Page 9

Sharks - Free Sample

Night Vision Device with a Curtain The sense of smell sends a command to the eyes in clear water at a distance under 100 meters on the way to the prey. Shark eyes are sophisticated sensors with a high degree of sensitivity, but low visual acuity: They can regulate incidental light intensity like a cat by opening or clos-ing their pupils to a mere slit. Thanks to a built-in night vision device, they can also see mov-ing objects in low light conditions rather well, even if the image is blurred. For this purpose, a reflective layer behind the retina reflects 90% of the light that has already passed through the photoreceptor cells back, so as to strengthen the nerve impulse as a whole. This reflective layer, called tapetum lucidum by scientists, is twice as efficient as that of a cat. Since excessive light destroys the highly sensitive rod cells, sharks that live near the surface "cover" the small mirror platelets in the back of the eye with movable, opaque pigments at daybreak. Moreover, a shark eye adapts itself to the cyclic day-night rhythm. During a process that lasts for an hour respectively, the retinal cones responsible for color vision reduce in size at dusk, making room for the subsequently expanding rod cells. These are responsible for changes in light intensity, making sharks extremely sensitive to light-dark contrasts. Not all sharks can see colors, however. This ability is important for fish that live near the coast or in reefs, whereas it is not important for deep sea sharks or other dwellers such as the big-eyed thresher shark. That's why Mother Nature equipped the sharks according to their individual needs and requirements. Navigation System in the Snout Moreover, sharks have clearly visible pores on their snout that have kept naturalists puzzled for more than 350 years now. The organ was first described in detail by the Italian Stefano Lorenzini in 1678. It took almost 300 years until the first of several functions of the Ampullae of Lorenzini could be decoded, these having been named after the naturalist. Sharks are able to perceive bio-electrical fields with this multi-sensor, as these would induce a beating heart or other muscle activ-ities. The sensor sets off an alarm at a voltage difference of only five billionths of a volt. This is the 17


Sharks - Free Sample
To see the actual publication please follow the link above