Granular and Agranular Cortex

Not all necortex has the same appearance. Although all have six layers, some layers may be expanded, others reduced. Motor cortices, sensory cortices (particularly visual cortex) differ particularly in the development of the internal pyramidal layer (V)and internal granular layer (IV). Go to Link 7 to compare somatosensory and motor cortices. Identify and then magnify the motor and somatosensory cortices.

Notice in the motor cortex (below right) that pyramidal cells in layer V are clearly visible even at this low magnification. In contrast, it is difficult to identify layer IV.

In somatosensory cortex (below left) layer 5 is not prominent, but the more superficial layers are well developed.

The most extreme example of specialization of neocortex is area 17, the primary visual cortex. This cortex has been named “striate cortex” because it contains a stripe of white matter (the Stripe of Gennari) that subdivides layer 4 into three sublayers (4a,b,c).

For visual cortex see Link 8. This is a low power view of the occipital cortex (Nissl stained), which permits you to see how the cortex changes in appearance from area 18 to area 17.

For a higher magnification of visual cortex, go to Link 9.

Golgi-stained sections make visible large portions of neurons, not normally seen with Nissl stains. A section through the visual cortex stained with silver stain can be seen by going to Link 10.

Notice that you can identify pyramidal-shaped neurons, their apical and basal dendrites and axons.

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