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Cerebral cortex is typically 2-4mm thick.
The largest part of brain is the cerebrum which is divided into left and right hemispheres. The surface of each cerebral hemisphere is covered by a highly folded layer of tissue called the cerebral cortex. The outer 3-4 millimetres (.06-.18 inches) of the cerebrum are part of the cerebral cortex. The cortex is what gives the brain a grey colour.
In the "higher" animals (especially the higher mammals), the surface of the cerebral cortex becomes folded. This creates grooves on the surface of the brain called "sulci" (singular = "sulcus"). The bumps or ridges on the surface of the brain are called "gyri" (singular = "gyrus"). The folding of the cortex increases the cortical surface area. The cerebral cortex, made up of four lobes, is involved in many complex brain functions including memory, perceptual awareness, "thinking", language and consciousness.
The cerebral cortex receives sensory information from many different sensory organs eg: eyes, ears etc and process the information.
Areas that receive this information are called sensory areas. The two hemispheres receive the information from the opposite sides of the body.
Parts of the cortex that receives this information are called primary sensory areas.
Other areas receive impulses from the primary sensory areas and integrate the information coming in from different types of receptors. These are known as association areas and make up a great deal of the cortex in all primates including us. The cortex is split into two areas: the motor and the association.
There are three association areas:
1st = in parietal, temporal and occipital lobes. It is involved in producing our perceptions resulting from what our eyes see, ears hear and other sensory organs tell us about the position of different parts of our body
2nd = in frontal lobe. Called prefrontal association complex and involved in planning actions and movement
3rd = in limbic association area. Involved in emotion and memory
The association areas of the left hemisphere, especially the parietal-temporal-occipital complex are also responsible for our understanding and use of language
Connecting the two halves of the cerebrum is a place called the motor area. The motor area is shaped like a pair of headphones stretching from ear to ear. The motor area controls all your voluntary muscles such as your biceps, hamstring, & gastrocnemius. Once again the right half of the motor area controls the left side of your body and vice versa.
Function of Four Motor Areas:
The Posterior Parietal Cortex Guiding voluntary movements in space
The Dorsolateral Prefrontal Cortex Deciding which voluntary movements to make
Secondary motor areas Selecting voluntary movements
Primary motor cortex Executing voluntary movements
Laminar pattern
The standard areas of cortex (isocortex) is characterized as having six distinct layers. From outside inward:
- Molecular layer
- External granular layer
- External pyramidal layer
- Internal granular layer
- Internal pyramidal layer
- Fusiform layer
However, there are no actual borders between the layers, and neurons cross layer boundaries with their dendrites and axons trees all over. The pyramidal cells (the majority of the neurons) span at least three layers, and in many cases all the layers. Thus it is not obvious that the layers have any functional significance.
Classification
Based on the differencies in lamination the cerebral cortex can be classified into two major groups:
- Isocortex (homotypical cortex), the part of the cortex with six layers.
- Allocortex (heterotypical cortex) with variable number of layers, e.g., olfactory cortex and hippocampus.
Auxiliary classes are:
- Mesocortex, classification between isocortex and allocortex where layers 2, 3 and 4 are merged.
- Proisocortex, Brodmann areas 24, 25, 32.
- Periallocortex is cortical areas adjacent to allocortex.
Based on supposed developmental differencies the following classification also appears:
- Neocortex that corresponds to isocortex.
- Archicortex
- Paleocortex
In addition, cortex may be classified on the basis of gross topographical conventions into the following:
- Temporal Cortex
- Parietal Cortex
- Frontal Cortex
- Occipital Cortex
- Limbic Cortex
- Insular Cortex
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