Science_Illustrated_Australia_-_Issue70_2019

Sharks feel the

heartbeat of prey

Sharks use electricity to sense the

outside world, and indeed hammerhead

sharks could not survive without

their delicate electrical sense.

As a supplement to sharks’ excellent senses of vision

and smell, their snouts are lined with ampullae of

Lorenzini – small pores filled with an electrically

conductive gel. These ampullae are influenced by even

very weak electrical discharges, with their reactions

carried to a bundle of nerve threads at the bottom of

each ampulla, which sends a message to the brain.

One single ampulla of Lorenzini can react to just five

billionths of a volt, so that a shark can find a shrimp

based only on the slight electrical charge generated by

the shrimp's heart. The lower side of a hammerhead

shark’s head is lined with ampullae. According to some

scientists, the hammerhead shark uses its special head

shape to make an electrical 3D image of the creatures

located right beneath its head. The ability is vital, as the

shape of the shark’s head means that it has a huge blind

spot under its snout and around the mouth. Experiments

have shown that if the shark’s electrical sense is blocked,

it has difficulties finding and catching its prey.

It isn’t suction discs or super-glue that allows a gecko

to cling to difficult surfaces at tricky orientations.

The gecko is climbing using an electrostatic effect.

Geckos are known to be able to climb all surfaces, from vertical

walls to the under-side of a window sill. They can do this

thanks to a phenomenon known as Van der Waals force.

All atoms are made up of positively-charged protons

and a cloud of negatively-charged electrons that are in

constant motion. In molecules with many atoms,

the electrons can move freely between the many

clouds that surround each atomic nucleus. If the

electrons unite at one end of the molecule, it is

temporarily negatively charged, whereas the

opposite end becomes positively charged. The

result is volatile electromagnetism that briefly binds

the molecules in the gecko’s feet to the window sill.

Gecko feet are studded

with electromagnets

A gecko’s feet contains about 2 billion electromagnetic

bindings that help it stick to any surface.

3

Subsequently, the current

flows through the gel to affect

the nerve fibres. An impulse is

passed on to the brain, which forms an

image of the creature beneath the sand.

2

If a shark comes into contact

with an electric field, such as

from a fish hiding beneath the

sand, the current is carried away from

the skin to the pores of the ampullae.

1

The lower side of a hammer-

head shark's head is dotted

with ampullae of Lorenzini

that consist of a pore leading to a canal

filled with electrically conductive gel.

Gel

AmLorenzinipulla of

Nerve fibres

Signal to the brain

FRANS LANTING/MINT IMAGES/IMAGESELECT

Gel picks up

electric signals

Lower side of the snout

66 | SCIENCE ILLUSTRATED

NATURE ELECTRIC ANIMALS