Reticular theory

Reticular theory is an obsolete scientific theory in neurobiology that stated that everything in the nervous system, such as brain, is a single continuous network. The concept was postulated by a German anatomist Joseph von Gerlach in 1871, and was most popularised by the Nobel laureate Italian physician Camillo Golgi.

However, the theory was refuted by later observations of a Spanish pathologist Santiago Ramón y Cajal, using a staining technique discovered by Golgi, which showed that nervous tissue, like other tissues, is made of discrete cells. This neuron doctrine turned out to be the correct description of the nervous system, whereas the reticular theory was discredited.

Paradoxically, the proponents of the two contrasting theories, Golgi and Ramón y Cajal were jointly awarded the Nobel Prize in Physiology or Medicine in 1906, "in recognition of their work on the structure of the nervous system."

In 1863 a German anatomist Otto Friedrich Karl Deiters described the existence of an unbranched tubular process (the axon) extending from some cells in the central nervous system, specifically from the lateral vestibular nucleus. In 1871 Gerlach proposed that the brain is composed of "protoplasmic network", hence the basis of reticular theory. According to Gerlach, the nervous system simply consisted of a single continuous network called the reticulum. In 1873 Golgi invented a revolutionary method for microscopic research based on a specific technique for staining nerve cells, which he called "la reazione nera" (the "black reaction"). He was able to provide an intricate description of nerve cells in various regions of the cerebro-spinal axis, clearly distinguishing the axon from the dendrites. He drew up a new classification of cells on the basis of the structure of their nervous prolongation, and he criticized Gerlach's theory of the "protoplasmic network". Golgi claimed to observe in the gray matter an extremely dense and intricate network, composed of a web of intertwined branches of axons coming from different cell layers ("diffuse nervous network"). This structure, which emerges from the axons and is therefore essentially different from that hypothesized by Gerlach, appeared in his view to be the main organ of the nervous system, the organ that connected different cerebral areas both anatomically and functionally by means of the transmission of an electric nervous impulse. Although Golgi's earlier works between 1873 and 1885 clearly depicted the axonal connections of cerebellar cortex and olfactory bulb as independent of one another, his later works including the Nobel Lecture showed the entire granular layer of the cerebellar cortex occupied by a network of branching and anastomosing nerve processes. This was due to his strong conviction in the reticular theory.

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