RETINA

 The retina 

The retina which is the deepest layer of the eye remember that we have a fibrous tunic which consists of the sclera and cornea then we have the vascular tunic which contains the choroid and then the neural tunic which has a lot of neurons as you can see and that really is just the retina and we'll go to this image real quick just for a minute but when light enters your eye it's gonna go through the pupil obviously and it's gonna go through to the back of the eye and here's the retina and so in doing so in following that path the light's gonna have to pass through the cornea the anterior chamber the posterior chamber the lens and then through the vitreous chamber and then finally that light is gonna strike the retina at the back of the eye in which you can see a little bit more macroscopically in this picture right here and within the retina we have three cell types the first type is called the photoreceptor cells or just photoreceptors and these are the cells that initially detect the light and there are two subtypes of photoreceptor cells and those are rods and cones we're gonna have a separate video where we go over the major differences between these but I'll just say this for now rods detect non colored light so non color vision just bright and dark and cones detect color okay see four cones see four color then we also have bipolar cells and then we have ganglion cells which eventually become continuous with the optic nerve these are the three major cell types there's also a couple other cell types called amacrine cells and horizontal cells and we're not going to get into these very much most Anatomy courses don't but they just exist pretty much to find tune and regulate the functions of these cell types particularly bipolar cells and ganglion cells okay now before we go any further I want you to notice something so we've got light that we mentioned was passing through the eye okay like this in this direction and then it strikes the retina but what's interesting about the setup of this is it actually doesn't encounter the photoreceptors first actually if we follow the passage of light the photoreceptors are at the back of the eye they're there actually we could say superficial to the ganglion cells so actually the light has to travel through the ganglion cells and then through the

bipolar cell layer and then finally is

able to make contact with the

photoreceptors but it's the

photoreceptors that initially detect

that light and then the photoreceptors

will have an effect on the bipolar cells

which will then in turn have effects on

the ganglion cells and we're gonna look

at that now in this slide okay now to

really understand what happens here we

have to understand what's happening in

the dark so imagine a situation where it

is complete darkness okay

so let's first of all say it's night

it's dark out you're in your room

there's no night lights doors are closed

and you have blackout curtains so you

can't see anything all right so I have

the photoreceptor cells in blue now

interestingly in the dark the

photoreceptor cells are actually

depolarized okay so the photoreceptor

cells are actually D polarized and that

not may not now that probably doesn't

make a lot of sense because usually only

think of depolarization we think of

activating but trust me this is how it

is and it will make sense in the end so

in the dark photoreceptor cells rods and

cones are depolarized that being said

that means the photoreceptors are

activated and they activate the next

neuron in sequence which is called a

bipolar cell it's also worth mentioning

that the way that photoreceptors

activate the bipol