The Discovery Of The Neuron

The discovery of the neuron
For most of the nineteenth century, there was an on-going debate among researchers about the organization of the nervous system. One group of researchers, the so-called reticularists, believed that the nervous system consisted of a large network of tissue, or reticulum, formed by the fused processes of nerve cells. The other group, the neuronists, argued that thenervous system consisted of distinct elements, or cells.
Both groups used the same methods to study nerve cells, but came to different conclusions about the fine structure of the nervous system, which could not yet be seen in detail because of the low magnification and poor resolution of the microscopes available to them at the time. Just as the observable universe increased in size with thedevelopment of increasingly powerful telescopes, so did understanding of the organization of the nervous system improve with advances in microscopy.
In 1838 Theodore Schwann and Matthias Schleiden proposed that the cell was the basic functional unit of all living things. The Cell Theory was not, however, believed to apply to the nervous system, and it was not until towards the end of the nineteenthcentury that it became generally accepted that the brain, too, consisted of cells. The discovery of the neuron was a milestone in brain research, and paved the way for modern neuroscience.
Advances in microscopy and improved histological methods meant that nerve cells could be examined in increasing detail, but at the time that the Cell theory was proposed, the relationship between the cell body,axons and dendrites was still unknown, because each of the components of the neuron had only been seen separately.
The complexity and small size of most neurons made elucidating the structure of the neuron the most formidable task in the field of histology, and the debate about the fine structure of the nervous system spanned most of the nineteenth century. But, because of the work of a number ofoutstanding individuals, the Neuron Doctrine would eventually prevail over reticular theory as the nineteenth century drew to a close.
The popularity of the reticulum theory peaked during the mid-nineteenth century. The main proponent of this theory was Joseph von Gerlach (1820-1896). Gerlach was interested in methods of staining nerve tissue, and used gold chloride or carmine to stain his tissuesamples, popularizing the use of the latter among his contemporaries. Based on his observations using these staining techniques, Gerlach concluded that:
the finest divisions of the protoplasmic processes ultimately take part in the formation of the fine nerve fibre network which I consider to be an essential constituent of the gray matter of the spinal cord. The…divisions… are none other than thebeginnings of this nerve fibre net. The cells of the gray matter…are therefore doubly connected…by means the nerve process which becomes the axis fibre…and through the finest branches of the protoplasmic processes which become a part of the fine nerve fibre net of the gray matter.
There were disputes among the reticularists about the nature of the nerve net. Whereas Gerlach believed that axons anddendrites fused, other investigators argued that only one or the other of the processes formed anastomoses.
In the 1820s, achromatic lenses were developed, and their use in compound microscopes provided investigators with the clearest images yet of tissue samples. One of the first people to use the new compound microscopes to investigate nervous tissue was Johannes Evangelista Purkinje(1787-1869, left), an anatomist born in Libochovice, Bohemia (in what is now the Czech Republic).
Purkinje studied medicine and philosophy at the University of Prague, graduating in 1819. He then wrote a doctoral dissertation on vision before being appointed as professor of physiology at Prague University. As a professor, Purkinje discovered the phenomenon (now known as the Purkinje effect) whereby, as...