The brain is a remarkably complex organ both in its structure and function. At the macroscopic level, it can be divided into three major components: (1) brainstem (which includes medulla, pons, and midbrain), (2) cerebellum (with its cortex and deep nuclei), and (3) cerebral hemispheres (which are composed of cerebral cortex, subcortical white matter, basal ganglia and thalamus, limbic system, and hypothalamus and pituitary). The cerebral cortex itself is divided into frontal, parietal, temporal, and occipital lobes. At the microscopic level, there are two primary cell types: (1) neurons (which receive, process, and transmit information by electrical and biochemical changes mediated, in part, by neurotransmitters) and (2) glia (which are a diverse group of cells with expanding roles in brain development, function, and disease).