THE ROLE OF REFLEX INHIBITION 



By C. S. SHERRINGTON, M.D., F.R.S. 



Professor of Physiology in the University of Liverpool 



It has been said, " The end of man is an action, not a thought." 

 The aphorism though striking is but half-true, for surely 

 thought is action. Yet that obiter dictum of Thomas Carlyle's 

 states with curious fidelity the line which Physiology must 

 follow in its study of nervous reactions. The nervous system, 

 driven itself by the external world, drives and controls the 

 organs of the body, and through these alone do its inner work- 

 ings find expression. These expressions constitute the whole 

 practical purpose or " end " of the nervous system. In the out- 

 come of nervous reactions it is with the material expressions 

 and with no other that Physiology can properly be said to deal. 



I. Reflex Inhibition 



Among the organs through which the inner workings of the 

 nervous system find expression are glands and muscles, especi- 

 ally the latter. And pre-eminent among muscles are those 

 clothing and actuating the bony levers of the bodily frame and 

 therefore called skeletal. So completely are these muscles sub- 

 jected to the nervous system that under natural conditions they 

 enter into action only when the nervous system calls on them. 

 A skeletal muscle after severance of its nerve, separating it 

 from all commerce with nervous centres, lapses into paralytic 

 quietude and its functional inactivity becomes so profound 

 that in many cases its structure becomes in due course hardly 

 recognisably muscular at all. 



The contraction of skeletal muscle has two main forms : the 

 mild, steady, more or less continuous form called tonic^ which 

 executes postures ; the transient, vigorous form {phasic) some- 

 times called alterative (von Tschermak) which executes movements 

 such as those of the chest in breathing and those of the limbs 

 in all their varied exercise. Both these forms of contraction 



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