Neuronenschichten

Neuronenschichten, also known as neuronal layers or cortical layers, refer to the distinct horizontal strata found within the cerebral cortex of the brain. These layers are characterized by differences in cell density, cell types, connectivity, and functional organization. The most widely recognized model of cortical lamination, described by Korbinian Brodmann, identifies six primary layers.

These layers are numbered from I to VI, starting from the surface of the cortex and moving inwards. Layer I, the molecular layer, is the outermost and contains few neuronal cell bodies, being primarily composed of axons, dendrites, and glial cells. Layer II, the external granular layer, is densely packed with small neurons. Layer III, the external pyramidal layer, contains larger pyramidal neurons and is a major source of corticocortical connections. Layer IV, the internal granular layer, is the primary recipient of sensory input from the thalamus. Layer V, the internal pyramidal layer, contains large pyramidal neurons, including Betz cells in the motor cortex, and is a major output layer to subcortical structures. Layer VI, the multiform layer, is the deepest layer and projects to and receives input from the thalamus.

The precise thickness and cellular composition of these layers vary across different cortical areas, reflecting their specialized functions. For instance, sensory areas have a more prominent Layer IV, while motor areas exhibit a highly developed Layer V. The study of neuronenschichten is fundamental to understanding the processing of information within the cerebral cortex and the organization of neural circuits.