The Organization of the Cerebral Cortex

The Organization of the Cerebral Cortex

The Organization of the Cerebral Cortex

The Organization of the Cerebral Cortex

Excerpt

The cerebral hemispheres of all vertebrates are hollow cylinders of nervous tissue with a ventricle for the cavity. At first they are only associated with impulses arising from the olfactory organs but, in the higher vertebrates, connections are developed so that impulses arising from all the sense organs are transmitted to the forebrain and interact there to control the behaviour of the animal.

The hemispheres may be divided into dorsal and ventral regions. Structures known as the basal ganglia develop in the ventral region while, in the dorsal or pallial region of reptiles and mammals, superficial sheets of cells appear that are separated by white matter from the ependymal lining of the ventricle. This pallium is the cerebral cortex, which can be divided into medial, dorsal and lateral regions. In mammals, the medial and lateral parts develop into allocortex, while the dorsal region becomes the much more extensive isocortex characteristic of these animals.

When the histologist begins the study of such a complicated organization, he is compelled to decide upon the features of his material that he will consider relevant to his investigation. As his work proceeds, he may change his views and modify his procedure.

The isocortex is a tissue organized for the transmission and interaction of nerve impulses. Different aspects of this organization are studied by the anatomist, the physiologist and the psychologist. The histologist may decide to study the features that seem relevant to the aspects considered by the other two disciplines. This will be one of the objects of this book.

The acceptance of the neuron theory implies the working hypothesis that three features of the cortex are of primary importance: the total number of neurons, their packing density and their pattern of connectivity. In the cortex, not only is the number of neurons large, but their shapes, sizes, packing density and connective patterns show large ranges of variation be-

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