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A neuron is the basic cellular building block of the brain and nervous system. It acts as a messenger and sends information to and from the brain and other parts of the body. It allows certain messages to be sent so that you can move and act in the ways that you choose.
A neuron is also called a “nerve cell” because groups of neurons make up a nerve, a term you’re probably familiar with. Nerves transmit information throughout the rest of the body.
A neuron has certain special structures that make it different from other cells. They allow it to function as a messenger within your body.
First, there is the soma, or the 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 your body contain, such as the nucleus containing DNA, the mitochondria, etc. The important thing to remember is that the soma is your cell body or the center of the neuron.
Outside of the soma are these little branching, tree-like structures, called dendrites.
Dendrites branch off into lots of smaller parts and receive information from other neurons. 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.
Extending out from the cell body is a long tail-like structure, 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 to other attached neurons.
The axon starts at the cell body and extends all the way to a button-like structure at the end, which is called the axon terminal.
The axon transmits an electrical impulse from within the cell, starting at the dendrites and the cell body, all the way across the tail and out to other neurons that might be attached to it. It's sort of like an electrical wire, and just like with an electrical wire, the transmission of that electrical signal can be improved by insulating it, or putting something around that axon to make the message transmit faster.
This is true in certain neurons within the brain itself; they have what is called a myelin sheath. The myelin sheath is an insulating layer of fat, called glial cells, which wrap around the axon and makes that electrical impulse shoot faster through the axon, down to other neurons that might be attached.
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The nervous system is essentially the body's communication system. It allows information to be sent to and from your brain, allowing you to control the rest of your body. These messages allow you to do all of the things that constitute your mind and behavior.
There are two different ways in which the nervous system communicates:
Taking a closer look at the areas between different neurons, you can see that at the very end of an axon of one neuron is a little button area, called the axon terminal. Normally, an axon sends an electrical impulse across the cell, but this electrical impulse is not transmitted to other neurons. This is because in between the axon and the dendrites of other neurons there is a space called a synapse, which is an actual gap between these different cells. Therefore, the electrical impulse can't jump over to other cells.
This means that another way is needed to communicate with those cells. Therefore, when that electrical impulse reaches the axon terminal, it releases what are called neurotransmitters.
Neurotransmitters are chemical messengers that attach themselves to the dendrites of other neurons surrounding them. This is helpful because it allows one neuron to communicate with many different neurons by sending out all of these different chemical messengers. It's not just one-to-one—the message could potentially go to hundreds of neurons.
Next, these neurotransmitters attach themselves to dendrites at what are called receptor sites. These receptor sites act as a sort of lock-and-key mechanism, meaning that one neurotransmitter fits that one particular receptor site. It's not a one-size-fits-all situation. All of the different receptor sites receive all of these neurotransmitters and eventually, when the neuron on the other side of the synapse receives enough chemical messengers, it activates itself and releases into an action potential, which fires a different neuron and then potentially other neurons surrounding it. You can imagine how it creates a cascade effect: one neuron potentially affecting a lot of different neurons.
There are many different types of neurotransmitters that are used in the brain and the nervous system. Remember, it's not a one-size-fits-all scenario. The reason for this is to allow for many different effects within the brain and the rest of the body itself.
There are two general types of neurotransmitters:
Excitatory neurotransmitters lead to the firing of neurons, or the threshold of excitation, and ultimately, to action potential.
The most common type of neurotransmitter is acetylcholine, which is abbreviated as ACH. This is an excitatory neurotransmitter, and it is used within the body to help with muscle movement, as well as the activation of the peripheral nervous system in different ways. In the brain itself, it is attached to attention and memory.
Inhibitory neurotransmitters prevent the firing of neurons, keeping that state of resting potential instead. This doesn't allow the other neurons to fire.
One of the more famous neurotransmitters is dopamine, which is actually considered both an excitatory and inhibitory neurotransmitter. It plays a role specifically in the motivation of people, as well as reward and reinforcement systems within the brain.
Lastly, there is a class of neurotransmitters called neuropeptides, which are a special group that regulate certain activities of neurons and systems within the brain itself.
An example of a neuropeptide is an endorphin, which acts to reduce pain and leads to feelings of euphoria or positivity about yourself, especially when you feel pain or are stressed out. Endorphins are what results in a runner's high. When you are running, you may get a sudden sensation of feeling exceptionally good—and good about yourself—which is the result of endorphins being activated within your brain.
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