Visual Pathways - UBC Neuroanatomy - Season 1 - Ep 6

the visual system is specialized to take visual information essentially photons and compose them into a coherent picture of our world the visual pathway begins of course in the eye the world around us is represented by this arrow these two circles represent what is seen by each eye in fact you can close over one eye and still see the entire arrow and the same is true for the other eye these are the visual fields for each eye but how does this visual field project onto the retina due to the refraction at the cornea the image is now reversed and the same is true for the other eye now we have two retinal representations of the world but how do we consolidate these two retinal images into one coherent cortical representation as it turns out our right visual field projects to the left side of our cortex and our left visual field projects to the right side of the cortex let's put a nose on this we can now describe the retinal fibers as either being nasal or close to the midline or temporal or lateral and the same is true for the other eye the nasal retina represents the temporal visual field we now need to sort these fibers from the right visual field to the left side of the cortex and from the left visual field to the right side of the cortex let's do that first let's take these temporal fibers down the optic nerve and they're going to travel in the ipsilateral optic tracts on the same side to the lateral geniculate nucleus here they will synapse and project to the primary visual cortex the nasal fibers from the other I carry that same visual information they're also going to come and travel down their optic nerve and then they're going to cross in the optic chiasm to the contralateral or opposite optic tract synapse in the lateral geniculate nucleus and also project to the primary visual cortex as you can see here in the optic tract the fibers have been lateralized to represent the opposite visual field let's do the same thing for the other side of the visual field first let's take these temporal retinal fibers I'm going to take them down the optic nerve and down the ipsilateral optic tract or the optic tract on the same side they're going to synapse in the lateral geniculate nucleus and from there travel to the primary visual cortex the nasal fibers from the other eye carried that very same visual information information is going to travel down the optic nerve and again fibers are going to cross over in the optic chiasm and then travel in the opposite optic tract to the lateral geniculate nucleus where they will synapse and travel to the opposite primary visual cortex again you can see that in this optic tract on the right side in this case information from the left visual field has been lateralized now that we've sorted out how the left and right visual fields projector their respective cortical areas let's have a look at how the upper and lower visual field project to the cortex so again the world around us is represented by this arrow this is the visual field of this particular eye and we can see that arrow in the visual field of this I this is the upper visual field and this is the lower visual field due to the refraction at the cornea the image as it projects on to the retina will be inverted this inverted image on the retina projects in that same inverted way all the way to the cortex so let's draw that in fibers in the upper retina contain information about the lower visual field they'll travel along the optic nerve and the optic tract to the lateral geniculate nucleus where they will synapse the same is true with the fibers from the lower part of the retina remember they contain information from the upper visual field they're also going to travel down the optic nerve and the optic tract to reach the lateral geniculate nucleus from the lateral geniculate nucleus the fibers are going to project to the primary visual cortex the fibers from the upper part of the retina containing information about the lower visual field will travel directly to the primary visual cortex and in fact these fibers project to the primary visual cortex that is superior to the calcarine fissure here now for the fibers from the lower part of the retina remember they have the information from the upper visual field their way to the cortex is blocked by the inferior horn of the lateral ventricle they're going to have to swing around that inferior Horn like this to reach the primary visual cortex and note that these fibers containing information about the upper visual field project to the primary visual cortex that is inferior to the calcarine sulcus here this part here where the fibers swing around the inferior horn of the lateral ventricle is called Mayer's loop this is important clinically because a lesion in the temporal lobe can lead to a visual field deficit in the upper visual field now let's have a look at the visual pathway in the brain here we're looking at an inferior view of the brain these are the optic nerves this is the optic chiasm this is the optic tract traveling to the lateral geniculate nucleus that's this little bump here on the thalamus which is part of the diencephalon here's the occipital lobe and here's the calcarine sulcus that's the primary visual cortex here's the inferior part and here's the superior part now watch the optic radiations here's the lateral geniculate nucleus and they're going to swing anteriorly around the inferior horn of the lateral ventricle and then they're going to project back to the primary visual cortex and you can see that they project to the part of the primary visual cortex that is inferior to the calcarine sulcus these fibers here as they swing around that inferior horn are called Mayor's loop in this specimen we have dissected away the lateral parts of the cortex this is anterior this is posterior this is where the lateral geniculate nucleus is and here are the optic radiations projecting to the primary visual cortex in the occipital lobe and note that these optic radiations go to the part of the primary visual cortex that is superior to the calcarine sulcus we have taken the image to the primary visual cortex remember the image is reversed and inverted so how do we make sense of this from the primary visual cortex fibers will go in a dorsal stream from the occipital lobe to the parietal and frontal Association areas this will tell us where things are and how they are a ventral stream will go from the occipital cortex to the temporal Association areas this will tell us the what or object recognition as you can appreciate the visual system is a complex system that has evolved to accommodate binocular vision and can sort the visual field to the respective cerebral hemispheres from here widespread areas of the cortex are engaged to make sense of the visual world around us

Channel: UBC Medicine - Educational Media

Views: 271,921

Rating: 4.96346 out of 5

Keywords: Neuroanatomy (Anatomical Structure), Central Nervous System, UBC, Claudia Krebs, Zachary Rothman, Dissection (Taxonomy Subject), Gross Anatomy Laboratory, Flexible Learning, visual pathways, optic nerves, Eye (Human Sense Organ)

Id: TbDFrbXiz2s

Length: 11min 21sec (681 seconds)

Published: Fri Feb 21 2014