Neocortex – Organization & Functions
NEOCORTEX – ORGANIZATION & FUNCTIONS
- Non-limbic portion of cerebral hemisphere.
- Phylogenetically referred as neocortex – One of cerebral cortex division.
- Forms major part (almost 90%) of cerebral cortex
- Comprised of the most superficial areas of brain
Note: Allocortex (old cortex) – Forms 10 % of entire cortex
Cerebral cortex:
- Layer of gray matter
- < than 4mm thick, lining the surface of cerebral hemisphere
- Foldy structures increase the surface area of cerebral cortex.
- Surface elevations created by folds are ‘Gyri’.
- Grooves separating them are called ‘Sulci’.
CELLS IN CEREBRAL CORTEX:
Cortical cells:
- Majority are pyramidal cells
- Pyramidal cells – “Sine qua non” for cerebral cortex
- Axons of pyramidal cells leave the cortex
- Forms descending tract (e.g. Corticospinal, Corticobulbar etc).
LAYERS OF CEREBRAL CORTEX:
Composed of 6 layers –
Layer/Lamina I – “Molecular layer”
- Contains nerve fibers.
- Mainly dendrites of pyramidal cells & axons of granular cells.
Layer/Lamina II – “External granule cell layer”
- Contains mainly granule cells.
Layer/Lamina III – “External pyramidal cell layer”
- Contains mainly small to medium size pyramidal cells
- Some granular cells also present
Layer/Lamina IV – “Internal granule cell layer”
- Contains predominately granule cells & nerve fibers.
- Specific sensory input through thalamocortical fibers terminate primarily in cortical layer IV on stellate (granule cells).
- Diffuse non-specific sensory afferents are distributed through layer I-IV.
Layer/Lamina V – “Internal pyramidal cell layer”
- Contains large pyramidal cells.
- Descending tracts, i.e. projection fibers from cortex (corticospinal tract, corticobulbar tract) are the axons of these pyramidal cells of Layer V
Layer/Lamina VI – “Multiform layer”
- Contains all types of cells
FUNCTIONAL DIVISION OF CEREBRAL CORTEX:
Divided into 2 areas –
- Primary cortical area
- Both motor & sensory areas
- Includes Primary auditory cortex, Primary olfactory area, Primary gustatory areas & Primary motor areas
Association areas:
- Higher functions are related to association areas
Other functions:
- First center activated to initiate skilled movements is “Neocortex”.
Exam Question
NEOCORTEX – ORGANIZATION & FUNCTIONS
- Non-limbic portion of cerebral hemisphere.
- Phylogenetically referred as neocortex – One type of cerebral cortex division.
- Forms major part (almost 90%) of cerebral cortex
- Comprised of the most superficial areas of brain.
CELLS IN CEREBRAL CORTEX:
Cortical cells:
- Majority are pyramidal cells
- Pyramidal cells – “Sine qua non” for cerebral cortex
- Axons of pyramidal cells leave the cortex
- Forms descending tract (e.g. Corticospinal, Corticobulbar etc).
LAYERS OF CEREBRAL CORTEX:
Composed of 6 layers –
- Layer/Lamina I – “Molecular layer”.
- Layer/Lamina II – “External granule cell layer”
- Layer/Lamina III – “External pyramidal cell layer”
- Layer/Lamina IV – “Internal granule cell layer”
- Contains predominately granule cells & nerve fibers
- Specific sensory input through thalamocortical fibers terminate primarily in cortical layer IV on stellate (granule cells)
Layer/Lamina V – “Internal pyramidal cell layer”
- Contains large pyramidal cells.
- Descending tracts, i.e. projection fibers from cortex (corticospinal tract, corticobulbar tract) are the axons of these pyramidal cells of Layer V
- Layer/Lamina VI – “Multiform layer”
FUNCTIONAL DIVISION OF CEREBRAL CORTEX:
- Primary cortical area
- Association area
Other functions:
- First center activated to initiate skilled movements is “Neocortex”.
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