ASPECTS OF INHIBITORY PATHWAYS AND SYNAPSES 45 



slow conduction velocities in such extremely fine elements, time relations of 

 inhibition allow such an assumption. The distances to cover are of course 

 short, i.e. of the order of 1-2 mm. 



It might be of interest to analyse also other centres from this point of view. 

 Especially the cerebellum, in which the number of different types of synapses 

 on the same final common element, the Purkinje cells and especially the clear 

 and uniform orientation of dendritic and neurite patterns, might present a 

 unique model for the study of such problems. The work of Granit and 

 Phillips (1956) and the three types of inhibition of Purkinje neurons are very 

 promising. Unfortunately stimulation of subcortical structures cannot furnish 

 definitive proof of the histological elements involved, since as already stated 

 by the authors, antidromic excitation of Purkinje axons, orthodromic volleys 

 in their recurrent collaterals, and orthodromic impulses of afferent systems 

 are likely to arrive more or less simultaneously in the cortex under such 

 circumstances. The rapid advance in the understanding of the anatomy of 

 afferent and cortico-cortical connexions in the cerebellum and the oriented 

 character of intracortical systems offers at least from the anatomical point of 

 view favourable chances which might be successfully exploited in the near 

 future. But any statement at present would be necessarily highly speculative. 



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