[Physiopathology of spasticity and flexion spasms].

Spasticity, flexion and extension spasms occur after lesions of motor descending pathways. Three different mechanisms can explain these disorders of tone: pure muscular alterations, segmental synaptic sprouting and liberation of spinal reflex activity. This last mechanism, which is also the most classically described has been studied long ago. Amongst all hypotheses which can explain spasticity (hyperexcitability of alpha motoneuron, gamma motoneuron, or reduction of presynaptic inhibition) reduction of presynaptic inhibition is the only one to have been clearly demonstrated. A new treatment is proposed: intrathecal Baclofen. It seems to act by reducing the excitability of alpha motoneuron.