Trigger a button Via Code?

Hello, im making the switch to AS3, and ive been coming across a few things once so simple that are confusing me a bit.

How do i trigger a button action via code?

in as2, i would simply type something like this

[AS]button.onRelease = releaseFunction

and the button would act like it was released.

in AS3, i can tell the button what function to call, but how do i tell the button to fire?

[AS]button.addEventListener (MouseEvent.MOUSE_UP, bRelease);[/AS]

…since [AS]button.onRelease()[/AS] doesn’t work?