[SalesForce] Action function not rerendering

Here is the visual force page:

<apex:page controller="MyNotesController" showHeader="false" sidebar="false" >
     <apex:includeScript value="/support/console/25.0/integration.js"/>
    <style> 
        html body.sfdcBody {
            background-color: #FFFFCC;
        }
    </style>



    <apex:form style="overflow:auto;width:750px;height:300px;background-color:#FFFFCC; border:0px; margin:0px;">


       <apex:outputPanel id ="noteListSection">
        <apex:dataList id="noteslist" value="{!noteslist}" var="note"  rendered="{!showNoteList}">
        <!--<apex:outputText value = "{!note.id}"/> -->
            <apex:outputLink onclick="openNote('{!note.id}');return false;"><apex:outputText value="{!note.Note_Header__c}"/> </apex:outputLink>
        </apex:datalist>

        </apex:outputpanel>


         <apex:outputPanel id="noteDetailPanel" rendered="{!showNoteDetail}">  

            <textarea id="notesInput">  {!Notes}</textarea>  
            <!--<textarea id="notesInput" style="overflow:auto;width:750px;height:300px;background-color:#FFFFCC; border:0px; margin:0px;" onkeyup="saveNotes();" >  {!Notes}</textarea>  -->
        </apex:outputPanel>

        <apex:actionFunction action="{!setNotes}" name="setNotesJS" reRender="">
            <apex:param name="note" assignTo="{!Notes}" value=""/>
        </apex:actionFunction> 
        <apex:actionFunction action="{!openNote}" name="openNotesJS" reRender="noteListSection,noteDetailPanel">
            <apex:param name="noteId" assignTo="{!noteId}" value=""/>
        </apex:actionFunction> 



    </apex:form>

    <script>
        var notesTextArea = document.getElementById('notesInput');        
        function saveNotes() {
            setNotesJS(notesTextArea.value);
        }
         function openNote(noteId) {
            //alert('opennote');
            //alert('opennote'+noteId);
            openNotesJS(noteId);
            return false;

        }


    </script>

</apex:page>

Controller code :

public class MyNotesController {

    My_Notes__c myNotepad;
    Integer notesCount;    
    public List <My_Notes__c>  noteslist {get;set;}
    public String Notes{ get; set;} 
    public String noteId{ get; set;} 
    public boolean showNoteDetail {get; set;} 
    public boolean showNoteList {get; set;} 

    public MyNotesController() {
         notesCount = [Select COUNT() from My_Notes__c where ownerId = :UserInfo.getUserId()];   
         //if(noteslist==null ||!noteslist.isEmpty())      
        getNoteslist();
         //showNoteList =true;
         //showNoteDetail =false;
    }

    //public void init() {
   public List <My_Notes__c> getNoteslist(){
         //My_Notes__c  notesObject;
         System.debug('init  method'+ NotesCount);
         if (notesCount > 0) {

             noteslist = [Select id,Note__c,ownerId,Note_Header__c,lastmodifiedDate from My_Notes__c where ownerId = :UserInfo.getUserId() order by lastmodifiedDate];   
              showNoteList =true;          
         }
System.debug('Notes noteslist ' + noteslist.size());
         return noteslist;
         //myNotepad = notesObject;
         //Notes = notesObject.note__c;
    }


    public void createNewNote(){
           // notesObject = new My_Notes__c();
           //  notesObject.ownerId = UserInfo.getUserId();

    }
    public pagereference openNote(){
           // notesObject = new My_Notes__c();

           System.debug('Inside openNote method');
        System.debug('Note Id1=>' + noteId);
        My_Notes__c notesObject  = [Select id,Note__c,ownerId,Note_Header__c,lastmodifiedDate from My_Notes__c where id = :noteId limit 1];             
           Notes = notesObject.note__c;
          System.debug('Notes data ' + Notes);  
        showNoteList=false;
        showNoteDetail =true;

        System.debug('Inside openNote method : showNoteDetail'+showNoteDetail);
        System.debug('Inside openNote method : showNoteList'+showNoteList);
        //PageReference thisPage = ApexPages.currentPage();
        //thisPage.setRedirect(true);
        return null;

    }
}

My problem here is that the output panel "noteDetailPanel" is not rendering. any pointers would be helpful.