magento Block instances can be accessed from the controller


Example

From an action controller:

$this->getLayout()->getBlock('head')->getTemplate();

/**
* Get specified tab grid
*/
public function gridOnlyAction()
{
$this->_initProduct();
$this->getResponse()->setBody(
$this->getLayout()->createBlock('adminhtml/catalog_product_edit_tab_' .
$this->getRequest()->gerParam('gridOnlyBlock')
)
->toHtml()
);
}