so vision your sense of vision your ability to see is relayed via your optic nerve or cranial nerve
to the neurons for this cranial nerve originate in the neural retina most of the oral half of these
axons are going to cross at a structure called the optic chiasm in this slide we can see the
optic nerve in situ the eyes are kind of down in this region and the optic nerve then comes
through the optic canal and you can see it coming right under the edge of the frontal
bones right here so here's the optic nerve so if not that you'd ever really want to know this but
if you're gonna take a brain out of a skull you got to cut the optic nerve to do it and here on
the under surface of the brain again we can see our beautiful olfactory bulb and our olfactory
tract and here we can see the cut ends of the optic nerve just posterior towards or caudally
towards the back of the brain is a structure called the optic chiasm and that's right here
and that optic chiasm that's just a rhesus you can see it better the optic chiasm is where
half of your optic axons are gonna cross so the visual fields are set up in a way that we have a
nasal visual field which is up against the retina that's against your nose and a lateral area of the
rip your visual field that's called the temporal the temporal part of your retina actually sees
images coming in from the nasal part of your visual field so it's a little confusing let me
draw it for you and see if this makes sense so if your nose is kind of here and your eyeball
is here and then your retina is across the back this part of your retina sees this part of the
visual field this part of your retina sees that part so this is going to be the temporal and this
is going to be the nasal so as you're learning about neuroscience and and when you get into a
more in-depth course and they're going to talk about areas of the retina the nasal retina or
the temporal retina and then they'll talk about visual fields nasal and temporal temporal and
their different so just keep that in mind as you study in the future to reiterate the crossing of
these fibers from the from the retina if I have a retina up here and I have my optic nerve that's
leaving half of fibers are going to stay on one side and half of the fibers are going to cross
to the other side and my other eyeball I've got half of the fibers crossing over and half staying
on the same side so this represents the optic chiasm that's all I want you to know for now
that half cross and half don't the ins and outs of the visual system and all of the projections
are very complicated and are beyond what we have time to talk about in this MOOC but if
you're really really interested I'm sure that there's another MOOC out there somewhere that
talks really in-depth about the visual system so I want to point out on the different parts
of this this pathway within the brain and so in an anterior piece of the brain here we can
see that we're anterior in the brain we see the lateral ventricles we see a little bit of our
third ventricle and here are the optic nerves just coming together to right in front of the chiasm in
this image we're a little bit more we're probably about in the middle of the brain again we have our
lateral ventricle and our third ventricle here on the midline and here is the optic chiasm in all of
its glory so half the fibers are crossing half or not a little bit more posterior in the brain
we have again our lateral ventricle a little bit of our third ventricle here and this is now the
optic tract and we call the pathway the object tracked after the chiasm so it goes nerve chiasm
tracked the optic tract specifically projects to an area of the thalamus called the lateral
geniculate nucleus or generate lateral geniculate body of the thalamus we'll
talk more about the lateral geniculate and some of the other important nuclei of the thalamus
when we talk about the cerebral cortex and some of the deep grey matter but this is a
way station for visual processing on the way on its way to that occipital cortex which of course
you know is in your occipital lobe where prime where vision comes to perception in this slide
what we can see it's a horizontal section of the brain and it's above the level of the optic chiasm
and the optic nerve but what we can see are the fibers that are leaving the thalamus which is
this midline structure and we'll talk more about the thalamus later but there's a big bundle of
fibers right here that's exiting the thalamus and headed toward the occipital cortex we call
this the optic radiations radiation I am NOT the best speller and that is how information gets from
the thalamus to the occipital cortex so from the retina through the optic nerve to the optic chiasm
at the optic chiasm half the fibers cross and have to not post chiasm we call it the optic tract the
optic tract then goes to the thalamus and then from the thalamus it goes to the occipital cortex
via the optic radiations in the next segment we'll talk about the special sense of taste