Cerebral cortex

The cerebral cortex and underlying connecting white matter, accounts accounts for the largest part of the human brain. It is composed of five different types of neuronsneurones arranged into distinct layers (in most places 6 layers) admixed with supporting glial cells (astrocytes (astrocytes, oligodendrogliaoligodendrocytes and microglia) and blood vessels. 

Types of neurones

Pyramidal cells

Pyramidal cells are by far the most common neurone type found in human neocortex, and are located in layers II, III V and VI (see below). They are, as their name suggests, pyramidal in shape with the apex pointing outwards, towards the pial surface of the brain. From the apex a thick single dendrite extends towards more superficial layers and branches into numerous dentrides. From the base of the cell body an axon extends into deeper layers and/or into the subcortical white matter. Additional dendrites extend form the base of the cell body to connect with other neurones in the same layer ¹. 

The largest examples of pyramidal cells are the Betz cells found in the motor cortex ¹. 

Fusiform cells

Fusiform cells extend orthogonally to their cell layer with dendrites extending from either end into deeper and more superficial layers. From the cell body an axon arises which passes superficially ¹. 

Cells of Martinotti

Cells of Martinotti are small cells with a limited number of short dendrites and an axon which extends superficially ¹. 

Horizontal cells of Cajal

Horizontal cells of Cajal are only found in layer I and are the least common cell type. They are also fusiform in shape but are aligned parallel to their cell layer with their axon extending laterally within the layer to synapse with nearby pyramidal cells ¹. 

Stellate cells

Stellate cells, also known as granule cells, are rounded with short dendrites radiating circumferentially out from the body. They are predominantly found in layers II, IV and VI ¹. 

Layers

The majority of the human cortex, with the exception of the olfactory cortex and cortical parts of the temporal lobe limbic system which have three layers, has six layers, numbered from superficial (I) to deep (IV) ¹. The layers are: 

1. plexiform layer
2. outer granular layer 
3. pyramidal cell layer
4. inner granular layer
5. ganglionic layer
6. multiform cell layer