Animal and Electrical Output Question (I don't know the correct wording...)

[INRM]

Okay...

Some animals like sharks I've been told can actually detect bio-electric fields produced by organisms (i.e. a shark can detect the electrical activity produced by the nerves signalling the heart muscles to beat at close range)... Does this capability apply to any land based animals? Or only animals that live in water where electrical current conducts better?

How much bio-electrical output does nerves signaling a heart to beat or muscles to contract produce?

[fuelair]

The only land animal I spotted in a quick search was land snails and magnetic rather than electrical field.

[casebro]

I think we have a surveillance device that works that way. The "sees through walls" stuff.

Hmmm, radio waves? I wonder what frequency it works on? Anybody got an ecg printout? or electromylogram? Or how a pacemaker works?

If so, do we know of any animals sensitive to radio waves? Epileptic seizures near radar towers?

[blutoski]

Okay...

Some animals like sharks I've been told can actually detect bio-electric fields produced by organisms (i.e. a shark can detect the electrical activity produced by the nerves signalling the heart muscles to beat at close range)... Does this capability apply to any land based animals? Or only animals that live in water where electrical current conducts better?

How much bio-electrical output does nerves signaling a heart to beat or muscles to contract produce?

I had a look at some experiments, and while it's clear the fish are detecting an electric field, I'm not sure that the field in question is produced by a prey's nervous sysem.

Even humans can detect an electric field - I can easily feel my hair standing on end in the presence of a sufficiently strong electric field. It's a matter of sensitivity, and secondly a question about whether a predator actually uses this ability for detecting prey, even if they have it.

ETA: regarding water as a conductor... it looks like the zoologists who are testing sharks believe it is the electric field that is detected, not a current.

[The Man]

http://en.wikipedia.org/wiki/Shark

Electroreception
Main article: Electroreception


Electroreceptors (Ampullae of Lorenzini) and lateral line canals in the head of a shark.
The Ampullae of Lorenzini are the electroreceptor organs of the shark, and they vary in number from a couple of hundred to thousands in an individual. Sharks use the Ampullae of Lorenzini to detect the electromagnetic fields that all living things produce.[29] This helps sharks (mostly the hammer head) find its prey. The shark has the greatest electrical sensitivity known in all animals. This sense is used to find prey hidden in sand by detecting the electric fields inadvertently produced by all fish. It is this sense that sometimes confuses a shark into attacking a boat: when the metal interacts with salt water, the electrochemical potentials generated by the rusting metal are similar to the weak fields of prey, or in some cases, much stronger than the prey's electrical fields: strong enough to attract sharks from miles away.[citation needed] The oceanic currents moving in the magnetic field of the Earth also generate electric fields that can be used by the sharks for orientation and may be used in navigation.[30]


See also

http://en.wikipedia.org/wiki/Electroreception

It is not so much the detection of “the electrical activity produced by the nerves signalling the heart muscles to beat at close range” but just the electromagnetic field produced by living organisms or disturbances in a field produce by the sensing creature (as in the case of active Electroreception). Were sharks able to distinguish between “nerves signalling the heart muscles to beat at close range” and just the galvanic reaction of a ship in the water they probably would not be attracted to and attack the boat.

[shadron]

We're drifting awfully close to he DKL LifeGuard dowsing machine (referring to casebro's posting above) that Clancy borrowed into his novel "Rainbow 6" (http://www.geocities.com/ResearchTriangle/Facility/1914/dkl-latimes.txt; also search here on randi.org in the archives and in the forum). It claimed to be able to detect the radio signals from heart beats through walls, but failed testing at Scandia Labs. The radio emanations from humans are very low frequency and very small power, which means you need a big antenna and lots of amplification (unless you're right on the spot, like an EKG machine is), and even with them you run into the inability to detect the signals in the noise.

Since human electromagnetic emanations aren't designed as radio, they wander all over the low frequency spectrum from single Hertz up to perhaps several kiloHertz. They certainly aren't coherent like a radio station carrier is. What the receptors on those creatures that have them actually senses is, I believe, the presence of a resistive/capacitive/inductive body's disturbance in the electromagnetic field that they themselves produce in the water or air around themselves - the same sort of thing that contact (touch) sensors use, as in the light fixtures that turn on/off at a touch.

[INRM]

Huh? Humans and animals produce an electromagnetic field?

INRM

[MRC_Hans]

Ahh, my specialty.

