Why don't electric fish shock themselves? | Hacker News Reader

Why don't electric fish shock themselves?

physics.stackexchange.com

81 pointsandrelaszlo29 comments

The explanation that the Eel doesn't shock itself because it has a larger resistance than smaller fish probably isn't correct, as it can eletrocute bigger animals as well, like a gator:

http://www.youtube.com/watch?v=aYwE9mNloO8

The electric eel has lots of insulating fat just under the skin - so it wouldn't be too much outside the realms of plausibility for it to have higher electrical resistance than something made primarily of muscle.

Of course, the insulating fat also likely provides a sort of faraday cage effect - any current that does hit the eel will just flow through its skin instead of hitting anything important.

Yep, I was going with Faraday cage. If the special electrical cells that an eel has on its skin are conducting, then surely there is some form of cage effect happening.

Having just done a very very quick search of relevant papers, I'm not entirely sure that anyone has actually looked into this. So the scientific answer would best be "I dunno".

Now, that explains better.

Why does fat have more electrical resistance than muscle?

Fat is a dielectric (electrical insulator). Fatty tissues contain a higher volume fraction of dielectric (fat) than do muscles, nerves, etc., which are mostly full of aqueous electrolyte solutions (Na+, K,+, Ca++) which are good electrical conductors.

That's really interesting. I learned something - thanks!

Muscle needs to be a conductor because that's how the 'tense' message is signalled—witness Luigi Galvani and his experiments on frogs' legs: apply a current, watch the leg spasm.

I'm not sure nerve impulses are similar to current flowing through a muscle.

An action potential (the phenomenon that underlies nerve impulses) is not just similar to an electric current; it is an electric current. From Wikipedia[1]: "An electric current is a flow of electric charge." It really is that simple. Any net movement of electric charge is a current. If I pick up a positively-charged baseball and throw it across the room (using insulating gloves so the charge stays with the baseball), that's an electric current. This isn't just a pedantic point, either. The moving baseball interacts with the Earth's magnetic field just like any other current, and an action potential also acts like a real electric current, because it is one.

However, you might contend that the electric current in an action potential moves across the membrane, not along it, and you would be correct. But that is because the voltages involved in the action potential are oriented across the membrane. The electrical conductors that carry this current are aqueous solutions of sodium, potassium, chloride, and other ions, and this solution will happily carry a current in any direction in which a voltage is applied. So when an external source (like an electric eel) supplies this voltage, the muscular tissue conducts the current. The ion channels in the membrane also ensure that the current is not stopped by the membrane as well.

Fat has high electrical resistance because lipids are predominantly hydrophobic and nonpolar, which means that they exclude both water and ions, both of which are necessary to carry a current in living systems. Muscle has a low resistance because part of its function is to carry an electric current.

Incidentally, if you think muscle doesn't conduct electricity, you might want to consider why the eel would even bother with all this electricity anyway. What's the point of zapping your prey if it doesn't even conduct electricity?

[1] http://en.wikipedia.org/wiki/Electric_current

They are. That's the whole point of that experiment.

Moreover: cut the conductor and the muscle doesn't move. Which is why nerve damage is so crippling. You literally have lost the ability to signal the muscle.

I'm still not sure potential differences across membranes throughout a muscle are like current flowing through a muscle.

You're describing a current without actually using the word current. Guess what happens when you have potential differences and a conductor. A current. It's literally the definition.

Smooth, skeletal and cardiac muscle cells and nerve cells do have some differences in their respective ion channel compositions. As a result, their action potentials will look somewhat different. And obviously muscle cells contract while nerves do not. Those differences aside, they are all are excitable tissues. Importantly, they all have voltage-gated ion channels. So they all will respond similarly when placed in electric fields.

The size of the animal doesn't really matter, the resistance of its body isn't function of its size.

According to the second answer the Eel is more resistant because it has a layer a fat. Unfortunately, there is no evidence of that, but at least it makes sens.

Does the alligator actually die in this video? I was expecting a very short shock that would scare the alligator, not the prolonged discharge shown.

And does the eel survive?

The alligator couldn't let go because of the current.

Alligator clip.

"Sympathy for Mr Vengeance" (2002, South Korea)

As someone who had stuck a pin in a socket as a kid, it was extremely painful for me to watch.

Oops, I mis-parsed your comment at first.

I thought you meant....

"it was extremely painful for me to watch [myself from outside my own body]."

What disturbed me most was the prolonged length of the event.

Hehe, I find it ironic(although completely expected) that the stackexchange users' google search link now results in the stackexchange question itself as well as this HN discussion as the top results.

Well, and I find it sad that link #4 takes you to an article that, among other things, says:

Science continues to show us complexity that defies chance explanations, and speaks eloquently of the Creator's hand.

That drawing is priceless.

I would assume the voltage drop per square inch is effectively minimal. Over the span of the body, it adds up. The catch is, the fish isn't contorting its posture to shock itself.

Poor small fish :(

http://www.youtube.com/watch?v=fbkv5xOLvnA

So, is that how it works for electric sheep as well?

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