Cytoarchitectonics of the brain cortex



Cytoarchitectonics is a method by which we study the structure of cortical regions of the brain. This method mainly studies the arrangement of neurons in the cerebral cortex.

The cytoarchitectonics of the cerebral cortex is best imaged by Nissl staining (contains toluidine blue - stains the granular endoplasmic reticulum), impregnation (shows the cytoskeleton, neurofibrils - neurofilaments, neurotubules) or staining for myelin (luxol blue). Neurons in the cerebral cortex are arranged linearly in six layers. There are two basic types of neurons - pyramidal neurons (predominant in the third and fifth layers), star-shaped (granular) neurons (predominant in the second and fourth layers). Other cells found in the cerebral cortex include spindle cells, Martinotti cells, horizontal Cajal cells (interneurons). Due to cytoarchitectonics, we divide the cerebral cortex into homotypic and heterotypic. The homotypic cortex contains six layers, while the heterotypic cortex is divided into the granular cortex (sensory areas, sensory centres - visual, auditory) and the agranular cortex (motor areas, most prominent in the gyrus precentralis). The basic six layers of the cortex include the lamina molecularis, lamina granularis externa, lamina pyramidalis externa, lamina granularis interna, lamina pyramidalis interna, and lamina multiformis.

Lamina molecularis (zonalis)
This layer is also referred to as the molecular layer. Here we find small multipolar neurons (mostly laid horizontally, their dendrites and axons are in this layer - associative function), nerve cell processes, membrana limitans gliae superficialis (formed by plasma astrocyte processes), horizontal Cajal cells and glial cells (predominant).

Lamina granularis externa
This layer is also referred to as the outer nuclear layer. In this layer, we find mainly the bodies of star-shaped cells and small pyramidal cells. These small pyramidal cells are usually polarized opposite to other cells in the cortex - the apex faces the base, the axon faces the molecular layer. The main function of the cells in this layer is associative; we also find dendrites of cells from deeper layers.

Lamina pyramidalis externa
This layer is referred to as the outer pyramidal layer. We find here mainly the bodies of smaller pyramidal cells (the main dendrite facing the lamina molecularis, the axon facing the white matter), star-shaped and Martinotti cells (multipolar neurons of star or spindle shape, which have dendrites close to the cell and the axon facing the lamina molecularis). The main function of most neurons in this layer is associative.

Lamina granularis interna
This layer is also referred to as the inner nuclear layer. This layer is strong in the sensory cortical areas (visual cortex), and almost absent in the motor cortical areas. Small star-shaped (granular) cells and interneurons are the main constituents.

Lamina pyramidalis interna
This layer is referred to as the inner pyramidal layer or lamina ganglionalis. Here we find large cells of - pyramidal cells of Betz (up to 120μm), which dendrite faces the lamina molecularis and axons are part of the pyramidal pathway

Lamina multiformis
It is also referred to as the multiform layer or polymorphic cell layer. There are mainly spindle, granular and Martinotti's cells (large polymorphic neurons).

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