All creatures that have muscles and a nervous system produce electrical signals. The most detectable signals come from muscles, both because they have greater amplitude and greater frequency range than heart signals. Brains also make signals.

Strengths and ranges (measured by skin electrodes):

EEG = Electroencephalography = Brain signals:
Amplitude ~ 0.1 mV
Frequency 10-300 Hz

ECG = Electrocardiography = Heart signals:
Amplitude ~ 1 mV
Frequency 0.5-50 Hz

EMG = Electromyography = Muscle signals:
Amplitude ~ 5 mV
Frequency 50-500 Hz

About transmission as radio waves:

Any alternating electrical signal passing through a conductor will, in principle, emit a radio wave. However, the energy emitted depends on the impedance match with the general environment.

The impedance of the general environment is around 300 ohms. The impedance of an antenna depends mainly on its length as a fraction of the wavelength of the signal.

The wavelengths of the above mentioned signals are in the range many miles to hundreds of mails. Thus, the "antenna", which is at best the entire body, is very short compared to the wavelength, which means it has a very high impedance, which means it only couples a very small fraction of the available energy into radio waves. And as the available energy is small to begin with, the emitted radio signal is extremely low, for most practical purposes non-existent.

For aquatic creatures it is a different matter: These signals couple galvanically to the environment, so wavelength is of no importance, and since the impedance of most creature's body is close to that of seawater, there is a very good coupling.

The electrical fields that people talk about when talking about shark's electro perception are not electrostatic fields, they are really electrical energy fields, that is, they consist of both voltage and current.

Hans

[shadron]

Huh? Humans and animals produce an electromagnetic field?

INRM

Electric eels do, lots of fish and sealife do. As Mr_Hans points out, that doesn't work so well for those of us in the air, so use of electrical sensing is not a factor for us (until we discovered radar, of course).

[godless dave]

Thanks for the explanation, Hans.

[Reality Check]

Okay...

Some animals like sharks I've been told can actually detect bio-electric fields produced by organisms (i.e. a shark can detect the electrical activity produced by the nerves signalling the heart muscles to beat at close range)... Does this capability apply to any land based animals? Or only animals that live in water where electrical current conducts better?

How much bio-electrical output does nerves signaling a heart to beat or muscles to contract produce?
As the Wikipedia article on electrolocation (http://en.wikipedia.org/wiki/Electrolocation) states, monotremes also use electrolocation (I knew about the platypus (http://en.wikipedia.org/wiki/Platypus#Electrolocation) but not that the other monotremes also had the ability).

[fuelair]

Huh? Humans and animals produce an electromagnetic field?

INRM
Yes - and unfortunately it 's existance and knowledge of that allows all sorts of fictitious/rip-off medical notions to attach to it's existence. ("Pssst, hey mister wanna get that imbalace in your aura fixed cheap?"):jaw-dropp

[INRM]

Why wouldn't the brain produce the highest electrical output... after all all the signals that the muscles receive to contract come from the brain...

Not just that the brain does a lot of other things (all electrical pretty much) that do not involve muscle signaling so there's all the electrical output to signal the muscles, and electrical output used for non muscle-control purposes...


INRM

[Reality Check]

Why wouldn't the brain produce the highest electrical output... after all all the signals that the muscles receive to contract come from the brain...

Not just that the brain does a lot of other things (all electrical pretty much) that do not involve muscle signaling so there's all the electrical output to signal the muscles, and electrical output used for non muscle-control purposes...


INRM
It depends on what you mean by "highest electrical output". Do you mean the highest voltage or current? Do you mean by volume or surface area? Do you mean when asleep or during vigorous activity?

[MRC_Hans]

Why wouldn't the brain produce the highest electrical output... after all all the signals that the muscles receive to contract come from the brain...

Not just that the brain does a lot of other things (all electrical pretty much) that do not involve muscle signaling so there's all the electrical output to signal the muscles, and electrical output used for non muscle-control purposes...


INRMThe outputs I mentioned are those available on the surface of the body (and thus, in most practical instances, to the outside world). The amplitude of a nerve impulse, if you were to measure it directly, is in the range of 50mV, no matter which kind of signal it is. The reason muscle signals are the most powerful is that muscles are generally close to the skin.

The brain is a faily compact organ stored away in the cranium, and the signal paths are short (if you were familiar with how a current distributes in a resistance network you would realize why this results in a small signal on the outside, but just now, I suggest you take my word for it), so the signal amplitudes are low. If it is any comfort for you, the brain signals are, by far, the most complex of them all.

Hans