The hemispheres consist of an inner core, referred to as white matter, and the cerebral cortex, the gray, wrinkled outer layer. The cerebral cortex is organized into six layers and is the location of most the activity in the cerebrum. The functional units of the cortex are vertical columns of neurons, or nerve cells, that run through the layers. Although specific functions are relegated to some of the layers, most of the neurons in the cerebral cortex are devoted to communicating with other neurons. Thus, the cerebral cortex is essentially a network of neurons necessary to coordinate various activities in brain.