Visual pathway

so the next lecture is about visual

pathway the visual message from the

world is carried by two optic nerves so

before that we need to know about the

binocular vision monocular vision so

binocular vision the vision which both

the eyes are used to get through at a

portion of the external world is seen

monocular the vision in which with each

eye is used separately now what do you

mean by temporal and the nasal field the

light rays from the different half of

each visual field as see in this diagram

there is this the left vision that is

left heart and then we have the right

half okay the light rays from the

different half of each visual field each

visual field multiple Ganic left which

will feel and then we have a right

visual field they do not fall on the

same half of Thera taina

that is light rays from the temporal

part so we have a temporal part and we

have a nasal part so the temporal part

is now what whatever you're trying to do

is just focus on your nose right now so

you're trying to focus on your nose

with the help of your nasal part of the

retina not by the temporal part of the

retina okay with the help of temporal I

can see the peripheral the bellyful

parts of the external scene so the

peripheral vision is because of the

temporal part of the retina which is

present so we have a nasal feel and we

have a temporal field so the light rays

from the temporal part of retina

temporal part of the sorry the temporal

part of the visual field it falls on the

nasal half of the retina of that eye

so as you can see over here we have two

different diagrams together now this

tree if i if I'm able to see only from

if I'm seeing only from a left-hander

monocular

vision and if I am using both odd and

that's a binocular vision so the left

eye and the red right eye so it has now

as you can see this red line is showing

the nasal field of the retina and this

blue line and this blue line is showing

the temporal part of the retina so we

have a temporal part of the retina and

then we have this is the temporal part

of both the eyes of the left eye and of

the right type and then and then we have

a nasal part this is the nasal part of

the retina so try to see that if I am

focusing from T so the temporal part is

able to see the objects which is present

on the left vision this person on the

left half of the visual field and the

right eye its able to see so with the

combination the right eye is seen the

right part of the vision of the visual

field with the combination of both of

them we have a binocular vision so the

visual field of each eye is divided into

two unequal parts outer temporal or the

inner and the nasal in the temporal part

action up to hundred degrees but the

nasal per action only up to sixty degree

because it is resting because it is

restricted by the nose so the visual

pathway the optic pathways in nervous

pathway that transmit impulses from the

retina to the visual center in the

cerebral cortex now in binocular vision

the light rays from the temple half of

visual field fall upon the nasal part

and the Rays from the nasal half of the

visual field fall upon the temporal part

of the retina so we have the primary

neurons then we have secondary neurons

and we have thought order neurons the

primary neurons of the first order

neuron so they are bipolar cells as we

have only talked about water bipolar

cells in theater

now now they sign up for the dendrites

of the ganglionic cell so here we can

see the ganglion cells okay and these

are the bipolar cells the green ones are

the bipolar cells the green ones of the

bipolar cells and these are the ganglion

cells so so the example bipolar cells

and up with the dendrites of the

ganglionic cells then the ganglionic

cells exons where they form the optic

nerve and now this optic nerve will

leave the eye and terminate in little

geniculate body

so this ganglion cell then the bipolar

cell and then here we have our

photoreceptors the rods and the cones

and from here what is her through this

into the last layer the optic nerve

leaves the eye on terminates in little

geniculate body and third-order neurons

that are in the LD body the fibers

arising from he reaches the visual

cortex and hence a person can be the

visual processing is present it is done

in the visual cortex so very clear

diagram direction of light this diagram

already shown you that the ganglion

cells synapse with the pipe with the

bipolar cells and this bipolar cell it

goes up to the photoreceptor in the rods

in the cones and then from here the

optic nerve leaves now in this diagram I

can tell you what do you mean by the

temporal part and the nasal part more

clearly so there is this is the left eye

and this is the right time this is the

left eye and this is the right eye left

eye the temporal part the blue the

temporal and the red is the nasal so if

you are able to see the red part is

focused on the temporal part of the left

eye okay

see this this new yes a connection

Vanara okay no try to understand if this

if this is your I it is divided into two

parts the eval apart okay I've got nasal

KK close to the nanos a yoga a temporal

part okay now this nasal part of the

retina is able to see the temporal field

of your left visual field and this

temporal part of a diner will receive

the nasal field of your left visual

field so it happens like this it comes

like a cross okay not on the same as an

eye making nasal field to the nasal up

you're part of a dynamic focus wavy

nasal goes to the temporal and the

temple goes to the nasal so from here

the optic nerve leave okay so up we

decree optic nerve the red and the blue

the optic nerve from the leaf from the

left and from the right eye now fibers

of the optic nerve originating in the

