Cerebral cortex

Last revised by Yoshi Yu on 26 Mar 2023

The cerebral cortex is the most superficial layer of the cerebrum. It and the underlying connecting white matter accounts for the largest part of the human brain.

Macroscopically, it is folded to form gyri and sulci allowing for increased surface area within the limited space of the cranium. Formation of the gyri and sulci are also important for functional organization of the brain. Two-thirds of the cerebral cortex is located within the sulci, while the other third is exposed on the gyrus.

Microscopically, it is composed of five different types of neurons arranged into distinct layers admixed with supporting glial cells (astrocytes, oligodendrocytes and microglia) and blood vessels. 

Approximately 90% of the human cortex consists of six layers forming the neocortex, while 10% of the cortex has only three layers, forming the allocortex (including hippocampus and olfactory cortex).

In the neocortex, the layers are numbered from superficial (I) to deep (VI) 1. The layers are: 

  1. molecular layer

  2. external granular layer 

  3. external pyramidal layer

  4. internal granular layer

  5. internal pyramidal layer 

  6. multiform layer

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