Factors affecting spasticity

Although the basic rhythm of stepping, walking, and running is present in the spinal cord, it is not manifest in patients with lesions of the spinal cord, on account of spasticity. Spasticity is an over-reaction to every kind of input. Every response is followed by an after-discharge. This affects the muscles which have reacted, and it spreads to involve many other muscles, more ipsilaterally than contralaterally. In the normal this is prevented by the corticospinal tract, by Renshaw inhibition, and by inhibition of the input to the spinal cord. Anything that reduces the input that finally reaches motor neurons reduces general excitability; it reduces spasticity permanently, allowing normal movements to occur.