Is the Brain a Calculating Machine? 



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connected with the cells by small swellings or knobs which are called 

 synapses. This junction has the special property that it will not let 

 signals pass until they reach a certain strength. The synapse thus gives 

 an 'all or none' response; if the signal is strong enough it passes; be- 

 low a certain strength nothing happens. 



One nerve may be joined in this way with many nerve cells, and 

 each nerve cell has synaptic contacts with many different nerves. This 

 provides an enormous number of pathways between the nerve cells. 



FIG. 26. A mammalian motor neurone, showing 

 various sizes of synoptic knobs, several of which 

 are often attached to one nerve fibre. (Adapted 

 from J. C. Eccles, The N europhysiological Basis of 

 Mind. [Oxford Press]) 



In order to excite a nerve cell, a definite number of signals must reach 

 it within a definite period through these synapses. When it is excited, 

 it fires a 'volley', i.e. a complete signal, through the axon going from 

 it. This 'volley' is independent of the nature of the stimulus, provided 



