Mystery?

When "most people"--including clinicians--think of brain and nervous tissue they think first of neurons. These are the big bosses, of course, and have the real mysteries within them. They are also essentially eternal, not reproducing and therefore maintaining continuity, but once gone are (as of today) gone forever.

But "the other nervous tissue", neuroglia, consisting of several types of supporting cells (micoglia, astrocytes, oligodendrocytes, ependymal cells, Schwann cells) is as critical to nervous system functioning as neurons. These cells feed, protect, insulate, and generally allow the neurons to do what they do--"think" and send orders (signals) to all other cells of the body. The "blood brain barrier", which is a function rather than an organ, is a neuroglial function. The special immune properties of the central nervous system (CNS) are mediated by microglia. 

Recent research has also suggested that it is these cells that are responsible for forging connections between neurons, and therefore are responsible for learning and adaptation and even evolution. They have one very serious "weakness", however, and that is that they divide rapidly and often, setting themselves up to be the target of genetic decay. Over 98% of malignant brain tumors are neuroglial in origin, and they are also involved in many neurologic disorders, including multiple sclerosis, Alzheimer's, and several other neurodegenerative diseases.

The brain--both types of cells--takes 20% of our oxygen and at least 15% of our glucose even though it is no more than 2% of our body weight. It is the first organ to develop and the last to die. In between it is a miracle of sublime and elegant power and complexity.