Neuron Doctrine Vs. Nerve Network
In order to understand the great debate of the Neuron Doctrine, which is associated with Cajal, Vs. the Nerve network, which is associated with Golgi, it is perhaps necessary to backtrack a little bit in order to see how these theories originated.
Technology (see technology tab) was finally developed enough for scientists to explore how the body functioned at the cellular level.
Equipped with the carmine stain, Otto Friedrich Karl Deiters observed the anatomy of nerve cells: particularly, the somas and dendrites. Deiters wondered how these nerve cells communicated. Because the staining techniques at that point were not well advanced, after looking at his slides Deiters, around 1865, hypothesized that perhaps nerve cells were fused together, as this is what it looked like on from his slides (the synapse was not visible to scientists until the 1950s). Joseph von Gerlach took the fusing idea a step further and suggested that all nerve cells are interconnected, which creates a giant web, thus the nerve network was established (Finger, 2000).
Not long afterward, in 1873 Golgi invents the silver stain which allows scientists much clearer view of nerve cells (Finger, 2000).
In 1886 Wilhelm His suggests that perhaps it is possible that nerve cells do not fuse together. He backs up his claim by pointing out that motor neurons are not connected to muscle fibers; therefore, he speculated that if nerve cells in the peripheral nervous system are not connected, nerve cells in the central nervous system may not be connected either . Around that same time, August Forel suggested that nerve cells may simply touch to send the nerve impulse, but they are not technically fused (Finger, 2000).
This was when Santiago Ramon y Cajal came into the scene. Cajal improved Golgi’s stain and created better slides. At the German Anatomical Society of 1889, Cajal presented his slides, and expressed his opinion that he found no evidence of nerve cells fusing together (Finger, 2000).
Thus, in 1891, Wilhelm von Waldyer, with his prestige, officially established that nerve cells are seprate entities called neurons. This theory thus became the neuron doctrine (Finger, 2000).
Though it was established that neurons were most likely seperate units, it was still not determined how they communicated or in what direction. Golgi believed that dendrites’ only job was to provide nutrition, so it was only the axons that commuicated information. Cajal however believed that communication flowed in one direction, but that dendrites received informaiton while axons send out information. He came up with this hypotheis by examining the sense organs. In the eyes, for example, neurons are all positioned with their dendrites outward, to recieve the information from the outside world, and then the axons are pointed in towards the brain to deliver that information (Finger, 2000).
However, Cajal still did not answer the question about how information passed between neurons. He hesitantly agreed with other scientists that perhaps dendrites communicate to axons via touching, but he was not entirelly convinced (Finger, 2000).
*Interesting Fact: Way back in 1872, before Golgi even invents the silver stain, Alexander Bain suggests that when learning takes place, nerve cells grow closer together, and when memory loss occurs, nerve cells grow further apart (Bain, 1873):
“For every act of memory, every exercise of bodily aptitude, every habit, recollection, train of ideas, there is a specific grouping, or co-ordination, of sensations and movements, by virtue of specific growths in the cell junctions.” (pp. 91).
“If the brain is a vast network of communication between sense and movement – actual and ideal – between sense and sense, movement and movement, by innumerable conducting fibres, crossing at innumerable points, — the way to make one definite set of currents induce a second definite set is in some way or other to strengthen the special points of junction where the two sets are most readily connected […]” (pp. 92)
Another interesting fact* The idea that perhaps nerve cells communicate either chemically or electronically can be traced back to 1877 to Emil Du Bois-Raymond.
Of known natural processes that might pass on excitation, only two are, in my opinion, worth talking about. Either there exists at the boundary of the contractile substance a stimulative secretionin the form of a thin layer of ammonia, lactic acid, or some other powerful stimulatory substance, or the phenomenon is electrical in nature. (qtd. Finger p. 260)
The answer to exactly how nerve cells communicate was answered by Otto Loewi, who did an experiment which showed that neurons can communicate via chemicals. Though the story varies in minute details, Otto Loewi was said to have insomnia and woke up often during the night. One time he woke up and got the idea for an experiment to test whether neurons respond via chemicals. He wrote it down, and later he did the experiment and was successful (Finger, 2000).
He took two frog hearts. One frog heart had its vagus nerve still attached while the other heart had its vagus nerve removed. He put neutral ringer’s solution on the heart with the vagus nerve. He stimulated the vegas nerve which made the heart slow down. He then took some of the ringer’s solution and applied it to the second heart, which immediately made it slow down its beating as well, just as if he had stimulated the second heart. This shows that the vagus nerve released some chemicals to tell the heart to slow its beating, and he was able to get some of those chemicals and make the other heart do the same thing (Sabbatini, 2003).
Bain, A. (1873). Mind and Body: The Theories of Their Relation. London. Henry S. King.
Finger, S. (2000). Minds Behind the Brain: A History of the Pioneers and Their Discoveries. New York NY: Oxford Press.
Sabbatini, R. M. E. (2003). Neurons and Synapses: The History of its Discovery. Retrieved November 5, 2010 from: http://www.cerebromente.org.br/n17/history/neurons5_i.htm
This page was created by Neil Thorne