# 20 - B. Special neuronal cell types

# B. Special neuronal cell types

© SPMM Course 
4. Cell types in the nervous system 
A. Cortical layers 
The human brain contains approximately 1011 neurons (nerve cells) and approximately 1012 glial cells. 
According to the distribution of the various types of neurons (i.e. the cytoarchitecture), Brodmann divided 
the cortex into 47 ‘specialised’ areas. 
The neocortex (most of the cerebrum) is made up of six layers, with pial surface above layer 1 to the white 
matter below layer 6. Layers 2 and 4 are mainly afferent (receiving inputs) while 5 and 6 are mainly 
efferent (sending outputs). 
The pyramidal neurons with their triangular-shaped cell bodies make up nearly 75% of the cortical 
neurons. Stellate cells (25%) are present in all the layers except layer 1. 
 
Layer 
Name 
Predominant cells 
Molecular/agranular 
Glial cells, dendrites from neurons of deeper layers and the 
horizontal cells of Cajal. 
External Granular layer 
Granule cells and small pyramidal cells (these get larger as you 
move down) 
External Pyramidal layer 
Small and medium sized pyramidal cells. 
Internal Granular layer 
 
Some pyramidal cells, mostly granule cells. Receives 
thalamocortical inputs. 
Internal Pyramidal layer 
Largest pyramidal cells (esp. in motor cortex: Betz cells) 
Multiform layer 
A mixture of all cells, spindle cells, Martinotti cells. The major 
source of corticothalamic fibres. Gives rise to 
association/commissural and projection fibres. 
 
The cerebellar cortex is three layered. The molecular layer consisting of basket cells and stellate cells, 
Purkinje layer consisting of Purkinje cells and a Granular layer consisting of granule and Golgi cells. 
 B. Special neuronal cell types 
Purkinje cells are a class of GABAergic neurons located in the cerebellar cortex only. Purkinje cells form 
the sole output of all motor coordination in the cerebellum they connect to the deep cerebellar nuclei via 
inhibitory projections. 
Granule cells are found within the granular layer of the cerebellum, layer 4 of the cerebral cortex, the 
dentate gyrus of the hippocampus, and in the olfactory bulb. 
Large pyramidal cells called Betz cells are seen in the primary motor cortex. Betz cells are pyramidal cell 
neurons located within the fifth layer of the grey matter in the primary motor cortex. These neurons are