temporal half of the retina they

continue see red is continuing in the

same direction as you are able to see

try to see the red is continuing if I

talk about the left eye okay remember I

keep asking you to blue hair temporal K

fiber so this is continuing into the

same side same side to continue over I

take a crisscross neck over a yeah happy

Jo red hair the red portion the red

portion okay so this the fibers of the

optic nerve what is nothing in the

temple half of retina it continues in

the optic tract of the same side but

those are originating in the nasal side

they cross over to the contralateral

optic tract - yeah happy you're happy

it crosses cross okay both the nasal

fibers fibers of both the eyes the

crosses to the controller to the side

the result is information from the right

visual field travels left optic tract

and

information from the left visual field

travel the right optic tract okay

because of the crisscrossing happening

in the nasal fibers in the nasal fibers

with the cliff crossing happening in the

nasal fibers on this crossing scope with

them optic chiasma on optic chiasm now

once it crosses the optic chiasma Scoble

the optic tract so yeah happy as you can

see the nasal fiber of the right eye

goes through the left portion of the

left part of the eye okay continues as a

s continue as a left optic tract and

then it goes up to the lateral

geniculate body now little gentle eight

bodies present in thalamus now from here

lateral geniculate body the optic tract

which originated in the contralateral

nasal retina okay which originated in

the contour little nasal retina it

terminates in the layers one four six of

the lateral geniculate nucleus I'll show

you

see we have layers in the little

geniculate layer we have six layers so

the the optic tract which originated in

the contralateral nasal retina it

terminates in layer one it terminates in

layer 1 for six of the LGN of the little

geniculate nucleus and the fibers in the

ipsilateral temple retina so absolute

rule my hair the same side my hair it

will terminate in layers two four five

and those the contralateral ones they

will terminate in one four six

so as you can see some epsilon fibers

are also going here and some continental

fibers are also going here so the

ipsilateral are dominating onto the two

determinating on the two three and five

okay they are terminating on two three

and five and the contralateral wants the

terminating on the layer of one four and

six

i hope now it's not on the other diagram

which is showing is the see the cross

two fibers from the control 8ly the

contralateral eye here it terminates in

layer 1 for 6

not a little here that is a temporal

portion of both the eyes it will

terminate in the layer two three and the

five of these little geniculate body

now this little geniculate body it

for the subdivides into some optic

radiation and this optic radiation

finally terminates in the visual cortex

in the Broadman area is area number 17

the visual cortex where with the

complete visual processing is done so

Colby object in its left visual field

will convey its presence via right optic

tract by means of the fiber some of

which are absolutely and half of them

are continental LGN little the nuclear

body it fans out to optic radiation

which summit in visual context the

primary visual cortex know the course of

the pathway first is the optic nerve

then is the optic chiasm then there is

this optic tract after the crossing over

land it called as optic tract then we

have little genuine dead body which fans

on to optic radiation and hence final is

the visual cortex so this is an

flowchart which is showing how the

visual receptors in at I now go to the

first order to bipolar cells and to

ganglionic cells then to optic nerve

chaos matrac elgyn body and then finally

their visual cortex the optic nerve

leads the eye to the optic disc the

fibers from the temporal part of the

retina are in Latorre part of the nerve

and carry the impulses from the so the

fibers from the temporal part of the

retina they carried impulses from the

nasal half of the visual field same aika

wish fulfilled much the burger left like

a visual field to left toe scar nasal

half cho hair would tempura part of

retina will carry correctly

the fibers from the nasal part of retina

are in the medial part of the nerves I'm

regarded in person from the temporal

half of the visual field of the same eye

now in the middle fibers of each optic

nerve will cross the midline middle five

movements of the nasal fibers okay and

the field cross and Phil join

contralateral quads are incurring in the

we'll join the uncrossed little fibers

of the opposite side okay

the L gene body majority of the fibers

of the optic tract terminate in the

neutral geniculate body which forms a

subcortical Center for the visual

sensation now some of the fibers do not

synapse in the littorals and include

body it goes up to the superior

colliculus which is the constant

reflects movements of the eyeballs in

the head protecting nucleus constant

light reflects and de su property

recluse of the hypothalamus which is

controlled which is generally concerned

with the corner at angle control of the

pituitary in the animals and not so much

helpful in the humans the visual cortex

is known as the area number 70 which is

concerned with the perception the visual

impulse the second divisional area of

the visual Association area concerned

with the interpretation of the visual

impulse so first is the primary which is

the perceptual Palio perceive caraga

then this interpretation the area number

18 and then the occipital I feeling your

number 9 to it is concerned with the

movement of the eye and in the primary

visual cortex is located in the middle

surface of the occipital lobe