentrated via they have unlikely converging that we
13:48 with the rod photoreceptors. They have divergent signal pathways and most uh and
13:59 their chromatic. So they have three of cones, each with a distinct
14:06 that is most sensitive The different parts the visible light spectrum. Remember we
14:12 a light spectrum 400-700 nm. So other receptors are going to be more
14:18 to low others timid and others to high wavelengths. High wavelengths of light
14:25 the visible spectrum. This for example blue. What it very clearly demonstrates
14:32 the area underneath the phobia and the retina. Blue is the density and
14:38 expression levels of the cone photoreceptors. you can see that the peak in
14:43 very central retina which is dominated by . And then red is the expression
14:50 the rod photoreceptors. So what you're is that the expression of rod photoreceptors
14:55 to almost none in the very central of the phobia and the rock quarter
15:02 expression and presence is dominating in the size of the retina. So your
15:11 is like a cup. It has temporal side and it has a nasal
15:17 . These are the peripheries of the , so the rods are dominating in
15:22 periphery. And this is another beautiful of the specialized area that the phobia
15:31 . And you can see that beyond the fact that the phobia will contain
15:36 highest concentration of cone photoreceptors. Phobia forms this little crater within the retina
15:45 and the circuit with a light with it strikes the retina here it will
15:51 impeded by these cellular elements. But the light is direct, it actually
16:00 a crater like a little tunnel gets further into the very central retina,
16:06 like gathered into that little cup. in this area and now you can
16:13 see that the cellular elements have been on the side so the light can
16:19 directly affect the cone photoreceptors. So is a really interesting anatomical shape,
16:26 a little cup in the podium in back of the retina that gathers light
16:31 uh direct access to cone photoreceptors. , green and red, red,
16:38 and blue. Ever wonder about the collars? And they say RgB.
16:45 when you print, you have different like Rgb or you have like now
16:50 have sam Y. K. So is red, green and blue.
17:00 Thank
-
+