The cerebral cortex is phylogenetically the youngest part of the brain, and carries out a huge range of discriminative and cognitive processes relating to affective behavior, motor function, somatosensory perception, integration, and mnemonic function. It is structurally highly organized in layers of nerve cells and processes.
In external appearance, the cerebral cortex has a convoluted, corrugated appearance both in situ and after removal from the cranial vault. The surface of the cortex is deeply folded, which greatly increases its surface area. The visible crest of a fold is called a gyrus, and the invisible depression between folds is called a sulcus. One of the main landmark sulci of the brain is the central sulcus (or sulcus of Rolando). Some sulci are relatively deep, and are termed fissures. The main fissures include the very large one separating the two hemispheres, the interhemispheric fissure. Another is the fissure that runs approximately horizontally along the lateral surface of the brain, called, appropriately, the lateral fissure or fissure of Sylvius. Viewed laterally, the surface is composed of four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe.
The frontal lobe is the largest of the cortex and extends from the central sul-cus to the front or rostral end of the cortex. Several gyri can be distinguished on the frontal lobe surface. These are the precen-tral gyrus, which is defined by the central and precentral sulci, and which holds within itself the motor cortex (see p. 176); rostral to the precentral sulcus are the superior, middle, and inferior frontal gyri.
The parietal lobe is the area immediately behind or caudal to the central sulcus and it runs caudally, approximately to the parieto-occipital sulcus. It is bounded ventrally by the lateral fissure. The somatosensory cortex (see p. 174) is con tained within the postcentral gyrus in the parietal lobe, just caudal to the central sulcus. Caudal to the postcentral gyrus is the superior parietal lobule, and ventral to that is the inferior parietal lobule.
The temporal lobe lies ventral to the lateral fissure, and includes the inferior, middle, and superior temporal gyri. These run approximately parallel to the lateral fissure. The superior temporal gyrus holds the area of the primary auditory cortex.
The occipital cortex occupies the most caudal end of the brain and may be considered to lie caudal to a line drawn through the parieto-occipital sulcus and the occipital notch. The visual cortex (see p. 286) is located in this lobe, around the calcarine sulcus.
Although not shown here, there is an area of cerebral cortex called the insula, which is buried, deep in the lateral fissure. Its borders are defined by the frontal, parietal and temporal cortex. The rostral end of the insula is a poorly understood part of the limbic system and the caudal end of the insula is involved in somato-sensory processing.
There is also a limbic lobe, defined by Broca. The limbic lobe is made up of the cingulate, hippocampal and parahippo-campal gyri. The cingulate gyrus is a primitive form of the cerebral cortex, having fewer layers of cells and is involved in the mediation of behavioral components of endocrine, olfactory, skeletal, and visceral function, and in aspects of memory.
precentral gyrus, precentral sulcu:
lateral view of left side of brain precentral gyrus, precentral sulcu:
superior fronta sulcus superior frontal, gyrus middle frontal, gyrus inferior frontal, gyrus lateral fissure.
Inferior temporal gyrus paracentral gyru:
superior frontal-gyrus straight gyru:
central sulcus central sulcus cingulate gyrus.
superior frontal-gyrus straight gyru:
.parietooccipital sulcus calcarine sulcus callosal fissure
.parietooccipital sulcus calcarine sulcus callosal fissure sagittal section of left side of brain
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