The cerebral cortex structure in the human being is composed of six layers of neurons and neuroglia cells. The Nissl silver impregnation of cell bodies in the early 20th century allowed scientists to make a histological division of the neocortex. It was done according to the dominant structure of each layer. Thus, the following layers were differentiated:
I - Molecular layer: it is the outermost layer, with relatively few nerve cells.
II - External granular layer: it is made up of mostly stellate neurons, with scattered small pyramidal nerve cells.
III - External pyramidal layer: it consists almost exclusively of small pyramidal neurons.
IV - Internal granular layer: it is formed by stellate and small pyramidal neurons.
V - Internal pyramidal layer: it is composed of large pyramidal neurons, which are known as Betz cells.
VI - Multiform layer: it is the innermost layer, which is made up of neurons of varied shapes and sizes.
Nerve tissue support cells (neuroglia), such as astrocytes and oligodendrocytes are found in every layer as they are inherent part of the cerebral cortex structure. Meanwhile, cortical areas that are concerned mainly with information processing are rich in granule (stellate) cells. The granular layers of these regions are also exceptionally thick. Areas, in which nerve impulses are transmitted out of the cortex (primary motor of frontal lobe) are distinguished by layers of large pyramidal neurons (Betz cells).
Image of layer III pyramidal neuron of pre-frontal cerebral cortex.
