Cerebral hemispheresh

• These comprise the cerebral cortex or pallium, a mantle of grey matter, and the underlying white matter. The white matter consists of multiple inter-and intra-hemispheric tracts connecting the cortical and subcortical structures of grey matter.

• Each hemisphere comprises four lobes: frontal, parietal, temporal and occipital.

• The neocortex comprises six layers: molecular or plexiform, external granular, external pyramidal, internal granular, internal pyramidal or ganglionic, and multiform or fusiform.

• The six-layered isocortex displays two patterns of cellular arrangement: the homotypical cortex with the six layers easily recognisable, and the hetero-typical cortex with a predominance of certain cell types.

• The surface of the cortex demonstrates convolutions and folds, the sulci and gyri respectively, which serve to significantly increase its surface area.

• The cortex is divided into cytoarchitectural areas based on the types, amounts and arrangement of neurons in each area. Brodmann's system of numbering cerebral surface areas (52 areas in each hemisphere), which is based on microscopically identified variations in neuronal architecture, is still widely used in spite of its imperfections. Along with regional variations in cytoarchitecture, there are variations in neurochemical activity and in physiological function.

• The lobes are connected by fibres of white matter, which can be classified as: Association fibres

Ipsilateral: short; long (cingulum; uncinate fasciculus; arcuate or short longitudinal fasciculus)

Commissural: anterior commissure; corpus callosum; posterior commissure Projection fibres Afferent: corticopetal Efferent: corticofugal

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