Why do some people twitch in their sleep?

Why do some people twitch in their sleep?

Chris Idzikowski (Director of the Edinburgh Sleep Centre) gives expert video advice on: What happens to my brain when I sleep?; What happens to my muscles when i sleep?; What happens to my breathing when I sleep? and more...

Everybody has some degree of twitching during sleep. It's not particularly clear why, possibly because movement isn't coordinated in any sense. And some parts of the brain decide to fire off volumes, some muscles twitch.