Spasticity II: Physiological measurements

Abstract

Direct tests by the microneuronographic recording of muscle afferent fibres of spastic human subjects show that the gamma system is not overactive, and the muscle spindles do not have an increased sensitivity to stretch in spasticity. A substantial body of work has compared the human H reflex with the tendon (T) reflex in an attempt to separate the contributions of the monosynaptic reflex as against those of the gamma system. Both electrical stimulation of the tibial nerve and a tap of the tendo Achilles would produce a monosynaptic reflex contraction of the soleus. The electrical stimulus, however, would bypass the muscle spindle, and produce an H reflex of amplitude dependent only upon the excitability of the monosynaptic reflex. Comparison of the H and T reflexes indicates the activity in the gamma system. A tendon tap produces a wave of vibration spreading through the muscle, and muscles' spindles are excited asynchronously, producing an input volley to the spinal cord lasting as long as 20–30 msec.