$(function() {
    function scroll(direction) {

        var scroll, i,
                positions = [],
                here = $(window).scrollTop(),
                collection = $('.message_box');

        collection.each(function() {
            positions.push(parseInt($(this).offset()['top'],0));
        });

        for(i = 0; i < positions.length; i++) {
            if (direction == 'next' && positions[i] > here) { scroll = collection.get(i); break; }
            if (direction == 'prev' && i > 0 && positions[i] >= here) { scroll = collection.get(i); break; }
        }

        if (scroll) {
        $('html, body').animate({"scrollTop": $(scroll).offset().top-50});
            $(scroll).css('color', 'blue');
            $(scroll).mouseleave(function() {
            $(this).css('color', 'black');
            });
        }

        return false;
    }

    $("#next,#prev").click(function() {
        return scroll($(this).attr('id'));
    });
$('body').keyup(function(event) {
  if (event.which == 74) {
     return scroll('next');
   }
});
$('body').keyup(function(event) {
  if (event.which == 75) {
     return scroll('prev');
   }
});

});

$('html, body').animate({"scrollTop": $(scroll).offset().top-50});

if (direction == 'next' && positions[i] > here + 50) {
    scroll = collection.get(i);
    break;
}