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Some sauropod dinosaurs had sensory afferent neurons over 50m in length. So if a sauropod accidentally touched a hot stove with its tail, it would take the brain over 25 seconds to realise it was burning itself (assuming C fibre conducting at 2 m/s). app.pan.pl/archive/publis… #pain 
Presumably evolution figured out a way of being quicker than this - perhaps by using fast myelinated A fibres or very fat C fibres for nociception instead.
But the point stands that throughout evolution, sensory afferents have had to increase & shrink their length by many orders of magnitude, while still staying quick enough to actually trigger a reflex or pain percept in a useful enough time frame for an organism to get away safely
It blows my mind that dorsal root ganglia neurons can have axons of anything up to 50m to less that 5cm. And yet the anatomy and molecular mechanisms are so well conserved. #pain #nociception
Could you culture a sensory afferent neuron in an obscenely long microfluidic culture maze and use guidance cues to just force it to keep on growing? Like would it just keep on going til it was 50 m long? :S
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