The Cerebral Cortex and the Neocortex

The cerebral cortex is a 600 grams grey sheet that constitutes 40% of brain weight and contains 25 BILLION neurons

The neurons weigh about 180 grams, the glial cells and blood vessels weigh 420 grams 

Cerebral cortices are 1.5 - 4.5 mm thick with a surface area of 2200 cm-sq

It is divided into a 6 layered neocortex that is organized into Brodmann’s scheme where he numbered areas based on the cytoarchitecture differences, which are called Brodmann numbers

Organization of the Neocortex

The Neocortex is organized into 6 horitizonal laminae / layers oriented parallel to the cortical surface

The basic functional units of the cerebral cortex are physiologically defined vertical, 3-dimentional slabs (0.5 mm in width)

The main INPUTS to the cortex are from the thalamus that pass through the internal capsule and terminating at layers 1 through 4

The main OUTPUTS out of the cortex are sent through layers 5 and 6 and they mostly descend through the internal capsule and go to various subcortical structures/ sites

Types of Neocortex

There are 3 types of neocortexes in the brain: Primary / Receptive Cortex, Secondary Association Cortices and Tertiary Cortices

1. Primary / Receptive Cortex

• Includes the: Primary Motor Cortex, Primary Somatosensory Cortex, Primary Visual Cortex and the Primary Auditory Cortex

• Directly receives thalamic input

• Damage to these areas can produce a loss of modality

2. Secondary Association Cortices

• Includes the: Motor Association Cortex, Somatosensory Association Cortex, Visual association Cortex and Auditory Association Cortex

• Responsible for the further processing, integration, and interpretation of information from the primary cortex

• Damage can produce agnosia

3. Tertiary Cortices

• Involved with higher-order functions related to reasoning, thought and language