Nerve cells on a silicon chip. Coloured scanning electron micrograph (SEM) of nerve cells (or neurons, grey) growing on the surface of a silicon chip. The neurons are linked by axons and dendrites, which are responsible for passing signals from one cell to another. The signals take the form of electrical impulses, which means that theoretically nerve cells can be linked in a circuit with electronic chips. Such a hybrid circuit could be used in the body to replace defective nervous tissue, for instance in the eyes of people with retinal degeneration. Magnification: x740 when printed at 10 centimetres wide.