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Cerebral Cortex
Cerebral Cortex
- Relatively thin shell of neuronal tissue
- Outer, cellular gray matter of the brain
Six cytoarchitectural layers of the neocortex
See: Neocortical Layers
From outside to inside (leptomeninges on the outside and white matter on the inside):
Layer I
- The Molecular (or plexiform) Layer
- A nerve fiber layer, meaning that it is cell sparse and predominantly comprises axons and dendritic processes.
Layer II
- The External Granular Layer
- Contains non-pyramidal cells 5-15 micrometers, and relatively few, small pyramidal cells.
Layer III
- The External Pyramidal Layer
- Predominantly contains pyramidal cells of varying sizes: 10 to 80 micrometers. Also, layer III is sparsely populated with non-pyramidal cells.
Layer IV
- The Internal Granular Layer
- Densely packed with non-pyramidal cells.
- Contains the horizontally oriented external band of Baillarger: a prominent thalamocortical nerve fiber layer. In the primary visual cortex, this nerve fiber band is called the line of Gennari.
Layer V
- Internal Pyramidal (or ganglionic) Layer
- Contains the largest pyramidal cells, most notably the Betz cells of the primary motor cortex – the major cortical motor neurons.
- The horizontally-oriented internal band of Baillarger lies deep within this layer.
Layer VI
- The Multiform (or fusiform) Layer
- Contains a wide variety of pyramidal and non-pyramidal cells.