eli5: How do MRIs make your muscles twitch

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Went for an MRI recently, and my mucl8wwrs twitching every time the machine made a sound. The tech said it was nerve activation, but how could a magnetic field make my arm twitch?

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Anonymous 0 Comments

Magnets and electricity are more-or-less the same thing- electrons- that is the negatively charged particles in atoms, moving around. In a magnet, they’re going around and around a certain way. In an electric current, they move around in a bunch of different ways, some of them inside of your body.

When your brain tells your muscles to do something, it sends an electrical impulse down your nerves, the parts of your body that tell it to move and then report back to the brain what the body is feeling, to the muscle, which makes them tighten or loosen. It’s also why when you electrocute yourself with something, your muscles might move on their own, and why seizures can make someone twitch, those electrical impulses are being interrupted or being thrown around in ways that don’t make a normal movement.

An MRI is basically a great big giant magnet that they aim at your body, and then take images based off the way those particles get bounced around. BUT, sometimes those particles hit a nerve by mistake, and that creates an electric impulse that your nerve sends down the line, and makes your muscles tighten or loosen, so you twitch.

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