When light energy strikes the retina, an electrochemical reaction takes place. The process through which environmental stimuli bring about neural changes and makes the sensory experience possible is called as transduction. The process of transduction in vision consists of three stages:
(1) In the first, light energy triggers a chemical event in the light sensitive pigments of the rods and cones.
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(2) In the second, receptor and generator potentials are created as a result of the photochemical activity.
(3) In the third, nerve impulses are generated and conducted along the fibres of the visual pathways to the brain.
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When light energy strike the retina, rods and cones are activated, they make synaptic connections with the bipolar cells and ganglion cells. Fibres from the ganglion cells compose the optic nerve. Fibres from the outer sides of the retina, the temporal half-retinas, do not cross at the optic chiasma but continue along to the brain on the same side they started from. The collection of the crossed and uncrossed fibres after the chiasma is known as the optic tract.
After running through the optic tract, the fibres reach the relay centre for vision in a part of the brainstem known as the thalamus. The specific portion of the thalamus that is the relay centre for vision is known as the lateral geniculate body.
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Here, the optic tract fibres end and make a synapse with the lateral geniculate cells. The fibres, or axons, of the lateral geniculate cells run toward the cerebral cortex and form the part of the visual pathway called the optic radiation the tract from the lateral geniculate body to the cerebral cortex. When the message is registered at the cerebral cortex, visual experience becomes possible.