J. C. ECCLES 



343 



synaptic terminals and account for at least part of the depressed synaptic 

 efficacy. It is important, therefore, to attempt by other procedures to 

 produce a profound diminution of the discharge of impulses from the 

 annulospiral endings of the muscle spnidles belonging to the muscles 

 under test. Several experimental procedures, either alone or in suitable 

 combination, have been tried (Wester man, unpublished). For example, 

 tenotomy or splinting the limbs in plaster should considerably reduce the 

 activation of the stretch receptors of a muscle, although it must be 

 realized that annulospiral endings arc extremely sensitive to mechanical 

 stimuli and certainly could not be silenced by these procedures (Matthews, 



Min 



Fig. 4 



Min 



Plots of the time courses of post-tetanic potentiations of EPSPs produced by a conditioning 

 tetanus of lo seconds at 400 c/s, as indicated by the hatched coknnns. Specimen records are 

 shown in Fig. 3. In Fig. 4 A the heights of the EPSPs are plotted relative to the control height, 

 open circles being for the operatively severed pathway (FDL) and filled circles for the control 

 pathway (FHL). Fig. 4B as for Fig. 4A, but for maxinuim slopes of the rising phases of the 

 EPSPs. Note that in Fig. 4A the time scale is greatly shortened after 3 minutes (reproduced 

 from Eccles, Krnjevic and Miledi (1959), with permission 01 the Jonnuil of Physiology). 



1933; Hunt and Kuffler, 195 1; Kobayashi, Oshima and Tasaki, 1952; 

 Granit, 1955). In attempting further to reduce their discharge, the appro- 

 priate ventral roots have been severed so as to suppress the activation of 

 muscle spindles by impulses in the gamma efferent fibres (Leksell, 1945; 

 Kuffler, Hunt and Quilliam, 195 i ; Hunt, 1951 ; Granit, I955)- I11 all these 

 experiments, controls were provided by the symmetrical reflex paths of 

 the other limb, where a suitable dummy operation had been performed; 

 and, in addition, the degree of post-tetanic potentiation gave a sensitive 

 measure of relatively small changes in synaptic efficacy. Finally tests for 

 the symmetry of monosynaptic reflexes were made with afferent paths 

 which were unrelated to those being investigated, e.g. the knee flexor 

 pathways when the operative procedures were restricted to muscles 

 acting on the ankle and digits. 



