Look all the way down to your toes and you’ll appreciate the feat (pun absolutely intended!) that your neurons accomplish in relaying signals over long distances to your brain. A recent paper discusses the interactions between the first sets of motor and sensory axons that find their way into limbs during development.
During development, motor and sensory axons align together as they project into a developing limb. A group recently showed how motor and sensory axons are mutually dependent on one another for their correct trajectories into a developing limb, and identified an important role for a protein called Neuropilin-1 in these interactions. Image above from the cover of PLoS Biology shows sensory (red) and motor (green) axons in the brachial plexus, a region where motor and sensory axons converge before being sorted into bundles. This tight bundling of the axons is affected in mice that lack Neuropilin-1 in either type of axon.
Huettl, R., Soellner, H., Bianchi, E., Novitch, B., & Huber, A. (2011). Npn-1 Contributes to Axon-Axon Interactions That Differentially Control Sensory and Motor Innervation of the Limb PLoS Biology, 9 (2) DOI: 10.1371/journal.pbio.1001020
Cover of PLoS Biology can be found here.