Find the Gap!

But then using Golgi's stain, Cajal, the Spanish surgeon's son, looked at the nerve cells of newborn birds and other small animals, which were simpler and easier to see than adult cells, and reproduced what he saw in a series of beautiful drawings. Cajal interpreted his observations differently to Golgi, proposing that there were gaps between the processes of each cell, and that each cell was actually a separate unit or neuron, not part of a fused network at all. Nerve signals, then, must be passed on from neuron to neuron across the gaps, later called 'synapses', in a kind of relay race.

Then Cajal, who shared the Nobel Prize with Golgi in 1906, noticed that axons on neurons that connect to sense receptors such as vision, touch and hearing (sensory neurons) point in towards the central nervous system, while axons on neurons that trigger the muscles to move (motor neurons) lead away. Neurons, then, must carry signals in one direction only, taking messages in through the dendrites, and transmitting them through the axon.

Anatomy of the nervous system.


Using Camillo Golgi's silver staining method and blessed with natural artistic talent, Santiago Ramón y Cajal created stunning representations of different areas of the nervous system. Here, Cajal's sketch of the retina shows clearly the variety of neurons present in the eye.
Image kindly provided by the History of Medicine (IHM).

Cajal began to realize that signals travel along particular pathways and that it might be possible to trace the paths through the nervous system from start to finish. It was a brilliant insight, which allowed scientists to explore how sense inputs from different parts of the body are wired into particular parts of the brain. By the middle of the last century neuroscientists such as American Wade Marshall, who trained the Nobel Laureate Eric Kandel, had shown how sense inputs from different parts of the body are wired into particular parts of the brain - a discovery summed up in a weird picture of a person called a 'sensory homunculus' which depicts areas of the body in proportion to how much brain space is needed to process the sense inputs.

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