AJAX :: To Make Expanding/collapsing CollapsiblePanelExtender From Code Behind Smooth And Animated

I've got a CollapsiblePanelExtender in place on a panel in test and it works like a champ. (I get excited about the simplest things). When I click the panel header it expands and collapses with smooth animation, as expected and desired.

But when I change its state via code behind, it seems I am merely changing its state and somehow bypassing the javascript that controls the smooth animation.

My markup is out of the box. I have added code behind and some javascript, but I am missing the connection. Here is the javascript:

function pageLoad(sender, args)
{
smoothAnimation();[code]....

And here is the code behind:

protected void btnExpand_Click(object sender, EventArgs e)
{
this.CollapsiblePanelExtender1.Collapsed = false;[code]....