Axon targetting

Every developing axon has a specific target that it wants to reach such as a motor neuron growing to a certain muscle. However, the axon does not the luxury of a video feed: when it leaves the spinal cord it cannot see its target which might be a muscle at the end of a limb. As if this wasn’t hard enough, the environment around the axon is continually changing as the embryo develops so that muscle target is moving away as the limb grows and extends! Yet somehow, axons reliably reach their targets to wire up the nervous system. Trying to decipher how they do this is the basis of the field of axon guidance.