General
- Based on laminar organization, the cortex is broadly divided into
- Neocortex
- Aka isocortex or neopallium
- Has six distinct layers
- Represents about 90% of the human cortical surface.
- It includes most of the cerebral cortex, such as primary motor and sensory areas, and association areas involved in higher cognitive functions.
- Allocortex
- Phylogenetically older
- Has three or four layers
- Includes areas like the hippocampus (archicortex) and olfactory cortex (paleocortex).
- It is involved in more fundamental processes like memory and olfaction.
- Between neocortex and allocortex is the periallocortex or paralimbic cortex, which is transitional with merged layers.
- Functionally, the cerebral cortex is composed of three types of areas:
- Motor areas that control voluntary movements (e.g., primary motor cortex).
- Sensory areas that process sensory input (e.g., primary visual cortex in occipital lobe).
- Association areas that integrate information and are involved in complex processing like planning, language, and cognition.
Neocortex
- Development
- Formed in vertical columns of functional units
- Starts at layer 6 then it migrates upwards
- Sturge–Weber syndrome: Localised cerebral cortical atrophy and calcifications (especially cortical layers 2 and 3, with a predilection for the occipital lobes
- External layers
- Communicates with adjacent gray matter
- Internal layers
- Communicates with further regions eg spinal cord, thalamus
- Granular layers
- Stellate and fusiform cells
- Good at receiving efferent signals
- Pyramid layers
- Pyramid cells
- Good at sending efferent signals
Layers
Cell type
Function
Connections
1 molecular
Horizontal cell (of cajal) + golgi type 2
Modulate excitability
primarily a synaptic area
primarily a synaptic area
1 & 2 layers
Diffuse afferent/efferent fibers from lower brain
Diffuse afferent/efferent fibers from lower brain
2 outer granular
Granule cells
Abundance of densely
packed neurons whose
packed neurons whose
- Dendrites project to layer I
- Axons project to deeper layers: 2 & 3 layers
Ipsilateral corticocortico association afferent fibers
3 Outer pyramid
Pyramidal cells
Martionotti cell
- Small multipolar neurons that sends axons up to molecular layer
- Function: a negative feedback to Molecular layer to dampen their signal
Cortico-cortical efferent
- Corpus callosum
Commissural fibers
4 inner granular
Stellate cells
Main sensory level
- Outer band of Baillarger in sensory cortex (red arrow)
- Equivalent to band of gennari in visual cortex (blue arrow)
- Can be seen after myelin stained
Main sensory afferents
5 inner pyramid
Pyramidal cells
- Betz cell (Largest pyramidal cell)
Martionotti cell present
Horizontal fibres of inner band of Baillarger
Main efferent supply to brainstem/spinal cord
6 multiform
Fusiform/Spindle cells
Efferent supply to thalamus
Allocortex (other cortex)
- Archicortex (beginning)
- In hippocampal formation
- Function: Memory
- Layers
- Molecular layer
- Pyramidal layer
- Polymorph layer
- Paleocortex (Old)
- Function: Olfactory system
- Layers
- Olfactory cortex
- Glomerular layer
- Mitral cell layer
- External plexiform layer and mitral cell
- Piriform cortex
- Layer 1
- Layer 2
- Layer 3
- Septal cortex
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