3-3b Listening - Nerve Cells

Having looked briefly at how chemicals and neurotransmitters in the brain can affect personality and behavior, we need to look now in more detail about the actual physical process that occurs in the brain, and in particular, in an individual nerve cell, or neuron. We'll start with the physical construction of the nerve cell itself, then describe the stages of how it fires, transmits energy, and finally we'll talk about some other types of drugs that work to speed up or slow down that process.

Let's get started by looking at a diagram of a neuron. It's best to understand the parts as well as the terminology before we look at the mechanism inside it. There are many smaller parts of a brain cell that all have specific names, but in the diagram here, you can see there are only really four main sections. The dendrites, soma, axon, and axon terminal.

First, if you can see the many pointy arms on the left side of the cell that look kind of like the antlers of a deer, these are called dendrites. At the right side of the cell, there are another set of tentacle-like objects, but these are called axon terminals because they are at the end, or terminus, of the axon, which is the long center part made of many oval-shaped sections. Now back to the left side again. In the middle of the mass of dendrites, there is a center part, which is the nucleus of the cell known as the soma. These are the four main parts of a neuron, and we'll be referring to them many times as we continue our discussion.

So this brain cell is used for transmitting energy to other cells in sequence, but how does it do that exactly? How do these cells communicate with each other? Well, one neuron on its own doesn't do much but send information to another, but when they are arranged in a long line one after the other, they can send information throughout the body. For example, information from your fingers, say sensing a hot object, can send that information from one cell to the next all the way to the brain, where neurons send information to many more neurons, and then that information is sent back to the hand and muscles that make the hand move away from an object. Information comes up a sensory pathway, information from the senses into the brain, then leaves the brain through motor pathways, which activates the muscles of the body. Imagine that if you can, like a series of people in a long line communicating information to one another without actually moving themselves.

That's the big picture of how nerve cells interact, but what about inside the brain cells themselves? Well, this process involves the triggering of electrical impulses and the use of chemicals, the neurotransmitters we talked about earlier. We say that these neurons are firing like a gun, so we call this process neurofiring. Picture two cells lined up with the axon terminal of cell A, next to, but not touching, the dendrites of cell B. Let's start things with a chemical change in the soma of cell A. This begins a reaction within cell A that creates an electrical impulse or shock that travels down the length of the axon until it reaches the axon terminal. Here, the electricity causes the axon terminal of cell A to release certain neurotransmitters. As I said, the axon terminal and the dendrites do not actually touch. In between them is an area known as a synapse. It's into here that the axon terminal of neuron A releases its neurotransmitters, which float across very quickly, of course, to the dendrites of neuron B. This starts a reaction in the soma of neuron B, which releases an electrical impulse that starts the process over again. Neuron B will connect to many more neurons, C, D, E, and so on, to create a long chain. One neuron causes the next to fire and the next, and on it goes.

Now let's bring this together with what we talked about last time regarding drugs and how they can affect the brain's release of certain neurotransmitters. Basically, the more or less of a neurotransmitter that is released into a synapse determines how quickly or slowly it will fire. More neurotransmitter means faster firing, and the reverse is also true. Different drugs have properties that will increase or decrease the release of neurotransmitters, so we are able to use them to speed up or slow down neural firing. This can relate to the sensory and motor pathways we discussed earlier. If I take a drug that makes the neurons related to the sensory pathway move slower, I may experience the world in a much different way. Things may seem fuzzy or the object may appear to move more slowly. The same effect on my motor pathway may mean that I react much slower to outside stimuli. I may not catch a ball that I could have otherwise.

An example of a drug that inhibits or slows down neural firing is alcohol. Many of you who have experience with alcohol or have seen someone who has had a lot of it to drink may know that slowing neural pathways, either sensory or motor, greatly affects this person's ability to talk, pay attention, or even walk. Other drugs, such as cocaine, do the opposite. Cocaine speeds up certain types of neural firing and can result in much faster brain processing and decision making. People taking this drug seem to have a more heightened sense of what is going on around them. Of course, I'm in no way advocating these drugs, but am only using them as examples of how they can affect the brain and, therefore, behavior on a chemical level.