The human brain is a battery, or rather, a collection of approximately 80 billion batteries. Each neuron.in the brain possesses the ability to accumulate a charge across its cell membrane, which results in a small, but meaningful voltage. The average neuron contains a resting voltage of approximately 70 millivolts or 0.07 volts. This is quite small when compared to the 1.5 volts in a AA battery or the 115 volts in a wall socket. What is interesting though, is that although 70 millivolts may seem insignificant, the microscopic scale at which it occurs is fascinating.
Voltage is defined as an electropotential difference between two points. In the case of the AA battery, this potential difference is measured between the top (+) and bottom (-) of the battery and is due to an excess of negative charge at the negative pole. In a neuron, this potential difference is measured across the lipid bilayer and the intracellular side is generally more negative. Normally, the lipid bilayer is around 5 nanometers thick, which means that the 70 millivolt potential difference is separated by only 5×10-9 meters. In contrast, a AA battery’s poles are at each end of the battery and are 2 inches (5×10-2 meters) apart.
When there is a potential difference between two separate points, like the potential difference across the lipid bilayer of a neuron, an electrostatic field is produced. A great example of an electrostatic field is the field generated between the clouds in the sky and the earth during a thunderstorm. This field is produced by a difference in charge that develops between the clouds and the surface of the earth. If this field becomes too strong, a spark of electricity shoots across the gap between the positive and negative poles and becomes lightning! Now the strength of this field is defined by a simple equation:
E = – Δϕ/d
where the strength of the field (E) is directly related to the potential difference (Δϕ, otherwise known as voltage) divided by the distance (d) between the poles. So, in a lightning storm, the electrical field would be measured as the difference in voltage of the earth and the clouds, divided by the distance between them. Lightning is produced when the electrostatic force (E) is around 3 million volts per meter!
How does a lowly neuron, with its 70 millivolts, compare to the awesome power of a lightning strike? We can simply calculate the electrostatic force across the lipid bilayer to find out. We know that the voltage across a neuron’s membrane is 0.07 volts and the average thickness of the membrane is 5 nanometers.
ENeuron = -(0.07 volts) / (5×10-9 meters)
ENeuron = 14 million volts per meter! That’s more than four times the electrostatic force required to produce lightning during a thunderstorm!
I think it’s safe to say that humans really are batteries, and the brain contains more than 80 billion of them. Even crazier is that each of these batteries contains four times the electrostatic force that normally results in lightning during a thunderstorm!
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