Our brain isn’t populated only by neurones. In fact, they are a minority. Other brain cells, called glial cells, are far more numerous. Unfortunately, they have long suffered from the ‘neuron doctrine’. All attention and research efforts went to the neurones. Only recently, more and more evidence surfaces of the immense importance of these glial cells.
The brain contains two kinds of cells: nerve cells, better known as neurones, and glial cells. Every human brain is made up of an estimated one hundred billion neurones. The number of glial cells is far bigger, about six- to ten-fold.
At the beginning of the 20th century, scientists had concluded neurones are the most important brain cells. By that time, new tissue staining techniques had just been developed with which brain tissue could be investigated. In the laboratory, a specially prepared slice of brain tissue was injected with a chemical solution containing silver. This solution reacted with individual neurones in the brain slice. These neurones became clearly stained in brown and black and thus stood out in their entirety from the brain pulp. Today, these and similar staining methods are still being used in laboratories all over the world.
With the limited research methods available at that time, glial cells appeared to do hardly anything. It seemed they only filled up the empty space between neurones. That’s why they were named glia, which is Greek for glue. This idea is where the popular belief came from that we only use ten percent of our brain, namely the part that is made up of neurones.
Nothing is more beside the truth. Nature doesn’t let things just come into being; everything that has no use will disappear in the course of evolution. Hence, it is a bit unreasonable to presume our brains come with a ninety percent reserve capacity.
Later research made perfectly clear most of us use our brains completely, the total one hundred percent. The glial cells have very important tasks in the functioning of the brain as well. The latest research gradually even points to the possibility glia are the most important brain cells.
They may be the ones that direct neurones. In Petri dishes (shallow glass or plastic dishes used to culture cells named after their inventor, the German bacteriologist Julius Richard Petri) in the laboratory, glial cells are able to survive on their own whereas neurones will only stay alive in the dish when they are accompanied by glia.
Glial cells have long played only a secondary role in brain science. Due to limited technology, all research efforts focused on the easier to understand neurone. Thanks to big technical advances it is possible now to study glia more in detail in laboratories and the results are surprising. More and more astonishing facts about these brain cells are emerging and it is becoming clear glia are very sophisticated cogs in the brain machinery.
The brain is made up of an incredibly complicated web of neurones. Glial cells are responsible for organising this tangle of excitable cells and give an efficient structure to the brain. They play a key part in orchestrating neuronal functioning and survival.
Different types of glia exist. The most common is called astrocyte. Collectively, these astrocytes form a kind of matrix in our brain. Every astrocyte controls and manages its own little piece of brain, including neurones and neurotransmitters – the chemical substances that take care of information transfer within the brain – present. When a problem arises astrocytes step in, for instance by closing off the damaged part from the rest of the brain. Sometimes astrocytes overdo it. They go haywire, grow explosively and become a brain tumour.
To be able to accomplish all their tasks, astrocytes are assisted by another type of glial cells, the microglia. These cells make up the immune system of the brain. They constantly scan their domain for intruders. The moment they encounter one, they will attack the alien cell and destroy it.
The third type of glial cell is of crucial importance for a well-functioning brain. It is the oligodendrocyte, a Greek word that means ‘cell with a few branches’. This glial cell enwraps the axons of neurones with a fatty, white substance, called myelin. This sheath enables better conductivity within the axon so as to make the electric currents reach the tip faster, comparable to the plastic wrapping of an electricity cable.
In various diseases, of which multiple sclerosis is best known, this fatty sheath is being affected and gradually disappears. The electric currents won’t pass through the axons anymore and information transfer becomes blocked.
It is clear glia are extremely important for the well-being of the brain. They are involved in just about all diseases in the brain, for better or for worse. The reactions of glial cells are of critical importance to the process of a neural pathology. Most drugs that have been developed so far though aim at neurones and specifically neurotransmitters. Future research has to come up with remedies to help glial cells continue to do their good work.
Through the ages, scientists have been intrigued by the intellectual capabilities of the human being in comparison to those of other animals. What makes one animal more intelligent than another? The size of the brain cannot be decisive since there are many animals with bigger brains than humans. And even the brains of the Neanderthals were larger than those of modern man.
Neurones don’t vary that much either. In comparison with neurones of rats and mice for instance those of humans are only a bit longer. The rise in intelligence does coincide with the number of glia. The brains of animals that are higher up on the intelligence ladder hold more glial cells per neurone. Astrocytes in human brains have proven to be bigger, faster and more complex than those in the brains of other animals.
It might just be we owe our bigger brainpower to the fact that our astrocytes are more sophisticated and have more complex processing abilities. The brain of the famous physics genius Albert Einstein which was preserved after his death, contained far more glia than the brains of ordinary men to which it was compared.
For the past century, brain science has been dominated by the neuron doctrine. We speak of neuroscience, neurosurgeon, and neurodegeneration. There even was a time, it was said we only use ten percent of our brains since neurones represent only ten percent of all brain cells. Maybe in the coming decade a revolution will take place as ‘the other’ brain cells will get their well-deserved attention.
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