Source: Electron Micrograh of human neurons by the NIMH; Public Domain (Gov) http://infocenter.nimh.nih.gov/il/public_il/image_details.cfm?id=306
In today's lesson, we're going to get a little bit more into the biological aspects of psychology, and explain exactly how things like our brain and nervous system work to create our minds and behavior.
To understand that, first we need to know what a neuron is . A neuron is the basic cellular building block of our brain and our nervous system. It's the thing within our body that acts as the messenger, and sends information to and from the brain and other parts of our body. It allows certain messages to be sent, so we can move and act in the ways that we intend.
This is different from a nerve, which you may have heard of, which are actually groups of neurons that transmit information throughout the rest of the body. In our arms, in our legs, we have nerves, which are just bundles of these neurons that are called together.
We're going to talk specifically about those individual neurons. Now a neuron has certain special structures that make it different from other cells, but allow it to function as this messenger within our body. So let's take a look at it.
First, we have our soma, or our cell body. This is the central area of the neuron that makes it just like other cells. It contains all the different structures that different cells in our bodies contain. Things like our nucleus, with the DNA inside of it, mitochondria, all the different sorts of things that other cells have. So the important thing to remember is the soma is our cell body. The center of the neuron.
Outside of that, we have these little branching, tree-like structures, which we call dendrites. Which actually comes from the Greek word, "dendri," for tree. So it's an easy way to remember. It looks like a tree, and it comes from the word for tree.
These aspects of the neuron, that branch off into lots of smaller parts, receive information from other neurons. So this is the receiving section of the neuron. It takes in messages that other cells and neurons send to it, and then transmits it to other cells outside of that. And we'll look at that transmission section next.
Extending out from the cell body, is this long tail-like structure, which we called the axon of the cell. While the dendrite's job is to receive information from other neurons, the axon's job is to transmit that information, across it, to other neurons that would be attached to this neuron, itself. It starts at the cell body, in the area we call the axon hillock, and extends all the way to this little button-like structure at the end, which we call the axon terminal.
When we say this is a long tail-like structure, this can vary wildly. Some axons can be only 1/10 of a millimeter long, but some of them can extend up to a meter long, especially in other parts of our body.
The axon essentially transmits an electrical impulse from within the cell, starting at the dendrites and the cell body, all the way across this tail, and then out to other neurons that might be attached to it.
So it's sort of like an electrical wire, and just like with an electrical wire, you can improve the transmission of that electrical signal by insulating it. By putting something around that axon to make the message transmit faster. And this is true in certain neurons within the brain itself. They have what's called a myelin sheath. The myelin sheath is this insulating layer of fat, which we call glial cells, which wraps around the axon, and makes that electrical impulse shoot faster through the axon, and then down to other neurons that might be attached. And because this myelin sheath is made of fat, it actually makes the neuron look like it's white, which is why we say in the brain, that there's white matter, which is the myelinated neurons within the brain, and then gray matter which is the non-myelinated ones.