Physio Textbook Reflex Q

Richard Norman rsnorman at earthlink.net
Mon Aug 11 19:54:23 EST 1997

In article <5snr8c$od1$1 at news1.bu.edu>, ariana at bu.edu says...
>        In Human Physio class, on reflex class, we learned the
>        Double reciprocal reflex (someone step on something sharp...)
>        The question is, would the reflex be present after upper spinal
>        cord transection?
>        The argument is;
>        a) Yes, it is a reflex and will ocurr regardless to transection,
>        b) No. There are no detectors to sense the sharp object (in
>                knee jerk, the spindles are the detectors). 
>                If the thalamus (pain) is the detector, then is it
>                still called reflex?
>        I thought I knew, but guess not...
>        Jeung-Woon
>        Boston U

A standard lab experiment (in the olden days when people actually
used live frogs in class) used to be to brain pith but not spinal
pith a frog.  After it recovered from the spinal shock, it would
respond with very healthy reflexes, including the flexor/crossed
extensor reflex that I believe you refer to.

Yes, spinal reflexes remain after upper spinal transection, although the
lack of descending influences alters them and the immediate barrage
of activity caused by transection also alters them. 

Yes, cutaneous Adelta and C fibers can signal "painful" objects to
spinal circuits without cerebral processing.

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