purkinje neuron from the human cerebellum
Ramón y Cajal’s theory described how information flowed through the brain. Neurons were individual units that talked to one another directionally, sending information from long appendages called axons to branchlike dendrites, over the gaps between them.
He couldn’t see these gaps in his microscope, but he called them synapses, and said that if we think, learn and form memories in the brain then that itty-bitty space was most likely the location where we do it. This challenged the belief at the time that information diffused in all directions over a meshwork of neurons.