The cortex comprises the heavily grooved surface of the brain and is composed primarily of gray matter, an area predominated by unmyelinated neurons and neuroglia. Also called the cerebrum or cerebral cortex, the distinctive folding shape of the human cortex developed during evolution as its volume grew more rapidly than the volume of the human skull. The confocal digital image displayed below reveals the structural detail of a rat cortex thin section that was double labeled for GFAP (orange) and cell nuclei (red).

Rat Cortex Specimen: Double fluorescent labels Technique: Confocal Microscopy

The wrinkles of the cortex are made up of grooves, known as sulci, and elevated ridges, called gyri. The deepest sulci are referred to as fissures and the longitudinal cerebral fissure divides the brain into its two hemispheres. At the bottom of the fissure is the corpus callosum, a thick bundle of nerve fibers that links the right and left hemispheres and enables them to communicate. In each person, one of the hemispheres is the most dominant, directing the specialized nervous operations for speech and thought, as well as establishing one’s spatial inclinations.

The cortex is further divided into four lobes using certain constantly present sulci as dividing points. The regions known as the frontal, parietal, temporal and occipital lobes are named for their overlying cranial bones and are each associated with different functions of the brain. For instance, residing in the frontal lobe is an area where complex movements are coordinated, while a portion of the parietal lobe receives sensory information from the body.