As found out before, the paralysis of the fish is caused by it's motor neurones. Now the setting with two differently prepared fish was repeated. First fish: brain and spinal cord destroyed. Second Fish: only brain destroyed. This is to check by which part of the nervous system the activation of the fish's motor neurons (it's movement) is caused. Either the central nervous system (fish 1) or the "decentral" branches (fish 2)

pithing is a method used while preparing specimen for experimental procedures and dissection. It is done by inserting a metal rod into the brain or spinal chord of a living specimen as to kill or immobilise in the least painful way. This method is useful in that it allows for the testing and examination of the physiology of the organs of the prey because they still work, but the animal feels no pain and has no control over their muscles.

The aim of this study was to show the influence of two stimuli (produced in a short time sequence and called doublet) on the time where a tetanus was observed. By using single motor units of rats, it was shown that the doublet induced an increase of the tetanic tension and fusion. Also that slow motor units showed higher reaction to the doublet sensitivity than fast units.

Researchers took muscle samples from cats and tried different tetanus on them. They seem to have found the efficient pulse and frequencies by the motor neuron to generate a optimum muscle tension.

The purpose of this study is to further understand the effects of the electric eel's attacks on their prey and to explore the multiple strategies that are used by the eel during the process of prey detection, hunt and capture.

Electric organs after millions of years of evolution have become a highly useful tools that are used by animals in many ways, such as communication, navigation, predation, or defense. Despite millions of years of evolution and many physical differences between the electrical cells of electrogenic species, it is seems that they all share the same origins and demonstrate the same cellular pathway and similar transcription factor.

Electric eels have been used as a model in the study of bioelectrogenesis, which is the study of electricity produced by living organisms. The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate.

Both bio-fuel cells and high voltage liquid electrolyte microbatteries have been inspired by the Electric Eel.

More recently a "protocell" was designed by Dr. David LaVan at the National Institute of Standards and Technology in Maryland in which the electric charge difference between two cells and the flow of ions through the shared membrane was used to generate electricity much like that generated by the cells of electric Eels.

to read more see: 1- http://www.economist.com/node/14790488

2- Xu, Jian, Fred J. Sigworth, and David A. LaVan. "Synthetic protocells to mimic and test cell function." Advanced Materials 22.1 (2010): 120-127.

a brief and single electric shock(stimulus) triggers a signal (action potential) in the muscle. After an activation delay ( due to the time it takes for the signal to reach its target) a muscle contraction occurs. The muscle usually relaxes after a few milliseconds unless another contraction signal is send out before the muscle fully relaxes where the muscle contracts again. The contraction that happens after the second contraction is greater that the first because it equals the sum of the tension from both signals being greater. Each of these signals causes the specie to involuntarily twitch and lose control over motor neuron and therefore movement.

Tetanus could refer to the disease caused by a bacterial infection or to rapid/continuous muscle contraction. In this context it is referring to the latter definition;muscle contraction. Each contraction produces an involuntary twitch. Because the electric shocks produced by the electric eel are very frequent the fish ends up constantly twitching with no breaks and no control over its movement .

for more information about muscle contraction; Mann MD (2011). "Chapter 14: Muscle Contraction: Twitch and tetanic contractions". The Nervous System In Action. Michael D. Mann

Electric eels are found in muddy bottoms of still fresh waters in the South America, specifically the fresh waters of the Amazon and Orinoco River basins. They are found in swamps, creeks, and small rivers, and coastal plains. They feed on invertebrates, and adults consume small fish and mammals.

Cells that carry messages and transmit signals. It is those cells that allow us to perform basic motor functions such as walking, eating, holding things etc.

Is a sturdy alternative to glass. made out of acrylic it is shatter proof as well as sound proof. this is ideal in this experiment because it is clear enough for the eel to se through but does not allow noise or movement of prey to go through, or electric shocks of eel.

Electric Eels; one of nature's many fascinating creations have long been known for their ability to produce electricity and harvest it to defend themselves against predators as well as catch their dinner. Electric Eels' are famous for their capacity to freeze the movement of their prey through electric discharges, but the magic behind this trick is still unknown. In this paper, Kenneth Catania explores this "Eelectric" phenomenon and tries to understand and unveil the mechanism behind it. What is the Electric Eel's secret you ask? Read on and be prepared to be shocked!

jelly like gelatine but made from algae

Eels always check if there is living prey by sending two fast electric signals (doublet). Only after the eels feel the movement of the fish, which they induced by their double shock, they attack the fish by really strong shocks.

The fish did not behave differently. Thus, the eel's shock activates "decentralised" motor neurons of the fish.

Prior researches study the optimal pulse sequence on the muscle that lets maximize the muscle contraction. This work is interesting because it is a report of the normal condition optimum for a muscular activation from the electrical pulse of the neuronal system. This allows the author of this paper to state that the eel's electrical pulse are optimal for the generation of an muscular tension.

