Biology: Visual System

Actions for '5. Visual System'

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It's easy to get swamped in details about the visual system. (This animation may help.)

Discuss the visual pathways that originate in the retina and "ascend" to the visual cortex via the thalamus.

In this week's resources the retina is revealed as more than a screen for images. Light falls on different classes of photoreceptors, rods and cones, which organize light stimulation according to their pigments by intensity and wavelength. From the duplex nature of the retina there arises a tradeoff between greater acuity in the center and greater sensitivity in the periphery. The output of the retina is further organized into receptive fields, and sideways connections between the photoreceptors and horizontal cells sustain lateral inhibition that sharpens contrasts. A retinotopic map is preserved by the visual pathways all the way to the visual cortex; on the other hand, the image still requires a lot of interpretation by the brain.

Yet when we look at the world we notice only the rich panorama of detail that relayed to the brain via the fovea.

Questions (answer one)

How is the retina different from a movie projection screen? Try to be specific.

How on earth did we end up with eyes that are mostly peripheral retina and only tiny foveas? Should a sensible retina have more foveas-or larger ones, perhaps? Or might peripheral retina be more than leftover real estate?