'Zebrafish growth cone' by Dr Steve Wilson. CC BY
Numerous neuronal threads knit the brain together, and almost all of them end up where we need them to be for the brain to function correctly. When a neuron extends its growing branches, both axons and dendrites, they often have a target connection. Even without senses or a brain of their own, the simple structures find their marks thanks to the process in this image.
Much like you might feel your way through your dark kitchen for a midnight snack, a growth cone explores its surroundings randomly. It strikes out with short-lived fingers that snap back into the main cone when they bump into unpleasant molecules. When they run into encouraging elements, however, they direct the cone to lay down rigid microtubules that let the branch advance, like a train carrying its own railroad ties as it goes.