Muscles are led by motor neurons, to better answer to the body demands, motor units emit three sorts of neuron's impulsion that modulate the muscular contraction and the motor system used.

Look at the annotation of the first reference. There you can find more information about this work

Eels are not the only ones to be studied for their ability to produce electricity to survive. Indeed, other astonishing animalas use this system, like Stargazers or Rays called "Torpedo".

When the order of generating electricity is given by the brain, the electrical cells of the Eels organ are activated. An entry of ions in the wall of each cell is created, this action changes the polarity of the entire cell. This works like a battery of a car that generates an electric current due to ion differences in the electrodes. This potential in addition of all the other cells generate a big potential up to 600volts !

Eelectrify your prey the shocking way!

The connection point between the motor neuron (carrying signal from the spinal chord) and a muscle fibre. This is the communication channel between the two where messages are transmitted using calcium ions. This is necessary to control muscles.

Latency refers to the time thats elapses between an action and a reaction in a system. In this context it refers to the time it takes for the activation of the motor neurone efferents of the prey after the release of the eel electric discharge.

They investigated the evolution of the electric organs of eels. They looked at the DNA of the electric eels and two other species with electric organs. They detected many different genes for the developement of electric organs. Their results show that despite big differences in the electric cells of the investigates species, they have leveraged similar transcription factors and developmental and cellular pathways in the evolution of electric organs.

Some electrical fish produce not enough voltage to get an offensive or defensive meaning. In this study, authors try to understand in which this sorts of fish use this system. It will be demonstrate that it is used as direction and finding of the fish.

Effects of high‐frequency stimulation and doublets on dynamic contractions in rat soleus muscle exposed to normal and high extracellular

By recording firing pattern in motor units of rats, authors demonstrates quantitatively that, contractile properties of the muscular system is improve by the tree different respond allowed (fast but easily fatigued, slow but fatigue resistant, both). Also this paper in studying and recording the normal value of muscular contraction of an healthy rats, will allow the searcher to notice if is somethings wrong or interact with the motor control system. Like in our articles where the Eels's electricity make the muscular system of the fish goes off. "Firing patterns of motor units in normal rats"

The researchers investigated the behaviour of electric fish in french guiana. Notably, they describe in first the prey-capture behaviour of the electric eels.

Fish electric organs seams to be derived originally from muscle therefore a source of acetylcholine receptor. The Eels' anatomy was used many in different science domain such as Anatomy, embryology, and physiology. In previous research it was shown that the pathway between the nerve and electric organ used acetylcholine receptor. This is why this species, source of acetylcholine, conduct to very detailed studies by biochemist and neurologist.

"The Shocking History of Electric Fishes: From Ancient Epochs to the Birth of Modern Neurophysiology" is a book written by Stanley Finger and Marco Piccolino. In this study they follow different types of animal (flat torpedo rays, the electric catfishes, and the "eel" of our article). All three are able to produce electricity shocks and explain how they helped to change the sciences and medicine.

By studying the electroplaques of Torpedo-nobilian, the researcher try to understand how depolarising or hyperpolarizing changes in membrane potential occur. Furthermore they relief the latency time during stimulation of the nerve and the polarisation of the cells.

This study revealed that Eels, through the process of evolution and survival for the fittest, have developed a very efficient system of prey detection and capture. The Eel's electrical powers work much like the way a TV remote control does. Using electrical pulses Eels turn off their prey's nervous system the same way a remote control turns off a tv screen. This happens because the electric pulses take advantage of the mechanism through which the Prey's nervous system works by hacking into it and telling it to freeze.

If you want to know more about acetylcholine gated ion channels leads to the muscular contraction. http://www.ncbi.nlm.nih.gov/books/NBK21586/

You can check this out if you want to know more about what happens during muscular tension: https://www.boundless.com/biology/textbooks/boundless-biology-textbook/the-musculoskeletal-system-38/muscle-contraction-and-locomotion-218/control-of-muscle-tension-829-12072/

length of a time step of delay

The eel's electric shock contracts the fish's muscles, which paralyses it.

sucking in food (a fish) to catch and eat it, like you suck through a straw

in this context volleys refers to multiple back-to-back electric discharges

While they are referred to as Eels, Electric Eels actually belong to the nocturnal family of knifefish which consists of electric fish that have organs that generate electric current. Eels are the largest Gymnotiformes and use electric current to defend and hunt.

when a neutron is described as being efferent it means that it carries orders away from the central nervous system, which acts like a control centre, towards organs, mainly muscles and glands

To test the hypothesis that eel's detect hidden fish with sending out doublets, fish were put in a plastic bag to electrically isolate them from the eel's signals. Thus, the fish didn't give any response (movement) to these signals. But fish movement could be simulated by a stimulater controlled by the experimenter.

