Allocortex

Isocortex and Allocortex ( gr ίσος isos "equal" or άλλος allos " different" and the Latin cortex " bark " ) are defined by histologic criteria and selected from various areas of the cerebral cortex. The division of the isocortex corresponds to the research of Korbinian Brodmann, the couple Oskar Vogt and Cécile Vogt as well as the works of Constantin von Economo.

History

A first, much-discussed cortex card designed by Karl Kleist (1879-1960), a pupil of Carl Wernicke ( 1848-1905 ).

Conceptual and methodological delimitations

From the histological differentiation in isocortex and Allocortex the phylogenetic classification of the cortex in the neocortex, and paleocortex Archicortex is basically delineate in terms of methodology. However, whether it is relationships between histological and developmental criteria, is subject to further research.

In humans, the vast majority (90%) of the cerebral cortex of six well-defined layers, the so-called laminae is constructed. These differ in their cellular composition and in the course of the dominant paths. The six-layered cortex called isocortex or homotypic ( same structure ) bark. Some evolutionarily old cerebral areas, especially in the olfactory bulb and the hippocampus, on the other hand is characterized by a varying number of layers, usually two or three laminae. These areas are called Allocortex or heterotypic (ie, " different structure " ) bark.

Layers of the isocortex

After Ariëns Kappers the type shown in the following six layers of cortical fields to have phylogenetically evolved from a primitive three- stratification. Such a three- stratification is typical of the Allocortex. However, objections have been raised against this promising and obvious theory.

Lamina I

• Lamina molecularis (molecular layer): - Receives input of feedback neurons - Has no pyramidal cells

Lamina II

• Lamina granularis externa ( outer nuclear layer): - Receives input of feedback neurons - Is made up of small pyramidal cells, which give it a characteristic granule -like appearance

Lamina III

• Lamina pyramidalis externa ( outer pyramidal layer ): - Is made up of pyramidal neurons, which form with their axons cortico- cortical fiber links

Lamina IV

• Granularis lamina interna ( inner nuclear layer): - Receives afferents from sensory neurons and is therefore very powerful, for example, in the primary visual cortex or in the primary auditory cortex, in the motor cortex, however, hardly pronounced - The inner nuclear layer is crossed by strong beams horizontally running fibers, which are collectively referred to as the outer Baillarger Strip and comes primarily from cortical afferents numerous specific thalamic nuclei - The inner nuclear layer is composed of partially heavily modified pyramidal cells with a stellate appearance and also from non- pyramidal cells

Lamina V

• Lamina pyramidalis interna (internal pyramidal layer ): - Are found in the inner pyramidal layer, the largest pyramid cells with their axons form the main part of the Kortexefferenzen to the deeper centers of the brain, such as the basal ganglia, but not to the thalamus, - Is also found in the precentral gyrus partly particularly large pyramidal cells, which are referred to there as the Betz giant cells, they form with their strong myelin sheaths a substantial part of the corticospinal tract ( pyramidal tract ) - The cells of the internal pyramidal layer, with their axons, the main output system from the cortex - The internal pyramidal layer is traversed by a horizontally extending strip heavily myelinated fibers, which is referred to as internal Baillarger strips, the inner Baillarger Strip houses axon collaterals of neurons of laminae II, III. and IV

Lamina VI

• Lamina multiformis ( Multiforme layer): - The multiforme layer runs without sharp boundaries in the underlying market - It contains, as is clear from the name, along with smaller, morphologically distinct pyramidal cells, numerous non- pyramidal cells - The cells of the sixth layer of the isocortex have afferents and efferents in other cortical layers or to the outside of the cortex ( extrakortikal ), in the lamina VI itself hardly synapses are formed - The pyramidal cells of the innermost layer of the isocortex direct their efferents mainly to the (specific) thalamic nuclei, the kortikothalamischen projections are therefore of the lamina VI, however, the thalamocortical traces terminate in layer IV

Physiology of the cerebral cortex

Set forth above are structures allow no means a comprehensive insight into the physiology of the Neo - and Allocortex in terms of functional anatomy. This is known to arise only from a combination of structural, systematic and topological aspects.

Cell types

The cortex contains at presentation with Golgi staining generally from 5 different types of neurons, which can be in addition to their distribution in the different layers to different functions think.

Layers of Allocortex

For Allocortex include the formations of paleopallium and Archipallium such as the dentate gyrus, with the exception of the cingulate gyrus, which is part of the isocortex - see also the above mentioned formations of the olfactory bulb and the hippocampus. When the phylogenetically old, for Allocortex adjoining structures also the names archicortex and paleocortex have naturalized. The Allocortex has the following layers:

• Lamina molecularis ( molecular layer ): apical dendrites of pyramidal cells
• Lamina pyramidalis ( stratum pyramidale ): cell bodies of pyramidal cells
• Lamina multiformis (stratum oriens ): basal dendrites of pyramidal cells