I was just wondering, since short people have shorter spinal cord,
do they have quicker nervous response?

Despite being a neuroscientist I had never considered that question! The answer is yes but the difference will be so small it will make no noticeable difference. In terms of reaction times (to say stepping on a pin or taking ones hand away from a hot flame) the difference comparing someone who is 5 foot to someone who is 6 foot tall (and remember the difference in arms and legs aren't as large as body height) would be milliseconds at most. Also to note the withdrawal reflex as described above is mediated at the local level of the spinal cord so the length of the cord is irrelevant since the reflex arc does NOT involve the brain.

As David said, the difference in axon length between short and tall people has a negligible effect on nerve impulse signal times, but it can make an appreciable difference if you compare different species. Blue whales, for example, have sensory axons that can be up to 30 meters in length. For slow moving signals (unmyelinated pain fibers can have a conduction velocity as low as 0.5m/s) a signal might take a full minute to reach the brain. Some extinct sauropods could have been almost twice as long so, hypothetically, it could have been almost two minutes before a big sauropod knew that the tip of its tail had been bitten! (http://sauroposeidon.files.wordpress.co … ted-ms.pdf)