Following the thread about sleep paralysis, I wondered we have REM while we’re dreaming. I mean : the muscles used to move our eyes are similar to the muscles we use to move a finger (or so I assume). Hence, why is it that these muscles aren’t paralyzed too? Of course, moving your eyeballs is inocuous, while moving your legs could result in standing up and walking right into the nearest wall. But nevertheless, I can’t fathom why whatever substance we produce to paralyze our other muscles wouldn’t have the same effect on the eyes’s muscles.
By the way, why isn’t say, the diaphragm, unaffected, either. I understand that we would die if it was the case, but still, how does it works? Though I’m less bothered by this second question, since I assume it has something to do with them being controled by the neuro-vegetative system…
Crudely put: The brain mechanism that paralyzes us so that we don’t go meandering while dreaming is below where the nerves to the eyes branch off. (Kind of like if you “cut off” the nerves from the middle of the back down, your arms won’t be affected.)
I can dig out a book for a cite when I get home if you wish.
I think the problem may be in thinking that the body “produces something” that paralyzes the body.
The brain while sleeping simply does not send movement signals to the body. That doesnt mean however that any “paralysis” happens.
The brain continues to recieve input which is why pain or other outside stimulus can still wake you.
As for the eye movement, there have been several studies that show that eye movement corresponds to brain function even while awake. For instance many people when deep in thought over a math problem often look up and to the right while someone thinking about something more verbal may look to the left while considering something.
Even in psycho-therapy there are procedures to essentially improve access to the subconcious by simply invoking eye-movements by for example following a light while the psychologist asks questions.
From here. Also worth noting are lab experiments where, for example, cats’ brains are lesioned in the area that is thought to inhibit voluntary motor movements during REM sleep. The cats will get up and hunt, stalk, etc., all while in the REM state.
The term paralysis is very misleading as is your example. The way you have stated it sounds as if all function to the spinal cord is impeded and that is incorrect. If it were true the lack of heartbeat, breathing and other important functions would make sleep a one way trip.
My point was that there is not some substance that is delivered throughout the body that paralyzes particular muscles. Yes there may be a central area that controls motor function but it is not at all clear that that one area is responsible for controlling or stopping movement during sleep.
Obviously no actual “paralysis” of any kind occurs. People move about in their sleep and also respond to outside stimulus such as pinpricks or discomfort, or loud noises, bright lights, etc… Anyone who has been woken suddenly can attest that there is usually not a “lag” between sleep induced “paralysis” and full body function.
Essentially the brain determines what is an appropriate signal to send to the motor functions and whether or not to send it.