Dr. Matt Walker

And that's the reason that we sometimes call it paradoxical sleep.

Your body is completely immobilized, utterly inactive, but your brain is fervent with its activity.

By the way, people should not worry when I say that your muscles are shut down.

And what happens is that just before you go into REM sleep,

there's a bursting activity that will go up into your brain to light up your cortex.

But there's another signal from the brainstem that's sent down all the way down the spinal cord to the alpha motor neurons in the spinal cord that will essentially create this inhibition.

It's only your voluntary skeletal muscles, meaning that your involuntary muscles, things, for example, such as your respiration that helps you breathe in your heart.

That's the reason that we

you know, survive and live another day after sleep.

So don't worry about that too much.

With two exceptions though, there are two sets of voluntary muscles for reasons that we still don't know either that are spurred from the paralysis of REM sleep.

One of them is the extraocular muscles.

And that's the reason that when you go into REM sleep, you can have these darting horizontal movements back and forth.

Those should also have been paralyzed, but they're not.

And then oddly, there is a muscle in the middle inner ear muscle

that does not undergo the paralysis.

And it will also twitch too, just like your eyes.

But I'm getting into the weeds.

So that's what's happening in these different physiological states.

And to your question, when you don't have any muscle tone whatsoever, maybe that is in part the reason why, A, you can start to have these dreams of absent gravitational pull, meaning you can start to fly.