Cerebral Cortex:
The cerebral cortex, which consists of the frontal, occipital and temporal lobes,
surrounds the limbic system. this youngest and most developed part of the brain is
involved in a variety of integrative processses necessary for such functions as
recognition and speech. Some areas of cerebral cortex are highly specialized to
serve the sensory processes of vision, audition, and touch, while others are specialized
for controlling the movement of skeletal muscles.
Some characteristics of the Cerebral Cortex:
- 80% volume of brain
- formed by active migration
- 6 layer structure
- 2-3 mm thick
- 1.5 sq. ft flattened
- more than 50-100 specializations.
Structurally similar across species
- changes from monkey to human mostly in the horizontal dimension, not in thickness
- developmental uniformity across species
- functionally diverse
- large OB in rats
- large hippocampus in birds
- large neocortex in mammals
3 parts:
- Paleocortex (old cortex)......1% (cingulate gyrus)
- Archicortex (primitive cortex)......3.5% (hippocampus)
- Neocortex (new cortex) 95.5% (frontal, parietal, occipital, temporal lobes)
3 types:
- Granular cortex -- consists of granule cells, which receive input, located in sensory
areas like V1, S1 and A1
- Agranular cortex -- located in motor cortex
- Homotypical cortex -- located in association areas, consists of a variety of granule
like cells
Two types of neurons:
- Spiny
- Pyramidal cells 70-80%
- form tuft in layer 1
- become elongated in mammals, have 6000 -10000 spines
- major source of output for cortex
- found in all layers except 1
- apical dendrites
- stable, unchanged in phylogeny
- Stellate cells........10%
- found in layer 4, receives input from thalamus
- no apical dendrites
- dendrites of equal length radiate out from soma, forming star shape
- Aspiny.......10% (local interneurons)
- smooth cells that utilize GABA, inhibitory
- modulate stellate and pyramidal functions
- less stable, adapt in response to environmental demands
- 3 important types: found in all cortical layers
- Basket cells --spatial introcortical distribution
- Chandelier cells -vertical axonal terminals, candles, short dendrites with wavy branches
- Double-bouquet cells -- long dendrites with short spine-like projections
Gradient in the sizes of Pyramidal cells found in different layers:
Apical dendrites only in neocortex, keep modularized architecture and allow input from
all layers
should always be anchored to layer 1 by dendritic bouquet and oriented perpendicular to
pial surface
Cortical Layers:
- No cells present
- Cortico-cortical connections, input from same hemisphere
- Cortico-cortical connections, input from other hemisphere, greatest # of spines
- Thalamic input
- Non- specific thalamic input, and also output from motor areas (Basal ganglia and
midbrain effector )
- Output to Thalamus
Cells compared to cerebellum
| Coritcal Cells |
Cerebellar cells |
| Pyramidal cells |
Purkinje cells |
| Stellate cells |
Granule cells |
| Interneurons |
Interneurons |
| (10 types of neurons) |
(3-5 types of neurons) |
Cortical modules: serves as input/output processing devices
- invariant number of cells (except striate cortex)
- minicolumns = basic unit that makes up cortex (110-260 neurons across)
- cortical columns = extensive lateral connections (200-800 mm
across), functionally homogenous
- receives specific input from thalamus, modulatory systems, and other cortical modules,
both ipsilateral and contralateral
- map several functional variables simultaneously (multi-representational)
Tanaka -- examined inferior temporal cortex and found that each column of cells
responds to different complicated stimuli
Ocular Dominance columns:
Overall, the primary visual cortex represents locations in the visual field and has a
larger, finer mapping of the central visual region than of the periphery. The
primary visual cortex is also divided into columns, alternating between ipsilateral
and contralateral input from the eyes (called ocular dominance columns). These
columns are futher divided int oregions of cells that respond best to such stimuli as
orientation, and recently it was discovered that blobs exist, spread out among the visual
cortex that repond best to color.
- strips of cells represent the ipsilateral and contralateral input from a certain area of
the visual field
- in one column, all cells are tuned to respond best to upright stimuli
- an adjacent column responds to 10 degrees off vertical...and so on
- there are blobs within the ipsilateral and contralateral bands that may be related to
color vision