[The neuron theory: one of the main scientific achievements of the 19th century]

Abstract

The cell theory, enunciated by Theodor Schwann in 1839, stated that all tissues in the body are composed of individual cells. The theory gained immediate acceptance for all organs except for the nervous system where some basic problems were encountered, among them the difficulties in establishing the relation between nerve cells, nerve fibers and terminal branches. Deiters observations (1865) had provided evidence that the basic structure of a nerve cell was made up of a cell body, protoplasmic prolongations (dendrites), and a single long axon. This helped to define the nerve cell as the basic unit of the nervous tissue but it remained then to understand how the nerve cells are connected since they do not make direct contact through their cell bodies and are separated by the 'neuroglia'. Two fundamentally different views of the organization of neurons arose, one holding that neurons are individual and contiguous units, connected in chains to form specific pathways (His, Forel, Nansen, Ramón y Cajal), the other that thin nerve cell branches from continuous diffuse networks through which the neuronal activity propagates (Gerlach, Golgi). The key technological advance that led to the resolution of most of these uncertainties came in 1873 with the introduction by Camillo Golgi of a new method of staining individual nerve cells. In 1887, Santiago Ramón y Cajal stumbled on the Golgi stain and began an intense study of neuronal morphology throughout the nervous system. As far back as 1887 it was shown that the nervous system is not a mass of fused cells showing a common cytoplasm, but a highly intricate network of discrete cells.(ABSTRACT TRUNCATED AT 250 WORDS)