Brain neurons carry electrical signals. Why is the brain unperturbed by electromagnetic fields, eg MR scans?
Answer:
Because the way we send a signal is be transmitting a positively charged potassium ion down an organic nerve. We aren't constructed using wires and chips, which are what get effected by emp's etc.
MRI scans work by shifting the dipoles in the water molecules in our bodies. That is a physical effect on the molecules and not a chemical effect so it doesn't change the brain and body chemistry behind the nervous system.
sorry
there are several aspects (some already mentioned in the anwers).
first, our brain evolved in an electromagnetic field of the Earth.
second; magnetic fields used in MRI scan have a certain oscillation speed - they are highly variable and resonate with some particles, but not the chemical nature of neurotransmission.
We wouldn't be using MRI if it wasn't the case!
yvannek makes some very good points. I would also like to add that our nervous system does not seem to respond well to external signals and electromagnetic fields because they are uniform and symmetrical. In other words, neurons respond best to signals made up of sharp rise and fall edges such as might be found in square-wave or triangle shaped signals. Brain cells do not respond well to signals in the shape of linear sine-waves.
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