Santiago Ramón y Cajal
Discoveries and theories

Ramón y Cajal made several major contributions to neuroanatomy. He discovered the axonal growth cone, and demonstrated experimentally that the relationship between nerve cells was not continuous, or a single system as per then extant reticular theory, but rather contiguous; there were gaps between neurons. This provided definitive evidence for what Heinrich Waldeyer would name " neuron theory ", now widely considered the foundation of modern neuroscience. He is also considered by some to be the first "neuroscientist" since in 1894 he stated to the Royal Society of London: "The ability of neurons to grow in an adult and their power to create new connections can explain learning." This statement is considered to be the origin of the synaptic theory of memory.

He was an advocate of the existence of dendritic spines, although he did not recognize them as the site of contact from presynaptic cells. He was a proponent of polarization of nerve cell function and his student, Rafael Lorente de Nó, would continue this study of input-output systems into cable theory and some of the earliest circuit analysis of neural structures.

By producing depictions of neural structures and their connectivity and providing detailed descriptions of cell types he discovered a new type of cell, which was subsequently named after him, the interstitial cell of Cajal (ICC). This cell is found interleaved among neurons embedded within the smooth muscles lining the gut, serving as the generator and pacemaker of the slow waves of contraction which move material along the gastrointestinal tract, mediating neurotransmission from motor neurons to smooth muscle cells.

In his 1894 Croonian Lecture, Ramón y Cajal suggested (in an extended metaphor) that cortical pyramidal cells may become more elaborate with time, as a tree grows and extends its branches.

He studied some psychological phenomena, such as hypnotic suggestion to alleviate pain, which he used to help his wife during labor. A book he had written on these topics was lost during the Spanish Civil War.

During his studies on the optic chiasma, Cajal developed a visual map-based theory offering an evolutionary explanation for the decussation of nerve fibres and the chiasm of the optic tract.
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