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How do static magnetic fields impact the nervous system?

I imagine with sufficiently intense magnetic fields the Lorentz force is going to change the behavior of nerve impulses, but at what field intensity do these issues occur? Which parts of the nervous system are most impacted by these fields? What specifically does the magnetic field interfere with? Are motor nerves more impacted than sensory nerves?

The WHO has some guidelines which suggest that fields of high intensity cause nerve issues, but this seems more related to MRI tech safety and doesn't really go into the biophysics of the situation. Additionally, they talk about issues which appear while moving through the fields, which seems to imply they're talking about low frequency field variation because an MRI field isn't spatially uniform.

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    $\begingroup$ I’m voting to close this question because whether or not something is safe for humans is more of a biology question. $\endgroup$ – BioPhysicist Dec 9 '20 at 16:36
  • $\begingroup$ What constitutes an on topic biophysics question? It seems like this question should also be closed as well then physics.stackexchange.com/questions/61679/… $\endgroup$ – alessandro Dec 9 '20 at 16:59
  • $\begingroup$ Biophysics questions on PSE should be primarily about the physics. I agree that MRI is an important biophysics topic, but since this is Physics Stack Exchange the biophysics problems here need to mainly be about the physics. $\endgroup$ – BioPhysicist Dec 9 '20 at 17:05
  • $\begingroup$ This is absolutely primarily about physics. Nerve impulses involve the motion of charges which are deflected by magnetic fields. Presumably the nerve is capable of dealing with some level of deflection before the impulse fails to transmit. This is only something that's possible in a magnetic field, and thus a question which falls much more in biophysics than in general biology. $\endgroup$ – alessandro Dec 9 '20 at 17:52
  • $\begingroup$ I agree, physics is extremely relevant in this system. I am sorry if I gave the impression I thought otherwise. I am saying that determining whether something is safe is more of a biology question. Physics will not tell you what is biologically safe. $\endgroup$ – BioPhysicist Dec 9 '20 at 18:01
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I don't know anything about long term health effects. The guidelines mentions that noticeable effects begin around 2 Tesla. This is in line with what I have heard. On the other hand, this mentions public exposure limits of 40 milliTesla. Here is a paper from the NIH that discusses health effects of neodynium magnets, but doesn't mention field strength.

Keep in mind that 2 Tesla is an extremely strong field. You are not likely to find it except right next to a large superconducting magnet. Or possibly between the poles of an exceptional research grade non-superconducting electromagnet.

Keep in mind that even if a strong magnetic field has no direct effect on a normal person, it could be harmful to a person with, say, a pacemaker.

Also, a field that strong can turn a stray piece of metal into a dangerous projectile.

Motion in a magnetic field matters because it exerts a force on moving electric charges. $\vec F = q \vec v \times \vec B$. This means for example, a copper wire feels no force, unless an electric current is moving inside it. In people, nerve impules are small brief currents. This may be why people feel effects in large fields. Walking means charges are moving faster.

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  • $\begingroup$ Two of the experimentalists at my university just use human sized water cooled electromagnets that can produce ~9+ tesla fields, so it's not that infeasible. $\endgroup$ – Triatticus Dec 5 '20 at 23:49
  • $\begingroup$ @Triatticus - Thanks. I was not aware of that. I updated my answer. $\endgroup$ – mmesser314 Dec 6 '20 at 0:11

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