In 1891, Cajal enunciated his Law of Dynamic Polarization at a Medical Congress in the city of Valencia. This Law says that the nervous impulse is polarized, going in only one direction. This is so, he explained, because the neuron receives the nerve impulse in its dendrites, transports it to the cell body and releases it through the terminal buttons of its axon, which come into contact with the dendrites of other cells. However, studying the optic tectum of birds in 1892, he found neurons whose axon does not emerge from the cell body, but from one of its dendrites, so his theory of Dynamic Polarization could not be fulfilled. He studies this phenomenon and realizes that, in these cases, the nerve impulse did not need to reach the cell body and have to go back through the dendrite to be able to exit through the axon, but was released directly through the axon without having to first reach the cell body. He then formulates a variation to his theory of Dynamic Polarization, which he enunciates as Theory of Axipetal Polarization. 3D print by Jeremy Swan based on an original illustration by Santiago Ramon y Cajal. Courtesy of the Cajal Institute, Spanish National Research Council or CSIC©