CEREBRUM

in human anatomy, the largest and uppermost portion of the brain. The cerebrum is one of the three main divisions of the brain (the others being the cerebellum and the brain stem). It consists of the cerebral hemispheres and accounts for two-thirds of the brain's total weight. The cerebrum is considered to be the seat of conscious mental processes; it contains centres for sensory integration and the controls of voluntary movement and higher intellectual functions, including speech and abstract thought. The cerebral hemispheres consist of an inner core of myelinated nerve fibres, the white matter, and a heavily convoluted outer cortex of gray matter; the extensive development of the outer cortex differentiates the brain of humans from those of other mammals. Nerve fibres in the white matter serve chiefly to connect functional areas of the cerebral cortex, although some core structures also have important independent functions. A deep fissure running from front to back divides the cerebrum into two hemispheres, each controlling the activities of the opposite side of the body. One of these hemispheres is functionally dominant, concentrating the specialized nervous apparatus for speech and thought and determining spatial preferences such as right- or left-handedness. The other controls more subtle, complex perceptions, such as the recognition of faces. A connection between the two hemispheres is effected by the corpus callosum, a thick band of white matter that allows the integration of sensory data and functional responses from both sides of the body. Other important cerebral structures include the hypothalamus, which controls metabolism and maintains homeostasis, and the thalamus, a principal sensory relay centre that is involved with the emotions and instincts. These structures surround spaces (ventricles) filled with cerebrospinal fluid, which helps to supply the brain cells with nutrients and provides the brain with shock-absorbing mechanical support.