Neurons use their long arms to reach out and almost touch other neurons. Those arms nestle extremely close together--just 20 nanometers apart--so make sure your hands are steady before trying to put the pieces of your brain together.

Across the tiny spaces between the cells, known as synapses, molecules called neurotransmitters ferry messages back and forth. Here, a rat neuron from the movement-coordinating cerebellum was dyed green and caught in the act of communicating with another neuron (shown in red). Each cell has one axon (the green tail snaking from the left side of the image), which transmits impulses to the dendrites (the candelabra-like branches) of another.

Michael Hausser and Beverley Clark at University College London acquired this image as part of their research on how cells transform signals from other neurons into plans for sending on more signals.