Call JS at end of UpdatePanels content loading

I'm trying to figure out how to call a javascript method at the end of an UpdatePanel's content reloading. I know this must be possible, but I'm not seeing how yet.

Here's what I have: one page with an update panel. Contained within the update panel is a series of controls, much like a wizard. Each control has a button that posts back to the server, which then loads a different control. By using the UpdatePanel, the postback is hidden, which is nice. What I want is for every time the control within the UpdatePanel is changed for some custom javascript to run. The script just resets a page-scoped timer that notifies the user his session is about to expire. How can I hook in to the postback and run my one line of script? Thanks.

Of course after hours of searching and posting I finally find an example using the PageRequestManager that does the trick nicely. For the record, the simple script was:

Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
function EndRequestHandler(sender, args)
{ extendSession();// My JS method }