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What's the source of electricity for the human brain?

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I keep hearing that there's always electrical activity taking place inside the human brain.Our heart and various other organs function because it receives electrical signals called impulse.But what's the "voltage source" for the brain? Where does it receives signals ?Does it generate on it's own ?If so how?

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[dead] mebesilly
The electrical potential is due to two effects: 1. the Donnan equilibrium 2. active ionic pumps that maintain differential concentrations of Ca++, K+, Na+, and Cl- across neural membranes.
hollerith
Almost all of the energy needs of the human body is satisfied by molecules of adenosine triphosphate (ATP) which is produced in the mitochondria. Every cell contains many mitochondria.

Neurons use the ATP to pump sodium and potassium ions across the cell membrane (from inside the cell to outside the cell or vice-versa) causing an electric gradient across the membrane much like the gradient in a capacitor. When the neuron "fires", the "capacitor" is discharged. The discharging happens much faster than the charging caused by the sodium and potassium pumps. The neuron is arranged so that this discharging process tends strongly to "cascade" or "propagate" down the long thin part of the neuron -- and that is a simplified explanation of how "electrical signals" travel in the brain.