Introduction

To begin the Cerebral Cortex Exercise click Link 1. This will take your web browser to a photomicrograph of a monkey brain.

You will observe a high magnification image of a Nissl stained section of the brain of a Macaque monkey as seen on the right:

Navigation: You can zoom in and out by clicking on the plus or minus in the toolbar. You can moved around on an image by clicking on the image and dragging.

Click the “-“ in the tool bar until you see the entire section.

To begin your analysis of the tissue, note several features:

The external surface of the hemispheres is covered with a laminated structure, the cerebral cortex.
Internal to the cortex is the white matter. The white matter extends across the midline as the corpus callosum and lateral to the thalamus as the internal capsules.
The white matter continues ventrally as the cerebral peduncle, which eventually enter the pons.

This section is labeled in order to facilitate your early examination of the tissue. In subsequent sections the structures may not be labeled.

Note that parts of the internal gray matter appear to be different. For example, examine the caudate and putamen (arrows) and compare them to the globus pallidus (arrow). Note that both caudate and putamen appear similar. They are more darkly stained than the globus pallidus. Even at this low magnification one can see that the thalamus (arrow) is composed of multiple nuclear groups. The different appearance of the various nuclei is because of the size and packing density of the neurons and Nissl body content. Now, by clicking on the “+” tool on the tool bar increase the magnification and examine the nuclear organization of the dorsal thalamus, caudate nucleus, putamen, globus pallidus and claustrum. These structures differ in neuronal size and cell packing density, characteristics that permit identification of structures from brain to brain.

Now go to Link 2.

On the right side the inferior temporal gyrus is labeled “ITG” (arrows in left illustration below). Go to the left side of the section and find the inferior temporal gyrus. Increase the magnification until you can clearly see the lamination of the gyrus (box in illustration below). As you know, the neocortex has six layers. You should be able to identify most of the layers of the cortex; from pial surface to white matter: a cell-poor molecular layer (I), the external granular (II) and external pyramidal (III) layers, which appear to merge with each other, a darkly stained internal granular layer (IV), a lightly stained internal pyramidal layer (V) and a darkly stained polymorphic (or multiform) layer (VI).

Nissl stains only permit you to see the cell bodies and proximal dendrites of neurons. Golgi impregnations stain only a small (~2%) percentage of neurons and a few glial cells, but stain more or less the entire neuron (depending on the type of stain used). Thus, it is possible to see more characteristics of individual neurons. Go to the following URL to examine a section of somatosensory cortex processed with the Golgi impregation technique.

Now click Link 3.

Reduce the magnification until you see the entire section (see below), then increase the magnification until you can identify individual Golgi-stained pyramidal cells (next page). If you look carefully, you will be able to identify other cortical neurons as well. Look for the apical dendrites and basal dendrites of pyramidal cells. Note that the portion of the apical dendrite that emerges from the cell body is free of spines, but that the more distal portions of this dendrite and the basal dendrites are covered in spines. You may be able to identify an axon emerging from the base of a neuron or from one of its basal dendrites.

To see another area of cortex stained by the Golgi method go to Link 4.

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