The brain owes its outer appearance of a walnut to the wrinkled and deeply folded cerebral cortex, which handles the innumerable signals responsible for perception and movement and also for mental processes. Indeed, in strictly biological terms, these structures can claim priority over the cere-įIGURE 2.1. But underneath this layer reside many other specialized structures that are essential for movement, consciousness, sexuality, the action of our five senses, and more-all equally valuable to human existence. The cortex contains the physical structures responsible for most of what we call “brainwork ”: cognition, mental imagery, the highly sophisticated processing of visual information, and the ability to produce and understand language. The preponderance of the cerebral cortex (which, with its supporting structures, makes up approximately 80 percent of the brain's total volume) is actually a recent development in the course of evolution. This schematic image refers mainly to the cerebral cortex, the outermost layer that overlies most of the other brain structures like a fantastically wrinkled tissue wrapped around an orange. We do not experience our brain as an assembly of physical structures (nor would we wish to, perhaps) if we envision it at all, we are likely to see it as a large, rounded walnut, grayish in color. Outside the specialized world of neuroanatomy and for most of the uses of daily life, the brain is more or less an abstract entity. 2 Major Structures and Functions of the Brain