giO HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOGY II 



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FIG. 1 6. Deficiency of reflex facilitation by gamma activation in an unilateral parkinsonian syn- 

 drome. Electromyograms of right (re) and left {li) biceps brachii in a patient with right-sided parkin- 

 sonism. Upper records show monosynaptic tendon reflexes elicited by striking the forearm. Lower 

 records show the same responses after clenching the contralateral fist, a procedure which produces 

 reflex facilitation of muscle spindles in man (i i8, 236). Marked potentiation of reflex appears on the 

 normal left side, but no potentiation on the affected right side. Some rhythmic tremor potentials 

 appear in the background of the right biceps EMG. [From Hassler (88).] 



the Jendrassik procedure for facilitating tendon 

 reflexes is less effective in Parkinson's disease (fig. 16). 

 It has been known since Sommer's (236) experiments 

 that this procedure works by facilitation of muscle 

 spindle activity. Since Leksell (159), Granit and co- 

 workers (71) and Hunt & Kuiffer (120, 121) have 

 shown that muscle spindle activity and reflex rein- 

 forcement are regulated by the gamma motoneurons, 

 one may conclude that activation of this system is 

 defective in parkinsonian patients having lesions in 

 the substantia nigra. 



Apparently two different reflex control mechanisms, 

 postulated by von Hoist (280) in his principle of 

 Reqfferenz, regulate muscle length and muscle tension 

 by negative feedback: a) for muscle length, involving 

 the annulospiral endings, modified by gamma in- 

 nervation and eliciting monosynaptic reflexes, and b) 

 for muscle tension, with the flower-spray endings ac- 

 tivating interneurons. Inhibiting impulses relaxing 

 muscle tension originate in the tendon organs. Two 

 kinds of alpha motoneurons exist with predominantly 

 either phasic or tonic function. The tonic neurons 

 show a more prolonged after-hyperpolarization, and 

 lower conduction velocities and discharge frequencies 

 than do the phasic neurons [Eccles (50, 51)]. In 

 parkinsonian rigidity the quick adaptation mecha- 

 nism of the gamma system is defective and the tonic 

 alpha system is overactive although the reflex mecha- 

 nisms of the phasic alpha system (the monosynaptic 

 reflexes) seem to be normal. 



A special kind of pathological exteroceptive inter- 

 segmental reflexes was described by Duensing & 

 Schneider (49) in human athetosis and further 

 studied by Duensing (44, 45) as pathologische Fremdre- 

 flexe. These reflexes were not observed in other extra- 

 pyramidal syndromes except in some cases of myo- 

 clonus, hemiballism and acute encephalitis. In the 

 electromyogram Duensing's reflexes show a biphasic 

 form of synchronous motoneuron discharge similar to 

 that of the monosynaptic reflexes, but their latency is 

 two to three times longer than that of corresponding 

 proprioceptive reflexes. The response in these reflexes 

 consists of single muscle twitches which are evoked 

 by striking, scratching or tapping wide and often 

 distant cutaneous areas. Duensing (45) believes that 

 these reflexes are release phenomena resulting from 

 facilitation in spinal interneurons controlled by brain- 

 stem structures, probably the reticular formation. 



Relation of Extrapyramidal Mechanisms to Thalamoreticular 

 System : Sleep and Arousal, Motor Patterns of Attention 



Clinical observations on extrapyramidal disorders 

 in man have long shown their dependence upon the 

 waking state. Every type of extrapyramidal hyper- 

 kinesis (tremor, chorea, athetosis and ballism) dis- 

 appears during sleep and reappears with arousal. Al- 

 though the profound muscular atonia of sleep influ- 

 ences all motor mechanisms including even spinal 

 reflexes, the relation of extrapyramidal mechanisms to 



