[Neural mechanisms underlying spasticity].

Considering the various studies conducted on spasticity, it is quite evident that the signs and symptoms of this disorder vary. In some cases of spasticity, spasms may be noted. An increase in velocity-dependent stretch reflexes has been proposed as a cardinal feature of spasticity. There are 2 possible mechanisms underlying increased stretch reflex of spasticity: one is the changes in gamma innervations and the other is one the changes in spinal motoneurons. Changes in gamma innervations for spasticity are not evident while the muscle are at rest. On the other hand, changes are clear in normal subjects during voluntary contraction of muscles, but not in sbjects with spasticity. We have discussed the changes in membrane properties caused by presynaptic inhibition, reciprocal Ia inhibitory function, recurrent inhibition, and autogenic Ib inhibition as the other candidate spinal mechanisms for spasticity.