Science Questions

What are the spasms that occur as you fall asleep?

Sun, 11th Jan 2009

Listen Now    Download as mp3 from the show New Year, New Naked Science


Vanbar Pontchartrain asked:

What about spasms that occur all over the body when youíre asleep?


Chris - I think what youíre thinking of is a hypnic jerk. When people fall asleep and you can notice this yourself you suddenly jerk violently. Often enough to wake you up again and certainly anybody whoíe sleeping next to you. If youíre on a bus with someone and you donít know them it scare the hell out of them because Iíve done that to people. This is a hypnic jerk and itís to do with the part of the nervous system that paralyses you when you go to sleep. When we go to sleep and we dream you donít want to be acting out your dreams because that could have unfortunate consequences. Thereís a region of the nervous system called the sub-cerulean nervous system in your brain stem which receives information about when youíre going to dream and it also has the ability to switch off the flow of motor systems going down to your spinal cord. It can paralyse your body when youíre going to sleep. When youíre switching in this system, sometimes it gets a bit carried away. You get these jerks as the system is turning on.


Subscribe Free

Related Content

Not working please enable javascript
Powered by UKfast
Genetics Society