Detailed Visual Pathway Anatomy and Associated Visual Deficits Explained

hello lovely people it's medicosis peratus where medicine makes perfect sense welcome back to my neuroanatomy

playlist in previous videos we talked about the cranial nerve such as cranial nerve one which is the olfactory nerve

and cranial nerve number two which is the optic nerve as for today will dig deeper into the optic nerve namely the

visual pathway you will recall that the optic nerve is sensory special sensory to be specific special sensory aent

that's what it is so let's say that I looked at an object this image will fall onto my retina and it will be flipped

meaning right will be left and left will be right it will also be inverted upside down so Up Is Down and Down is up which

is orwellian if you think about it no one will understand this joke after this I am now in the optic nerve carrying

nerve impulses you go optic nerve optic kaym optic tract after the optic tract there is the lateral geniculate body on

the left and on the right then I have my optic radiation which will radiate me towards the visual cortex in the

occipital lobe of my cerebral cortex click the like button click the Subscribe button and let's get started

please watch the videos in this Anatomy playlist in order especially the videos on olfactory nerve and the optic nerve

remember here's the brain you draw the Line in the Sand by the central sulcus right here anything in front motor

anything behind is sensory most of the time look at this look at this I'm trying to see a tree I want to see

something oh to see is to sense that's a sensory function that's why it's in the back of the brain behind this imaginary

line the primary visual cortex is here now which broadman areas are in the visual cortex please comment below is it

broadman Area 1 is it 2 is it three is it 17 or what what's the nervous system we have central nervous system and

peripheral nervous system the central nervous system is made of brain and spinal cord the peripheral nervous

system is the cranial nerves and the spinal nerves all of the 12 pairs of cranial nerves are peripheral nervous

system except only the optic nerve the optic nerve is Central look at this here is my neuron this is the Soma or the

cell body and this is the axon as we have discussed before a collection of Somas or cell bodies in the central

nervous system is called a nucleus but a collection of Somas in the peripheral nervous system is called the gangion

next a collection of axon fibers in the central nervous system is ATT tract but in the peripheral nervous system this is

called the nerve recall the distribution of the cran nerves cran nerve 1 and two come from the four brain three and four

from the midbrain 5 6 7 8 from the pwns 9 10 11 12 from the Meda 22 44 four brain midbrain ponds M two nerves from

here two nerves from there four from here four from there Al Factory nerve is attached to that t enlon which is a part

of the for brain but the optic nerve is attached to the diyon which is part of the foror brain

as well dilon includes anything that has the word Thalamus in it because as we'll see will go retina optic nerve optic

kaym optic tract and then lateral geniculate body which is part of the thalamus and the thalamus is part of the

dilon and the dilon is part of the proen sephylon if you have watched my previous videos in this neuro Anatomy playlist

everything that I've said should make perfect sense to you you can download these colorful notes on my website

medicosis perfectionalis tocom I help you understand and pass exams let's review cran nerve one what did we have

we had the mucosal cells in the roof of your nose then what from between them we have the bipolar neurons oh so I have

epithelium and then from within the epithelium emerges nerve fibers these nerve fibers where relay onto the mitel

cell of the olfactory bulp and then after the olfactory bulp we have the olfactory checked which will take us to

the tanyon part of the proen sephylon so you go epithelium then nerve fibers then bulb then tract then for brain now look

at the optic nerve it's the exact same story we're talking epithelium here what kind of epithelium oh remember the

retinal epithelium yeah like layers of the retina yeah which part of the layers which layer gangan cell layer the

ganglion cell layer will make us the axons of the optic nerve and then you go nerve instead of bulb say kaym and after

the bulb what do we have we have a tract and after the tract what do we have part of the forbrain but here it's the Dylon

instead of the telencephalon so retina optic nerve optic kaym optic tract dilon namely that lateral geniculate body then

optic radiation one goes upstairs the other goes downstairs until we end up on the visual cortex in the occipital lobe

of the cerebrum recall that the definition of a collection of cell bodies in the peripheral nervous system

is called what a gangan hence ganglion cell layers in the retina a collection of axons in the peripheral nervous

system I.E outside the brain is called what it's called a nerve hence optic nerve and after this as I get closer to

the brain and into the brain I have what a collection of axons in the cental nervous system what's that called that's

the definition of a tract see medicine makes so much sense once you understand what the french toast you're talking

about now on to today's topic the visual pathway and the deficits or the defects of the visual pathway again retina optic

nerve optic kaym optic tract one on the left one on the right then after this lateral geniculate body here and here

then optic radiation which will radiate me towards the visual cortex what's the name of the artery that supplies the

