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Cerebral Hemispheres
Introduction
The cerebral hemispheres contain the very essence of our being. They allow us to speak, form complex thought, interact with the world, have interpersonal relationships, understand humor, and more. They accomplish this through complex organization and specificity. A theme throughout the organization of the nervous system is that everything is arranged in a highly organized and predictable manner. Nothing in the nervous system is an accident.
Structural Organization
The major landmarks of the cerebral hemisphere are shown in Fig. 2.2.1 . During the explosive development of the central nervous system, the cortex develops gyri (folds of brain tissue) and sulci (the spaces between them) to increase surface area. Several deeper sulci are the fissures. The interhemispheric fissure separates the left and right halves of the brain. On each side, the central sulcus separates the frontal and the parietal lobes, and the deeper Sylvian fissure separates the frontal and parietal lobes from the temporal lobe. The parietooccipital sulcus, only visible on the medial aspect of the cortex, separates the parietal lobe from the occipital lobe. The gyrus just rostral (anterior) to the central sulcus is the precentral gyrus, and the gyrus just caudal (posterior) to it is the postcentral gyrus. A key in the structural arrangement of the cortex is that the brain is typically relatively symmetric; this is structural symmetry rather than functional symmetry. In most people, the left hemisphere is the dominant hemisphere. It is identified as such because of its role in language.
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