The Basics: The Cellular Constituents of the Brain

So Notorious has been a neuroscience student for a long, long time now, and he was cleaning out the (metaphorical in his case) attic the other day and realized he has a lot of extra notes lying around collecting dust. In what will no doubt be a vain attempt to not just toss them, he has decided to write some of this stuff down as an extended primer to the basics of neuroscience.

So here goes. The basic of the very basic: what types of cells is make up the brain? What do those cells do?

There are four types of cells that compose the brain -- that is aside from the cells that make up other parts of the body like blood vessel cells, bone cells, etc. There are plenty of those other cells in the brain too, as you would realize if you were to attempt to take a representative sample of someone's brain using a standard 2 x 4. What you would find is that the clear distinction between "brain" and "rest of body" is largely a matter of convenience, but being convenient we will be sticking with it here.

The four types of cells that compose brain tissue exclusively are neurons and three types of glia: astrocytes, oligodendrocytes or Schwann cells (depending on whether you are in the peripheral or central nervous system), and microglia. The word glia comes from the Greek word for glue, which tells you something about how important the people who named these things though they were.

Now if I might engage in a brief rant here, most textbooks I read when I was in college viewed the neurons as the first among equals from the group of four. Neurons were the Jaggers and the rest were just roadies. The assumption among much neuroscience research coming to the turn of the last century was that glial cells functioned primarily to provide physical or metabolic support, to respond to injury, and to direct development of the otherwise more important neurons. The assumption was that they were definitely not involved in information processing in the brain. However, while the generalization that neurons are the primary information processors in the brain is probably a fair one, more and more recent evidence points to a function for glia in information processing. In my summary, I am going to try to give you a taste of that evidence, so that you won't wander through life thinking that glia are pathetic losers like I did for the first decade or so.

Neurons: The defining characteristic of