scroller wheel

I have a functioning scroll bar using the below code but the mouse wheel doesn't work with it.  Can anybody tell me what would need to be added to make that work?

var rect:Rectangle;

var scrollerMinY:Number = scrollbar_mc.scroller_mc.y;

var contentMaxY:Number = content_mc.y;

var padding:Number = 40;

scrollbar_mc.scroller_mc.buttonMode = true;

scrollbar_mc.scroller_mc.addEventListener(MouseEvent.MOUSE_DOWN, dragIt);

function dragIt(e:MouseEvent):void {

  rect = new Rectangle(3, 3, 0, 327);

  scrollbar_mc.scroller_mc.startDrag(false, rect);

  stage.addEventListener(MouseEvent.MOUSE_UP, dropIt);

  scrollbar_mc.scroller_mc.addEventListener(Event.ENTER_FRAME, scrollIt);

}

function dropIt(e:MouseEvent):void {

  scrollbar_mc.scroller_mc.stopDrag();

        scrollbar_mc.scroller_mc.removeEventListener(Event.ENTER_FRAME, scrollIt);

}

function scrollIt(e:Event):void {

  var scrollerRange:Number = rect.height;

  var contentRange:Number = content_mc.height - mask_mc.height + padding;

  var percentage:Number = (scrollbar_mc.scroller_mc.y - scrollerMinY) / scrollerRange;

  var targetY:Number = contentMaxY - percentage * contentRange;

  content_mc.y = targetY;

}