Command for Max y on scrolling MC?

Hi guys,

So I have a movieclip that scrolls via a 'up' and 'down' button on the right, they work fine, however, they don't recognise the top or bottom of the movieclip and as such continue scrolling indefinitely.

Is there a way to set my max/min scroll height so it doesn't go past y(0) or like y(2000)?

code:

onClipEvent (enterFrame) {
if (scrollDown) {
_root.ScrollPaneMain.GuruQuestions._y = _root.ScrollPaneMain.GuruQuestions._y-2;
}

scrollDown = 1;
}
on (rollOut) {
scrollDown = 0;
}