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Question on Speed of Human REFLEX System

Sundeep Gupta sundeep at casbah.acns.nwu.edu
Wed Mar 13 16:38:17 EST 1991

In article <11929 at uhccux.uhcc.Hawaii.Edu> leeky at wiliki.eng.hawaii.edu writes:
>Hi everyone, 
>Hope this is the right place to post this novice question...
>I was just wondering if anyone out there could enlighten me on a 
>topic regarding instantaneous speed of human reflex system.
Well, I'm just a 1st year med student, so I could be totally off base here.
A reflex would include the nerve impulse travelling to the spinal cord, then
through a reflex interneuron, then through an efferent neuron to the muscle
being activated.  After this, one would need to account for the time between
the nerve impulse reaching the muscle and the contraction actually
occurring.  So there are four parts to the reflex.

1.  Muscle tendon afferent impulses travel at about 100 m/s - from the knee
to the spinal cord is approximately 1/2 meter, giving a time of
5 milliseconds.

2.  The reflex interneuron impulse time should be negligible since it is
only millimeters in length and even a slow nerve fiber of 50 m/s would give
a time of about .02 milliseconds.

3.  The efferent nerve impulse should also travel at about 100 m/s and
should therefore also take about 5 milliseconds.

4.  For fast twitch muscle fibers, the time between innervation and maximal
contraction is about 10 milliseconds.

This comes to a total of about 20 milliseconds, or 1/50th of a second.
Parts of this I may not have included would be the time for synaptic
transmission of the impulses between the two neuron synapses.  I do not
know if these are negligible or not.

--------------------------{ Sundeep Kumar Gupta }------------------------
     Internet:sundeep at casbah.acns.nwu.edu        Bitnet:sundeep at nuacc
     Academic Computing and Network Services, Northwestern University

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