B R O
10-25-2009, 09:39 PM
مآ أبيْ أسمع " رجـآإوٍيْ " . .
مآ أبيْ أسمع حلـوـوٍف . .
هذآ بحث بسيط عن كيفية وصول الصورهـ اللي نراها بالعين الى المخ .. سويته بـ مسآعدة [ Google ] و [ Word ] .. و حبيت تستفيدون منه ..
,’
The Pathway
Vision is generated by photoreceptors in the retina, a layer of cells at the back of the eye. The information leaves the eye by way of the optic nerve, and there is a partial crossing of axons at the optic chiasm. After the chiasm, the axons are called the optic tract. The optic tract wraps around the midbrain to get to the lateral geniculate nucleus (LGN), where all the axons must synapse. From there, the LGN axons fan out through the deep white matter of the brain as the optic radiations, which will ultimately travel to primary visual cortex, at the back of the brain
Visual fields
Information about the world enters both eyes with a great deal of overlap. Try closing one eye, and you will find that your range of vision in the remaining eye is mainly limited by your nose. The image projected onto your retina can be cut down the middle, with the fovea defining the center. Now you have essentially two halves of the retina, a left half and a right half. Generally, the halves are referred to as a temporal half (next to your temple) and a nasal half (next to your nose)
http://vb.ml7-alswalf.com/uploaded/23_11256495401.gif
Visual images are inverted as they pass through the lens. Therefore, in your right eye, the nasal retina sees the right half of the world, while the temporal retina sees the left half of the world. Notice also that the right nasal retina and the left temporal retina see pretty much the same thing. If you drew a line through the world at your nose, they would see everything to the right of that line. That field of view is called the right hemifield
So, what you see is divided into right and left hemifields. Each eye gets information from both hemifields. For every object that you can see, both eyes are actually seeing it - this is crucial for depth perception - but the image will be falling on one nasal retina and one temporal retina
Why bother to divide the retinas at all? Recall that the brain works on a crossed wires system. The left half of the brain controls the right side of the body, and vice versa. Therefore the left half of the brain is only interested in visual input from the right side of the world. To insure that the brain doesn't get extraneous information, the fibers from the retina sort themselves out to separate right hemifield from left hemifield. Specifically, fibers from the nasal retinas cross over at the optic chiasm - whereas the temporal retinas, already positioned to see the opposite side of the world, do not cross. Here is what it looks like
http://vb.ml7-alswalf.com/uploaded/23_01256495401.gif
The practical consequences of this crossing are that damaging the visual system before the chiasm will affect one eye, both hemifields - analogous to closing one eye. Damaging the pathway after the chiasm, though, will damage parts of both eyes, and only one hemifield. There is no easy way to imagine what this would look like. Your field of view would be only 90°, from straight ahead to one side
و بالمرفقـآت .. آلبحث بـ ملف [ Word ] ..
دعوآتكم لي بالتوفيق ..
. . كلْ عـآإشـقْ يخطيْ " مرهـ "
. . و أنت تخطيْ بـ " الألو و و ف " ! ! !
مآ أبيْ أسمع حلـوـوٍف . .
هذآ بحث بسيط عن كيفية وصول الصورهـ اللي نراها بالعين الى المخ .. سويته بـ مسآعدة [ Google ] و [ Word ] .. و حبيت تستفيدون منه ..
,’
The Pathway
Vision is generated by photoreceptors in the retina, a layer of cells at the back of the eye. The information leaves the eye by way of the optic nerve, and there is a partial crossing of axons at the optic chiasm. After the chiasm, the axons are called the optic tract. The optic tract wraps around the midbrain to get to the lateral geniculate nucleus (LGN), where all the axons must synapse. From there, the LGN axons fan out through the deep white matter of the brain as the optic radiations, which will ultimately travel to primary visual cortex, at the back of the brain
Visual fields
Information about the world enters both eyes with a great deal of overlap. Try closing one eye, and you will find that your range of vision in the remaining eye is mainly limited by your nose. The image projected onto your retina can be cut down the middle, with the fovea defining the center. Now you have essentially two halves of the retina, a left half and a right half. Generally, the halves are referred to as a temporal half (next to your temple) and a nasal half (next to your nose)
http://vb.ml7-alswalf.com/uploaded/23_11256495401.gif
Visual images are inverted as they pass through the lens. Therefore, in your right eye, the nasal retina sees the right half of the world, while the temporal retina sees the left half of the world. Notice also that the right nasal retina and the left temporal retina see pretty much the same thing. If you drew a line through the world at your nose, they would see everything to the right of that line. That field of view is called the right hemifield
So, what you see is divided into right and left hemifields. Each eye gets information from both hemifields. For every object that you can see, both eyes are actually seeing it - this is crucial for depth perception - but the image will be falling on one nasal retina and one temporal retina
Why bother to divide the retinas at all? Recall that the brain works on a crossed wires system. The left half of the brain controls the right side of the body, and vice versa. Therefore the left half of the brain is only interested in visual input from the right side of the world. To insure that the brain doesn't get extraneous information, the fibers from the retina sort themselves out to separate right hemifield from left hemifield. Specifically, fibers from the nasal retinas cross over at the optic chiasm - whereas the temporal retinas, already positioned to see the opposite side of the world, do not cross. Here is what it looks like
http://vb.ml7-alswalf.com/uploaded/23_01256495401.gif
The practical consequences of this crossing are that damaging the visual system before the chiasm will affect one eye, both hemifields - analogous to closing one eye. Damaging the pathway after the chiasm, though, will damage parts of both eyes, and only one hemifield. There is no easy way to imagine what this would look like. Your field of view would be only 90°, from straight ahead to one side
و بالمرفقـآت .. آلبحث بـ ملف [ Word ] ..
دعوآتكم لي بالتوفيق ..
. . كلْ عـآإشـقْ يخطيْ " مرهـ "
. . و أنت تخطيْ بـ " الألو و و ف " ! ! !