Complex sentence: The first is the cerebral cortex which is the gray matter covering the outer layer of the brain, and the other is a structure located in the brainstem, called reticular activating system (RAS or ARAS).
Split into simpler sentences: The first is the cerebral cortex which is the gray matter covering the outer layer of the brain. The other is a structure located in the brainstem, called reticular activating system (RAS or ARAS).