A network similar to the Internet is formed in our brains. Nerve cells are grouped together and communicate with each other through synapses. I will explain in detail how nerve cells communicate with each other in the head.
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A network in the brain that was later connected to the Internet
What kind of signals are exchanged in the neural networks in our brains? Let me introduce you to the fun of the “network” in our brains.
Italian anatomist Camilo Golgi used a unique staining method to examine the human brain and revealed that the brain is made up of many nerve cells (neurons). After that, the Golgi examined the structure of neurons in the brain more carefully, and found that long, thin fibers called neurites extend from the central part (= cell body) of neurons, and the ends reach other neurons. We found that a net-like network was formed.
When I teach about the structure and function of the brain in my physiology class at university, I explain that the brain has a network of nerves, just like the Internet. Strictly speaking, the “Internet-like” description is incorrect. This is because the neural network was first discovered, and it can be said that the modern Internet was created based on this. Inspired by the network in the brain, people built a communication network by connecting the telephones of each home with electric wires as a means of contacting each other, and further developed it to create the Internet of today.
Looking back, the reason why everyone is using the Internet to read my articles is based on the neural network in the brain that Golgi discovered a long time ago. When you think about it, brain science has a big impact on our lives.
The Mystery of Neural Networks: Are Neurons Connected Together?
I had a bit of a problem with the neural network that Golgi discovered. It’s a bit technical, but what Golgi advocated is called the “reticular theory,” in which the ends of the neurite fibers extending from one nerve cell attach to other nerve cells, forming a network of the entire brain. The idea was that they are completely connected. Spanish neuroanatomist Santiago Ramón y Cajal disagreed with this idea.
While observing the structure of the brain in detail using the Golgi staining method, Cajal discovered that the nervous system is composed of discontinuous units called neurons, and that the ends of the neurite fibers are attached to other cells. Instead, I claimed that it was interrupted.
In a neural network, are neurons attached to each other or separated? A great controversy ensued. Some of you may think, “I don’t care about such a small thing,” but in fact, this controversy would later lead to major advances in brain science.
At the time, I had no means of confirming that, so I was inconclusive. However, this controversy had such an impact on the scientific community that both Golgi and Cajal were awarded the 1906 Nobel Prize in Physiology or Medicine. However, the two, who had a confrontational relationship, gave their award commemorative lectures in completely different places, and it seems that they did not exchange words with each other at the award ceremony.
Discovery of “Synapse”! Between cells seen with an electron microscope
It was finally time to settle the dispute between Golgi and Cajal, the Nobel Prize winners who were still in dispute. The electron microscope was invented.
A conventional optical microscope is a device that magnifies and observes an object to be observed with a lens while illuminating it with visible light. Electron beams have much shorter wavelengths than visible light, so we can see things with higher resolution. In layman’s terms, high resolution means being able to distinguish smaller objects. Viruses are invisible under a light microscope but visible under an electron microscope.
When observed with an optical microscope, the nerve cells appeared to be stuck together, but when observed with an electron microscope, there was a slight gap. As for the fine structure of neural networks, Cajal’s theory was the winner.
After that, the junction of nerve cells, including the gap, came to be called “synapse”. It was named by British physiologist Charles Scott Sherrington. The word is derived from the Greek word synapsis, which means “joint, handshake”. I guess they wanted to express the situation where each other’s hands are reaching out to shake hands, but the hands are not touching. By the way, the first part of synapse, syn-, has the meaning of matching, and is the same root as shin, which is used when things happen at the same time. Sherington was awarded the Nobel Prize in Physiology or Medicine in 1932 for his work on neurons.
Structure and function of synapse …… Input terminal and output terminal of nerve cell
The discovery of “synapse” made great strides in brain science. I would like to refrain from explaining all of its history here, and would like to conclude this article by explaining the structure and function of synapses that have been clarified by research so far.
As shown in the diagram below, there are countless neurons in the brain that form a complex network. Nerve cells differ greatly from skin and muscle cells in that they have an arm-like structure called neurites. Neurites are further divided into dendrites and axons. Dendrites are relatively short and have many branches, whereas axons are usually single and very long. In the neural network of the brain, dendrites correspond to input terminals that receive signals emitted by other neurons, and one axon corresponds to output terminals that transmit signals to other neurons.
Structure of a neuron, which is the smallest unit of the neural network in the brain (original diagram created by the guide)An electrical signal is generated when a nerve cell is activated. The electrical signal travels quickly down long axons to reach their ends. You can think of it as the same way that electricity flows through a telephone line and information is sent. It would be easy if the electrical signal that reached the end of the axon was transmitted to the neighboring nerve cell as it is, but there is a synaptic gap there. Since they are not directly attached, electricity cannot be transmitted. How is information transmitted at the synapse?
Nerve cells communicate at synapses
What do you do when you want to tell someone something? phone? Email? There are many ways to do this, but if the other person is right in front of you a little further away, you can quickly communicate by speaking out loud.
In fact, information is transmitted in a similar way at synapses, which are the connections between nerves. As shown in the diagram below, what corresponds to the voice of nerve cells is a “neurotransmitter”. Neurotransmitters are stored in small sacs called “synaptic vesicles” at the ends of axons, and when an electrical signal is transmitted, they jump out of the sacs and are released into synaptic clefts. .
Electrical signals are transmitted through the axons of nerve cells, but information is transmitted through neurotransmitters at synapses (original diagram created by the guide)However, no matter how much you speak out, if the other person doesn’t hear you properly, your message won’t get across. In the nerve synapse, the structure called “receptor” that exists on the dendrite on the receiving side plays the role of the ear that properly hears the voice. When a receptor catches a neurotransmitter, a message has been delivered.
In this way, the mechanism by which neurons communicate and transmit information at synapses is called “synaptic transmission.” When our brain is working, here and there, neurons talk to each other at synapses.
However, even if it is a conversation between nerves, it does not mean that each other can talk freely. The speaker and listener are decided, and the conversation is one-way, so it may be closer to a message game than a conversation. In the information transmission in the neural network, returning backwards causes confusion. To prevent this from happening, please understand that it is a one-way street where the listener does not give back to the speaker, but only conveys the message ahead.