How does the brain communicate? Introduction to the neuron

Written by: Jacinda Taggett

Edited by: Hannah Kim

Are you interested in learning more about neuroscience or psychology? If you want to understand how the brain works in its full capacity, we have to start smaller. As small as… a microscopic brain cell? The neuron is the fancy name for this nervous system cell, and is absolutely essential to begin your deep dive into the brain.

So, what is a neuron?

The neuron is what allows the brain to communicate not only within the different sections of itself, but also with the body as a whole. Each brain contains billions of neurons; some estimate up to 86,000,000,000!

The structure of neurons

In order to best understand how communication works, you need to know the structure of the neuron. Let’s dissect Figure 1 below.

Figure 1. Anatomy of a neuron, provided by https://byjus.com/biology/diagram-of-neuron/

1. Dendrite: these extensions of the neuron are responsible for receiving information from other parts of the body. Equipped with receptors (i.e., the neuron’s biological “lock”), the dendrites accept signals via neurotransmitters (i.e., the neuron’s chemical “key”).

2. Soma: the cell body for the neuron that aggregates the information received from the dendrites and sends it to the axon via the axon hillock. If the signal is strong enough to be sent down the axon, we refer to it as an action potential.

3. Axon: the main highway for action potentials to transfer distances across the nervous system.

4. Node of Ranvier: gaps that lie outside of the axon and in between the Schwann cells, this part of the neuron allows the action potential to “jump” across the axon in a quick fashion

5. Axon Terminal: at the end of the neuron, this part is necessary for transferring information to other neurons via chemical or electrical signals

6. Schwann Cell: insulation for the neuron’s axon, producing the myelin sheath

7. Myelin Sheath: the fatty layer that cover the Schwann cells, allowing for faster propagation of the signal

8. Nucleus: similar to any other cell in biology, this part of the neuron holds the DNA, or genetic material, of the cell

However, all of these parts don’t make sense without context. In order to understand, let’s discuss how the brain actually uses the neuron to communicate.

The communication between neurons

When one neuron wants to communicate with another, it relays information via chemical or electrical signals from its axon terminal to another neuron’s dendrites. This section between two neurons is called the synaptic cleft, and is also termed as part of the overall synapse. This cleft leads neurons to never even physically touch! Due to the terminology, the neuron with the axon terminal expelling signals is called presynaptic and the neuron receiving the information through its own dendrites is called postsynaptic.

The signal of the presynaptic neuron started from receiving a form of stimulation at its own dendrites beforehand, and this stimulation was strong enough to form an action potential. Once the action potential leaves the soma and moves down the neuron, it jumps between schwann cells covering the axon until it reaches the axon terminal. At the terminal, the action potential allows small sacs (vesicles) of chemical or electrical messengers (neurotransmitters) to merge with the edge of the neuron and release the neurotransmitter into the synaptic cleft (Figure 2).

Figure 2. Diagram of synaptic transmission, provided by https://www.geeksforgeeks.org/biology/synaptic-cleft-anatomy-structure-disease-function/

After reaching the synaptic cleft, the neurotransmitter molecules act as keys to the receptors of the postsynaptic neuron. If enough signal from these neurotransmitters excites the postsynaptic neuron, then this new neuron will undergo the same process as the prior one to transmit the signal to any subsequent neurons. Through this process, we have the capability to transmit information from one part of the brain to limbs across the length of our own body within milliseconds. It’s a beautiful process!

What to learn next?

Before you can get to the nitty gritty of curing Alzheimer’s disease or understanding how AI replicates human intelligence, you need to learn the fundamentals of neuroscience and psychology. If you are a complete beginner, I recommend taking a look at Neuroscientifically Challenged on YouTube. These videos are what introduced me to neuroscience! If you have reached a point where you can move onto more complex topics, feel free to read the articles by our blog, Academic Memories!