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Would it be possible for a creature to have a nervous system working at 250 volts? What kind of physiology would it need to sustain that?

Could you use that creature as a power source, to power a television set, for example?

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    $\begingroup$ Voltage by itself is not dangerous/strong. Look at the en.wikipedia.org/wiki/Van_de_Graaff_generator which can generate 100,000 volts and is still safe to touch... $\endgroup$ – Tim B Nov 9 '14 at 12:23
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    $\begingroup$ See the electric eel. $\endgroup$ – Oldcat Nov 13 '14 at 19:56
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It would be infeasible to use such high voltages for the entire nervous system, but very feasible to have multiple voltages in different regions of the nervous system, some of which could be as high a voltage as you are looking for.

The main limiting factor for high voltages is the need for insulation. With wires and nerves, this is manageable (though potentially inconvenient). However, within the brain's computing centers themselves, the amount of insulation needed would have catastrophic effects on the computational density of the brain. Forming a high voltage brain would simply be an evolutionary dead end. It would also prevent any "switching" style logic like that which computers use, as the heat generated during a switch would be overwhelming

Computer CPUs show this trend. They used to operate on 24V, then 12V, then 5V, then 3V. Now some are operating on 1.7V. This was essential as the chips got smaller and densities grew

However, the body is not so lazy. It has no qualms with having different behaviors for different parts. Having a low voltage brain connected to a medium voltage nervous system connected to a high voltage periphery organ designed to emit an electric shock is totally reasonable (and is visible in nature: electric eels).

If you wish to power a TV, voltage is not enough. You also need current, and current*voltage = wattage. Those numbers work out in your favor: A LCD monitor draws about 30W. A quick conversion from watts to Calories per hour (for unit purists like me: kcal/hr) shows that to be about 25 Calories per hour. Powering a LCD monitor wouldn't even qualify as strenuous exercise, though I would probably want the voltage-generating organ to be reasonably large to make sure blood flow would be sufficient (don't make it a pinprick sized point on the left pinkie finger).

A plasma TV can consume around 135W, or 110 Calories. If I were powering that with biology, I would consider making the voltage generating organ on the order of a bicep, just to make sure it can get the energy and oxygen delivered to it for sustained use.

Also, do remember that electricity is a circuit. Electric eels are more than comfortable completing the circuit any-ol-way with the salt water around them. If you want to power a TV, make sure your organism has two "electrodes," so that electrons can flow out of the negative "electrode" and into the positive one. To power a TV, you would thouch those two electrodes to the TV power plug.

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Maybe.

You could have a high voltage, low current nervous system which functioned much like our own. You'd need some explanation of how the high voltage is produced and (if you care about that sort of thing) why the animal ended up with that arrangement, but since there are animals alive today which produce high voltages (though not within their nervous system) and the animal kingdom is full of ad hoc solutions to problems, that shouldn't be too hard.

To power a television set, you're talking about (relatively) high current. Within the brain, we can rule that out immediately, I think. High-voltage, high-current will produce a lot of heat when the same thought processes could be carried out at lower voltage. The same argument applies to sensory neurons. You could have an arrangement where everything is high-voltage and only the motor neurons are high-current; the neural impulse is actually what powers the muscles. That would need relatively little justification (or none) and gives you your scenario where you can tap in to the animal for electrical power.

This physiology can look just like ours, except instead of energy being supplied via chemicals in the blood to a given organ it comes from the nervous system. Presumably something in the brain/spine/whatever is consuming food to produce electrical energy.

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Short answer: No

Longer answer: There's a question at https://physics.stackexchange.com/questions/106966/electric-impluses-inside-nerve-cells that explains fairly well how neurons don't carry electrons like the wires in your TV does, so at minimum you would need an adapter to convert the "bio-energy" for lack of a better word, into regular electricity. Secondly most electric gadgets not running on batteries runs on AC, so you would need to not just feed it electrons, but alternate the flow 50-60 times pr second (different countries different standards), again something the body doesn't do.

Finally neurons are not actually even sending ions along the nerves, but create an electric differential between the inside and outside of the nerve, and when it's triggered at one end, a cascade flows along the nerve releasing that differential. (Then a new electric differential is build up for the next signal that needs to be sent)

So even if we were to somehow superpower the way the nerves works with electric potential, a lot of modification would be needed to that energy to make it usable for regular electric appliances.

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In human-made computers, lower voltage usually means much less power consumption and less heat dissipation.

A neural cell acts like a tiny capacitor, with inner and outer media making two electrodes separated by the rather tiny membrane. The amount of energy required to charge this capacitor is proportional to the square of the voltage. The action potential is usually about 150 mV, so making it 150 V would increase the amount of the required energy by 1000 * 1000 so one million times.

Hence, even if the membrane would be able to hold such a huge potential (a membrane of the usual real world cell cannot), a "high voltage brain" is likely to be very energy inefficient. Apart from the energy consumption, cooling may become a problem. And the brain already uses lots of metabolic energy.

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