Figure 21.

Reciprocal reflex connections in humans. For the study of reciprocal reflex connection in humans, the H reflex is used as an indicator of activity level of motoneurons. Reciprocal reflex effects are measured by giving stimuli to the nerve innervating their antagonists (conditioning stimuli) at various time intervals preceding a test H reflex and at various intensities measured by threshold of the M wave (XMT). Effects of reciprocal reflex connections at rest are shown for a normal subject on the left and an adult cerebral palsy subject on the right. Left figure. A normal subject. The time course of effects of the antagonist muscle nerve stimulation on the H reflex in the calf muscle is shown. The amplitudes of the test H reflexes are expressed as a percentage of the control amplitude, which is indicated on the ordinate with its standard deviation at the right side of graphs A and B. The abscissa shows the time interval between conditioning and test stimuli on a logarithmic scale. A: conditioning stimulus intensity was 1.05 XMT. B: 1.34 XMT. C: diagram of the time course of ankle joint movement by a strong conditioning volley on the same time scales as that of A and B. Upward deflection indicates ankle dorsiflexion. Right figure. A patient with bilateral athetosis. A: similar illustration to the left figure. The scale of the abscissa is different. Strong inhibition is observed within 5 msec of the conditioning-test stimuli intervals. The intensity of conditioning stimulation was 1.3 XMT. B: photographic records of the control (c) and effects at earlier intervals less than 7 msec (1–4). C: potential spread to the calf muscle (soleus and gastrocnemius) from the evoked EMG in pretibial muscles by conditioning stimulus alone. (From Mizuno, Tanaka and Yanagisawa, 1971⁶⁹⁾).