This is almost five times more voltage than what you would get out of an Electrical outlet in a US household (120V) and more than twice the voltage of an outlet in Europe (220-240 V)

Fig. 4 tab G: Also without the plastic bag isolation, frozen fish weren't attacked by the eels. Conclusion from G and H: eel's don't attack fish when they see them, they need the fish's movement stimulated by their doublet or the experimenter to attack the fish

Fig. 4 tab C: The fish's movement following the eel's doublet is stimulated by the experimenter. The eel recognises this movement and attacks. Conclusion: the eel always attacks when there is movement from the fish

Fig.4 GENERAL - panel A: plastic bag: isolates the fish electrically from the eels attacks. Thus the fish isn't affected by the attack, and doesn't move. stimulater: a movement of the fish can be stimulated to simulate a fish's reaction to the eel's attack

Fig. 4 tab H. The eel doesn't react to visual signals. the fish behind the glass moved, but the eel didn't attack, because he couldn't feel the movement through the thick glass barrier.

fig. 4 tab F: Frozen fish don't move as well, so like in E no attack

Fig. 4 tab E: When there is no fish to be moved, no attack follows

fig. 4 tab D: the eel even reacts to fish movement with an attact, when it didn't send out it's question "Is there living fish?". The doublet represents this question.

Fig. 4 tabB: Fish doesn't move after the eel's doublet because of the plastic bag isolation. Thus no response for the eel that there is a fish behind the agar barrier and no attack.

Location by electricity. In using this tools the eels can explore extreme environment such as muddy water.

mechano referes to mechanical stimulus, which is a physical change such as direct contact, change in pressure or vibration. This change can be sensed by special sensory cells that are found all over the body. These cells allow us to sense vibrations from and contact with other objects.

Fig. 3 Tab F. same as in D, the only difference is that the doublet to find the finish is a triplet

Fig. 3 tab D: At 2: doublet of electric signal to find the fish Starting at 6: strong attack of the fish to paralyse it

fig.3 tab C:

1. Fish is hidden behind an agar (algae jelly) barrier
2. Eel sends out weak electric signal
3. Fish moves due to the eel's electric signal. The eel recognises this movement.
4. Eel attacks with strong electric shocks

Fig. 3 tab B: This panel is a zoomed picture of the first signal of panel A. It shows that the fish moves only some Milliseconds after the eel's doublet of shocks.

Fig. 3 Tab A: Each shock by a eel (red peak) makes the fish move (black graph)

Eels can also detect hidden fish. Weak electric shocks make the fish move, the eel detects this movement and strikes strongly

The eel's shock affects the nervous system (motor neurons) of the fish.

the poisoned fish didn't move anymore when shocked by the eel

To find out how the muscle contraction is caused, two fish were prepared differently: 1. the first fish was injected with a nerve poison to check if the muscle contraction by a chemical effect 2. the second fish was only given a placebo to check if it's a electrical effect

The fish connected to the force transducer was behind a jelly barrier. When the eel sent out a strong electric shock the fish moved. The fish did not react to weak electric signals.

Fig.2 tab C: experimental setup with two fish with a force transducer for each one

poison that stops a chemical messenger

To understand how the eel's electric shocks affect the fish, anesthetized fish were connected to force transducers to record their movement.

Fig. 2 tab D: red: the eel's cascades of electric shocks green: fish tension = fish moves After the fish is treated with curare (molecule, poison for chemical messenger), it doesn't react to the eel's shocks anymore

fig. 2 tab B: Eel EOD = eel electric organ discharge = every red peak represents an electric shock by the eel When the eel starts shocking in a cascade, the fish tension changes, which means that it moves. little top right figure: Also when the eel sends only out single shocks with longer Pauses, the fish moves very time.

Fig.2 tab A: experimental setup: the fish an the eel were separated by a electrically conductive jelly barrier. It can be measured by the force transducer if the fish moves, when the eel emits an electric shock.

Fig. 1. - tab A The eel's shocks start after 60 ms. It sends out many fast consecutive shocks

Fig. 1 -tab B: the little fish is paralysed starting from 60 ms till the end. This is indicated by the red filter on the photographs.

Fig. 1. tab C: If the eel hadn't paralysed the fish (shown in green), the fish would have been able to escape, because it swims faster. But because the eel shocked it, it was slow enough to be caught by the eel. (shown in red)

Eels have three strategies: (i). mild electric shocks to get information about their environment (like radar) (ii). strong double or triple shocks (iii). many strong back-to-back shocks to catch fish or to defend themselves

electrical cells

Neurotransmitter (molecule, chemical messenger) that takes part in muscular contraction

To check the validity of the previous conclusion that the eel's electric shock causes muscle contraction, two fish with destroyed brains were tested.

very strong glue

able to produce a change in the electrical potential of a cell