visual cortex it is the posterior cerebral artery because light has to travel in straight lines when I look at

the tree up will become down in the retina and down in order to travel in a straight line will become up in the

retina Up Is Down Down is up now let's suppose that we had a left branch and a right Branch coming out of the tree

right will become left and left will become right which means the right visual ual field will fall onto the left

retina and vice versa by the same token that Superior in my visual field will become the inferior in my retina and

vice versa let's talk about this this is my left eyeball this is my right eyeball and this is the visual field in front of

my left eye and this is the visual field seen by my right eye what would you call this orange color oh it is closer to my

nose so this is the nasal visual field here's the nasal field on the left side and here is the nasal field on the right

side let's follow the nasal visual field because light has to travel in straight line the nasal becomes temporal in the

retina so this is nasal field but this is temporal retina the temporal retina closer to your temple will continue as

temporal Fibbers inside the optic nerve let's talk about the temporal visual field oh it will fall onto my nasal

retina and the nasal retina will continue on as nasal fibers in the optic nerve how about the right eye here is my

nasal visual field it will fall onto the temporal retina and then temporal retinal fibers in the right optic nerve

how about this this is my temporal field thus nasal retina and nasal fibers in the right optic nerve then what then you

go to the optic kaym in the optic kaym only the nasal fibers will cross to the other side so the left nasal fibers will

go to the right optic tract and the nasal fibers in the right optic nerve will cross to the left optic tract but

how about these orange temporal fibers they will continue as is without Crossing to the other side so who

crossed when it comes to fibers only the nasal fibers cross to the other side when it comes to field since the nasal

fibers are responsible for the temporal field it is the temporal field that crossed to the other side don't forget

that the nasal fibers carry temporal visual field while the temporal fibers carry nasal visual field and then after

the optic tract on the left and on the right we go to the lateral genicular body which is part of the thalamus if

you read an old textbook this was part of the meta Thalamus but now the metalis is considered a piece of the thalamus

and the word meta Thalamus which included LGB and MGB fell out of favor in other words if you consider LGB as

part of the thalamus that is correct if you consider it part of the meta Thalamus that's correct as well it's

just a matter of lingo how we classify the thalamus how you slice it and dice it after the lateral genicular body we

go to the optic radiation which will radiate me to the visual cortex now let's add some deficits imagine that I

have a problem here at number one which is the left optic nerve suppose that I severed my left optic nerve what's going

to happen well the entire left eye is gone which means the entire left visual field is gone what do you call this this

is called left anopia or left anopsia what does the word anopia mean N means no Opia means Vision there is no vision

on the left side you can also call it left monocular vision loss monocular means mon no ocular one eye only one eye

is toast the other is healthy here is a different scenario suppose that I have a tumor such as a ptary edoma let's make

it a prolactinoma for example or a crano feroma growing here pressing on the center of the optic kaym who's going to

suffer the blue fibers I.E the nasal fibers which are responsible for what for the temporal visual field so the

patient will complain of what I cannot see the temporal area here and I cannot see the temporal area there so temporal

and temporal by temporal half and half hem cannot see cannot see anopsia or anopia I want you to pause the video

rewind and replay the last two minutes because the next section will get brutal so you need to master these two facts

first remember that light has to travel in straight lines like this the superior visual field will become the inferior

ior retina and the inferior retinal fibers but the inferior visual field will become the superior retina and

therefore Superior retinal fibers so here is the visual field here is the retina optic nerve optic kaym optic

tract until the lateral genicular body then we go towards the brain itself the optic radiation because one optic

radiation will go upstairs the other will go downstairs and then we'll talk about the visual cortex let's go the

upper visual field I use the green color for the leaves will become inferior or lower retina which means lower retinal

fibers inside the optic nerve lower optic nerve fibers lower optic kaym lower optic tract lower part of the

lateral geniculate body then what in the optic radiation I'll take the lower route which one is lower anatomically

speaking is it the parietal lobe or the temporal lobe think about it oh of course the temporal is lower which means

I'll go to the temporal lobe and since this is near the ventral surface of the brain we call it ventral optic radiation

so I am in the lower lobe I mean the temporal lobe and I am downstairs and I will form a loop around the inferior

