The Alzheimer's Association has an easy-to-understand slideshow about how Alzheimer's Disease affect the brain:

Here is another view of how massive cell loss changes the whole brain in advanced Alzheimer's disease. This slide shows a crosswise "slice" through the middle of the brain between the ears.

In the Alzheimer brain:

* The cortex shrivels up, damaging areas involved in thinking, planning and remembering.

* Shrinkage is especially severe in the hippocampus, an area of the cortex that plays a key role in formation of new memories.

* Ventricles (fluid-filled spaces within the brain) grow larger.

Link - Thanks Kathy Dunderdale!