Mapping the Nervous System

One of the first of the great pioneers of nerve research to receive the Nobel Prize, a Spanish surgeon's son called Santiago Ramón y Cajal said, "The brain is a world consisting of a number of unexplored continents and great stretches of unknown territory." And towards the end of the 19th century that is how it must have appeared as the power of the microscope revealed just what a complex and amazing network the human nervous system is.

We know now that the nervous system consists essentially of the command centre in the central nervous system - the dense cluster of nerve cells in the brain and spinal cord - and the signalling network of peripheral nerves - fibres that stretch out into every corner of the body. But nerves are incredibly fine. A nerve fibre can be less than a hundredth of the thickness of a human hair, so with the microscopes available in the 19th century, nerve fibres were very hard to see indeed.
When they peered down a microscope, 19th century scientists could just about make out that the nervous system was made of what they took to be a network of nerve cells. But nerve cells looked like no others. Whereas most body cells are essentially parcels of some shape, nerve cells looked more like spiders with a bulky body off which spread countless thin threads, called 'processes'. They knew nerves played a part in signalling, so they guessed all these cell bodies and threads were fused together in one continuous network. But it was all so tangled and tiny that no-one could really see. Then in 1871, a young Italian anatomist named Camillo Golgi made a remarkable discovery in the hospital kitchen where he carried out his own experiments.

Golgi found that if he soaked a bundle of nerve fibres over a few nights in silver nitrate - an idea some suggest he may have got from its use in photographic film - a few of the nerve cells stained a dark and inky black and showed up clearly under the microscope. Suddenly, complete nerve cells revealed their full appearance for the first time, and Golgi saw how the processes consisted of a single long tail or axon and an array of spindly branches or dendrites that spread out from the spider-like cell body. But he still thought they were all part of a tangled, inseparable web of fused fibres through which signals must flow this way and that.

Unmasking nerve cells

Working from a makeshift laboratory, Camillo Golgi developed a revolutionary silver staining method that allowed him to visualize individual nerve cells. Golgi continued to develop staining techniques and teach about them; here he is seen at the age of 77 in his laboratory at the University of Pavia, Italy.
The photo was kindly provided by Museo di Storia dell'Università di Pavia - Museum for the History of the University of Pavia.

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