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CEREBRAL CORTEX

The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different composition in terms of neurons and connectivity. The human cerebral cortex is 2–4 mm thick.

Outer layer of brain is gray in colour, hence the name "gray matter". It is formed of non myelinated neurons. The White matter lies below is formed predominantly by myelinated axons interconnecting neurons in different regions of the cerebral cortex with each other and neurons in other parts of the central nervous system.

The surface of the cerebral cortex has many folds in large mammals, such that more than two-thirds of it in the human brain is buried in the grooves. The recent part of the cerebral cortex evolved through phylogenetically is the Neocortex (Isocortex). It is differentiated into six horizontal layers. The ancient part of the cerebral cortex called the Hippocampus (Archicortex), has three cellular layers, and is divided into subfields. Neurons in various layers connect vertically to form small microcircuits, called Columns.

Sensory areas

The most important part of the cortex is the Sensory areas that receive and process information from the sense organs. Parts of the cortex that receive sensory inputs from the thalamus are called Primary sensory areas. The senses of vision, hearing, and touch are served by the Primary visual cortex, Primary auditory cortex and Primary somatosensory cortex. In general, the two hemispheres receive information from the opposite side of the body (Contralateral).

Motor areas

The motor areas are located in both hemispheres of the cortex. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa. The Motor areas are

1. Primary motor cortex, for voluntary movements

2. Supplementary motor areas and premotor cortex, which select voluntary movements.

In addition, to these the motor functions are also involved in

1. Posterior parietal cortex, which guides voluntary movements in space

2. Dorsolateral prefrontal cortex, which decides which voluntary movements to make according to higher-order instructions, rules, and self-generated thoughts.

Association areas

Association areas function to produce a meaningful perceptual experience of the world, enable us to interact effectively, and support abstract thinking and language.

1. The parietal, temporal, and occipital lobes - all located in the posterior part of the cortex - organize sensory information into a coherent perceptual model of our environment centered on our body image.

2. The frontal lobe or prefrontal association complex is involved in planning actions and movement, as well as abstract thought.

3. Language abilities are localized in the left hemisphere in areas called Broca's area, for language expression and the Wernicke's area, for language reception.

Layers of Cortex

Based on the differences in lamination the cerebral cortex can be classified into two major groups:

1. Isocortex or Homotypical cortex is the part of the cortex with six layers.

2. Allocortex or Heterotypical cortex the part of the cortex with less than six layers. The Allocortex includes the olfactory cortex and the hippocampus.

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