Cerebrum

The cerebrum is the largest part of the brain. It's what you probably visualize when you think of brains in general. The outermost layer of the cerebrum is the cerebral cortex, also called the "gray matter" of the brain. Deep folds and wrinkles in the brain increase the surface area of the gray matter, so more information can be processed.

The cerebrum is divided by a deep groove, also known as a fissure. The groove divides the brain into two halves known as hemispheres. The hemispheres communicate with each other through a thick tract of nerves called the corpus callosum at the base of the groove. In fact, messages to and from one side of the body are usually handled by the opposite side of the brain.