When the human brain is examined under a microscope,  it is possible to detect two basic types of cells.  These are known as neurons and glia.
	Neurons (shown here in yellow) have traditionally been regarded as the key  actors which control brain activity.   In contrast, glia (shown above in black, gray, and tan) have traditionally been relegated to secondary roles, such as nourishment and infection response.  [Interestingly, these concepts are now overly simplistic and outdated].
	For the purpose of this lecture, it will suffice to appreciate the fact that human behavior and intelligence depend upon the proper functioning and survival of neurons.  In fact, the death of neurons is a common feature of all disease processes which result in dementia.