Fig. 2.

Grand synthesis of structure and function based on Cajal’s law of dynamic polarization. Left panel: Sherrington’s definition of synapses was first stated in 1897 and illustrated using this figure in Foster’s Textbook of Physiology, Part 3, which he co-wrote [30]. This illustration shows the influence of Cajal’s ideas with an axon drawn (A) to terminate in close proximity to the dendrites and soma of a motor neuron and provide information to them (bottom arrow). The motor neuron then passes this signal to the periphery via its axon (upper arrow). Right panel: Four years earlier [31] Cajal provided the connectionist viewpoint for behavior showing how sensory information originating in the skin (D1) might pass from one cell to another from spinal cord (B) to the cortex (A) and back down the spinal cord leading eventually to action as muscle fibers become activated by a motor neuron axon (C). This conception is the foundation of the connectomics approach: tracing out all the synaptic connections between neurons