The neuronal circuitry of the photoreceptors

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In addition to their distribution on the retina, photoreceptors exhibit differences in their circuitry with downstream neurons, a factor that also influences visual acuity. From front to back, the approximately 120 million photoreceptors gradually reduce their signal amount and merge with the 1 million ganglion cells, the extension of which leads out of the eye as the optic nerve. Due to the larger quantity, an average of 120 rods and only six cones converge in each ganglion cell. Considering that many cone cells of the optic pit exclusively connect to one ganglion cell, this discrepancy becomes even more significant.

Figure 9 (Neuronal wiring and visual acuity) illustrates the practical effect of convergence. The visual system can’t figure out that there are two separate light stimuli based on how the two rod receptors are excited and how the ganglion cell responds to them, since they converge with three other cells. On the other hand, the cone receptors of the fovea centralis exclusively connect to one ganglion cell each, leading to the perception of a stimulus response from two separate receptors.

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Main Visual acuity

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