$(this)?

$(this)?

So, I've just recently become enlightened by jQuery and would like to add it to my site, but I'm having a little trouble. I made this basic function:
  1. function showPanel(id) {
  2.      var panel = $(".further_info." + id + "");
  3.      panel.slideToggle();
  4.      $(this).toggleClass("minus");
  5.      $(this).toggleClass("plus");
  6. }
To give an example of its use:

  1. <a class="panel_control plus" onclick="showPanel(0);"></a> <div class="further_info 0">blah blah blah</div>

The panel is displayed correctly, but the classname of the link isn't toggled between "plus" and "minus." Any insight as to what I'm doing incorrectly? Thanks!