[DanInMa]

I would do it this way, but you may have other concerns

<script type="text/javascript">
function expander() {
// Variable to detect window width.
var windowWidth = jQuery(window).width();

 if (windowWidth>768) {
  jQuery(".MenuContent").hide();
  jQuery(".Menuheading").click(function()  {
    jQuery(this).next(".MenuContent").slideToggle(500);
  });
}
};
// Wait for the page to load
jQuery(document).ready(function ($) {
        // Load expander.
expander();
$(window).resize(function(){
expander();
});
});
</script>