Indiana University explains that gyri and sulci, which comprise the wrinkled surface of the brain, are an adaptation that allows the brain to have more surface area. This is important because the internal volume of an animal’s skull limits the size of its brain. By developing a greater amount of surface area, the brain can contain more neurons, despite the limits to its volume, which are imposed by the skull.
The outer covering of the human brain is called the cerebral cortex. As explained by Wikipedia, the cerebral cortex is primarily composed of gray matter, which contains blood vessels and the bodies of neurons. The gyri are the raised portions of the cortex, while the sulci are the deep fissures. The University of Washington asserts that the sulci and gyri are very successful at increasing the surface area of the brain. In total, the cerebral cortex has a surface area of over 300 square inches, or about the size of an unfolded piece of newsprint, despite weighing only about 3 pounds.
The University of Washington states that the cerebral cortex is divided into two hemispheres, each of which is divided into four different lobes. The occipital lobes are located at the rear of the head, while the frontal lobes are located at the front. The parietal lobes are on top of the head, and the temporal lobes are on the sides of the head.