Eyes See Inside Out
The light-detecting receptor cells within the retina, called rods and cones, are actually at the back of the retina under several layers of cells. The neurons and support cells within the retina are fairly translucent, so light is able to pass through them and reach the receptors.
No Octopus Blind Spot
The octopus has a single layer of cells in the back of its eye. These receptor cells project directly back to the brain via the optic nerve. Because the optic nerve forms behind the receptors rather than passing through them, the octopus has no blind spot.
No Pain in Brain
There is no sense of pain within the brain itself. This fact allows neurosurgeons to probe areas of the brain while the patient is awake. Feedback from the patient during these probes is useful for identifying important regions, such as those for speech, that are spared if possible
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