Which block is responsible for rendering javascript in Magento?

Mage_Core_Model_Layout
Mage_Core_Model_Layout_Update
Mage_Core_Model_Design
Mage_Core_Model_Design_Package
Mage_Core_Controller_Varien_Action

Mage/Core/Block/*

Mage_Core_Block_Abstract
Mage_Core_Block_Template
Mage_Core_Block_Text
Mage_Core_Block_Text_List
Mage_Page_Block_Html_Head