Recent concepts in the pathophysiology and evaluation of spasticity.

Spasticity is still a challenge to clinicians and scientists. The participation of Ia, Ib, II, III and IV afferents pathways, as well as those related with presynaptic inhibition. Renshaw cells modulation, and alpha and gamma motoneurons hyperexcitability, in this medical problem are reviewed. A brief overview on the more common neurophysiological tests performed during the evaluation of human spasticity is presented.