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Studying for a test? Prepare with these 8 lessons on Advanced nervous system physiology.
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Video transcript
In this video, we're going to talk about visual processing, so how our brain is able to make sense of what we're looking at. So in most of our body, we have the right side of the body being controlled by the left side of the brain and the left side of body is controlled by the right side of the brain. So how does this work in vision? So let's imagine that this rectangle that I drew is our entire visual field. And if these two eyeballs were focused in at the center of this rectangle, so if they were both focusing on this purple line, all they can see are these two colors. So we have a ray of light coming in from the left visual field. It'll hit the eyeball. It'll hit the left eyeball. It'll kind of be bent a little bit by the lens. And it'll hit the right side of this eyeball. And so the inner side of the eyeball-- so this side of the left eyeball and this side of the right eyeball is known as the nasal side because the nose would be right in the middle the eyes. So the nasal side is the side of the eyeball closest to the nose. And then this outside part of the eyeball, which is over here and over here, is known as the temporal side of the eyeball because it's closest to your temples. So this is the side closest to the temples. This is the side closest to the nose. So a ray of light coming from the left visual field will hit the nasal side of the left eye. And a ray of light coming from the left visual field will hit the right eye, be bent a little bit by the lens, and it'll hit the temporal side of the right eye. So let's look at a ray of light coming from the right side of the visual field. A ray of light coming from here would enter the right eye. And it would be bent a little by the lens and hit the nasal side of the right eye. Whereas, a ray of light coming in would hit the left eye, be bent a little, and hit the temporal side of the left eye. So let's look at what happens next. So the eye is basically connected to the brain via the optic nerve. So there is an optic nerve that kind of exits the back of the eye and goes into the brain. So interestingly, the optic nerve from both eyes actually converge. So they actually reach a point where they converge. And this point right here where they converge is known as the optic chiasm. So they kind of converge and then break off again and then move even deeper into the brain. So this point where they converge is known as the optic chiasm, so optic chiasm. Let's look at how this information is transmitted to the brain through the optic chiasm. The retina is lining the back of the eyeball. And we had this yellow ray of light hit the nasal side of the left eye and it hit the temporal side of the right eye. So let's go ahead and trace this information to the brain. So the information will be sent via axons through the back of the eye into the optic nerve. And basically, it'll come in. And what it'll do is it'll actually cross at the optic chiasm and then go this way. And what we also have is this ray of light will come into the back of the eye and it will actually go down the optic nerve. But it's not going to cross. So all light that hits the temporal side of either eyeball does not cross the optic chiasm. So let's go ahead and trace this green ray. So the green ray coming from the temporal side of the left eye is going to exit the back of the eye, go down the optic nerve, and it's just going to stay in place. So it's not going to cross the optic chiasm. Whereas, this ray of light is going to go through the back of the eye and it's going to cross over here. It's going to cross the optic chiasm and go down to the brain. And so what this effectively does is it actually takes the right visual field and allows all the information that's entering the eye from the right visual field to go to the left side of the brain. So this is the left side of the brain. This is the right side of the brain. So like the rest of the body, all the information coming from the right visual field actually goes to the left side of the brain and all the information coming from the left visual field goes to the right side of the brain.