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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



alpha and of the gamma systems of motoneurons. 

 Alpha hyperactivity occurs after anemic decerebra- 

 tion, gamma hyperacti\ity after midbrain transection. 

 Although the gamma system may show certain dis- 

 turbances in human parkinsonism, the.se are opposite 

 to that in the decerebrate state and the conditions in 

 animals and man after midbrain lesion cannot be 

 honiologized. 



In man lesions of the higher le\els of the extra- 

 pyramidal system, especially the striatum and sub- 

 thalamic nucleus, induce contralateral hyperkinetic 

 movements, such as tho.se of hemiballism and chorea. 

 Combined lesions of the higher extrapyramidal cen- 

 ters in the telencephalon and diencephalon cause 

 athetotic and dystonic syndromes. Lesions of lower 

 extrapyramidal centers in the midbrain, especially 

 in the nigra, cause parkinsonian tremor, rigidity and 

 akinesis. 



Pathological Manifestations and J\ormal Fuintion 

 of Extrapyramidal Structures 



To attribute special functions to special nuclei of 

 the extrapyramidal system would be a crude simplifi- 

 cation. Nevertheless an effort to suggest the role of 

 the structures of the extrapyramidal system in motor 

 coordination should be made although only with 

 caution. 



The striatum (caudatum and putamen) receives 

 afferent impulses from many different receptors, but 

 the main afferent pathways come from the centro- 

 median nucleus of the thalamus. Striatal lesions in 

 man result in hyperkinesis accompanying intentional 

 mov'ements as in chorea. In animals striatal stimula- 

 tion causes contralateral de\iation or general inacti- 

 vation. Lesions in cats and monkeys are followed only 

 by slight hyperkinesis and surprisingly few defects of 

 longer duration. The coordinating function of the 

 striatum seems to be very complex and may be tenta- 

 tively circumscribed as regulation of intentional 

 movements by suppressing and screening additional 

 motor mechanisms in some functional association 

 with the nonspecific thalamorcticular svstem regulat- 

 ing sleep and general acti\ity. 



The role of the pallidum in extrapyramidal dis- 

 orders has had to be re\ised as a result of recent experi- 

 ences with stereotaxic lesions in man. The old concep- 

 tion that pallidal lesions cause muscular rigidity was 

 not confirmed; stereotaxic pallidotomy in parkin- 

 sonian states and other extrapyramidal diseases has 

 the opposite effect of diminution of muscular rigidity. 

 Electrical stimulation of the human pallidum does 



not result in any direct motor effects but causes a 

 partial blocking of voluntary movements and arousal 

 or ad\ersi\e effects. Destruction of the pallidum 

 causes a general inactivation or sleep syndrome of 

 short duration and a diminution of muscular tone 

 at the contralateral side of the body of long duration, 

 as well as of rigidity in parkinsonism. The functional 

 role of the pallidum may be tentatively designated a) 

 increasing the tonic background of intended and 

 automatic movements, and b) general activation in 

 coordination with the thalamorcticular system. 



The corpus subthalamicum of Luys has two-way 

 connections with the external pallidum. Lesions of 

 this nucleus in monkeys and man result in contra- 

 lateral choreiform or hemiballistic movements. The 

 function of the subthalamic nucleus cannot be defined 

 exactly but may be similar to that of the striatum by 

 restraining motor activity of the contralateral side 

 in collaboration with the activating influence of the 

 pallidum. 



The ccntromedian nucleus of the thalamus seems 

 to be the main crossroad for the coordination of the 

 nonspecific activating and the extrapyramidal motor 

 system. Electrical stimulation mav cause sleep or 

 arousal effects in animals and man, depending upon 

 the frequenc) and strength of stimulation. Control 

 of the general motor patterns of attention and arousal 

 may be tentatively ascribed to the function of this 

 nucleus. 



The role of the red nucleus in the extrapyramidal 

 motor system is still obscure. The fact that, while in 

 the lower animals it is predominantly magnocellular 

 and gives ri.se to the rubrospinal tract, in man it is 

 mainly parvicellular, and originates the large de- 

 scending central tegmental tract and renders gener- 

 alizations concerning its functions hazardous. In cats 

 stimulation of the magnocellular part of the red 

 nucleus and ruijrospinal tract caases raising of head 

 and foretrunk. Although adequate evidence is lacking, 

 the anatomical connections seem to indicate that the 

 parvicellular red nucleus of man exerts a controlling 

 function by negati\e feedback to the cerebellum \ia 

 the central tegmental tract and inferior olive, so regu- 

 lating upright posture and gait and making possible 

 the postural corrections required for the teleokinetic 

 or intentional motor actions. 



Selective destruction in man of the substantia nigra, 

 which has connections with the striatum, cerebral 

 cortex and reticular formation, causes the parkin- 

 sonian syndrome. Human tremor shows all the 

 phenomena of relative coordination, described by 

 \^on Hoist (278) in the fin movements of fishes (fig. 



