It looks like an impenetrable forest. Or maybe an enchanted underwater world. It is certainly beautiful, it is unmistakably a work of art.
Growing up in a small town in Spain, Santiago Ramón y Cajal (1852 - 1934) wanted to be an artist. He spent most of his childhood drawing, painting and taking photographs.
But his father had other ambitions. He was a doctor teaching anatomy at the university of Zaragoza, and he wanted his son to pursue a career as physician. Asking his son to help draw dissections for an anatomical atlas, he managed to arouse the interest of the young aspiring artist. In the words of Cajal himself: “My pencil, which was formerly the cause of so much bitterness, at last found grace in the eyes of my father [...] Gradually, my anatomical watercolors grew into a very large portfolio of which my father was quite proud.”
Cajal gave up his artistic talents for a while and enrolled at the medical school in Zaragoza.
After a few years practicing as a physician, Cajal turned to histology; the microscopic examinations of bodily tissues. Using a method developed by Camillo Golgi (1843 - 1926), Cajal improved the technique of staining brain cells to be viewed in the microscope. And applying his talents for painting, he would easily transfer his observations in the microscope into histological drawings. His illustrations would soon help answer some of the most important questions in neurobiology at that time.
A century earlier, Luigi Galvani (1737 - 1798) had established that nerves transmit information by electrical impulses. But how the information was passed from cell to cell was unknown. Further, the microscopic structure of the brain and nervous system was not yet recognized; it was unclear whether it was made of individual cells or by an extensive continuous network. Supporters of the reticular theory argued that the nervous system was formed by an undivided plexus of continuously interconnected cells - an argument reflecting the debate in functional neurology about cortical localization and the indivisibility of the brain.
Golgi had already described brain cells as composed of a cell body (soma) with a number of extensions protruding from it. Most protrusions were dendrites, but one long extension formed the axon and branched out to connect with other cells. It was also recognized that signals ran from the dendrites through the cell body and out the axon.
With the improved techniques of staining and imaging, Cajal was now able to identify discrete neurons in the brain. He realized that they were individual cells divided by gaps. Like trees in a forest, they could branch and interweave, but never fuse or unite.
Cajal presented his findings in Berlin in 1889. And although disapproved of by Golgi, the presentations gained the support of many others. German anatomist Wilhelm Waldeyer synthesized the ideas from cell theory with the observations made by Cajal and formulated the neuron doctrine. In fact, Waldeyer learned spanish just to fully appreciate the works of Cajal. He also coined the term neuron for the cells of the nervous system, including brain cells and nerves.
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This up-to-date illustration of the neuron may be correct in every detail; the cell body, the axon and the synapsing with another neuron. But it lacks the aesthetic simplicity of Cajal's. |
Waldeyer’s neuron doctrine was a new paradigm. In short, it stated that the nervous system is composed of individual cells. Like every other cell in the body, the neuron is a single entity. And although connected in an intricate network, the neuron works independently.
This doctrine was proved with the introduction of electron microscopy in the 1950es. This technology confirmed the existence of individual neurons in the nervous system. It also demonstrated a gap between the axon on one neuron and the dendrite on another. This gap is called the synapse, and it transmits the signal from one neuron to another by releasing a chemical substance (a neurotransmitter) into the gap. When an electric impulse travels down the axon, the neurotransmitter is released into the synapse and is then picked up by receptors on the dendrite of the receiving neuron. The signaling between neurons via synapses is the mechanism of information transmission in the nervous system. The human central nervous system holds around 100 billion neurons, each connecting to other neurons with several thousand synapses. And the plasticity and ability to form new synapses from one neuron to the another is probably what enables the brain to learn and to remember.
Cajal never saw his observations confirmed by electron microscopy. But he dedicated his life to the histology of the brain, comparing the cerebral cortex to “a garden filled with innumerable trees, the pyramidal cells, which can multiply their branches thanks to intelligent cultivation, send their roots deeper, and produce more exquisite flowers and fruits every day.”Cajal was a poet among scientists.
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Swanson LW: The Beautiful Brain: The Drawings of Santiago Ramon y Cajal. Abrams. 2017
Jabr F: Know Your Neurons: The Discovery and Naming of the Neuron. Scientific American. 2012
Geneser F: Histologi. Munksgaard. 2002
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The History of the Brain
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