zoology-biology-benno-meyer-rochow-florian-nock photoreceptors physics electricity

The Incomparable Sense


Luigi Galvani and Alessandro Volta’s observations ca. 250 years ago on frogs, whose legs twitched due to muscular contractions when touched with two different metals, can be regarded as the start of electro-biological studies. Although an animal’s nerves are not telephone wires and the muscles aren’t electromotors, activities such as thinking and moving are indeed registrable as electric events: one may think, for example, of the electrocardiogram, the electroencephalogram, or the electroretinogram. The trouble is that the electric events accompanying the various activities of live animals are so weak in nature that sophisticated electronic gadgetry is required to amplify and record them. But there are animals, which can detect bioelectricity with particular sense organs, which the zoologist calls electroreceptors.

The first animals, in which this sense was documented were small-eyed fishes from murky East African lakes and turbulent South American rivers. These fishes produce brief electric pulses of 3 millisecond duration and 3-7 Volt magnitude. When Cambridge Prof. Lissmann tested what use this ability was, he found to his surprise that the fish could use distortions of the electric field surrounding them to gain information on objects nearby that they could not see. For example, the fish had no difficulty in distinguishing in the dark 3 rods of identical dimensions but different material: wood, glass, and metal. The 3 materials distorted the electric field (set up by the fish around itself) in non-identical ways due to their different electrical properties. The distortions were detected by the fish’s electroreceptors.

The next group of fishes investigated were sharks. Although they don’t produce electric pulses, they too were found to possess electroreceptors (small pimples around the face with an opening to the outside and a microscopic canal filled with electroconductive jelly), which they use to locate prey hidden in the sand. The shark’s so-called Ampullae of Lorenzini were found to be unbelievable sensitive, responding to field changes of 0.000001 Volt per metre (corresponding to one flashlight battery 1,500 km away). This together with its good sense of smell, vision and ability to detect water currents, makes sharks the ultimate predator.

The only mammal that could join this “club” of electrosensitive animals was the Australian Platypus, also known as “duckbill”. It could be shown that it too possessed electroreceptors on its bill that could detect (over a distance of a few centimetres) the electric events accompanying burrowing in the sand and breathing in worms, snails and insects. But why aren’t there electrosensitive insects, spiders or crustaceans? They’ve had, after all, a much longer evolutionary history than the Platypus. Perhaps one day an electrosensitive insect or crab will be discovered, but there are anatomical limitations and electrophysical reasons that make small bodies unsuitable. And finally, what about humans? There are some, who claim they develop headaches, seeing problems and irritated skin when surrounded by strong electric fields. Dismissed as improbable by physicists and physiologists alike, I actually know such a person and he’s a professor of visual arts at a respected university. Is he lying, sick or unwittingly deceiving himself? I was told that there is even a webpage of people reporting their own sensitivity to electric fields. So, have scientists missed something here?

eye discovery pond snail photoreceptor

Turn your mind upside-down with this article !

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

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