Horn of the lateral ventricle who discovered this looping action someone called Meer hence Myers's Loop now let's

talk about the stem of the tree which was downstairs in my visual field but in my retina it will be upstairs upper

retina upper part of optic nerve upper part of optic kaym upper part of optic tract upper part of lateral genicular

body in the thalamus or The Meta Thalamus and then upper lobe what do you mean parietal or temporal which one is

higher anatomically speaking the parietal lobe until I end up on the visual cortex did you form any loop

around any structure no I did not loop I went straight ahead across through the internal capsule without

looping around any structure so what's the name of this one since this is closer to the dorsum of the brain or the

dorsal surface we call it the dorsal optic radiation but this one is the ventral optic radiation so let's end up

on the visual cortex the one upstairs will end up upstairs above the calcarine sulcus and the one downstairs that form

that Meers Loop will continue downstairs and will end downstairs below the calcarine sulcus Supra calcarine infra

calcarine what's the name of this gyrus above the calcarine sulcus it is called the cus gyrus and what's the name of

this gyrus below the calcarine sulcus it's called the lingual gyrus how do I remember which is which easy one of the

Primal urges of humans is to eat very Primal very basic so we'll think of downstairs basic and then when I eat

what do I do I like the food M delicious yum yum yum yum yum yum yum yum with the m okay which reminds me of what yummy

and delicious the M reminds me of Myers's Loop in that temporal lobe and what do you do when something is

delicious you do exactly like this Emoji you Loop your tongue around your lips I am looping this ventral optic radiation

around the inferior Horn of the lateral ventricle because as you recall the inferior Horn of the lateral ventricle

is inside the temporal lobe of course it makes sense so lower Primal urges meaning lower retina and lower fibers

remember yummy which means Meer which means temporal L what did Meer do Loop his tongue around his lips Loop the

vental optic radiation around the inferior Horn of the lateral ventricle and because this is a primal urge it

will end up below the calcarine sulcus infra calcarine in the Ling gyrus because I did this Emoji with my tongue

all of this was true for the lower fibers responsible for the upper visual field that's the only pneumonic that you

need to remember the yummy pneumonic and therefore the other one is the other one how about the upper retina upper fibers

upper optic nerve upper optic tract upper LGB Etc you go to that not the temporal but upstairs parial not around

the inferior Horn of the lateral ventricle but through the internal capsule not below the calcarine but

above the calcarine sulcus or supracalcarine towards the cunius gyrus later when we talk about the spinal cord

you will discover the catus and gracillis tract the catus tract is in the back of the spinal cord posterior

just like the cus gyrus posterior because posterior is sensory behind my imaginary line neurom makes sense

finally quick note don't forget that this visual cortex is is also known as the striate cortex now to belabor this

point because it's worth belaboring please bring pen and paper and let's draw this together I need two colors

Okie doie here is the tree and then what this green which is super visual field will become inferior retina then what

inferior optic nerve optic kaym optic tract inferior part of the lateral genicular body then what I go to the

inferior lobe I.E temporal lobe by making a loop around the inferior corn of the lateral ventricle only to end up

below the calcarine sulcus or infra calcarine inside the lingual gyus how about the stem of the tree downstairs in

my visual field will become upstairs in my retina Superior retina Superior fibers Superior optic nerve optic kism

optic tract upper part of the LGB upper lobe which means temporal lobe straight through the internal capsule and then

what and then I end up on the visual ual cortex above the calcarine sulcus IE supracalcarine in the cus gyrus so here

is the retina optic nerve optic nerve optic kaym then we have optic tract on the left optic tract on the right left

lateral geniculate body right lateral geniculate body then we have optic radiation the one downstairs is the

Myers Loop goes to the temporal lope which is responsible for the superior visual field and the one upstairs goes

to the par Ral L responsible for the lower visual field then we end up on the visual cortex supplied by the posterior

cerebral ortery now let's talk about visual pathway deficits we already talked about one and two one is severing

my optic nerve or destroying the entire left eye this will cause left anopia which is left complete monocular vision

loss number two is the pituitary edoma or crano forenom pressing on the central part of the optic kaym before you know

it I have tunnel vision by temporal hemianopia I lost the temporal side on the left visual field and the temporal

side on the right visual field as well how about Aion in the left optic tract or left lateral geniculate body or left

optic radiation up and down IE in the parial L and the temporal L what do you think is going to happen let's think

about this logically you see here I cut the temporal fiber on the left side the temporal fibers are responsible for the

nasal visual field so I will lose the nasal visual field on the left eye how about the blue oh this blue belongs to

the right side it was the nasal fiber for the right eye which means temporal visual field so I will lose the temporal

visual field on the right eye so my left visual field lost the nasal but my right visual field lost the temporal now I

want you to look at this the legion was on the left side of the brain but the visual deficit was felt on the right

half of H ey here's the right half of this eye gone here's the right half of that eye also gone when the legion is on

the left and the deficit is on the right it's called controlateral Left became right amazing since this is the right

side or right half of this eye and the right half of this eye they are homonymous or synonymous homologous oh

okay got it and then what half of this eye and half of this eye Hemi anopia this is complete anopia this is Hemi

