Magnetic Field of the Human Body?

[Proteus]

I can't seem to find this anywhere. I know that the nervous system produces a magnetic field, as it basically consists of electrical conductors. What I wonder is, how strong is this magnetic field in teslas?

[insane_alien]

you'd have to find out how much current is in the nerve first. and there will only be a miniscule magnetic field when the nerve is active.

 

according to this http://en.wikipedia.org/wiki/Magnetoencephalography

 

magnetic fields are on the order of 10^-15 T (1fT)

 

the earths magnetic field is 10 orders of magnitude greater than this.

[Proteus]

Blasted. I can't seem to find any relevant numbers, neither for the total number of axons in the body nor for the current per axon. Hasn't the magnetic field of the body ever been observed?

[insane_alien]

read the link. its all about looking at the magnetic field of the mind.

 

the body itself does not have a static magnetic field. only a varying one due to currents in the nervous system which are very very tiny and have a correspondingly tiny magnetic field.

[Mokele]

The nervous system doesn't really work the same way a wire does - it's not a stream of electrons, but rather a localized change in potential that propagates down the axon.

 

It's also worth noting that information flows in *both* directions in most nerves, at frequencies that constantly vary. Plus, muscles are electrically excitable and are HUGE relative to nerves.

 

Humans *do* produce a magnetic field, but it's chaotic and messy.

[Proteus]

Ah, sorry, I didn't see the link last time I looked.

 

Mokele, is the electrical activity of the muscles, or even of the peripheral nervous system, really that significant? You'd expect most of the magnetic field to be caused by the brain. Besides, if the magnetic field of the rest of the body was comparable, would magnetoencephalography even still be possible?

[Mokele]

It depends where you're looking. In the head, the brain vastly predominates the signal, in the legs, the muscles dominate. To do magnetoencephalography, you just have to focus the detector on the head rather than the rest of the body. Besides, no real processing occurs until the spinal cord, and even there it's minimal.

[GDG]

The brain produces around 10^-14 to 10^-12 Tesla; skeletal muscle, around 10^-10 T; the heart, around 5 x 10^-10 T. See, e.g., S. Yamada and I. Yamaguchi, "Magnetocardiograms in Clinical Medicine: Unique Information on Cardiac Ischemia, Arrhythmias, and Fetal Diagnosis", Internal Med (2005) 44:1-19. There's a handy chart on the third page. Unfortunately, it does not have figures for the body as a whole.

[Mokele]

Excellent find!

[Fimbulfamb]

If such a field is produced (which it very probably is, since there definitely are charges moving about in the body) it will be very weak, since each charge's field points in a random direction, so as to cancel out with others.