4 - ORGANIZATION OF THE CEREBRAL CORTEX
LEARNING GOAL 4.1: CELLULAR ORGANIZATION OF THE CORTEX.
DISCUSS THE CELLULAR ORGANIZATION OF THE CEREBRAL CORTEX. WHAT ARE THE
MAJOR CELL TYPES AND HOW ARE THEY ORGANIZED IN LAYERS?
CYTOARCHITECTURE
• Cortex is organized into functional units (cortical columns) – specialized to process specific inputs
or outputs
• Architecture of columns will differ depending on their function, whether they are input or output
• These differences in the cytoarchitecture of the cortex led to the first mapping of the cortical mantle
by Brodmann
o Assigned a numbering system to every cortical area with a different histological organization
o Penfield later found out that these histologically different areas correlate with functionally
different areas
PYRAMIDAL AND GRANULAR NEURONS
• There are 2 major neuronal cell types in the cortex:
1. Pyramidal neurons – layers III and V
a. Have a triangular structure, one apical dendrite, abundant dendritic trees coming from the
cell body
b. Axons project out of the cortex into other regions of the brain and spinal cord
c. MAIN OUTPUT CELLS
, 2. Granular neurons (stellate) – layers II and IV
a. Shorter axons, smaller dendritic trees
b. Remain within the cortex
c. MAIN INTERNEURONS
POINT OUT THE DIFFERENCE BETWEEN NEOCORTEX AND ALLOCORTEX, AND
EXPLAIN WHAT “LIMBIC” CORTEX IS.
• Each cerebral hemisphere can be divided into 5 lobes: frontal, parietal, temporal, occipital &
• limbic lobes.
HISTOLOGICAL ORGANIZATION OF THE CORTEX
• Organized in a layered fashion, with different cell types predominating in each layer
• Neocortex – 6 layers (majority)
o Largest part of cortex
o Newer part
• Paleocortex – the part of the cortex in the olfactory bulb that has only 3 layers
• Archicortex – the part of the cortex in the hippocampus that has only 3 layers
• Allocortex – paleocortex + archicortex
o Oldest part
• Limbic cortex – represents the edge of the cerebral cortical sheet bordering the lateral ventricles
o Named limbic cortex since it overlies limbic system structures
• Cortex comprises the gray matter of the forebrain
o This is where the cell bodies of neurons are located
o The cortex is a layered structure, and the cortical cytoarchitecture reflects the different
functional areas of the cortex
• Cortex is highly folded into gyri and sulci
• The areas of the cortex are connected to one another through subcortical fiber bundles
o Include association fibers that pass between areas within one hemisphere, commissural
fibers that connect the 2 hemispheres to each other, and ascending or descending
projection fibers that travel to or from the cortex to interconnect it with more caudal areas
of the CNS
DISCUSS THE FUNCTIONAL SIGNIFICANCE OF THE DIFFERENT LAYERS, AND HOW
LAYERS DEFINE CORTICAL FIELDS OR AREAS
• Layer I – molecular layer, contains mainly neuronal processes
• Layer VI – multiform layer, contains output neurons of varying shapes and sizes
• Not every area of the cortex has the same distribution of cells in all layers
o Primary motor cortex – contains large number of pyramidal neurons that will project to
lower motor neurons via the corticospinal and corticobulbar tracts
LEARNING GOAL 4.1: CELLULAR ORGANIZATION OF THE CORTEX.
DISCUSS THE CELLULAR ORGANIZATION OF THE CEREBRAL CORTEX. WHAT ARE THE
MAJOR CELL TYPES AND HOW ARE THEY ORGANIZED IN LAYERS?
CYTOARCHITECTURE
• Cortex is organized into functional units (cortical columns) – specialized to process specific inputs
or outputs
• Architecture of columns will differ depending on their function, whether they are input or output
• These differences in the cytoarchitecture of the cortex led to the first mapping of the cortical mantle
by Brodmann
o Assigned a numbering system to every cortical area with a different histological organization
o Penfield later found out that these histologically different areas correlate with functionally
different areas
PYRAMIDAL AND GRANULAR NEURONS
• There are 2 major neuronal cell types in the cortex:
1. Pyramidal neurons – layers III and V
a. Have a triangular structure, one apical dendrite, abundant dendritic trees coming from the
cell body
b. Axons project out of the cortex into other regions of the brain and spinal cord
c. MAIN OUTPUT CELLS
, 2. Granular neurons (stellate) – layers II and IV
a. Shorter axons, smaller dendritic trees
b. Remain within the cortex
c. MAIN INTERNEURONS
POINT OUT THE DIFFERENCE BETWEEN NEOCORTEX AND ALLOCORTEX, AND
EXPLAIN WHAT “LIMBIC” CORTEX IS.
• Each cerebral hemisphere can be divided into 5 lobes: frontal, parietal, temporal, occipital &
• limbic lobes.
HISTOLOGICAL ORGANIZATION OF THE CORTEX
• Organized in a layered fashion, with different cell types predominating in each layer
• Neocortex – 6 layers (majority)
o Largest part of cortex
o Newer part
• Paleocortex – the part of the cortex in the olfactory bulb that has only 3 layers
• Archicortex – the part of the cortex in the hippocampus that has only 3 layers
• Allocortex – paleocortex + archicortex
o Oldest part
• Limbic cortex – represents the edge of the cerebral cortical sheet bordering the lateral ventricles
o Named limbic cortex since it overlies limbic system structures
• Cortex comprises the gray matter of the forebrain
o This is where the cell bodies of neurons are located
o The cortex is a layered structure, and the cortical cytoarchitecture reflects the different
functional areas of the cortex
• Cortex is highly folded into gyri and sulci
• The areas of the cortex are connected to one another through subcortical fiber bundles
o Include association fibers that pass between areas within one hemisphere, commissural
fibers that connect the 2 hemispheres to each other, and ascending or descending
projection fibers that travel to or from the cortex to interconnect it with more caudal areas
of the CNS
DISCUSS THE FUNCTIONAL SIGNIFICANCE OF THE DIFFERENT LAYERS, AND HOW
LAYERS DEFINE CORTICAL FIELDS OR AREAS
• Layer I – molecular layer, contains mainly neuronal processes
• Layer VI – multiform layer, contains output neurons of varying shapes and sizes
• Not every area of the cortex has the same distribution of cells in all layers
o Primary motor cortex – contains large number of pyramidal neurons that will project to
lower motor neurons via the corticospinal and corticobulbar tracts
