Muscle rigidity in cats with severed spinal cords

cblanco at cblanco at
Wed Nov 25 17:19:11 EST 1998

That is not completely true. When the spinal cord is sectioned you will see
two different syndromes. The motor pathway is conformed generally by two
neurons. One of them placed in the brain called upper motoneuron and the
other placed at the spinal cord (lower motoneuron) The upper motoneuron play
an inhibitory roll on the lower motoneuron. So when a lesion occurs over the
spinal cord two different events take place. The body part innerved by the
spinal nerves arising from the damaged region get a flaccid paralysis (no
movements and relaxed muscles) because the lover motoneurons involved are
destroyed, the regions placed down the lesion get a rigid paralysis because
the lover motoneurons are intact but they are disconnected from the upper
ones, so they discharge continuously. This situation change in 4 or 5 days
after damage and the paralysis became flaccid because the uninnervated lower
motoneurons get exhaust and became atrophy. The two syndromes are called
"upper motoneuron syndrome" and "lower motoneuron syndrome ". In man occurs
exactly the same but in general the changes are less obvious than in animals
for the special control of motility coming from brain cortex.

In article <73e986$i8a$1 at>,
  eladyt at wrote:
> Hello,
>   I have been told that when the spinal cord of a cat is cut, the muscles
> controlled by the cut nerves become rigid. This suggests that motor commands
> to muscle "tell" the muscle how much to relax, and not how much to contract.
>    Could anyone point me to a reference about this phenomena (in cats or
> possibly in humans) ?
>                      Thanks,
>                           Elad.
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