I won't be exhaustive on the subject, but hopefully at least some of what I say may be helpful. I want to be fairly even-handed on the issue, though I have no doubt that some readers (including fellow professionals) may have a different take on what I have to say. Feedback is welcome, as always.
Here are the titles of the next few Friday posts, to give you an idea where we are headed:
- What is a neuron? (today)
- How does neuronal signal transmission work?
- What is serotonin?
- What is the monoamine hypothesis?
- How are SSRI antidepressants supposed to work?
Then we'll go from there.
So let's start with the basics, before we even look at medications. For some this will be just a bit TOO basic, for which my apologies.
What is a neuron?
The brain is made up of neurons, or neural cells, and glial, or support cells (which greatly outnumber the neurons). Most scientific attention has been given to the neurons because they seem to be the important ones. Essentially, all they do is communicate with one another using electrochemical impulses.
Until recently it has been assumed that glial cells simply act as insulators or feeder cells for the neurons, and so they have seemed to be of less interest. Lately, however, suspicions have been growing that the glial cells have more roles than we once thought. Like most treatments of the subject, however, I’ll pretty much ignore them.
Neurons are typically described as being in three sections.
- The cell body contains the DNA and most of the cell organs – mitochondria and the like – that are common to most cells.
- The axon (or axons) is a channel down which an electrical signal can pass. At the end of the axon are terminal buttons, which look a bit like little feet sitting on adjacent neurons. Calling these “buttons” was a bad idea, because these days we think of a button as something that gets pressed, thereby receiving a signal. In fact, the buttons send the signal.
- Dendrites are the receivers – the stretches of cell upon which other cells’ terminal buttons sit.
The simplest-looking neurons are long cells used in sensation or movement. As a result, most of us learned about neurons from diagrams of these.
Imagine a monstrous creature that walks erect like a human. Its head has one central eye (the cell nucleous), crowned with a nest of spiky hair (the dendrites). It has a long, impossibly skinny body (the single axon) ending in multiple tiny feet (the terminal buttons). Pull back and we see that it’s standing in the hair of another neuron, which is standing in the hair of another, and so on.
In reality, most neurons don’t look like this. They’re more like a bush of axons, dendrites, and terminal buttons, sitting in a tangled mass of other bushes. Neurons in the brain communicate with dozens or hundreds of others.
Now: How do neurons communicate with one another? That's for next week.