cakephp ajax function issue

I have 2 functions in "events" (index, event_ajax)controller in my cakephp(2.5) web site. I'm trying to load HTML block to 'index.ctp' page by calling to 'event_ajax' function using ajax. When I call to this function it shows nothing. Look at 'net' tab in firebug it shows internal server error and 'net'->'Response' tab I can see whole layout is loaded.

I'm little confuse about in this scenario, can any one give a little explanation for following questions??? thanks in advance :)

1. Is it possible to call actions in same controller using ajax function ??
2. How 'Response' tab shows layout when '$this->layout' is set to NULL ??
3. when type url 'example.com/events/event_ajax', output data still '$this->autoRender=false'. how can this happen ??

this is my 'event_ajax' action.

   public function event_ajax($x=1) {
        $this->layout       =   NULL;
        $this->autoRender   =   false ; 
        $contName           = $this->Page->conName($x);
        $latestContEvents    = $this->Page->latestContEvent($x);

        $internal   =   '';
        if (!empty($latestContEvents)){ 
          foreach ($latestContEvents AS $latestContEvent){ 
                $internal   .=   '<li class="pull-left"> <div class="content-wrapper">'..... //do something                  
        }
        else {
            $internal   =   '<p>&nbsp;&nbsp;&nbsp; No events found for this continent</p>';          
        }

        $ContEvents =   '<div class="carousel events-location-carousel">'.$internal.'</div> ';

        return $ContEvents; 
       // return json_encode($ContEvents);

    }