anopia this also is hemianopia you can call this one heteronomous hemianopia because here's the left half and the

right half but here it is right half and right half so it is homonymous hemianopia heteronymous hemianopia

homonymous hemianopia what if the legion is in the Myers Loop I.E temporal lobe this is the vent optic radiation what's

going to happen look the leion is on the left side which means the deficit will be on the right side the right part of

this eye and the right part of that eye as well since the Meer Loop is downstairs it is responsible for the

visual field upstairs so I will lose this upper right quadrant and this upper right quadrant so is this Hemi anopia no

not that's not Hemi that's quarter so quadrant anop the lesion is on the left side of the brain but the deficit was

felt on the right part of the eyes right part of the visual field so controlateral which quadrants did you

lose on the right side did you lose the upper ones or the lower ones the upper ones so Superior quadrant anopsia

because all of these are named from the patient perspective not from the perspective of what happened in their

brain but from their experience in reality so this one could be be called contralateral homonomous hemianopia

because the lesion was on the left but the deficit on the right you can simply also call it right homonymous hemianopia

because I lost the right half and the right half similarly you can call this controlateral Superior quadrant anopsia

because controlateral to the legion but you can just name it since I know that this is the left side so the deficits

will be felt on the right side I can simply call this right Superior quadrant anop next how about damaging the other

optic radiation I.E the dorsal optic radiation oh it is upstairs which means responsible for downstairs in my visual

field so I lose downstairs and downstairs leion is on the left so the deficit is on the right right lower oh

so it's controlateral inferior quadrant anopsia or right inferior quadrant anopsia what if I damage my visual

cortex on the left side such as stroke or thrombus in my left posterior cerebral ory it will be very similar to

damaging both of the optic radiations such as number five just like this however the most important part of your

retina is the macula here and here the macula has bilateral cortical representation even if one cortex or one

half or one hemisphere is screwed the maula is spared because the maula also gets Supply from the other cortex so

number eight is exactly the same as number five with one exception the macula which is the phobia which is the

central vision is spared so what do you call this exactly like you call this this was called controlateral homonymous

hopia so this is controlateral homonymous hemianopia with macular sparing because I spared the central

macula because the macula has bilateral cortical representation even if one side is gone the other side will also Supply

the macula next number nine where is number nine oh this is is age related macular degeneration a rmd or AMD oh

what's going to happen it destroys the central vision it destroys the macula it's called macular degeneration For

Heaven's Sake what do you think is going to happen well this happened in my right eye so my right visual field will suffer

this happened in my right macula so the right macula is gone I lost this right central vision so it's called right

Central scotoma what does scotoma mean it means Darkness as for deficit number 10 and deficit number 11 what are these

please let me know the answer in the comment section now let me blow you away here is my left visual field here is my

right visual field let's use colors please so this is what my left eye is seeing right now so here is temporal

here's nasal visual field this is superior this is inferior visual field which means this is superior nasal this

is inferior nasal Superior to temporal visual field inferior temporal visual field on the left side and you repeat

the same thing for the right side remember that the visual field is the exact opposite of the retina let's

follow the orange here the orange was inferior nasal but here it is superior temporal how about the green it was

Superior nasal in my visual field but now the green is inferior temporal in my retina just like George Orwell down is

up nasal is temporal down is up down is up temporal is nasal Up Is Down temporal is nasal and on the right side the

retina is the inverse of the visual field and then what in the optic nerve we are similar to the retina but

slightly rotated look at the pink color for example it became here oh so we're flipped a little but no one cares now

look at the lateral genicular body why does it have only two colors instead of four because remember that the nasal

fibers on this side on our side went to the other side so they no longer exist as far as the left visual field is

concerned see the inferior part of the visual field became Superior in the LGB and the Superior in the visual field

became inferior in the latal geniculate body no more Crossing they will end up in the visual cortex as is the orange

will go Supra calcarine and the green will go infra calcarine which means that the supracalcarine upstairs in my cortex

was responsible for the infra or inferior visual field conversely the infra caline is responsible for the

superior visual field how about the other colors oh that's the other LGB as you can see and same thing here Supra

calcarine is infra in the visual field and infra calcarine is Supra in the visual field and don't forget that in

reality your left visual field and right visual field are convergent so they are not two separate circles in fact these

two circles will kiss and hug and get closer to one another until they intersect please take a moment to pause

and review quiz time look at this can you name the visual deficit and can you you tell me where is the problem in the

brain and for this one please name the visual deficit and tell me the site of injury in the brain you will find the

answer key in the next video in this neuroanatomy playlist the next video is titled ocul motor nerve do you want to

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