Shutter on m4/3 cameras - how it work?

So on my SLR like cameras the shutter is two cloth (or occasionally metal) curtains which whoosh past the sensor with a small open slit open on them to define the time of the exposure. As you reduce the time of the exposure the gap between the two curtains gets smaller.

In the composition phase the curtains are closed - the mirror is down and protects the sensor.

Anyone know how a m4/3 camera manages exposure time? AFAIK the sensor is always exposed - no curtain or mirror covering it. So how does exposure work with m4/3 cameras?

Before the flaming starts - I'm asking out of genuine curiosity / ignorance. I don't have view on the superiority of either system.