Isn’t it fantastic that we are able to think about how we are able to think. Our brains are so ingeniously formed that we even have the ability to get to such an abstraction level. Most people take our thinking capability for granted and don’t give it much thought. But knowing just the basics about how our brains form our thoughts will leave you even more in awe.
Our brain is made up of an enormous amount of cells. In the history of brain research, scientists have given these cells names, based on their physiology. Cells that looked alike were joined into a cell group. The two main cell types in the brain are neurones and glial cells (for an explanation about glial cells, click here).
In the early days of brain research, it was very hard to study the extremely tiny cells with nothing more than a simple microscope. The picture we have of the functioning of the different brain cells is getting clearer now. This is thanks to new research methods and ever smaller and more sensitive measuring equipment that becomes available.
In the laboratory, it is even possible at present to attach tiny measuring devices to one single neurone. This is nothing short of a miracle; considering the fact neurones averagely have a diameter of about twenty micrometer (one micrometer is one-thousandth of a millimetre).
Many different types of neurones exist. The most common type consists of a nucleus, a long sprout on one side, called axon, and one or more short sprouts with several branches on the other side. These little fingers are called dendrites.
Neurones are champions in information transfer. Via their dendrites, they catch a signal from another neurone or from a glial cell. This signal is processed within the neurone, which results in another signal being sent out via the other side of the neurone, via the axon. The next neurone in the chain subsequently catches and processes the signal, and so forth.
The transfer of information is made up of small electric currents. These impulses pass relatively slow through the neurone, varying from 1 to at most 120 meters per second. For comparison: the cruise speed of a Boeing 747 passenger jet is 250 meters per second.
In general, neurones don’t make physical contact with each other. There’s a minute opening between the axon of one neurone and the receiving dendrite of the next neurone, called the synapse. Every time the electric current in the neurone reaches the end of the axon, it spits out a chemical substance. This substance crosses the synapse and sticks to one of the dendrites of the neurone on the other side. The chemical reaction this causes brings into being another electric current that travels through the receiving neurone. This process repeats itself infinite times.
The chemical substance a neurone spits out via its axon is called neurotransmitter. Many types of neurotransmitters have already been discovered, but it is very likely more substances exist that function as neurotransmitter and that we don’t know yet. Some well-known names of neurotransmitters are serotonin, acetylcholine, glutamate, and GABA.
Every neurotransmitter has its own tasks within the nervous system. Serotonin, for example, stimulates neurones involved in learning and memory, but also neurones that regulate our mood. Dopamine is the neurotransmitter of the reward circuit in our brain. Acetylcholine among other things takes care of information transfer to the muscles. Glutamate is the most common neurotransmitter and is involved in learning and memory. GABA is the chief inhibitory neurotransmitter. It regulates neuronal excitability.
One neurone communicates with on average about seven thousand other neurones. These contacts are variable. Depending on requirement, a neurone at one time communicates with this neighbour and at another time with that one. The better it knows its neighbour the easier it starts talking to her. Contacts with new neighbours or neighbours it hasn’t spoken to for a long time are harder.
During the growth of a baby in the womb, neurones make contacts in abundance. Stimulated by nutrients present in the brain and not hindered by information from the exterior, the neurones keep on chattering with as many neighbours as they encounter. It is as if they are practicing for the time they will be functioning in the outside world. They end up with far too many, often useless contacts.
After birth, most of these connections will be broken again. Fine-tuning takes place influenced by information that enters the brain from outside. With the maturation of the brain, extensive pruning of axons happens and stronger connections form between the cells in one sensory system, sharpening and separating the senses. This process continues throughout life, but is going on rather rigorously in the first years of one’s existence.
Everything our brain contains, so everything we know and do, can be brought back to contacts between neurones and glial cells. The many billions of brain cells all have their specific tasks and form specialised networks. Whenever we learn something new, another network is created.
All neurones that have been involved in for instance driving a car have created an invisible bond. One neurone has communicated with another one, its neighbour. At first, they only greeted from a distance. But now that they know each other, next time they meet they will have a casual chat across the hedge. If they see each other often enough there even may result a shortcut through the hedge so they can easily visit each other for a cup of coffee.
Close-knit networks of neurones that frequently communicate with each other are being established this way. The contacts one neurone makes with other neurones are not fixed. They can change constantly. Depending on necessity a cell is in contact with one cell one moment and with another cell another moment. This all is influenced by what you are doing, what you are thinking, what is going on around you.
Contacts come and go. Cells that have to communicate regularly gain very strong links that normally won’t be broken again. Contacts made during a one-off activity or for something you have learned a long time ago, may be lost if the connections aren’t used anymore. That is why it is so hard to remember certain difficult things you learned at school.
A good functioning brain is all about making contacts. And for the brain, a good neighbour is worth more than a far friend.
Library of US congress © nickjene – Fotolia.com
Neurone © sfischka – Fotolia.com
Chatting neighbours © Lorelyn Medina – Fotolia.com