The neocortex have 6 layers and allocortex have only 3 layers.
The 6 layers of Neocortex:
Orientation of layers:
- Outer: Towards meaninges
- Inner: Towards white matter
Idea about the layers:
- Molecular or plexiform: Only cell processes
- Granular layer: Densely packed stellate cells
- Pyramidal layer: Medium and Large pyramidal cells
- Multiform layer: Different types of cells
- Pyramidal cells are absent in inner granular layer
|I – Molecular||Axons and Dendrites (Cell processes)||From other regions of Cortex and Brainstem||To other regions of cortex|
|II – External granular||Densely packed Stellate cells + Small pyramidal cells|
|III – External pyramidal||Loosely packed Stellate cells + Medium pyramidal cells|
|IV – Internal granular||Densely packed Stellate cells only||+ From Thalamus|
|V – Internal pyramidal||Large pyramidal cells only (few stellate cells) – Giant Pyramidal cells of Betz||+ From Brain stem||To Brain stem & Spinal cord (Projection fibers)|
|VI – Multiform||Multiple sized pyramidal cells + Loosely packed stellate cells||To Thalamus|
The 3 layers of allocortex:
- Molecular layer
- Pyramidal layer
- Multiform layer
Allocortex is found in: Limbic system
- Olfactory cortex
- Hippocampal formation
Mesocortex: A transitional type of 3 to 6-layered cortex between neocortex and allocortex –
- Parahippocampal gyrus
- Pre- and Para-subiculum
Neurons of the cortex:
- Pyramidal cells:
- Large layer V pyramidal cells project axons to brainstem and spinal cord.
- Smaller layer II and III pyramidal cells project axons to other cortical areas.
- Stellate cells: Interneurons whose axons remain within the cortex
- Fusiform cells (in deeper layers): Gives rise to corticothalamic projections
- Horizontal cells of Cajal
- Cells of Martinotti
Bands of Baillarger: Formed by high concentration of horizontally arranged nerve fibers.
- External band: In layer IV
- Internal band: In layer V
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