Cerebral cortex

The cerebral cortex is a brain structure in vertebrates, including humans. It is the outermost layer of the cerebrum and has a grey color. The human cerebral cortex is 2-4 mm (0.08-0.16 inches) thick and is highly folded.

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 processes the information. Areas that receive that particular information are called sensory areas. The two hemispheres receive the information from the opposite sides of the body. Parts of the cortex that receive 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 comprised of the motor areas and the association areas.

There are three association areas:

1. in the 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
2. in the frontal lobe. Called prefrontal association complex and involved in planning actions and movement
3. in the 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

The motor areas connect the two halves of the cerebrum. They are shaped like a pair of headphones stretching from ear to ear. The motor areas control your voluntary muscles such as your biceps, hamstring, & gastrocnemius. The right half of the motor area controls the left side of your body and vice versa.

Function of four motor areas:

• Posterior Parietal Cortex: Guiding voluntary movements in space
• 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:

1. Molecular layer
2. External granular layer
3. External pyramidal layer
4. Internal granular layer
5. Internal pyramidal layer
6. 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.

Theorists such as Jeff Hawkins have posited that these layers, particularly in the neocortex, form part of a laminar memory system of classification and lateral association which underpins human cognitive function. Although new, it brings an intriguing perspective on the unusual structural consistency of the most physically large cortex of the brain.

Classification

Based on the differences 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 differences the following classification also appears:

• Neocortex or Neopallium that corresponds to the 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

See also

• Microgyrus
• Frontal lobe
• Temporal lobe
• Parietal lobe
• Occipital lobe
• Limbic lobe
• List of regions in the human brain

External links

• Webvision - The primary visual cortex Comprehensive article about the structure and function of the primary visual cortex.
• Webvision - Basic cell types Image of the basic cell types of the monkey cerebral cortex.