ANATOMY [ DIFFERENT PARTS & DIFFERENT RESPONSIBILITIES ( THE AMAZING BRAIN ) ]

FOUR DIVISIONS

Moving inward, we come to the organ itself. The brain may appear to be a Ulllform mass of folded, pink tissue. But a closer look reveals different lobes, regions, structures, and parts that all help regulate body functions, interpret information from the body, and react to stimuli. The brain has four main parts: the cerebrum, diencephalon, cerebellum, and brain stem.

• SHAKESPEARE WEIGHS IN on the human brain in his plays:
• “Tell me where is fancy bred, Or in the heart, or in t he head?”-The Me rchant of Venice
• “The brain may devise laws for the blood, but a hot temper leaps o’er a cold decree.” – The Merchant of Venice
• “Her beauty and her brain go not together. ” – Cymbeline
• “He has not so much brain as ear-wax.” – Trai/us and Cressida

CEREBRUM

This largest, topmost layer of the brain is the cerebrum. It’s what most people visualize when they use their brains to picture their brains. The external layer is called the cerebral cortex. Its outer por- tion is gray from the presence of billions of nerve cell bodies, while the inner portion is white from the tangle ofaxons coated in their myelin sheaths.

In 1999, scientists discovered that Albert Einstein’s inferior parietal lobe, associated with mathematical and spatial reasoning, was 15 percent wider than that of an average brain.

In the cerebral cortex lies the core of information processing that separates humans from other animals, including reason, language, and creative thought. Homo sapiens has more of its brain in the cerebral cortex-approximately 76 percent-than any other animal. (Chimpanzees rank second at 72 percent, while dolphins have only 60 percent.)

FISSURES AND HEMISPHERES

The cerebrum is divided into parts by deep fissures. The largest of the brain’s fissures is immediately evident to the naked eye. Down the center of the cerebrum, separating it into left and right hemispheres, is the longitudinal fissure. The left and right halves of the cerebrum appear to be nearly mirror images of each other.

While they look alike, the two halves perform and control very different functions. The left hemisphere long has been considered the dominant half because of its role in processing language, but the right hemisphere is gaining new attention for its role in emotions and spatial cognition, as well as the integrative function that helps bring bits of information together to create a rich image of the world.

Connecting the two hemispheres are bands of nerve fibers that allow information to be passed back and forth between the two halves of the brain. The largest bundle, contain- ing about 200 million nerve fibers, is the corpus callosum.

Two divides known as the Sylvi an fissure and central sulcus lie on the outside edges of the hemispheres. Their locations serve as boundaries on a map, dividing the hemispheres further into four lobes. The frontal lobe lies forward of the central fissure. Between the Sylvian and central fissures are two lobes that merge together, the parietal followed by the occipital. Behind the Sylvian fissure is the temporal lobe.