Re: Does the distance a nerve impulse travel affect the speed of reaction.

 Dear Antonia
Firstly can I commend you on your aspirations to be a scientist… I hope I 
can help you some way on your journey!  
You asked if reaction time can be influenced by the distance a nerve 
impulse (technically called an action potential) travels along an axon.   
The speed an action potential travels is known as the conduction velocity 
and this is determined by the diameter of the axon (larger axons conduct 
faster), and whether or not the axon is myelinated (surrounded by 
insulation called myelin sheaths - insulated axons conduct faster). 
Conduction velocity is important because the faster a fibre conducts the 
quicker the brain receives the signal and the faster it can react to the 
information.  
Action potentials are conducted at speeds between 0.5 and 120 metres per 
second (m/s) and different fibres conduct different types of signals at 
different speeds.  For example, pain is conducted via Ad- fibres at 25m/s 
and C-fibres at 0.5m/s.   Thus a pain stimulus travelling from your 
fingertip to your spinal cord along a C-fibre, a distance of 1 metre, will 
take 2 seconds to make the journey.  Pain travelling along a Ad-fibre will 
take mere milliseconds.  You can feel this difference in speed between Ad 
and C-fibre pain conduction.  Say you burn your foot, the immediate 
shooting pain you feel is conducted by the fast Ad-fibres and the dull 
throbbing pain that follows about 2 or 3 seconds later is the C-fibre 
conduction!  Touch is transmitted by very very fast Ab and Aa fibres at 
conduction velocities between 35 and 120m/s.   
So to answer your question, the distance traveled along a nerve matters not 
so much as the type of stimulus you are using.  Most fibres conduct so fast 
that if you stimulated the tip of your toe or the tip of your nose you 
wouldn't be able to sense the time difference (it would be in the order of 
milliseconds) so you couldn't possibly react faster.  The only difference 
distance would make is with the slow pain-conducting C-fibres.  You might 
have to get the person to react to the stimulus only when they first feel 
slow throbbing pain… good luck with finding people to help you out in this 
study!!  

Reference:
Kandel, Schwartz & Jessell.  1991. Principles of Neural Science.  Appleton 
and Lange, London.