How do you pass an argument from a menu to an existing node? I've read many articles on hook_menu but they seem to all talk about creating a page which references the arguments.

for example:

function myModule_menu(){
  $items['node/123/%'] = array(
    'page arguments' => array(1),
    'access callback' => TRUE,
  );
  return $items;

In my Navigation menu, I'd want to use a menu item with: node/123/option1

How would I get the argument 'option1' available to me in for example, the node.tpl.php file to manipulate the rendering of node/123 ?

At the end of the day, I'm trying to do is execute some jquery code based on a menu's argument, but the initial hurdle, how do I get access to these optional arguments on the url?