The relationship between structure and function in the brain has an interesting counterpart in the scientific relationship of Santiago Ramon y Cajal and Charles Sherrington. In their search for the principles of organization of the nervous system, both men met at the synapse. For Sherrington, who coined the word 'synapse', the neuron was the functional unit that integrated excitatory and inhibitory input. For Cajal, the synapse was the explanation for how neurons could be individual elements, yet connected to form circuits. Both men were primarily concerned with local circuits in spinal cord and brain, but imaginatively extrapolated their discoveries on simple circuits to higher cognitive functions. Both men wrote poetically about their discoveries and so provided neuroscience with a rich vocabulary, vivid and memorable images, and concepts that remain part of the currency of 21st century neuroscience.