THE EXTRAPYRAMIDAL MOTOR SYSTEM 



869 



ANATOMY OF EXTRAPYRAMIDAL MOTOR SYSTEM 



The caudate nucleus and putamen, jointly forming 

 the striatum [V'ogt (266)], are the highest subcortical 

 centers in the extrapyramidal motor system. They 

 may be regarded as anatomically independent of the 

 cortex to a great extent, since they show only spaise 

 retrograde degeneration following cortical deafTer- 

 entation or ablation, and are often extensively de- 

 veloped in human brains with extensi\e congenital 

 cortical abnormalities. 



Affi'ieril Pathways 



As shown in figure 4, the most important afferents 

 to the putamen (Put) and caudate [Cd] arise in the 

 centruiTi medianum of the thalamus [\'ogt & Vogt 

 (271)]. The larger cells in the dorsal part of the 

 nucleus project to the caudate, and the smaller 

 \'entral cells project to the putamen. In view of the 

 essentially complete degeneration of the centrum 

 medianum following destruction of the caudate 

 nucleus and putamen, this nucleus may be considered 

 as a major afferent pathway to the striatal system. In 

 turn, the centrum medianum receives afferents from 

 the midbrain reticular formation, according to elec- 

 trophysiological studies [Starzl et al. (247J] and 

 human anatomical findings [Hassler (87)]. Further 

 afferent pathways reach the centrum medianum 

 through the superior cerebellar peduncle [Uemura 

 (259)]. Our own findings in inan [Hassler (83)] sug- 

 gest that this pathway originates in the nucleus 

 emijoliformis which receives afferents from the 'in- 

 termediate part' (Hayashi) of the cerebellum. This 

 specifically cerebellar afferent pathway to the centruin 

 medianum, projecting in turn to the striatum, may 

 be of special significance in view of the integrative 

 role of efferent cerebellar impulses in most higher 

 motor activities. Such a role in extrapyramidal 

 mechanisms is no longer generally attributed to 

 efferents from the dentate nucleus. 



Cortical afferent pathways to the putamen originate 

 in the precentral motor cortex, probably chiefly in 

 area 6, and afferents may reach the caudate nucleus 

 from the so-called area 4s [the strip region of Hines 

 (113)]. Brockhaus (15) has described a medial zone, 

 the fundus striati, lying in front of the putamen and 

 medial to the caudate nucleus and receiving afferents 

 from the parafascicular thalamic nucleus [Hassler 

 (81), Simma (234)]. 



Efferent Pathways 



There are three major efferent systems, viz. the 

 striopallidoreticular, striopallidocortical and stri- 

 onigral. These will be discussed in more detail below. 

 These three systems may converge either in the 

 anterior gra>' matter or perhaps in the reticular 

 formation. 



STRIONIGRAL .SYSTEM (cAUDATE PORTION). Efferent 



fibers from the caudate nucleus and putamen follow 

 different routes to the substantia nigra and also 

 terminate there in different parts. Efferents from the 

 caudate follow the ventral surface of the internal 

 capsule mainly to the anterior part of the substantia 

 nigra and also to a dorsomedial cell group of the 

 posterior part (fasciculus caudonigralis). Besides a few 

 fibers from the tractus peduncularis transversus (Mar- 

 burg) from the optic tract and some from the nucleus 

 praestitialis [Hassler (87)], the two major paths 

 to the anterior part of the substantia nigra appear to 

 originate in the caudate nucleus and frontal cortex. 

 Extensive degeneration in the anterior part of the 

 substantia nigra following destruction of these two 

 afferent pathways has been erroneously interpreted as 

 indicating an ascending direction of nigral neurons 

 [Rosegay (220)]. Myelogenetic studies and examina- 

 tion of cases of cortical aplasia have confirmed its 

 independence of the cerebral cortex and the caudal 

 direction of its projections to the contralateral side via 

 the anterior quadrigeminal commissure, but their 

 further course is unknown. 



PUTAMiNONiGRAL CONNECTIONS. Efferent fibers from 

 the putamen traverse the pallidum and peduncle to 

 terminate in the large-cell groups of the posterior 

 substantia nigra. These cells also receive cortical 

 afferents from area 6, and from postcentral, parietal 

 and temporal fields, and they degenerate after com- 

 bined lesions of the putamen and cortex. Their 

 efferents are directed contralaterally, as described 

 above. The medial group of small cells of the posterior 

 substantia nigra receive afferents from the fundus 

 striati and probably from the prefrontal c'ortex. 

 Direct pallidal connections to the substantia nigra are 

 unknown. 



STRIOPALLIDORETICULAR SYSTEM. The Other main 

 efferent pathway from both the putamen and caudate 

 nucleus goes to the external pallidum which also 

 receives other afferents, particularly from the intra- 

 laminar nuclei and the nucleus limitans of the 



