Abstract image of brain connections

Abstract image of brain connections (illustrart, iStockphoto)

Neurons: The Building Blocks of Your Brain

Tammy Rosner
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How does your brain allow you to do and experience so much? It’s all because of the building blocks of your brain - neurons!

Have you ever taken a moment to think about how incredible your brain is? Your brain allows you to do… well… everything. It is because of your brain that you can read and understand stories in books, talk to your friends and family, or listen to music. Even the activities your body does naturally, like breathing, are controlled by your brain. Something that feels like a very simple action, like petting a dog, is all because of your brain!

But how does your brain allow you to do and experience so much? It’s all because of the building blocks of your brain.

Like the rest of your body, your brain is made up of billions of cells. Every part of your body (as well as the bodies of animals and plants) are made up of cells, which are like microscopic building blocks that keep the body running. There are different types of cells for the different parts of your body, like skin cells or blood cells. The cells that make up your brain are called neurons.

What is a Neuron?

Neurons have three main sections.

  1. The cell body is the part of the neuron that contains everything cells need to stay alive and healthy. 
  2. Dendrites are the parts of the neuron that receive information from other neurons. 
  3. The axon is the main branch that grows from the cell body. At the end of the axon is the synaptic terminal, which is the part of the neuron that sends information in the form of electrical signals to other neurons. There are many synaptic terminals per neuron.
Parts of a neuron
Parts of a neuron (Source: Let’s Talk Science using an image by Dhp1080 [CC BY-SA 3.0] via Wikimedia Commons).
Graphic - Text version

Parts of a neuron including the axon terminals, axon, myelin sheaths, Schwann’s cells, Nodes of Ranvier, cell body, nucleus and dendrites.

Your brain is made up of billions and billions and billions of neurons, which all need to communicate with one another. This is done with chemical signals and electricity.

The Action Potential: How Neurons Communicate!

When a neuron receives a message from another neuron, there is a change in electricity in the axon near the cell body. When a certain amount of electricity is reached, an action potential occurs. This means a signal is sent down the axon away from the cell body.

The Nervous System, Part 2 - Action! Potential! (2015) by Crash Course (11:43 min).

Did you know?

Axons can be as short as a centimetre or as long as a whole metre! 

Especially for long axons, the signal might get lost before it can reach the next neuron. It’s very important that the electricity produced at the beginning of the axon is still present at the end of the axon. Therefore, axons are covered in a fatty substance called a myelin sheath, similar to how wires in your home are covered in plastic, to make sure the signal gets to the end of the axon.

It’s also important for the signal to travel down the axon very quickly. The myelin sheath helps with this, as well. Unlike the plastic on wires in your home, the myelin sheath does not cover the entire axon. The parts of the axon that are uncovered are called nodes of Ranvier. Rather than slowly travelling down the whole axon, the signal ‘jumps’ from node to node, making sure it gets to the synaptic terminal quickly. This is similar to trying to get a football from one end of a field to the other. You can try to run the whole distance with the football, or you can throw the football to someone else. The football will travel much faster if it is being thrown.

When the electrical signal makes it to the end of the axon and reaches the synaptic terminal, then a message can be sent to the next neuron. The space between the synaptic terminal of one neuron (which sends a message) and a dendrite of the next neuron (which receives a message) is called a synaptic cleft. The synaptic terminal will release chemicals called neurotransmitters, which allow neurons to communicate with one another.

messages are passed from neuron to neuron using neurotransmitters
The message, in the form of neurotransmitters, crosses from the synaptic terminal of one neuron to the dendrite of another neuron (Let’s Talk Science using an image from ttsz via iStockphoto).

Neurotransmitters

When neurotransmitters are sent out of the synaptic terminal of one neuron, they will move across the synaptic cleft and send a signal to the dendrites of the next neuron. There are lots of different neurotransmitters, and which one is sent out depends on the role of the neuron.

In general, neurotransmitters can have two different effects; both are equally important in making sure all of our neurons are working properly. Some neurotransmitters are inhibitory, which means that when they are released by the synaptic terminal, they reduce the electricity in the next neuron. This makes it less likely that an action potential will occur. These neurotransmitters are inhibitory because they make it harder for a neuron to send a message to the next neuron.

The other type of neurotransmitters are excitatory, which means that when they are released by the synaptic terminal they increase the electricity of other neurons. This means an action potential is more likely to occur. If a synaptic terminal sends excitatory neurotransmitters to the next neuron, then another action potential will occur, and the whole process will start again! This is how neurons are able to communicate with one another, and how information is sent throughout your brain.

To summarize, there are five key steps for a neuron to communicate with other neurons.

  1. An action potential occurs. This means there is enough electricity at the beginning of a neuron to send a signal.
  2. This electrical signal is sent from the cell body to the axon.
  3. The signal travels down the axon by “jumping” between the axon nodes.
  4. When the electrical signal reaches the end of the synaptic terminalneurotransmitters are released into the synaptic cleft.
  5. These neurotransmitters send a signal to the dendrites of the next neuron.

These five steps are responsible for everything your body is able to do.

 

Five key steps for neuron communication
Locations of where the five key steps take place (Let’s Talk Science using an image from ttsz via iStockphoto).

So what happens when you see a dog you want to pet? Seeing the dog means that neurons receive a message that there’s a dog in front of you. Different neurons send a signal to your arm to reach out to the dog. When you pet the dog, you might notice how soft its fur is, which means other neurons received a message about the way the dog feels. At any given moment, there are billions of neurons sending messages around your brain to one another. Neurons even allow you to consider just how incredible your brain is! Which is pretty incredible, when you think about it.

 

References

Brain Facts. (2012, April 1). The Neuron. https://www.brainfacts.org/Brain-Anatomy-and-Function/Anatomy/2012/The-Neuron 

Lodish, H., Berk, A., Zipursky, S. L., Matsudaira, P., Baltimore, D., Darnell, J. (2000). Molecular Cell Biology (4th ed.). New York: W. H. Freeman. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK21535/

Queensland Brain Institute. (n.d.). What are neurotransmitters? The University of Queensland. https://qbi.uq.edu.au/brain/brain-physiology/what-are-neurotransmitters