Neurophysiology of spasticity

The central nervous system includes the pyramidal and extrapyramidal systems. There are complex interconnections between these systems and the spinal cord. ¹

Spasticity is due to a chronic reduction in inhibition. Loss of presynaptic inhibition results from the inability to synthesize or transport g-aminobutyric acid (GABA) to the anterior horn cell. Alterations in the membrane properties, synaptic input and a change in continuous descending inhibition produce the characteristic hyperexcitability of motor neurons.²

1. Dormans JP, Pellegrino L. Definitions, Etiology, and Epidemiology of Cerebral Palsy. In: Caring for Children with Cerebral Palsy. 2nd ed. Baltimore, Md: Paul H Brooks Publishing Co; 2000:3-30.
2. Mayer NH. Spasticity and the stretch reflex. Muscle Nerve 1997;20(suppl 6):S1-S13.