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
| Layers | Components | Afferents | Efferents | |
| I – Molecular | Axons and Dendrites (Cell processes) | From other regions of Cortex and Brainstem | To other regions of cortex (Intra-cortical Association functions) | |
| 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
- Subiculum
Mesocortex: A transitional type of 3 to 6-layered cortex between neocortex and allocortex –
- Parahippocampal gyrus
- Pre- and Para-subiculum
- Insula
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
He is the section editor of Orthopedics in Epomedicine. He searches for and share simpler ways to make complicated medical topics simple. He also loves writing poetry, listening and playing music.
