Seeing without eyes

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Seeing without eyes

Post by Dreamweaver » 24 Sep 2017, 19:19

The photoreceptors scientists have found beyond the eyes are most commonly located in the central nervous system. Almost all animals have several types in the brain and often in the nerves as well. “Extraocular photoreceptors” are usually found in the central nervous system or in the skin, but also frequently in internal organs. In general, identifying a potential extraocular photoreceptor means searching for the proteins that can detect light, the opsins. What are light-sensing molecules doing in places beyond the eyes?

They reach their highest development in the cephalopods: octopus, squid and cuttlefish. Animals actively control their color or pattern for several reasons, most often for camouflage (to match the color and pattern of the background) or to produce bright, prominent signals for aggression or attracting a mate.

A second class of light-sensitive molecules besides the opsins, never used for vision (as far as we know). They show up in some nervous structures, such as the brains or antennae of some insects and even in bird retinas. These are the cryptochromes, originally discovered in plants, where they control growth and annual reproductive changes. Typical functions include the timing of daily cycles of alertness, sleep and wake, mood, body temperature and numerous other internal cycles that are synchronized to the changes of day and night. Biological clocks that maintain regular physiological cycles – and cause the discomforts of jet lag – nearly always are controlled by these photoreceptors.

In some animals, they have a quite different, and rather amazing, task – providing magnetoreception, the ability to detect the Earth’s magnetic field. They apparently underlie mechanisms for magnetic orientation in animals as different as birds and cockroaches.

People have nonvisual photoreceptor abilities, too.This light-sensitive protein can regulate blood vessels’ contraction and relaxation. This could partially explain the increase in heart attacks in the morning, which are perhaps associated with blood pressure changes occurring at that time. ... tion-79166
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