Cerebral Cortex Layers (Microanatomy) Simplified

The neocortex have 6 layers and allocortex have only 3 layers.

Cerebral cortex layers microanatomy

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
LayersComponentsAfferentsEfferents
I – MolecularAxons and Dendrites (Cell processes)From other regions of Cortex and BrainstemTo other regions of cortex

(Intra-cortical

Association functions)

II – External granularDensely packed Stellate cells + Small pyramidal cells
III – External pyramidalLoosely packed Stellate cells + Medium pyramidal cells
IV – Internal granularDensely packed Stellate cells only+ From Thalamus
V – Internal pyramidalLarge pyramidal cells only (few stellate cells) – Giant Pyramidal cells of Betz+ From Brain stemTo Brain stem & Spinal cord (Projection fibers)
VI – MultiformMultiple sized pyramidal cells + Loosely packed stellate cellsTo Thalamus

The 3 layers of allocortex:

  1. Molecular layer
  2. Pyramidal layer
  3. Multiform layer

Allocortex is found in: Limbic system

  1. Olfactory cortex
  2. Hippocampal formation
  3. Subiculum

Mesocortex:Β A transitional type of 3 to 6-layered cortex between neocortex and allocortex –

  1. Parahippocampal gyrus
  2. Pre- and Para-subiculum
  3. Insula

real cortex

Neurons of the cortex:

  1. 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.
  2. Stellate cells: Interneurons whose axons remain within the cortex
  3. Fusiform cells (in deeper layers): Gives rise to corticothalamic projections
  4. Horizontal cells of Cajal
  5. 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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