parent inherit from child - sort of

Hi all
At the moment i am looking to make a menu system were the all the sub items of the menu are hidden (and the sub nodes appear for each node when the user clicks on the parent node just like a normal menu) but were the as the user goes from page to page i want the menu to appear open up to the particular node that represents the current page the user is on. The way in which i am identifying this selected node is by giving it an ID or class name of "selectedNode". As this node could be several layers down (i am basing the menu around nested unordered) what i would like to do is some sort of inheritance were i give the class identified by "selectedNode" display:block instead of display:none and then i somehow say that the 'ul with a child element identified by "selectedNode" is display:block instead of display:none'.

Now i know you can do this the other way around by doing something like below
    #mainMenu ul {
        display:block
    }
and what this will do is make any child element that has the parent identified by "mainMenu" display. I need to do the reverse, so in others words a parent who’s child is identified by "selectedNode" will display.

Thanks
ant

This is a snippet of what the menu structure is like

    #mainMenu ul {
        display:block
    }
       <ul id="mainMenu">
          <li>Weblog</li>
          <li>Articles
             <ul>
                <li>Red Fox</li>
                <li id="selectedNode" >Pitching Inning                  <<<< This item is the one that relates to the current page
                   <ul>
                      <li>Part I</li>
                      <li>Part II</li>
                   </ul>
                </li>
                <li>That Long</li>
             </ul>
          </li>
          <li>About</li>
          <li>Cars
             <ul>
                <li>Holden</li>
                <li>Ford</li>
             </ul>          
          </li>
       </ul>

At the moment its default view would look like            
    - Weblog
    - Articles
    - About
    - Cars


But with the way i hope i can get this inheritance to work its like the following were all i have to do is give red fox and id of selectedNode
    - Weblog
    - Articles
          - Red Fox
          - Pitching Inning
    - About
    - Cars