Questions Regarding the Optic Nerve
March 30th, 2007 | No Comments »The following text was excerpted from the Wiki entry “Optic Nerve”:
“The optic nerve contains 1.2 million nerve fibers. This number is low compared to the roughly 130 million receptors in the retina, and implies that substantial pre-processing takes place in the retina before the signals are sent to the brain through the optic nerve.”
This is an example of what I believe to be thinking that leads (has led) to a dead end in unraveling the vision process.
In my explanation the rods of the peripheral retina, that constitute the bulk of the above mentioned 130 million receptors, function as the wide angle ‘light meter’ controlling constriction of the light entrance pupil of the eye. It is even understood in vision literature that these peripheral rods are largely connected in parallel in support of this assertion.
It is cones of the fovea and parfovea, together the with lesser number of rods encompassed within approximately 20 degrees of retinal angle that, detecting direction and intensity of the three primary wavelengths, are involved in the image formation process of the eye. There is certainly some pre-processing of visual information involved in the sub-retinal ‘circuitry’ of the retina. The number of optic nerve fibers involved in
transmitting this processed image information then probably will be found to be consistent with the 1.2 million quoted above.
The statement quoted above is critically misleading!
Regarding the optic nerve, I would like to find an electron micrograph of a cross section of the 1.2 million fibers…can anyone help? Specifically, I would like to ascertain if all of the fibers are of the same diameter…..or might they spatially replicate the plan of the retina. I have been told that the visual image of the retina appears as an actual image in the visual centers of the brain. I want to use the term ‘coherent’ here implying that there is a one-to-one correspondence of pixels in the spatial plan of the image appearing in the brain and the initial retinal representation. If this is so it presents the idea that the optic nerve acts as a ‘coherent fiber optic bundle’…might this be so?
I have guessed that the fundamental geometric principle defined on the retina (the ‘rule of two circles’ discussed in the paper) might be carried forward in transmission of the image through the optic nerve and thus might give some clue to the organization of neural networks in the brain.
?????
GCH
3/30/0
