In humans the cortex is 2-4 mm thick and has six layers, numbered I to VI, starting from the pial surface:
- Layer I, the molecular layer, receives substantial inputs from the thalamus.
- Layer II, the external granular layer contains densely packed stellate cells.
- Layer III, the external pyramidal layer, receives inputs from other areas of the cortex, including the contra-lateral hemisphere.
- Layer IV, the internal granular layer, contains stellate neurones and is the main target of thalamocortical pathways as well as fibres crossing over in the corpus callosum.
- Layer V, the internal pyramidal layer, contains large pyramidal neurones whose axons project through the internal capsule to subcortical structures including the striatum, brainstem and spinal cord. The largest of these are known as Betz cells.
- Layer VI, the polymorphic or multiform layer has precise reciprocal connections with the thalamus.