We now know that neurons are the basic unit of the nervous system. These electrically excitable cells make up the brain and the nervous system, and there are different types of neurons in a variety of shapes, serving a plethora of functions. But the word neuron, as we know it today, didn’t exist before 1891. Yes, the word did exist, but it had a different meaning which is now obsolete.
Two opposing camps
Discovering the neuron and figuring out the idea that they are the building blocks of the nervous systems was one of the greatest successes of the 19th Century. The cell that had been observed by 17th Century English physicist Robert Hooke was known to be the discrete unit making up tissues of plants, animals and all living things, by the middle of the 19th Century. But the nervous system proved to be more tricky with no clear consensus about it.
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One popular idea that existed then was that the brain and the nervous system could not be split up into structural units, like in the case of the heart or liver. While this camp of reticulists believed that the nervous system consisted of a network of continuous tissue or reticulum, the other side, now dubbed the neuronists, argued that the nervous system too should be made up of discrete entities.
Golgi’s black reaction
Italian physician Camillo Golgi came up with his black reaction in 1873 that allowed examination of nervous tissue in much greater detail than possible before. His technique of hardening a piece of brain in potassium dichromate and soaking the preserved tissue in a silver nitrate solution helped reveal the complete structure and arrangement within the unstained tissue.
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Golgi was able to distinguish two types of projections based on his reactions, a long slender cable that didn’t branch much and a cluster of branching fibres that were much shorter. Golgi, however, didn’t oppose the idea of the reticulum and instead believed that all the long slender cables probably connected to form one network.
Cajal catches on
When Spanish anatomist Santiago Ramon y Cajal stumbled upon Golgi’s work in 1887, he was not only certain that this was the most advanced method available to study the nervous tissue, but was also confused as to why so few scientists had carried out this staining procedure in the intervening 14 years. He improved upon the technique and applied it to various nervous tissues, both from animals and people.
Cajal was able to show based on his studies that there was no reticulum and that the cell bodies didn’t fuse into one. His detailed sketches showed that the nervous system too was made up of individual building blocks, just like any other living tissue. Cajal called these discrete units “absolutely autonomous unit[s]”.
The neuron doctrine
Cajal’s ideas were initially made fun of, but he slowly started winning over people to his point of view. German anatomist Wilhelm Waldeyer – the first to use the term ‘neuron’ to mean ‘nerve cell’ in his paper published on July 13, 1891 in the German journal Berliner Klin. Wochenschr – synthesised Cajal’s detailed research along with the cell theory of the 1830s. By adding ideas from other leading figures in the field, Waldeyer came up with the neuron doctrine in 1891. The discovery of the concept that the nervous system is made up of distinct individual cells finally gained ground after that.
Even though Cajal and Golgi were in opposing camps with respect to their ideas, they shared the 1906 Nobel Prize in Physiology or Medicine. Cajal’s beautiful sketches showed the diversity in terms of the structure of the brain and the nervous system and his detailed drawings continue to be used by scientists and teachers even today.