Human brain. Healthy human brain, seen obliquely from the front. The brain is made up largely of the convoluted folds (sulci) and ridges (gyri) of the cerebrum. The pattern of folds and ridges is similar, though not identical, in all people. The extensive folding allows a large surface area of brain to be fitted within the head. The cerebrum is divided into two hemispheres which are separated from front to back by a deep fold known as the longitudinal fissure. The cerebral tissues are involved in conscious thought processes and in voluntary body activity. Some of these activities are controlled mainly by just one hemisphere. An adult human brain weighs about 1400 grams.