document.observe('dom:loaded',function(){ 
    var scrollbar = new Control.ScrollBar('scrollbar_content','scrollbar_track','scroll_arriba','scroll_abajo');
    
    $('scroll_arriba').observe('click',function(event){
		scrollbar.scrollBy(-50);
		event.stop();
	});
	
	$('scroll_abajo').observe('click',function(event){
		scrollbar.scrollBy(50);
		event.stop();
	});
	
});