Ascending reticular activating system

The ascending reticular activating system (ARAS) is a network of nerve cells in your brain that helps you stay alert and wake up each day. It does this by sending messages to the parts of your brain that control your level of alertness. So, for example, if something exciting or scary happens, the ARAS will send a message to the parts of your brain that control alertness and make you more aware and ready to respond. As well, if you're tired, the ARAS will send a different message and help you become more alert and awake.